Study On Hydrogenation Modification Of Polydivinyl Acetylene Over Pd-M?Ni,Zn?/Al₂O₃ Catalyst

Divinylacetylene(DVA)is a by-product of the production process of chloroprene rubber.The structure of DVA contains a triple bond,two double bonds and forms conjugated structure,so the chemical properties are very active and it is highly prone to polymerization to form polydivinylacetylene(PDVA).PDVA which belongs to unsaturated polymers,is insoluble in most organic solvents and is stable to acids,alkalis,chlorine and water.It can be used in surface coatings,such as waterproof coatings,metal surface protective layers,etc.However,there are some problems in the application process.Due to the poor adhesion,the coating can be wrinkled,peeled,or even peeled off after being dried by light,which limits its application.In response to this problem,the chemical modification method can be used to change the structure and properties of the PDVA,which is expected to improve its application performance.The chemical modification methods of unsaturated polymers mainly include hydrogenation,halogenation,hydrohalogenation,cyclization and cis-trans isomerization,etc.Among them,catalytic hydrogenation is a common method for chemical modification of unsaturated polymers.The process is clean and non-polluting,and the structure and properties of the hydrogenation product can be selectively regulated by optimizing the catalyst and hydrogenation conditions.At the same time,the heterogeneous catalyst used in the catalytic hydrogenation process has an incomparable advantage in actual production,because it is easy to separate from the product and can be used repeatedly.In view of the technical needs of factory for chemical modification of PDVA,combining with the technical advantages of catalytic hydrogenation,the preparation of Pd-based catalysts and related applications were carried out.Specifically,Al2O3 was used as support,and Pd/Al2O3 and Pd-M/Al2O3catalysts(M=Ni,Zn)were prepared via the impregnation method by introducing the second metal promoters Ni and Zn.The catalytic performanceof the hydrogenation reaction of PDVA was investigated,and the anti-cracking performance of the hydrogenated product was also investigated by using a simulated solar device.The catalysts were characterized by N2-physisorption,H2-TPR and NH3-TPD,etc.to analyze the texture,reduction properties and surface acidity,and the reasons for the differences in structure and catalytic performance of various catalysts were explored in depth.On this basis,Pd-Zn/Al2O3 with better activity was used as the research object.The effects of reaction pressure,temperature,time and catalyst dosage on the hydrogenation degree of the PDVA were investigated to ensure the suitable technological conditions.Finally,the reusability of the catalyst was also investigated.The main contents include the following aspects:1.The catalytic activities of Pd/Al2O3,Pd-Ni/Al2O3 and Pd-Zn/Al2O3 catalysts for PDVA hydrogenation reaction are significantly different.Compared with Pd/Al2O3,the introduction of Zn exhibits obvious promotion on the catalytic activity,while Ni suppresses the hydrogenation activity.At the same time,the hydrogenation products on the Pd-Zn/Al2O3 catalyst show better property of crack resistance.Various characterization results show that the addition of Zn facilitates the formation of more ?-Pd Hx and reduces the amounts of strong acid sites on the catalyst surface,thus the dispersion and reduction of the active component are promoted.Therefore,the Pd-Zn/Al2O3 catalyst exhibits excellent hydrogenation activity.After the addition of Ni,the amounts of strongly acidic sites on the surface of the catalyst significantly increase due to the strong interaction with the support and Pd,which results in the aggregation of particles on the surface of the support.Thus the hydrogenation activity of PDVA is inhibited.2.Suitable technological conditions for the hydrogenation reaction of polydivinylacetylene with Pd-Zn/Al2O3 catalyst,namely: the amount of raw materials is 30 ml,the reaction pressure is 1.0 MPa,the reaction time is 2 h,the reaction temperature is 100 ?,the stirring speed is 300 r/min,and the amount of catalyst is 1.0 g.The results of reuse performance tests show thatthe catalytic activity of the Pd-Zn/Al2O3 catalyst decreases after the first use under these conditions,but after repeated use for four consecutive times,the hydrogenation degree of the PDVA gradually becomes stable and shows a certain degree of reusability.