Real-Time Raman Monitoring and Control of the Catalytic Acetalization of Glycerol with Acetone over Modified Mesoporous Cellular Foams

Abstract

The acetalization of glycerol with acetone over modified mesoporous cellular foam materials has been widely investigated using in situ Raman spectroscopy during reaction. Mesoporous cellular foams (MCFs) modified by niobium or tantalum and (3-mercapto­propyl)­tri­methoxy­silane (MP) followed by H2O2 treatment were used as catalysts in the acetalization of glycerol with acetone. The influence of the type of catalyst, which determines the solid texture and number of Brønsted acid sites, and different reaction parameters, such as reaction time, reaction temperature, glycerol/acetone ratio, and catalyst amount on acetalization reaction, were investigated. The results obtained in the characterization of the catalysts show that the materials obtained differ in the number of Brønsted acidic sites. Raman spectroscopy provides noninvasive insight during acetalization of glycerol with acetone in the presence of acid heterogeneous catalysts. The progress of the acetalization reaction was monitored following the variation in intensity of characteristic Raman bands and using chemometric analyses. The results obtained by real-time Raman monitoring confirm the mechanism proposed for the reaction, which proceeds via the formation of the 3-(2-hydroxy­propan-2-yloxy)­propane-1,2-diol intermediate, whose presence is confirmed by Raman spectroscopy. Under optimal reaction conditions, the 5-membered ring ketal 2,2-di­methyl-1,3-di­oxolane-4-yl methanol (solketal) was obtained with the highest selectivity (99%). Raman monitoring enables real-time control of the reaction, thus enabling the optimization of reaction conditions for a more efficient reaction. Raman monitoring illustrates the reversibility of the reaction upon evaporation of acetone, even under reflux.

Acetalization Catalysts for Synthesis of Valuable Oxygenated Fuel Additives from Glycerol

“…Subsequently, this ion will be attacked by a single pair of electrons of neighboring hydroxyl group with a tertiary carbon atom, which leads to the formation of a 5-membered acetal. The formation of a 6-membered acetal occurs when electron pair on -OH group interacts with a tertiary carbon atom [87]. It is worth noting that acetal formation strongly depends on electronic and steric factors.…”

Acetalization of glycerol and benzaldehyde to synthesize biofuel additives using SO42-/CeO2–ZrO2 catalyst

“…Properties of biodiesel such as lubricity, high flash point, close heat combustion, viscosity, limited exhaust emissions and superior cetane number make it more attractive ( Al-Mashhadani and Fernando, 2013 ; Kulkarni et al., 2020 ). With the rapidly expanding biodiesel industry, a glut of crude glycerol (approximately 10%) is also being generated, resulting in the drastic reduction of fuel yield ( Alhanash et al., 2007 ; Adhikari et al., 2009 ; Calvino-Casilda et al., 2014 ). Therefore, methods to utilize this glycerol to synthesize products of high value must be innovated ( Johnson and Taconi, 2007 ).…”

Kinetic modelling of the solventless synthesis of solketal with a sulphonic ion exchange resin

“…Specifically, cyclic ketals (like solketal) may be obtained through the reaction of polyols (like glycerol) with said carbonyl compounds through a reaction mechanism that consists of the formation of a highly unstable intermediate species and then the cyclation of said intermediate to yield the ketal [23,24].…”