Recovery and utilization of crude glycerol, a biodiesel byproduct

Abstract

Biodiesel production has increased significantly in the past decade because it has been demonstrated to be a viable alternative and renewable fuel. Consequently, the production of crude glycerol, the main byproduct of the transesterification of lipids to biodiesel, has risen as well. Therefore, the effective recovery and utilization of crude glycerol can provide biodiesel with additional value. In this review, we first summarized the state-of-the-art progress on crude glycerol recovery and purification. Subsequently, numerous approaches have been reviewed for the utilization of crude glycerol, including use as animal feeds, for combustion, anaerobic fermentation, and chemical conversion. Finally, an extensive discussion and outlook is presented in relation to the techniques and processes in the chemical conversion of crude glycerol.

Fig. 1. Average emissions impact of biodiesel for heavy-duty highway engines. Source: EPA 2002.

Fig. 2. Global biodiesel and crude glycerol production from 2003 to 2020 (ref. 6).

Scheme 1. Utilization of glycerol and crude glycerol.

Fig. 3. Summary of glycerol purification technologies.

Fig. 4. End use of glycerol in 2020 (ref. 5).

Fig. 5. Probable catalytic pathways for the conversion of glycerol into useful chemicals.

Scheme 2. Glycerol to hydrogen or syngas.

Fig. 6. Schematic of experimental set-up.

Fig. 7. Schematic of the experiment for enhanced H₂ production through the aqueous-phase reforming of glycerol.