Molecular Simulation Study On Benzene Formation In Vinyl Acetate Production By Acetylene Method

Vinyl acetate is a very important organic chemical raw material.It can produce a variety of high-molecular polymers.China is the largest producer of vinyl acetate in the world.Based on the energy distribution of rich coal,poor oil and little gas in China,most of vinyl acetate is produced by the acetylene gas-phase method.There are many by-products in the acetylene method.And as one of by-products,benzene is not easy to separate from vinyl acetate and affects the quality of other products in subsequent sections.At present,the reaction mechanism of benzene is more focused on the trimerization process,and the formation of benzene in the process of acetylene to vinyl acetate has not been systematically studied.In this paper,DFT method and KMC method are combined.Meanwhile,the main reactions and various side reactions in the process of producing vinyl acetate from the acetylene are summarized.How to generate benzene and how to inhibit the formation of benzene have been studied systematically and comprehensively.The reaction network of acetylene to benzene on zinc acetate catalyst is supplemented.The adsorption and co-adsorption of related species are systematically studied by DFT method.The energy barrier and reaction heat of all the elementary reactions in the reaction network are calculated.The trimeric cyclization of acetylene has the least difficulty in producing benzene.The path of acetylene isomerization to acetylene and the dehydrogenation of acetylene to ethynyl may generate benzene.The generation of benzene through the hydrogenation of acetylene to vinyl groups is difficult.As an important by-product in the production of vinyl acetate from acetylene,acetaldehyde is formed by the reaction of acetylene and water,which can be used as a competitive reaction in the process of benzene formation.Using DFT method,the reaction network of acetylene to acetaldehyde on the surface of zinc acetate is analyzed and calculated.It is found that the direct reaction between acetylene and water is the least difficult to generate acetaldehyde.The formation of acetaldehyde from vinylidene and ethynyl are two other possible pathways.It is difficult to achieve the path of acetaldehyde formation through vinyl.Based on the data of reaction network and reaction energy barrier provided by DFT calculation,KMC method is used to explore the influence of reaction temperature,pressure and acetylene / acetic acid molar ratio on the reaction process of acetylene to benzene on zinc acetate.When the reaction temperature is set to 453 K,the yield of benzene is the lowest.The selectivity and yield of benzene increase with the increase of pressure,so the reaction pressure should be reduced.In order to ensure the production rate and yield of the main product vinyl acetate,reduce the yield of benzene to a certain extent,it is reasonable to set the acetylene/acetic acid molar ratio in the range of 2-3.