Tetramethylguanidine Ionic Liquid And Its Immobilization As Catalysts In PET Glycolysis

The rapid development of polyester industry has brought convenience to people,but also caused the corresponding environmental pollution problems.With the improvement of people's awareness of environmental protection,effective recycling is still a problem to be solved.Glycolysis is a method of reacting PET and glycol to produce small monomers.The reaction conditions are mild,and the product ethylene terephthalate(BHET)can be directly polycondensed into PET to realize the same level of recycling.The main shortcomings that currently limit this method are low reaction catalysis efficiency,low product selectivity,and complex product purification processes that result in excessively high cost of monomer BHET,so this process is difficult to popularize.Tetramethylguanidine ionic liquids exhibit high-efficiency catalytic performance in transesterification reactions.In this paper,tetramethylguanidine ionic liquid was applied to PET catalytic degradation reaction for the first time,and good results were achieved.Then we loaded the ionic liquid on the ZIFs material with stable structure and good catalytic performance to form a heterogeneous catalyst to increase its catalytic performance and recyclability.In this paper,three tetramethylguanidine metal salt ionic liquids([TMG]Cl/FeCl3,[TMG]Cl/ZnCl2 and[TMG]Cl/CoCl2)were synthesized and tested under the same reaction conditions for their catalytic activity and selectivity to degrade PET and found[TMG]Cl/ZnCl2 ionic liquid has the highest catalytic activity and selectivity.Subsequently,the influence of ionic liquid composition,reaction time,reaction temperature,amount of catalyst and amount of ethylene glycol on its catalytic performance was systematically studied.The results were as follows:The molar ratio of[TMG]Cl to ZnCl2 is 2:1,the catalyst when the mass is 10 wt%,the reaction temperature is 195?,the reaction time is 70 min,and the mass ratio of EG to PET is 5:1,PET is completely converted and the yield of the main product BHET is 83.9%.The catalytic activity and selectivity of ZIF-8 and ZIF-67 materials were tested under the same reaction,conditions,and it was found that ZIF8 is more suitable as a carrier of[TMG]Cl/2(ZnCl2)ionic liquid,and the synthesis ratio of ZIF-8 was further optimized.Then the[TMG]Cl/2(ZnCl2)ionic liquid was impregnated on the ZIF-8 material,and the reaction conditions of the[TMG]Cl/2(ZnCl2)@ZIF-8 composite catalyst to degrade PET were further studied by single factor analysis.The results show that when the catalyst mass is 0.5wt%,the reaction temperature is 195?,the reaction time is 30 min,and the mass ratio of EG to PET is 5:1,the conversion rate of PET is 100%and the yield of BHET is 85.3%.After 5 cycles of experiments,the catalytic activity of the[TMG]Cl/2(ZnCl2)@ZIF-8 composite catalyst did not decrease significantly.Finally,the kinetic relationship of the catalytic degradation reaction of PET under the optimal conditions of[TMG]Cl/2(ZnCl2)@ZIF8 composite material was studied,and it was found that the reaction conformed to the first-order reaction kinetic model,and the activation energy was 155.3 kJ/mol.