Continuous Valorization of Glycerol into Solketal: Recent Advances on Catalysts, Processes, and Industrial Perspectives

Abstract

With the global biodiesel production growing as never seen before, encouraged by government policies, fiscal incentives, and emissions laws to control air pollution, there has been the collateral effect of generating massive amounts of crude glycerol, a by-product from the biodiesel industry. The positive effect of minimizing CO2 emissions using biofuels is jeopardized by the fact that the waste generated by this industry represents an enormous environmental disadvantage. The strategy of viewing “waste as a resource” led the scientific community to propose numerous processes that use glycerol as raw material. Solketal, the product of the reaction of glycerol and acetone, stands out as a promising fuel additive capable of enhancing fuel octane number and oxidation stability, diminishing particle emissions and gum formation, and enhancing properties at low temperatures. The production of this chemical can rely on several of the Green Chemistry principles, besides fitting the Circular Economy Model, once it can be reinserted in the biofuel production chain. This paper reviews the recent advances in solketal production, focusing on continuous production processes and on Process Intensification strategies. The performance of different catalysts under various operational conditions is summarized and the proposed industrial solketal production processes are compared.

Glycerol Valorization towards a Benzoxazine Derivative through a Milling and Microwave Sequential Strategy

“…Moreover, the P2 product was purified by column chromatography from the reaction media, employing ciclohexane-ethylacetate (7:3) as solvent system and silica as the stationary phase. The 1 H and 13 C NMR spectra of the pure product were acquired, confirming the formation of the proposed structure for the P2 product (Figures S4 and S5). The 13 C NMR spectrum confirmed the presence of nine carbons, with the presence of six and three signals in the aromatic and aliphatic regions, respectively.…”

“…The 13 C NMR spectrum confirmed the presence of nine carbons, with the presence of six and three signals in the aromatic and aliphatic regions, respectively. 13 C-NMR chemical shifts of 143.74 ppm and 133.42 ppm were associated with C(5) and C(4), respectively (Scheme 2). In addition, C(8) was assigned to the signal located at 51.23 ppm.…”

“…(A) MS-spectrum of the obtained product by employing K 2 CO 3 , appearing at retention time of 16.7 min in the chromatograms. (B) MS-spectrum of the commercial pattern; Figure S4: 1 H-NMR -spectrum of the purified product, appearing at retention time of 16.7 min in the chromatograms; Figure S5: 13 C-NMR -spectrum of the purified product, appearing at retention time of 16.7 min in the chromatograms; Figure S6: FT-IR spectrum of the purified product P2, appearing at retention time of 16.7 min in the chromatograms; Figure S7: FT-IR spectrum of the purified product P1, appearing at retention time of 11.7 min in the chromatograms. Table S1: Set of experiments under ball milling conditions; Table S2: Set of experiments under microwave-assisted conditions; Table S3: Set of experiments under microwave and mechanochemical-assisted conditions.…”

“…In this regard, several strategies have been proposed to date, including the preparation of solketal [13], acrolein [14], cyclic acetals [15], glycidol [16], glycerol carbonate [17], diacetins [18], and mono-and polyesters/ethers [19], among others. Furthermore, the use of glycerol has been also reported for the synthesis of aryloxypropanediols with pharmaceutical activity, via reaction with several phenol derivatives, such as ortho-methoxyphenol, ortho-methylphenol, and para-chlorophenol, to name a few [20].…”

Perspectives for the Upgrading of Bio‐Based Vicinal Diols within the Developing European Bioeconomy

“…Alternative, metal‐free innovative DODH protocols relying on acidic catalysts receive an increasing attention from the scientific community [24,55,70] . Figure 6 illustrates the breakdown of DODH protocols according to the catalytic system used [15] .…”