Current and Future Trends for Crude Glycerol Upgrading to High Value-Added Products

Abstract

Crude glycerol is the main byproduct of biodiesel manufacturing from oleaginous crops and other biomass-derived oils. Approximately 10% crude glycerol is produced with every batch of biodiesel. Worldwide, there is a glut of glycerol and the price of it has decreased considerably. There are real opportunities for valorizing crude glycerol into higher value-added chemicals which can improve the economic viability of biodiesel production as an alternative fuel. Exploring new potential applications of glycerol in various sectors is needed such as in pharmaceuticals, food and beverages, cosmetics, and as a transportation fuel. However, crude glycerol produced directly from biodiesel often contains impurities that hinder its direct industrial usage and thus, a refining process is needed which is typically expensive. Hence, this review reports on current upgrading crude glycerol technologies—thermo-, bio-, physico-, and electrochemical approaches—that valorize it into higher value-added chemicals. Through comparison between those viable upgrading techniques, future research directions, challenges, and advantages/disadvantage of the technologies are described. Electrochemical technology, which is still underdeveloped in this field, is highlighted, due to its simplicity, low maintenance cost, and it working in ambient condition, as it shows promising potential to be applied as a major glycerol upgrading technique.

Electrochemical Valorization of Glycerol via Electrocatalytic Reduction into Biofuels: A Review

“…Comparison of current glycerol reduction pathways. [11,15,16] Pathways electrode to attract cations towards it. [37] Next, they conduct reduction to synthesize surface-bound atomic hydrogen (H*).…”

“…The effects of these parameters toward ECR performance will be primarily illustrated deliberated using its conversion (GC) values, product yield (PY), each product selectivity (PY), electrochemical efficiency (EE) and coulombic efficiency (CE) (also called faradaic efficiency or current efficiency), as follows [Eqs. (9)(10)(11)(12)(13)].…”

“…Recently, less attention has been given to electroreduction pathways, compared to oxidation, albeit it comprises various significant valorization reaction -hydrogenolysis, hydrodeoxygenation, and electro-deoxygenation -in the recent decade. [4] These specific reactions are significant in generating biofuels from crude glycerol, removing oxygen molecules from the compounds. Here, in Scheme 2, we map out various possible electrochemical reactions of glycerol that occurred within the electrochemical cell.…”

“…[3] Thus, currently, the rapid development of the biodiesel industry has resulted in a significant surplus of glycerol on the world market. Considering that glycerol is an abundant waste product [4,5] and that it is the second simplest sugar molecule, [6] glycerol upgrading to valuable products has a significant impact on the biodiesel economy [7] whereas, according to Nomanbhay et al, [8] major biodiesel producers are currently refining the crude glycerol to pure glycerol through expensive purification processes. The study of new and low-cost processes for crude glycerol upgrading is paramount.…”

“…Recently, glycerol has been considered as an alternative candidate of biofuel resources for the electrochemical valorization process, into propanol (see Scheme 1), along with other upgrading reaction‐thermochemical (hydrogenolysis, catalytic pyrolysis, and reforming), etherification, and biochemical (via fermentation) routes [11] . According to our previous publication, [11] summarized in Table 1, we could conclude that electrochemical pathway is more superior than the others in terms of performance, complexity and economic‐wise. There has been increasing commercial demand in electroreduction, also known as electrocatalytic reduction (ECR).…”