Effect Of Sulfur On The Performance Of Non-mercury Catalysts For Acetylene Hydrochlorination

Vinyl chloride monomer?VCM?is mainly used for the synthesis of polyvinyl chloride?PVC?,which is one of the five engineering plastics.Based on the energy structure of?coal-rich,oil-poor?in China,acetylene method has become the main method for the production of VCM.The activated carbon supported mercuric chloride is the catalyst which exhibits serious environmental pollution and high toxicity to human bodies.Thus,it is urgent to explore non-mercury catalysts replace the mercury catalysts for acetylene hydrochlorination.In this thesis,we embarked on the research work from two aspects:sulfur-modified active carbon of non-metallic catalysts and sulfur-controlled gold-based catalysts.Firstly,the effect on the sulfur-doped activated carbon was investigated for acetylene hydrochlorination.The optimal catalytic performance is obtained over 9%S/B-SAC catalyst.The acetylene conversion is 83%after 12 h on stream under the conditions of 180°C,C₂H₂ gas hourly space velocity?GHSV?of 90 h^-1,and the feed volume ratio HCl/C₂H₂ of 1.1,which is higher 10%than blank carrier;the selectivity to VCM of 99.9%.The results were obtained by combining with the characterizations of thermogravimetric analysis,temperature-programmed desorption,X-ray photoelectron spectroscopy and the density function theory computing method.It is shown that the doping of sulfur atoms into the skeleton of activated carbon can change the charge density and spin density on the surface of carbon;more lively chemical property of activated carbon is conductive to reaction;more active sites can inhibit carbon deposition and enhance adsorption of two reactants and desorption of product.Then,on the base of sulfur modified,the Au-glutathione?GSH?complex catalysts were prepared and used to study effect of GSH on the catalytic performance of gold catalysts for acetylene hydrochlorination.The results of activity evaluation show that Au1-GSH3/AC?pH 8.3?exhibits the optimal catalytic properties,with the acetylene conversion of 83%after 12 h on stream under the conditions of 170°C,C₂H₂ gas hourly space velocity?GHSV?of 360 h^-1,and the feed volume ratio HCl/C₂H₂ of 1.1,which is higher 30%than the Au/AC catalyst.The addition of GSH can lead to the reduction of Au³⁺to Au⁺,the species of Au⁺and Au⁰ coexist in the fresh Au-GSH3/AC catalysts,with the individual content close to 50%.The presence of Au⁺plays an important role in enhancing the catalytic activity.Adjusting the pH values of the catalyst to a suitable value can make more active species disperse well on the catalysts,inhibit coke deposition and enhance the adsorption ability of reactants.Finally,the ionic liquid?IL?of trimethylsulfonium iodide was chosen to formation the Au-based complex catalyst to catalyze the reaction of acetylene hydrochlorination.The Au-IL/SAC catalyst was prepared after confirm the optimum preparation condition.The evaluation results show that the acetylene conversion of0.3%Au-IL/SAC is 90%after 24 h on stream under the conditions of 170°C,GHSV?C₂H₂?of 360 h^-1,and the feed volume ratio HCl/C₂H₂ of 1.2,the selectivity to VCM of 99.9%,which is higher 30%than the 0.3%Au/SAC catalyst.The catalytic activity can be stablized at 97%under the condition of GHSV?C₂H₂?of 90 h^-1 even after 200h later.The characterization results show that the addition of?CH₃?₃SI can make active Au species dispersed uniformly and suppress the reduction of active gold species;but also inhibit carbon deposition and improve the adsorption ability of C₂H₂and HCl,at the same time,enhance the desorption property of VCM.