The Alkylation of Benzene with Bromoethane to Synthesize Ethylbenzene
|Course||Chemical Engineering and Technology|
|Keywords||Ethylbenzen Bromoethane Benzene Alkylation Zinc oxide catalyst|
The alkylation of benzene with ethylene to produce ethylbenzene is widely used in the petrochemical industry. Ethylbenzene is the main material for styrene production, and styrene is an important intermediate to produce macromolecule material, such as polystyrene, its copolymer, acrylonitrile-butadienestyrene (ABS) resin, acrylonitrile-styrene (AS) resin, styrene-butadiene rubber, and unsaturated polyester.In this dissertation we studied the alkylation of benzene with bromoethane to prepare ethylbenzene(EB). Supported ZnO catalysts were mainly investigated as the catalysts of the alkylation of benzene with bromoethane. At the same time, the reaction mechanism of benzene alkylation with C2H5Br was also discussed.The influences of loading concentration of ZnO, reaction temperature, benzene: C2H5Br mole ratio, C2H5Br weight hour space velocity (WHSV), and the catalyst calcination temperature on C2H5Br conversion and production distribution were investigated over ZnO-SiO2 catalysts. It was found that the catalyst containing 12wt% of ZnO and calcined at 450℃performanced the best activity. The optimum reaction conditions were found to be that:1) the reaction temperature is 240℃,2) the benzene: C2H5Br mole ratio is 4:1, and 3) WHSV of C2H5Br is 0.48 h-1.The SiO2 and HZSM-5(Si:Al=140:1) supported ZnO catalysts were investigated for the alkylation of benzene with C2H5Br. The influence of ZnO concentration on C2H5Br conversion and product distribution were investigated. It was found that below certain amount of ZnO loading, the C2H5Br conversion and ethylbenzene selectivity increased with the increase of ZnO concentration in catalysts. ZnO was found to be the catalytic component of these catalysts. We thought that ZnO reacted with HBr formed in the reaction to form ZnBr2, which is a Lewis acid. Since the existence of Lewis acid ZnBr2, it can catalyze the formation of ethyl carbon cation, which could attack the adsorbed benzene to form ethylbenzene.The influences of reaction temperature and acidity of catalysts on reaction were investigated over the 12 wt%ZnO-SiO2 and 24 wt%ZnO/HZSM-5 catalysts. It was found that the Br(?)stond acid sites might be the active sites for the ethyl transferring reaction. It was found that the C2H5Br conversion increased with reaction temperature, but the ethylbenzene selectivities changed differently over the two catalysts. The ethylbenzene selectivity increased with the reaction temperature increase over catalyst 24 wt%ZnO/HZSM-5, but decreased over 12 wt%ZnO-SiO2. The reason was that the Br(?)stond acid site concentration over 24 wt%ZnO/HZSM-5 was higher than that over 12%ZnO-SiO2. Hence, the ethyl-transferring reaction activity between benzene and multi-ethyl substituted benzene was higher over 24 wt%ZnO/HZSM-5 than that over 12 wt%ZnO-SiO2, which lead to high ethylbenzene selectivity at high reaction temperature over 24 wt%ZnO/HZSM-5.Based on our investigation, we suggested the following reaction mechanism. In the reaction, there are two pathways occurred over the surface of catalysts in the formation process of ethylbenzene. The first way is that C2H5Br was adsorbed on to the surface acid sites to form ethyl carbon cations, which attacked the adsorbed benzene to for ethylbenzene and HBr. The other reaction pathway is that C2H5Br dehydrobromide to form HBr and ethylene, then ethylene was adsorbed on acid sites to form carbon cations, which attacked benzene to form ethylbenzene. There are also other reactions occurred, such as the carbon cations could attack ethylbenzene or multi-substituted ethylbenzne to form even heavily substituted ethylbenznes and also the multi-substituted ethylbenznes could react with benzene to form ethylbenzene, which is the ethyl transferring reaction.