用于二甲苯异构化的HZSM-5分子筛改性研究

采用碱性试剂和含氟试剂对二甲苯异构化专用HZSM-5分子筛进行液相改性，结合多项表征手段及脱乙基型二甲苯异构化反应评价，对改性的效果进行评估。结果表明：改性对分子筛形貌产生了修饰作用，碱改性增加了表面粗糙度，氟化铵改性使晶体表面出现纳米级的微晶团簇；碱改性通过脱硅作用降低了分子筛的硅铝比，增加了酸量，氟化铵改性对硅铝脱除没有选择性，但酸量明显减少；碱改性提高了异构化催化活性及二甲苯收率，对催化剂性能改善的效果优于氟化铵改性。

RESEARCH OF ZEOLITE MODIFICATION FOR XYLENE ISOMERIZATION

The effect of liquid modification on the HZSM-5 zeolite for the xylene isomerization using alkaline reagents and fluorine-containing reagents (ammonium fluoride) was conducted; the modified samples were characterized by NH3-TPD, BET, XRD and XRF techniques. The isomerization performance was evaluated by de-ethyl type xylene isomerization reaction. The changes of morphology after modification by both reagents were observed. The alkali modification increases the surface roughness, lowers the Si/Al ratio due to removing the Si atoms selectively, resulting in more amount of acid; while for fluoride modified samples, some nano-scale microcrystalline clusters appear on the modified surface, ammonium fluoride modification has no selectivity for silicon removal, but the amount of acid is significantly reduced. The isomerization activity and xylene yield are improved by the alkali modification, indicating the better catalytic performance than the fluoride modification.