Lactic Acid Pre-treatment for Lactide Production – a Techno-economic Feasibility Study for the Dehydration Step

Abstract

Lactic acid (LA) can be synthesized via carbohydrate microbial fermentation; such acid is a bifunctional compound containing hydroxyl and carboxylic acid as chemical groups, having optical activity due to an asymmetric carbon in its structure. A common application for lactic acid is the synthesis of poly(lactic acid) (PLA) via direct polycondensation. This polymerization route needs a dehydration process of the commercially available LA (aqueous, 85% w/w). It is an important step since the presence of water negatively affects the lactide isomerism, which is crucial for the final PLA properties. Considering this, the present work aims to evaluate this pre-treatment process by establishing two configurations, using COCO® simulator. The first is the association of a heat exchanger and a flash vessel. By applying a temperature of 115 °C and a pressure of 383.8 mmHg, the flash liquid stream has a water content of 2.02% w/w. In such conditions, the Total Annual Cost (TAC) is $ 30,663.80. The second configuration has a heat exchanger and a distillation column. The same water content is achieved (2.02% w/w) when a three-stage column operates at 456.0 mmHg and reflux ratio = 1.0 – with a TAC = $ 67,857.71. Therefore, a flash vessel system is the favourable configuration.