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.
Table M-VI 6.3: Favorable Conditions for Different Reforming Reactions
naphthenes to aromatics
Isomerisation of naphthenes
paraffins to aromatics
Temperature is the most important operating parameter
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
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
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
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
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
Advantages Of Bimetallic And Multimetallic Catalyst Over Monometallic Catalyst
Enhanced Resistance to Coking
Better yield stability
Lower temperature requirement
Better tolerance to high temperature
High ultimate life
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
MAX. LEVEL WT%
SR or Cracked Naphtha