Abstract
Alkylation of benzene with ethanol was analysed using unmodified as well as modified shape selective HZSM-5 (Si/Al = 31) zeolite catalysts. The reaction was carried out in a continuous fixed bed flow reactor in the temperature range of 300–500 °C at atmospheric pressure to investigate the activity of various catalysts for the selectivity and yield of ethylbenzene (the desired product). The alkylation of benzene with ethanol (2:1 by volume) produces ethyl benzene as primary product and others like diethylbenzene, triethylbenzene and xylene mixtures as secondary products. The modification of HZSM-5 was done by impregnation using boron and magnesium. The modification caused changes in the surface area, acidity and pore volume of zeolite sample. The physiochemical properties of catalysts were characterised by XRD, TEM, BET, TGA, FTIR, NH3-TPD and SEM. The feed and products were analysed by gas chromatography. The conversion of benzene was found to be better in bi metallic (B and Mg) modified HZSM-5 followed by unmodified HZSM-5. The modified catalysts gave better selectivity (72.8 %) and yield (38.1 %) of ethylbenzene.
Highlights
The conversion of benzene was found to be better in bi metallic (B and Mg) modified HZSM-5 followed by unmodified HZSM-5
Ethylbenzene (EB), which is one of the most important products used as the chemical intermediate, is the main feedstock for the synthesis of styrene which is polymerised into polystyrenes [1]
The high intensity of peaks in the XRD patterns indicates that the zeolite samples were highly crystalline materials and the highest diffraction peaks were seen at 2h = 23o
Summary
Ethylbenzene (EB), which is one of the most important products used as the chemical intermediate, is the main feedstock for the synthesis of styrene which is polymerised into polystyrenes [1]. The current industrial production of ethylbenzene is based on benzene alkylation with ethene forming ethylbenzene in the presence of an acidic catalyst [4]. Phase alkylation process using zeolite-based catalysts was commercialised, overcoming the main drawbacks of the AlCl3 and supported phosphoric acid technology [4, 6]. The catalytic reaction which uses ethanol for benzene alkylation, instead of ethene, would eliminate the ethene production step and, leading to the commercial and environmental benefits in the ethylbenzene manufacturing [10]. Unmodified HZSM-5 catalysts have numerous micro-porous void spaces and strong acidic sites, leading to the generation of secondary products like diethylbenzene These two drawbacks result in lower selectivity and a variety of secondary reactions in the alkylation process. The fraction in this size range was used in the reactor for the activity test runs
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