The Synthesis Of Ethylbenzene By Alkylation Of Benzene With Bromoethane

Ethylbenzene (EB) is an important synthesis intermediate, which is feed stock for styrene production. Currently, ethylbenzene is synthesized from the alkylattion of benzene in the presence of ethene, which is obtained from the thermal craking of naphtha and thermal dehydrogenation of ethane. In the traditional ethylene production process, there is about 1/3 of ethylene produced from thermal dehydrogenation, which is an energy consuming and green house gas CO₂ polluting process. Hence, the replacement of ethene by ethane as an alkylation agent in the synthesis of EB would bring in both economical and environmental benefits in ethylbenzene production.Based on our previous investigation of the synthesis of bromoethane from oxidative bromination of ethane , we studied the new technology on the alkylation of benzene with bromoethane to synthesize ethylbenzene which eliminate the ethene production step.As a good beginning, zeolites HZSM-5 with different Si/Al ratios were tested as catalysts to evaluate the catalytic performances in terms of of bromoethane conversion and ethylbenzene selectivity. HZSM-5 with a Si/Al ratio of 140/ (HZSM-5-140) was found to be the best catalyst and support. Therefore, we choice HZSM-5-140 as"leader"catalyst for following investigations. After testing metal oxide modified HZSM-5 catalysts and optimized the catalyst compositions, 2wt%ZnO/HZSM-5-140 was found to be the best catalyst among all the tested catalysts. Then, we optimized the reaction conditions, such as: reaction temperature, feed ratios (mol), and weight hourly space velocity (WHSV). It was found that almost 100% bromoethane conversion with 92.2% ethylbenzene selectivity was achieved over 2wt%ZnO/HZSM-5-140 at 360°C at benzene to bromoethane ratio of 6:1 and WHSV of 0.37h^-1. The life-time testing showed that under the above reaction conditions, the catalyst could maintain high activity (>99.5% C2H5Br conversion) within 650 h.The investigations show that the deactivation of catalyst (2wt%ZnO/HZSM-5-140) is because of coke formation. The deactivated catalyst can be regenerated in oxygen at 500°C by burning off the coke.Based on our investigation, the possible reaction mechanism for the alkylation of benzene by C2H5Br is suggested. The reaction started with the absorption of bromoethane on the acid sites of the catalysts to produce carbocations, which then take part in the alkylation of benzene to produce ethylbenzene.