Study On The Modification Of Ru-based Catalyst For Acetylene Hydrochlorination

Polyvinyl chloride（PVC）is a thermoplastic resin formed by the polymerization of vinyl chloride（VCM）under the action of an initiator.PVC resin is the world’s second-largest general-purpose resin and is widely used in industry,construction,agriculture,and daily necessities etc..The key to the production of PVC resin is the synthesis of VCM monomer.However,the industrial synthesis of VCM mainly includes two routes:ethylene and acetylene.Due to the energy status of rich coal,lean oil,and low gas in China,the production of vinyl chloride in China is mainly determined by acetylene hydrochlorination method.At present,HgCl₂/AC is mainly used as a catalyst in the production of vinyl chloride monomer.However,mercury is easily sublimated and deactivated under high temperature conditions.In addition,toxic mercury on human health and the environment caused serious threat.In order to achieve the sustainable development goals of the acetylene production PVC industry,the development and research of environment-friendly mercury-free catalysts is imminent.The main research content of this paper is divided into the following four aspects:（1）First,we screened different types of oxidants,namely hydrogen peroxide,potassium permanganate,nitric acid,ferric chloride,ammonium persulfate,and selected the best oxidation effect using nitric acid as an oxidant.Then,nitric acid was selected as the oxidant,and the way of ruthenium oxide-based catalyst was explored.The results of the activity test showed that the Ru-O/AC-O catalyst obtained by oxidizing the active carbon carrier and then oxidizing the active component had the best catalytic effect.Under the reaction conditions of 180℃,V_HCl/V_C2H2=1.15 and GHSV（C₂H₂）=180 h^-1,the initial conversion of acetylene was 99.3%,and the reaction could still reach 93%after 24 h.Under the same conditions,with Ru/AC comparison,the activity was relatively increased by 31.0%,and the vinyl chloride selectivity was greater than 99.0%.The characterization results showed that the Ru-O/AC-O catalyst obtained by oxidizing the activated carbon carrier and then oxidizing the active component had the best catalytic effect.The modification strengthens the adsorption of reactants,and it can also well disperse Ru species and augment the amount of high-valent active species,consequently enhancing the catalytic activity.（2）The plasma technology was used to treat the catalyst.First,the atmosphere（O₂,H₂,Air and N₂）treated by plasma was screened.The best effect of the ruthenium based catalyst was treated by plasma technology under nitrogen atmosphere.The acetylene conversion of（Ru/AC）-N₂ catalyst at 180℃,V_HCl/V_C2H2=1.15 and GHSV（C₂H₂）=180 h^-1 reaction conditions.The conversion rate can reach 87.2%,and the selectivity of vinyl chloride is higher than 99%.The results of characterization showed that the plasma modification enhanced the interaction between the carrier and the active components,enhanced the dispersion of the ruthenium species,enhanced the adsorption capacity of the reactant,and reduced the active components of the ruthenium based catalyst to about 2 nm,thus improving the catalytic activity of the catalyst.（3）According to the results of previous DFT simulations,it can be seen that the enthalpy chloride ratio has an effect on the acetylene hydrochlorination reaction.Therefore,a series of Ru_xCl_y/AC catalysts have been prepared.First,Ru/Cl was screened to select the best ratio of 5:7.Under the reaction conditions of 180℃,V_HCl/V_C2H2=1.15 and GHSV（C₂H₂）=180 h^-1,Ru₅Cl₇/AC catalyst acetylene conversion can reach 96.1%,vinyl chloride selectivity greater than 99.0%,consistent with the simulation results.The results of characterization analysis show that the appropriate coordination numbers of ruthenium and chloride could increase the amount of ruthenium oxides,improve the dispersion of Ru species on the carrier,enhance the adsorption ability of the catalyst,consequently improving the catalytic performance.And TPPB additives can further improve the activity and stability of the catalyst.（4）Preparation of N-heterocyclic carbene Ru complex catalyst instead of RuCl₃ as precursor.The results showed that the initial conversion rate of acetylene for Ipr（Ru）/AC catalyst was 99.3%at 180℃,V_HCl/V_C2H2=1.15 and GHSV（C₂H₂）=180h^-1,and the conversion rate of acetylene was 97.9%after the reaction of 48 h.The characterization results show that Ru complexes can improve the dispersion of active components on the carrier,and the ligands have anchoring effect on metal Ru,reducing the loss and agglomeration of the active components in the reaction process,thus improving the catalytic performance.