Improvement Of Preparation Process Of WO₃/SiO₂&MgO Metathesis To Propylene Catalyst

Propylene is the low-carbon which status is second only to ethylene.Its added value is high,and the demand for its downstream derivatives is also increasing year by year.In order to supplement the gap in the production of propylene by steam cracking,various technologies for producing propylene are received more and more attention.According to the market demand for ethylene and propylene,the olefin metathesis process can reasonably adjust the output ratio and make full use of cheap n-butene to realize the rational use of C₄ resources.At present,WO₃/Si O₂catalyst is the only metathesis catalyst for industrialization among because of its low price,long life and easy carbon removal.However,based on the previous research of the group,we found that the catalytic system is sensitive to the purity and impurities of raw materials.In a short time,trace CO₂ will inactivate the poisoning of Mg O catalyst.In addition,reducing the isobutene selectivity of the WO₃/Si O₂ catalyst facilitates the separation of subsequent products while increasing the propylene yield.Therefore,this paper starts from the aspects of improving product selectivity and stability,improving the preparation process of WO₃/Si O₂&Mg O metathesis catalyst.Firstly,I improved the preparation process of WO₃/Si O₂ catalyst from the silica support and calcination temperature.And the selectivity of by-product isobutylene was reduced from 1%to 0.05%.The optimal preparation method of the highly active and highly selective WO₃/Si O₂ catalyst is determined according to different process requirements.Afterwards,in order to adapt to the trace CO₂ impurities in the raw materials,the effects of CO₂ impurities on the stability of Mg O catalysts were verified.From the three perspectives of magnesium oxide source,calcination conditions and preparation methods,I improved the preparation process of the Mg O catalyst.The results show that the poorer crystallinity of Mg O catalyst and the smaller grain size,the anti-CO₂ impurity performance is better.The optimized Mg O catalyst has a significantly improved stability and its service life is extended to 28 h,which is twice as high as that of foreign catalysts.At last,I explored the optimum process conditions of WO₃/Si O₂catalyst and Mg O catalyst from three aspects of ethylene concentration and purity,feed molar ratio and pressure.Studies have shown that the longer the residence time of ethylene feedstock on the catalyst,the more favorable the metathesis reaction occurs.The impurity inactivating catalyst poisoning is a mutation behavior.Metathesis reaction cannot occur under normal pressure.Besides,the pressure is lower,the conversion of n-butene and the selectivity of propylene are higher.