Glycerol: from waste regarded oleochemical by-product to value-added chemicals through green conversions

Abstract

Glycerol is widely produced and a by-product in oleochemical and biodiesel industries and its over-production causes a sharp drop in its price. This glut coupled with its low demand lead to an extent that it is now even regarded as a waste to get rid of by its producers. Future scenarios for worldwide glycerol market will mostly be related to the supply and demand of glycerol and its application in other industries. The reality is, glycerol has all the potential to be converted into high value products on the basis of its chemical functionality. Due to the unique structure of glycerol, properties and renewability feature of it, new opportunities for the transformation of glycerol into high-valued chemicals have merged in recent years. Glycerol has been demonstrated to be transformed into oxygenated biocomponents as alternatives to conventional petroleum-derived fuel additives. Oxygenate additives could assist in octane rating increment and combustion quality that reduce particulate emission and carbon monoxide production. Various types of oxygenated biocomponents have been developed and rigorous studies of glycerol transformation into fuel additives through etherification, acetylation and acetalation processes have been conducted. Success in these green conversions depends very much on the use of the right catalytic materials and optimized process conditions to selectively produce the desired substances. Catalytic etherification of glycerol to polyglycerols is another option to add value to glycerol. Polyglycerols are biodegradable and biocompatible products that can be used in various industries. Biocompatibility is an attractive feature of aliphatic polyether structures containing hydroxyl end-groups, including polyglycerols or linear polyethylene glycerols (PEGS). Glycerol can also be reacted with fatty acids to form monoglycerides that find wide application in food and pharmaceutical industries. Current research focus in these areas circulates around novel catalysts to improve conversions while showing high yield of the desired product. The use of heterogeneous reaction system is critical towards improving the green features of the processes involved. Technical hurdles, opportunities and critical technical aspects that are currently receiving research attention worldwide will be critically discussed. Indeed, glycerol should be serve as an example for 'Waste to Wealth' concept in chemical industries, particularly in vegetable oil producing nations like Malaysia.