Catalytic Reforming (Part- 2) | Chemical Technology - Chemical Engineering PDF Download

Process Variables

Following variables affect the reformate yield and quality of the product . Favorable conditions for different reforming reactions is mention in Table M-VI 1.3.

• Reaction temperature
• Space velocity
• Reaction pressure
• H2/HC ratio
• Feedstock Characteristics

Table M-VI 6.3: Favorable Conditions for Different Reforming Reactions 

Feed Quality 

• Naphthenes dehydrogenate very fast and give rise to aromatics. Therefore, N + 2A is taken as index of reforming. Higher the N + 2A, better is quality to produce high aromatics.   N = Naphthenes %   A = Aromatics %
• Lighter fraction have a poor naphthene and aromatic content are, therefore, poor feed for reforming. Low IBP feed results in lower aromatics and H₂ yield.
• Heavy fractions have high naphthene and aromatic hydrocarbon content. Therefore, good reforming feed but tendency of coke formation is high.

Reaction Temperature 

Temperature is the most important operating parameter

• By simply raising or lowering reactor inlet temperature, operators can raise or lower the octane number of the product.
• Since all the reactor inlet temperatures are not necessarily identical, it is commonly accepted to consider the Weighted Average Inlet Temperature (WAIT) 

Space Velocity 

• Liquid hourly space velocity (LHSV)
• Weight hourly space velocity (WHSV) 

Reforming LHSV range = 1.0 to 3.0 l/hr

Below 1.0 LHSV, undesired side reactions namely hydrocracking occurs which reduce reformate yield .i.e., for every rise in LHSV of 0.1 between 1 to 2, about the 2oC rise in temperature is required. The lower the space velocity (i.e., higher contact time), the higher the severity assuming all other conditions unchanged. Lowering the space velocity has the same effects as increasing temperature, i.e. Increase the octane, decrease the product yield, decrease H₂ purity, Increase coke deposit

Reaction Pressure  

Reforming reaction pressure ranges (5 – 35 kg/sq. cm.). Decreasing pressure increases dehydrogenation of naphthenes and dehydrocyclisation of paraffins which favours an increase in production of aromatics and hydrogen (increase catalyst coking and shorter cycle life). Higher pressure causes higher rates of hydrocracking reducing reformate yield but decreases coking of catalyst resulting in longer cycle life. HYDROGEN TO

Hydrocarbon Ratio 

Hydrogen : Hydrocarbon Ratio = 

Main purpose of hydrogen recycle is to increase hydrogen partial pressure in the reaction.H2 reacts with coke precursors removing them from the catalyst reforming polycyclic aromatics. Higher the H₂/HC ratio, higher the cyclic length. Two main reasons for reducing H2:HC ratio

• Reduction in energy costs for compressing and circulating H₂.
• Favours naphthene dehydrogenations and dehydrocyclisation reaction

Lowering of H₂/HC Ratio, From 8 to 4 carbon increase in 1.75 times and from 4 to 2 carbon increase 3.6 times

Catalyst in Catalytic Reforming 

Monometallic: (Pt),  

Bimetallic: (Pt, Rhenium)

Acid Activity: Halogens/silica incorporated in alumina base.  

Metallic Function: It promote dehydrogenation and hydrogenation. It also contribute to   dehydrocyclisation and isomerisation.

 Acid Function: It promotes isomerisation, the initial step in hydrocracking, participate in   paraffin dehydrocyclisation.  

Stages in historical development of reforming catalyst in Indian scene

• Development of lows Pt monometallic catalyst IRC-1002 by IPCL for BT Production.
• Commercialization of IRC-1001 catalyst in the first reactor of IPCL’s three reactor system for Xylenes Production-1987.
• Scale up and manufacture of bimetallic catalyst IPR-2001 at IPCL’s catalyst division
• Commercialization of bimetallic catalyst at MRL for gasoline production 1990
• Commercialization of bimetallic catalyst IRC-1002 by IPCL for BT Production
• Commercialization of monometallic catalyst at IRC-1002 in BPCL Reformer for BT production -1990
• Development of improved versions of reforming catalysts:
  • High Rhenium Catalyst – Recipe ready for scale up. 
  • Multimetallic Catalyst – Recipe ready for commercial trial.
• Spheroidal Catalyst - CCR operations recipe in advanced stage
  • Catalyst used now a days is platinum on alumina base.
  • For lower pressure stability is increased by combining rhenium with platinum.
  • Pt serve as a catalytic site for hydrogenation and dehydrogenation reactions
  • Chlorinated alumina provides acid site for isomerization, cyclization & hydrocracking reactions.
  • Catalyst activity reduced by coke deposition and chlorine loss
  • As catalyst age’s activity of the catalyst decreases so temperature is increased as to maintain the desired severity.

 Advantages Of Bimetallic And Multimetallic Catalyst Over Monometallic Catalyst 

Enhanced Resistance to Coking

• Lower Fouling · Higher coke tolerance
• Longer cycle length for S-R units
• Low pressure and low H₂/HC ratio

Operation

• High Octane · High aromatics
• High yields of desirable products

Better yield stability

Lower temperature requirement

Better tolerance to high temperature

Better regenerability

High ultimate life

Catalyst Poisons 

Temporary Poisons: Temporary poisons are those impurities which can be removed during various pretreatment process like sulphur, nitrogen

 Permanent Poisons: Permanent Poisons are those impurities present in the feed which is irreversible damage to the catalyst Source and maximum level of catalyst poisons are given in Table M-VI 1.4.

Table M-VI 1.4: Source and Maximum Level of Catalyst Poisons