Synthesis of Lactic Acid by Alkaline Hydrothermal Conversion of Glycerol at High Glycerol Concentration

Abstract

The synthesis of lactic acid by alkaline hydrothermal conversion of glycerol at high glycerol concentrations under autogenous pressure is described. Temperature (250−290 °C), NaOH/glycerol molar ratio (1.1−1.75), glycerol concentration (2.5−3.5 M), and reaction time (30−250 min) have been the variables studied with temperature and NaOH/glycerol molar ratio having the major influence. An 84.5% lactic acid (as sodium lactate) yield is obtained at 280 °C and 90 min with a 2.5 M glycerol concentration and a 1.1 NaOH/glycerol molar ratio. The same yield is obtained starting from crude glycerol from biodiesel production as raw material. Sodium acrylate, oxalate and formate, and sodium carbonate have been identified as the main byproducts with carbonate being the major one. Several conversion routes based on the experimental results are proposed. A process for lactic acid separation based on electrodialysis is outlined.

Hydrothermal conversion of high-concentrated glycerol to lactic acid catalyzed by bimetallic CuAux (x = 0.01–0.04) nanoparticles and their reaction kinetics

“…High NaOH concentration probably caused the decomposition of resultant products to carbonate. 12 The results revealed that high NaOH/glycerol mole ratio favored the hydrothermal conversion of glycerol. But excessive NaOH decreased the selectivity of lactic acid.…”

“…The presence of CuAu x catalysts decreased the reaction temperature by 80 C as compared to the hydrothermal method. 11,12 The CuAu x catalysts gave higher lactic acid yield at a higher glycerol concentration than the noble metal catalysts.…”

“…11 It was found that alkali metal hydroxides exhibited higher catalytic activity than alkaline earth metal hydroxides. Ramírez-López et al 12 reported that the lactic acid yield of 84.5% was obtained when the hydrothermal conversion of glycerol (2.5 mol L À1 ) was carried at 280 C for 1.5 h with a NaOH/glycerol mole ratio of 1.1 : 1. According to the above-mentioned results, NaOH as a homogeneous catalyst exhibited good catalytic activity for the hydrothermal conversion of glycerol to lactic acid.…”

An efficient one pot conversion of glycerol to lactic acid using bimetallic gold-platinum catalysts on a nanocrystalline CeO2 support

“…Higher glycerol concentrations were applied by Lopez et al, which resulted in 84% lactic acid yield in 1.5 h at 553 K [29]. KOH has superior activity compared to NaOH in the reaction [30].…”

Production of Lactic Acid From Glycerol by Applying an Alkaline Hydrothermal Process Using Homogeneous Catalysts and High Glycerol Concentration

“…Several studies have reported high yields of lactic acid (> 90%) from many carbon sources (glycerol, sorbitol, mannitol) (Kishida et al, 2005;Ramírez-López et al, 2010;Shen et al, 2009;Zhou et al, 2010). These studies, however, started from low concentrations of the carbon source (< 0.05 v/v).…”