Catalytic Hydrocracking Mohammed Ba-Shammakh Outline

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Catalytic Hydrocracking

• Mohammed Ba-Shammakh

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Outline

• Introduction
• Hydrocracking Chemistry
• Hydrogen consumption
• Hydrocracking process
• Conclusion

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Introduction

• A process similar to catalytic cracking in its
  industrial purpose but effected under hydrogen
  pressure and on a catalyst
• Purpose process gas oil to break carbon-carbon
  bonds of large aromatic compounds
• Hydrogenation (addition of hydrogen)
• Cracking (aromatic bonds)

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Hydrocracking process
Straight chain
Cracking Hydrogen Catalyst
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Introduction

• Hydrocracking does a better job of processing
  aromatic rings without coking than catalytic
  cracking
• Hydrogen used to hydrogenate aromatics
• Hydrocracking not as attractive as delayed coking
  for resids high in resins, asphaltenes poison
  hydroprocessing catalysts
• Feeds require large amounts of hydrogen

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Hydrocracker Feeds

• Typical feeds
• Cat cracker cycle oil
• ?? Highly aromatic with sulfur, small
  ring, catalyst fines
• Hydrocracked to form high yields
  of jet fuel, kerosene, diesel,
• Gas oil from visbreaker
• ?? Aromatic
• Gas oil from the delayed coker
• ?? Aromatic, olefinic, with sulfur
• Usually more economical to route atmospheric
• vacuum gas oils to the cat cracker to produce
• primarily gasoline some diesel

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Hydrocracker Products

• Products
• Hydrocracking primarily to make distillates
• Intent is to minimize the production of heavy
  fuel oil
• Light ends are approximately 5 of the feed.
• Middle distillates (kerosene, jet fuel,
  diesel)

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Hydrocracking Chemistry

• Cracking reactions
• Saturated paraffins cracked to form lower
  molecular
• weight olefins paraffins
• Side chains cracked off small ring
  aromatics
• cycloparaffins (naphthenes)

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Hydrocracking Chemistry

• Hydrogenation reactions
• Exothermic giving heat
• Hydrogen inserted to saturate newly formed
  molecule
• from aromatic cracking
• Olefins are saturated to form light
  hydrocarbons,
• especially butane
• Aromatic rings hydrogenated to
  cycloparaffins
• (naphthenes)
• Carbon-carbon bonds cleaved to open
  aromatic
• cycloparaffins (naphthenes) rings

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Hydrocracking Chemistry

• Isomerization Reactions
• Isomerization provides branching of alkyl groups
  of paraffins and opening of naphthenic rings

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Hydrogen Consumption

• Carbon bonds broken saturated
• Creates light ends
• Heavier distillates make more light ends from
• breaking more complex molecules
• Sulfur converted to hydrogen sulfide
• Nitrogen converted to ammonia
• Oxygen converted to water
• Organic chlorides converted to hydrogen
  chloride

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Hydrogen Consumption

• Saturation of carbon-carbon bonds
• Olefins saturated to form light
  hydrocarbons.
• Consumption stoichiometric one
  hydrogen
• molecule added for each double bond
• Aromatic rings hydrogenated to
  cycloparaffins
• (naphthenes).
• Severe operation hydrogen
  consumption strong
• function of complexity of the
  aromatics
• Metals deposited directly on the catalysts
• Excess metals reduce catalyst activity
  promote
• dehydrogenation

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Hydrogen Consumption

• Have cracking of carbon-carbon bonds
• Severe operation hydrogen consumption strong
  function of complexity of the aromatics
• Hydrogen lost in mixture with products
• Absorbed in liquid products
• Usually small compared to hydrogen
  used for sulfur removal
• Lost with purge gas

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Hydrocracking Catalysts

• 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

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Catalyst Deactivation Regeneration

• Catalysts deactivate coke does form even with
• hydrogen present
• Hydrocrackers require periodic
  regeneration of the fixed bed catalyst systems

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Effect of Process Variables on Hydrocracking

• Severity
• Mild operation for diesel or fuel oil from
  heavy gas oil
• Severe operation for kerosene or naphtha
  from a light
• gas oil
• Temperature
• Temperature not used to increase severity
• Temperature adjusted to offset decline in
  catalyst
• activity
• Consider 650F to 750F as a descriptor of
  mild
• operations 750F to 850F for severe
  operations

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Effect of Process Variables on Hydrocracking

• Pressure Hydrogen Consumption
• Lower operating pressure 1,200 psig
  hydrogen
• consumption 1,000 - 2,000 scf/bbl
• More severe operations to destroy heavier
  components
• open rings 2,000 psig 2,000 to 3,000
  scf/bbl or more
• These hydrogen consumptions primarily for the
• hydrocracking reactions with low sulfur
  removal
• olefin/aromatic saturation
• Mild or severe hydrocracking with
  extensive desulfurization or
  olefin/aromatic saturation willincrease hydrogen
  consumption, possibly by 25

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Hydrocracking Process Description

• Single stage or two stage processes
• Severity of the operation
• Products desired
• Nature of the feedstock
• feed pretreating for contaminant removal
• Two extremes
• Mild one stage hydrocracking system
• Severe two stage operation

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Two stage hydrocracking

• May use separate reactors with desulfurization
• olefin saturation in 1st reactor
  hydrocracking in 2nd reactor
• 1st reactor removes contaminants
  saturates aromatics
• Can also do part of the hydrogenation
  conversion
• Effluent from 1st reactor sent to fractionator
• fractionator bottoms sent to the 2nd stage
• hydrocracking reactor

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Conclusion

• The process involves two reactions
• (cracking hydrogenation)
• It consumes a lot of hydrogen to saturate
  aromatic
• Produce products in Kerosene range (larger) than
  gasoline.

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Thank you