Downstream Processing of Crude Glycerol into Useful Products and Chemicals

Glycerol is a stoichiometric co-product from the production biofuels. Large amounts of glycerol are released as triglycerides undergo transesterification in the production of first-generation biofuels (biodiesel). This implies that a lot of glycerol is now available as a cheap renewable feedstock to produce functional products and chemicals. This review paper aims to give an overview of the different chemical/catalytic pathways for crude glycerol purification and processing into useful chemicals and products and shows the potential of glycerol as a central raw material for future chemical industry. Glycerol is an excellent raw material for obtaining commercially important chemicals and medium heating value gases such as hydrogen through reforming. Theoretically, 1 mol of glycerol can produce upto 4 mol of hydrogen thereby enhancing the overall heating value of product gases. Besides, the presence of three-OH groups in glycerol makes it a highly versatile raw material with respect to chemical transformation which makes it possible to capitalize on the surplus glycerol to produce new commercially valued products such as glycerol carbonate, telomers, branched alkyl ethers, propanediols and epoxides. Today, industrial plants producing glycerol are closing down and others are opening that use glycerol as a raw material. Furthermore, there are various methods of purification of crude glycerol for downstream processing which include acidification (done by hydrochloric and phosphoric acid), distillation (commonly practiced method), ion-exchange techniques (uneconomical), adsorption (cost inefficient), nano-cavitation technology (challenging) and to name others. The same can also be accomplished by using different catalysts at different temperatures and pressures. Various reactor set up such as fixed bed, slurry bubble column, circulating fluidised bed and fixed fluidised bed can be used for various processes to accomplish. Phosphoric acid is found to be the best purifying agent.