Synthesis and economical analysis of high purity lactide in a continuous fIxed bed reactor

Abstract

Among bioplastics, Polylactic Acid or Polylactide (PLA) are linear aliphatic polyesters, which are produced by starch fermentation obtained from corn and potatoes, or are derived from monosaccharides derived from plant cellulose, which is a typical environmentally friendly thermoplastic polymer. The industrially produced PLA processes reported so far are through lactide formation. First, prepolymer was obtained by polycondensation reaction of lactic acid (low molecular weight PLA), then depolymerized with lactide, and finally obtain higher molecular weight through a ring opening mechanism. That is, there is a difference in the ratio of L-, D-, and meso-lactide depending on lactide synthesis reaction time, pressure and catalyst. As a result, it is economically affected by separation and purification. To address these problems, we present reaction conditions for a pilot-scale process design capable of optically pure lactide production regardless of driver skill. Therefore, it is possible to produce domestic Lactide which was dependent on imports. In addition, if the oligomeric (low molecular weight) PLA produced by the dehydration reaction of lactic acid accumulates in the reactor, it should be removed by periodic cleaning because it affects the lactide purity and quality. In generally commercial processes, it is known to remove residues using organic solvents (Ethyl lactate, DMF, THF etc.). This requires distillation for organic solvent reuse, which is not economical and environmentally friendly due to high energy consumption. To solve this problem, the condition of removing the residue with steam instead of organic solvent is suggested. Also, instead of the conventional lactide synthesis method, a method of synthesizing lactide by vaporization of lactic acid using an inexpensive commercial catalyst and an inert material was studied. As a result, it showed a high lactide yield and purity without any pressure drop in the reactor, and developed a new process capable of continuous reaction.