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非晶质的氧化硅-氧化铝和晶质的丝光沸石催化剂的表面上都有表面OH。可用硅烷偶联剂进行表面改性。由于催比剂的孔径不同以及硅烷偶联剂分子尺寸差异,对氧化硅-氧化铝的改性是在整个内、外表面上进行;而对丝光沸石,由于偶联剂分子不能进入沸石的内孔道中,所以这种改性只能在沸石窗口及外表面上进行。另外,沸石催化剂上酸量适中,酸中心分布较为理想,所以改性的沸石催化剂的选择性,总是比硅铝催化剂有较大增高。改性用的硅烷偶联剂以二甲基二乙氧基硅烷较为适宜。改性后的非晶质硅铝催化剂的对二甲苯选择性由14.6增到34.0%,晶质丝光沸石催化剂改性后由33.3增到43.7%。增加催化剂用量可提高对二甲苯的摩尔百分数到23%,接近它的理论值。
The surface OH of the amorphous silica-alumina and the crystalline mordenite catalyst all have OH. Surface modification with silane coupling agent. Due to the different pore size of the catalyst and the molecular size difference of the silane coupling agent, the modification of the silica-alumina is carried out on the entire inner and outer surfaces; and for the mordenite, the coupling agent molecules can not enter the zeolite In the channel, so this modification can only be carried out in the zeolite window and the outer surface. In addition, the acidity of the zeolite catalyst is moderate and the acid center distribution is ideal, so the selectivity of the modified zeolite catalyst is always higher than that of the silica-alumina catalyst. Modified silane coupling agent with dimethyl diethoxy silane is more appropriate. The para-xylene selectivity of the modified amorphous silica-alumina catalyst increased from 14.6 to 34.0%, while that of the crystalline mordenite catalyst increased from 33.3 to 43.7%. Increasing the amount of catalyst increases the mole fraction of paraxylene to 23%, approaching its theoretical value.