Lesson 1, Topic 4
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Catalytic Processes

Abdulaziz July 6, 2020
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// Catalytic Reforming/Reforming

Catalytic reforming is the process of converting heavy naphtha (with low octane) to aromatics and iso paraffins (with high octane) in the presence of a catalyst in the reforming reactors

  • Feed
    • Hydrotreated heavy naphtha (C7 to C10)
  • Product
    • Reformate
  • Byproducts
    • Light ends (C3)
    • Hydrogen

// Reformer in the Refinery

Courtesy from The American Petroleum Institute

// Reforming

  • Reforming unit is one of the critical units in a refinery
    • Produces more than 35 wt% of the total gasoline pool
    • Hydrogen is a by product in the reforming reaction (desired by product)
Fig. 8
Kaiser, M.J. A review of refinery complexity applications. Pet. Sci. 14, 167–194 (2017). (optional reading)
  • Research Octane Number (RON) order is
    • Paraffins < Iso paraffins < Naphthenes < Aromatics
  • RON is improved by reforming the hydrocarbon molecules in the
    presence of catalyst through chemical reactions
  • Reforming reactions
    • Breaks some of the molecules into smaller molecules
    • Transforms low octane heavy naphtha into high octane reformate

// Reforming Feed Characterization

  • Hydrotreated to remove the contaminants (catalyst poisoning)
  • Feed is characterized by
    • Watson characterization factor (Kw)
      • Naphthenes (N) vol% and Aromatics (A) vol%
  • Naphthenic feed gives a higher yield than paraffinic feed
  • C5 to C6 (light naphtha) should not be present
    • May crack and produce gases
    • If C6 is present in the feed, benzene would be formed (undesirable)
  • Heavier fractions tend to coke

// Reforming Reaction Chemistry

  • Desired reactions
    • Dehydrogenation of naphthene to aromatics
    • Dehydrocyclization
      • Dehydrogenation of n paraffin to form naphthene
      • Naphthene rearranges to form aromatics
    • Isomerisation of n paraffins to iso paraffins
  • Undesired reaction
    • Hydrocracking of paraffins to lower molecular weight
  • Dehydrogenation and dehydrocyclization are endothermic reactions

// Reforming Process Steps

  • Hydrotreating
    • Removes the catalyst poisons (e.g. sulfur, nitrogen)
    • H2S, Ammonia form as byproducts
  • Preheating
    • Feed pre heated in a furnace to about 340 °C
  • Reaction
    • Multiple reactors with the furnaces in between (endothermic)
    • Pressure is between 5 and 35 barg
  • Stripping
    • Removes the light material from the reformate
    • Multiple stripper towers based on the product needs

// Catalysts

  • Catalyst is alumina base
    • Bi metallic (Pt)
    • Acid (Halogens/silica)
  • Catalyst performance decreases over time
    • Coke deposition
    • Contamination of the active sites
    • Catalyst poisoning

// Critical Process Variables

  • Feed quality
  • Reaction temperature about 340 °C
    • High temperature favours the desired reaction
    • Temperature is linear to octane number
  • Space Velocity – LHSV between 1.0 and 3.0 per hour
    • LHSV = Vol. of reactor charge / Vol. of catalyst
    • Below 1.0, cracking occurs and higher octane yield
  • Reaction pressure is between 5 and 35 barg
    • Low pressure favors the desired reaction but increases catalyst coking
    • High pressure causes higher rate of cracking; also reduces reformate yield
  • H2/Hydrocarbon ratio
    • Hydrogen is required to maintain the partial pressure to prevent the coking; H2 reacts with coke precursors and removes them from the catalyst
    • Lower ratio favors the desired reaction and lower energy (compression and H2 cost)
    • Higher ratio extends the cycle length

// Catalyst Regeneration

  • Temporary catalyst poisons are those impurities which can be removed
    during various pretreatment process like sulphur, nitrogen
  • Permanent catalyst poisons are those impurities present in the feed which may cause irreversible damage to the catalyst (e.g. metals such as nickel, chromium)
  • Catalyst performance decreases over time due to
    • Deactivation
    • Coke formation
    • Contamination on active sites
    • Catalyst poisoning
  • Catalyst regeneration needs to be carried out to regain catalyst activity
    • The time between two regenerations is called a cycle
    • The catalyst retains its usefulness over multiple regenerations
  • Catalyst activity could be restored if deactivation occurred because of
    coke formation or temporary poisons

// Reactor Types

  • Fixed bed reactor
    • Individual reactors are taken offline by a special valving and manifold
    • Regenerated while the other reformer unit continues to operate
  • Semi regenerative fixed bed
    • Unit shuts down for the catalyst regeneration
  • Continuous Catalytic Reformer (CCR)
    • Fluidised bed, catalyst regenerated on the run and continuously used in the reactor
    • The catalyst in the CCR is in a moving bed and regenerated frequently
      • This allows a low low-pressure operation

// Reforming Summary

  • Reformate gasoline component
  • Catalyst regeneration
  • Hydrogen production