Preparation And Properties Of Cobalt-based Catalysts For Ethylene Oxide Carbonylation

As an important chemical intermediate,1,3-propanediol is a polymerized monomer for the production of high-performance polyester materials-polytrimethylene terephthalate.It is widely used in medicine,dyes,inks and other fields,and contains huge economic value,making the rapid growth of 1,3-propanediol market demand.The ethylene oxide carbonylation method can be used as the preferred strategy for the preparation of 1,3-propanediol due to its low cost,mature technology and high product quality.At present,the research on the synthesis of 1,3-propanediol by carbonylation of ethylene oxide focuses on the process optimization,and there is a lack of reports on the relevant reaction mechanism and reaction kinetics,and further research is needed.In addition,the current process mainly uses homogeneous cobalt carbonyl and rhodium/complex catalysts,which are difficult to recover and difficult to separate products,which limit its industrial application.Therefore,it is very necessary to study heterogeneous catalysts to realize the reusability of hydroesterification catalysts.In this paper,the single-factor method is used to conduct experimental design first,to explore the comprehensive influence of different catalyst types,concentrations,ligand types,temperature,pressure and other conditions on the experimental results,so as to determine the optimal process operating conditions.At this time,the conversion rate of reactants can reach93%,and the yield of the product methyl 3-hydroxypropionate is over 91%.On this basis,the intrinsic kinetics of the reaction was studied,the relationship between the concentration of ethylene oxide and time under different temperature and pressure conditions was measured,and the order of the reaction to the concentration was determined to be 2,and the order of the pressure to CO was determined.The number is 0.29.Using the Arrhenius formula,the least squares method was used to obtain the pre-exponential factor A of 1.59×1013 and the activation energy Ea of 84.82 k J/mol.The kinetic model was determined.After that,a series of Co/CNT catalysts were prepared by four different preparation methods: impregnation method,deposition precipitation method,sol method and microemulsion method.Characterization methods were used to test each sample,and the catalytic effects of different catalyst preparation methods on the carbonylation of ethylene oxide were compared,and the effects of catalyst/substrate ratio,reaction conditions and other factors on the activity of Co/CNT-C catalysts were explored.The results of characterization analysis showed that the characteristic peaks of Co appeared on the four Co/CNT catalysts,the cobalt nanoparticles were successfully loaded on the carbon nanotubes,and the Co/CNT-C catalyst prepared by the sol method had a small particle size of Co species.,good dispersion,the most surface Co0 content,high reduction degree,and reduced Co0 is the active center of catalytic ethylene oxide carbonylation reaction,which can adsorb/activate CO;in addition,there is a strong bond between the metal and the carrier.The interaction can enhance the stability of the catalyst,so that the metal is not easy to precipitate.Compared with the four different preparation methods,the catalyst prepared by the sol method has higher catalytic activity for ethylene oxide carbonylation.The EO conversion of 33.7% and the selectivity to methyl 3-hydroxypropionate of 92.6% were achieved,while the impregnation activity was only 7.16% conversion and 86.9%ester selectivity.