丙交酯的合成新工艺研究
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摘要
聚乳酸因其良好的生物相容性、可降解性和优异的加工性能，正受到世人广泛的关注，但它高昂的成本极大地限制着它的应用。丙交酯是制备聚乳酸的重要原料，其成本的降低对于扩大聚乳酸的应用范围有着非常重要的作用。本文从乳酸生产过程中的中间体——乳酸乙酯和乳酸铵出发，避开乳酸的纯化工艺，直接进行合成丙交酯的研究。这对于简化聚乳酸的生产工艺、降低聚乳酸的成本具有重要意义。
本文率先进行了乳酸乙酯缩聚反应动力学研究，确定乳酸乙酯缩聚反应遵循二级反应动力学规律，并证明氮气在反应中所起的作用十分关键，它一方面防止氧化，另一方面推动反应向正方向进行；随后考察了催化体系、氮气流量、反应温度、齐聚时间和齐聚物相对分子质量等因素对丙交酯收率的影响，最终选定了合成的最佳条件。
接下来进行了从乳酸铵制备丙交酯的工艺路线探索。结果表明，反应过程中，乳酸铵分解成乳酰胺和水的副反应不可忽略；全回流预处理工序是反应能否获得成功的关键；精馏装置与氮气装置的使用均有利于氨与反应体系的分离；溶剂水的引入，可以较大幅度地提高丙交酯的收率。通过比较，最后初步设计了实验室用的反应装置。
最后对合成的丙交酯进行定性表征，并比较了乙酸乙酯和丙酮两种溶剂纯化丙交酯的重结晶效果。摸索色谱条件，自行建立了反相高效液相色谱法测定丙交酯和乳酸乙酯含量的方法。结果表明，该法灵敏度高、线性范围宽、重现性好、分析速度快，用于实际样品的测量，效果令人满意。
Polylactide has attracted much attention due to its biodegradability, bioenvironmental compatibility and excellent mechanical properties. However, its applications is restricted by its high price. Since lactide is an indispensable material to prepare polylactide, reducing its cost will greatly extend application range of polylactide. To avoid the high cost in purifying lactic acid, lactide was prepared directly in the thesis from ethyl lactate and ammonium lactate, which are intermediate products in the manufacture of lactic acid. Therefore, the production technique of polylactide is simplified and the cost is reduced.
Reaction dynamics of ethyl lactate was investigated first in this paper. The results show that polycondensation reaction of ethyl lactate obey second-order reaction kinetics and the nitrogen can prevent oxidation and drive the reaction to the right direction. It was also found that the yield of lactide was affected by catalyst system, flow rate of nitrogen, reaction temperature, oligomerization time and molecular weight of oligomers. The optimum conditions were obtained finally.
Secondly, a lot of probes have been done to prepare lactide from ammonium lactate. The obtained results were as follows: (1) Ammonium lactate decomposition, which produces lactamide and water can’t be ignored in the reaction. (2) Pretreatment procedure of total reflux was essential to attain successful reaction. (3) The use of rectification and nitrogen help ammonia to be separated from reaction system. (4) The added water can greatly improve the yield of lactide. A laboratory-scale reaction devices were chosen after a series of comparisons.
Finally, the structure of lactide was characterized and the solvent effects on the recrystallization were compared between ethyl acetate and acetone. Some exploring experiments were carried out and a stable, accurate and highly sensitive HPLC method was constructed for quantitative analysis of lactide and ethyl lactate. The wide linear range, rapid analysis and good recurrence gave satisfying results about quantitative measurement of actual samples.
本文率先进行了乳酸乙酯缩聚反应动力学研究，确定乳酸乙酯缩聚反应遵循二级反应动力学规律，并证明氮气在反应中所起的作用十分关键，它一方面防止氧化，另一方面推动反应向正方向进行；随后考察了催化体系、氮气流量、反应温度、齐聚时间和齐聚物相对分子质量等因素对丙交酯收率的影响，最终选定了合成的最佳条件。
接下来进行了从乳酸铵制备丙交酯的工艺路线探索。结果表明，反应过程中，乳酸铵分解成乳酰胺和水的副反应不可忽略；全回流预处理工序是反应能否获得成功的关键；精馏装置与氮气装置的使用均有利于氨与反应体系的分离；溶剂水的引入，可以较大幅度地提高丙交酯的收率。通过比较，最后初步设计了实验室用的反应装置。
最后对合成的丙交酯进行定性表征，并比较了乙酸乙酯和丙酮两种溶剂纯化丙交酯的重结晶效果。摸索色谱条件，自行建立了反相高效液相色谱法测定丙交酯和乳酸乙酯含量的方法。结果表明，该法灵敏度高、线性范围宽、重现性好、分析速度快，用于实际样品的测量，效果令人满意。
Polylactide has attracted much attention due to its biodegradability, bioenvironmental compatibility and excellent mechanical properties. However, its applications is restricted by its high price. Since lactide is an indispensable material to prepare polylactide, reducing its cost will greatly extend application range of polylactide. To avoid the high cost in purifying lactic acid, lactide was prepared directly in the thesis from ethyl lactate and ammonium lactate, which are intermediate products in the manufacture of lactic acid. Therefore, the production technique of polylactide is simplified and the cost is reduced.
Reaction dynamics of ethyl lactate was investigated first in this paper. The results show that polycondensation reaction of ethyl lactate obey second-order reaction kinetics and the nitrogen can prevent oxidation and drive the reaction to the right direction. It was also found that the yield of lactide was affected by catalyst system, flow rate of nitrogen, reaction temperature, oligomerization time and molecular weight of oligomers. The optimum conditions were obtained finally.
Secondly, a lot of probes have been done to prepare lactide from ammonium lactate. The obtained results were as follows: (1) Ammonium lactate decomposition, which produces lactamide and water can’t be ignored in the reaction. (2) Pretreatment procedure of total reflux was essential to attain successful reaction. (3) The use of rectification and nitrogen help ammonia to be separated from reaction system. (4) The added water can greatly improve the yield of lactide. A laboratory-scale reaction devices were chosen after a series of comparisons.
Finally, the structure of lactide was characterized and the solvent effects on the recrystallization were compared between ethyl acetate and acetone. Some exploring experiments were carried out and a stable, accurate and highly sensitive HPLC method was constructed for quantitative analysis of lactide and ethyl lactate. The wide linear range, rapid analysis and good recurrence gave satisfying results about quantitative measurement of actual samples.
引文
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