Para-Xylene Maximization. Part VIII: Promotion of H-ZSM-5 Zeolite by Pt and HF Doping for Use as Catalysts in Toluene Alkylation with Methanol

Toluene was alkylated with methanol in a flow type reactor at temperatures between 300 and 500 °C using H-ZSM-5 zeolite, 0.2%Pt/H-ZSM-5 and hydrofluorinated 0.2%Pt/H-ZSM-5 with HF concentrations of 1.0%, 2.0%, 3.0%, or 4.0%. Pt primarily enhances toluene conversion, total xylenes production, and p-xylene relative to its thermodynamic equilibrium. As the concentration of HF increases from 1.0% to 3.0%, the catalyst activity increases because of the increase in the number of acid sites and their strength. Additionally, the surface area and Pt dispersion also increases. An advantage of increased HF doping is that the formation of voluminous trimethylbenzene (TMB) byproducts is inhibited. However, at a HF concentration of 4.0%, Al and Si are partially leached and then deposited mostly in the wider catalytic pores. This was determined by evaluating the pore volume distribution and we determined that reactivity inhibition was obviously present and was due to diffusion restriction.

Toluene was alkylated with methanol using catalysts containing Pt/HZSM-5 zeolite doped with 1%, 2%, 3%, or 4% HF. The highest HF doping caused debris deposition in the wider pores of HZSM-5 whereas 1%-3% HF enhanced the activity, p-xylene selectivity, and p-xylene relative to the thermodynamic equilibrium, and Pt dispersion was high in these catalysts.Figure optionsDownload as PowerPoint slide