oxychem caustic handbook

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OxyChem Caustic Soda Handbook 1 of 44 Page Introduction & Principal Uses . . . . . . . . . . . . . . . . .2 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Methods of Shipping Caustic Soda . . . . . . . . . . . .4 Safety in Handling Caustic Soda . . . . . . . . . . . . . .5 Unloading and Handling Liquid Caustic Soda . . . .7 Equipment for Handling Caustic Soda . . . . . . . .14 Technical Data . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Dilution Calculations . . . . . . . . . . . . . . . . . . . . . . .32 Methods of Analysis . . . . . . . . . . . . . . . . . . . . . . .34 "Important: The information presented herein, while not guaranteed, was prepared by technical personnel and is true and accurate to the best of our knowl- edge. NO WARRANTY OF MERCHANTABILITY OR OF FITNESS FOR APARTICULAR PURPOSE, OR WARRANTY OR GUARANTY OF ANY OTHER KIND, EXPRESS OR IMPLIED, IS MADE REGARDING PERFORMANCE, SAFETY, SUITABILITY, STABILITYOR OTHERWISE. This information is not intended to be all-inclusive as to the manner and conditions of use, handling, storage, disposal and other factors that may involve other or additional legal, environmental, safety or performance considerations, and OxyChem assumes no liability whatsoever for the use of or reliance upon this information. While our technical personnel will be happy to respond to questions, safe handling and use of the product remains the responsibility of the customer. No sugges- tions for use are intended as, and nothing herein shall be construed as, a recommendation to infringe any existing patents or to violate any Federal, State, local or foreign laws." Occidental Chemical Corporation 2009 CellBW NaOH NaOH Caustic Soda Handbook OxyChem OxyChem is a registered trademark of Occidental Chemical Corporation. Foreword This handbook outlines the methods for handling, storing, preparing and using caustic soda. It includes information on the manufacture, physical properties, safety considerations and analytical methods for testing caustic soda. Additional information and contacts can be found at www.oxychem.com Occidental Chemical Corporation (OxyChem) Basic Chemicals Group Occidental Tower 5005 LBJ Freeway Dallas, TX 75244

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OxyChem Caustic Handbook

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Page 1: OxyChem Caustic Handbook

OxyChemCaustic SodaHandbook 1 of 44

Page

•• Introduction & Principal Uses . . . . . . . . . . . . . . . . .2

•• Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

•• Methods of Shipping Caustic Soda . . . . . . . . . . . .4

•• Safety in Handling Caustic Soda . . . . . . . . . . . . . .5

•• Unloading and Handling Liquid Caustic Soda . . . .7

•• Equipment for Handling Caustic Soda . . . . . . . .14

•• Technical Data . . . . . . . . . . . . . . . . . . . . . . . . . . .17

•• Dilution Calculations . . . . . . . . . . . . . . . . . . . . . . .32

•• Methods of Analysis . . . . . . . . . . . . . . . . . . . . . . .34

"Important: The information presented herein, while not guaranteed, was prepared by technical personnel and is true and accurate to the best of our knowl-edge. NO WARRANTY OF MERCHANTABILITY OR OF FITNESS FOR A PARTICULAR PURPOSE, OR WARRANTY OR GUARANTY OF ANY OTHERKIND, EXPRESS OR IMPLIED, IS MADE REGARDING PERFORMANCE, SAFETY, SUITABILITY, STABILITY OR OTHERWISE. This information is notintended to be all-inclusive as to the manner and conditions of use, handling, storage, disposal and other factors that may involve other or additional legal,environmental, safety or performance considerations, and OxyChem assumes no liability whatsoever for the use of or reliance upon this information. Whileour technical personnel will be happy to respond to questions, safe handling and use of the product remains the responsibility of the customer. No sugges-tions for use are intended as, and nothing herein shall be construed as, a recommendation to infringe any existing patents or to violate any Federal, State,local or foreign laws."

Occidental Chemical Corporation 2009

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CellBW

NaOHNaOH

Caustic SodaHandbook

OxyChemfifiOxyChem is a registered trademark of Occidental Chemical Corporation.

ForewordThis handbook outlines the methods for

handling, storing, preparing and using causticsoda. It includes information on the manufacture,physical properties, safety considerations andanalytical methods for testing caustic soda.

Additional information and contacts can befound at www.oxychem.com

Occidental Chemical Corporation (OxyChem)Basic Chemicals GroupOccidental Tower5005 LBJ FreewayDallas, TX 75244

Page 2: OxyChem Caustic Handbook

Principal Uses andConsumption ofCaustic Soda

Introduction 2 of 44

Caustic soda (sodium hydroxideor NaOH) is most commonly manu-factured by the electrolysis of asodium chloride (NaCl) solution.OxyChem manufactures causticsoda using either membrane ordiaphragm electrolytic cells.OxyChem does not use mercurybased electrolytic cells to producecaustic soda. The co-productsformed from the electrolytic produc-tion of caustic soda are chlorineand hydrogen.

The largest users of caustic sodaare the pulp and paper, detergentand chemical industries. Causticsoda is also used in the alumina,oil and gas and textile industries,mostly for its alkalinity value.

OxyChem has played a leadingrole in providing caustic soda tomeet the increasing demands ofindustry. OxyChem plants arestrategically located to convenientlyand economically serve industry.

Terminals are used to maintainstocks of our caustic soda in manyprincipal cities. Distributor stocksare also available in these andmany other cities and form a net-work of supply for the end user’sconvenience.

Liquid caustic soda is available asa 50% solution in two main grades.The name of the grades corre-sponds to the equipment used toproduced the caustic soda; mem-brane grade and diaphragm grade.Specification sheets for each gradecan be found on our website atwww.oxychem.com

To be technically correct, onlymolten caustic soda should becalled liquid, but since the term liq-uid caustic soda has historicallybeen used to describe solutions ofcaustic soda, it is used in this doc-ument interchangeably with theterm solution.

OxyChem produces caustic sodaat the following locations:• Battleground, TX (Diaphragm)• Convent, LA (Diaphragm)• Geismar, LA (Membrane and

Diaphragm)• Ingleside, TX (Diaphragm)• Niagara Falls, NY (Diaphragm)• Taft, LA (Diaphragm)• Wichita, KS (Membrane and

Diaphragm)

Caustic soda is one of the veryfew chemicals utilized in a verybroad range of applications. Someprincipal products or processes inwhich caustic soda is used are:

• Acid Neutralization• Agricultural Chemicals• Aluminum • Battery Recycling • Bleach • Boiler Compounds• Cellulose Film• Chemicals:

AmmoniaAmyl AminesCresolEthylene AminesFormic AcidGlycerine

Maleic AnhydridePentaerythritolPhenolPropylene OxidePolycarbonatesSalicylic AcidSodium AluminateSodium HydrosulfideSodium HypochloriteSodium PhosphatesStyreneVinyl Chloride Monomer

• Cleaning Formulations• Corn Syrup • Detergents• Drain Cleaners• Dyestuffs• Ethanol Fermentation • Food Processing• Fruit & Vegetable Peeling

• Glass-Batch Wetting• Ion-Exchange Resin

Regeneration• Metal Production and Casting• Ore Flotation and Processing• Paint Removers• Petroleum Refining• pH Adjustment• Pharmaceuticals• Pigments• Pool & Spa chemicals• Pulp & Paper• Rayon• Silicates• Soap• Surfactants• Textile Bleaching, Dyeing, and

Mercerizing• Vegetable Oil Processing• Water Treatment

Page 3: OxyChem Caustic Handbook

3 of 44

Caustic soda is produced byOxyChem by an electrolyticprocess as shown below. Brine,prepared from sodium chloride(NaCl), is electrolyzed in either amembrane cell or a diaphragm cell.The production of caustic soda(NaOH) also results in the co-prod-ucts of chlorine and hydrogen.

In the membrane process, asolution of approximately 30% instrength is formed. The solution isthen sent to evaporators, whichconcentrate it to a strength of 50%by removing the appropriateamount of water.

The diaphragm process is verysimilar to the membrane processexcept that a solution of only 10-12% is formed in the cell.Therefore, additional evaporation isrequired to reach the saleable con-centration of 50%.

The caustic soda solution isinventoried in storage tanks prior toshipment. The product is shippedin tank trucks, railcars, barges andships.

The major difference in the twogrades is the amount of startingmaterial (sodium chloride) remain-ing in the final product. Membranegrade caustic soda will have lessthan 100ppm of the sodium chlo-ride remaining in the product.Diaphragm grade material will haveless than 1.2% sodium chloride.Several other differences can beseen in the products when thespecification sheets are compared.

ManufacturingProcess

2NaCl + 2H2O electricity 2NaOH + Cl2 + H2Production Flowcharts

NaCl + H2O = Brine

Brine Treatment

ElectrolysisDiaphragm Cell

Concentration

Filters

50% LiquidCaustic Soda Storage

Cell Liquor12% Caustic Soda

NaCl + H2O = Brine

Brine Treatmentand purification

ElectrolysisMembrane Cell

Concentration

50% LiquidCaustic Soda Storage

30% Caustic Soda

hydrogen

chlorine

hydrogen

chlorine

DiaphragmMembrane

electricityelectricity

NaCl

Page 4: OxyChem Caustic Handbook

4 of 44Methods of ShippingLiquid Caustic Soda

Liquid caustic soda is availablefrom OxyChem’s many plants andterminals in tank truck, tank car,barge and ship quantities. Eachform of transportation has its ownadvantages. The type of serviceselected will depend upon suchfactors as size and location ofstorage, rate of consumption,plant location, freight rates, etc.

Caustic soda, liquid, is regulated bythe U.S. Department ofTransportation (DOT) and is classi-fied as a corrosive material.

The DOT identification number is UN I824 for liquid caus-tic soda.

Page 5: OxyChem Caustic Handbook

5 of 44Safety in HandlingCaustic Soda

Caustic soda in any concentra-tion must be respected by every-one who handles and uses it.Before starting to work with it,the user should be aware of itsproperties, know what safetyprecautions to follow, and knowhow to react in case of contact.Accidental exposure to causticsoda may occur under severalconditions. Potentially haz-ardous situations include han-dling and packaging operations,equipment cleaning and repair,decontamination following spillsand equipment failures.Employees who may be subjectto such exposure must be pro-vided with proper personal pro-tective equipment and trained inits use. Some general guidelinesfollow.• Read and understand the latest

Material Safety Data Sheet.• Provide eyewash fountains and

safety showers in all areas wherecaustic soda is used or handled.Any caustic soda burn may beserious. DO NOT use any kind ofneutralizing solution, particularlyin the eyes, without direction by aphysician.

• Move the patient to a hospitalemergency room immediatelyafter first aid measures areapplied.

FIRST AID MEASURESFor Eyes: If for any reason

caustic soda contacts the eyes,flood the eyes immediately withplenty of clean water. Continueflushing for at least 15 minutes.While flushing, forcibly hold theeyelids apart to ensure rinsing ofthe entire eye surface. Do not useany kind of neutralizing solutionin the eyes.GET MEDICAL ATTENTIONIMMEDIATELY.

For skin: If caustic soda comesin contact with skin or clothing,flush with plenty of clean water forat least 15 minutes. Remove conta-minated clothing and footwear.Thoroughly wash affected clothingand rubber/vinyl footwear. Discardcontaminated leather footwear.GET MEDICAL ATTENTIONIMMEDIATELY.

For inhalation: If a worker isovercome due to the inhalation ofcaustic soda dust, mist or spray,remove them from the contaminat-ed area to fresh air. If breathing isdifficult, have a trained personadminister oxygen. If breathing hasstopped, have a trained personadminister artificial respiration. GET MEDICAL ATTENTIONIMMEDIATELY.

For ingestion: Although it is unlikely in an industrial situation that caustic soda wouldbe ingested, it could be swallowedaccidentally. If that occurs, DONOT induce vomiting. Give largequantities of water. If vomitingoccurs spontaneously, position indi-vidual’s head to keep airway clear.NEVER give anything by mouth toan unconscious person. GET MEDICAL ATTEN-TION IMMEDIATELY.

PROTECTIVE EQUIPMENTOSHA requires employers to

supply suitable protective equip-ment for employees. When han-dling caustic soda, the followingprotective equipment is recom-mended:• Wear suitable chemical splash

goggles for eye protection dur-ing the handling of causticsoda in any concentration. Thegoggles should be close-fittingand provide adequate ventilationto prevent fogging, without allow-ing entry of liquids.

• The use of a face shield may beappropriate when splashing canoccur, including loading andunloading operations.

• Wear rubber gloves or glovescoated with rubber, syntheticelastomers, PVC, or other plas-tics to protect the hands whilehandling caustic soda. Glovesshould be long enough to comewell above the wrist. Sleevesshould be positioned over theglove wrists.

• Caustic soda causes leather todisintegrate quite rapidly. For thisreason, wear rubber boots. Wearthe bottoms of trouser legs out-

FACESHIELD

CHEMICALSUIT

RUBBERBOOTS

CHEMICALSPLASH

GOGGLES

RUBBERGLOVES

Page 6: OxyChem Caustic Handbook

6 of 44Safety in HandlingCaustic Soda

side the boots. DO NOT tuck in. • Wear chemical resistant clothing

for protection of the body.Impregnated vinyl or rubber suitsare recommended.

• Wear hard hats for some protec-tion of the head, face and neck.

• If exposures are expected toexceed accepted regulatory limitsor if respiratory discomfort isexperienced use a NIOSHapproved air purifying respiratorwith high efficiency dust and mistfilters.

PROTECTIVE PRACTICES• Avoid breathing dust, mist or

spray of caustic soda.• Wear proper protective equip-

ment. If warranted, wearapproved respiratory protection.

• Keep equipment clean by wash-ing off any accumulation of caus-tic soda.

• Weld pipelines where practical.Use flanged joints with gasketsmade of caustic soda resistantmaterial such as rubber, PTFE,or EPDM rubber. If a screwed fit-ting is used, apply Teflon® tape tothe threads.

• When disconnecting equipmentfor repairs, first verify that thereis no internal pressure on theequipment and that the equip-ment has been drained andwashed.

• Provide storage tanks with suit-able overflow pipes. Overflowpipes should be directed near thebottom of the diked area.

• Shield the packing glands ofpumps to prevent spraying ofcaustic solutions in the event of aleak.

• When releasing air pressure froma pressurized system, take everyprecaution to avoid spurts orsprays of caustic solution.

• When making solutions, alwaysadd the caustic soda slowly tothe surface of the water with con-stant agitation. Never add thewater to the caustic soda.Always start with lukewarm water(80 -100°F). Never start with hotor cold water. Dangerous boilingor splattering can occur if causticsoda is added too rapidly,allowed to concentrate in onearea or added to hot or cold liq-uids. Care must be taken toavoid these situations.

• In case of a spill or leak, stop theleak as soon as possible. Aftercontainment, collect the spilledmaterial and transfer to a chemi-cal waste area. Remove large liq-uid spills by vacuum truck.Neutralize residue with diluteacid. Flush spill area with waterand follow with a liberal coveringof sodium bicarbonate or otheracceptable drying agent.

HANDLING LIQUIDCAUSTIC SODA

In handling caustic soda solu-tions, care must be taken to avoidsolidification which will plugpipelines and equipment. Graph 1(pg. 29) shows the freezing pointsfor solutions of caustic soda at vari-ous concentrations.

Should a caustic soda solutionbecome frozen in process equip-ment or piping, care must be takenwhen thawing the material. Useonly low pressure (10 PSIG orless) steam. Accelerated corrosioncan occur in areas where equip-ment is subjected to extremely hightemperatures.

Page 7: OxyChem Caustic Handbook

7 of 44Unloading and Handling LiquidCaustic Soda in Tank Cars

GENERAL INFORMATIONCaustic soda in liquid form

has a markedly corrosive actionon all body tissue. Even dilutesolutions may have a destructiveeffect on tissue after prolongedcontact. Inhalation of concentrat-ed mists can cause damage tothe upper respiratory tract, whileingestion of liquid caustic sodacan cause severe damage to themucous membranes or other tis-sues where contact is made. Inaddition, considerable heat isgenerated when liquid causticsoda is mixed with water whichcan result in boiling or splatter-ing. When diluting, always addcaustic soda to water; never addwater to caustic soda.

It is important that those whohandle caustic soda are aware ofits highly reactive and corrosiveproperties and know what pre-cautions to take. In case of acci-dental exposure, immediatelyflush exposed area with largeamounts of water and seek med-ical attention. For more specificinformation refer to the Safety inHandling Caustic Soda sectionof this handbook and to theMSDS.

PLACEMENT OF THE CAR FORUNLOADING1. After the car is properly spot-

ted, DOT regulations requirethat the hand brake be set andthe wheels blocked before anyconnections are made.

2. Caution signs must be placedat both ends of the car beingunloaded to warn people andswitching crews approachingthe car. DOT regulations statethat caution signs must beplaced on the track or car togive warning to personsapproaching the car from theopen end or ends of siding.Caution signs must be left up

until the car is unloaded anddisconnected from the dis-charge connections. Signsmust be made of metal or othersuitable material, at least 12x15inches in size, and bear thewords, “STOP-TANK CARCONNECTED”, or “STOP-MENAT WORK.”

3. It is recommended that derailattachments be placed at theopen end or ends of siding,approximately one car lengthaway.

4. Before hooking up a car, theresponsible individual shouldfirst locate and test the nearesteyewash and safety shower.Purge water through each toremove rust that may haveaccumulated.

UNLOADING PRECAUTIONS1. Only responsible and well

supervised employees shouldbe entrusted with the unloadingof liquid caustic soda.Unloading operations must bemonitored while the car is con-nected.

2. Since serious burns can resultfrom contact of caustic sodawith the skin and eyes, workersshould be well protected andcautioned to exercise care.Persons hooking up a carshould wear the following per-sonal protective equipment:• Hard hat• Chemical splash goggles• Face shield• Rubber, steel-toed boots• Rubber gloves or

equivalent• Vinyl or rubber jacket and

pants• If warranted, wear approvedrespiratory protection

3. A car of caustic soda should beunloaded only when adequatelighting is available throughoutthe entire unloading process.

4. Before starting to unload, makecertain that the tank car is vent-ed and that the storage tank isvented and has sufficientcapacity.

5. No one should enter the carunder any circumstances.

6. If a tank car needs to be movedwhen partially unloaded, DOTregulations require that allunloading lines must be discon-nected and car closures mustbe replaced.

7. A suggested method for sam-pling is to draw intermittentsamples from a 1/2” sampleline, connected to a verticalsection of the unloading line.The sample line should be fittedwith a valve and a 1/4” nipple.

8. OxyChem’s liquid caustic sodais shipped in well insulated andspecially lined tank cars. Liningsin these tank cars will withstandtemperatures up to 225°F.Recommended steam pressureused to heat up a rail car is lim-ited to 10psig max due to thisfact. To prevent damage to thelinings, neither water nor steamshould be added directly intothe tank cars if the car containsa level of caustic.

9. Unloading lines should be cov-ered with suitable insulation andheated just prior to transfer ofliquid caustic soda to storage.The preferred method of heat-ing is to provide electric orsteam heat tracing around theunloading line, under the insula-tion. An alternate method is toprovide tees in the unloadingline so that steam (or hot water)can be run through the unload-ing line just prior to its use.

Page 8: OxyChem Caustic Handbook

Unloading and Handling LiquidCaustic Soda in Tank Cars 8 of 44

These precautions will preventthe solidification of liquid caus-tic soda in cold unloading lines.Running steam throughunloading lines will increasecorrosion in unlined steelpiping systems and ironpickup in the product.

10. If compressed air is used inunloading operations, it isimportant that all fittings beinspected for leaks or otherdefects before unloading.Dome fittings in particularshould be inspected. If leaksare found, unloading operationsshould be suspended until theyare corrected.

11. General purpose caustic railcar tanks are structurallydesigned and constructed for100 psig, and have a designburst rating of 500 psig. Per 49CFR 179 and the AARSpecifications for Tank Cars, apressure relief device isinstalled sized for a fire sce-nario, that is set for 75 to 165psig. The higher set pressure isallowed due to the prematurefailure of the lower rated reliefdevices that occurred duringtransport handling, and resultedin injuries to rail road person-nel. Even through they aredesigned and equipped assuch, these are NOT pressurerail cars, nor should they bepadded above what OxyChemand the Chlorine Institute rec-ommends (20-25 psig).After a rail car is loaded withproduct, it is leak checked atapprox 30 psig to meet theDOT shipping requirement, andthat test pressure is releasedprior to shipping. Because of inherent shakingand jarring experienced by therail car and contents during theshipping process, gaskets andjoints can loosen up and cus-tomers should be cautious ofthat possibility. If pressure

unloading, particular areas towatch are the manway gasket,the bottom flange gasket (whenbottom unloading), and the topoperator gland area for bottomoutlet valve (if so equipped). Additionally the top operatedbottom outlet valve reach rodscan in rare instances, comedetached during transit, andthere have been reports thatthese rods can be 'pushed up'from a rail car if unloadingpressures > 30 psig are used.

HANDLING IN COLD WEATHERSince OxyChem tank cars

are well insulated and liquid causticsoda is loaded hot, it usuallyarrives at its destination in a liquidcondition. However, since 50% liq-uid caustic soda begins to crystal-lize at 54°F, in cases of unusualdelays in transit, freezing may takeplace in cold weather. If freezinghas occurred, the following proce-dure should be used.1. Carefully open tank car dome

cover.2. If a layer of caustic soda has

formed over the contents of thecar, this crust should be brokenbefore admitting steam to thejacket around the bottom dis-charge valve. The puncturing ofthe crust permits expansion ofthe liquid as it increases in tem-perature.

3. If no crust is present, determineif crystals have formed on thebottom of the car by probing thebottom with a rubber-cappedrod introduced through thedome opening.

4. If freezing has occurred, con-nect a steam line (10 psig orless) to the jacket around thebottom discharge valve.Connect a condensate returnline at the valve jacket steamoutlet. If a condensate returnline is not used, it is advisableto connect a valve at the steam

outlet, which should be openedsufficiently to relieve conden-sate and direct it toward theground or into a sewer. As con-tents liquefy, the valve may beclosed further to conservesteam.

5. If necessary, steam can be con-nected to the rail car steamcoils. A condensate return line,pressure reducing valve, and/orsteam trap should be used. Donot exceed a steam pressure of10 psig. Using steam pressureabove 10 psig may damage therailcar lining.

6. The amount of material that isfrozen in a caustic soda rail caris dependent upon the outsidetemperature, wind chill, and thetime between when the rail caris loaded and unloaded.Although it is unlikely, it is pos-sible for a caustic soda rail carto be totally frozen. If the caus-tic soda in a rail car is totallyfrozen, it may be necessary toapply steam to the rail car jack-et for two days (48 hours) to liq-uefy all of its contents.

7. When examination indicatesthat the contents have liquefiedand operation of the valve rodshows that the bottom dis-charge valve is free, the causticsoda is ready for unloading.The unloading temperature of50% caustic soda should beless than 120oF to minimizecorrosion of unlined steelpiping systems and equip-ment.

8. If the above measures do notliquefy the contents on the car,contact your OxyChem repre-sentative.

Page 9: OxyChem Caustic Handbook

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11. Bottom Outlet Valve

12. Steam Chamber

13. Steam Inlet16. Steam Outlet

21. Plug Cock

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Rail Car DrawingDetails of Caustic Soda Car

Figure 1

9 of 44

Page 10: OxyChem Caustic Handbook

Unloading Liquid Caustic Soda in Tank Cars 10 of 44

Rail cars can be either bottomunloaded (gravity, pump or pressure)or top unloaded (with air pressure).Refer to appropriate unloading proce-dure based on the method to beemployed.

UNLOADING THROUGHBOTTOM OUTLET VALVE1. Open the dome cover and deter-

mine if the contents of the carare liquid. If not, see “Handlingin Cold Weather.” Keep thedome cover at least partiallyopen during the entire unloadingoperation to vent the tank car.

2. Refer to Figure 1. Insure that thebottom outlet valve is closedtightly. The valve rod which oper-ates the bottom discharge valvehas a handle on it which is locat-ed outside the dome of the car.The handle can be reversed andserves as a cap in transit.

3. Remove the pipe plug, then care-fully open the supplementaryvalve to drain any liquid that mayhave seeped past the bottomoutlet valve during transit. If thesupplementary valve cannot beopened, the application of steamfrom a steam lance, directed on

the valve, should free it for open-ing.

4. Attach the unloading line to thebottom of the supplementaryvalve.

5. Check the unloading line to seethat all valves are in the properposition for unloading.

6. Open the bottom outlet valve byturning the valve rod to allowcontents to flow by gravity topump or tank. If the bottom outletvalve does not open upon appli-cation of light pressure, frozencaustic soda is probably presentin the bottom of the car.Application of steam to the heatcoils may be necessary. See“Handling in Cold Weather.”

7. Compressed air can be used toincrease the flow rate of causticsoda to storage or to transfer liq-uid without the use of a pump. Ifcompressed air is to be used,check the rupture disk in thedome to be sure it is intact.Close the dome cover securely.Remove the one-inch air inletplug and connect a flexible airline at this point. The air lineshould have a release valve, oiltrap, pressure relief valve set at

20 PSIG, pressure reducingvalve set at 18 PSIG and a shut-off valve. Apply air pressure tothe car slowly. Note that thepressure relief device (rupturedisk and/or pressure relief valve)in the dome will relieve at a pres-sure between 75 PSIG and 165PSIG, depending on the type ofcar. Refer to the stenciling on theside of the railcar.

8. When the car and unloading lineare empty, shut off air supply andopen the release valve.

9. When the tank car is empty andthe discharge pipe has complete-ly drained, disconnect the airline, if used, close the bottomoutlet valve and supplementaryvalve, and detach the unloadingline at the car.

10. Prepare the car for return.

Steam jacket

UnionPump

2” Steel pipe

Pump inlet valve

Low line drain valveRail carunloading valve

Vent

Tank inlet valve

To process

Drain

TANK CAR

STORAGE TANK

Steam coils

Figure 2: Bottom Unloading

Page 11: OxyChem Caustic Handbook

11 of 44Unloading Liquid Caustic Soda in Tank Cars

UNLOADING THROUGHDOME WITH AIR PRESSURE

1. Open the dome cover to deter-mine if the contents of the carare liquid. If not, see “Handling inCold Weather.”

2. Close the dome cover and fastensecurely, making certain that it isair tight. Check that the rupturedisk in the dome is intact.

3. Check that the product storagetank is vented and has sufficientcapacity.

4. After opening the protectivehousing cover, connect theunloading line to the two-inch topunloading valve. After removingthe protective housing cover, aflexible steel hose connection forthe unloading line is recommend-ed since a car may rise as muchas 2” during unloading.

5. Connect the flexible air supplyline to the one-inch air inletvalve. This line should have arelease valve, oil trap, pressurerelief valve set at 20 PSIG, pres-sure reducing valve set at 18PSIG and a shut-off valve. Notethat the relief device (rupture disk

or pressure relief valve) in thedome will relieve at a pressurebetween 75 and 165 PSIG,depending on the type of car.Refer to the stenciling on theside of the railcar.

6. Apply air pressure slowly untilthere is a normal flow of liquid tothe storage tank. The pressureshould be adjusted and main-tained until the tank car is com-pletely empty. A drop in air pres-sure or the sound of air rushingthrough the unloading line indi-cates that the tank car is empty.

7. Shut off the air supply, open therelease valve, and allow theeduction pipe to drain.

8. When the eduction pipe hasdrained and the tank car is atatmospheric pressure, discon-nect the air supply line at the car.

9. Do not enter the car to make aninspection.

10. Open the dome cover and deter-mine if the car is empty. If empty,disconnect the unloading line atthe car, replace pipe plugs andtightly replace the dome coverand the protective housing cover.

11. Care should be taken not to spill

caustic soda on the car, since itwill cause damage to the car andmay endanger workers handlingthe empty car on its return.

12. Prepare the car for return.

PREPARING EMPTY TANKCARS FOR RETURN1. Make sure the bottom outlet

valve and supplementary valveare closed.

2. Disconnect the unloading lineand replace the bottom outletplug. Do not replace closures onsteam openings.

3. Close dome cover and fastensecurely.

4. Return the empty tank carpromptly in accordance with theshipper’s instructions. The ship-per’s routing directions must befollowed in all instances.

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Page 12: OxyChem Caustic Handbook

Unloading Liquid Caustic Soda in Tank Trucks 12 of 44

CARRIER RESPONSIBILITIESOxyChem tank truck drivers have

received instructions regardingequipment and delivery proce-dures. If an OxyChem arrangedcarrier, delivering caustic soda toyour plant, fails to adhere to the fol-lowing guidelines, please contactOxyChem so that corrective actioncan be taken.

EquipmentEquipment must meet

Department of Transportation regu-lations, Code of FederalRegulations (CFR), Title 49.

Tank Truck SpecificationTank trucks should meet the

established DOT requirements forhauling liquid caustic soda.

Four DOT “CORROSIVE” plac-ards must be permanently affixedto the cargo tank.

Unloading EquipmentIf unloading is by gravity to stor-

age or customer’s unloading pump,no special equipment is needed.

If unloading is by truck-mountedpump, use only an all iron or nickelunit. The pump can be driven by atractor powered take-off or an aux-iliary gasoline engine. Use at leasta 2-inch pump line.

If unloading is by compressedair, the tank vessel must meet theDOT requirements of the CFR, Title49. The line used to supply air tothe tank truck is required to beequipped with: pressure reducingvalve, pressure release valve,pressure gauge, pressure reducingvalve and pressure relief valve.The relief valve should be set at amaximum pressure of 20 PSIG andthe pressure reducing valve shouldbe set at 2 to 3 pounds lower.Whether this equipment is attached permanently to the tank or carriedas an assembled unit to beattached at each unloading, itshould be properly maintained andperiodically tested.

A 40 foot length of air hose isrequired if the customer’s air sup-ply is used. When compressed airis not available from the customer’splant, trucks equipped with pumpsor air compressors can be providedat the customer’s request.

Unloading LinesUnloading hoses must be con-

structed of material resistant tocaustic soda. Hoses should be atleast 2 inches in diameter and 15to 30 feet in length.

Whether the unloading hose isfitted with a union, pipe flange, or aquick type coupler, the truck drivershould have available matching fit-tings and tools to facilitate a con-nection to a 2-inch or 3-inchthreaded pipe.

TRUCK DRIVER RESPONSIBILITIES

Truck drivers must obtain permis-sion to unload from the properauthorities and observe any specialinstructions from the customer.

Truck drivers must wear the pro-tective equipment required byOxyChem as listed underProtective Equipment, (pg. 6) or bycustomer, whichever is more inclu-sive, and at all times follow safehandling practices. Customersmust not allow truck drivers who donot meet these requirements tounload.

The following unloadingprocedures are recommended:• Check the operation of the safety

shower and eyewash fountain.Purge water through each toremove rust that may have accu-mulated.

• If a shower and eyewash are notavailable, a water hose connect-ed to a source of water isrequired. If the valve on the lineis not conveniently located nearthe unloading area, leave astream of water flowing duringunloading.

• Connect one end of the unload-ing hose to the customer’s stor-age tank fill line.

• During cold weather and if facili-ties are provided, preheat withsteam the fill line, the unloadinghose, and, if needed, the truckoutlet.

• Check the unloading line to besure that it is open.

• Connect the unloading hose tothe discharge outlet on the tanktruck.

• Start the pump or start pressuriz-ing the tank, depending on thetype of equipment used.

• Open the valves on the truckdischarge line.

• Stand by until the truck cargo iscompletely unloaded.

• If compressed air is used,allowthe air to flush out the lines to thestorage tank and then cut off theair supply.

• When a pump is used, flush outthe unloading line before discon-necting the hose. If water isavailable, a small quantity canbe added into the truck while thepump is running to flush out theline. Air or water can be used toflush the caustic soda in the lineinto the storage tank or back tothe truck. If no water is availablefor flushing out lines, exercisegreat caution when lines are dis-connected.

Page 13: OxyChem Caustic Handbook

13 of 44Unloading Liquid Caustic Soda in Tank Trucks

• Close the valve on the storagefill line.

• Close all valves on the tanktruck.

• In some installations the cus-tomer’s fill line is fitted with adrain to be used instead of flush-ing the line before the hose isdisconnected.

• Disconnect the hose with cautionand discharge any caustic sodaremaining in the hose to a suit-able container.

• Unload caustic soda in an areawith adequate safeguards forspill control. No caustic sodashould be spilled, but in theevent a small amount is spilled,hose down the area with water.Clean up all spills and dispose inaccordance with federal, stateand local regulations.

FACILITY EQUIPMENTTypical installations of storage

vessels for receipt of truck ship-ments are similar to those shown inFigures 2 and 3 for rail car deliver-ies.

A storage tank with a minimumcapacity of 1.5 tank cars is recom-mended.

A fill line to the top of the storageis strongly recommended. If a bot-tom fill line is used, the truck drivermust be informed.

A permanent fill line in closeproximity to the tank truck unload-ing area is required.

A 2-inch or larger fill line is rec-ommended.

A 3/4-inch valve connection isrecommended on the fill line foruse in flushing out the line with air,water, or steam. It can be used asa drain.

Cap or close the end of the fillline when not in use.

A source of running water for useduring unloading operations isrequired. A safety shower and eye-wash fountain are recommended.

Page 14: OxyChem Caustic Handbook

14 of 44Equipment For HandlingCaustic Soda

GENERAL CONSIDERATIONSCaustic soda is a corrosive

chemical which is normally handledin either steel, nickel, nickel alloysor certain types of plastic equip-ment. The specific material willdepend on the conditions underwhich the material is being used.Temperature, solution concentra-tion, location and safety considera-tions are all important factors inequipment selection.

MATERIALS OF CONSTRUCTIONThe most common construction

materials for handling and storingcaustic soda solutions are blackiron and mild steel; however, liquidcaustic soda will attack these met-als at elevated temperatures. Theideal storage temperature for caus-tic soda solutions is 80 to 100°F. Insteel systems, temperatures above120°F will cause accelerated corro-sion and iron contamination of thecaustic (above 120°F, cracking canoccur if concentrated caustic isprocessed in steel equipment thathas not been stress relieved.)Where iron contamination or corro-sion is unacceptable, epoxy linedsteel, 316L and 304L stainlesssteels are recommended. 316Land 304L stainless is acceptable to200°F. At temperatures above200°F, nickel is typically used butMonel®, Inconel®, or Hastelloy®can also be used. Consult with theepoxy supplier about the workingtemperature range of a particularepoxy lining.

Plastics, such as polyethylene,polypropylene, PVC, and CPVC,are chemically suitable with causticsoda. They can be used to preventiron contamination if maximumtemperatures for each material arenot exceeded. The manufacturer ofthe tank, drum, piping or equipmentin question should be contacted to

determine the exact limitations ofthe specific plastic. Aluminum, cop-per, zinc, lead and their alloys(e.g., brass and bronze) are NOTsuitable. Caustic soda readilyattacks these materials.

STORAGE TANKSTanks can be either vertical or

horizontal. They are usually fabri-cated from at least 1/4-inch steelplate. A 1/8-inch corrosionallowance should be included inthe design. If iron contamination isa problem, tanks can be fabricatedfrom 304L or 316L stainless steel.If the tanks are large, it’s usuallymore economical to fabricate asteel tank and line it with an epoxycoating. Plastic tanks are usuallyfabricated from polypropylene orFRP (Since caustic can attackglass reinforcement fibers ofimproperly constructed FRP tanks,care must be taken to ensure thatthe FRP tanks are built with theproper reinforcing materials, resins,catalysts, curing procedures andcorrosion barriers).

The product draw-off line shouldbe at least 4 inches above the bot-tom of the tank and the drain con-nection should be at the lowestpoint in the tank. This will facilitatedrainage during periodic cleaningof the tank. Most tanks have a leveltransmitter for measuring liquidlevel.

Where heating is required, anexternal heat exchanger with a cir-culating pump or internal steamheating coils are most commonlyemployed. The preferred materialsfor the coils are nickel, Monel®, orInconel®. Despite this, stainlesssteel is most commonly usedbecause of cost considerations.(At

high temperatures, stainless steelmay crack). If it is necessary toinsulate the storage tank, a two-inch layer of polyurethane foam orcellular glass should be adequate.

Proper design of a storage sys-tem will include adequate contain-ment in case of tank failure. Stateand local regulatory authoritiesshould always be consulted duringthe design phase of construction.

TANK CLEANING ANDPASSIVATION

Tank cleaning is dependent onthe product stored in it previously.A tank that previously containedcaustic soda requires scaleremoval, wall thickness testing,rinsing, passivation, floor cleaning,and immediate filling. A tank previ-ously containing another productrequires cleaning with an appropri-ate solvent or soap, as well as theother steps mentioned above.

Scale removal is accomplishedby blasting the walls with an abra-sive such as sand or pecan shells.Abrasives containing high percent-ages of metals are not recom-mended.

The wall thickness of the tankshould be measured to ensure thatthe tank has structural integrity forthe density of the product and theheight of product in the tank.

Passivation requires permeationof the steel tank walls with causticsoda. This is usually accomplishedby spraying the cleaned walls witha hot solution of caustic soda.Temperatures of 100 - 140°F andsolutions of 5 - 20% are recom-mended. While this is more of anart than a science, a standard rec-

Page 15: OxyChem Caustic Handbook

15 of 44Equipment For HandlingCaustic Soda

ommendation would be sprayingthe walls for 2-4 hours with 10%solution at 140°F. The larger thetank the longer it should besprayed to complete the passiva-tion. Utilizing a hotter and strongersolutions will require less time forpassivation. One way to achievethe solution heat necessary is todilute 50% caustic soda to 20%.The heat of dilution will cause thecaustic soda temperature to rise.Additional heat may be necessaryto achieve optimal solution temper-atures. The coating of the tankwalls is best accomplished with anelliptical sprayer. If this type ofsprayer is not available, the spray-ing may be done manually withextreme caution taken to protectthe operator.

After passivation, the tank bottommust be cleaned out as well aspossible. The quality of the initialproduct stored in the tank willdepend greatly upon the extent towhich the tank bottom is cleaned ofscale abrasive compound. If anelliptical sprayer is used for thecleaning, a squeegee will need tobe used to clean the tank bottom. Ifmanual spraying is used for clean-ing, the sprayer can be used topush the scale and abrasive towardthe sump followed up by use of a

squeegee.

After cleaning, the tank should befilled with caustic soda as soon aspossible. This will prevent the tankwalls from losing their passivation.If the tank cleaning is not complete-ly successful, it may be necessaryto filter the initial product from thetank to keep it free from particulatematter. This would require a 5-10micron filter media housed in a unitthat would be acceptable with thetemperature, pressure, and chemi-cal.

PIPING AND VALVESPipelines are usually at least two

inches in diameter and constructedof Schedule 40 black iron or mildsteel with welded or flanged joints.Where disconnects are necessary,flanged joints are preferred to facili-tate maintenance. A safety shield ofwrap-around polypropylene is rec-ommended for all flanged joints.This will protect against spraying incase a gasket leaks.

Proper pipeline design includesan adequate pitch to permit com-plete draining. Avoid any loops orpockets. Lines should also includewater or air connections for purgingafter use.

Where slight iron contaminationis unacceptable, CPVC, polypropy-lene, polypropylene-lined steel, andTeflon® lined steel pipe are suit-able materials. Pay special atten-tion to suitable operating tempera-

tures and pressures with thesematerials.

Ductile iron, cast steel, stainlesssteel, Alloy 20, and Teflon®-linedquarter-turn plug or ball valves arerecommended for caustic soda ser-vice. Various other types of valvescan also be used; however, keep inmind that less elaborate fittingsprovide better reliability in this ser-vice.

PUMPSCentrifugal pump of stainless

steel or Alloy 20 construction, witheither double mechanical seals or adeep packing gland, is recom-mended. Packing material shouldbe Teflon® impregnated, causticresistant fibers, or equivalent. Toavoid seals altogether, magneticallycoupled pumps could be used.

Pump location should receivecareful consideration. For ease ofoperation, keep the suction lines asshort as possible. A recirculatingline will help prevent excess wearon the pump and, in many cases,can assist in controlling flow rates.

METERSCaustic soda solutions can be

metered through standard rotame-ters having non-glass tubes andnickel or stainless steel floats.Magnetic, coriolis or orifice-typemeters are preferred for strong, hotsolutions. They should be made ofcorrosion resistant materials suchas stainless steel, alloy 20, monelor nickel.

Page 16: OxyChem Caustic Handbook

16 of 44Installation of Tanks

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Figure 6: Typical Storage Tank Installation

Page 17: OxyChem Caustic Handbook

3

TechnicalData 17 of 44

Table 1 Density and Caustic Soda Content of Rayon/Membrane GradeCaustic Soda Solutions at 60°F

DEGREES TOTAL WT TOTAL WTWT% % SPECIFIC BAUMÉ NaOH NaOH SOLUTION NaOH SOLUTIONNaOH Na2O GRAVITY [AM STD] G/L LB/GAL LB/GAL LB/CU FT LB/CU FT

1.0 0.775 1.0120 1.706 10.118 0.084 8.437 0.631 63.1132.0 1.550 1.0230 3.259 20.457 0.171 8.529 1.277 63.8043.0 2.325 1.0342 4.782 31.019 0.259 8.622 1.935 64.4974.0 3.100 1.0453 6.274 41.803 0.349 8.715 2.608 65.1915.0 3.874 1.0564 7.736 52.811 0.440 8.807 3.295 65.8856.0 4.649 1.0676 9.170 64.042 0.534 8.900 3.995 66.5817.0 5.424 1.0787 10.580 75.496 0.630 8.993 4.710 67.2778.0 6.199 1.0899 11.960 87.174 0.727 9.087 5.438 67.9739.0 6.974 1.1010 13.310 99.076 0.826 9.180 6.181 68.670

10.0 7.748 1.1122 14.630 111.210 0.927 9.273 6.937 69.36711.0 8.523 1.1234 15.930 123.550 1.031 9.366 7.707 70.06312.0 9.298 1.1345 17.200 136.130 1.136 9.459 8.492 70.75913.0 10.080 1.1457 18.440 148.920 1.242 9.552 9.290 71.45514.0 10.850 1.1569 19.660 161.930 1.351 9.645 10.110 72.15015.0 11.630 1.1680 20.850 175.170 1.461 9.738 10.930 72.84516.0 12.400 1.1791 22.030 188.630 1.573 9.830 11.770 73.53917.0 13.180 1.1902 23.170 202.300 1.687 9.923 12.620 74.23118.0 13.950 1.2013 24.300 216.200 1.803 10.020 13.490 74.92219.0 14.730 1.2124 25.400 230.310 1.921 10.110 14.370 75.61220.0 15.500 1.2234 26.480 244.640 2.040 10.200 15.260 76.30021.0 16.280 1.2344 27.530 259.180 2.162 10.300 16.170 76.98722.0 17.050 1.2454 28.570 273.940 2.285 10.390 17.090 77.67223.0 17.830 1.2563 29.590 288.910 2.409 10.480 18.030 78.35524.0 18.600 1.2672 30.580 304.090 2.536 10.570 18.970 79.03525.0 19.370 1.2781 31.550 319.470 2.664 10.660 19.930 79.71326.0 20.150 1.2889 32.510 335.070 2.794 10.750 20.910 80.38927.0 20.920 1.2997 33.440 350.870 2.926 10.840 21.890 81.06228.0 21.700 1.3105 34.350 366.870 3.060 10.930 22.890 81.73129.0 22.470 1.3212 35.250 383.070 3.195 11.020 23.900 82.39830.0 23.250 1.3317 36.120 399.450 3.331 11.110 24.920 83.05731.0 24.020 1.3424 36.980 416.070 3.470 11.200 25.960 83.72232.0 24.800 1.3529 37.830 432.860 3.610 11.280 27.010 84.37933.0 25.570 1.3634 38.650 449.850 3.751 11.370 28.070 85.03334.0 26.350 1.3738 39.450 467.010 3.895 11.460 29.140 85.68135.0 27.120 1.3842 40.240 484.370 4.039 11.540 30.220 86.32736.0 27.900 1.3944 41.020 501.910 4.186 11.630 31.310 86.96837.0 28.670 1.4046 41.770 519.630 4.333 11.720 32.420 87.60538.0 29.450 1.4148 42.510 537.520 4.482 11.800 33.530 88.23739.0 30.220 1.4248 43.230 555.590 4,633 11.880 34.660 88.86440.0 31.000 1.4348 43.940 573.830 4.785 11.970 35.800 89.48741.0 31.770 1.4447 44.640 592.240 4.939 12.050 36.950 90.10542.0 32.550 1.4545 45.310 610.810 5.094 12.130 38.110 90.71743.0 33.320 1.4643 45.980 629.530 5.250 12.210 39.270 91.32444.0 34.100 1.4739 46.630 648.420 5.407 12.290 40.450 91.92645.0 34.870 1.4835 47.260 667.450 5.566 12.370 41.640 92.52246.0 35.650 1.4930 47.880 686.640 5.726 12.450 42.840 93.11347.0 36.420 1.5023 48.480 705.970 5.887 12.530 44.040 93.69748.0 37.200 1.5116 49.080 725.440 6.049 12.610 45.260 94.27549.0 37.970 1.5208 49.650 745.040 6.213 12.680 46.480 94.84750.0 38.740 1.5298 50.220 764.780 6.377 12.760 47.710 95.41251.0 39.520 1.5388 50.770 784.640 6.543 12.830 48.950 95.97152.0 40.290 1.5476 51.310 804.630 6.710 12.910 50.200 96.523

Page 18: OxyChem Caustic Handbook

18 of 44TechnicalData

Table 2 Density and Caustic Soda Content of Diaphragm GradeCaustic Soda Solutions at 60°F

DEGREES TOTAL WT TOTAL WTWT% % % SPECIFIC BAUMÉ NaOH NaOH SOLUTION SOLUTIONNaOH Na2O NaCl GRAVITY [AM STD] G/L LB/GAL LB/GAL LB/CU FT LB/CU FT

1.0 0.775 0.020 1.0121 1.726 10.120 0.084 8.438 0.631 63.1222.0 1.550 0.040 1.0233 3.300 20.463 0.171 8.532 1.277 63.8233.0 2.325 0.060 1.0346 4.842 31.032 0.259 8.626 1.936 64.5254.0 3.100 0.080 1.0459 6.351 41.827 0.349 8.719 2.610 65.2275.0 3.874 0.100 1.0571 7.829 52.846 0.441 8.813 3.297 65.9306.0 4.649 0.120 1.0684 9.282 64.095 0.535 8.908 3.999 66.6367.0 5.424 0.140 1.0797 10.710 75.568 0.630 9.002 4.714 67.3418.0 6.199 0.160 1.0911 12.100 87.269 0.728 9.096 5.444 68.0479.0 6.974 0.180 1.1024 13.460 99.195 0.827 9.191 6.188 68.752

10.0 7.748 0.200 1.1137 14.800 111.350 0.928 9.285 6.946 69.45811.0 8.523 0.220 1.1250 16.110 123.730 1.032 9.379 7.718 70.16412.0 9.298 0.240 1.1363 17.390 136.340 1.137 9.474 8.505 70.87013.0 10.080 0.260 1.1476 18.650 149.170 1.244 9.568 9.305 71.57514.0 10.850 0.280 1.1589 19.880 162.220 1.353 9.662 10.120 72.27915.0 11.630 0.300 1.1702 21.090 175.500 1.464 9.756 10.950 72.98316.0 12.400 0.320 1.1815 22.270 189.000 1.576 9.850 11.790 73.68517.0 13.180 0.340 1.1927 23.430 202.730 1.691 9.944 12.650 74.38718.0 13.950 0.360 1.2040 24.560 216.680 1.807 10.040 13.520 75.08819.0 14.730 0.380 1.2152 25.670 230.840 1.925 10.140 14.400 75.78720.0 15.500 0.400 1.2263 26.760 245.230 2.045 10.230 15.300 76.48521.0 16.280 0.420 1.2375 27.830 259.830 2.167 10.320 16.210 77.18022.0 17.050 0.440 1.2486 28.870 274.650 2.291 10.410 17.140 77.87423.0 17.830 0.460 1.2597 29.900 289.690 2.416 10.510 18.080 78.56624.0 18.600 0.480 1.2708 30.900 304.930 2.543 10.600 19.030 79.25525.0 19.370 0.500 1.2818 31.880 320.400 2.672 10.690 19.990 79.94326.0 20.150 0.520 1.2928 32.840 336.070 2.803 10.780 20.970 80.62827.0 20.920 0.540 1.3037 33.780 351.940 2.935 10.870 21.960 81.31028.0 21.700 0.560 1.3146 34.700 368.020 3.069 10.960 22.960 81.98829.0 22.470 0.580 1.3254 35.600 384.310 3.205 11.050 23.980 82.66530.0 23.250 0.600 1.3362 36.490 400.800 3.342 11.140 25.010 83.33831.0 24.020 0.620 1.3470 37.350 417.490 3.482 11.230 26.050 84.00732.0 24.800 0.640 1.3576 38.200 434.370 3.622 11.320 27.100 84.67333.0 25.570 0.660 1.3683 39.030 451.450 3.765 11.410 28.170 85.33534.0 26.350 0.680 1.3788 39.840 468.720 3.909 11.500 29.240 85.99435.0 27.120 0.700 1.3893 40.630 486.170 4.054 11.590 30.330 86.64836.0 27.900 0.720 1.3997 41.410 503.820 4.201 11.670 31.430 87.29937.0 28.670 0.740 1.4101 42.170 521.640 4.350 11.760 32.540 87.94438.0 29.450 0.760 1.4204 42.920 539.650 4.500 11.850 33.670 88.58639.0 30.220 0.780 1.4306 43.640 557.830 4.652 11.930 34.800 89.22340.0 31.000 0.800 1.4407 44.360 576.190 4.805 12.020 35.950 89.85441.0 31.770 0.820 1.4508 45.050 594.710 4.959 12.100 37.100 90.48142.0 32.550 0.840 1.4607 45.740 613.400 5.115 12.180 38.270 91.10343.0 33.320 0.860 1.4706 46.400 632.260 5.272 12.270 39.440 91.72044.0 34.100 0.880 1.4804 47.060 651.270 5.431 12.350 40.630 92.33045.0 34.870 0.900 1.4901 47.690 670.440 5.591 12.430 41.830 92.93546.0 35.650 0.920 1.4997 48.320 689.760 5.752 12.510 43.030 93.53547.0 36.420 0.940 1.5092 48.930 709.220 5.914 12.590 44.250 94.12948.0 37.200 0.960 1.5187 49.520 728.830 6.078 12.670 45.470 94.71649.0 37.970 0.980 1.5280 50.100 748.580 6.242 12.740 46.700 95.29750.0 38.740 1.000 1.5372 50.670 768.460 6.408 12.820 47.940 95.87251.0 39.520 1.000 1.5506 51.490 790.690 6.594 12.930 49.330 96.71152.0 40.290 1.000 1.5604 52.070 811.250 6.765 13.010 50.610 97.317

Page 19: OxyChem Caustic Handbook

TechnicalData

Table 3 Specific Heats of Caustic Soda Solutions in BTU’s per PoundPERCENT TEMPERATURE °FCAUSTIC 32 40 50 60 80 100 120 140 160 180 200 220 240 260 280 300

0 1.004 1.003 1.001 0.999 0.998 0.997 0.998 0.999 1.000 1.002 1.004 - - - - -2 0.965 0.967 0.968 0.969 0.972 0.974 0.977 0.978 0.980 0.983 0.986 - - - - -4 0.936 0.940 0.943 0.946 0.951 0.954 0.957 0.960 0.962 0.965 0.966 - - - - -6 0.914 0.920 0.924 0.928 0.933 0.938 0.941 0.944 0.946 0.948 0.950 - - - - -8 0.897 0.902 0.907 0.911 0.918 0.923 0.927 0.930 0.932 0.934 0.936 - - - - -10 0.882 0.888 0.893 0.897 0.905 0.911 0.916 0.918 0.920 0.922 0.923 - - - - -12 0.870 0.877 0.883 0.887 0.894 0.901 0.906 0.909 0.911 0.912 0.913 - - - - -14 0.861 0.868 0.874 0.879 0.886 0.892 0.897 0.901 0.903 0.903 0.904 - - - - -16 0.853 0.860 0.866 0.871 0.880 0.886 0.891 0.894 0.896 0.897 0.897 - - - - -18 0.847 0.854 0.860 0.865 0.873 0.880 0.885 0.888 0.890 0.891 0.891 - - - - -20 0.842 0.848 0.854 0.859 0.868 0.875 0.880 0.884 0.886 0.886 0.887 - - - - -22 0.837 0.844 0.849 0.854 0.863 0.870 0.876 0.880 0.882 0.882 0.883 - - - - -24 - 0.839 0.844 0.849 0.858 0.866 0.873 0.877 0.879 0.879 0.880 - - - - -26 - 0.835 0.840 0.845 0.854 0.863 0.869 0.874 0.875 0.876 0.876 - - - - -28 - 0.830 0.836 0.841 0.850 0.859 0.866 0.870 0.872 0.872 0.873 - - - - -30 - 0.826 0.832 0.837 0.846 0.855 0.862 0.866 0.868 0.869 0.869 - - - - -32 - 0.822 0.828 0.833 0.842 0.850 0.857 0.862 0.863 0.864 0.864 - - - - -34 - - 0.823 0.828 0.837 0.845 0.852 0.856 0.857 0.858 0.858 - - - - -36 - - 0.819 0.824 0.832 0.840 0.845 0.849 0.850 0.851 0.851 - - - - -38 - - 0.816 0.820 0.827 0.833 0.837 0.841 0.842 0.842 0.843 - - - - -40 - - 0.812 0.815 0.821 0.826 0.829 0.831 0.832 0.832 0.832 - - - - -42 - - 0.807 0.809 0.813 0.816 0.819 0.819 0.820 0.820 0.820 - - - - -44 - - - 0.802 0.804 0.806 0.807 0.807 0.807 0.806 0.804 - - - - -46 - - - 0.793 0.794 0.795 0.794 0.794 0.793 0.791 0.789 - - - - -48 - - - - 0.783 0.782 0.781 0.780 0.779 0.777 0.776 - - - - -50 - - - - 0.771 0.769 0.768 0.767 0.765 0.765 0.764 0.763 0.762 0.762 0.761 0.76152 - - - - 0.759 0.757 0.756 0.754 0.753 0.752 0.751 0.749 0.748 0.747 0.746 0.74554 - - - - 0.746 0.744 0.741 0.739 0.739 0.738 0.737 0.735 0.733 0.731 0.730 0.72856 - - - - 0.733 0.730 0.728 0.726 0.724 0.723 0.722 0.721 0.719 0.717 0.715 0.71358 - - - - - 0.719 0.717 0.715 0.713 0.711 0.709 0.707 0.705 0.703 0.702 0.70060 - - - - - 0.706 0.705 0.703 0.701 0.699 0.697 0.696 0.693 0.691 0.690 0.68862 - - - - - - 0.694 0.692 0.690 0.688 0.687 0.685 0.683 0.681 0.679 0.67764 - - - - - - 0.684 0.682 0.681 0.679 0.677 0.675 0.673 0.671 0.670 0.66866 - - - - - - 0.675 0.673 0.671 0.669 0.668 0.666 0.664 0.662 0.660 0.65868 - - - - - - - 0.663 0.662 0.660 0.658 0.656 0.655 0.653 0.651 0.64970 - - - - - - - 0.655 0.653 0.651 0.649 0.647 0.646 0.644 0.642 0.64072 - - - - - - - - 0.645 0.643 0.641 0.639 0.637 0.635 0.634 0.63273 - - - - - - - - - 0.639 0.637 0.635 0.633 0.631 0.630 0.62874 - - - - - - - - - 0.635 0.633 0.631 0.629 0.628 0.626 0.624

74.5 - - - - - - - - - 0.633 0.631 0.629 0.627 0.626 0.624 0.62276 - - - - - - - - - 0.628 0.627 0.625 0.623 0.621 0.619 0.61778 - - - - - - - - - - 0.620 0.618 0.616 0.615 0.613 0.611

19 of 44

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20 of 44TechnicalData

Properties of Anhydrous Caustic Soda

Table 4Miscellaneous Properties

Property ValueChemical Formula . . . . . . . .NaOHMolecular Weight . . . . . . . .40.00Freezing or meltingpoint . . . . . . . . . . . . . . . . . .318°C or 604°FBoiling point . . . . . . . . . . . .1388°C or 2530°F at

760 mm Hg pressureSpecific heat . . . . . . . . . . . .0.353 cal/gm/°C at

20°C or 0.353BTU/Ib/°F at 68°F

Free energy offormation . . . . . . . . . . . . . . .-90,762 cal/mol at

25°C, 760 mm Hg pressure

Refractive index forlight wavelength of5894 A . . . . . . . . . . . . . . . . .N = 1.433 at 320°C

N = 1.421 at 420°C

Latent heat of fusion . . . . . .40.0 cal/gm or 72.0 BTU/lb

Lattice energy . . . . . . . . . . .176.2 kg-cal/molEntropy . . . . . . . . . . . . . . .12.43 kg-cal/mol/°K

at 25°C, 760 mm Hg pressure

Heat of formation . . . . . . . . 101.723 kcal/molNa+1/2O2+1/2H2 = NaOH

Table 5Specific Gravity of Solid Caustic Soda

Temp.°C 20 299.6 320 350 400 450

Specificgravity 2.130 2.08 1.786 1.771 1.746 1.722

Note:The average bulk density of flake Caustic Soda is about 60 pounds per cubic foot. This value varies with the packing conditions and flake characteristics.

Table 6Enthalpy of

Anhydrous Caustic Soda(Above 32°F base temperature)

Solid NaOH Molten NaOHTemp.°F BTU/lb Temp.°F BTU/lb

32 0.00 605.1 356.0650 5.57 650 381.47

100 21.71 700 408.94150 38.82 750 435.59200 56.91 800 461.28250 75.98 850 486.48300 96.01 900 510.70350 117.03 950 534.12400 139.02 1000 556.72450 161.98 1050 578.52500 185.92 1100 599.51550 210.83 1150 619.68600 281.27 1300 675.35

605.1 283.97 1350 692.29

Table 7Viscosity of

Molten Caustic Soda Temp. °C . . . . . . . . . . . 350 400 450 500 550Viscosity, centipoise . . . 4.0 2.8 2.2 1.8 1.5

Table 8Vapor Pressure of

Molten Caustic Soda

Temp.°C . . . . . . . .1000 1050 1100 1200 1300 1388Vapor Pressurein mm Hg . . . . . . . . . .41 66 103 225 447 760

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TechnicalData 21 of 44

Properties of Caustic Soda Solutions

Table 9Coefficient of Expansion of

Caustic Soda Solutions

The coefficient of expansion is the volume changeper unit change in temperature. It may be derivedfrom data on the change of density with tempera-ture according to the following formula:

d = 1.0200 + 0.0105OX - (0.0005+0.0000049X)t

Note: “d” is the density in g/cc; “X” is the concen-tration in percent by weight of NaOH; and “t” is thetemperature in °C. The formula is limited to con-centrations from 10% to 70% NaOH and to tem-peratures from 15°C to 70°C.

Table 10Compressibility of

Caustic Soda Solutions

Moles H2O/Mole NaOH Density B x 10

6

25.01 1.08670 31.2350.09 1.04391 36.15

100.15 1.02114 39.12

Note: The compressibility coefficient B is expressed as compressibilityper cc per megabar at 25°C. Data is valid between 100-300 megabars.

Table 11Heat of Solution of Caustic Soda

Heat Liberated % Moles H2O/ BTU/lb. BTU/lb. cal/g

NaOH Mole NaOH NaOH Solution NaOH0.44 500 455.8 2.0 253.20.55 400 456.0 2.5 253.31.10 200 456.6 5.0 253.72.17 100 458.3 9.9 254.64.26 50 462.0 19.7 256.78.16 25 462.6 37.7 257.0

14.14 13.5 470.1 66.5 261.219.80 9 462.2 91.5 256.824.10 7 457.9 110.4 254.430.77 5 419.2 129.0 232.942.55 3 323.5 137.6 179.7

Table 12Heat of Dilution of

Caustic Soda Solutions

Wt.% BTU/lb BTU/lbNaOH NaOH Solution

0 0 02 + 1.18 + 0.02364 - 2.04 - 0.08086 - 4.78 - 0.2878 - 7.15 - 0.572

10 - 8.60 - 0.86012 - 9.13 - 1.0914 - 8.65 - 1.2116 - 7.34 - 1.1718 - 4.99 - 0.89720 - 1.50 - 0.30122 + 3.28 + 0.72124 9.47 2.2726 17.14 4.4628 26.43 7.4030 37.34 11.2032 49.97 15.9934 64.05 21.7636 79.63 28.6638 96.50 36.6740 114.2 45.6942 132.8 55.7844 151.7 66.7646 170.7 78.5248 189.7 91.04

Note: Enthalpy of solutions at 68°F relative to infinitely dilute solutions.

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22 of 44

Table 13

Index of Refraction ofCaustic Soda Solutions

NaOHTemp.°C g/L Refractive Index

20°C 0 1.333027.88 1.33517

13.12 1.3366035.44 1.3423655.12 1.3471498.48 1.35685

131.52 1.36364

25°C 0 1.332517.88 1.33467

13.08 1.3360535.4 1.3417455.04 1.3464498.28 1.35603

131.2 1.36279

30°C 0 1.331967.88 1.33411

13.04 1.3355135.36 1.3410854.96 1.3457298.08 1.35530

130.92 1.36204

TechnicalData

Table 14

Hydrogen Ion Concentrations ofCaustic Soda Solutions at 25°C

NaOH% NaOH Moles/L pH

7.40 2.0 14.03.83 1.0 13.81.96 0.5 13.60.39 0.1 12.90.20 0.05 12.60.04 0.01 12.0

Due to the difficulty of obtaining accurate pH read-ings at values above 12, pH is not a valid methodto determine concentration.

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23 of 44TechnicalData

Graph 1Boiling and Solidifying Temperatures of Aqueous Caustic Soda Solutions

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24 of 44TechnicalData

Graph 2Specific Gravity of Aqueous Caustic Soda Solutions

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Graph 3Viscosity of Aqueous Caustic Soda Solutions

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Graph 4Vapor Pressures of Aqueous Caustic Soda Solutions

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27 of 44TechnicalData

Graph 5Approximate Resultant Temperature When Diluting Caustic Soda

Note: Graph for use starting with 50% Caustic Soda Solution using 70°F water.

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28 of 44TechnicalData

Graph 6Relative Enthalpy of Aqueous Caustic Soda Solutions

To approximate the final temperature after diluting a NaOHsolution, start on the bottom axis at the percentage of the origi-nal solution. Proceed up until the temperature of the originalsolution is reached. From that point, draw a line that intersectson the y-axis at the temperature of the water used for dilution.Then find the final diluted percentage on the x-axis and draw avertical line that intersects the second line drawn. The intersec-tion point of those lines represents the resultant temperature.

Example: Diluting 50% NaOH at 120°F to 20% using 80°F water.

* Approximate resultant temperature 143° F

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29 of 44TechnicalData

Graph 7Solubility of Sodium Chloride in Aqueous Caustic Soda Solutions

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30 of 44TechnicalData

0.32

0.33

0.34

0.35

0.36

0.37

0.38

0.39

0.4

0.41

0.42

0 10 20 30 40 50 60 70 80

30 F

50 F

70 F

90 F

100 F

130 F

170 F

190 F

Percent NaOH by weight

Th

erm

al C

on

du

ctiv

ity -

BT

U/h

r x

Sq

. Ft x

F

Graph 8Thermal Conductivity of Aqueous Caustic Soda Solutions

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31 of 44TechnicalData

Graph 9Specific Conductance of Aqueous Caustic Soda Solutions

Page 32: OxyChem Caustic Handbook

32 of 44Dilution CalculationsHOW TO DILUTE CAUSTIC SODA SOLUTIONS

Sometimes it is necessary to dilute caustic sodabefore it is used, or when the potential for freezingexists. A procedure for calculating the amount ofconcentrated caustic and water required is givenbelow.

DILUTING A SOLUTIONProblem: To dilute 3,000 gallons of 50% NaOH to

a 20% solution. How much water is necessary toaccomplish this task?

Solution: The dilution can be simplified by usingthe following formula:D=V[A(B-C)/C]

Where:A=Specific gravity of strong solutionB=Concentration of strong solution (% NaOH)C=Concentration of desired solution(% NaOH)D=Volume of water to be addedV=Volume of strong solution(The specific gravity of 50% NaOH is 1.5372 takenfrom Table 2)

Therefore:D=3,000((1.5372)(50-20)/20)D=3,000(2.3058)=6,917 gallonsResult: It will take 6,917 gallons of water to dilute3,000 gallons of 50% NaOH to a 20% solution.

VOLUME OF FINAL SOLUTIONIt should be noted that when diluting caustic soda,

volumes are not additive. Therefore, in the previousexample, the final volume of the solution would notbe 6,917 gallons of water + 3,000 gallons of 50%NaOH = 9,917 total gallons. The actual volume willbe slightly less. To calculate the final volume, thewater and caustic soda must be converted to aweight basis, and then divided by the density of thedesired solution.

DILUTION GRAPHGraph 10 can also be used to determine approxi-

mate volumes of 50% NaOH and water necessary toachieve a particular dilution. For example, you wantto produce 3,000 gallons of a 25% NaOH solutionand want to know how much water and 50% NaOHare needed to accomplish this goal.

Using the chart, start on the bottom axis at the3,000 gallon line. Proceed upward until you intersectthe first 25% line on the bottom half of the graph.From the intersection point go to the right and leftaxes to determine the volume and weight of waterneeded. In this case the volume is read at 1,920 gal-lons and the weight at 16,000 pounds.

Then continue upward until you intersect the 25%line at the top of the graph. Again from the intersec-tion point go to the left and right axes to determinethe volume and weight of 50% NaOH needed. In thiscase the volume is read at 1,248 gallons and theweight at 16,000 pounds.

Therefore, it would take 1,248 gallons of 50%NaOH to be added to 1,920 gallons of water to pro-duce 3,000 gallons of a 25% solution.

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33 of 44DilutionCalculations

Graph 10Approximate Dilution Chart For 50% Caustic Soda

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34 of 44Methodsof Analysis

DETERMINATION OFTHE TOTALALKALINITY OF CAUSTIC SODA

PURPOSE AND THEORYThe accurate determination of

the total alkalinity value for causticsoda is necessary for calculatingthe correct billing concentrations ofthis product.

Total alkalinity in caustic sodaproducts is determined by titrationof a sample with a standardizedsolution of 1N hydrochloric acid.Modified methyl orange indicator isused to determine the titration endpoint.

This procedure is based on ASTME291-04, Standard Test Methodsfor Chemical Analysis of CausticSoda and Caustic Potash, sections8 through 14.

APPARATUS100 ml Buret; Class A

Volumetric, Fisher Scientific Cat #:03-775 or equivalent.

Analytical Balance; capable ofweighing to 0.001 grams.

250 ml Erlenmeyer Flasks; widemouth, Fisher Cat#: 10-090B orequivalent.

Magnetic Stirrer; Fisher Cat#:14-493-120S or equivalent.

Magnetic stirring bars; 1 1/2” x5/16” dia. Fisher Cat#: 14-511-64or equivalent.

REAGENTS1N Hydrochloric Acid;

measure 83.0 ml of ACS Reagentgrade concentrated hydrochloricacid into a graduated cylinder andtransfer it to a one liter volumetricflask containing approximately 500ml of deionized water. Dilute to vol-ume with additional water, mix welland store in a tightly closed con-tainer. A prepared solution of 1N

HCl can also be purchased (FisherScientific Cat# SA48-20 or equiva-lent). Hydrochloric Acid must bestandardized to ±0.0001N beforeuse.

Sodium Carbonate;anhydrous, volumetric grade (EMScience Cat#: 6394-2 or equiva-lent.) Dry at 250°C in a platinum orporcelain crucible for 4 hours. Storein a desiccator.

Modified methyl orangeindicator; dissolve 0.14 grams ofmethyl orange (Fisher Cat#: M216-25) and 0.12 grams of XyleneCyanole FF (Fisher Cat#: BP565-10) in deionized water and dilute to100 ml.

Water, Deionized & CarbonDioxide free; boil and cool thedeionized water or purge it withnitrogen for two hours.

SAFETYRefer to the MSDS for the proper

handling procedures for each of thechemicals listed in this procedure.

Caustic soda is a strong base.Hydrochloric acid is a strongacid. These chemicals are corro-sive to body tissue and cancause immediate and severeburns to eyes. Wear propergloves, proper eye protectionand other protective clothingwhen handling these chemicals.

PROCEDUREA. STANDARDIZATION OF 1NHYDROCHLORIC ACID1. Weigh 4.2 grams of sodium

carbonate to the nearest0.0001 gram into a weighing dish. Carefully transfer toan Erlenmeyer flask. Add 75ml of deionized water and swirl to dissolve. Add threedrops of the modified methylorange indicator and titrate

with the HCl solution to asteel gray color change.

2. The following formula is usedto calculate the normality ofthe HCl.Let:N = Normality of HClW = Weight (g) of Na2CO3

usedV = Volume (ml) of HClrequired to endpoint.Milliequivalent weight ofNa2CO3= 0.053N = W/V x 0.053

3. Determine the normality byaveraging the result of atleast three titrations.

B. ANALYSIS1. To a clean, dry Erlenmeyer

flask, accurately weigh, to thenearest 0.001 grams, 6 to 7grams of 50% NaOH. Weighingshould be performed as rapidlyas possible.

2. Immediately add 50 ml of deion-ized water, making sure thesides of the beaker are washeddown.

3. Add 3 to 4 drops of modifiedmethyl orange indicator andcarefully add the magnetic stir-ring bar.

4. Titrate the sample to a steelgray color with 1N HCl. Samplesshould be titrated as soon aspossible to avoid pick up of car-bon dioxide from the air.

5. Record the volume of acidrequired to reach this color.Estimate the buret reading tothe nearest 0.02 ml.

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Methodsof Analysis 35 of 44

C. CALCULATIONSThe following are formulas used

to calculate total alkalinity.Let:W = Weight (g) of sample titratedN = Normality of HClV = Volume (ml) of HCl requiredMilliequivalent wt. of Na2O =0.03099

% Na2O = (V) (N) (0.03099)(100)W

% NaOH = 1.2907 (%Na2O)

EXAMPLE6.530 grams of caustic soda

required the addition of 81.77 ml of1.0011N HCl to reach the modifiedmethyl orange endpoint.

% Na2O = (V) (N) (0.03099)(100)W

% Na2O = (81.77)(1.0011)(3.099)6.530

% Na2O = 38.85%% NaOH = (1.2907) (38.85)% NaOH = 50.14%

QUALITY ASSURANCEWith each batch of samples

being analyzed, at least one of thesamples should be analyzed induplicate. On a regular basis, sam-ples that have been previouslyanalyzed for total alkalinity shouldbe reanalyzed and the results com-pared.

Alkalinity values obtained foreach sample should be comparedwith OxyChem specifications forthat product. Hydrochloric acidshould be restandardized at least monthly.

DETERMINATION OFSODIUM HYDROXIDEIN CAUSTIC SODA

PURPOSE AND THEORYThe sodium hydroxide content of

caustic soda is determined byadding barium chloride to a pre-pared sample and titrating with 1 NHCl to the phenolphthalein endpoint. The results are reported aspercent NaOH on a sample weightbasis.

Even with the utmost care, the sep-arate determination of total alkalini-ty (previous method) and hydroxidealkalinity often provides significantdifferences. This difference is thentypically attributed to the presenceof carbonate. It has been foundthat separate titrations for totalalkalinity and hydroxide alkalinity,or dual end-point titrations thatattempt to quantify total andhydroxide alkalinity in a single pro-cedure, often provide results forcarbonate that are many timeshigher than the actual carbonatecontent of the material.

Although the method for hydrox-ide alkalinity is included here,because the usual carbonate con-tent of caustic soda is very low, wesuggest the use of the method fortotal alkalinity alone. The carbonatecontent is typically as low as orlower than the measurement errorinherent in the analytical methods.As an alternative, we suggest theuse of the method for total alkalini-ty, the method for sodium carbon-ate determination (next method inthis handbook), and a calculationfor hydroxide alkalinity as shown inASTM E291-04, Standard TestMethods for Chemical Analysis ofCaustic Soda and Caustic Potash,section 12.

APPARATUS100 ml Buret; Class A

Volumetric, Fisher Scientific Cat #:03-775 or equivalent.Analytical Balance; capable ofweighing to 0.001 grams.250 ml Erlenmeyer Flasks; widemouth, Fisher Cat#:10-090B orequivalent.Magnetic Stirrer; Fisher Cat#: 14-493-120S or equivalent.Magnetic stirring bars; 1-1/2” x5/16” dia. Fisher Cat#: 14-511-64or equivalent.

REAGENTS1N Hydrochloric Acid; the

preparation of this reagent isdescribed in the method for:“Determination of Total Alkalinity”.

1% Phenolphthalein Indicator;dissolve one gram of phenolph-thalein (Aldrich Cat#: 10,594-5 orequivalent) in 100 ml of methanol.

10% Barium Chloride; Dissolve120 g of reagent grade BaCl2.2H2O(Fisher Cat#: B34-500) in 880 ml ofdeionized water.

Water, Deionized & CarbonDioxide free; boil and cool thedeionized water or purge it withnitrogen for two hours.

SAFETYRefer to the MSDS for the

proper handling procedures foreach of the chemicals listed inthis procedure. Caustic soda is astrong base. Hydrochloric acidis a strong acid. These chemi-cals are corrosive to body tissueand can cause immediate andsevere burns to eyes. Wearproper gloves, proper eye pro-tection and other protectiveclothing when handling thesechemicals. Barium chloride ishighly toxic. Avoid inhaling bari-um chloride dust.

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36 of 44Methodsof Analysis

PROCEDUREA. STANDARDIZATION OF 1N

HYDROCHLORIC ACIDStandardization procedure is

described in the method for:“Determination of Total Alkalinity”.

B. ANALYSIS1. To a clean, dry Erlenmeyer

flask, accurately weigh, to thenearest 0.001 grams, 6 to 7grams of 50% NaOH. Weighingshould be performed as rapidlyas possible.

2. Immediately add 100 ml of bari-um chloride solution, makingsure the sides of the beaker arewashed down.

3. Add 3 to 4 drops of phenolph-thalein indicator and carefullyadd the magnetic stirring bar.

4. Titrate the sample with 1N HCluntil the pink color changes towater white. The sample shouldbe titrated as soon as possibleto avoid pick up of carbon diox-ide from the air.

5. Record the volume of acidrequired to reach this color, esti-mating the buret reading to thenearest 0.02 ml.

CALCULATIONSThe following are formulas used

to calculate % NaOH.Let:W = Weight (g) of sample titratedN = Normality of HClV = Volume (ml) of HCl requiredMilliequivalent wt. of NaOH =0.04000

% NaOH = (V) (N) (0.04000) (100)

W EXAMPLE

6.467 grams of caustic sodarequired the addition of 80.85 ml of1.0020N HCl to reach the phe-nolphthalein endpoint.

% NaOH = (V) (N) (0.04000) (100)W

% NaOH = (80.85) (1.0020)(4.000)6.467

% NaOH = 50.11%

QUALITY ASSURANCEFor each batch of samples being

analyzed, at least one of the sam-ples should be analyzed in dupli-cate. On a regular basis, samplesthat have been previously analyzedfor total alkalinity should be reana-lyzed and the results compared.Alkalinity values obtained for eachsample should be compared withOxyChem specifications.

Hydrochloric acid should berestandardized at least monthly.

DETERMINATION OFSODIUM CARBONATEIN CAUSTIC SODA(Gravimetric)

PURPOSE AND THEORYThe sodium carbonate

content of a sample of caustic sodais determined by a direct gravimet-ric method. The method involvesacidification of the caustic sodasample with dilute sulfuric acid,boiling, and weighing the carbondioxide evolved. Accurate resultscan be obtained when the sodiumcarbonate content is 0.01% orgreater. This method should beused to analyze samples of liquidcaustic soda containing 0.01% to0.25% Na2CO3.

This procedure is based on ASTME291-04, Standard Test Methodsfor Chemical Analysis of CausticSoda and Caustic Potash, sections25 through 33. Although it is includ-ed as a reference for anyone whomay wish to perform the analysis, itshould be noted that the procedureis rather lengthy, may show poorprecision and is susceptible to errorbecause of air intrusion into theapparatus.

OxyChem typically utilizes a car-bon analyzer in inorganic mode forthe rapid and precise determinationof carbonate content of causticsoda. For further informationregarding the carbon analyzermethod, please contact technicalService.

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3

Methodsof Analysis 37 of 44

APPARATUSSee the CO2 train sketch on the

previous page.Air for sweep isdrawn in through “A.” This air mustbe scrubbed free of CO2. Theground-glass jointed tube fitted intothe top of “A” should be packedwith 8-20 mesh ascarite with alayer of anhydrous granular coppersulfate on top.

U-tube “D”Add a few glass beads and 5 to

10 ml of concentrated H2SO4. Theacid takes up the bulk of the mois-ture passing through condenser “C”and should be changed oftendepending on frequency of use.

U-tube “E”Pack with dehydrated copper sul-

fate pumice. This packing materialis prepared by soaking pulverizedpumice having the grain size ofwheat in saturated copper sulfatesolution drying at 150 -180oF. Theproduct must be kept in a wellstoppered bottle.

U-tube “F”Pack with anhydrous

magnesium perchlorate. Thisremoves all final traces ofmoisture carried through the sys-tem.

Ascarite - Absorbing Tower “G”Pack inside tube with 8-20 mesh

ascarite. Over the top layer addabout 0.25 inch of magnesium per-chlorate and cover with absorbentcotton. The cotton will prevent lossof weight due to carry-over of dustparticles. After tower is packed, itshould be hooked into the systemand swept with CO2-free air for aperiod of 15 to 20 minutes.

U-tube “H”Pack with 8-20 mesh ascarite.

REAGENTSSulfuric Acid; 12 N with 27.8 g.FeSO4.7H2O per liter.Sulfuric Acid, concentrated.Ascarite II; 8-20 mesh (sodium hydrox-ide coated silica.)Magnesium Perchlorate, anhydrous.

Copper (II) Sulfate, anhydrous.Water, Deionized & Carbon Dioxidefree; boil and cool the deionized wateror purge it with nitrogen for two hours.

SAFETYCaustic soda as dust or mist is

intensely irritating to the respiratory system, skin, and eyes.Become familiar with the first aidmeasures recommended in thisHandbook.

When preparing 12 N sulfuric acid,the concentrated acid must bepoured slowly into water with con-stant stirring.

Wear safety glasses with sideshields when handling caustic sodasamples or acid solutions.

PROCEDURE1. Sample Preparation

50% liquid caustic soda will solidifyat 54oF. If the sample is solidified at the time of analysis, it may be thawed out byplacing the container in hot wateruntil no solids are present. The lip ofthe bottle may be wiped before thesample is poured into a weighingbottle.

Carbonate and moisture pickupshould be avoided by rapid samplehandling.

In all cases, samples for carbonateanalysis should be the first takenfrom the sample bottle to minimizecarbon dioxide pickup from theatmosphere.

2. AnalysisThe train must be conditioned

daily before any samples are run.This is done by making a regulardetermination using a sample thatcontains carbonate. Following this,a blank should be run on the trainto make sure that the train is leakfree. This is done by making a reg-ular determination but omitting thesample. If the ascarite weighingtower gains more than 0.2 mg inweight during the blank run, thetrain probably has a leak.

After the train has been condi-tioned and found to be leak free,the samples are run as follows:

1. Two absorbing towers (G) mustbe conditioned and weighed priorto analysis. These will be calledG1 and G2 in the procedure. Theuse of two towers will enable theanalyst to conserve time whenperforming more than one analy-sis.

2. Weigh a sample of at least 20g.(50% basis) or large enough tocontain 5 mg of CO2 into a flask“B” using an analytical balance.Add 4 or 5 glass beads and 80 mlof CO2-free deionized water andimmediately place the flask into itsproper position in the train.

3. Add 50 ml of 12 N sulfuric acid tofunnel “A.”

4. Place tared tower G1 between U-tubes “F” and “H.”

5. Open the system starting at U-tube “H” and working back to “D.”

6. Open cock on funnel “A” andallow acid to run into flask “B” andimmediately hook vacuum line totube “H.” Adjust the flow of air to 4bubbles per second through thetip of the stem of funnel“A.”

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7. Apply heat to flask “B” and bringto a boil. Hold “B” contents to boil-ing point for 3 minutes andremove heat.

8. Sweep the system for 20 minutes.While this is being done, the nextsample can be weighed intoanother flask (B), and the beadsand distilled water added. Thisflask is then stoppered and setaside until needed.

9. At the end of 20 minutes, the vac-uum line is removed,tower G1 isshut off and removed and towerG2 placed into position. The cockon funnel “A” is closed and 50 mlof 12 N sulfuric acid is againadded to funnel “A.”

10.Flask “B” is removed, the stem offunnel “A” is washed down withdeionized water and the new sam-ple is placed into position.

11.Tower G2 is opened and the pro-cedure is repeated beginning atStep 6.

12.When G1 is removed from thetrain, a period of 20 minutes will

condition the sample for weighing.During this 20 minute sweep time,another sample is prepared andtower G1 is reweighed in order todetermine the weight of CO2 foundin the first sample. Tower G1 isthen ready for Run No. 3.

CALCULATIONS Report results as percent Na2CO3

calculated to the nearest 0.01. Let:W(CO2) = Weight of CO2

evolvedW(S) = Weight of sample% Na2CO3 = (W(CO2)(2.409)(100)

W(S)EXAMPLE

If a 25 gram sample were usedand the weight of CO2 absorbed intower “G” = 0.0125 grams, then:% Na2CO3 = (0.0125)(2.409)(100)

25% Na2CO3 = 0.12%

DETERMINATION OFSODIUM CHLORIDE INCAUSTIC SODA

PURPOSE AND THEORYChloride is a contaminant in all

grades of caustic soda. Sodiumchloride is present at <100 ppm in50% membrane caustic soda andat approximately 1% in 50%diaphragm caustic soda. Higherconcentrations of this compoundcan have undesirable effects inmany applications of the product.Consequently, accurate determina-tion of this impurity is most impor-tant.

When acid solutions of silver ionand an alkali thiocyanate are mixedin the presence of a ferric salt, thethiocyanate has a selective actiontoward silver, resulting in the for-mation of silver thiocyanate. Any

excess of thiocyanate not requiredby the silver reacts with ferric saltto form reddish-brown ferric thio-cyanate. This color indicates thecompletion of the reaction.

An excess of silver nitrate andthe ferric indicator is added to asample of caustic soda that hasbeen acidified with nitric acid. Anychloride that is contained in thesample will react with the silvernitrate to form a silver chloride pre-cipitate. The silver nitrate that isremaining in the sample solutionafter this reaction is titrated with astandardized solution of ammoniumthiocyanate. The equationsinvolved are:AgNO3 + NaCl ⇒ AgCl + NaNO3

Excess AgNO3 + NH4CNS ⇒AgCNS + NH4NO3

6 NH4CNS + Fe2(SO4)3 ⇒2Fe(CNS)3 + 3(NH4)2SO4

(reddish brown color)

This procedure is based on ASTME291-04, Standard Test Methodsfor Chemical Analysis of CausticSoda and Caustic Potash, sections34 through 40.

OxyChem typically utilizes tur-bidimetric determination, potentio-metric titration (similar to ASTME29-104, sections 41 through 48,with modifications to account forthe low chloride content of mem-brane grade caustic soda) or ionchromatography. For further infor-mation regarding any of thesemethodologies, please contactTechnical Service.

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APPARATUS25ml Buret; Class A Volumetric,Fisher Scientific Cat#:03-724-10Aor equivalent.20ml Pipet; Class A Volumetric,Fisher Cat#: 13-650-2N500ml Erlenmeyer flasks; widemouth, Fisher Cat#: 10-090C orequivalent.Magnetic stirrer; Fisher Cat#:14-493-120S or equivalent.Magnetic stirring bars; 1 1/2” x5/16” dia, Fisher Cat#: 14-511-64or equivalent.Analytical Balance; capable ofweighing to 0.001 grams.

REAGENTSWater, Deionized.0.1N Silver Nitrate; accuratelyweigh 16.99 grams of ACSReagent grade silver nitrate (driedat 110°C for 1 hr) and transfer to a1L volumetric flask. Dilute to vol-ume with deionized water, mix welland store in a tightly closed ambercontainer. Silver nitrate and itsaqueous solutions are photode-composed by light and should bestored in a dark place.0.1N Ammonium Thiocyanate;accurately weigh 7.612 grams ofACS Reagent grade ammoniumthiocyanate and transfer to a onevolumetric flask. Dilute to volumewith deionized water, mix well andstore in a tightly stoppered glassbottle. The thiocyanate solutionmust be standardized to within±0.0001N prior to use.Ferric Indicator; prepare a satu-rated aqueous solution of ferricammonium sulfate [FeNH4(SO4)2],Aldrich Cat# 22,126-0 or equiva-lent.1% Phenolphthalein Indicator;dissolve one gram of phenolph-thalein (Aldrich Cat#: 10,594-5 orequivalent) in 100 ml of methanol.Nitric Acid, 1:1 (v/v); slowly pour500 ml of ACS Reagent grade nitricacid in 500 ml of deionized wateras it is stirring. Allow the solution tocool.

SAFETYRefer to the MSDS for the

proper handling procedures foreach of the chemicals listed inthis method.

Caustic soda is a strong baseand nitric acid is a strong acid.These chemicals are corrosiveto body tissue and can causeimmediate and severe burns toeyes. Wear proper gloves, prop-er eye protection and other pro-tective clothing when handlingthese chemicals.

Silver Nitrate is a strong oxidizing agent. Wear rubbergloves when handling. Contactwith skin causes a black discol-oration. Keep away from heat,sparks and open flames.

PROCEDURE

A. STANDARDIZATION OF0.1N SILVER NITRATE

Since this procedure determinesthe chloride content of a sample bycomparing the amount of unreactedsilver nitrate remaining in a samplewith the amount that is remainingin a reagent blank, the exact nor-mality of the silver nitrate need notbe known. If a reagent blank is notused, silver nitrate standardizationis essential. A manual titrationmethod is described in “ASTMStandard Practice for Preparation,Standardization and Storage ofStandard Solutions for ChemicalAnalysis”, Vol 15.05; E200-91, 44-48.

B. STANDARDIZATION OF0.1N AMMONIUM THIOCYANATE1.Use a volumetric pipet to transfer

20.00 ml of freshly standardized0.1 N silver nitrate into a 250 mlErlenmeyer flask containing 50ml deionized water, 5 ml of 1:1nitric acid and 1 ml of ferric indi-cator. Titrate the AgNO3 with theNH4SCN solution until the firstpermanent reddish-brown colorappears and persists after vigor-ous shaking for 15 seconds.Record the volume of NH4SCNrequired. Repeat the above pro-cedure on at least three moresolutions of silver nitrate.

2.Use the following formula to cal-culate the normality of theammonium thiocyanate solution:N1 = (N2)(V2)/(V1)where:N1 = Normality of NH4SCNN2 = Normality of AgNO3

V1 = Volume of NH4SCNrequiredV2 = Volume of AgNO3 added

3.Determine the normality by aver-aging the results of at least threetitrations.

C. PROCEDURE1. To a clean dry Erlenmeyer flask,

accurately weigh, to the nearest0.001 g for smaller samples and0.01 g for larger samples, anamount of product as determinedin the following table. Weighingshould be performed as rapidlyas possible.

SAMPLE SIZE FOR CHLORIDEANALYSIS

Product Sample size

50% Diaphragmgrade caustic soda . . . . . . . . . .6 g

50% Membranegrade caustic soda . . . . . . . . .80 g

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2. Immediately add 100 ml ofdeionized water, making sure thesides of the beaker are washeddown.

3. Add 2 drops of 1% phenolph-thalein indicator and carefullyneutralize the sample with 1:1nitric acid. Caution: The samplesolutions generate consider-able heat when being neutral-ized with acid. The flaskshould be continuously cooledin an ice bath while the acid isslowly added. After the phe-nolphthalein endpoint hasbeen reached (color changesfrom pink to colorless), add anadditional 5.0 ml of acid.

4. Allow the solution to cool to roomtemperature and add a stirringbar to the flask.

5. Using a volumetric pipet add20.00 ml of 0.1N silver nitrate,also add approximately 1 ml ofthe ferric indicator solution (seeNote 1).

6. Prepare a reagent blank byadding two drops of phenolph-thalein, 5ml nitric acid, 20.00 mlsilver nitrate solution and 1ml offerric indicator to a flask contain-ing 100 ml of deionized waterand a stirring bar.

7. Place the flask containing thereagent blank on a magnetic stir-rer and titrate the solution with0.1N ammonium thiocyanateuntil a reddish-brown color per-sists for at least 15 seconds (seeNote 2). Record the volume ofNH4SCN required to reach thecolor change.

8. Titrate the sample solution with0.1N ammonium thiocyanateuntil the same color change isreached and record the volumeof NH4SCN (see Notes 3 and 4).

D. CALCULATIONSThe following is the formula

used to calculate the percent chlo-ride in the sample.Let:W = Weight of sample titratedN = Normality of NH4SCNV1= Volume of NH4SCN

required to titrate blankV2= Volume of NH4SCN

required to titrate sampleMilliequivalent wt. of Cl =

0.03545% Cl = (V1-V2)(N)(0.03545)(100)

WCalculate the percentage of sodi-

um chloride as follows:%NaCl = (%Cl)(1.6485)

EXAMPLE79.28 grams of 50% Membrane

grade caustic soda required theaddition of 19.54 ml of 0.1005 NNH4SCN to reach the titration end-point while the reagent blankrequired 19.95 ml of NH4SCN toreach the same endpoint.% Cl = (V1-V2)(N)(0.03545)(100)

W= (19.95-19.54)(0.1005)(3.545)

79.28% Cl = 0.00180% NaCl = (% Cl)(1.6485)% NaCl = (0.00180)(1.6485)% NaCl = 0.0030% or 30 ppm

NOTES1. Sample solutions should be

titrated within several minutes ofadding the silver nitrate. The sil-ver chloride has a tendency todecompose with exposure tolight giving the solution a pur-plish color. This color can inter-

fere with an accurate determina-tion of the endpoint colorchange.

2. From the outset of the back-titra-tion with ammonium thiocyanate,an appreciable quantity of silverions are absorbed on the sur-face of the precipitates. Becauseof this, there is a tendency for apremature appearance of theendpoint color. Vigorous stirringor shaking of the solution isessential to bring about desorp-tion of silver ions from the pre-cipitates so they can react withthe thiocyanate.

3. As the endpoint is approached,increasing amounts of silverthiocyanate precipitating out ofsolution will actually increase thesolubility of silver chloride. Silverchloride that has precipitated willredissolve, allowing additionalsilver ions to react with the thio-cyanate. This causes a fadingendpoint and results in low chlo-ride values. For samples con-taining concentrations of chlo-ride greater than 0.01%, it isadvisable to filter the samplesolution through semi-quantita-tive paper after the addition ofsilver nitrate but prior to titrationwith thiocyanate. Removingmost of this precipitate willgreatly decrease the amount ofsilver that can be redissolvedduring the titration.

4. The white precipitate of silverthiocyanate interferes withobservation of the color changeat the titration endpoint. It issometimes helpful to stop thestirring or shaking of the sampleand allow the precipitate to set-tle, in order to observe the colorof the sample solution. If it isdetermined during this observa-tion that the endpoint has not yetbeen reached, resume vigorousstirring before addition of moreNH4SCN.

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Methodsof Analysis 41 of 44

QUALITY ASSURANCEBecause of difficulties in deter-

mining the exact endpoint whenusing this method, only skilled lab-oratory personnel should attempt toperform these titrations.

On a regular basis, samples thathave been previously analyzed forchloride content should be reana-lyzed and the results compared.

Chloride values should bechecked against OxyChem specifi-cations.

DETERMINATION OFIRON IN CAUSTICSODAPURPOSE AND THEORY

Iron can result from contamina-tion during storage or transport ofthe product. Since iron is oftendetrimental to the end use of theproduct, accurate quantitation ofthis element is essential.

Caustic soda is neutralized withhydrochloric acid and the resultingsolution buffered with sodiumacetate. Hydroxylamine hydrochlo-ride reduces any iron present in theferric state to the ferrous state. o-phenanthroline (1,10-phenanthro-line) forms an orange-red complexwith ferrous iron. The intensity ofthe color is proportional to theamount of iron present. By measur-ing the color intensity with a spec-trophotometer, the concentration ofiron in a sample of caustic sodacan be determined.

This procedure is based onASTM E291-04, Standard TestMethods for Chemical Analysis ofCaustic Soda and Caustic Potash,Sections 58 through 66.

APPARATUSVisible Spectrophotometer: ableto measure absorbance or percenttransmittance at 510 nanometers.Analytical Balance: capable ofreading to 0.01 grams.Volumetric Flask, 1 l, class A:Fisher catalog # 10-210-8G orequivalentVolumetric Flask, 100 ml, class A:Fisher catalog # 10-210-8C orequivalentPipets, Volumetric, Class A:

1 ml - Fisher catalog #13-650B or equivalent

2 ml - Fisher catalog #13-650C or equivalent

5 ml - Fisher catalog #13-650F or equivalent

10 ml - Fisher catalog #13-650L or equivalent

15 ml - Fisher catalog #13-650M or equivalentIndicator Paper, Hydrion, pH 3.0to 5.5: Fisher catalog # 14-853-70or equivalent)Disposable plastic pipets("Dispo-pipet")Cuvettes, quartz: appropriate tothe spectrophotometer in use, 25mm diameter is typical but otherpath lengths providing detectionlimits suitable for the user areacceptable

REAGENTSDeionized WaterHydrochloric Acid, concentrated:reagent grade, Fisher catalog #A144 or equivalentSodium Acetate, 164 grams perliter: weigh 164.0 (+/- 0.1) grams ofsodium acetate, Fisher catalog #S210-500 or equivalent, dissolveand dilute to 1 liter with deionizedwater in a 1 liter volumetric flask

Hydroxylamine Hydrochloride,100 grams per liter: weigh 100.0(+/- 0.1) grams of hydroxylaminehydrochloride, Fisher catalog #H330-500 or equivalent, dissolveand dilute to 1 liter with deionizedwater in a 1 liter volumetric flask o-phenanthroline, 0.25 %: weigh2.50 (+/- 0.05) grams of o-phenan-throline monohydrate, Fisher cata-log # P70-10 or equivalent, dis-solve and dilute to 1 liter withdeionized water in a 1 liter volu-metric flask 1000 μg/ml Iron Standard, suit-able for ICP/AA, Spex standardavailable from Fisher as catalog #PLFE2-2Y or equivalent

SAFETYRefer to the MSDS for the

proper handling procedures foreach of the chemicals listed inthis procedure.

Caustic soda is a strong base.Hydrochloric acid is a strongacid. The Iron ReferenceSolution is acidified with HCl. Allof these chemicals are corrosiveto body tissue and can causeimmediate and severe burns toeyes. Wear proper gloves, prop-er eye protection and other pro-tective clothing when handlingthese materials.

Refer to instrument manual forthe proper use of equipmentdescribed in this method.

PROCEDUREA. SAMPLE ANALYSIS1.Weigh the appropriate sample,

based on the table below, into aclean 100 ml volumetric flask.Record the sample weight.

50% diaphragm grade caustic soda5-10 g

50% membrane grade causticsoda 15-20 g

2.Add deionized water to the flask,such that the flask is slightly lessthan half-full, and swirl to mix thesolution.

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3.SLOWLY and CAREFULLY, addconcentrated hydrochloric acid tothe flask while constantly swirlingthe flask. Continue to add untilthe solution is just acidic. Checkthe pH by dipping a clean glassrod into the flask and touchingthe rod to the pH indicator paper.If acidic, the paper will turn red.If it is still basic, the paper will beblue. (If another type of indicatorpaper is used, verify the appro-priate colors for the paper youare using.)CAUTION:This is a reactioninvolving a strong base and astrong acid. Be sure to add theacid slowly and to maintainswirling so that spattering doesnot occur. The solution and flaskwill become quite warm. Coolthe flask in an ice bath or undercold running water if desired.

4. If additional samples are to beanalyzed, repeat steps 1 to 3above for each sample.

5.Prepare a blank by adding about40 mls of deionized water andabout 2 mls of concentratedhydrochloric acid to a separate,clean 100 ml volumetric flask.

6.Using a dispo-pipet, add suffi-cient sodium acetate solution tothe flasks (the samples and theblank) to buffer the solution topH 3.5 +/- 0.5 pH units. Checkthe pH by dipping a clean glassrod into the flask and touchingthe rod to the pH indicator paper.At the proper pH, the paper willhave a light green color. (Ifanother type of indicator paper isused, verify the appropriate colorfor the paper you are using.)

7.Pipet 5 mls of hydroxylaminehydrochloride solution to eachflask.

8.Pipet 5 mls of o-phenanthrolinesolution to each flask.

9.Fill the flasks to volume withdeionized water and shake well

to mix. Allow a minimum of 15minutes for color developmentbut complete the reading of thesamples within 30 minutes.

10. Rinse a clean cuvette twicewith small portions of the blanksolution. Then fill the cuvettewith the blank solution. Assurethat there are no bubbles pre-sent and wipe off the outside ofthe cuvette with a soft, lint-freetissue. Place the cuvette into thespectrophotometer and zero theinstrument at 0 (zero)absorbance (A) or 100% trans-mittance (T). Operate the spec-trophotometer as directed in yourinstrument manual. Remove thecuvette from the instrument.

11. Fill a cuvette with the samplesolution and load it into the spec-trophotometer in the same fash-ion as described in step 9 above.Record the instrument readingas either A or T, depending uponhow your calibration curve wasconstructed. (See section Cbelow.)

B. QUALITY CONTROL1.Perform a duplicate analysis with

each batch of samples. Simplyrepeat the Sample Analysis insection A above using an addi-tional aliquot of a sample. Iflarge numbers of samples aretested, it is suggested that aduplicate analysis is performedon one of every ten samples.

2.Perform a sample spike analysiswith each batch of samples. Todo so, prepare a second aliquotof a sample as directed in steps1 and 2 of the Sample Analysisin section A above. Then pipet 2mls of the 10 μg/ml iron stockstandard (see step 1 in section Cbelow) into the flask. Completethe sample preparation asdescribed in the remaining stepsof section A. This procedureprovides about a 1 (one) μg/g (1ppm) spike for membrane caus-tic soda or about a 2 to 4 μg/g (2

to 4 ppm) spike for diaphragmcaustic soda. Different spike lev-els may be obtained by addingmore or less of the iron stockstandard or using different ironconcentration solutions.

3.The relative percent differencebetween duplicates should be nomore than 20%.

4.The spike recovery should be inthe 80% to 120% range.

C. SPECTROPHOTOMETER CALIBRATION1.Prepare a stock 10 μg/ml iron

standard by pipetting 1 ml of the1000 μg/ml iron standard to a100 ml volumetric flask and dilut-ing to volume with deionizedwater.

2.Obtain six 100 ml volumetricflasks and label them as 'Blank','10 μg', '20 μg', '50 μg', '100 μg'and '150 μg'. To each of these,add about 25 mls of deionizedwater and 2 mls of concentratedhydrochloric acid.

3.Pipet 1 ml of the 10 μg/ml ironstock standard (prepared in step1 above) to the flask labeled '10μg'. Similarly, pipet 2 mls of theiron stock to the flask labeled '20μg', 5 mls to the flask labeled '50μg', 10 mls to the flask labeled'100 μg', and 15 mls to the flasklabeled '150 μg'.

4.Complete the preparation andreading of the standards by fol-lowing steps 6 through 11 in sec-tion A above.

5.Many spectrophotometers willallow storing the calibrationcurve directly on the instrument.If this is not the case, you maywish to use a least squaresregression analysis to store the

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calibration on a calculator or PCprogram. Finally, calibrationcurves may be drawn manuallyusing normal graph paper if plot-ting concentration vs.absorbance (A) or semi-logpaper if plotting concentration(linear axis) vs. transmittance (T- log axis).

CALCULATIONCalculate the ppm iron by dividing

the micrograms of iron foundfrom the calibration curve (C) bythe sample weight (W):

ppm Fe = C / W

DETERMINATION OF OTHER ELEMENTS IN CAUSTIC SODA

OxyChem typically utilizesInductively Coupled Argon Plasma-Atomic Emission Spectroscopy(ICAP-AES) for the analysis of met-als or elements in caustic soda.

For the determination of mercury,an automated cold vapor atomicabsorption (CVAA) method, basedon EPA Method 245.1 and ASTME538, is utilized.

Since the operation of these instru-ments varies from manufacturer tomanufacturer, a specific method isnot included here. Follow yourinstrument manufacturer's instruc-tions and recommendations forperforming analysis of this type.

IMPORTANT!!!

Regardless of the brand of instru-ment, it is necessary to keep inmind that calibration standardsmust be similar to the samplebeing analyzed if results are to beconsidered accurate.

Caustic soda will form a significantamount of salt when neutralized:for example, sodium chloride ifneutralized with hydrochloric acidor sodium nitrate if neutralized withnitric acid. Since the sample con-tains a high amount of dissolvedsolids, calibration standards mustbe prepared in a similar matrix orsample results will be in error.

One means of addressing this is toprepare standards containing thesame amount of dissolved salt thata sample would contain. Thisrequires obtaining high purity salts,which can be quite costly. Anothermore economical means of accom-plishing the "matrix match" is touse calibration by standard addi-tion.

In general, analytical resultsobtained for elements in causticsoda will be significantly higherthan the actual values if the sam-ples are analyzed using a calibra-tion based on "clean" aqueousstandards as might be used forwater analysis.

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44 of 44Notes

® Viton is a registered trademark of DuPont de Nemours.

® Teflon is a registered trademark of DuPont de Nemours.

® Hastelloy is a registered trademark of Haynes International.

® Inconel is a registered trademark of Inco Limited.

® Monel is a registered trademark of Inco Limited.