Study On The Modified ZrO₂/SiO₂ Catalyst For The Synthesis Of 1,3-butadiene From Ethanol

1,3-butadiene is an important chemical product in petrochemical industry which is widely used in the production of synthetic rubber.Currently,butadiene is predominantly obtained via extractive distillation from C4 steam cracker fractions.With the overexploitation of oil resources,the promotion of our environmental consciousness and the impact of shale-gas revolution on the butadiene industry,there is a strong urge to seek a green route in producing 1,3-butadiene.The mature production technology of biomass ethanol makes ethanol become a potential feedstock in the synthesis of butadiene.In this work,we studied the modified ZrO₂/SiO₂ catalyst which was obtained by Sol-Gel method,the deactivation and regeneration of the catalyst and the method of coking inhibition during the reaction.Various additives?Cu,Zn,Ag,Mn,Mg?were investigated and the results showed that ZrO₂/SiO₂ catalysts modified by Zn had a better activity and excellent selectivity to the target product.The acid?Lewis acid sites?strength was more important to the formation of butadiene than acidic amount for modified ZrO₂/SiO₂ catalysts.The influences of two different doping methods on the catalytic activities were investigated,and the method of mixed Sol-Gel performed better.Catalysts prepared by this method had higher specific surface area,bigger pore size and suitable acid strength on the surface.Moreover,the interaction between Zn and Zr also enhanced the catalytic activities.The 0.5 wt% ZnO modified ZrO₂/SiO₂ catalyst was the most beneficial to the formation of butadiene.The results of process technological optimization showed that the optimal conditions for the synthesis from ethanol were temperature of 320 ?,3.5:1 molar ratio of ethanol-to-acetaldehyde,and a WHSV of 1.8 h^-1.The highest butadiene selectivity of 84.2% was obtained.It was shown that the selectivity of butadiene and conversion on the catalyst would decrease by about 10% after reaction for 60 h.The deactivation of the catalysts was caused mainly by the carbon deposition,and the deposed carbon content was linearly increasing with the reaction time.There were two types of carbon deposition,namely low temperature?400 ??and high temperature?520 ??carbon deposition.The carbon species mainly consisted of saturated carbon,carbon-oxygen single bond carbon and a small quantity of aromatic carbon and olefins carbon.The existence of carbon species could lead to the decrease of specific surface area,the average pore diameter and the coverage of weak acid sites.The deactivated catalyst could be regenerated by the simple oxidation treatment process with air.Moreover,adding a certain amount of water in feed could not only inhibit the carbon deposition,but also enhance the selectivity of 1,3-butadiene.