Study On Palladium-based Catalysts For Catalytic Hydrogenation Of Maleic Anhydride To Succinic Anhydride

Maleic anhydride(MA)and its hydrogenation products succinic anhydride(SA),gamma-butyrolactone(GBL)and tetrahydrofuran(THF)are all chemical raw materials with high added value and widely used in industry.Succinic anhydride is used as an intermediate of the degradable plastic PBS.Therefore,the synthesis and preparation of succinic anhydride has become a recent research hotspot.The selective catalytic hydrogenation of maleic anhydride to prepare succinic anhydride has the features of simple process flow,low production cost and environmental protection.It is currently one of the most widely used method for preparing succinic anhydride in industry,but the catalytic hydrogenation of maleic anhydride is a relatively complicated parallel and consecutive reaction.Mainly facing two problems of how to selectively hydrogenate C=C and C=O double bonds,and avoid side reactions,producing water and acid.Indeed,how to develop and design a catalyst with high selectivity and high stability is the important and difficult point of this research.For the above two issues,a Pd-based double metal catalyst with a special alloy structure was designed and prepared in this thesis,followed by design experiments to verify and determine the ideas.First,a series of Pd-based bimetallic catalysts with different metal promoters and different monometallic catalysts were prepared by chemical precipitation and impregnation methods.It was found that the reaction activity and SA selectivity of Pdbased bimetallic catalysts were significantly higher than that of monometallic catalysts.Through structure-activity relationship analysis,it is found that the PdNi bimetallic catalyst has strong hydrogenation activity.The catalyst actually has a strong hydrogen activating ability and is more effective to adsorb the substrate.The 0.5Pd2Ni-AC catalyst has the strongest hydrogen activating ability compared with other catalyst,and the cheaper transit metal Ni and precious metal Pd have the best synergistic effect,making the catalytic MA hydrogenation performance the most excellent.The second study is on the effect of the support and loading on the selective hydrogenation of the PdNi bimetallic catalyst.By changing the support of the Pd-based catalyst and the loading of active component Pd,the effect of the characteristics of the support,the distribution and the existence of Pd on the performance of the hydrogenated maleic anhydride was studied,and the appropriate catalyst composition was screened out.Pd-based bimetallic catalysts have stronger hydrogen activating ability than singlemetal catalysts,and the hydrogen activating ability of Pd-based bimetallic catalysts increases with the increase of the precious metal Pd loading,while the 0.5Pd2Ni-AC catalyst has a moderate ability to activate hydrogen and provides a moderate number of active sites compared with other catalysts,so the selectivity of S A can reach 100%.The Pd-based bimetallic catalyst with a special alloy structure has good reaction activity and selectivity,which is beneficial to the stability of the catalyst.Finally,the influence of process conditions on the reaction system and the evaluation of catalyst stability are studied.The experiment found that 0.5Pd2Ni-AC was used as the catalyst,and after adding 0.1 g of catalyst at 443 K and 2.0 MPa and reacting for 2 h,the conversion of MA reached 99.7%and the selectivity of S A reached 100%.Moreover,test the acid resistance of the catalyst under harsh conditions.The catalyst is treated with different concentrations of succinic acid(1%～10%)before performing activity evaluation.The conversion of MA can still reach more than 98%,and the selectivity of SA is also maintained above 90%,which proves that the catalyst has excellent stability.