Innovative continuous synthesis of solketal

Enhancing the catalytic properties of silicalite-1 through ammonium fluoride modification for waste glycerol acetalization

Silicalite-1 is a silica with a zeolitic MFI (Mobil Five) structure devoid of noticeable catalytically active (e.g., acid) sites. In this study, we present its modification with NH4F solutions of varying concentrations (0.5-3 M), which generates efficient and selective acid sites for the acetalization of glycerol with acetone towards solketal (2,2-dimethyl-1,3-dioxolane-4-methanol). The creation of acid sites is attributed to the partial elimination of external silanol groups in silicalite-1 and the generation of some framework defects, resulting also in increased porosity. The characterization of the modified materials was performed using various techniques, i.e. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (TPD-NH3), and Fourier-transform infrared spectroscopy (FTIR). The results demonstrate that the newly created acidic sites of Brønsted and Lewis nature exhibit significantly higher acidic strength and enhanced accessibility for reagents compared to the pristine one, resulting in exceptional glycerol conversion in the acetalization of glycerol with acetone and notable selectivity towards solketal. Glycerol conversion over modified silicalite-1 reached nearly 70%, with the selectivity to solketal exceeding 98% at 70° C after 1 hour of reaction time, using a mixture of glycerol and acetone in a 1 : 1 ratio. The proposed reaction mechanism takes into account a combination of Brønsted and Lewis acid sites. The obtained results indicated that Brønsted acid sites, especially those of higher strength, are the most beneficial in this process. The remarkable catalytic performance and stability of modified silicalite-1 make it a promising candidate for potential industrial applications in the utilization of waste glycerol formed in the biofuel industry.

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

The previous decade has witnessed a drastic increase of European incentives aimed at pushing forward the transition from an exclusively petro-based economy toward a strong and homogeneous bio-based economy. Since 2012, numerous programs have been developed to stimulate and promote research and innovation relying on sustainable and renewable resources. Terrestrial biomass is a virtually infinite reservoir of biomacromolecules, the biorefining of which provides platform molecules of low complexity yet with tremendous industrial potential. Among such bio-based platform molecules, polyols and, more specifically, molecules featuring vicinal diols have gained tremendous interest and have stimulated an increasing research effort from the chemistry and chemical engineering communities. This Review revolves around the most promising process conditions and technologies reported since 2012 that specifically target bio-based vicinal diols and promote their transformation into value-added molecules of wide industrial interest, such as olefins, epoxides, cyclic carbonates, and ketals.