Effect of Platinum content of Catalyst
Platinum content of the catalyst is in range (0.3 –0.8 % wt).
At higher levels there is some tendency to effect dimethylation and naphthene ring opening, which is undesirable, while at lower levels the catalyst tends to be less resistance to poisons.
The high platinum catalysts (0.6 – 0.8 % wt pt) are used for sever operations such as the production of 100 octane number gasoline from feeds with only moderate naphthene contents.
The latest development is the use of bimetallic catalyst which incorporated other metals (Rhenium and Tin) in addition to platinum this catalyst can operate at lower hydrogen partial pressure than can the normal platinum catalyst without deactivation.
Reactions Mechanisms
The platinum on chlorinated alumina catalyst has two functions:
- A hydrogenating-dehydrogenating function provided by the platinum. (Pt active sites)
- An acid function provided by the alumina. (acid active sites)
Reactions Mechanisms
Reactions Mechanisms
Dehydrogenation of Naphthenes
Main Reaction in producing Aromatics
Very Rapid, goes to Completion,& Highly Endothermic
Favored by High Temperatures & Low Pressures
Naphthenes is the most desirable component for the production of H2 & the Speed of Reaction
Isomerization
Isomerization of Alkylcyclopentane to Alkylcyclohexane before converting to Aromatics
Possible Paraffin Formation, for ring rearrangement
Thermodynamic Equilibrium favors isomer formation, which increases the ON
Dehyrocyclization of Paraffins
The most difficult Reaction to promote
Consists of molecular rearrangement of P to N
High M.wt Paraffins are easier to Cyclize & Crack
Favored by Low Pressures & High Temperatures
Hydrocracking of Paraffins
Not Desirable as it consumes hydrogen and reduces liquid product
Favored by High Temperatures & High Pressures
Concentrates Aromatics and increases ON
Dealkylation of Aromatics
Shortening of the Alkyl Group
Removal of the Alkyl Group
Favored by High Temperature & High Pressures
Long side chains lead to similarity to paraffin cracking
Reactions Mechanisms
Hydrogen Action
Effects on Product & Yield
Effects on Reaction Kinetics
Effects on Coking
Sulfur Action
Reactions Mechanisms
Hydrogen Action
Effects On Product & Yield
Low H2 increases olefinic content in the reformate
(1%) Olefinic Content for (5 bar) H2 Pressure
Effects on Reaction Kinetics and Coking
Next figures will show this effect better
Reactions Mechanisms
Hydrogen Action
Reactions Mechanisms
Hydrogen Action
Reactions Mechanisms
Hydrogen Action
Reactions Mechanisms
Sulfur Action: Sulfur influences the performance of mono and bimetallic reforming catalyst. In such cases:
(Pt-Re/Al2O3), it was found that sulfur on Rhenium restricts the formation of graphitic coke, thus improving the stability of the catalyst.
(Pt-Ir /Al2O3), the high activity resulting from the addition of Iridium allows some degree of sulfur in the feed.
An increase in sulfur conc. has 2 principles effects:
1. Initial inhibition of aromatics formation.
2. Declined the accelerated catalyst activity.
The sulfur acts to enhance the acidity and inhibit the dehydrogenation activity of catalyst.