Study On New Type Composite Catalyst And Ternary Copolymerization Of Carbon Dioxide

The air is rich in carbon dioxide(CO₂),and products such as urea,dry ice and beverages can be produced using CO₂ as a raw material.In order to expand the scope of CO₂ utilization,CO₂ can be used as a raw material for polymer production to explore,so as to reduce the dependence of polymer production on petroleum and coal resources,and achieve the goal of"carbon peak"on schedule.CO₂ capture and utilization is currently considered to be one of the most effective ways to reduce carbon emissions.CO₂can be turned into a treasure,and CO₂ can be used as a resource while reducing emissions.Due to the relatively stable nature of CO₂,it becomes more difficult to convert it into other substances,and it is necessary to explore efficient catalysts.An ideal high-efficiency catalyst usually requires high catalytic activity,high selectivity and good thermal stability at the same time.Under high temperature and high pressure reaction conditions,it is often difficult for a single catalyst to have the above advantages at the same time.In this study,according to the characteristics of the catalyst,a promoter is added to improve the catalytic performance of the catalyst.According to the respective advantages of the homogeneous catalyst and the heterogeneous catalyst,two or three catalysts are combined to prepare a composite catalyst.The composite catalyst is left alone.The advantages of the catalyst also show unique synergistic catalytic properties,which can further improve the efficiency of catalytic chemical reactions.Under the action of a catalyst,CO₂ and propylene oxide(PO)can directly react to form a binary polycarbonate copolymer,which is a degradable polymer material,but its physical and chemical properties are poor,such as brittleness and lack of Flexibility is not conducive to practical applications.In order to improve the physical and chemical properties of the copolymer,a third monomer is introduced in the reaction to react with CO₂ and PO to obtain a terpolymer.Terpolymer is a biodegradable polycarbonate with superior thermal and mechanical properties.In this study,the newly prepared catalyst was used to catalyze the copolymerization of CO₂,PO and the third monomer,and the synergistic effect and catalytic mechanism were studied.Finally,the obtained product was degraded.The main research work is as follows:1.The ternary polymerization of CO₂,PO and DL-lactide with quaternary ammonium salt(QAS)assisted Zn-Fe DMC catalyst was studied.The results show that adding QAS as a co-catalyst to the Zn-Fe DMC catalyst can significantly improve the efficiency of the polymerization reaction of CO₂,PO and DL-lactide.The polymer PPCLA obtained by the reaction has a lower polymer dispersibility index(PDI),the catalyst shows better activity and selectivity.The polymerization process was studied.The chain growth of CO₂,PO and DL-lactide ternary polymerization reaction takes zinc atom as the active center.In the chain growth reaction of copolymerization reaction,the steric hindrance of the intermediate product increases with the insertion of CO₂.The chain increases.The auxiliary catalyst QAS can effectively reduce the steric hindrance of CO₂,PO and DL-lactide copolymerization products,promote the insertion of DL-lactide and CO₂ into the main chain of the copolymer,greatly increase the conversion rate of CO₂,and promote the chain growth of the copolymer After the reaction,the degree of polymerization of the product was significantly increased,and the carbonate content reached 41.44%.It shows that the introduction of QAS into Zn-Fe DMC catalyst can significantly improve the catalytic activity and selectivity of CO₂,PO and DL-lactide polymerization.2.By preparing a zinc glutarate/rare earth ternary compound(ZnGA/RET)composite catalyst to catalyze the copolymerization of CO₂,PO and itaconic anhydride(ITA),a polycarbonate with good molecular weight and thermal stability was obtained.Based on the single factor experiment,the ZnGA/RET composite ratio and the influencing factors of the copolymerization reaction were optimized through the response surface.The results show that the Box-Behnken mathematical model based on the response surface simulation has high significance,the predicted value has good consistency with the actual value,the data has no obvious deviation,and the data simulation is normal.Therefore,the model can reasonably analyze the influencing factors of the synthesized product PPCITA,optimize the polymerization reaction conditions,and predict the relative molecular weight of PPCITA.Through simulation,the optimal ternary polymerization reaction conditions are:70.52?,4.6MPa,20h,PO:ITA=13.18:1.Three parallel tests were carried out under optimal conditions.The average molecular weight of PPCITA is 8.87×104(g/mol),the relative deviation from the best response value of 9.03×104(g/mol)predicted by the model is 1.81%,and the relative error is small.The maximum temperature of PPCITA's thermal stability is386?,indicating that the optimized reaction parameters of the response surface model can truly reflect the process conditions.3.By preparing a zinc glutarate/salicyaldimine cobalt(ZnGA/Salen-Co(?))composite catalyst to catalyze the copolymerization of CO₂,PO and maleic anhydride(MA),a higher yield and better quality Polycarbonate.The catalyst retains the original structure and characteristics of ZnGA and Salen-Co(?)catalysts,and produces unique catalytic characteristics after being compounded.In the experiment,the catalytic effects of different composite ratios were investigated.Among them,ZnGA/Salen-Co(?)-10:1 catalyst synthesized aliphatic polycarbonate in the copolymerization of CO₂,PO and maleic anhydride(MA).The molecular weight is 7.97×104(g/mol),and the yield is 69.3 g/g.During the reaction process,the Salen-Co(?)catalyst not only provides active CO₂ for the ZnGA catalyst,but also provides the intermediates with alternating structures to the ZnGA catalytic reaction to generate the three with better thermal and mechanical properties.Yuan copolymer.4.The catalytic effect of the DMC/RET/ZnGA composite catalyst on the ternary copolymerization of CO₂,PO and trimellitic anhydride(TMA)was studied,and the difference between the composite catalyst and the single catalyst was compared and analyzed.The results show that compared with the traditional single-use catalyst,the DMC/RET/ZnGA composite catalyst system can simultaneously exhibit the high catalytic activity of DMC,the high catalytic selectivity of RET and the good thermal stability of ZnGA.During the experiment,the effects of different preparation methods on the crystallinity and particle size of the double metal cyanide catalyst(DMC)and the effect of DMC on the ternary copolymerization of CO₂,PO and trimellitic anhydride(TMA)catalyzed by the composite catalyst were also deeply studied.The results show that the mechanical ball milling process can significantly reduce the particle size and crystallinity of DMC,increase its surface active sites,and increase the contact area of the DMC catalyst.The DMC/RET/ZnGA composite catalyst obtained by combining with RET and ZnGA is more active.It has the advantages of higher product yield and stronger thermal stability in the catalytic reaction,and the yield is as high as 66g poly/g cat.5.The degradation of 5 kinds of copolymers including PPC,PPCLA,PPCITA,PPCMA and PPCTMA were studied.The results showed that in the phosphate buffer with p H=7.4,all five copolymers were degraded.Among them,the terpolymers PPCLA,PPCITA,PPCMA and PPCTMA were the most degradable.At the 15th week,the degradation reached 90%.The structure of the product was destroyed,and the large molecular weight substance no longer existed.The experiment verified the good degradability of polycarbonate.