Study On Catalytic Hydrogenation And Decarbonylation Of Dimethyl Oxalate

With the depletion of global oil resources and over-exploitation of oil,environmental problems have become increasingly serious.Considering the national conditions of lean oil,less gas and more coal in China,it is becoming increasingly important to develop C1 chemistry and a non-petroleum route to develop an efficient and green synthesis process.Dimethyl oxalate?DMO?can be formed by the gas-phase CO coupling reaction,which is a mature route in coal chemical industry.Therefore,dimethyl oxalate can be selectively hydrogenated to methyl glycolate?MG?and ethylene glycol?EG?,and decarbonylated to dimethyl carbonate?DMC?,forming a new non-oil-based synthesis method.This dissertation carried out the following work around the above process route:?1?Catalytic Hydrogenation of Dimethyl Oxalate to Methyl Glycolate andEthylene Glycol on Ag/SiO₂Ag/SiO₂ catalysts with different Ag particle size were prepared by in-situ ammonia evaporation method.The effects of silver loading,calcination temperature,and ammonia evaporation time on the catalytic activity were investigated.During the gas-phase hydrogenation of dimethyl oxalate,10%Ag/SiO₂ catalyst showed the best activity with 85%conversion and 95%selectivity to methyl glycolate at 195?.The catalyst was further optimized and it was found that the catalytic activity was best at a calcination temperature of 350?and an ammonia evaporation time of 0.5 h.At240?,the conversion is more than 99%,the selectivity to ethylene glycol is greater than 97%,and the high activity and selectivity are maintained for 600 h during the stability test.Moreover,the formation of Ag₆SiO₇ was confirmed by characterizations,favoring the enhancement of the interaction between the active metal species and the support and thus,facilitating the formation of uniformly dispersed silver nanoparticles.Ag nanoparticles with suitable size can not only ensure the adsorption of DMO molecules,but also improve the hydrogenation reaction,delivering good catalytic activity.?2?Catalytic Decarbonylation of Dimethyl Oxalate to Dimethyl Carbonate on Rb₂CO₃@CRb₂CO₃ catalysts supported on activated carbon or carbon nanotubes showed high catalytic activity and selectivity for DMO decarbonylation to DMC.However,due to the weak interaction between Rb₂CO₃ with the support and the sensitivity of Rb₂CO₃ to moisture,the active sites of the catalyst are easily lost during the reaction.Therefore,it is still a challenging subject to improve the stability of catalyst.Based on the above-mentioned key issues,an extremely simple carbon coating method was designed.A layer of carbon was wrapped over the surface of Rb₂CO₃ to prepare Rb₂CO₃@C catalyst in one step.The catalyst preparation conditions were optimized for decarbonylation of dimethyl oxalate,including alkali metals,loadings,and calcination temperatures.Meanwhile,the catalytic activity was measured at different reaction temperatures and reaction times.Preliminary studies showed that 80%DMO conversion and 99%selectivity to DMC could be achieved over Rb₂CO₃@C catalysts.