Study On Ruthenium-based Catalytic System For Selective Hydrogenation M-Phenyldimethylamine To 1,3-Cyclohexamethylamine

1,3-cyclohexanedimethylamine,as an important organic chemical and fine chemical intermediate,has been widely used in epoxy resin,composite materials and other fields,and is also an important raw material for the synthesis of isocyanate.At present,some efforts have been made in the study of the catalytic system for the selective hydrogenation of m-phenyldimethylamine to 1,3-cyclohexanedimethylamine,while there are still some challenages:(1)the occurrence of side reactions such as demethylamine in the reaction system can not be effectively suppressed;(2)there are only a few reports about the process conditions of fixed-bed hydrogenation,which need to be further explored and studied;(3)The stability of the catalyst still needs to be improved.In this paper,the supported ruthenium-based heterogeneous catalytic system for catalytic hydrogenation of m-phenyldimethylamine was explored,and the reaction thermodynamics,the screening of catalysts,the characterization of catalysts and the correlation of catalytic structure and activity,stability of catalyst and reaction conditions were studied systematically.The fixed bed hydrogenation conditions of m-phenyldimethylamine were also explored.The main contents and conclusions were summarized as:(1)Impregnation method was employed to prepare ruthenium-based catalysts with diverse supports,and Ru/Al2O3 catalyst showed superior activity.Under the optimal conditions of Ru loading of 5%,130?,5 MPa,4 h,the conversion of m-phenyldimethylamine was 100%with 87.7%selectivity of 1,3-cyclohexyldimethylamine.NH3-TPD results suggested that the strength and the number of acidic sites on the surface of alumina support were less,which could inhibit the side reaction.In addition,the thermodynamic data of the reaction were calculated via the group contribution method,and the results discolsed that the by-product in this reaction could be ascribed to the further hydrogenation of 1,3-cyclohexyldimethylamine.(2)Li2CO3,LiNO3 and LiOH were introduced to optimize the catalytic performance of Ru/Al2O3 catalyst,and it found that the catalyst modified by LiOH exhibited better performance.The characterization results of catalyst showed that Li2Al4CO3(OH)12·3H2O,new substance,was formed after the introduction of LiOH promotor,which could enhance the surface strength and the number of alkaline sites.Meanwhile,the Ru particle size decreased with a greater dispersity.Under the optimized reaction conditions,the selectivity of the 1,3-cyclohexanedimethylamine was 97.9%.(3)Under the conditions of 0.5 g catalyst,3 MPa,130?,0.3 h-1 LSVH,y and 200 molar ratio of hydrogen to amine,the conversion of m-phenyldimethylamine was 100%and the selectivity of 1,3-cyclohexane was 96.9%in the fixed bed with 5Ru-25Li/Al2O3 as catalyst.During the on-stream test,the structure of Ru and Li2Al4CO3(OH)12·3H2O,the active component of catalyst was maintained,and the strength and number of alkaline sites maintained a balance level almost.The loss of Ru which was responsible for the active component of the catalyst was serious,leading to the decrease of XDA conversion during the reaction.At the same time,the decrease of specific surface area and pore volume of the catalyst is not benefitial to mass transfer of the reaction liquid and providing more hydrogenation active sites.