环己烷在Pt/HY-Al_2O_3催化剂上加氢转化反应的研究

Cyclohexane Hydroconversion on Pt/HY-Al_2O_3 Catalysts

采用高压微型反应器,在压力为4.0MPa,温度260℃～350℃、氢油比为500∶1、空速1.0h-1条件下,研究了不同酸性载体HY Al2O3负载的铂(Pt)催化剂上环己烷的催化反应规律.结果表明,反应温度和载体酸性是影响催化剂异构化活性、裂化活性的两个重要因素,增加反应温度或提高催化剂酸性都会导致催化剂的异构化活性降低、裂化活性增强.当反应温度为290℃,含15%HY的Pt/HY Al2O3催化剂的异构化活性最好,异构化产物的选择性为91.6%,环己烷转化率为71.6%.提高催化剂载体中分子筛含量,有利于环己烷开环反应的发生,从产物的分布可以看出,在Pt/HY Al2O3催化剂上环己烷的开环过程是首先异构化为甲基环戊烷继而发生开环反应,反应最终达到平衡状态,致使开环产物中nH∶3MP∶2MP=1∶1∶2比值不变,开环机理符合β 断裂的正碳离子机理.

Platinum catalysts supported on HY-Al_2O_3 have been prepared and characterized by TG-DTA. Isomerization and ring-opening mechanism of cyclohexane on these platinum catalysts have been investigated by performing hydrogenation of cyclohexane with a high pressure microreactor under the conditions of 260 ℃～350 ℃, 4.0MPa, WHSV1.0h^(-1), hydrogen flowed velocity 100 mL/min. Isomerization, ring-opening and cracking activity of cyclohexane on catalysts increased with increasing of catalyst acidity and reaction temperature. Isomerization selectivity of the catalyst with 15% zeolite is best under the condition of 290 ℃: conversion is 71.6%, selectivity of methylcyclopentane is 91.6%. Cyclohexane was isomerized into methylcyclopentane first , products of methylcyclopentane ring opening included n-hexane, 3-methylpentane and 2-methylpentane. Equilibrium mixture of ring opening products was nH∶3MP∶2MP=1∶1∶2. Ring-opening of methylcyclopentane complied with carbenium ions mechanism on these platinum catalysts.