磷镍复合改性HZSM-5催化乙醇脱水制乙烯积炭行为研究

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。

Coke Deposit Research of Catalytic Dehydration of Ethanol to Ethylene over Phosphorous-Nickel Modified HZSM-5 Catalysts

Ni-Modified HZSM-5 has been developed in our research group. Its channel structure and acid properties were preliminarily modified. Although the higher activity and selectivity has been obtained at 260 ℃, carbon deposit and the short life-span of the catalysts are still the urgent problem to be solved. Based on the Ni-modified HZSM-5 synthesized via ion-exchange method, a series of phosphorus-nickel modified HZSM-5 catalysts were prepared by impregnating the Ni-HZSM-5 with phosphoric acid aqueous solution. The activity of the catalyst was improved to some extent but coke deposit still existed. According to our research, phosphorus was not lost in the process of the reaction, and surface area as well as channel structure was not largely affected by carbon deposit. Characteristic of the catalysts before and after reaction revealed that the deactivation of catalyst resulted from the coverage of acid sites by coke deposit. As the reaction proceeded, the rate of coke formation decreased and the proportion of coke that could be eliminated at relatively high temperature increased. The carbonaceous materials consisted mainly of olefin polymers containing CC, aromatics and some compounds containing ester group.