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

Abstract

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 °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.

Mechanism study of the conversion of esters to high‐octane‐number aromatics over HZSM‐5

“…The samples (liquid products) were analysed using an offline GC to give the following results: xylenes and trimethylbenzenes as major components and small quantities of benzene, toluene, tetramethylbenzenes, ethyldimethylbenzenes, naphthalene derivatives, indane derivatives, olefins and paraffinic compounds. The kinds of light alkanes and alkenes for MTH over this catalyst were reported in previous work . The high alumina content of this catalyst prevents the formation of considerable amounts of light olefins and paraffins under our experimental conditions.…”

“…The selectivity and reactivity of the catalyst before and after the reaction of methanol and ketene were not changed in considerable amount over HZSM‐5 (Si/Al: 9) at 400°C. The fused ring aromatics (42.6%) had no effect on the zeolite network upon activation . As a result, HZSM‐5 (Si/Al: 9) is suitable for reactions that produce a high percentage of heavy compounds such as conversion of esters and ketones to hydrocarbons.…”

“…AA was decomposed to water ( 12 ) and ketene ( 13 ). Dabbagh and co‐workers proposed that ketene converts to a mixture of oxygenates and aromatic hydrocarbons over HZSM‐5 depending on the temperature and contact time . Also, 6 was converted to ethyl propionate ( 7 ) and methyl butyrate ( 8 ) through oxygen‐to‐carbon rearrangement to provide chain‐extended esters.…”

“…This conversion produced considerable amounts of carboxylic acids, ketones, phenol derivatives, pyran and furan as main oxygenates and was without a significant amount of gas. Also, a wide range of aromatics with high octane number (including xylenes, trimethylbenzenes, tetramethylbenzenes and other alkylbenzenes) were produced during the reaction …”

“…Also, a wide range of aromatics with high octane number (including xylenes, trimethylbenzenes, tetramethylbenzenes and other alkylbenzenes) were produced during the reaction. [30] Kukulska-Zając and co-workers studied the formation of acetate ion from the catalytic conversion of AA over NaHY zeolite. They concluded that at low temperature acetate ions tightly attached to the hydroxyl group of the zeolite, and above 297°C ions began to decompose to ethane and carbon oxide molecules.…”