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Chapter 5c -hydrocracking_i

petroleum refining

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Chapter 5c -hydrocracking_i

  1. 1. CHAPTER 5c HYDROCRACKING
  2. 2. CHAPTER 5c - OUTLINE HYDROCRACKING I. Principles II. Hydrocracking reaction III.Feed preparation IV.Process requirements V. Hydrocracking Catalyst
  3. 3. HISTORY • Hydrocracking is the conversion of higher boiling point petroleum fractions to gasoline and jet fuels in the presence of a catalyst. • Hydrocracking process was commercially developed in 1927 by I.G. Farben in Germany for conversion of lignite (rarely black coal) to gasoline. • Esso and Chevron applied this process later in USA. • Due to importance of this process, it has been heavily researched and modified in petroleum industry.
  4. 4. PRINCIPLES • Hydrogenation – oldest catalytic processes used in petroleum refining. • Why hydrocracking? WHY? demand of petroleum products By-product hydrogen at low cost Environmental concern • Demand shifted to high ratios of gasoline and jet fuel compared with the usages of diesel fuel and home heating oils. • By-product hydrogen at low cost and in large amounts has become available from catalytic reforming operations • Environmental concern limiting sulfur and aromatic compound concentrations in motor fuels have increased.
  5. 5. ADVANTAGES OF HYDROCRACKING • Hydrocracking is one of the most versatile process, which facilitate product balance with the market demand. Improved gasoline pool octane numbers
  6. 6. MODERN REFINERY • Catalytic cracking (FCC) & hydrocracking work as a team. • FCC takes more easily cracked paraffinic gas oils as charge stocks, while hydrocracker is capable of using aromatics and cycle oils and coker distillates as feed (these compounds resist FCC) • Cycle oils and aromatics formed in FCC make satisfactory feedstock for hydrocracking. • Middle distillate and even light crude oil can be used in hydrocracking.
  7. 7. FEEDSTOCK • Typical hydrocracker feedstock is shown below • LCGO = light coker gas oil • LCO = light cycle oil (produced in FCC, high in aromatics and sulfur) • HCGO = heavy coker gas oil
  8. 8. HYDROCRACKING PROCESSES • There are a number of hydrocracking processes available for licensing. • These processes are fixed bed catalytic processes, in which liquid is moving downward and gas is moving upward/downward. • The process employs either single stage or two stage hydrocracking. • The temperature and pressure may vary with the age of catalyst, desired products and the properties of feedstock.
  9. 9. HYDROCRACKING PROCESSES PROCESS COMPANY Unicracking UOP GOFining EXXON Research & Eng Ultracracking British Pet.Amoco Shell Shell Development Center BASF-IFB Badische Anilin, IFP Unibon UOP, LLC Isomax Chevron, UOP, LLC There are other processes such as LC-Fining, which are not based on fixed bed reactors. (expanded bed reactor with continuous on stream addition and withdrawal of catalyst)
  10. 10. HYDROCRACKING OBJECTIVE REMOVE FEED CONTAMINANTS NITROGEN SULFURMETALS CONVERT LOW VALUE GAS OILS TO VALUABLE PRODUCTS NAPHTHA MIDDLE DISTILLATES ULTRA CLEAN LUBE BASE STOCKS
  11. 11. PRIMARY PROCESS TECHNIQUE Hydrogenation in fixed hydrotreating catalyst bed to improve H/C ratios & remove feed contaminants Followed by one or more reactors with fixed hydrocracking catalyst beds to dealkylate aromatic rings, open naphthene rings & hydrocrack parafin chains
  12. 12. HYDROCRACKING BFD
  13. 13. HYDROCRACKING PROCESS FLOW Fresh feed is mixed with H2 and recycle gas (high in H2 content) and passed through a heater to the first reactor Feed that high in sulfur & nitrogen a guard reactor is employed to convert sulfur to H2S and N2 to NH3 ( to protect precious catalyst in the following reactor) HC reactors are operated at high temp to produce materials with boiling point below 400 F
  14. 14. HYDROCRACKING PROCESS FLOW Reactor gaseous effluent goes tru heat exchangers and a high pressure separator where the H2 rich gases are separated and recycled to the first stage. Liquid product from the reactor is sent to a distillation column where C4 and lighter gases are taken off and the jet fuel, naphta and diesel fuel streams are removed as liquid side streams Distillation bottom product is sent back to hydrocracker
  15. 15. REACTIONS • Hundreds of simultaneous chemical reactions occuring in hydrocracking Assumption – mechanism of hydrocracking is that of FCC with hydrogen superimposed In FCC, the C-C bond is broken Hydrogenation – H2 is added to C=C Cracking – endothermic reaction Hydrogenation – exothermic reaction
  16. 16. MAIN CHEMICAL REACTIONS CATALYTIC CRACKING of heavy hydrocarbons into lighter unsaturated hydrocarbons SATURATION of the newly formed hydrocarbons with hydrogen HYDRO CRACKING
  17. 17. HYDROCRACKING REACTIONS CRACKING & HYDROGENATION AS BELOW – the scission of a C-C followed by hydrogenation
  18. 18. HYDROCRACKING REACTIONS Aromatics which are difficult to process in FCCU are converted to useful products in Hydrocrackers
  19. 19. • Cracking provides olefins for hydrogenation and hydrogenation provides heat for cracking. • Overall reaction provides excess of heat as hydrogenation produces much larger heat than the heat required for cracking operation. • Therefore, the process is exothermic and quenching (rapid cooling) is achieved by injection cold hydrogen into the reactor and apply other means of heat transfer • Isomerization is another type of reaction, which occurs in hydrocracking. HYDROCRACKING REACTIONS
  20. 20. CATALYSTS • Hydrocracking catalyst are dual functional (having metallic and acidic sites) promoting cracking and hydrogenation. Cracking Hydrogenation – unsaturated hydrocarbons Hydrogenation of aromatic compounds Hydrogenolysis of naphthenic structure
  21. 21. CATALYST SITE FUCNTIONS Cracking is promoted by metallic sites of catalyst Acid sites transform the alkenes formed into ions Hydrogenation reactions also occurs on metallic sites Both metallic and acidic sites take part in the 4th reactions To minimize coke formation a proper balance must be achieved with the two sites on the catalyst, depends on the conditions of the operation
  22. 22. HYDROCRACKING CATALYSTS • Generally a crystalline silica alumina base. • Catalysts susceptible to sulfur poisoning if hydrogen sulfide is present in large quantities. • Catalysts not affected by ammonia. • Sometimes necessary to remove moisture to protect the catalyst. • Catalyst deactivate and coke does form even with hydrogen present. • Hydrocarbons require periodic regeneration of the fixed bed catalyst systems.

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