Catalytic Reforming/Reforming

// 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

A catalytic reformer comprises a reactor and product-recovery section.

There are many different commercial processes including platforming, powerforming, ultraforming, and Thermofor catalytic reforming.

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

// Reformer in the Refinery

// 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)

• 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