Catalytic reforming and Isomerization Flashcards
What is catalytic reforming used for?
Catalytic reforming is used in the refining industry to produce gasoline blending components with a high octane number.
What are the primary feed components for catalytic reforming?
Paraffins, naphthenes, and aromatics.
What are the key reactions in catalytic reforming?
- Dehydrogenation of naphthenes to aromatics.
- Isomerisation of paraffins and naphthenes.
- Dehydrocyclisation of paraffins to aromatics.
- Hydrocracking and dealkylation.
What factors affect reforming catalyst performance?
Contaminants like sulfur, nitrogen, water, and metals such as arsenic, copper, and lead poison the catalyst.
What advantages do bimetallic catalysts provide in catalytic reforming?
Longer catalyst lives.
Operation at lower hydrogen partial pressures for higher reformate yields.
Lower recycle gas rates, saving energy.
Combination of the above.
What is Continuous Catalyst Regeneration (CCR)?
A mechanical concept allowing continuous catalyst regeneration, maintaining high activity under severe reforming conditions.
What happens to paraffins during dehydrocyclisation?
Paraffins cyclize to naphthenes, which are subsequently dehydrogenated to aromatics.
What dual functions must reforming catalysts have?
- Metal function (Pt): Promotes dehydrogenation, hydrogenation, hydrocracking, and rapid hydrogenation of coke precursors.
- Acid function (Cl): Promotes isomerisation, initial hydrocracking, and paraffin dehydrocyclisation.
What are common catalyst poisons, and why are they problematic?
- Sulfur: Forms H₂S, affecting hydrogenation.
- Nitrogen: Forms NH₃, neutralizing acid sites.
- Metals like As, Cu, Pb: Poison catalysts even at trace levels.
- Water: Strips halogens off catalysts.
What is the purpose of isomerisation in refining?
To convert straight-chain alkanes into branched isomers with higher octane numbers.
Which catalysts are used for paraffin isomerisation?
Initially, aluminium chloride with HCl, and later, platinum-based catalysts.
What is the significance of thermodynamic equilibria in isomerisation?
Lower reaction temperatures favor the formation of highly branched isomers
What is the main reaction type in isomerisation?
Reversible first-order reactions limited by thermodynamic equilibria.
Why is feedstock preparation critical for isomerisation processes?
Contaminants like sulfur, water, and benzene deactivate the catalyst and must be minimized.
What are the limitations of aluminium chloride catalysts in isomerisation?
- Sublimation at reaction temperatures.
- Solubility in liquid phase causes reactor plugging and system failure.
