Study And Development Of The Catalysts Forparaffinic Naphtha To Aromatics

The chemical utilization of paraffin naphtha is an important topic in the catalytic field in China.This thesis focuses on the development and application of new catalysts to improve the aromatics selectivity of paraffinic naphtha.Good catalytic performance,physical and chemical properties of ZSM-5 zeolite are the main component of aromatization catalyst,hence the activation and directional transformation of raw materials depend on the acidity of molecular sieve in the field of catalytic application.While strengthening the active center of catalyst and inhibiting the generation of by-products depend on the pore structure of molecular sieve,which will affect the diffusion of product molecules to achieve selective catalysis.Therefore,the acid site and pore structure of ZSM-5 zeolite should be reasonably regulated based on the bulk structure of ZSM-5 zeolite to improve its catalytic performance.In this thesis,the catalytic conversion of paraffin naphtha to aromatics was chosen as the research object.With modification and regulation of ZSM-5 molecular sieve,the aromatization temperature,Si/Al ratio of molecular sieve catalyst(hereinafter referred to as “Si/Al”),modified metal and its load concentration were evaluated,and the ZSM-5(Si/Al = 40)-Zn-1% catalyst was developed.The main content includes the following two aspects:(1)Aromatics molecular sieves prepared by alkane catalytic conversion was selected.ZSM-5 molecular sieves with different Si/Al ratios were selected,and the template agent was removed by high temperature roasting.The morphology was characterized,then the temperature was controlled to test the aromatization performance of alkane naphtha catalyzed by ZSM-5molecular sieve to obtain the optimum temperature for aromatics selectivity.Based on the experimental data,it was found that the selectivity of different Si/Al molecular sieves owned the highest performance when the temperature was 550 ℃.Among them,ZSM-5(Si/Al=40)zeolite catalyst posessed the best aromatization effect.In general,different Si/Al zeolites could exhibit different aromatization properties at 550 ℃,suggesting that the acidic sites of ZSM-5 zeolites have an important influence on their aromatization properties.(2)Catalytic modification and performance of ZSM-5 zeolite were investigated.ZSM-5(Si/Al=40)zeolite catalyst with the best aromatization effect of paraffin naphtha at 550 ℃ was used to modify and characterize the morphology and structure supported by different metal elements(Ga,Zn,Cu,Cr,Fe,Ni,etc.)by impregnation method.The ZSM-5(Si/Al=40)molecular sieves were used to catalyze the aromatization of alkane naphtha at 550 ℃.According to the experimental results,Zn was used as the supporting element to modify the aromatization performance of ZSM-5(Si/Al=40).After that,ZSM-5(Si/Al=40)zeolite was modified by loading different concentrations(1%,3%,5%,7%)of Zn with the same impregnation method.The morphology and structure of ZSM-5 zeolite were characterized,then the aromatization performance of the modified zeolite was explored at 550 ℃.In order to ensure the accuracy of the experiment,it also carried out modification studies on other ZSM-5 zeolites with different Si/Al concentrations of Zn elements,then obtained the changes of the modified ZSM-5 zeolites with different Si/Al aromatization properties.The results indicated that ZSM-5(Si/Al=40)catalyst modified by 1% Zn had high selectivity of target products,good selectivity of high added value products and good catalytic stability.This study can provide a theoretical basis for the subsequent element modified ZSM-5 zeolite catalytic aromatization of naphtha.