Pyrrolidone Ligand Modified Cu-based Catalyst Used In Acetylene Hydrochlorination

The energy structure of"rich coal,poor oil and little gas"in China determines that the main way to produce PVC in China is to use acetylene hydrochlorination reaction to produce vinyl chloride.The traditional Hg Cl₂ catalyst is toxic and volatile,which causes serious harm to the environment and human beings.With the increasing attention of the global community to environmental protection,it is urgent to develop an environmental-friendly,high activity and stable mercury-free catalyst.In this paper,the supported Cu-based catalyst with high activity and stability was studied.The Cu-based catalyst was modified by pyrrolidone ligand in the form of ligand coordination.The catalytic performance of the catalysts was tested in the acetylene hydrochlorination.The catalytic effect of pyrrolidone ligand on Cu-based catalyst was explored by a series of characterizations and theoretical calculation.Firstly,the catalytic effect and mechanism of Cu-pyrrolidone catalyst were discussed.Under the reaction conditions of T=180℃,GHSV（C₂H₂）=180 h^-1,V（HCl）/V（C₂H₂）=1.2,the catalytic activity and stability of 16%Cu Cl-0.25NMP/SAC were the best.The initial conversion of C₂H₂ reached 98.3%,and then decreased to97.4%after 12 hours.The selectivity to VCM was stable over 99%.The life evaluation of 12%Cu Cl-0.25NMP/SAC catalyst showed that the acetylene conversion was over99.1%in 215 h,showing high catalytic activity and stability.The results of XRD,BET,TEM,TGA,H₂-TPR and XPS showed that the addition of NMP ligand could effectively promote the dispersion of Cu species,inhibit the agglomeration of metal particles,the formation of carbon deposition as well as the reduction of active species,stabilize the valence of active component Cu^α+,and further enhance the activity and stability of Cu-based catalyst.Then,the modification mechanism of pyrrolidone ligands on Cu-based catalysts was explored.The results of catalytic activity showed that the difference between activity of Cu Cl₂ and Cu Cl as precursors was less than 2%.So,we constructed Cu Cl,Cu Cl cluster,Cu Cl₂ and Cu Cl₂ cluster as models to carry out DFT calculation.The results showed that the Cu Cl₂ model which can stably exist in hydrochloric acid could more reasonably explain the reason of excellent catalyst performance.It was found that Cu and O from NMP could form stable coordination structure and stabilize the valence state of active component Cu^α+,thus improving the activity and stability of Cu-based catalyst,which was also consistent with FT-IR and Raman characterizations.DFT calculation showed that the addition of NMP ligands could enhance the adsorption of HCl on the catalyst,effectively reduce the adsorption of C₂H₂ and VCM and inhibit the formation of carbon deposition in the reaction process,and further enhance the stability and life of Cu-based catalyst.The research in this paper has certain guiding significance for the acetylene hydrogenation catalyzed by Cu-based catalyst modified by ligands.On this basis,the future research should further explore the methods of high activity and stable Cu-based catalyst.