Deactivation Mechanism Of Soluble Alkali And Magnesium Oxide Catalysts For The Synthesis Of Carbonate By Transesterification

Ethyl carbonate?EMC?,which is an extensive used asymmetric carbonate,is mainly applied as a co-solvent for lithium-ion batteries.Currently,CH₃ ONa is industrially used for production of EMC by the transesterification of dimethyl carbonate?DMC?with ethanol?EtOH?.Due to the formation of three binary azeotropes during this reaction stystem,reactive distillation was devoted to increase the purity of desired product EMC.The catalytic efficiency of CH₃ ONa is excellent,but the activity decreased obviously after recycling and a large number of white insoluble solids were formed,resulting in the decline of EMC purity.In this work,we studied the deactivation of soluble base as well as magnesium oxide catalysts for the synthesis of carbonates during different transesterifications.The effect of various Na-based soluble basic catalysts?C₄H₉ONa,C₂H₅ONa,CH₃ONa,KOH,NaOH,Na₂CO₃,Na HCO₃ and Na F?on catalytic activity of EMC synthesis were investigated.The relationship between alkali strength and catalytic activity was established by introducing p Kb value?alkalinity coefficient?.The results indicated that NaOH and CH₃ONa catalysts were obviously deactivated,while Na₂CO₃ with low efficiency showed excellent stability.A series experiments about soluble base were investigated from the catalyst structures,amounts,reaction atmospheres and reactants treatment,the results revealed that reactant DMC was the key reason of the deactivation.Pretreatment of NaOH or CH₃ONa catalysts with DMC for different time,respectively.Characterization and analysis of catalysts fresh,DMC-treated,recycled NaOH and CH₃ONa samples was carried out.The XRD and FT-IR analysis showed that the formation of new species CH₃OCOONa intermediate.Combined with Raman,TG and SEM characterization results,the final deactivation species was Na₂CO₃ during this reaction system.Based on the above results,a possible deactivation mechanism about soluble base catalysts was proposed.The CH₃ONa catalyst might first react with H₂O coming from reactant to form NaOH,and then NaOH could react further with DMC to produce CH₃OCOONa.OH-would attack the intermediate CH₃OCOONa,causing the formation of Na HCO₃.NaHCO₃ might further react with NaOH to produce Na₂CO₃,which has poor catalytic activity and solubility in the system,leading to the complete deactivation of soluble base.The stability and deactivation of heterogeneous MgO catalyst during different transesterification routes were also investigated.When MgO catalyst was used for EMC synthesis by the transesterification of DMC with EtOH,DMC with diethyl carbonate?DEC?,exhibiting the excellent stability for a few hundred hours.However,when MgO was applied for the transesterification of ethylene carbonate?EC?with methanol?Me OH?,propylene carbonate?PC?with Me OH to synthesize DMC,obvious deactivation phenomenon was observed.The properties of catalysts before and after deactivation were characterized using XRD,FT-IR,TG,BET and CO₂-TPD techniques.BET and CO₂-TPD results showed that the pore size,pore volume and total alkalinity decreased seriously after catalyst deactivation,which indicated the loss of MgO with high catalytic activity and strong basicity.According to the several characterizations,the reason of MgO deactivation might be related to the adsorption of reactant or product on the surface of catalyst.