Oligomer distribution in concentrated lactic acid solutions

Lactic acid (2-hydroxypropanoic acid) is a significant platform chemical for the biorenewable economy. Concentrated aqueous solutions of lactic acid (>30 wt.%) contain a distribution of oligomers that arise via intermolecular esterification. As a result, the titratable acidity changes non-linearly with acid concentration. In this work, the oligomer distribution of lactic acid is characterized using GC, GC/MS, and HPLC to extend existing literature data, and titratable acidity is measured via titration with NaOH. A thermodynamic model with a single parameter is proposed that accurately represents oligomer distribution and titratable acidity over the full range of lactic acid concentrations.