L-乳酸合成L-丙交酯过程中的定量问题及其提高选择性的方法

L-lactide quantification problems during its synthesis from L-lactic acid and the way to improve its selectivity

聚乳酸(PLA)是一种很有前途的可降解、可再生和生物相容性的聚合物,L-丙交酯作为生产聚乳酸的重要中间体,其纯度直接影响聚乳酸的质量和生产成本。丙交酯通常采用气相色谱法(GC)、液相色谱法(LC)或核磁共振氢谱法(^(1)H NMR)定量。然而,发现GC在乳酸生产丙交酯的过程中并不适用于定量,丙交酯收率总是比LC高得多。详细的分析表明,一些在反应过程中没有完全转化的乳酸低聚物在高温下可以发生解聚生成丙交酯,从而使丙交酯的产率比实际的高。因此,LC是一种较为准确的丙交酯定量分析方法。基于这一现象,采用固定床反应器模拟GC分析的反应条件,大大提高了丙交酯的选择性和收率。优化后的反应条件可使丙交酯的最高收率达到100%。

Polylactic acid(PLA)is a promising degradable,renewable and biocompatible polymer.As an important intermediate in the production of PLA,the purity of L-lactide directly affects the quality and production cost of PLA.Lactide is usually quantified by gas chromatography(GC),liquid chromatography(LC)or hydrogen nuclear magnetic resonance spectroscopy(1H NMR).However,we found that GC was not suitable for quantification in the production of lactide from lactic acid,and the yield of lactide was always much higher than LC.Detailed analysis showed that some lactic acid oligomers,which were not completely transformed during the reaction process and then can depolymerize to produce lactide at high temperature,so that the yield of lactide was higher than the actual.Therefore,LC was a relatively accurate method for quantitative analysis of lactide.Based on this phenomenon,a fixed bed reactor was used to simulate the reaction conditions for GC analysis,which greatly improved the selectivity and yield of lactide.The optimized reaction conditions can make the maximum yield of lactide reach 100%.