Pd-Pb双金属催化剂上甲苯歧化与烷基转移反应性能

Disproportionation and Transalkylation of Toluene with Heavy Aromatics on Pd-Pb Bimetal Catalyst

为提高甲苯歧化与烷基转移生成苯和二甲苯反应的收率,采用了ZSM-12分子筛负载钯和铅的双金属甲苯歧化与烷基转移催化剂,在连续操作的小型固定床反应器中考察了钯金属负载量、钯-铅物质的量比、反应条件对反应性能的影响。结果表明:引入钯金属能提高重芳烃转化率,同时也加剧了苯环加氢副反应;适当降低钯金属负载量、采用钯-铅双金属体系能有效抑制芳烃加氢副反应,优化催化剂整体反应性能;提高反应温度、降低氢气纯度及反应压力有利于抑制加氢副反应,改善催化剂反应性能。基于钯含量为0.2%,Pb/Pd比为3的双金属催化剂体系,在原料组成苯与碳九及其以上重芳烃的质量比为30:70,反应温度390℃,反应压力2.5 MPa,进料空速4.0 h-1,氢烃比2.0的较佳条件下,甲苯的转化率为21.7%,重芳烃转化率61.6%,二甲苯的质量收率达36.2%,苯的纯度为99.5%,表现出了较高的重芳烃处理能力及二甲苯收率。

Pd-Pb/ZSM-12 catalysts were applied in disproportionation and transalkylation of toluene with heavy aromatics to increase xylenes product yield. The effect of loading Pd, the molar ratio of Pb to Pd and reaction conditions on catalyst performances were investigated in a continuous operation miniature fixed bed reactor. The results show that addition of Pd can improve heavy aromatics conversion, but also cause hydrogenation of aromatic ring. Addition of Pb to a low Pd content catalyst is effective to reduce aromatic ring hydrogenation and maintain high xylenes yield. Furthermore, the reaction conditions of high reaction temperature, low hydrogen pressure and hydrogen purity were favorable to reduce aromatic ring hydrogenation to obtain higher product purity. The optimized bimetallic catalyst containing 0.2%Pd metal and certain amount of Pb metal （molar ratio of Pb to Pd is 3） was used to catalyze the reaction under favorable reaction conditions of reaction temperature of 390 ℃, reaction pressure of 2.5 MPa, feed space velocity of 4.0 h-1 and hydrogen/hydrocarbon ratio of 2.0 with a feedstock containing 30%toluene and 70%heavy aromatics. The conversion of toluene and heavy aromatics was 21.7%and 36.2%respectively and the product purity of benzene reached 99.5%, which exhibits improved performance on enhancing heavy aromatic conversion and xylenes yield.