Methanol-to-Hydrocarbons Product Distribution over SAPO-34 and ZSM-5 Catalysts: The applicability of Thermodynamic Equilibrium and Anderson-Schulz-Flory Distribution

The product distribution of methanol to hydrocarbons conversion over SAPO-34 and ZSM-5 catalysts was studied using thermodynamic equilibrium and Anderson-Schulz-Flory (ASF) distributions. The equilibrium compositions were calculated using constrained Gibbs free energy minimization. The effect of catalyst type was considered by setting upper limits to product carbon number due to shape selectivity according to zeotype catalyst channel size; that is, n£5 for SAPO-34 but n£6 for aliphatic and n£10 for aromatic compounds over H-ZSM-5 catalyst. The equilibrium selectivity of kinds of paraffin is negligible over SAPO-34 system while that of olefins is very small over H-ZSM-5, both in agreement with experimental results for methanol to olefins and to gasoline, respectively. The methanol to olefins hydrocarbon product distributions over SAPO-34 and H-ZSM-5 showed fair agreements with thermodynamic equilibrium and ASF distributions, respectively. It was found that propylene is the only product the selectivity of which can be maximized among hydrocarbon products over both SAPO-34 and ZSM-5 catalysts, and therefore, it can be an easier target molecule in methanol to hydrocarbon conversions.