水对3Si-5P-3Mg-ZSM-5催化剂催化甲苯甲醇烷基化反应性能的影响

EFFECT OF WATER ON CATALYTIC PERFORMANCE OF 3Si-5P-3Mg-ZSM-5 CATALYST FOR ALKYLATION OF TOLUENE WITH METHANOL

复合改性3Si-5P-3Mg-ZSM-5催化剂用于甲苯甲醇烷基化制备对二甲苯(PX),在进料过程中引入一定比例的水蒸气,考察水蒸气用量对催化剂反应活性、PX选择性和稳定性的影响,采用X射线衍射、N2吸附-脱附、NH3程序升温脱附、吡啶吸附红外光谱等表征手段对3Si-5P-3Mg-ZSM-5催化剂的新剂和7次再生剂进行分析。结果表明:在甲苯甲醇烷基化反应过程中,适量通水可提高该反应的甲苯转化率、PX选择性和催化剂抗积炭性能,这是由于水的通入降低了催化剂表面和微孔内强酸中心数量,抑制了二甲苯异构化和积炭前体生成的速率;在n(H2O)/n(甲苯+甲醇)为10∶1、反应时间为50h的条件下,甲苯转化率可维持在23%左右,PX选择性可达74%。对3Si-5P-3Mg-ZSM-5催化剂的再生剂反应性能评价表明,积炭是导致催化剂活性下降的主要原因,通水并未对催化剂的骨架结构和活性组分有严重破坏作用,且反复再生后的催化剂反应性能均可恢复到新鲜催化剂的水平。

Para-xylene(PX)was synthesized through alkylation of toluene with methanol over composite modified ZSM-5 zeolite catalyst with a certain amount of steam introduced into the reaction.The influence of water vapor dosage on the conversion of toluene,PX selectivity and the stability of the catalyst was investigated.The fresh 3Si-5P-3Mg-ZSM-5 catalyst and the catalyst regenerated seven times were analyzed by XRD,N 2 physical absorption-desorption,NH 3-TPD,Py-FTIR,and 27 Al MAS NMR techniques.The results showed that toluene conversion,PX selectivity and anti-carbonization composite of modified 3Si-5P-3Mg-ZSM-5 catalyst were improved by introducing appropriate amount of water in the process of toluene alkylation with methanol.This could be attributed to the reduction of the content of strong acid center of the catalyst,the inhibition of the isomerization of p-xylene and the formation rate of the precursor of carbon deposition.When the mole ratio of water/(toluene+methanol)was 10∶1,the conversion of toluene could be maintained at about 23%and the para-selectivity could be up to 74%within 50 h reaction time.The performance of regenerated 3Si-5P-3Mg-ZSM-5 catalyst showed that carbon deposition was the main cause of catalyst deactivation,no seriously damage of the framework structure and active components of the catalyst was found by adding steam.The catalyst could be restored to the level of fresh catalyst after repeated regeneration.