Study On Synthesis Of Pet Polyester By New Type Environmentally Friendly Titanium Catalys

Polyethylene terephthalate(PET)is the most widely used and produced thermoplastic polyester.At present,more than 80% of PET is prepared by antimony catalysts.However,the use of antimony,a heavy metal that pollutes the environment,is increasingly restricted at home and abroad,so antimony catalysts will eventually be eliminated.In contrast,titanium catalyst is the best choice to replace antimony catalyst because of its environmental protection,high catalytic activity and low price.At present,the United States and Japan have mastered the technology of mature titanium catalysts,while the domestic market mainly relies on imports.In view of this,we set out to prepare liquid titanium catalysts and evaluate their catalytic performance for PET synthesis.The purpose is to provide theoretical and industrial reference for the production of PET.Firstly,two kinds of liquid titanium catalysts were prepared by using titanate compounds as titanium source,introducing different hydroxycarboxylic acid,phosphoric acid and phosphate compounds,combining with different solvents and other promoters.One is low concentration titanium chelate mixed with alkali metal acetate catalyst LCLT,the other is HCLT with high concentration of titanium chelate.The titanium content and structure of the catalyst were characterized by ultraviolet spectrophotometry and infrared spectroscopy.The results showed that the titanium content of LCLT catalyst was 0.45%,which had a simple complex structure.The titanium content of HCLT catalyst was 5.04%,which had a relatively stable chelate structure.The storage stability and hydrolysis resistance of the catalyst showed that both catalysts had certain hydrolysis resistance,and the storage stability and hydrolysis resistance of HCLT catalyst were better than those of HCLT catalyst.Secondly,PET was synthesized in a 5 L polymerizer,and the performance of the two catalysts was evaluated.The effects of reaction temperature,catalyst dosage and catalyst addition method on the polymerization were explored.After comprehensive analysis,the optimum reaction conditions were obtained.The result shows that the two catalysts have good catalytic activity for the synthesis of PET;the best adding time is before esterification;the best stirring speed is 90 r.p.m;the best discharge power is 100 W;the best esterification temperature range is 220～240 ℃;the best reaction temperature range of prepolycondensation is 260～270 ℃,and the reaction time is 30 min.Under the condition of vacuum degree less than 100 Pa in polycondensation stage,the optimal addition amount is6～7 ppm,polycondensation reaction temperature is 275～280 ℃,and the reaction time is about 90 min for LCLT catalyst.As for HCLT catalyst,the optimal addition amount is 5～6ppm,the polycondensation reaction temperature is 270～275 ℃,and the reaction time is about 60 min.The performance of PET products prepared by the two titanium catalysts reached the same level as that of PET products prepared by ethylene glycol antimony.Finally,the scale-up experiment of PET synthesis was carried out in a 10 L polymerizer with HCLT catalyst.The result shows that the product indexes of 10 L polymerizer and 5 L polymerizer were similar.