A continuous process for glyoxal valorisation using tailored Lewis-acid zeolite catalysts

Abstract

The aqueous-phase heterogeneously catalysed isomerisation of bio-oil derived glyoxal is herein introduced as a novel route for the sustainable production of glycolic acid. While commercial ultra-stable Y zeolites displayed only moderate performance, their evaluation enabled to highlight the crucial role of Lewis acidity for the reaction. Gallium incorporation in these zeolites boosted the glycolic acid yield, but the best catalytic results were obtained over tin-containing MFI-type zeolites, reaching 91% yield of the desired product at full conversion. These materials comprised hydrothermally-synthesised Sn-MFI as well as a novel catalyst obtained by the introduction of tin in silicalite-1 by means of a simpler and more scalable method, i.e. alkaline-assisted metallation. In-depth spectroscopic characterisation of these systems uncovered a substantial similarity of the tin centres obtained by the top-down and bottom-up synthetic approaches. NMR spectroscopic studies gave evidence that the reaction follows a 1,2-hydride shift mechanism solely catalysed by Lewis-acid sites. The Sn-MFI analogue could be reused in 5 cycles without the need for intermediate calcination, did not evidence any tin leaching, and demonstrated suitable for utilisation under continuous-flow operation. Both tin-based zeolites exhibited remarkable performance also in alcoholic solvents, leading to the one-pot production of relevant alkyl glycolates.

Advances in the Conversion of Short-Chain Carbohydrates: A Mechanistic Insight

“…Again, Sn-based zeotype catalysts seemed superior for this reaction. Indeed, during batch experiments, Sn-MFI yields 91 % GLA after 18 h at 90 °C, whereas a commercial USY with extra-framework Al (e.g., CBV600) only yields 62 % [ 115 ]. As in the conversion of trioses and tetroses, the mechanism was shown to occur via a 1,2-hydride shift, in agreement with earlier performed theoretical studies; see Fig.…”

“…GLA is currently produced by carbonylation of formaldehyde in the presence of H 2 SO 4 at high temperature and pressure. Recently, a new route to synthesize GLA was proposed based on the heterogeneously catalyzed isomerization of GLX in water under mild conditions [ 115 ]. As with GA, bio-oils from the pyrolysis of biomass can contain ca.…”

Lewis Acid Zeolites for Biomass Conversion: Perspectives and Challenges on Reactivity, Synthesis, and Stability

“…Unfortunately, very few in-depth flow studies have been conducted with Lewis acid zeolites. Some notable examples are liquid-phase flow studies of Hf-, Zr-, and Sn-Beta zeolites for the transfer hydrogenation and etherification of HMF to produce 2,5-bis(alkoxymethyl)furans (25) and for the MPV reduction of furfural to furfuryl alcohol (107); of Sn-Beta for the conversion of DHA and formaldehyde to HBL (22); of Sn-MFI synthesized by alkali-assisted metalation for the production of glycolic acid from glyoxal (84); and of Sn-MFI, MOR, BEA, and FAU for the isomerization of dihydroxyacetone and xylose (108). The flow study of hydrogenation and etherification of HMF reveals important trends in deactivation that could not have been seen with simple batch reactions (25).…”

Tandem catalysis for the production of alkyl lactates from ketohexoses at moderate temperatures

“…Considerable progress has been achieved with the production of lactic acid and alkyl lactates from trioses [glyceraldehyde (GLA) and dihydroxyacetone (DHA)], with nearly quantitative yields obtained with state-of-the-art catalysts, e.g., tin-containing zeotypes Sn-Beta and Sn-MFI, which are known for their capacity to catalyze 1,2-intramolecular hydride shift (1,2-HS) reactions, at moderate temperatures (around 100°C) (8). Similarly, the C 2 and C 4 products (glycolic acid, 2-hydroxy-3-butenoic acid, 2,4-dihydroxybutanoic acid, and esters thereof) can be produced in good yields when glycolaldehyde, glyoxal, or tetroses (erythrose, threose, and erythrulose) are used as substrates (4,6). However, the substrates required for these reactions are not easily obtained or isolated from biomass, as the majority of terrestrial biomass comprises cellulose and hemicellulose (polymers of hexoses and pentoses) (5).…”

“…retro-aldol reactions | alkyl lactates | heterogeneous catalysis C hemocatalytic routes for the production of α-hydroxy carboxylic acids, e.g., glycolic acid, lactic acid, 2-hydroxy-3-butenoic acid, and 2,4-dihydroxybutanoic acid, from biomassderived sugars have been extensively investigated in the recent years, as these acids, as well as their esters and lactones, have been recognized to have a large potential to function as renewable, platform chemicals for a number of applications such as polymers, solvents, and fine chemicals (1)(2)(3)(4)(5)(6)(7). Considerable progress has been achieved with the production of lactic acid and alkyl lactates from trioses [glyceraldehyde (GLA) and dihydroxyacetone (DHA)], with nearly quantitative yields obtained with state-of-the-art catalysts, e.g., tin-containing zeotypes Sn-Beta and Sn-MFI, which are known for their capacity to catalyze 1,2-intramolecular hydride shift (1,2-HS) reactions, at moderate temperatures (around 100°C) (8).…”