A study on highly concentrated lactic acid and the synthesis of lactide from its solution

Abstract

Lactic acid is an important platform compound used as raw material for the production of lactide and polylactic acid. However, its concentration and composition distribution are not as simple as those of common compounds. In this work, the mass concentration distribution of highly concentrated lactic acid is determined by back titration. The components of highly concentrated lactic acid, crude lactide, and polymer after the reaction are analyzed by HPLC. Different concentrations of lactic acid solution were prepared for the synthesis of lactide and its content in the product was determined by 1H NMR analysis. We found that lactide is more easily produced from high-concentration lactic acid solution with which the condensed water is easier to release. Hence, the removal of condensed water is crucial to the formation of lactide, although it is not directly formed by esterification of two molecules of lactic acid.

Lactide Synthesis Using ZnO Aqueous Nanoparticles as Catalysts

“…In this study, we adopted the conditions determined by Hu et al [10], who achieved a remarkably higher production yield of 91%, coupled with a high lactide purity of 95%. This notable result might be attributed to the low pressure (1 kPa) used in their process, which not only prompted the reaction to progress forward but also facilitated the removal of water, a crucial factor for lactide molecule formation [9,17].…”

“…The synthesis of lactide typically begins with the distillation of lactic acid, followed by its oligomerization, wherein heating lactic acid at high temperatures leads to the release of condensed water. Subsequently, some of the resulting oligomers with specific molecular weights undergo depolymerization to yield lactide [7][8][9].…”

“…However, lactide synthesis via ROP is known for its high cost and low yield [9]. Therefore, researchers have focused on exploring the most suitable catalytic systems and optimal reaction conditions to enhance the overall yield and properties of synthesized PLA [4,6].…”