From batch to continuous: Au-catalysed oxidation of d-galacturonic acid in a packed bed plug flow reactor under alkaline conditions

Abstract

Comparing the Au-catalysed oxidation of sugar acids: highest selectivity obtained in batch, superior productivity in flow.

Carbohydrate structure–activity relations of Au-catalysed base-free oxidations: gold displaying a platinum lustre

“…All catalytic oxidation reactions were performed in a packed bed plug flow reactor set-up as described in detail previously. 26 The catalyst bed of the packed bed reactor was filled with 1 wt% Au/TiO 2 (7.7 g; crushed and sieved), and the catalyst particles were mixed with additional inert silicon carbide powder to fill the voids. For each reaction, the desired temperature was set (variation between 40–100 °C), and 0.1 M aqueous solutions of the carbohydrates were fed to the reactor at a flow rate of 10 mL min −1 .…”

Selective Oxidation of Arabinose on Gold Catalysts: Process Design and Techno‐economic Assessment

“…As mentioned above, selectivity and activity of gold‐catalyzed oxidation are pH‐dependent 42. Interestingly enough, selectivity in the oxidation of galactogluronic acid on a gold catalyst even under pH drift is only slightly affected as 94 % selectivity was obtained in a continuous reactor with uncontrolled pH in comparison with 99 % for a batch reactor with controlled pH 30. Kinetic models developed in the previous studies for gold catalysts 6, 9 can be used in a larger scale.…”

“…An alternative approach would be to feed sodium hydroxide at several points along the reactor length. Van der Klis et al 30 reported a possibility of continuous galacturonic acid oxidation using a plug‐flow reactor without a pH control. Moreover, it was demonstrated that the selectivity in a plug‐flow reactor was in the same range as in the batch reactor, namely, 94 and 99 mol %, respectively.…”

“…Kinetics and reaction conditions for oxidation of arabinose are typically studied in batch and semi‐batch laboratory‐scale reactors 6, 9, even if there are successful examples of continuous operation 30. Bitter and co‐workers 30 did not adjust the pH of the reaction media along the reactor length, thus operating in a pH drift mode. An alternative approach, as already mentioned, would be to adjust the pH by introducing an alkali solution, i.e., NaOH, at different points.…”

Obtaining Protoanemonin through Selective Oxidation of D‐Fructose and 5‐(Hydroxymethyl)furfural in a Self‐catalysed Reaction

“…This system has been successfully employed in the synthesis of galacturonic acid to galactaric acid under alkaline conditions. [15] When the reaction was conducted using H 2 O 2 , an increase in the yield to DFF was not observed; instead, the formation of protoanemonin (PA) was detected, which was evidenced in all acid solids at the lowest yields (< 30%) ( Table 1, entries 5-7, Figure S2). The formation of PA was explained through the formation in situ of formic acid via Baeyer-Villiger oxidation, while the formation of DFF was conducted via aerobic oxidation.…”