Effect of ketene additive and Si/Al ratio on the reaction of methanol over HZSM-5 catalysts

The influence of ketene as possible intermediate for the reaction of methanol to aromatics was investigated over HZSM-5 catalysts (Si/Al ratio of 15 and 9) using diketene-acetone (2,2,6-trimethyl-4H-1,3-dioxin-4-one) as ketene precursor under atmospheric pressure at 300 degrees C. The physicochemical properties of HZSM-5 catalysts were investigated by NH3-TPD, BET, XRD and ICP analysis. The distribution of products was measured by GC-Mass spectrometer. These catalysts exhibit high reactivity and selectivity for the conversion of methanol and/or ketene to hydrocarbons (mostly high octane number xylenes, trimethylbenzenes, tetramethylbenzenes and 1.5% benzene). The conversion of neat diketene-acetone over these catalysts produced aromatics compounds and significant amounts of oxygenated compounds (ketone, carboxylic acid, phenol, furan, pyran and others) depending on Si:Al ratio. These catalysts with high acid content produced small amount of saturated and unsaturated hydrocarbons without releasing significant amount of gas. The ketene and produced oxygenates from ketene appears to act as intermediates for the formation of aromatic compounds.