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The Preparation Method And Conditions Of Propane Dehydrogenation To Propylene Vanadium/aluminum Catalyst

Posted on:2019-07-03Degree:MasterType:Thesis
Country:ChinaCandidate:Q Q YangFull Text:PDF
GTID:2351330548958324Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
The propylene is an important petrochemical intermediates.The rapid development of the downstream products of polypropylene,polyacrylonitrile,acrolein and acrylic acid increased the demand for propylene.The propylene by-product of conventional steam cracking and coking production process cannot meet the market demand.There are abundant propane resources in our country.Dehydrogenation of alkenes is the key research direction in petrochemical industry.At present,platinum and chromium based catalysts are two commonly used catalysts for propane catalytic dehydrogenation.However,the platinum catalyst is expensive,and the chromium catalyst has a great harm to the environment.Vanadium has attracted more and more attention because of its lower price,relatively friendly environment and better catalytic performance.In this paper,several different methods are used to prepare vanadium catalyst,and on this basis,the conditions are optimized.First of all,coprecipitation and impregnation on Al2O3,two times of impregnation on aluminum hydroxide,impregnation on homemade alumina,impregnation on commercial alumina,five different ways to prepare catalysts.The best preparation method is determined by the evaluation and comparison of various characterization and catalytic activity.The experimental results show that the maximum surface area can be obtained by impregnating ammonium vanadate on the surface of aluminum hydroxide.This is due to the formation of a flocculent structure on its surface,which increases the specific surface area.Because of its larger surface area,the dispersion of vanadium oxide on its surface is better,and the degree of polymerization of vanadium is the lowest in five samples.After impregnating ammonium metavanadate to the surface of aluminum hydroxide,the effects of different calcination temperatures on the final samples were investigated.With the rise of the calcination temperature,the sample did not increase the effect of the anticipated increase in surface area,but the specific surface area decreased because of the high temperature sintering.With the decrease of surface area,the degree of polymerization of vanadium on the sample surface began to increase,resulting in the selectivity of carbon and cracking products increased,and the selectivity of propylene decreased and the deactivation rate of samples increased.Therefore,the suitable calcination temperature of the catalyst is 600?.Different amount of ammonium vanadate was impregnated on aluminum hydroxide and calcined at 600?to investigate the effect of different vanadium loading on the catalyst.It is found that the specific surface area of the catalyst increases first and then decreases with the increase of the vanadium loading.When the load reaches2.9wt%,the sample has the largest specific surface area,which makes the surface vanadium degree of polymerization is low,and the selectivity to carbon and cracking products is low,which makes the catalyst deactivation rate smaller and propylene selectivity higher.At the same time,the number of active sites on the surface is more,and it has a high activity for dehydrogenation of propane.
Keywords/Search Tags:propane dehydrogenation, aluminum hydroxide, flocculent structure, vanadium polymerization degree, impregnation method
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