Effects Of Carrier Size And Non-metallic Modification On Catalytic Activity Of N-butane Aromatization Over Zn/HZSM-5

Aromatics are very important chemical materials in petrochemical industry,such as benzene,toluene and xylene（BTX）.In recent years,BTX has been in short supply as the demand for downstream products of aromatic hydrocarbons has soared.At the same time,a large number of by-products in the petrochemical industry,such as natural gas,paraffin-based low-carbon hydrocarbon resources have not been effectively exploited.The aromatization process of low-carbon hydrocarbon can not only improve its effective utilization rate but also alleviate the supply and demand contradiction of BTX market.In current paper,taking the n-butane as probe molecule,the influence of carrier size,Zn content and non-metal modification on the pore structure and surface acid properties of Zn/HZSM-5 zeolite catalyst was investigated systematically,and the effect on the non-oxidative aromatization activity of n-butane was discussed.In addition,the effects of the impregnation order of P and Zn species and the process conditions on the catalytic activity were discussed in detail.Firstly,the micron-sized HZSM-5（M）and nano-sized HZSM-5（N）were used as carriers respectively,and the effects of carrier size on the non-oxidative aromatization performance of Zn/HZSM-5 were studied.The results demonstrated that the specific surface area and pore volume increased with the decrease of the carrier size.After loading Zn species,the amount of strong acid decreased,and the weak acid content increased,along with the obviously improved conversion rate of n-butane,selectivity of aromatics and stability.Due to the characteristics of short pore pathway,intergranular mesoporous,which is beneficial to diffusion and mass transfer,the Zn/HZSM-5（N）catalyst possessed high catalytic activity and stability.In addition,the effect of Zn loading content on the catalytic performance was investigated,and the suitable Zn loading content could effectively promote dehydrogenation reaction.The optimum Zn loading was 1.0%.Secondly,various non-metal（F,P,B）modified Zn/HZSM-5（N）catalysts were prepared,and the effects of different non-metal modification on the structure and acid properties of the catalysts were investigated,and the effects on the aromatization activities were also analyzed.The results revealed that the acid solution produced by hydrolysis of non-metals（F,P）has significant influence on the specific surface area,porosity and the surface acidity of zeolite.Among all of various non-metal modified Zn/HZSM-5（N）catalysts,the aromatization activity of P-modified Zn/HZSM-5（N）catalyst was the best,and the aromatics yield was as high as 37.9%.In addition,the optimal P loading content（1.0%）was determined.Finally,the influences of different impregnation order on the structure and acid properties of the catalysts were investigated.The results showed that the suitable impregnation order can effectively distribute the reactive sites,adjust the surface acid properties of the catalysts,and have a significant effect on the activity and stability of zeolite catalysts.And the amount of acid of the catalysts obtained by introducing P after Zn was reduced and the weak acid content was increased,which demonstrated the optimal aromatization performance.At the same time,the optimal reaction temperature and space velocity were determined,with the values of 580℃and 1000m L·g^-1·h^-1,respeactively.