unit-ii.pdf

7/23/2019 UNIT-II.pdf

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NAPHTHA AND GAS CRACKING FOR

PRODUCTION OF OLEFINS


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Olefins: ethylene and propylene

The largest volume petrochemicals produced inwhich Annually global production of ethylene isabout 120 million tons with a continuous annual

increase of some 4 - 5 %.Ethylene and propylene have no end use, they arebuilding blocks for a large variety of chemicals and

petrochemical products.Polymers are the dominating end-users.


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Olefins are major building blocks for petrochemicals. Becauseof their reactivity and versatility, olefins especially the light

olefins like ethylene, propylene, butenes, butadiene, etc., therehas been tremendous growth in the demand of the olefins.

Olefins are finding wide application in the manufacture ofpolymers, chemical intermediates, and synthetic rubber.

Ethylene itself is basic building block for large number ofpetrochemicals and is quoted as king of chemicals.

Some of ethylene manufacturing company and their capacity isgiven in Table M-VII 2.1.

The global ethylene capacity at January 1, 2011, net additionsand closings was more than 138 million tones compared withnearly 130 million tones in 2008 [Oil & gas J. Vol 129, 2011].

Global ethylene capacity is given in Table M-VII 2.2.


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STEAM CRACKING FOR PRODUCTION OF OLEFINS

The steam cracker remains the fundamental unit and is the heart

of any petrochemical complex and mother plant and produceslarge number of products and byproducts such as olefinsethylene, propylene, butadiene, butane and butenes, isoprene,etc., and pyrolysis gasoline.

The choice of the feedstock for olefin production depends on theavailability of raw materials and the range of downstreamproducts.

Naphtha has made up about 50-55percent of ethylene feedstock

sources since 1992. Although basic steam cracking technologyremain same for naphtha, gas oil and natural gas, differentconfiguration of steam cracking plant are available from variousprocess licensors [Petrochemical processes, 2003].


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Steam cracking challenges

The steam cracking process has high yields withhigh temperature in the cracking furnaces.

Steam cracking furnace valves play an important

role in ensuring proper ethylene processperformance.

Reliable and accurate control, on-off and valve

performance is vital during normal production andfrequent furnace decoking operations to ensuretotal process productivity and safety.


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The indicated feedstock's (ethane, propane, butane, naphthaand gas oil) are fed to a pyrolysis (steam cracking) furnace,

where they are combined with steam and heated totemperatures between approximately 1450 - 1600 F (790 -870 C). Within this temperature range, the feedstockmolecules "crack" to produce ethylene as well as methane,

hydrogen, ethylene, propylene, butadiene, benzene, tolueneand other co-products.

After the pyrolysis reaction is quenched, the rest of the

plant separates the desired products into streams that meetthe various product specifications.

Process steps include distillation, compression, process gasdrying, hydrogenation (of acetylenes), and heat transfer.


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Hot Section:

The cracker furnace may be divided into three sections:convection zones, radiation zones and quench section.

The hydrocarbon feed stock is preheated by quench water andsteam before entering the convection zone of the furnace whereit is further preheated and mixed with superheated steam, which

is added as a diluent.The steam minimizes the side reaction responsible for the

formation of coke during pyrolysis and improves the selectivityto produce desired olefins by lowering hydrocarbon partial

pressure.The requirement of steam will depend upon the type of

feedstock; the lighter hydrocarbon requires less steam ascompared to heavier feedstock.


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The hydrocarbon and steam preheated in convection zone in theupper part of the furnace enter the radiant section of furnace atabout 6500C & total pressure of 1.7 bar, where pyrolysis of feed

takes place. The coil length in the radiant section varies from 60m for a

naphtha cracker to 85m for an ethane cracking unit.

The resistance time varies for different feedstock is around 0.15-

1.2 sec and Reynolds number is around 3,00,000. The effluent leaves at a temperature of 830-8700C and Pressure of

1.7 bar.

The flue gas temperature may be of the order of 12000C with theinner tube skin temperature of 10080C.

The reaction is endothermic. Here heat flux ranges from 55-85kJ/m2.

The radiant coil outlet temperature is controlled to achieve desiredethylene and propylene yield.


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Pyrolysis of any hydrocarbon feedstock is always accompaniedby coke formation, which deposits on the walls of the reactor

under typical operating conditions. the furnace effluent is rapidly quenched in double pipe heat

exchangers and multi-tubular heat exchangers which cools to ata temperature of 3500C.

The effluent is further quenched by direct contact with quenchoil before entering the quench oil tower where besides coolingthe furnace effluent, the separation of gasoline and lighterproducts from fuel oil also takes place.

here quenching is essential in order to restrict the

polymerization reactions.Ethylene cracking effluent must be quenched uniformly and

rapidly for high product yield.


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Quenching is performed in two ways directly by oil orwater (OR) Indirectly by a quench cooler.

The basic requirements for cracked product quenchcoolers are rapid and uniform cooling, small pressuredrop, maximum heat recovery, long continuous runlength and low maintenance.

The cracked gas overhead of the quench oil tower isfurther cooled in the quench water tower by directcontact with water and is finally sent to primaryfraction column.

The gases are separated at the top and are sent tocompression section for separation and purification ofcracked products.


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Agreenerchemistry

17


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Agreenerchemistry

18


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Cracked gas compression and dehydration:

The effluent from primary fraction column is compressed in four or

five stages on centrifugal compressor containing intercoolers and thento a separator drum.

The condensate from separator drum enters a stripper where thehigher fractions are recovered.

The gas before entering the final stage compression is desulfurized by

passing through a caustic scrubber where the separation of sulphurcompounds and CO2takes place.

The removal of CO2from gas is essential in order to meet the productquality.

The removal of CO2 also avoids corrosion and formation of CO2icein the cold section.

The cracked gases are dried in dehydrators containing molecular sievesbefore entering the cold section.


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Cold section:

The dried cracked gas after removal of sulphur

compounds, CO2 and moisture are sent to cold sectionwhere it is cooled to -1650C in cascade refrigerationsystem using propylene and ethylene.

The cold section contains demethanizer, deethanizer,

acetylene hydrogenation unit, ethylene separation,depropanizer, C3 hydrogenation and debutanizer.

Here refrigeration system is an important part of anyethylene plant.

The recovery of ethylene will depend on reliability andflexibility of the system, as a coolant at differenttemperature levels.


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Demethanizer:

The cracked gases after cooling to -165

0

C are sent todemethanizer which operates at a pressure of about 7 atmin case of low pressure demethanizer or 355 atm in case ofhigh pressure demethanizer.

The purpose of demethanizer is to make sharp separationbetween methane and ethylene.

Demethanizer operating performance is very muchdependent on its feed condition, temperature, pressure andflow rates.

Demethanizer operation is most sensitive to flow rates andtemperature and least sensitive to pressure.


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Deethanizer:

The demethanizer bottom portion consisting of ethylene and heavierfraction is sent to deethanizer which is essentially as fractionator

operating pressure of about of 24 kg/cm2 and temperature -100C. The deethanizer separates the demethanizer bottom into C2 overhead

and C3 sent to depropanizer for separation of propane.

Acetylene hydrogenation Unit: the deethanizer overhead is sent to acetylene hydrogenation system

where acetylene is catalytically hydrogenated to ethane and ethylene inthe presence of palladium catalyst at a temperature of 400C & 3 atmpressure.

the removal of acetylene is important because of its presence duringethylene polymerization gives a polymer containing double bonds,which is cross linked to give a non-linear product.


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Ethylene separation:

the acetylene free effluent is cooled and sent to ethyleneethane

separator, which is essentially a distillation where ethylene isseparated in the column which operates at -350C and 20 kg/cm2.

Depropanizer:

The bottom of the deethanizer containing C3 and higher fractions

are sent to depropanizer column where separation between C3and C4 compounds are achieved.

C3 Hydrogenation:

The C3 cut at the top of the propanizer is sent to C3

Hydrogenation unit where methyl acetylene and propadiene arecatalytically converted to propylene and propane in a liquid phasereactor in presence of hydrogen before carrying out separation ofpropylene.


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Debutanizer:

The bottom portion from the depropanizer is sent todebutanizer, which produces a butadiene rich, C4 cut at the top.

The bottom stream, which is essentially pyrolysis gasoline is sentto pyrolysis gasoline processing unit for separation of aromatics.

Pyrolysis gasoline fractionator:

Feed to the gasoline fractionator is from the bottom portion ofthe debutanizer. Here the gasoline is separated from the wash oiland heavier fraction.

Fuel oil stripper:

fuel oil stripper separates wash oil from heavier fuel oilcomponents.


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Agreenerchemistry

27

Olefins complex: a steam-cracking unit

Mixed

Products

Quench

Drier

Fuel Oil

Hydrogen

Compressor and

Chilling

team

Quench

Methane

cetylene

Converter

Ethane

Ethylene

Propane

Propylene

N PD

Converter

Mixed

Butanes

Gasoline

Cracking

Furnaces

Ethane

Naphtha

cid Gas

Primary

Fractionator

Feeds

Material Movements

Utilities


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OPERATING VARIABLES IN STEAM CRACKING

Some of the operating variables which affects the performance of

steam crackers are: type of feedstock, reaction temperature,pressure, steam to hydrocarbon ratio and outlet pressure.

Type of feed stock:

The various feed stocks for steam cracking are naphtha, natural

gas liquid and gas oil.The yield of the ethylene varies depending upon the type of feed

stock used.

Ratio of ethylene and propylene yields decreases steadily from

ethane to the heavier fractions like naphtha and gas oil, while thepyrolysis gasoline yield increases with the increase in thehydrocarbon heaviness.

Here pyrolysis gasoline is an important source of aromatics.


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Pyrolysis temperature and Residence Time

The effluent gas exit temperature is generally considered asignificant indicator of the operation of a furnace.

As the furnace exit temperature rises, the yield also rises, whilethe yields of propylene and pyrolysis gasoline (C5-200oC at)

decrease. With respect of ethylene yield, each furnace exittemperature, correspond to an optimum.

The highest ethylene are achieved by operating at high severely,namely, around 850oC with residence time ranging from 0.2 to0.4s However, operating at high temperature results in high cokeformation.


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Partial Pressure of Hydrocarbon & Steam to Naphtha Ratio

Pyrolysis reaction producing light olefins are more advanced at lower

pressure. Decrease into the partial pressure of hydrocarbons bydilution with steam, reduces the overall rate reaction rate, but alsohelp to enhance the selectivity of pyrolysis substantially in favor of thelight olefins desired.

Other role of steam during pyrolysis is

(1) to increase the temperature of feed stock(2) reduction in the quantity of heat to be furnished per linearmeter of tube in the reaction section(3) to remove partially coke deposits in furnace tubes.

The ethylene yield decreases as the partial pressure of hydrocarbon

increases. The effect of H2O/naphtha on ethylene yield is gives theeconomic reason a value of 0.5 to 0.64 of steam per ton of naphtha.

Steam to hydrocarbon weight ratios range between 0.21 for ethaneand approximately 11.2 for liquid feeds.


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Severity and Selectivity

Severity is often used to describe the depth of cracking or extent ofconversion.

The definition of severity varies with the different manufactures andmay differ accordingly to the type of hydrocarbon treated.

In the case of steam cracking of the ethane and propane, it isconvenient to express the severity of the operating conditions in

terms of feed conversion. At very high severities, the methane and ethylene yield level off,

while those of propylene and C4 cut reach a peak and then declineconsequently.

The ratio of ethylene and propylene yield increases with severity,

which hence favors the formation of ethylene. The relativeproduction of C5+ cut passes through a minimum and at the veryhigh severity tends to increase.

Modern ethylene plants are normally designed for near maximumcracking severity because of economic considerations.


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Furnace Run Length

Furnace run length can be calculated from the equation


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Coke formation decoking

During steam cracking of hydrocarbons, coke is formed dueto undesired side reactions involving unsaturated moleculesand aromatic nuclei.

Due to coke deposit, the surface temperature of coil is

increased which effects the service life of coil;

Pressure drop is increased due to reduction in the innerdiameter of the coil upon coking;

Corrosion of the coil also occurs; Reduces the product yield,

Increases the energy consumption;


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At present three mechanisms have been proposed to

account for coke formation in hydrocarbon pyrolysis:

Coke formation via surface catalyzed reactions due tocarbides.

Coke formation via polycyclic aromatic hydrocarbonsin the gas phase

Coke formation directly through the reactions of small

gas phase species e.g. acetylene, butadiene and freeradicals such as methyl, ethyl, vinyl, phenyl and benzylradicals.


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If coke is formed inside the tube reduces the heat

transfer area; increase the pressure drop, whichaffects the ethylene production due to higher inletpressure.

The coke formation inside the will depend upon:Characteristics of feed stock;

Hydrocarbon partial pressure

Thermal condition of coil Feed flow rates


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Some of the techniques used for reducing coke formation:

pretreatment of feedstock

Material of construction of reactor

Addition of coke inhibitors such as antimony, copper,

phosphorous and chromium etc.,catalytic gasification of coke to form CO and hydrogen

Coating and surface enrichment using Mg, Si, Al, Cr, etc.,

Increasing steam dilution

pretreatment of inner surface of coil.


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Thermal cracking furnace design

Pyrolysis furnace design during the last three decades made significant

development.Prior to 1960, the ethylene pyrolysis furnaces were box type with

horizontal radiant tubes. The capacity of these furnaces were smallcapacity (40 MM lb/y) today standards (250 MMlb/y).

High thermal efficiency furnace design can contribute greatly tominimum overall plant utility costs.

Higher efficiency can be achieved by

Upgrading of pyrolysis furnace capacity

Increasing cracking severity

Improving ethylene selectivity

Improving thermal efficiency

Reducing downtime for decoking

Reducing maintenance cost.


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This can be achieved by radiant coil with shorter

residence time and lower pressure drop,combustion air preheating and short residence time.

Small diameter coils coupled with increased

dilution steam, with use of booster compressors toreduce furnace outlet pressure can increaseefficiency ethylene selectivity.

Radiant coils with a short residence time and lowhydrocarbon partial pressure give higher ethyleneselectivity.


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Various technological developments for steam

crackers have been incorporated with basic objectiveto have:

lower energy consumption per ton of ethylene

improved overall yield of ethylene by shortresidence time and high severity.

total feed stock flexibility, gas to liquid

higher furnace availabilityincrease furnace tube life

reduced the maintenance cost


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Gas sweetening unit

Steam cracker plants using natural gas as feedstock containgas-sweentening unit.

It can be defined as removal of acid gases like H2S and CO2present in the natural gas.

the composition of natural gas before sending into the

sweetening unit:Component Percentage

C1 84.06

C2 9.38

C3 0.99

C4 0.04

CO2 5.52

H2S 4 ppm

N2 0.01


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Natural gas contains C02 and H2S and this gas is fed to a C2-C3recovery unit for cryogenic separation.

If CO2 component of the gas is not removed it will freeze(-770C) resulting in the choking the pipelines.

Some of the process technologies available for separation of CO2are amine sweetening using MEA,DEA process and membrane

process. However, amine sweetening process is most commonly used and

CO2 removed by absorption in two parallel high pressureabsorbers.

The gas is fed to two absorber columns at 52 kg/cm2 and 300Coperating in parallel.

the raw gas is taken into raw gas drum for separation of anymoisture present in the gas before passing to the absorber.


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Each absorber is fitted with valve trays. Lean diethanolaminesolution is fed to column top at tray-2 at 51.4 kg/cm2 and 450C.

The gas is counter currently contacted with the absorbent DEAso that CO2 in the gas gets absorbed into the solution.

CO2 in the gas reacts with amine to form amine carbamate.

CO2 + 2R2NH R2NCOO-+ R2NH2+

CO2 also reacts with water and hydroxyl ions to form carbonicacid and bicarbonate ions.

CO2 + H2OH2CO3

CO2 + OH-

HCO3-

The carbonic acid reacts with amine to form amine bicarbonate(HCO3 & R2NH2) and amine carbonate(CO3(R2NH2)2)


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the treated gas leaves form the column top at 450C and itcontains


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After CO2 absorption the treated gas is fed into the bottom ofsweet gas wash water column where the gas is counter-currentlycontacted with circulating water to remove any DEA solution

carried over with the treated gas.

The treated gas after cooling is sent to the C2/C3 recoverysection for extraction of C2/C3 component.

C2/C3 Extraction unit


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C2/C3 Extraction unit

The sweetened gas from gas sweetening unit is fed to the

feedstock drum for separation of any entrapped liquid form thefeed gas and then it is compressed and cooled to 170C.

It is then sent to feed gas moisture separator and feed gas dryingsection for removal of traces of moisture.

The gases after passing through filter are sent through series ofexchangers for cooling to below -600C and then sent to the coldsection.

in the cold section the gases are sent to demethanizer column for

separation of methane form the C2/C3. The temperature in this column maintained is about -1010C


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Alpha olefins


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Alpha Olefins

Application:

To produce high-purity alpha olefins (C4 C10)suitable as copolymers for LLDPE production andas precursors for plasticizer alcohols .

Production of polyalphaolefins using the AlphaSelect process.

This process is simple;

It operates at mild operating temperatures andpressures and only carbon steel equipment isrequired.

The catalyst is nontoxic and easily handled.


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(1). Liquid-phase Reactor (2). Catalyst separator(3). Distillation column (4). Fractionation column

Linear


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Polymer-grade ethylene is oligomerized in the liquid-phase reactor (1) with a catalyst/solvent system designedfor high activity and selectivity. Liquid effluent and

spent catalyst are then separated (2); the liquid is distilled(3) for recycling unreacted ethylene to the reactor, thenfractionated (4) into high-purity alpha-olefins. Spentcatalyst is treated to remove volatile hydrocarbons and

recovered. The table below illustrates the superior purities

attainable (wt%) with the Alpha-Select process:

Component Purity

n-Butene-1 >99%

n-Hexene-1 >98%

n-Octene-1 >96%

n-Decene-1 >92%


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Yields: Yields are adjustable to meet market requirements andvery little high boiling polymer is produced as illustrated:

Alpha-olefin product distribution, wt%

In particular, the Alphabutol process for producing

butene-1 for which there are 19 units producing 312,000tpy.

Licensor: Axens, Axens NA.

Component Yield (wt%)

n-Butene-1 33-43

n-Hexene-1 30-32

n-Octene-1 17-21n-Decene-1 9-14


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The -Sablin process produces -olefins such as butene-1,hexane-1, octene-1 decene-1, etc. from ethylene in a

homogenous catalytic reaction. The process is based on a highly active bi-functional catalyst

system operating at mild reaction conditions with highestselectivities to -olefins.

Ethylene is compressed (6) and introduced to a bubble-columntype reactor (1) in which a homogenous catalyst system isintroduced together with a solvent.

The gaseous products leaving the reactor overhead are cooled in

a cooler (2) and cooled in a gas-liquid separator for reflux (3)and further cooled (4) and separated in a second gas-liquidseparator (5).

Unreacted ethylene from the separator (5) is recycled via a


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Unreacted ethylene from the separator (5) is recycled via acompressor (6) and a heat exchanger (7) together with ethylenemakeup to the reactor.

A liquid stream is withdrawn from the reactor (1) containing liquid-olefins and catalyst, which is removed by the catalyst removal unit(8).

The liquid stream from the catalyst removal unit (8) is combinedwith the liquid stream from the primary separation (5).

These combined liquid streams are routed to a separation section inwhich, via a series of columns (9), the -olefins are separated into theindividual components.

By varying the catalyst components ratio, the product mixture can beadjusted from light products (butene-1, hexene-1, octene-1, decene-1)to heavier products (C12 to C20 -olefins). Typical yield for lightolefins is over 85 wt% with high purities that allow typical productapplications.

One plant of 150,000 metric tpy capacity is currently underconstruction for Jubail United in Al-Jubail, Saudi Arabia.


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(1). Bubble column type Reactor (2). Cooler (3). Gas- liquid separator(4). Cooler (5). Unreacted ethylene separator (6). Compressor(7). Heat exchanger (8). Catalyst removal unit (9). Series of distillation columns

P d ti f l h l fi b Th l ki


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Production of alpha olefins by Thermal crackingwax

Thermal cracking of wax is carried out in a tubular furnace at 500-6000C for 5-15 sec.

The products are separated from primary fractionation column andstabilization column.

Mild condition is used to maximize the yield of alpha-olefins.

Wax

Ethylene,Propylene

C4-C18alpha Olefins

PurificationVaporizer and

Preheater Fractionator

C20 +

Sh ll Hi h Ol fi P


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Shell Higher Olefins Process

Basic info on the SHOP

OligomerizationThe process of converting a monomer or amixture of monomers into an oligomer (consists of limitted no ofmonomers)

Isomerizationrearrangement reaction that occurs whencompounds with the same formula exhibit different structures (e.g.1butene and 2butene)

Metathesis

catalytic reaction in which alkenes are converted intonew products by breaking - up and reformation of C-C doublebonds.


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Metathesis of C4C8 and C16C40 internal olefins

Short and long chain internal olefins disproportionate

CH3CH=CHCH3 + CH3(CH2)8CH=CH(CH2)8CH3 2 CH3CH=CH(CH2)8CH3

C4 Internal olefin C20 internal olefin C12 internal olefin


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P d fil f l h l fi


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Product profile of alpha olefins C4 alpha olefins: LLDPE, MA, MEK,Butene-1Plastics, solvents,

etc., C4-C8: Comononers for LLDPE, HDPE,C9 Oxo-alcohols, C10

olefinsPlastics, plasticizers and detergents etc.,

C6-C12Improved flexible PVC

C8-C12: Mercaptans and rubber chemicalschain transfer agents,oxo-alcohols etc.,

C10-C16Detergents etc.,

C14-C18: Alpha olefin sulphonateshousehold and industrialdetergents and toilet soaps etc.,

C20-C24: Chlorinated paraffins, polybutenesplasticizers andleather tanning etc.,

C24+: Waxes and emulsionsCandles, coating papers and textileprocessing

Ol fi b t t ti di till ti


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Olefinsbutenes extractive distillation

Application:

Separation of pure C4 olefins from olefinic/paraffinic C4 mixturesvia extractive distillation using a selective solvent. BUTENEX is the Uhde technology to separate light olefins from

various C4 feed stocks, which include ethylene cracker and FCCsources.

Description: In the extractive distillation (ED) process, a single-compound

solvent, N-Formylmorpholine (NFM), or NFM in a mixture withfurther morpholine derivatives, alters the vapor pressure of thecomponents being separated.

The vapor pressure of the olefins is lowered more than that of theless soluble paraffins.

Paraffinic vapors leave the top of the ED column, and solvent witholefins leaves the bottom of the ED column.

Th b d f h ED l f d h


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The bottom product of the ED column is fed to thestripper to separate pure olefins (mixtures) from the

solvent. After intensive heat exchange, the leansolvent is recycled to the ED column.

The solvent, which can be either NFM or a mixture

including NFM, perfectly satisfies the solventproperties needed for this process, including highselectivity, thermal stability and a suitable boilingpoint.

Two commercial plants for the recovery of nbutenes have been installed since 1998.


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Olefinsbutenes extractive distillation


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Olefins conversion technology

OCT converts normal butylenes andethylene to polymer grade propylene viametathesis.

The two main equilibrium reactions takingplace are metathesis and isomerisation.

Propylene is formed by the metathesis ofethylene and butene-2, and butene-1 is

isomerised to butene-2 as butene-2 isconsumed in the metathesis reaction.


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Fresh C4s (plus C4 recycle) are mixed with ethylenefeed (plus recycle ethylene) and sent through a guardbed to remove trace impurities from the mixed feed.

The feed is heated prior to entering the vapour phasefixed-bed metathesis reactor where the equilibriumreaction takes place.

The catalyst promotes the reaction of ethylene andbutene-2 to form propylene and simultaneouslyisomerises butene-1 to butene-2.

The per-pass conversion of butylene is greater than 60

per cent, with overall selectivity to propyleneexceeding 90 per cent.

The product from the metathesis reactor is primarilypropylene and unreacted feed.


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Reactor effluent is sent to the ethylene recovery tower where

the unreacted ethylene is recovered and recycled to the

reactor.

The C2 tower bottoms is processed in the C3 tower to produce

propylene product and a C4 recycle stream. Purge streams

containing non-reactive light material and C4s and heavier arealso produced.

Depending on the quantity of isobutylene in the C4 feed, the

unit design may include a deisobutaniser to extend reactorrun-length OCT process flow schematic between regenerations

and reduce OCT unit throughput, resulting in an overall lower

capital cost plant.


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MTO PROCESS


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MTO PROCESS

Application:

To produce ethylene, propylene and butenes from natural gas orequivalent, via methanol, using Hydro MTO (methanol to olefins)process.

Description:

This process consists of a reactor section, a continuous catalystregeneration section and product recovery section. One or morefluidized-bed reactors (1) are used with continuous catalyst transferto and from the continuous catalyst regenerator (2).

The robust regenerable MTO-100 catalyst is based on a nonzeoliticmolecular sieve. Raw (nondewatered) methanol is fed to the low-pressure reactor (1), which offers very high (99%+) conversion ofthe methanol with very high selectivity to ethylene and propylene.

Th i d i d d d b ill


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The recovery section design depends on product use, but willcontain a product water recovery and recycle system (3), a CO2removal system (4), a dryer (5), a deethanizer (6), an acetylenesaturation unit (7), a demethanizer (8), and a depropanizer (9).The process can produce polymer-grade ethylene and propylene

by adding simple fractionation to the recovery section.

The process gives very high total olefins yields. Ethylene topropylene product weight ratio can be modified between therange of 0.75 to 1.3 by altering reactor operating severity.

Commercial plants: Hydro operated a demonstration unit thatwas installed in Norway in 1995. The first commercial MTOunit is planned for startup in 2008 in Nigeria.

Licensor:UOP LLC/Hydro.


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(1). Fluidized-bed reactors (2). Continuous catalyst regenerator(3). Water removal unit (4). CO2 removal system (5). Dryer(6). Deethanizer (7). An acetylene saturation unit (8). Demethanizer(9). Depropanizer

MTO PROCESS


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Olefins by dehydrogenation

Application: The Uhde STeam Active Reforming STAR process produces

(a) propylene as feedstock for polypropylene, propylene oxide,cumene, acrylonitrile or other propylene derivatives, and

(b) butylenes as feedstock for methyl tertiary butyl ether (MTBE),alkylate, isooctane, polybutylenes or other butylene derivatives.

Feed:

Liquefied petroleum gas (LPG) from gas fields, gas condensate fields andrefineries.

Product:

Propylene (polymer- or chemical-grade); isobutylene; n-butylenes;

high-purity hydrogen (H2) may also be produced as a byproduct.


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Description:

The fresh paraffin feedstock is combined with paraffin

recycle and internally generated steam. After preheating, the feed is sent to the reaction section. This

section consists of an externally fired tubular fixed-bedreactor (Uhde reformer) connected in series with anadiabatic fixed-bed oxyreactor (secondary reformer type).

In the reformer, the endothermic dehydrogenation reactiontakes place over a proprietary, noble metal catalyst.

In the adiabatic oxyreactor, part of the hydrogen from theintermediate product leaving the reformer is selectivelyconverted with added oxygen or air, thereby forming steam.


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This is followed by further dehydrogenation over the same noble-metal catalyst.

Exothermic selective H2 conversion in the oxyreactor increasesolefin product space-time yield and supplies heat for furtherendothermic dehydrogenation.

The reaction takes place at temperatures between 500C600C

and at 4 bar6 bar The Uhde reformer is top-fi red and has a proprietary cold

outlet manifold system to enhance reliability.

Heat recovery utilizes process heat for high-pressure steam

generation, feed preheat and for heat required in thefractionation section.

f l d d h d


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After cooling and condensate separation, the product issubsequently compressed, light-ends are separated and the olefinproduct is separated from unconverted paraffins in thefractionation section.

Apart from light-ends, which are internally used as fuel gas, theolefin is the only product. High-purity H2 may optionally be

recovered from light-ends in the gas separation section. Commercial plants: Two commercial plants using the STAR

process for dehydrogenation of isobutane to isobutylene havebeen commissioned (in the US and Argentina). More than 60

Uhde reformers and 25 Uhde secondary reformers have beenconstructed worldwide.

Licensor: Uhde GmbH.


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