Study On A New Synthetic Process Of L-Lactide

With the promulgation of the plastic restriction order,polylactic acid as a biodegradable material has attracted much attention.L-lactide,an important chemical intermediate for the synthesis of polylactic acid,has become increasingly important.Currently,there is still a technical bottleneck in the synthesis of L-lactide,and the domestic production capacity is insufficient,mainly relying on imports.Therefore,it is particularly important to develop a process for large-scale production of L-lactide.In recent years,basic research on the synthesis of L-lactide has mainly focused on the design of catalytic systems.Since the synthesis of L-lactide requires high temperature(above 200 ℃),in order to economically and efficiently synthesize high-purity L-lactide,a catalytic system that is resistant to high temperature and has high catalytic activity must be designed.Polyaniline is a non-toxic and harmless compound that does not cause harm to humans or the environment.Polyaniline catalysts have good stability and heat resistance,can maintain catalytic activity at high temperatures,are not easily deactivated or decomposed,and can be reused,reducing catalyst usage costs and environmental pollution.Therefore,the use of polyaniline catalysts is a good choice for the synthesis of L-lactide.This article will focus on the catalytic synthesis of L-lactide using polyaniline catalysts loaded with metals.The specific research content is as follows:1.In order to reduce the metal content in the catalytic system,the polyaniline catalyst was successfully synthesized by the green and environmentally friendly hydrogen peroxide oxidative polymerization method,and the zinc-supported polyaniline catalyst was finally synthesized by screening the catalytic activity of transition metal ions.Through the single factor variable experiment,the influence of the substituent of aniline,the condensation polymerization time of the reaction,the amount of catalyst,and the cracking temperature on the reaction were investigated,and the optimal reaction conditions were obtained.Under these conditions,L-lactide with an optical purity of 98.2%can be synthesized with a yield of 84%,and only a small loss of catalytic activity after 9 cycles,indicating that the catalyst has excellent catalytic performance.Afterwards,the material characterization was carried out,and the most likely reaction mechanism was obtained through the experiment of mechanism exploration,which provided a catalyst with low metal content suitable for industrial production for the synthesis of L-lactide.2.To design a biocompatible catalytic system,a calcium-supported polyaniline catalyst was successfully synthesized by oxidative polymerization of ammonium persulfate,and a calcium composite catalytic system was designed to synthesize L-lactide.The amount of calcium oxide,the prepolymerization time,the amount of cracking catalyst,and the cracking temperature were investigated through single factor experiments,and finally the best reaction conditions were determined.Under these conditions,L-lactide with an optical purity of 98.1%can be synthesized with a yield of 74.5%,and the yield can still be maintained above 70%after 4 cycles,although the cycle performance is slightly lower than that of Zinc-loaded polyaniline system,but this catalyst is green and environmentally friendly.Afterwards,in order to explore its mechanism,the method of material characterization was used to explore.It was found that the specific surface area of the material increased by 96.8%after calcium doping,which improved the catalytic activity,and the most likely reaction mechanism was obtained through mechanism exploration experiments.A new catalytic strategy for the green synthesis of L-lactide is provided.3.By comparing the work of the previous two parts,the more durable Zinc-supported polyaniline catalyst was finally selected for the kilogram-scale amplification reaction.At the same time,the synthesis process route was optimized,and the polymerization time,catalyst dosage and cracking temperature of the kilogram-scale reaction were designed through orthogonal experiments,and the feeding sequence was optimized.After optimization,the yield increased by 8.7%.Afterwards,the recrystallization solvent of lactide was screened,and the impurities in L-lactide were analyzed to provide help for the establishment of a quality control system for L-lactide.