A Study Of Lactide Synthesis Process On Pilot Scale

PLA(Poly-Lactic Acid) is characterized by its biodegradation. It will be widely used. Ring-opening polymerization is the main path to synthesize PLA through intermediate compound lactide. Any fluctuation in production costs of lactide is bound to influence price of PLA. For the sake of PLA, the research on continuous process flow of lactide synthesis, as well as auxiliary recovery techniques, which are aimed to further the industrialization, bring down the manufacturing costs, and broaden field of application, need to be studied.Thermodynamic, transitive, and conductive properties of lactic acid, lactide and water, which are regarded as the main materiel in the synthetic process, are of vital importance to production engineering. However, all of the properties mentioned above for lactic acid and lactide were lack of experimental data. Aimed at resolving the problem, the main physical aspects, such as critical parameters, viscosity and thermal conductivity, were estimated referring to coherent documents in the second part of this article.The optimized conditions including doses of catalyst, temperature, vacuum level for synthesizing lactide were determined through theoretical research of techniques and analysis of influencing factor on the base of grasping the intrinsical discipline by orthogonal test. It was also proved that the byproduct, named oligomer, reaching up to 30% of mass of the feedstock, was inevitable. An effort on properly recycling the byproduct which was one of the most significant steps to realize industrialization was made. Recovery scheme and operating conditions directed at the property of oligomer was explored elementarily with features in synthesizing lactide after had been compared between fresh and recovery lactic acid. After several experiment, the technologic method on recover and recycle were fixed.Experiment launched further using technology and economic as indicators which derived from the experimental results the foregoing mentioned on the semi-plant within the capacity of producing 100t lactide per year. Either the process flow or the feature of equipment was elaborated on. On what the many different kind of factors influenced the medium scale pilot was discussed, and how to solving the current problems were advised in brief.After repeating experiment on semi-pilot, technological conditions and process flow were feasible, while technology and economic indicators were credible. Current semi-pilot laid the first stone for the process units within capacity of 1000t lactide per year. The new larger scale plant was made a preliminary sketch, optimizing the process flow, and making the cost-effectiveness analysis for economic viability.It was of great significance to make preparation for standardized mass production of PLA that engineering data were provided through the test from small scale units to semi-pilot.