Abstract
Once a biorefinery is ready to operate, the main processed materials need to be completely evaluated in terms of many different factors, including disposal regulations, technological limitations of installation, the market, and other societal considerations. In biorefinery, glycerol is the main by-product, representing around 10% of biodiesel production. In the last few decades, the large-scale production of biodiesel and glycerol has promoted research on a wide range of strategies in an attempt to valorize this by-product, with its transformation into added value chemicals being the strategy that exhibits the most promising route. Among them, C3 compounds obtained from routes such as hydrogenation, oxidation, esterification, etc. represent an alternative to petroleum-based routes for chemicals such as acrolein, propanediols, or carboxylic acids of interest for the polymer industry. Another widely studied and developed strategy includes processes such as reforming or pyrolysis for energy, clean fuels, and materials such as activated carbon. This review covers recent advances in catalysts used in the most promising strategies considering both chemicals and energy or fuel obtention. Due to the large variety in biorefinery industries, several potential emergent valorization routes are briefly summarized.
Highlights
Glycerol is an organic compound with hydrophilic and hydrophobic properties [1,2]
This supposes a constant source of glycerol that is unable to be assimilated by current markets and opens the possibility for the development and implementation of new industrial processes
This trend can already be seen in the literature, especially in reforming with the introduction of combined process of CO2 separation and purification for later uses or the market, in which effective and low-cost processes/materials for CO2 separation are needed
Summary
Glycerol (propane-1,2,3-triol) is an organic compound with hydrophilic and hydrophobic properties [1,2]. For special issues (for instance, New Glycerol Upgrading Processes, in the Catalyst journal [25]), books [26,27], book chapters [28], local density theories [29], and even large European projects like “Production of cyclic carbonates from CO2 using renewable feedstocks” [30] and “Glycerol Biorefinery Approach for the Production of High Quality Products of Industrial Value” [31] In this scientific literature (Figure 1), many routes or technologies have been described and developed to valorize glycerol, with the most common being thermochemical conversion, oxidation, hydrogenolysis, esterification, biological conversion, aqueous phase reforming, bioconversion, electro-conversion, etc. In order to cover a gap in the literature, this review briefly summarizes several emergent strategies recently reported or with not many publications, such as activated carbon production, crude glycerol direct usages, fuel additives, sacrificed molecules, templates for catalyst synthesis, polymers, CO2 capture, and the direct use of glycerol
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