Aromatization Of C5-C8 Paraffins Over Modified Nano-sized ZSM-5 Zeolite

Light hydrocarbon aromatization is an important approach of producing aromatics.Many kinds of light hydrocarbon by-products in the petroleum refineries and petrochemical industries can be converted into aromatics with added value by the technique of light hydrocarbon aromatization.In this paper,using nano-sized HZSM-5 as the parent catalyst,the effect of alkali metal ion(K⁺ Na⁺) and transional metal ion Zn²⁺ joint modification on the surface acidity and aromatization performance of C₅～C₈ chain alkanes over obtained catalysts was studied by NH₃-TPD,Py-FTIR,XRD,and small fixed bed reactor.The effect of steaming treatment and transitional metal ion Zn²⁺ joint modification on the surface acidity and aromatization performance was also studied.Meanwhile,the effect of temperature on aromatization performance of catalysts was also investigated.The following conclusions were reached:(1) For the catalysts modified by K⁺(Na⁺) and Zn²⁺ impregnation,as the loading of K⁺(Na⁺) increasing,the feedstock conversion of the catalysts decreased,aromatics selectivity increased, dry gas selectivity obviously decreased,and C-H bond activation selectivity increased.In the study on the effect of impregnation sequence on aromatization performance of catalysts,it was found that the catalysts modified in the ways of first K²⁺(loading 0.5wt.%) and then Zn²⁺ impregnation or first Zn²⁺ and then Na⁺(loading 0.8wt.%) impregnation showed the better aromatization performance.(2) In the experiment of estimating proper ZnO loading,it is found that when the ZnO loading was 3 wt.%,the catalysts showed the best aromatization performance.(3) For the catalysts modified by steaming treatment and Zn²⁺ impregnation,as the steaming treatment temperature increasing,the feedstock conversion,aromatics selectivity,and dry gas selectivity all show the trend of first increasing and then decreasing.