UNIT-IIIProcessing of olefinic C4 and C5 Cut from

Steam cracking and Fluid catalytic cracking

Contents Introduction FCC Various Petroleum Products from FCC and their uses Product profile of C5 Hydrocarbons Description of FCC and FCC gases as petrochemical feedstock Processing of C4 stream from stream cracker and FCC

(Separation of C4 hydrocarbons from FCC and Steam Crackerplants) Oxygenates from refinery C4 & C5 stream

Methyl tertiary butyl etherTertiary amyl methyl ether

Upgrading Of C5 Cuts For Recovery Of C5 Chemicals

Introduction With the rising demand of ethylene and propylene,

there has been a tremendous growth in the steamcracking of hydrocarbons during the last fourdecades.

Similarly, FCC (Fluid Catalytic Cracking) hasdeveloped into a major upgrading process in thepetroleum refinery industry for the conversion ofheavy fuel oil into more valuable products rangingfrom light olefins to naphtha and middle distillate.

Large amounts of C4 and C5 compounds are producedalong with the production of ethylene in steam crackingand gasoline in FCC.

C4 & C5 streams are an important source of feedstock forsynthetic rubber and many chemicals.

With increasing demand of C5 hydrocarbons andoxygenates, upgrading of C4 and C5 streams from steamcrackers and catalytic cracker is important to theeconomic performance of the above processes.

The quantity and composition of the C4 and C5 streamdepends on the severity of the steam cracker operationand feedstock processed.

Importance of utilization of C4 stream can be realized fromthe fact that global demand for butadiene, isobutylene, and1-butene, three major C4 olefins will climb to 11.2,18.8,1.7 million tones by 2010.. global demand for butadiene over the long term will grow

3.3percencent per year on an average as compared to 4.9percent per year for ethylene. The main C5 compounds like isoprene, n-pentenes, 2-

methyl-2-butene, Cyclopentene and cyclopentadiene. C5 hydrocarbons are present with pyrolysis gasoline

obtained after separation of C4 stream in the butanizer.

Fluid catalytic cracking Although FCC is an important petroleum refining process, and FCC

gases are important petrochemical feedstock for production of LPGwhich can be converted to aromatics and C3, C4 andC5 hydrocarbons,i.e. propylene, butene, isobutene, pentene, etc.

Cracking one of the important secondary processes is conversion of alonger hydrocarbon molecule to small one either by thermal orcatalytic cracking.

To control reactions in order to avoid too much coke formation or theformation of very small molecules, industrial cracking of petroleumheavy fractions are aided by catalyst.

With the advent of fluidized technology, fluidized bed reactors foundcommercial application in chemical petroleum and petrochemicalindustries.

During 1940, FCC was introduced in petroleum industries for theconversion of gas oils and residue into more valuable product.

Various Petroleum Products fromFCC and their uses

Product profile of C5 HydrocarbonsC5 hydrocarbons –are an important source of synthetic rubber, solvents,chemical intermediate, MTBE, plasticizers, TAME, rubber chemicals,herbicides, lube oil additives, pharmaceuticals.

Description of FCC FCC unit can be divided into two sections: (i). The reactor and

regenerator system and (ii) the fractionation column. The feed to the unit along with the recycle streams is preheated to a

temperature of 365-3700C and enters the riser where it comes incontact with hot regenerated catalyst at a temperature of about 630-6500C.

The hot catalyst vaporizes the feed and the cracking reaction takesplace in the riser.

This vaporization fluidizes the catalyst up the riser to the disengagingT-section at the top of the riser.

The cracked hydrocarbons exit from the reactor through a cyclone tothe fractionation column where overheated FCC gases including LPGand gasoline are removed as vapour.

The extruded catalyst is collected in the cyclone and returned to thereactor. The spent catalyst flows through the regenerator where thecoke is burnt off.

In the fractionator, the reactor vapors are fractionated intorecycle gas oils which are released to the riser for furthercracking and converted to following products such as clarifiedslurry, heavy cycle oil, cracked light cycle oil, unstabilizedgasoline and wet gas. Unstabilized gasoline separated from the lighter products is

sent to debutanizer for separation of C3 and C4 as overheadproducts. The main column bottom is sent to slurry setter where

settled slurry containing catalyst is recycled. Water and gasoline vapors are withdrawn from the top of the

fractionator and further separated in stripper and absorber.

The function of the stripper-absorber section is separate themain fractionator overhead product into a dispropanized fuel gasproduct and a liquid feed to the debutanizer of low ethanecontent. The fractionator overhead product enters the stripper-absorber

section as both a liquid stream and a vapor stream. The various products from the stripper-absorber section are:

LPG, light naphtha, C3 & C4 gases and heavy naphtha. Important variables for spent catalyst stripper performance are

temperature, pressure, steam rate, steam and catalystdistribution, diameter and height of the stripper. The coke on the catalyst is drawn off in the regenerator mainly

depends on temperature, pressure O2 Conc., superficial airvelocity, residence time of the catalyst and air in the regenerator.

Unstabilized gasoline from the bottom of the primary absorberunit is sent to stripper where light components are removedand then it proceeds to debutanizer where C3 and C4 areremoved overhead as LPG. LPG is treated with amine by Merox Process to remove

sulphur compounds and then sent to LPG pool as a feedstockto propylene recovery unit. Propylene is recovered from cracked LPG which is a mixture

of propane, propylene , butane and butylene. First a mixture ofpropane and propylene is obtained from splitter, which isfurther fed to a splitter from where propylene is obtained as aseparate stream.

There has been a steady increase in Zeolite content of FCC catalystsfrom 10% in the 1960’s to over 35% today.

Some of today’s FCC catalysts contain up to 50% zeolite. The catalysts are the heart of the FCC process and they provide: low coke yield and effective carbon rejections high selectivity to derived products (light olefins and gasoline) enhancement of desired properties such as octane number in-situ control of emissions such as SOx.

ZSM-5 which is crystalline aluminosilicate substance has been used asan additive to increase octane number and light olefins yield.

Most of the Indian refineries are used to ZSM-5 catalyst instant ofamorphous silica-alumina catalyst , which has resulted in increase inLPG yield, increase in propylene content in LPG from 5.6(wt%) to15-19(wt%) in octane number and reduction in coke.

India’s first RFCC has been commissioned in the Panipat refinery with acapacity of 0.7 MPTA Licensed by Stone and Webster.

The unit is designed to process a blend of 85.7(wt%)hydrocracker bottomsand 14.3(wt%) vacuum residue as well as 100% hydrocracker bottoms.

FCC Gases as Petrochemical feedstock• FCC off gases are considerable importance as feed stock for petrochemicals.

• Some of the important building blocks, which can be derived from FCC are:dilute ethylene stream, LPG, Propylene, and C4 streams containing

butane/butylene.

Typical composition of C4 streams form FCC with availablequantities for 1 MPTA and 0.6 MPTA capacities.

The LPG as well off gases for the FCC unit are in olefins. Theformer contain up to 20-30% propylene while the latter couldhave 5-10% ethylene.

Components Boiling point(0C) Wt% range Avg. Wt%Isobutane -11.4 35-36 35.5Isobutene -6.9 15-17 161-Butene -6.3 10-14 11.5n-Butane 0.5 11-14 13Cis-Butene-2 3.7 9-16 9.5Trans-Butene-2 0.9 13-16 14.5

Processing of C4 stream from streamcracker and FCC

The processing of C4 streams after the recovery of butadieneform the stream cracker and from FCC. C4 cut from the steam cracker is first sent for butadiene

recovery which include selective hydrogenation of acetylenic inthe presence of palladium catalyst, then separation of butadieneby solvent extraction.in this process get the high yield ofbutadiene by using suitable solvent. solvent used for separation of butadiene are furfural, dimethyl

formamdie (DMF), n- Methyl pyrrolidone(NMP) and dimethylacetamide. After separation of butadiene the C4 streams from cracking

and FCC are processed for production of n-butene, 1-butene,2-butene and isobutene.

Isobutene recovery includes either hydration of the C4 streamand subsequent decomposition or etherification of methanolto yield MTBE, which is cracked to give isobutene. Separation of 1-butene is done by selective hydrogenation

followed by adsorption for separation of 1-butene and furtherprocessing for separation of isobutene and 2-butene bydistillation. Separation of 2-butene involves hydroisomerization and

subsequent distillation for separation of isobutene and 2-butene.

Separation of C4 hydrocarbons from FCC and SteamCracker plants

Separation of C4 hydrocarbons from FCC and SteamCracker plants

OXYGENATES FROM REFINERY C4 & C5 STREAM

The oxygenates from refinery streams are MTBE, TAME and ETBE. all oxygenated fuels reduce hydrocarbons in the automobile exhaust. MTBE is one of the most important oxygenates used in the production

of lead free gasoline. the oxygenated MTBE and ETBE are produced by the reaction of

methanol/ethanol and isobutylene. TAME are produced by etherification of isoamylenes. isobutylene and isoamylene can be removed from C4 and C5 Streams

of stream crackers. Till recently MTBE was a major additive in reformulated gasoline,

however due to recent concern over the potential water pollutionproblems caused by leaking underground gasoline storage tanks, moreUS state governments are adopting legislation to either phase outMTBE or restrict the MTBE usage as a gasoline additive.

METHYL TERTIARY BUTYL ETHER MTBA is an excellent front end octane supplier with no

compatibility problems with hydrocarbons. it is the most widely used octane enhancer in the current

gasoline pool. MTBE is one of the important oxygenate. MTBE increases the oxygen content of gasoline results in the

reduction of harmful emissions. MTBE which is made by etherification of C4 gases from

cracker and FCC is also used for production of polymer gradeisobutylene for synthetic rubber. The catalyst is a macro reticular ion exchange resin based on

sulphonate styrene divinyl bezene copolymer.

MTBE is produced by the reaction of methanol with isobutylenecontained in C4 streams from thermal crackers in the presence of ionexchange resin at 40-90oC and a pressure of 5 to 10 kg/cm2.

Convention process and catalytic distillation are the two commercialprocesses.

The acidic ion exchange resin catalyst used for MTBE production issusceptible to some impurities present in the feedstock which includebasic compounds, cations, nitrites, and surface compounds. thesepoisons neutralize the acid sites of the catalyst causing deactivation.

Acetonitrile is the most significant poison in FCC. These impurities areremoved by washing thoroughly with water.

After washing the feed is mixed with methanol and fed to thereactor. the inlet temperature and pressure of the reactor is controlled

and sufficient care to taken not to allow any increase in thetemperature of the reactor. presence of butadiene in the feedstock also reduces catalyst

activity. butadiene if present in high concentration in the feedstock can

result in isomerization of the butadiene inside the matrix of thecatalyst. MTBE produced by conventional technology using two fixed

bed reactors in which the first reactor is either a cycle or tubularreactor , which performs most of the isobutylene conversion.The finishing reactor which performs at low temperature.

MTBE from reaction mixture is separated in distillation column.

In the Catalytic distillation process, the fixed bed reactorprovides the bulk of conversion and the finishing reaction is doneby installing catalyst in the column in a special packing to providesimultaneous reaction and distillation. In this process, after the reaction, the equilibrium converted

reaction mixture is fed to the catalytic distillation reaction columnwhere the reaction is continued and the product MTBE isseparated from the unreacted C4s in the catalytic distillationcolumn. The C4 distillation stream from the catalytic distillation column is

fed to the methanol extraction column where water is used toseparate methanol and water extract containing methanol is sent tothe methanol recovery column for separation of methanol. The C4 stream is recovered from the top of the exact column.

MTBE by Catalytic Distillation Process

Tertiary amyl methyl ether TAME is another important oxygenate which is

produced by the reaction of methanol withisoamylenes present in the FCC gases and streamcracker C4 streams. TAME has slightly low octane number, it compares

favorably for vapor pressure, boiling point, densityand water miscibility. TAME is obtained when methanol reacts with the

isoamylenes. Isoamylenes are 2-methyl-1-butene, 2-methyl-2-

butene are reactive while 3-methyl-1-butene is non-reactive.

TAME

In the conventional two fixed bed reactor,etherification process is accomplished in two reactorsusing strong acid macro porous palladium loadedion exchange resins as a catalyst. the palladium resin selectively hydrogenates dienes

in the feed, ensuring a long etherification catalyst lifeand a water white clear product. further separation of TAME is accomplished in the

distillation column. methanol from the top product of distillation is

recovered by water extraction followed bydistillation.

TAME Manufacture by Conventional Fixed Bed Technology

Upgrading Of C5 Cuts For Recovery Of C5Chemicals

The C5 cut from stream cracker and FCC can be processed forrecovery of valuable C5 chemicals. Stream cracker C5 cuts contain unsaturated Hydrocarbons that can

be upgraded, particularly isoprene and pentadiene, as they arepresent in high concentration when naphtha feedstock is used. Typical C5 cuts from steam cracking contains:

C4 -- 1%; n-pentene -- 26%;isopentane -- 24%; n-pentenes-- 4.5%;methyl butenes –12%; cyclopentenes --1.5%;isoprene-13.5%; pentadiene(piperylene)-9%;cyclopentadiene-7.5%; and C6+ ---1%.

Dicyclopentadiene is formed of high boiling point and separated fromC5 stream by simple distillation.

Typical composition of C5 cuts from catalytic cracking:C4 -- 2%; n-pentene – 5.5%;isopentane -- 31.5%; n-pentenes– 22.5%;methyl butenes –37.5%; and C6+ ---1%.

The raw C5 is separated from pyrolysis gasoline by distillation. Cyclopentadiene is typically removed in two stages as the dimer

dicyclopentadiene. Tthe raw C5 Stream is heat isolated at a temperature >1200C causing

the cyclopentadiene to dimerize. The process conditions are chosen to ensure dicyclopentadiene is

produced with optimum selectivity. Dicyclopentadiene is then separated from the remaining by C5 stream

distillation. A high purity dicyclopentadiene concentrate of 93-94% can be made

this way.

Processing C5 streams: The cyclopentadiene depleted C5 stream contains traces of

cyclopentadiene, which is dimerized completely by using anotherdimerization and distillation. The C5 stream, which is now virtually completely free of

cyclopentadiene is fed to the extractive distillation column forisoprene recovery where dimethylformamide is used as a solvent. This yields an isoprene and pipeylene stream and a C5 raffinate

stream containing C5 olefins and paraffins. Light acetylenes from the isoprene- piperylene stream are

removed by distillation. The isoprene and piperylene are separated by distillation. The isoprene monomer with purity >99% can be produced. And

Piperylene is usually obtained as concentrate with 60-75% byweight.

Recovery of the C5 chemicals from C5 Stream involves dimerization ofcyclopentadiene, as well as extraction of di-olefins and acetyleniccompounds.

Raffinate from the extraction column contains pentanes, pentenes andDicyclopentadiene.

from the extraction column, the raffinate passes on to a distillationcolumn which contains the recovered light C4 components and 1,4-pentadiene.

The bottom portion from the distillation column goes to the strippingsection for recovery of the solvent, where as the top portion from thestripping section goes to the absorption column. Here piperylene andC5+ acetylenics are recovered from the bottom.

The extract containing these hydrocarbons go from the absorptioncolumn to two distillation columns for recovery of piperylene and C2+acetylenics compounds.

The absorption column top contains a purification section, comprisingtwo distillations in series for recovery of 2-butene and isoprene.

(1). Cyclopentadiene Isomerization (2). Extractor (3). Distillation of extract(4). Debutanizer (5). Stripper (6). Absorber (7). Solvent stripper(8) & (9). Execrative Distillation columns. Processing of C5 Stream