Synthesis and catalytic evaluation of acidic carbons in the etherification of glycerol obtained from biodiesel production

Critical Review of the Various Reaction Mechanisms for Glycerol Etherification

This review provides in-depth coverage of numerous mechanisms available for the etherification process of glycerol, including alcohol solvent, olefin solvent and solvent-free routes along with products that are formed at various stages of the reaction. Mono tert-butyl glycerol ether (MTBG), di tert-butyl glycerol ether (DTBG), and tri tert-butyl glycerol ether (TTBG) are the three general ether compounds obtained through tert-butyl alcohol (TBA) etherification. Glycerol etherification with n-butanol results in the formation of glycerol ether products that are linked to the substituted butyl groups. These products include two mono-butyl glycerol ethers, two di-butyl glycerol ethers and a tri-butyl glycerol ether. Two mono-benzyl glycerol ether isomers, two di-benzyl glycerol ether isomers and tri-benzyl glycerol ether are the most reported results when benzyl alcohol is used as a solvent in the etherification reaction. The etherification of glycerol with 1-butene involves a series of equilibrium reactions to produce mono-ethers, di-ethers, and tri-ethers, whereas the etherification of glycerol with isobutene is carried out via tert-butylation of glycerol, yielding similar glycerol ether products when TBA is used as a solvent. As the by-product may be easily removed, the solvent-free glycerol etherification approach may have several advantages over the other conventional methods. Therefore, further studies on base-catalyzed glycerol etherification that employs a solvent-free reaction route may reveal a method for improving the conversion, selectivity, and yield of reaction products. This review study is crucial in improving knowledge of numerous mechanisms and how they relate to the effectiveness of the product’s catalytic process.

Recovery and utilization of crude glycerol, a biodiesel byproduct

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.

Glycerol Valorization—The Role of Biochar Catalysts

The conversion of renewable feedstocks into new added-value products is a current hot topic that includes the biodiesel industry. When converting vegetable oils into biodiesel, approximately 10% of glycerol byproduct is produced. Glycerol can be envisaged as a chemical platform due to its chemical versatility, as a scaffold or building block, in producing a wide range of added-value chemicals. Thus, the development of sustainable routes to obtain glycerol-based products is crucial and urgent. This certainly encompasses the use of raw carbonaceous materials from biomass as heterogeneous acid catalysts. Moreover, the integration of surface functional groups, such as sulfonic acid, in carbon-based solid materials, makes them low cost, exhibiting high catalytic activity with concomitant stability. This review summarizes the work developed by the scientific community, during the last 10 years, on the use of biochar catalysts for glycerol transformation.

Cultivation Method Effect on Schizochytrium sp. Biomass Growth and Docosahexaenoic Acid (DHA) Production with the Use of Waste Glycerol as a Source of Organic Carbon

Inexpensive carbon sources offering an alternative to glucose are searched for to reduce costs of docosahexaenoic acid production by microalgae. The use of waste glycerol seems substantiated and prospective in this case. The objective of this study was to determine the production yield of heterotrophic microalgae Schizochytrium sp. biomass and the efficiency of docosahexaenoic acid production in various types of cultures with waste glycerol. Cultivation conditions were optimized using the Plackett–Burman method and Response Surface Methodology. The highest technological performance was obtained in the fed-batch culture, where the concentration of Schizochytrium sp. biomass reached 103.44 ± 1.50 g/dm3, the lipid concentration in Schizochytrium sp. biomass was at 48.85 ± 0.81 g/dm3, and the docosahexaenoic acid concentration at 21.98 ± 0.36 g/dm3. The highest docosahexaenoic acid content, accounting for 61.76 ± 3.77% of total fatty acids, was determined in lipid bodies of the Schizochytrium sp. biomass produced in the batch culture, whereas the lowest one, accounting for 44.99 ± 2.12% of total fatty acids, in those of the biomass grown in the fed-batch culture.

Optimizing Docosahexaenoic Acid (DHA) Production by Schizochytrium sp. Grown on Waste Glycerol

The aim of this study was to optimize biomass and docosahexaenoic acid (DHA) production by Schizochytrium sp. grown on waste glycerol as an organic carbon source. Parameters having a significant effect on biomass and DHA yields were screened using the fractional Plackett–Burman design and the response surface methodology (RSM). Schizochytrium sp. growth was most significantly influenced by crude glycerin concentration in the growth medium (150 g/dm3), process temperature (27 °C), oxygen in the bioreactor (49.99% v/v), and the concentration of peptone as a source of nitrogen (9.99 g/dm3). The process parameter values identified as optimal for producing high DHA concentrations in the biomass were as follows: glycerin concentration 149.99 g/dm3, temperature 26 °C, oxygen concentration 30% (v/v), and peptone concentration 2.21 g/dm3. The dry cell weight (DCW) obtained under actual laboratory conditions was 66.69 ± 0.66 g/dm3, i.e., 1.27% lower than the predicted value. The DHA concentration obtained in the actual culture was at 17.25 ± 0.33 g/dm3, which was 3.03% lower than the predicted value. The results obtained suggest that a two-step culture system should be employed, with the first phase focused on high production of Schizochytrium sp. biomass, and the second focused on increasing DHA concentration in the cells.