DFT And Experimental Study On The Catalytic Synthesis Of Vinyl Acetate From Acetylene

As an extremely important organic chemical,vinyl acetate is widely used in different fields.Vinyl acetate is mainly produced from gas-phase acetylene method by using zinc acetate/activated carbon catalyst in China.Benzene is an important by-product in the production of vinyl acetate.It is rather difficult to separate benzene from vinyl acetate owing to the low content of benzene.Hence,the formation of benzene would directly affect the purity of polyvinyl alcohol at the subsequent stage.However,up till now,no researchers have investigated the source of benzene in the production of vinyl acetate,and the issue of how benzene is generated remains to be settled.Therefore,the key issues of how the by-product benzene is produced and how to suppress benzene formation are systematically investigated using both DFT method and experimental method.It is hoped that our work could provide some guidance for technology improvement in vinyl acetate synthesis.Firstly,through TEM characterization,it was found that zinc acetate is loaded on the surface of activated carbon in the form of crystals,and the exposed surface should be the?220?facet of zinc acetate by measuring the lattice spacing.Therefore,the periodic model of zinc actate?220?facet was constructed,and the adsorption and co-adsorption properties of each related species were systematically investigated on the zinc acetate?220?facet.It was found that acetylene,vinylidene,benzene and other adsorbates could be chemically adsorbed on the zinc acetate?220?facet.At the same time,the electron transfers between the adsorbates and the catalyst surface were carried out.Secondly,in order to explore whether the active component zinc acetate showed catalytic activity for benzene formation from acetylene,DFT simulation method was used to search the transition states in all elementary reactions involved in the reaction network of benzene formation on zinc acetate?220?facet.Different possible reaction paths were analyzed.It was found that zinc acetate?220?facet showed catalytic activity for benzene formation,and pathway 1?CHCH+CHCH?CHCHCHCH,CHCHCHCH+CHCH?C₆H₆?was the predominant pathway.In addition,it was found that the adsorption strength of acetic acid?Eads=-1.20 eV?was greater than that of acetylene on zinc acetate?220?facet?Eads=-0.98 eV?.Finally,the effects of reactor materials,Zn?OAc?2/AC catalyst and acetic acid as reactant on benzene formation were investigated through experimental methods.It was found that the material of reactor tube itself did not show catalytic activity on benzene formation,but a small amount of acetylene would undergo the self-polymerization to generate little benzene at higher temperature,and the initial temperature for acetylene self-polymerization was 156?.The Zn?OAc?2/AC catalyst could catalyze the formation of benzene from acetylene.However,the content of benzene would significantly decrease after the addition of acetic acid,and also decreased with the decreased acetylene/acetic acid molar ratio.It is concluded that the addition of acetic acid could effectively suppress the formation of benzene.The experimental results were fairly in consistent with the simulation results.