Hydrothermal Transformation of Glycerol to Lactic Acid in Alkaline Medium Using Cu Catalysts Obtained from Hydrotalcite-Like Precursors

Abstract

The conversion of glycerol into lactic acid in alkaline medium using heterogeneous catalysts has been highlighted and has proved to be an e cient alternative to the conventional fermentative route. This work investigated the production of lactic acid from glycerol in alkaline medium using copper catalysts obtained from hydrotalcite-like precursors in a continuous ow reaction system and the effect of different copper loading on catalytic behaviors in terms of yield and selectivity to lactic acid. The catalysts were synthesized by the coprecipitation method and characterized by XRF, XRD, N 2 adsorption-desorption, H 2 -TPR, CO 2 -TPD, and the copper dispersion was determined by N 2 O oxidation. The reaction was performed for 30 h at 240°C, 35 atm, using space velocity (WHSV) of 2 h − 1 , solution of 10 vol% glycerol, and NaOH/glycerol molar ratio of 0.75. Although the 30CuHT catalyst presented higher BET surface areas, Cu dispersion, and basicity than the 20CuHT catalyst, the best results in terms of glycerol conversion (96.5%) and yield (64%) to lactic acid were obtained in the catalytic test performed with the 20CuHT catalyst. This result may be related to the reaction steps that occur in the liquid phase in the presence of the hydroxyl group (OH -). Furthermore, the high content of Cu may favor the hydrogenation of the reaction intermediates (2-hydroxypropenal and pyruvaldehyde), increasing the formation of 1,2-propanediol and consequently reducing the yield of lactic acid. Finally, the catalytic activity of the reduced and nonreduced catalysts was investigated, and the results showed that copper oxide also has catalytic activity.However, the reduction of copper oxide provides better results. Statement Of NoveltyThis study is a new contribution to green chemistry production from biomass-derived products, focusing on the production of lactic acid from glycerol in an alkaline medium using copper catalysts obtained from hydrotalcite-like precursors in a continuous ow reaction system. The motivation for this study is the lack of works that evaluate the effect of the copper loading on the catalysts used in transforming glycerol into lactic acid. In addition, no studies were found in the literature that used hydrotalcite-type precursors for this reaction. Some researchers have evaluated the use of copper oxide as a catalyst.However, in this study, it was observed that for higher yields in the conversion of glycerol into lactic acid, it is necessary to use reduced copper (Cu°) catalysts.

Direct Synthesis of Calcium Lactate through the Reaction of Glycerol with Calcium Hydroxide Catalyzed by Bimetallic AuCu/SiO2 Nanocatalysts

“…Active components and surface acidic/basic performance play important roles in catalytic glycerol conversion to lactic acid [10,[15][16][17]. Considering that noble metal catalysts can catalyze glycerol conversion at a mild reaction temperature, whereas copper-based catalysts exhibit higher lactic acid selectivity at a higher temperature, we suggest that combining non-precious Cu with noble Au could produce good catalytic performance in glycerol conversion to lactate in an alkaline aqueous solution under anaerobic atmosphere.…”

“…It was reported that the glycerol conversion and lactic acid selectivity on the Cu/ZIF-8 catalyst were 97.5% and 84.2% when the glycerol conversion was conducted in sodium hydroxide aqueous solutions under an anaerobic N 2 atmosphere at 230 • C for 8 h [15]. When the synthesis of lactic acid through hydrothermal glycerol conversion in sodium hydroxide aqueous solutions was conducted on a 20CuHT catalyst bed at 240 • C, the glycerol conversion and lactic acid yield were around 96.5% and 64%, respectively [16]. It was also reported that when the hydrothermal conversion of glycerol to lactate was conducted in calcium hydroxide aqueous solutions at 230 • C, the lactate selectivity was above 91% at a glycerol conversion of around 93% [10].…”