Purification of glycerol and its conversion to value-added chemicals: A review

An increase in demand for biodiesel production has resulted in increased production of glycerol, which is the main co-product of the process. Glycerol resulted from the biodiesel production is deemed as crude glycerol as it contains impurities such as free fatty acid, inorganic salts, water, and methanol. These impurities decrease economic value of glycerol, and for this reason, crude glycerol cannot be utilized as such. Hence, this low value product needs to be exploited via purification and value-addition for the benefit of biodiesel industry. In this review, the processes and different techniques employed for glycerol purification have been reviewed. Different methods of glycerol purification are compared for their suitability for various value-added chemicals from glycerol. There is no size one-fit all approach for glycerol purification, and the most promising method – membrane purification has not been optimized for industrial scale. In this review, conversion of purified glycerol into value-added chemicals such as 1,3-propanediol and glycerol carbonate via both catalytic and biochemical conversion processes have been explored. Furthermore, techno-economic aspect, which is crucial for industrial adaption of the process, has been discussed. Purified glycerol, when used for the production of value-added products, can be a promising income stream for biodiesel industry.