The principle of the formation of the by-product toluene in the production of ethylbenzene from dry gas

When pure ethylene is alkylated, some toluene and xylene are formed; whereas when dry gas containing certain amounts of propylene and butylene is used to produce ethylbenzene, the content of toluene in the product is significantly higher than that obtained using pure ethylene. Catalytic cracking dry gas contains not only ethylene but also a certain amount of propylene and butylene. The alkylation reaction rates of these latter two olefins with benzene are about twice as fast as that of ethylene. In order to improve the utilization rate of the raw material benzene, the cumene and styrene produced by the alkylation of the dry gas are generally fed into an alkylation transfer reactor for recycling. During the transalkylation process, cumene and styrene produce toluene. The resulting toluene may react with ethylene in the dry gas to form methyl ethylbenzene; this compound then decomposes into xylene. The boiling points of xylene and ethylbenzene are very similar, making separation difficult and thus significantly affecting product quality. An increase in reaction temperature, raw material concentration, and pressure all facilitate the conversion of cumene and styrene, while the yield of toluene also gradually increases. Order of toluene production: propylbenzene > butylbenzene > diethylbenzene. During the reaction process, ethylbenzene does not produce toluene; cumene and butylbenzene facilitate the formation of toluene. Reaction equation: C6H4(C2H5)2 (diethylbenzene or butylbenzene) + C6H6 = C6H4CH3C2H5 + C6H5CH3; C6H4CH3C2H5 + C6H6 = C6H4(CH3)2 + C6H5CH3; C2H4 + 2C6H6 = 2C6H5CH3