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(^(NASA-Case-NPO- 14001- 1) H E M B B A K E CONSISTINGOF P O L Y Q U A T E B N A R Y A M I K E ION E X C H A N G E P O L Y H E BN E T W O R K IBTEBPEBETBMIBG THE CHAINS OFTHERMOPLASTIC HATBIX P O L Y M E R «-*—«• '

J1 P

https://ntrs.nasa.gov/search.jsp?R=19810005564 2019-03-10T18:25:23+00:00Z

).581 United States PatentRembaum et al.

M/°o- /y, oot — f[ i t ] 4,119,581[45] Oct. 10, 1978

oCVJ

[54] MEMBRANE CONSISTING OFPOLYQUATERNARY AMINE IONEXCHANGE POLYMER NETWORKINTERPENETRATING THE CHAINS OFTHERMOPLASTIC MATRIX POLYMER

[75] Inventors: Alan Rembaum, Altadena; Carl J.Wallace, La Crescenta, both of Calif.

[73] Assignee: California Institute of Technology,Pasadena, Calif.

[21] Appl. No.: 771,245

[22] Filed: Feb. 23, 1977

[51] Int. Q.2 C08L 39/08; C08J 5/22;B01D 15/04

[52] U.S. a 521/27; 210/24 R;260/2.1 E; 260/17 A; 260/858; 260/886;

260/895; 260/898; 260/900; 260/901; 521/62;521/32

[58] Field of Search 260/2.2 R, 17 A, 823,260/895, 2.1 R, 2.1 E; 210/24 R

[56] References Cited

U.S. PATENT DOCUMENTS

3,944,485 3/19764,007,138 2/19774,014,798 3/1977

Rebawnela l 260/2.1 EKonig 260/2.1 ERebawn 260/2.2 R

Primary Examiner—Joseph L. SchoferAssistant Examiner—Peter F. KulkoskyAttorney, Agent, or Firm—Marvin E. Jacobs

[57] ABSTRACT

An ion-exchange membrane is formed from a solutioncontaining dissolved matrix polymer and a set of mono-mers which are capable of reacting to form a polyquat-ernary ion-exchange material; for example vinyl pyri-dine and a dihalo hydrocarbon. After casting the solu-tion and evaporation of the volatile components, a rela-tively strong ion-exchange membrane is obtained whichis capable of removing anions, such as nitrate or chro-mate from water. The ion-exchange polymer forms aninterpenetrating network with the chains of the matrixpolymer.

28 Claims, 2 Drawing Figures

COce

UJ

oo

U.S. Patent Oct. 10,1978 sheet 2 of 2 4,119,581

oc.LUco

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U.S. Patent Oct. 10, 1978 Sheet 1 of 2 4,119,581

di

3.MUIN-Wdd

[54]

N390M1IN- ON-Wdd

4,119,581

MEMBRANE CONSISTING OFPOLYQUATERNARY AMINE ION EXCHANGEPOLYMER NETWORK INTERPENETRATINGTHE CHAINS OF THERMOPLASTIC MATRIX

POLYMER

ORIGIN OF THE INVENTION

The invention described herein was made in the per-formance of work under a National Aeronautics andSpace Administration contract and is subject to theprovision of Section 305 of the National Aeronauticsand Space Act of 1958, Public Law 83-568 (72 Stat. 435;42 USC 2457).

BACKGROUND OF THE INVENTION

1. Field of the InventionThe present invention relates to ion-exchange materi-

als and, more particularly, to the in-situ polymerizationof a cationic ion-exchange material in a solution of ther-moplastic matrix resin.

2. Description of the Prior ArtThe need to comply with ever-tightening environ-

mental standards dictates that serious consideration begiven to novel techniques for removing and/or recover-ing harmful contaminants from our waters. Chromiumis one of these contaminants which has been classified asa toxic pollutant and, consequently, should not be dis-charged into waterways. Because of its widespread usein the plating industry and as a corrosion inhibitor incooling tower systems, chromium is ubiquitous in theenvironment and its recovery would result in economicreturns as well as producing a positive environmentalimpact.

Nitrate has been established as one of the ten inor-ganic chemicals designated by the National InterimPrimary Drinking Water Regulations for systematicanalysis in all public water supplies (effective June1977). Nitrate is recognized as a noxious contaminant inwater not only because it is a rich nutrient for biologicalgrowth such as algae blooms but because it is toxic tohumans and animals resulting in methemoglobinemia, adisease effecting the oxygen carrying capacity of theblood hemoglobin. Infants are extremely susceptible(blue babies).

With the discovery that nitrosamines may be toxi-genic and even carcinogenic, another dimension hasbeen added to the chronic effects of nitrate. Nitrosa-mines are formed by the interaction between nitritesand secondary or tertiary amines under conditions simi-lar to those found in the mammalian stomach. Nitratesare normally removed from waters by anaerobic deni-trification, ion-exchange, electrodialysis, and reverseosmosis. Activated carbon is not effective as a scaven-ger for nitrate since it leaves high residual nitrate in theeffluent.

Since ion-exchange hollow fibers require little pump-ing cost and no regeneration, it is conceivable thathighly stable hollow fibers could provide a cost-effec-tive means of simultaneously removing these contami-nants and possibly even concentrating them for subse-quent fertilizer usuage.

I Current technology for removal of ions from dilute1 streams is largely oriented to the use of conventional| packed, ion-exchange beds. These processes, however,I have their problems. There is, for example, significantI current effort toward the development of macroreticu-

lar pores in the ion-exchange beads which would be less

15

20

25

30

susceptible to irreversible clogging. There are problemsin the preparation of beads which have adequate poros-ity but which are still not unduly fragile. In the prepara-tion of commercial ion-exchange beads, the process is as

5 follows:A cross-linked polymer bead is formed by reacting,

for example, styrene and divinylbenzene. The percent-age of cross-linker (divinylbenzene) determines theextent of swelling in the final bead as ions are ex-

10 changed. The greater the percentage of cross-linker, theless the swelling. Concurrently, the greater the level ofcross-linker, the slower will be the diffusion of exchang-ing ions into and out of the beads, and the slower will bethe process.

After the bead is formed, a chemical reaction such assulfonation or chlormethylation is used to form theion-exchange sites. From the description it is apparentthat there are conflicting demands: high cross-link den-sity helps stability but reduces product rate. Similarly,high ion-exchange capacity from the second step in-duces large swelling excursions, but provides greatercapacity. Swelling of the resin beads occurs due to theosmotic pressures which are generated when the beadsare exposed to different concentrations of various elec-trolytes. Pressure drop build-up is irregular and trouble-some in regeneration processes. The choice of operatingcycles is not straightforward at all and the beads are notinexpensive.

An alternative exists in semipermeable flat mem-branes but the technology is still in its infancy and thecost to efficiency ratio of membrane processes is notvery satisfactory. Ion-exchange membranes offer signif-icant advantages in separation processes with respect to

35 ion-exchange resin beads. When the ion-exchange resinsare in the form of membranes, they can be in contactwith the solution to be separated and the stripping solu-tion simultaneously and the ion-exchange process canbe continuous rather than cyclic.

Ion-exchange membranes cannot be manufactured bythe same techniques utilized to form ion-exchange beadssince the swelling resulting from the formation of theion-exchange site is too great to be borne by membraneswhich have a low degree of cross-linking. However, if

45 the degree of cross-linking is raised, the membrane istoo brittle to be useful. Most flat ion-exchange mem-branes are formed by first forming ion-exchange beadsand then milling the beads into a thermoplastic resin asa binder for the resin structure. In a more recent pro-

50 cess, the thermoplastic resin is milled in the presence ofa swelling agent which is then replaced with a graftableionic monomer. After grafting, the ionic site is bound tothe membrane. The mechanical requirements are satis-fied by using relatively thick sheets, in the range of

55 100-300 microns.Anionic exchange hollow fibers have not been re-

ported. Sulfonic acid cationic exchange type of hollowfibers have been prepared by irradiating polyethylenehollow fibers, immersing the irradiated fibers in styrene

60 and heating the mixture to effect grafting. The fibers arethen swollen in dichloromethane and sulfonated withchlorsulfonic acid, followed by hydrolysis. This proce-dure requires several steps, effects a random ion-ex-change capacity and is limited to special reactants. Post-treatment of hollow fibers is further limited since thevery small cross-section of the fibers and the fine poros-ity of the walls prevents introduction of preformedpolymers into the bore or impregnation into the walls.

40

65

4,119,5814

Ion-exchange fibers are disclosed in U.S. Pat. No.3,944,485 in which monomers are extruded into the boreof a hollow fiber and into the pores of the wall and reacttherein to form insoluble ion-exchange material. Thisprocess which is practiced on preformed fibers, affectsthe permeability thereof and is unduly complicated andexpensive.

SUMMARY OF THE INVENTION

A novel ion-exchange membrane is provided in ac- 10cordance with the invention which can be utilized insheet form or in the form of hollow or solid fibers. Themembrane is produced in a simple and inexpensive man-ner and the membranes are capable of rapid and contin-uous removal of anions from aqueous solution. The 15membranes are more uniform and more denselycharged than impregnated membranes and stability isgreatly improved.

The membranes are fabricated by forming a solutionof a matrix resin and monomers in common solvent. 20The monomers are capable of reacting to form a poly-quaternary, ion-exchange polymer. The solution isformed into either a sheet or fiber by pouring the solu-tion into a casting form such as a continuous belt or traywith raised runner edges or the solution is extruded 25through a die to form a solid rod or a hollow fiber. Aftercasting or extrusion, as the solvent is evaporated themonomers react to form cross-linked, ion-exchangepolymers which interpenetrate the matrix resin. Excessunreacted monomers are removed from the film by 30washing with solvent before use. The membrane be-haves more like a homogenous resin than a heteroge-nous composite since the matrix resin is a continuousphase with the polyquaternary resin interpenetratingthe matrix resin which strengthens rather than weakens 35the matrix resin.

The matrix resin is a linear thermoplastic polymercapable of solution in a common solvent for the ion-ex-change monomers. Representative materials are acrylicresins such as polyacrylonitrile, polyolefins such as 40polypropylene, polystyrene, cellulose esters, polyure-thanes and fluorocarbons. Preferred materials aretough, high tensile strength elastomers which can with-stand the repeated flexing and pulsing experienced inmembrane and hollow fiber water treatment apparatus. 45Best results have been obtained with polyether or poly-ester polyurethanes such as Estanes and vinylidenefluoride and hexafluoropropylene or chlorotrifluoro-ethylene copolymers such as Viton or Kel-F. Further-more, these matrix resins are capable of functioning in 50oxidizing environments.

The ion-exchange resin must be present in a minimumamount of 20% based on total resin content in order toprovide adequate ion-exchange function. The ionichalogen content of the. membrane should be at least 5% 55by weight, generally 10-20% by weight. However, ation-exchange resin content of 80% by weight, the mem-brane becomes too brittle. Preferred range of ion-ex-change resin is from 20% to 65% by weight. J

The common solvent is an inert, volatile organic 60'solvent and may be a ketone or an ether such as tetrahy- Idrofuran (THF). The total resin-monomer dilutionshould usually be no more than 40% w/v in order toobtain adequate dispersion, usually from 5 to 25% w/v.

The polymerizable ion-exchange monomers react to 65form a cross-linked, water insoluble polyquaternarypolymer in which the quaternary nitrogens are presentin the chains or in bridges joining the chains. The poly-

mers are formed from the reaction of polytertiary aminecompounds with organic polyhalides, each containingat least three carbon atoms.

One series of polymers disclosed in U.S. Pat. No.3,899,534 are prepared by reaction of a halomethylatedaromatic compound with a tertiary amine compound;one of the compounds being at least trifunctional inorder to form a cross-linked material as follows:

(CHjCl), + N — R ' —

where n is 2,3 and m is 1-3, the sum of n and m being atleast 4 and R2, R3and R4are alkyl to 1 to 6 carbon atomsor may be joined into a saturated or unsaturated ringstructure and R1 is an aliphatic aromatic group contain-ing at least 3 carbon atoms. Terpolymers can also beformed by reacting a diamine and an organic dihalidewith the use of 0.1 to 30% 2,3,6,-trichloromethyl mesit-ylene as a cross-linking agent.

Unsaturated intermediates capable of cross-linking byfree radical or condensation reaction are also utilizablein the invention. The intermediates are selected fromcompounds of the formula:

where R5 is an organic group containing ethylenic un-saturation, preferably as a terminal vinyl group and R1

is a divalent group of 2 to 20 or more carbon atomswhich may be alkylene, arylene, alkenylene, alkyny-lene, alkarylene, etc.

The intermediate may be prepared by reacting aditertiary amine with a quarternizing reagent, R2Zwhere Z is an anion such as chlorine or bromine or byreacting an unsaturated monotertiary amine with a di-quaternizing reagent Z-R'-Z. The amine may be a terti-ary-aminoacrylate ester such as N,N-dime-thylaminethyl acrylate or methacrylate or a vinyl pyri-dine. The acrylate compounds form quaternized inter-mediates which can be further polymerized by heat,radiation or free radical catalyst to form a cross-linkedinsoluble, polyquaternary polymer. However, the vinylpyridine intermediates, spontaneously proceed to cross-linked polymers at room temperature.

Quaternized, cross-linked, insoluble copolymers ofunsubstituted and substituted vinyl pyridines and adihalo organic compound are spontaneously formed atambient temperature on mixing the two monomers inbulk, in solution or in suspension as disclosed in U.S.Pat. No. 3,754,055, the disclosure of which is incorpo-rated herein by reference. The amount of cross-linkingmay be varied according to the composition and reac-tion conditions.

The polyquaternary, water insoluble, cross-linkedmaterials are prepared by reacting a vinyl pyridine witha dihalo organic compound of the formula:

> • ' • ,x - R, - x |!J, Two mole

j saturated enwhere X is halo, preferably bromo, chloro or iodo and!-''vinyl 'group iR, is a divalent organic radical such as alkylene, alkeny-j of the formu

i. . amine, laming

) .ii No.•,' ivlated>i pound;:• onal in

,1-1 ng at, • iMoms.tl ring.uitain-also beuhalide1 mesit-

from

4,119,581

nic un-and R'

n atoms.iH.yny-

-1 inkediiie with

. alkt-ny-

lene, alkynylene, arylene, alkarylene or aralkylene. R,may also be alkylthioalkylene or alkyloxyalkylene ofthe formula (CHi\,(Z)f(CH2)l, where Z is oxygen orsulfur and x, y and z are integers from 1 to 100. R, mayalso be of prepolymer or polymeric length of up to6,000 molecular weight such as a bromo-terminatedpolybutadiene, but, preferably has a carbon content offrom I to 20 carbon atoms to provide an increasedcharge center density per unit volume and weight of thepolymeric product. R, may be substituted with othergroups that do not interfere with the polymerizationreaction or properties of the polymer product such ashydroxyl, alkyl, aryl, nitro, cyano or similar groups.

Representative dihalo organic compounds are a,co-alkylene or alkenylene halides such as dibromo meth-ane, 1,2-dibrotnoethane, 1,3-dibromopropane, 1,4-dibromobutane, l,4-dibromo-2-butene, l,4-dichloro-2-butene, l,4-dibromo-2,3-dihydroxy butane, 1,5-dibromopentane, 1,6-dibromohexane, 1,8-dibromooc-tane, 1,10-dibromodecane, and 1,16-dibromohexadec-ane. The alkenylene compounds such as 1,4-dibromobu-tene are found to be more reactive than the correspond-ing saturated compounds. Dihaloaromatics such as o, mand p-dichloro- or o, m and p-dibromoxylene are alsosuitable. Cross-linked, insoluble products would also beformed from tertiary brominated prepolymers such aspolyethylenes, polypropylenes, polybutylenes, polybu-tadienes, polyoxyethylene, etc. As the number of car-bon atoms in the dihalide increases, elastomeric proper-ties are favored and polyelectrolyte properties decrease.

4-vinyl pyridine is the most reactive of the vinylpyridine isomers. However, 2-methyl-5-vinyl pyridineis available at lower cost and provides products of simi-lar properties. 2-vinyl pyridine has been found to bemuch less reactive than the other monomers.

The polycationic, cross-linked products are preparedsimply by mixing the vinyl pyridine monomer with thedihalide in various proportions and allowing the mix-ture to react until solid materials are formed.

The reaction is believed to proceed through a firststage in which two molecules of vinyl pyridine reactwith a molecule of a dibromide to form a quaternaryintermediate as illustrated below:

20

30

35

+ X-R|—X +

CH,=CH

Two molecules of the intermediate dicationic, diun-saturated cross-linking agent then react through thevinyl group to form an intermediate having a structureof the formula:

—CH,—en

10

15

CH=CH CH = CH;

The intermediate reacts further to give a cross-linkednetwork with a small amount of residual unsaturation.Although this mechanism is dominant, other intermedi-ates are also formed. The reaction proceeds spontane-ously at room temperature, about. 25° C, but may beaccelerated by heating the reaction to a higher tempera-ture, usually below 100" C., and suitably from 25°-60°C. The unsaturation on the growing polymer as well ason the finished resin may be utilized in further reactions,e.g. grafting onto substrates by means of Co y radiation.

Cross-linking of the product is also facilitated byirradiating the mixture with radiation capable of form-ing reactive species to cross-link the vinyl groups, suit-ably gamma radiation from a cobalt source. The reac-tion may be conducted in bulk, in a solvent for themonomer or in water suspension. The reaction proceedsfaster in bulk, but yields are higher in solvents. Higheryields are favored in polar solvents such as dimethyl-sulfoxide, dimethylformamide, methanol, ethanol, orcombinations thereof. Particularly high yields havebeen obtained with a 1/1 volume mixture of dimethyl-formamide and methanol. Slower reaction occurs insolvents such as benzene.

The rate of reaction is found to be much higher with40 bromides, as compared to the corresponding chlorides.

The ratio of monomers is controlled such that there isan excess of dibromide in the mixture. A suitable ratio isa stoichiometric ratio of 2 mols of vinyl pyridine to atleast 1 mol of the dibromide. It has been found that

45 when the polymerization is conducted with an excess ofvinyl pyridine, unchanged vinyl pyridine can be recov-ered. It has further been found that oxygen and carbondioxide interfere, inhibit and slow the reaction. Alsofree radical inhibitors such as hydroquinone do not

50 interfere or slow down the reaction rate. Higher poly-merization rates are favored by conducting the reactionin vacuum. The properties of the polymer products canbe varied by using excess of dihalide. The resultingproduct in this case contains nonionic halogen capable

55 of further reaction. Any residual halogen in the ion-ex-change resin particle or the nonionic halogen intro-duced by use of excess dihalide can be further reactedwith a monoquaternizing reagent such as trimethyl-amine, dimethylamine or pyridine to increase the ion-

60 exchange capacity of the particles and of the fiber.The properties of the polymer products can be fur-

ther varied by conducting the polymerization in thepresence of excess monomer and a molecule capable ofmonoquaternization such as alkyl or alkenyl halide,

65 hydrogen halide, dimethylsulfate, etc. The amounts ofthe quaternizing species are varied in such a way as tomaintain the proportions: 2 moles of vinyl pyridine to 1mole of dihalide and, 1 mole of vinyl pyridine to 1 mole

4,119,581

of quaternizing species. Thus, for a polymer formedfrom a mixture containing 1 mole of dihalide and 0.5mole of quaternizing agent, 2.5 moles of vinyl pyridineare required. By varying these proportions, differentamounts of cross-linking are obtained and the resultingresins differ mainly in their swelling properties.

The novel ion-exchange membranes of the inventionwill find use in reverse osmosis, electrodialysis andconventional ion-exchange. The solvent casting tech-nique has been shown to be an excellent method forincorporating a positively charged ion-exchange resininto a polymeric substrate and the membrane fibers arefairly uniform in composition and exhibit high chargedensity.

These and many other features and attendant advan-tages of the invention will become readily apparent asthe invention becomes better understood by referenceto the following detailed description when consideredin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a graph showing nitrate removal from water

with PPM-NO3 as nitrogen as one ordinate, PPM-Nitrate as the other ordinate and Time (Hours) as ab-scissa; and

FIG. 2 is a set of curves demonstrating removal ofdichromate ions, the upper curve showing initial fluxmeasured over the initial 15 minutes and the lowercurve showing flux over the initial 2 hours, the ordinatebeing flux expressed as mg Cr+6/hr cm2and the abscissabeing progressive test numbers on the same film.

DESCRIPTION OF THE PREFERREDEMBODIMENTS

Membranes were cast on glass plates using stoichio-metric mixtures of 2 moles of 4-vinyl pyridine (4-VP)and 1 mole of dibromohexane (DBH). These wereadded to commercially obtained polymers of eitherKel-F, Viton or polyurethane, dissolved in methylethylketone (10-20% w/v) or other organic solvent.

EXAMPLE 1A 10% tetrahydrofuran (THF) solution of Goodrich

Estane 5710-Fl(100g) was mixed wizh 4-vinlypyridine(6.3g)and l,6-dibromohexane(7.32g). Estane 5710-F1 isa solution coating grade aromatic polyester based poly-urethane. The mixture was poured into a leveled 7x7inch glass dish in a hood. The glass dish was coveredwith a polyethylene sheet and left at room temperaturefor 120 hours. The 18 mil thick formed membrane (ionicbromine content 14.0%) was covered with methanol (2hours), removed from the dish and washed with metha-

8nol (200cc) and distilled water (200cc). It was then keptin distilled water before testing.

EXAMPLE 2

5 Kel-F (copolymer of vinylidene fluoride and chloro-trifluoroethylene) membranes of 10 and 11 mil thicknesswere prepared with 50% vinyl pyridine-dibromohexaneresin content by the solvent casting technique of Exam-ple 1.

10 The test equipment for determining transport proper-ties of the various resin-impregnated membranes con-sists of two glass cylindrical compartments separated byan O-ring seal and the membrane under study. A metalclamp holds the compartments together and compresses

15 the O-ring resulting in a sealed system. The lower com-partment is equipped with a Teflon stirring bar and ismounted on a magnetic stirrer while the upper compart-

. ment has an externally driven stirring mechanism. Totalmembrane contact area is 15 cm2.

20 For nitrate removal studies with chloride pumpingion, 140ml. of a solution of 10~2MNaNO3, correspond-ing to 140 PPM NOj-N (nitrate expressed as nitrogen),and 10~' M NaCl was contained in the lower compart-ment and served as the strip or pump solution. The

25 upper compartment contained the feed solution, 100ml.of 50 PPM NO3-N. NaNO3 was included in the pumpsolution in order to demonstrate NO3~ transport againsta concentration gradient.

The method of analysis of nitrate in water was the30 Cadmium Reduction Procedure (colorimetric). This

procedure is adaptable to both high nitrate levels, mg/1or PPM range, and low nitrate levels, jig/1 or PPBrange. Details of these methods are discussed in theHach Chemical Company Catalog.

35 Free chlorine, present as hypochlorous acid and/orhypochlorite ion, was determined by the DPD proce-dure of Standard Methods. It offers high sensitivity ofapproximately 0.02 mg/1 chlorine (CI), rapid color de-velopment, and minimal fading.

40 Nine tests for nitrate transport with chloride pumping1 ion were performed with the 11 mil Kel-F sample. The

10 mil Kel-F film was tested three times by the usualprocedure and demonstrated a decreasing nitrate flux.

The polyurethane film of 18 mils thickness (Example45 1 was tested a total of 15 times covering 40 days for

nitrate removal with chloride ion. The film is stored incontact with pumping solution and is repeatedly avail-able for nitrate removal after an extended time, e.g., 6months and 1 year.

50 The results of the Kel-F and polyurethane tests arepresented in Tables 1 and 2 respectively.

TABLE 1NITRATE TRANSPORT BY KEL-F FILMS IMPREGNATED WITHV1NYLPYR1D1NE-D1BROMOHEXANE RESIN (chloride pumping ion)

STRIPOR

PUMPING FEEDMON- SOLUTION i SOLUTION

SUB-STRATE

Kel-F(11 mils)Test 1

Test 2

Test 3

OMER Cone.CONC. (Molar-

<*> ity)50 ID"2 N-NO,

lO-'N.Cl

" "

"

Vol- Cone. CONTACTume (Molar- Vol.(ml) ily) (ml)

140 3.58 X 10'J 100

" " "

" " "

TIME(hr)

01.02.0

19.001.02.0

20.001.0

ANALYSISOF FEED

SOLUTION( PPM ^^ NOj-N )

4239368

474540173935

( PPM ^I a- J

18120

' • Ta t 7

'f. Tol 8<M i

f Test 9

.:.

Tett)

Tail

Tesl3

Tat 4

'Test 5

Test 6

Tests

Te»l9

fat 10

4,119,58110

3.c). \ \ : - Hhenkept TABLE 1 -continuedNITRATE TRANSPORT BY KEL-F FILMS IMPREGNATED WITH

/ , -ff. VINYLPYRIDINE-DIBROMOHEXANE RESIN (chloride pumping ion)* .' \

•luorr ,nd chloro-j jnd 1 . (1 thickness•kline-d'i pmohexaney technLJeof Exam-

u.ig transport proper-v-d membranes con-i iments separated byi.-rJer study. A metal•, iher and compressesiu-rn. The lower com-vii stirring bar and is!_• the upper compari-ng mechanism. Total

*"

iih chloride pumpingi XaNOj, correspond-•}. pressed as nitrogen),'-, the lower compart -

;iump solution. Thecccl solution, 100 ml.

,-;- STRIP'•*; OR**. PUMPING; MON- SOLUTION

FEED ANALYSISSOLUTION OF FEED

nMFR Cone. Vol- Cone. CONTACT SOLUTION«UB- CONC. (Molar- ume (Molar- Vol. TIME ( PPM ^ ( PPM ^ITRATE <%) «v) («»') »y> <•"» (hr) (, NO}-N ) { c\- )

• '.V

J T«t 4;/ 11

j Tetii

V Toltif"

j.tj

Vf -r— 1 "

^«:• TeM 8

V T»u 9 " ".V . » c** ', J

2.0 3218.5 120 401.0 4450 ISi.U JO

20.0 1292.0 <2

" " n ^HU 302.0 44

19.0 15" " 0 47

2 4318 1742 <30 47

288 <20 47

24 60 501.0 36.5

30185310

2.0 33.5MEMBRANE PUNCTURED BY STIRRING ROD

i*>. Kd-F 50 " " " " ?. «Deluded in the pump * (jotnita); >.- transport against

,.sr ,.le in water was the

colorimetric). Thisi i - i nitrate levels, mg/1'levels, ng/1 or PpB

ire discussed in the

« nlorous acid and/or;; by the DPD proce-•f - high sensitivity of., ,c\), rapid color de-

,1 ih chloride pumping•r 1 Rei-F sample. The

-> „

. Tm } " " "lew *.. *>

'" Test 3

i$#'

l.U 342.0 32

20.0 270 392.0 40

18.5 32" 0 4 2

1.0 502.0 52

20 4792 45

6060

;^ TABLE 2;; NITRATE TRANSPORT BY POLYURETHANE FILMS*• IMPREGNATED WITH VINYLPYRIDINE-DIBROMOHEXANE RESINt (chloride pumping ion)J STRIP

•X OR•'{ PUMPING

fix '• MON- SOLUTION-, - times by the usual J - , OMER Cone. Vol-" -teasing nitrate flux. 4t;,

v SUB. CONC. (Molar- ume

\, ,v,;^n«, (Example K STRATE (%) ««x) W)covering 40 days for *J Polyumhane Igl.''^1 '*

, The film is stored in ft. ««•*> J8 by weight I0

, j is repeatedly avail- h> .xtended time, e.g., 6 fe . .

I'-'!' Tea 1t t CH *

i .)vurethane tests are K-.I n'vely. ,||

fi'

l i. \n t

A N A L Y S I SOF TEEDSOLUTION

,, T ( PPM ^^ JJLfii-l—-

{ ?' Ten 3

*>'' T«l 4 "'•>. * el1 i-"i.",-'

:^TeiiJ . _ . • -::?.

i *i. Tea 6•- '— • L-'T*«i7

-i' "'- • CH ' ft ,, ,,

.tj- /T-*t AVC*i , 1 Cal O*»«.•

Me . . ' :' >^'f^"i«*i 4 .• "Jy * ***

• ' • 1 2 0 & : • ' • • : ' ^.^^f^ctt 10

FEEDSOLUTION

Cone. CONTACT(Molar- Vol. TIME (

iiy) (ml) (hr) 1

3.58 X 10 ' 100 0NaNO, 0.5

1.02.0

202200.51.02.0

19.025.00

6500.51.02.0

190

91 5(BOTTOM AGITATION ONLY)

019.5002.07.0

7202.0

2401.0

ANALYSISOF FEED

SOLUTIONPPM ^ ( PPM ^

N J { a- }47382921

<2<2 ' 1005236.530203

<250i

523827193

477

505

50521510

<25216

<25235

11 4,119,581

TABLE 2-continued

12

NITRATE TRANSPORT BY POLYURETHANE FILMSIMPREGNATED WITH VINYLPYRIDINE-DIBROMOHEXANE RESIN

(chloride pumping ion)

SUB-STRATE

Test 11

Test 12

Test 13

Test 14

Test 15

STRIPOR

PUMPING FEEDMON- SOLUTION SOLUTIONOMER „ Cone. Vol- Cone. CONTACTCONC. (Molar- ume (Molar- Vol. TIME

(%) ity) (ml) ity) (ml) (hr)

3.0220

' 724. . . 04

7207.0

23" " " 0 \No

1.5 JAgita-72 / tion02.0

22

ANALYSISOF FEED

SOLUTION( PPM ^ ( PPM "\1 N J ( a- )

203

507

<252113

509

<25032

3. 55

193

Chloride ion as a pumping ion was used because it isinnocuous in low concentrations, contributing only to 25total dissolved solids, and is inexpensive. In addition,polymer stability is good in chloride solution.

Of the resin impregnated membranes tested for ni-trate removal from water with chloride pump ion,Kel-F and polyurethane gave the most promising re- 30suits. Kel-F films of 11 and 10 mil thicknesses weretested nine times for the 11 mil sample and three timesfor the 10 mil. It is apparent from Table 1 that the 11 milmaterial continued to remove nitrate over the threeweeks testing period without any evidence of reduced 35flux. Essentially total nitrate removal was observed intests 4 and 7 where the contact times were 92 and 288hours, respectively.

Polyurethane of 18 mils thickness was subjected to 15separate tests covering 40 days. Essentially total nitrate 40removal was observed in approximately 20 hours withno noticeable loss of nitrate flux during the testing per-iod.

Referring now to FIG. 1, the Figure graphicallydepicts the nitrate reduction for the 15 tests. Also in- 45eluded in the graph is a shaded region below 10 PPMNO3-N corresponding to standards from the NationalInterim Primary Drinking Water Regulations as issuedby EPA in December 1975. Effective date for compli-ance is June 1977. 50

An initial flux value of 1 mg NO3-N/hr. cm2, mea-sured over the first two hours of contact, was observedfor the 15 tests. This time period corresponds to a highnitrate concentration and, therefore, a high nitrate flux.For the time period from 7 to 20 hours, which corre- 55sponds to a nitrate reduction from 8 to less than 2 mg/1NOj-N, the flux was 0.02 mg NOj-N/hr. cm2. The poly-urethane impregnated film showed no noticeable deteri-oration over the 40 days of testing. Furthermore, fluxvalues remained very consistent for the testing period. 60

EXAMPLE 3

The solvent casting procedure of Example 1 was usedfor the preparation of Viton (copolymer of vinylidinefluoride and chlorotrifluoropropylene) membranes con- 65taining 33, 50 and 67 percent by weight 4-VP-DBH ionexchange resin. Film thickness ranged from 6 mils forone specimen of 33 percent to 28-33 mils for a very

irregular 67 percent sample. The 50 percent material of10 mils thickness was very uniform in thickness andappearance, and was tested for nitrate removal a total ofsix times, after which a severe split was observedaround the O-ring seal. A second Viton 50 percentsample of 9 mils thickness was tested five times withconsistent results.

The Viton 33 percent (10-12 mils) experienced cracksafter contact for only two days. Two samples of Viton33 (6 mils) were tested for different periods of time.Specimen 1 was tested only once and gave very slownitrate reduction after 19 hours in one test and 91.5hours in the second. The Viton 67 percent film wasextremely thick and brittle, irregular in appearance, andnot suitable for testing.

In order to perform an economic evaluation of ionexchange membranes or hollow fibers, it is first neces-sary to determine projected surface area requirements.The following calculation, based on a capacity of 10,000gal/day, illustrates this:

Assumed capacity:Feed water:Effluent water:

Strip or pumping solution:Membrane or Hollow Fiber:

10,000 gal/day50 PPM Nitrate-N10 PPM Nitrate-N (Interimdrinking water standard)10-' molar NaCIPolyurethane

flux/measured over initial 2 hr. *

30 mg N XI

15cm2

This calculation is based on the nitrate removal rateover the initial 2 hours for the polyurethane film of thisstudy (see FIG. 1).

Membrane or Fiber Requirement:

hr. cm2

I mgjV.. in2 .. ft.'

6.45 cm2 144 in268 ft.1

Fiber requirement for 10 X. 10* gal/day plant

•sisEDION

PPMci-

ent material ofthickness and

noval a total ofwas observedon 50 percentive times with

.•rienced cracksmples of Vitoneriods of time.;ave very slow' test and 91.5rcent film wasopearance, and

aluation of ionit is first neces-ii requirements,pacity of 10,000

te-Nic-N (Interimr standard)

68 ft.2

5 cm2 .. hr. cm2

ae removal rate ;hane film of this '

_ ,R ft."'

~ 10.000 gal/day

= 68 X 10'fl.-'

13

10 X 10" gal/day

4,119,58114

EXAMPLE 5

For comparative purposes, the calculation of mem-brane or fiber area requirements should be determinedfrom FIG. 1 for NO,-N reduction from 8 ppm to ap-proximately 2 ppm.

Nitrate nitrogen flux:

flux/measured from 7 to 20 hr. =1

15 cm' hr. cm

Membrane/Fiber requirement based on this nitrateflux:

-003 ingVV~~ 6.45crnJ " ,44'inJ ~ 3"° ft'

Fiber requirement for 10 X 106 gal/day plant

340- ft2

10,000 gal/day

= 0.340 X 10« ft2

X 10 X 10' gal/day

This compares with fiber requirements for reverse os-mosis applications as follows:

typical R.O. Flux

Of the nitrate removal methods — reverse osmosis, ionexchange, and electrodialysis-ion exchange appears tobe the primary competitor for the proposed hollowfiber ion exchange system. Cost estimates for a 10 MODplant based on 1970 data are:

reverse osmosiselectodialysision exchangeion exchange hollow Tiber

cents/ 1000 gallons

41.617.012.09-17.5

Greatly improved transport rates should be experiencedwith thinner membranes and with the hollow fiber ge-ometry where fluid velocities would be much higher.

EXAMPLE 4

Freshly distilled 4-vinyl pyridine (6.3 g) and 1,6-dibromohexane (7.32 g) were mixed with Viton dis-solved in methylethyl ketone (lOOg, 13.1% of Viton).The mixture was poured into leveled containers cov-ered with glass plates and left to polymerize for 140hours at room temperature. At the end of this time, themembranes were washed with methanol and rinsedwith distilled water. The ionic bromine content of thedry membrane was 13.0%.

Other Viton membranes containing 60, 67 and 70%4-VP-DBH ion exchange resin were prepared by the

5 procedure of Example 4.

EXAMPLE 6

Kel-F membranes containing 57, 73 and 84% 4-VP-DBH iori exchange resin were prepared by the proce-

10 dure of Example 4 except that the polymerization per-iod was 80 hours.

Testing equipment was as described before. For mosttests, a solution containing 10~2 molar K2Cr2O7 and10~' molar NaCl was in the lower compartment and

15 served as the strip solution while 10~4 molar K2Cr2O7•was above the membrane and served as the feed orwaste solution. These solutions afforded the advantagesof 1) visual detection of dichromate removal, 2) highchloride concentration, and 3) high dichromate concen-

20 tration gradient against which the system must pump (agood test of the transport mechanism).

To confirm pumping action, 10~4 molar K2Cr2O7 wasplaced in the lower chamber and 10~' molar NaCl in theupper chamber. Movement of all the dichromate from

25 the lower chamber, through the membrane, and into theupper chamber confirmed that Donnan pumping wasactually occurring.

All dichromate analyses were performed by the col-orimetric diphenylcarbazide procedure of Standard

30 Methods. The minimum detectable concentration ofchromium by this method is 0.005 PPM.

The Viton film containing 51 percent by weight ionexchange resin (Example 4) gave the most stable resultsretaining its initial chromium flux of 0.033 mg Cr+6/hr

35 cm2 for nine tests covering a contact time of 7 days.Rapid deterioration was observed for tests ten andeleven with a final flux of 0.007 mg Cr+Vhr cm2.

The effect of contact time, as measured by the num-ber of tests, on the chromium flux is presented graphi-

40 cally in FIG. 2. The flux for the initial 0.25 hours, de-picted by the upper curve in FIG. 2, decreases veryslowly for the first five tests and then decreases muchmore rapidly. The average flux over the initial twohours of transport showed a very stable value for nine

45 tests as represented in the lower curve of FIG. 2. Thetests shown were conducted on one membrane with thetime between each test varying greatly. The membranecontact time between tests 1 and 9 was 7 days.

Resin content in the membranes is quite critical in50 determining stability of the film to dichromate. It ap-

pears that a .resin content about 67 percent by weightyields a material much too brittle for sustained opera-tion. Cracks and tears are observed to occur at stresspoints for film with high resin content. Resin content or

55 charge density is also critical in establishing a high de-gree of dichromate transport.

The Kel-F membrane containing 73 percent ion-ex-change resin developed tears after the second test whilethe 84 percent sample was much too brittle and split

60 into many pieces prior to any testing for dichromatetransport.

An initial flux of 0.033 mg Cr+Vhr cm2 was observedfor the 57 percent by weight resin, Kel-F membrane,however, rapid deterioration and loss of dichromate

65 transport capability was observed.The Viton film with'51 percent by weight ion-ex-

change resin gave a high chromium flux and proved tobe the most stable, Riving the same 2 hour f lux for nine

154,119,581

16tests covering seven days of contact. Kel-F films dem-onstrated rapid chromium transport but, in general, lostpumping action more rapidly than the Viton films. Highresin content yields films which are much too brittle forion transport. It appears that resin content of approxi- 5mutely 50-60 percent by weight gives maximum trans-port and demonstrate adequate flexbility. Commercialanion exchange membrane tested gave decreasing chro-mium transport with time. The initial two hour flux waslower than most membranes prepared by the solvent 10casting procedure. Solvent casting is an excellentmethod for preparing charged membranes of highcharge density. Dichromate transport rates are of suit-able magnitude to give reasonable and competitive arearequirements for commercial applications.

It is to be realized that only preferred embodiments ofthe invention have been described and that numeroussubstitutions, modifications and alterations are permissi-ble without departing from the spirit and scope of the .invention as defined in the following claims.

What is claimed is: 20

1. A method of forming an ion-exchange membranecomprising the steps of:

dissolving in common solvent a thermoplastic matrixpolymer, a first monomer selected from polyterti-ary amines or vinyl pyridines and a second mono- 25mer selected from organic polyhalides said first andsecond monomers being capable of reaction toform a cationically charged, polyquaternary, ion-exchange polymer;

evaporating the solvent while reacting the monomers 30to form said cationically charged, polyquaternary,ion-exchange polymer which forms a network in-terpenetrating the chains of the matrix polymer.

2. A method according to claim 1 in which the matrixpolymer is a linear thermoplastic polymer. 35

3. A method according to claim 2 in which the matrixpolymer is selected from acrylic, polyolefin, polysty-rene, cellulose esters, polyurethanes and fluorocarbons.

4. A method according to claim 3 in which the matrixpolymer is a polyether or polyester polyurethane elasto- 40mer.

5. A method according to claim 1 in which the ion-ex-change monomers are present in an amount of at least20% by weight based on total polymer.

6. A method according to claim 3 in which the sol- 45vent is selected from ketones and ethers.

7. A method according to claim 6 in which the poly-mermonomer dilution is no more than 40% w/v.

8. A method according to claim 2, in which the mon-omers react to form a cross-linked, water-insoluble, 50network polyquaternary polymer in which the quater-nary nitrogens are present in the polymer chains or inbridges joining the chains.

9. A method according to claim 8 in which the firstmonomer is a polytertiary amine compound and the ,,second monomer is an organic polyhalide.

10. A method according to claim 8 in which the ionichalogen content of the membrane is at least 5% byweight.

11. A method according to claim 10 in which at leastone of the monomers is at least trifunctional.

12. A method according to claim 11 in which the firstmonomer is a vinyl pyridine and the second monomer isa dihalo organic compound of the formula:

60

X-R'-X 65

where X is selected from bromo, chloro or iodo andR1 is a divalent organic radial selected from alkyl-

ene, alkenylene, alkynylene, arylene, alkarylene,aralkylene or — (CH2),(2),,(CH2)Z— where Z isoxygen or sulfur and x,y and z are integers from 1to 100.

13. A method according to claim 12 ,in- which R1

contains from 1 to 20 carbon atoms and the vinyl pyri-dine is 4-vinyl pyridine.

14. A method according to claim 1 in which the solu-tion is cast into a sheet form before evaporation of thesolvent.

15. A method according to claim 1 in which the solu-tion is extruded into fiber form before evaporation ofsolvent.

16. An ion-exchange membrane comprising:a linear thermoplastic matrix polymer; anda cross-linked, cationically charged, polyquaternary,

ion-exchange network polymer interpenetratingthe chains of the matrix polymer, said polyquater-nary polymer comprising the reaction product of afirst monomer selected from polytertiary amines orvinyl pyridines and a second monomer selectedfrom organic polyhalides.

17. A membrane according to claim 16 in which thematrix polymer is selected from acrylic, polyolefin,polystyrene, cellulose esters, polyurethanes and fluoro-carbons.

18. A membrane according to claim 17 in which thematrix polymer is a polyether or polyester polyurethaneelastomer.

19. A membrane according to claim 16 in which theion-exchange polymer is a polyquaternary polymer inwhich the quaternary nitrogens are present in the poly-mer chains or in bridges joining the chains.

20. A membrane according to claim 19 in which theion-exchange polymer is present in an amount of at least20% by weight.

21. A membrane according to claim 20 in which thepolyquaternary ion-exchange polymer is the reactionproduct of a polytertiary amine and an organic polyha-lide.

22. A membrane according to claim 20 in which theionic halogen content of the membrane is at least 5% byweight.

23. A membrane according to claim 22 in which thepolyquaternary polymer is the reaction product of avinyl pyridine and dihalo organic compound of theformula:

X-R'-X

where X is selected from bromo, chloro or iodo and R1

is a divalent organic radial selected from alkylene, alke-nylene, alkynylene, arylene, alkarylene, aralkylene or—(CH^Z^/CHz),— where Z is oxygen or sulphurand x, y and z are integers from 1 to 100.

24. A membrane according to claim 23 in which R1

contains from 1 to 20 carbon atoms and the vinyl pyri-dine is 4-vinyl pyridine.

25. A membrane according to claim 16 in sheet form.26. A membrane according to claim 16 in fiber form.27. A method of removing anions from aqueous solu-

tion comprising the steps of:interposing the membrane as defined in claim 16 be-

tween first aqueous solution containing the anionand a second aqueous .stripping solution; and

permeating the anions through the membrane fromthe first solution to the second solution.

28. A method according to claim 27 in which theanions are selected from chromates and nitrates.