碱金属离子改性对纳米HZSM-5沸石丁烯裂解催化性能的影响

摘要

Nano-HZSM-5 was modified by different alkali metal ions; the effect of the modification on its acidity and catalytic performance in butene cracking was investigated by using NH3-TPD characterization and catalytic evaluation in a small fixed-bed reactor. The results indicated that although the catalysts modified with various ions of Li, Na and K are different in their metal loading required to achieve the highest selectivity to ethylene and propylene, the best selectivity value obtained over all these modified catalysts is located in 50% ~ 60%. The activity of the alkali modified catalysts decreases slowly with the extension of the reaction time on stream; however, the selectivity to ethylene and propylene does not increase accordingly. The conversions of different butene isomers over the zeolite catalysts are decreased in the sequence of butene-1 > trans-butene-2 > cis-butene-2 > iso-butene, which may reflect the order of their reactivity towards cracking.%利用NH3-TPD表征和小型固定床反应评价研究了不同碱金属离子浸渍改性对纳米HZSM-5沸石的酸度及混合碳四液化气中丁烯催化裂解性能的影响。结果表明，尽管锂、钠、钾改性在达到最佳乙烯和丙烯选择性时对应的负载量不同，但其最佳乙烯和丙烯选择性为50％～60％。碱金属离子改性催化剂在连续运转过程中其催化活性缓慢下降，但乙烯和丙烯选择性没有明显增加。丁烯异构体在催化剂上转化率由大到小的顺序为:丁烯-1＞反丁烯-2＞顺丁烯-2＞异丁烯。