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开发了镍改性HZSM-5,对分子筛进行了孔道和酸性的初步调变,在260℃下获得了较高的活性和选择性,但存在的问题是寿命较短,易积炭失活。因此,在Ni-HZSM-5的基础上,继续采用等体积浸渍法制备了不同磷酸负载量的复合改性HZSM-5,虽然提高了催化性能,但是仍然存在着失活的问题。通过对催化剂失活原因分析表明,反应过程中并没有发生磷的流失,且积炭对比表面积和孔道结构的影响较小,研究认为催化剂失活主要是由积炭对酸性位的覆盖导致。对积炭过程和积炭物种进行研究发现,随反应时间延长,催化剂表面积炭速率越来越低,且高温型积炭在积炭中所占比重逐渐增加,说明积炭不饱和度增加。积炭物种主要是含碳碳双键的烯烃聚合物、芳香族化合物和含酯基的物质。
Nickel modified HZSM-5 has been developed to modify the pore and acidity of the molecular sieve. The higher activity and selectivity are obtained at 260 ℃. However, the problem is that the life of HZSM-5 is short and the coke is easy to deactivate. Therefore, on the basis of Ni-HZSM-5, the composite modified HZSM-5 with different phosphoric acid loadings has been continuously prepared by the same volume impregnation method, although the catalytic performance is improved, there still exists the problem of inactivation. Analysis of catalyst deactivation shows that phosphorus loss does not occur during the reaction, and the influence of the surface area of coke and the pore structure is small. It is considered that the deactivation of the catalyst is mainly caused by the coke covering the acidic sites. The study shows that with the reaction time prolonged, the rate of carbon deposition on the catalyst surface is getting lower and lower, and the proportion of high temperature coke in the carbon deposition gradually increases, indicating that the carbon deposition unsaturated degree increases. Carbon deposits are predominantly olefin polymers containing carbon-carbon double bonds, aromatics and ester group-containing substances.