【作者】 李娜；

【导师】 杨维冉； 易玉俊；

【作者基本信息】 南昌大学 ， 资源与环境（专业学位）， 2023， 硕士

【摘要】 随着石油资源的不断消耗,生物基塑料越来越受到人们的重视。聚乳酸作为一种生物质基塑料是当前研究的热门材料之一。乳酸被认为是聚乳酸未来最大的应用领域,目前工业上主要通过微生物发酵法制备,该工艺乳酸产率高,副产物少。然而,乳酸提取过程中产生的废乳酸给环境带来了很大污染。本文对废乳酸的增值化利用进行了一系列研究。（1）废乳酸中的乳酸提取及丙酸制备:由于废乳酸直接制得丙酸收率低,产物难分离,因此,将废乳酸提纯后合成丙酸。本文探讨了从废乳酸中提纯乳酸的方法,采用无水乙醚和无水乙醇混合溶剂萃取法（无水乙醚和无水乙醇体积比为90:10）,乳酸回收率最高,为79.1%。精馏提纯后,采用高效液相色谱法分析测得乳酸纯度>99.0%。此外,设计的废乳酸连续萃取装置,不仅提高了废乳酸的处理效率,而且实现了萃取剂的循环利用。以纯化乳酸为原料,以NaI为催化剂,在220℃,2.8 MPa H₂,10 h条件下,丙酸最高收率为96.7%。（2）乳酸制备丙交酯: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（¹H NMR）进行定量。然而,气相色谱法并不适用于乳酸产丙交酯的定量分析,其收率总是比LC高得多。详细分析表明,一些在反应过程中未完全转化的乳酸低聚物在高温下解聚生成丙交酯,使得丙交酯产率比实际高。因此,LC是一种比较准确的丙交酯定量分析方法。基于这一现象,我们采用固定床反应器模拟气相色谱分析的反应条件,将间歇反应液置于无催化剂的石英砂填充的高温固定床反应器中,优化后的反应条件可使丙交酯最高收率达到100%,对丙交酯的工业化生产具有重要意义。在此条件下,纯化乳酸的丙交酯收率也可达到100%。更多还原

【Abstract】 With the constant consumption of petroleum resources,people pay more and more attention to biobase plastics.Polylactic acid（PLA）as a biomass-based plastic is one of the hot materials in current research.Lactic acid is considered to be the largest application field of polylactic acid in the future.At present,it is mainly prepared by microbial fermentation in industry,which has a high yield of lactic acid and fewer by-products.However,waste lactic acid produced in the process of lactic acid extraction brings great pollution to the environment.In this paper,a series of studies have been conducted on the value-added utilization of waste lactic acid.（1）Lactic acid extraction and propionic acid preparation from waste lactic acid:Propionic acid was synthesized from waste lactic acid by purifying waste lactic acid because the yield of propionic acid was low and the product was difficult to separate.In this paper,the method of extracting lactic acid from waste lactic acid was discussed.The extraction method of anhydrous ethyl ether and anhydrous ethanol was used（the volume ratio of anhydrous ethyl ether and anhydrous ethanol was 90:10）.The lactic acid recovery rate was 79.1%.The purity of lactic acid was more than 99.0%by HPLC after distillation and purification.In addition,the designed continuous extraction device for waste lactic acid not only improves the treatment efficiency of waste lactic acid,but also realizes the recycling of extraction agent.With purified lactic acid as raw material and NaI as catalyst,the highest yield of propionic acid was 96.7%at 220℃,2.8 MPa H₂ and 10 h.（2）Lactide preparation from lactic acid:Lactide is usually quantified by gas chromatography（GC）,liquid chromatography（LC）or hydrogen nuclear magnetic resonance spectroscopy（¹H NMR）.However,gas chromatography is not suitable for quantitative analysis of lactide from lactic acid,and the yield is always much higher than LC.Detailed analysis showed that some lactic acid oligomers which were not completely transformed in the reaction process were depolymerized at high temperature to produce lactide,which made the yield of lactide higher than the actual one.Therefore,LC is a relatively accurate quantitative analysis method of lactide.Based on this phenomenon,we used a fixed bed reactor to simulate the reaction conditions of gas chromatography analysis.The batch reaction liquid was placed in a high temperature fixed bed reactor filled with quartz sand without catalyst.The optimized reaction conditions can make the maximum yield of lactide reach 100%,which is of great significance for the industrial production of lactide.Under these conditions,the yield of lactide from purified lactic acid can reach 100%.更多还原