Conversion of biomass-derived alcohols to aromatics over modified HZSM-5 catalysts

Abstract

The conversion of biomass-derived alcohols (methanol, ethanol, n-propanol and n-butanol) to hydrocarbons over modified HZSM-5 (30) at 450 ℃ and atmospheric pressure under nitrogen flow using a fixed bed flow reactor was studied. The effects of alkali treatment and silylation via chemical liquid deposition (CLD) were focused. Fresh and spent catalysts were characterized by several techniques including BET, TPD, TPR, TPO, XRD and XRF. With the catalytic activity over parent HZSM-5 (30) at WHSV of 3.33 h-1, all feed stocks were completely converted to hydrocarbons. Toluene and xylenes were formed as the main products. Methanol, ethanol, n-propanol, and n-butanol produced aromatics selectivity of 56, 59, 62, and 64%, respectively and larger alcohols were found to give higher yields of aromatics. Alkali treatment caused mesopores in the HZSM-5 zeolite, which gave higher aromatic yield compared to the parent HZSM-5. However, excessively high NaOH concentration could induce the collapse of the zeolite framework. The p-xylene selectivity in xylene was enhanced with increasing TEOS. The silylated HZSM-5 catalyst prepared by two-cycles of TEOS deposition exhibited higher p-xylene selectivity but lower aromatic yield compared to the single deposition step. The production of aromatics from alcohols mainly comes from dehydration, oligomerization and aromatization.