Study On The Construction Of Synergistic Catalysis System And Reaction Mechanism For PET Catalytic Alcoholysis

Polyethylene terephthalate(PET)has a wide range of applications.The output and consumption of PET increase year by year,resulting in a large number of waste PET,will bring serious ecological and resource problems.The chemical recovery of PET polyester is of great significance to solve the white pollution,protect the environment and reduce the dependence of plastics industry on petrochemical resources.PET alcoholysis can degrade waste PET into bis(2-hydroxyethyl)terephthalate(BHET)under mild conditions.After that,rPET can be obtained by separating and purifying BHET and then polymerization,which is an effective way to realize the green cycle of PET.In this dissertation,a variety of catalysts with different properties were designed for PET alcoholysis,and the internal relationship between the structure and properties of the catalyst and the degradation efficiency of PET was explored.The possible catalytic reaction mechanism of different catalysts was proposed,which provides an important theoretical basis for the efficient alcoholysis of PET and the separation and purification of products.Major innovative developments are as follows:(1)A series of L acid supported metal oxide catalysts were prepared with SBA-15 as support,and the catalytic activity and reaction mechanism of the catalysts for alcoholysis of PET were studied.Compared with the traditional catalyst,5%ZnO/SBA-15 has higher catalytic activity.Under the optimized reaction conditions,the PET conversion rate is 100%,the BHET yield is 91.0%,and the BHET color of the product has obvious advantages.The catalytic activity of 6 cycles remained unchanged.The results show that the metal oxides supported by SB A-15 mainly break the PET ester chain through the interaction between the L-acid and the PET carbonyl group on the catalyst surface.The high specific surface area and large pore size are favorable for the adsorption of PET on the catalyst surface.The mechanism of action of PET on different crystal surfaces of ZnO and the first order reaction kinetics of catalytic alcoholysis of PET ethylene glycol were obtained.The apparent activation energy was 215.9 kJ/mol.(2)The functionalized amino acid nonmetallic ionic liquid catalyst was prepared.Among them,[Bmim]Pro has a good catalytic activity in the alcoholysis of PET.Combined with theoretical calculation,it is found that the efficiency of alcoholysis of PET is closely related to the electronegativity of the anionic carboxyl oxygen.The stronger the electronegativity,the higher the catalytic efficiency.Response surface methodology(RSM)was used to investigate the effects of independent parameters on the PET efficiency of catalytic alcoholysis.The order of the effects of independent parameters on the reaction was as follows:temperature>time>mass ratio of ethylene glycol to PET.The optimized reaction parameters were obtained as follows:temperature 197?,time 89 min,mass ratio of ethylene glycol/PET=5,PET conversion rate was 100%,BHET yield was 75.5%,and the catalytic activity was not significantly reduced after 6 cycles.The possible mechanism of[Bmim]Pro catalyst catalyzing PET alcoholysis with multiple hydrogen bonds was proposed.The reaction process of catalytic alcoholysis PET was consistent with the kinetic model of nuclear shrinkage reaction,and the apparent activation energy was 142.5 kJ/mol.(3)The strengthening mechanism of alkaloids in the process of PET alcoholysis was studied,and the reaction mechanism of acid-base synergistic catalysis of PET alcoholysis was proposed.The catalytic efficiency of alkaloids and their derivatives in PET alcoholysis was investigated.It was found that the basic site was strongly beneficial to the breaking of PET ester bond.When the ratio of betaine/Zn(NO3)2 was 1:4,the yield of BHET was 83.7%after 70 min of complete alcoholysis.The mechanism of the synergistic catalysis of PET alcoholysis by the hydroxy hydrogen bond between betaine and ethylene glycol and the coordination of Zn(NO3)2 and PET carbonyl group was proposed.At the same time,the changes of PET morphology in the three catalytic systems were investigated,and the transformation mechanism of PET swelling and etching in the acid-base synergistic catalytic system was obtained.Kinetic results further confirmed the strengthening effect of betaine in the reaction.(4)The solubility of ethylene glycol alcoholysis product BHET in ethylene glycol,methanol,ethanol,water and different proportions of ethylene glycol and water binary solvents was studied by static method.With the increase of temperature,the solubility of BHET in various solvents increases.At the same temperature,the order of solubility of BHET in different solvents was as follows:methanol>ethanol>ethylene glycol>water.The solubility of BHET in binary solvent system increases with the increase of the mass fraction of ethylene glycol.The Gibbs free energy,enthalpy and entropy of dissolution of BHET in various solvents were calculated by using different models.