CHAPTER 5c

HYDROCRACKING

CHAPTER 5c - OUTLINE

HYDROCRACKINGI. PrinciplesII. Hydrocracking reactionIII. Feed preparationIV. Process requirementsV. Hydrocracking Catalyst

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.

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.

ADVANTAGES OF HYDROCRACKING• Hydrocracking is one of the most versatile process,

which facilitate product balance with the market demand.

Improved gasoline pool octane numbers

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.

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

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.

HYDROCRACKING PROCESSESPROCESS COMPANYUnicracking 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)

HYDROCRACKING OBJECTIVE

REMOVE FEED CONTAMINANTS

NITROGEN

SULFURMETALS

CONVERT LOW VALUE GAS OILS TO VALUABLE PRODUCTS

NAPHTHA

MIDDLE DISTILLATES

ULTRA CLEAN LUBE

BASE STOCKS

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

HYDROCRACKING BFD

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

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

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

MAIN CHEMICAL REACTIONS

CATALYTIC CRACKINGof heavy

hydrocarbons into lighter

unsaturated hydrocarbons

SATURATION of the newly

formed hydrocarbons

with hydrogen

HYDROCRACKING

HYDROCRACKING REACTIONS

CRACKING & HYDROGENATION AS BELOW – the scission of a C-C followed by hydrogenation

HYDROCRACKING REACTIONS

Aromatics which are difficult to process in FCCU are converted to useful products in Hydrocrackers

• 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

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

CATALYST SITE FUCNTIONSCracking 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

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.