The Research Of Steam Pretreatment And Regeneration On Bi-based Mercury-free Catalysts For Acetylene Hydrochlorination

Polyvinyl chloride?PVC?,which is one of five universal synthetic resins in the world,is widely used in industry,agriculture and construction.Vinyl chloride monomer?VCM?manufacture is a crucial raw material for PVC production,and there are three kinds of synthesis methods: acetylene method?acetylene hydrochlorination method?,ethylene method and ethane method.Basing on the "rich coal,poor oil" energy characteristic,acetylene method is a dominant synthesis routes,which is coal-based chemical production process and takes activated carbon?AC?supported HgCl₂ as catalyst.However,emissions of mercury hazard to human and environment.Hence,it is of the essence to explore the green mercury-free catalyst.Currently,the research of mercury-free catalyst mainly includes carriers and active species?noble metals and non-noble metals?.For carriers,AC has been widely studied because of its special physical and chemical properties and low price.For active species,we have found that the catalyst took the non-noble metal Bi with abundant resources and lower cost as active component shows high catalytic activity.But its catalytic activity still needs to be improved compared with the noble metal catalyst.Steam pretreatment to AC can optimize pore structure of AC,improve its specific surface area,and improve the activity of the catalyst.In addition,steam regeneration of the deactivated catalyst can restore the catalytic activity and the regenerated catalyst is green and recycled.Steam method is applied in the AC pretreatment and catalyst regeneration,but it has not reported in acetylene hydrochlorination,and there are no exhaustive discussions of structure-activity relationships between AC properties and catalytic performance for acetylene hydrochlorination.Therefore,the paper takes Bi/AC catalyst as a research object,and screens the process conditions of steam pretreatment to AC by using the single-factor experiment and orthogonal experiment,and discusses effects of steam pretreatment on catalytic performance,which are combined with the BET,SEM,FT-IR,XRD,TEM,TGA,XPS and NH3-TPD characterization methods.And steam regeneration to deactivated catalyst,the interactions between steam regeneration and catalyst are investigated.We also try to improve the catalytic performance by using addition of additives,oxidation pretreatment of AC and acid modification of catalyst.The research content and conclusions are as follows:?1?The Bi/AC catalysts were preparated,which took the coal AC as the carrier,and BiC_l3?mass fraction: 25%?solution as impregnation liquid,and used in acetylene hydrochlorination.To improve the catalytic activity?C₂H₂ conversion?,steam pretreatment to AC was used to optimize its pore structures.The single-factor experiment and orthogonal experiment were designed to optimize the steam pretreatment conditions.At the temperature of T = 600 ?,time of t = 3h and flow rate of Q = 30 mL/min,AC had higher specific surface area of 786 m²/g.And the C₂H₂ conversion of its supported Bi-based catalyst was up to 86.06%,the conversion increased by 34.4% compared with the catalyst without steam pretreatment?the C₂H₂ conversion was 64%?.The range and variance analysis of orthogonal data found that the influencing order of three factors?steam pretreatment temperature?A?,time?B?and steam flow?C??on the catalyst performance was as follows: A ? B > C.?2?Two kinds of AC?AC1 and AC2?with different pore structures were pretreated by using steam.The catalyst performance of steam-pretreated AC?SAC1 and SAC2?supported Bi-based catalyst?Bi/SAC1 and Bi/SAC2?were compared.And combined with characterization methods,effects of steam pretreatment on AC and catalysts were analyzed.The results showed that Bi/SAC1 catalyst had the best catalytic activity,and the increment of catalytic activity in Bi/SAC1 catalyst was higher than that of catalytic activity in Bi/SAC2 catalyst.Characterizations results showed that AC1 was the domination of mesopore,but for AC2,micropore was primary.Steam pretreatment reorganized the pore size and channel structure of AC,increased its specific surface area.But effects of steam pretreatment on mesoporous structure AC1 were more obvious,and new micropore structures were formed.To the Bi/SAC1 catalyst,the crystallinity and dispersity of active component Bi OCl were increased,and the amount of coke deposition was decreased.Meanwhile,additing the auxiliaries to modify catalyst,the results showed that the addition of La improved the catalytic activity,and the C₂H₂ conversion was up to 91.20%.Adding the auxiliary Ba,the catalytic stability was improved obviously,and the C₂H₂ conversion remained 80% after 11 h.?3?The deactivated catalysts were regenerated by using steam,and the catalytic performances of regenerated catalysts were tested.The results showed that the activity of regenerated catalyst was recovered,the C₂H₂ conversion was 76% and recovery rate was 87.9% comparied with the fresh catalyst?C₂H₂ conversion was 86%?.Characterizations results showed that the generation of coke deposition caused a rapid deactivation of catalyst.After steam regeneration,coke deposition was removed,the specific specific area of catalyst was increased,and globular active component BiOCl was appeared.At the same time,by using HNO₃ oxidation to activated carbon and HNO₃ modification to catalyst,the catalytic activity was improved.Characterizations results showed that the coke deposition was removed,and the morphology and crystallinity of active component BiOCl were also changed after steam regeneration.