Phosphate modified ZSM-5 for the shape-selective synthesis of para-diethylbenzene: Role of crystal size and acidity

• Alkylation of ethylbenzene with ethanol over phosphate modified ZSM-5.
• Effect of phosphate modification on activity and selectivity.
• Relation between acid site density and phosphate content.
• Detailed study on crystal size and acidity on activity and para-selectivity.
• Detailed study on effect of operating parameters on catalyst performance.

Pore engineered ZSM-5 zeolite in extrudate form was prepared and used as shape-selective catalyst for vapor phase ethylation of ethylbenzene to selectively form para-diethylbenzene. The physico-chemical properties of the catalyst were established by XRD, N2 sorption, FTIR, FESEM, NH3-TPD and 31P MAS NMR. Alkylation of ethylbenzene with ethanol was carried out in a continuous, down-flow, tubular reactor, at atmospheric pressure and H2 as a carrier gas in vapor phase. Effect of silica to alumina ratio (SAR), crystal size, acidity of phosphate modified ZSM-5, stepwise phosphate modification and reaction conditions were studied in detail. ZSM-5 with SAR 187 was found to contain optimum acidity for phosphate modification to achieve good conversion and high selectivity for p-diethylbenzene. Under optimized reaction conditions, viz. temperature = 380 °C, ethylbenzene:ethanol mole ratio = 4:1, WHSV = 3 h−1, H2/reactants = 2, 5PZSM-5 W catalyst gave 22.8% of ethylbenzene conversion with ∼98% selectivity for para-diethylbenzene.

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