Glycerol valorization: conversion to lactic acid by heterogeneous catalysis and separation by ion exchange chromatography

The consumption and production of biodiesel has grown dramatically in recent decades, motivated by a strong interest in renewable energy. This has generated a surplus of its main by-product, glycerol. Several catalytic processes have been proposed to generate alternatives for using this excess glycerol, mainly focusing on its transformation into high value-added chemical products. Various products, ranging from syngas to organic acids, such as acrylic or lactic acid, along with 1,2-propanediol, 1,3-propanediol, glycerol ethers or even polymers, have been produced starting from glycerol. Among this multitude of possibilities, the production of lactic acid is one of the most interesting alternatives to valorize glycerol, because of the wide range of applications described for this organic acid. This review focuses on recent studies dealing with the catalytic conversion of glycerol to lactic acid, using different heterogeneous catalysts, and evaluates the factors influencing the oxidation catalytic process and the proposed reaction mechanisms. Finally, recent studies on the separation and purification of lactic acid using ion exchange chromatography resins are also reported.