Study On Hydrochlorination Of Acetylene Catalyzed By Polymer Modified Ruthenium Catalyst

In view of the abundant coal resources and technical conditions in China,calcium carbide acetylene method has become the mainstream technology of VCM production in China.However,mercuric chloride catalysts needed for the process are prone to volatilization and loss and cause serious environmental problems,so it is urgent to develop environmentally friendly catalysts.Because of the high production cost of gold-based catalysts and the relatively low-cost of Ru,whose electrode potential is similar to that of Au,it has become a research focus to explore the influence of Ru catalyst on acetylene hydrochlorination.Considering the drawbacks,such as the poor dispersity,serious carbon deposition and lack of persistent active sites,of traditional Ru/AC catalysts,a series of Ru catalysts were synthesized by using polymer modifiers with special physical and chemical properties,such as polydopamine with strong adhesion and catecheol structure,polyethyleneimine rich in amino group and polyimide containing-CO-N-CO-structure.The structure-activity relationship and inactivation of Ru active domain during acetylene hydrochlorination were investigated.（1）Firstly,based on the shortcomings of poor dispersion,metal loss and serious carbon deposition of ruthenium catalyst,the supported ruthenium catalyst（Ru/AC@PDA-T）was prepared by dopamine-self-polymerization method.Compared with the reference Ru/AC catalyst（74.73%）,the conversion rate of acetylene was up to 99.37%under the catalytic action of Ru/AC@PDA-100 catalyst coated with PDA layer.Because dopamine has strong adhesion and abundant oxygen/nitrogen functional groups,the introduction of PDA formed the PDA layer on the surface of catalyst,and the coordination between the heteroatoms and Ru precursor constructed the active domains,which balanced the activation of acetylene and hydrogen chloride at the same time,promoted the electrophilic addition reaction,and reduced the coke deposition on the surface of catalyst,ensuring continuous exposure of more active sites.The local structural forces in the active domain during heat treatment also resulted in atom-level dispersion of the active component.However,the strong saturation coordination between Ru and heteroatoms under high temperature treatment hindered the attack and activation of acetylene,making the single atom-dispersed Ru species unfavorable to catalyze the reaction.Therefore,the preparation of Ru/AC@PDA-100 catalyst promotes its potential industrial application.（2）Secondly,due to the lack of durable active sites for Ru catalyst,we designed and constructed Ru and polyethyleneimine（PEI）anchor sites,and synthesized a series of catalysts containing highly dispersed Ru active domain for acetylene hydrochlorination reaction.Because polyethyleneimine contains a large number of basic amino functional groups,which were adsorbed on the surface of Ru/AC catalyst,the lone pair electrons on N are inclined to the vacant orbital of Ru atom and the atoms around,thus forming the coordination effect,and then the active structure of Ru-N was constructed.This coordination structure improved the stability of Ru atom and enhances the adsorption and activation of HCl.In addition,the proper heat treatment has little effect on the performance of the catalyst,but the alkaline pyridine N species generated during heat treatment can enhance the adsorption and activation of HCl on the catalyst.At the same time,more Ru-C interfaces can be formed on the surface of Ru/AC@PEI-T catalyst,which is conducive to the effective contact of HCl and C₂H₂.In addition,the relative inactivation rate of the optimized Ru/AC@PEI catalyst is only 7.32%through 300 h long-term stability test,which also provides experimental basis for the industrial application of Ru catalyst.（3）Finally,a series of Ru-polymer/AC catalysts were prepared based on the problem that the surface of the catalyst is easy to form carbon deposition,and the modification effect of polyimide ligand（containing-CO-N-CO-structure）on Ru catalyst was discussed in detail.According to the activity test,the acetylene conversion rate of Ru-PI₂/AC catalyst can still be maintained at 80%after 24 h reaction at high space velocity(GHSV（C₂H₂）=360 h^-1).Through characterization analysis,it was found that the coordination structure of the polyimide ligand with Ru precursor can anchor the dispersed Ru active center and inhibit its sintering and Ru loss by the spatial effect of the ligand.Moreover,the synergistic action of multiple sites of heteroatoms and metal centers can effectively activate HCl and C₂H₂.Furthermore,the catalytic activity was significantly increased.The proper heat treatment was beneficial to the generation of more active sites in the catalyst.In addition,intermittent activity tests showed that the deactivation of catalyst may be related to surface carbon deposition.HCl reactivation can partially recover the activity of deactivated catalyst.After150 h activity test of regenerated catalyst,the initial acetylene conversion of（Ru-PI₂/AC）-300 catalyst can be increased to 99.45%.However,the deactivation rate increased slightly,which can provide some experimental basis for the regeneration of deactivated catalyst.