A Heat-Integrated Reactive Distillation Process for Methyl Lactate Hydrolysis

Abstract

Lactic acid is predominantly produced through microbial fermentation of renewable feedstocks. However, direct separation and purification of lactic acid from the fermentation broth is difficult. A two-step process involving (1) esterification of raw lactic acid with methanol to produce methyl lactate, and (2) hydrolysis of the methyl lactate to produce high-purity lactic acid, is commonly used. The hydrolysis step is typically carried out in a reactive distillation (RD) column to overcome equilibrium limitations by continuous removal of the product(s). However, the conventional RD process is highly energy intensive and has relatively low thermodynamic efficiency. We show that the energy requirement of the RD column can be significantly reduced by implementing external heat integration via a heat pump. Specifically, we show that a vapor-recompression-based reactive distillation (VRC-RD) column offers up to 63.4% energy savings relative to the conventional RD column. The energy savings are further increased to 64.9% in a pre-compressor split (PCS-VRC-RD) configuration. This reduction in the total utilities requirement results in an increase in thermodynamic efficiency from 21.4% for the conventional RD column to 38.7% for the VRC-RD column and to 40.3% for the PCS-VRC-RD column. For a payback period of 5 years, these energy savings respectively correspond to 32.0% and 33.8% reduction in the total annual cost (TAC) relative to the conventional RD column.