Study On The Pd Catalyst For The Hydrogenation Of Dimethyl Terephthalate To Dimethyl 1,4-cyclohexanedicarboxylate

DMCD is an important chemical intermediate which has attracted much attention at home and abroad in recent years.It is widely used in the synthesis of polyester resin,polyamide,alkyd resin and plasticizer.In the field of polymer industry,1,4-cyclohexanedimethanol?CHDM?occupies an important position especially for the synthesis of highly valued polyesterand polyester fibers.Because of its high symmetry,CHDM is preferred to ethylene glycol and other polyol in the production of polyester resins with good thermal stability and thermoplastic.Industrially,CHDM is prepared by a two-step process using reactors.The first step is the conversion of DMT into DMCD by the hydrogenation of the phenyl group,the second one is the scheduled conversion of carboxylic ester to corresponding alcohol,resulting in the production of CHDM.With regard to the hydrogenation of DMT,many procedures used Pd/Al₂O₃ as the catalysts.Esters are normally produced by catalytic hydrogenation over traditional Cr₂O₃–promoted Cu-based heterogeneous catalysts.However,the selectivity of Pd/Al₂O₃ catalyst for DMCD in the hydrogenation of benzene in DMT is not high,which affects the final yield.To solve this problem,our research group mainly focuses on the following three aspects:?1?Pd/Al₂O₃ with different palladium loading were prepared by equivolumetric impregnation and coprecipitation.The catalysts were used for the hydrogenation of DMT to DMCD.When the reaction temperature is 180?,pressure is 4.5 MPa,the reaction time is 4 h,the yield of 87%recycling use six times more highly active and good stability.?2?Pd/MgO with different palladium loading were prepared by equivolumetric impregnation and coprecipitation.The catalysts were used for the hydrogenation of DMT to DMCD.When the reaction temperature is 180?,pressure is 4.5 MPa,the reaction time is 3 h,the yield is 99%of highly active,recycled after five times,began to deactivation.?3?The catalysts Pd/MgAl,Pd/ZnMgAl and PdCu/ZnMgAl were prepared by coprecipitation.The catalysts were used for the hydrogenation of DMT to DMCD.When the reaction temperature is 180?,pressure is 4.5 MPa,the reaction time is 4 h,highly reactive and yield of 98%recycled six times the better stability of deactivation.