Recovery of Chemicals from FCC And Steam Cracker (Part - 1) | Chemical Technology - Chemical Engineering PDF Download

Recovery of Chemicals from Fcc And Steam Cracker

With the rising demand of ethylene and propylene, there has been a tremendous growth in the steam cracking of hydrocarbons during the last four decades. Similarly, FCC (Fluid Catalytic Cracking) has developed into a major upgrading process in the petroleum refinery industry for the conversion of heavy fuel oil into more valuable products ranging from light olefins to naphtha and middle distillate. Large amounts of C₄ and C₅ compounds are produced along with the production of ethylene in steam cracking and gasoline in FCC. C₄ & C₅ streams are an important source of feedstock for synthetic rubber and many chemicals.

With increasing demand of C₅ hydrocarbons and oxygenates, upgrading of C₄ and C₅ streams from steam crackers and catalytic cracker is important to the economic performance of the above processes. It also provides a rich resource of reactive molecules, which forms the backbone of the synthetic rubber industry. The quantity and composition of the C4 and C5 stream depends on the severity of the steam cracker operation and feedstock processed.  Product profile C4 and C5 hydrocarbons are given in Figure M-VII 3.1 and Table M-VII 3.1. 

Figure M-VII 3.1: Product Profile of C4 and C5 Hydrocarbon 

Product Profile of C5 Hydrocarbon 

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

• Conventional FCC 4-7% propylene and 1-2 % Ethylene
• High Severity FCC:10% propylene
• Petro FCC^TM (UOP): Ethylene 6%, Propylene 20-22%, Higher aromatics (18%) in Naphtha
• Higher C4-8 olefins yield which can be cracked to yield lower olefins by Total Petrochemicals ATOFINA/UOP Olefin cracking Process
• Although FCC is an important petroleum refining process, however, FCC gases have now become important petrochemical feedstock for production of LPG that can be converted to aromatics and C3, C4, & C5 hydrocarbons, i.e. propylene, butene, isobutene, pentene, etc.

Product distribution from FCC depends

• Reactor temp
• Feed preheat temperature
• Catalyst activity
• Catalyst circulation rate
• Catalyst activity
• Recycle rate 

Table M-VII 3.2: Various Petroleum Products from FCC and their uses

Propylene Recovery from FCC: FCC gases has  important source of propylene from refinery and now  FCC units are being operated both in gasoline mode and propylene mode. Details of propylene from FCC are given in Lecture 5 Module 6. Propylene from FCC may be as high as 25% with new FCC based propylene technologies. increased production of olefins from FCC unitsc has been achieved through changes in operations,base cracking catalyst and additive catalysts . and in hardware designs 

Upgrading Of C₄ and C₅ Streams

C₄ and C₅ Streams fromSteam Cracker and FCC contains C4 and C5 hydrocarbons  recovery of which has become important steps for improving the overall economy of these processes. Some of the important C4 streams from Cracker and FCC butadiene(from cracker plant only) ,butene1, 2- butane, isobutylene, mixed n-butene, isobutene..C4 stream of steam cracker contains appreciable amount of butadiene which is being recovered from naphtha  cracker plants.  Typical composition of C4 stream of naphtha cracker and FCC is given Table M-VII 3.3. The distribution product will depend on thefeed stock,cracking severity and catalyst in case of FCC

Table M-VII 3.3: Typical Compositions of C4 Fractions 

• The production of chemical intermediates
• Butene-1, isobutylene, mixed n-butene
• Production of motor fuel component (alkylate, dimate, MTBE)

Processing of C4 cut from Steam Cracker and FCC

There is not much difference in the processing of C4 streams after the recovery of butadiene from the steam cracker and C4 streams from the FCC. C4 stream Butadiene f romC4 stream of naphtha cracker/ gas cracker is first recovered, followed by separation Isobutylene, isobutanee, butane, butane-1 and butene-2 from C4 stream/ FCC and cracker using various process like etherification, hydrolusis, cracking, adsorption distillation etc. plant by various  C4 cut from steam cracker and FCC is shown in Figure M-VII 3.2 . Isobutene recovery includes either hydration of the C4 stream and subsequent decomposition or etherification with methanol to 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 further processing for separation of isobutene and 2-butene by distillation. Separation of 2-butene involves hydroisomerisation and subsequent distillation for separation of isobutene and 2-butene. 

Figure M-VII 3.2: Separation of C4 hydrocarbons from FCC and Steam Cracker plants 

After separation of butadiene, the C4 streams from cracking and FCC is processed for production of n-butene, 1-butene, 2-butene, and isobutene. Process flow diagram for treatment of