Catalytic Cracking: Fluid Catalytic Cracking And Hydrocracking (Part - 1) Chemical Engineering Notes | EduRev

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Chemical Engineering : Catalytic Cracking: Fluid Catalytic Cracking And Hydrocracking (Part - 1) Chemical Engineering Notes | EduRev

The document Catalytic Cracking: Fluid Catalytic Cracking And Hydrocracking (Part - 1) Chemical Engineering Notes | EduRev is a part of the Chemical Engineering Course Chemical Technology.
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Catalytic Cracking

Catalytic cracking process was developed in1920 by Eugene Houdry for upgradation of residue was commercialized latter in 1930. Houdry process was based on cyclic fixed bed configuration. There has been continuous upgradation in catalytic in catalytic cracking process from its incept of fixed bed technology to latter fluidized bed catalytic cracking (FCC).The feed stock for catalytic cracking is normally light gas oil from vacuum distillation column. Catalytic cracking cracks low value high molecular weight hydrocarbons to more value added products (low molecular weight) like gasoline, LPG Diesel along with very important petrochemical feedstock like propylene, C4 gases like isobutylene, Isobutane, butane and butane. Main Catalytic Cracking Reaction is given in Table M-VI 5.1. 

Main reactions involved in catalytic cracking are

  • Cracking
  • Isomerisation
  • Dehydrogenenation  
  • Hydrogen transfer
  • Cyclization  
  • Condensation
  • Alkylation and dealkylation Major primary reactions taking place in catalytic cracking is given in Table  

 Paraffins               →           Smaller paraffins   + olefins  

Alkyl naphthene    →           naphthene +    olefin

Alkyl aromatic       →           aromatic +    olefin 

Multiring naphthene    →     alkylated naphthene with fewer rings


Table M-VI 5.1 Main Catalytic Cracking Reaction  


Cracking -------- ► Paraffins + Olefins


Cracking -------- ► LPG Olefins

Cyclization ------- ► Naphthenes


Isomerization —►Branched Olefins —► H Transfer —► Branched Paraffins

H Transfer ------ ► Paraffins

Cyclization------- ► Coke

Condensation------- ► Coke

Dehydrogenation ------ ► Coke


Cracking -------- ► Olefins

Dehydrogenation —► Cyclo- Olefins —► Dehydrogenation —► Aromatics

Isomerization ------- ► Naphthenes with different rings


Side chain cracking ------- ► Unsubstituted aromatics + Olefins

Trans alkylation------- ► Different alkyl aromatics


Dehydrogenation —► Polyaromatics —► Dehydrogenation —► Coke


Hydrogen Transfer------- ►Naphthene + Olefin------- ►Aromatic + Paraffin

Fluid Catalytic Cracking  
Fluid catalytic cracking is now major secondary conversion process in Petroleum refinery since 1942. there are more than 400 FCC units in world. The process provides around 50 percent of all transportation fuel and 35 percent of total gasoline pool. Major land marks in the history of FCC has been: 
  • Introduction of zeolite catalyst during 1960 which has resulted in lower residence time
  • Introduction of ultra stable Y-zeolite in mid 60’s
  • Switch over from bed cracking to riser cracking
  • Introduction of large number of additives for boosting of gasoline octane/yield of light naphtha
  • SOx control
  • Nickel and vanadium passivation FCC is a multi-component catalyst system with circulating fluid bed reactor system with reactor Regenerator system configuration. Figure M-VI 5.1 shows details of FCC process and FCC reactor. 

Catalytic Cracking: Fluid Catalytic Cracking And Hydrocracking (Part - 1) Chemical Engineering Notes | EduRev

Catalytic Cracking: Fluid Catalytic Cracking And Hydrocracking (Part - 1) Chemical Engineering Notes | EduRev

Figure M-VI 5.1: Fluid Catalytic Cracking Process and FCC Reactor

Feed Stock 

Vacuum gas oil (VGO), Hydro-treated VGO, Hydro-cracker bottom, Coker gas oil (CGO), Deasphalted oil (DAO), Reduced crude oil (RCO), Vacuum residue (VR)

  • Typical feedstock consists of Vacuum and Atmosphere gas oil but may include other heavy stream.
  • Major contaminant in the feed includes carbon residue and metals.
  • While FCC process feed containing up to 4% Conradson carbon MSCC can process all kinds of feed.

Process Steps

Three basic functions in the catalytic cracking process are:

Reaction - Feedstock reacts with catalyst and cracks into different hydrocarbons;  

Regeneration - Catalyst is reactivated by burning off coke; and recerculated to reactor

Fractionation - Cracked hydrocarbon stream is separated into various products like LPG and gasoline, like light cycle oil and heavy cycle oil are withdrawn as side stream

Reactor and Regenerator Section: Catalyst section consists mainly of the reactor and regenerator

  • The feed to unit along with recycle streams is preheated to temperature of 365oC-370Oc and enters the riser where it comes in contact with hot regenerated catalyst ( at a temperature of about 640-660oC. Finely divided catalyst is maintained in an aerated or fluidized state by the oil vapors.
  • The catalyst section contains the reactor and regenerator & catalyst re circulates between the two.
  • Spent catalyst is regenerated to get rid of coke that collects on the catalyst during the process. Spent catalyst flows through the catalyst stripper to the regenerator, where most of the coke deposits burn off at the bottom where preheated air and spent catalyst are mixed. Fresh catalyst is added and worn-out catalyst removed to optimize the cracking process

 Fractionation - Cracked hydrocarbon stream is separated into various products. LPG and gasile are removed overhead as vpour. Unconverted product like light cycle oil and heavy cycle oil are withdrawn as side stream. Overhead product is sent to stabilsation section where stablised gasoline is separated from light products from which LPG is recovered. 

Typical operating parameter of FCC

Raw oil feed at heater inlet    :      114 cubic meter /h

Furnace outlet temperature    :    291oC

Reactor feed temperature      :    371oC

Reactor Vapour temperature  :   549oC

Product Obtained 

  • Light gas -H2, C1, and C2s
  • LPG C3s and C4s – includes light olefins
  • Gasoline C5+ high octane component for gasoline pool or light fuel
  • Light cycle oil (LCO) blend component for diesel pool or light fuel
  • Heavy cycle oil (HCO) Optional heavy cycle oil product for fuel oil or cutter stock  
  • Clarified oil (CLO) or decant oil: slurry for fuel oil
  • Coke by-product consumed in the regenerator to provide the reactor heat demand 

FCC Catalysts 

Major breakthrough in the catalytic racking process was development zeolite catalysts which demonstrated vastly superior activity, gasoline selectivity, and stability characteristics compared to original amorphous silica alumina catalyst . 

Year                           1950        1970         1990

Zeolite content, wt%    0             10 Up to 40

Particle density, g/cc    0.9           1             1.4

Relative Attrition Index  20           5              1 

Today’s FCC catalysts Porous spray dried micro-spherical powder  

  • Particle size distribution of 20 -120 micron & particle density ~ 1400 kg/m3 
  • Comprising Y zeolite in many derivatives of varying properties
  • Supplied under various grades of particle sizes & attrition resistance  
  • Continuing improvement metal tolerance, coke selectivity New bread of catalyst are high metal tolerance with high matrix catalyst having better accessibility, regenerability and strippability .

Options for Clean Fuel: 

For upgrading FCC products into acceptable blending components following three steps are being used ;

  • Severe hydro processing of feed to FCC
  • Treating each of the products in hydrotreater
  • Combination of both upstream and downstream processing 

Modified Catalytic Cracking Processes 

Resid FCC (RFCC) Process: The RFCC process uses similar reactor technology as the FCC process and is targeted for residual feeds greater than 4 wt-% Conradson carbon. A two stage regenerator with catalyst cooling is typically used to control the higher coke production and resulting heat.

Deep Catalytic Cracking (DCC):

Milli Second Catalytic cracking (MSCC) Process: Improvements in riser termination devices have led to significant decreases in post-riser residence time and post-riser cracking. The benefits of shorter catalyst-and oil contact time have been lower dry gas yields, lower delta coke on catalyst and more selective cracking to gasoline and light olefins.

  • Due to improvement in reactor design there is lower regenerator temperature and higher catalyst recovery. 

Petro FCC Process

 The Petro FCC process targets the production of petrochemical feedstock rather than fuel products. This new process, which utilizes a uniquely designed FCC unit, can produce very high yields of light olefins and aromatics when coupled with aromatics complex. The catalyst section of the Petro FCC process uses a high-conversion, short-contact time reaction zone that operates at elevated reactor riser outlet temperatures

Indmax Technology- Residue to Olefin was developed by IOC R&D center and has been successfully commissioned in IOC Guwahati Unit .

Some of the special features of the technology are:

Operational features of Indmax technology

  • Very high cat/oil ratio(15-25)
  • Higher riser temperature (>5500 C)  
  • Higher riser steam rate
  • Relatively lower regeneration temperature.


  • LPG 35-65 wt%
  • Propylene 17-25 wt% feed
  • High octane gasoline (95+)  

Multifunctional proprietary catalyst

  • Higher propylene selectivity
  • Superior metal tolerance
  • Lower coke mate 
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