Catalytic_Hydrocracking

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					Catalytic Hydrocracking


   Mohammed Ba-Shammakh
                  Outline
 Introduction
 Hydrocracking Chemistry
 Hydrogen consumption
 Hydrocracking process
 Conclusion
               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)
     Hydrocracking process




                      Straight chain


Cracking + Hydrogen
     Catalyst
               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
                 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
      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)
       Hydrocracking Chemistry


   Cracking reactions
    » Saturated paraffins cracked to form lower
    molecular
      weight olefins & paraffins
    » Side chains cracked off small ring aromatics &
      cycloparaffins (naphthenes)
        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
     Hydrocracking Chemistry

 Isomerization   Reactions

 Isomerizationprovides branching of alkyl
 groups of paraffins and opening of
 naphthenic rings
       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
         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
      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
         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
         Catalyst Deactivation &
              Regeneration

   Catalysts deactivate & coke does form even with
    hydrogen present
     » Hydrocrackers require periodic regeneration
    of the fixed bed catalyst systems
     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 650°F to 750°F as a descriptor of mild
   operations & 750°F to 850°F for severe operations
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%
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
     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
              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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posted:12/9/2011
language:English
pages:23