催化裂化干气与苯烷基化催化蒸馏制乙苯反应网络热力学研究

Thermodynamics of Ethylbenzene Synthesis through Alkylation of FCC Off-Gas with Benzene by Catalytic Distillation

高温气相反应条件下的催化裂化干气制乙苯过程中 ,容易生成甲苯和二甲苯等副产物 ;在该过程中采用催化蒸馏技术 ,使苯与乙烯在低温条件下进行反应 ,可大幅度降低产品中二甲苯的含量 .通过对催化裂化干气与苯烷基化催化精馏过程中的各反应步骤进行分析与热力学计算 ,结合反应的实际产物组成 ,提出了苯与乙烯烷基化的反应网络 ,探讨了苯与乙烯烷基化反应过程中甲苯和二甲苯的形成机理及影响因素 .结果表明 ,增大苯 /乙烯比对提高乙烯平衡转化率及乙苯收率有利 ;在较低温度下进行烷基化反应 ,可大大减缓C C键裂解速度 ,抑制甲苯和二甲苯生成 。

A catalytic distillation technique for synthesis of PhEt through alkylation of FCC off-gas with C_6H_6 was developed. C_6H_6 could react with C_2H_4 at a much lower temperature, being favorable to PhEt selectivity and prohibiting C_6H_4Me_2 production. The results of the calculated equilibrium constants show that it is more favorable to produce PhMe and C_6H_4Me_2 than PhEt and C_6H_4Et_2, compared with the alkylation of C_6H_6 with C_2H_4 under liquid-phase condition, and the equilibrium constant for PhMe or C_6H_4Me_2 is 100 times as high as that for PhEt or C_6H_4Et_2 in the reaction of C_6H_6 with C_2H_4. In order to prohibit the formation of PhMe and C_6H_4Me_2 from the point of dynamics, it is very important to develop catalysts with high selectivity for PhEt and C_6H_4Et_2. By analyzing the complicated reaction process, a new dynamics network for alkylation of C_6H_6 with C_2H_4, as well as that for transalkylation of C_6H_6 with diethylbenzene, has been proposed according to the detailed thermodynamics calculation and the factual product distribution. The effects of different reaction conditions on product distribution are also discussed. Low temperature, high C_6H_6/C_2H_4 molar ratio and appropriate pressure are suitable for the increase of C_2H_4 conversion and PhEt selectivity. The formation mechanism of PhMe and C_6H_4Me_2 ,and its influence factors have been studied. The formation of PhMe and C_6H_4Me_2 is dynamically determined by cleavage of C-C bonds in C_2H_4. For the catalytic distillation process, lower temperature can greatly put off the cleavage velocity of C-C bonds and suppress the formation of PhMe and C_2H_4Me_2.