Continuous production of lactic acid from glycerol in alkaline medium using supported copper catalysts

• One of the first paper that employs fixed bed reactor for transformation of glycerol into lactic acid.
• Copper catalysts supported on Al2O3, ZnO and MgO shown yield and selectivity to lactic acid around 80 and 90 %, respectively.
• The Cu/MgO catalyst showed the best results considering the glycerol conversion and lactic acid yield.

With increasing demand for biodiesel, large quantity of crude glycerol has been produced both in Brazilian and world market, and this excess glycerol has become a problem that must be solved. Several studies have been performed with the objective to transform glycerol in value-added chemical products. Lactic acid has wide uses in chemical and food industries, and the hydrothermal transformation of glycerol to lactic acid is presented as an alternative to conventional production process. In this study, the production of lactic acid from glycerol under alkaline conditions, using copper (20 wt.% CuO) catalysts supported on Al2O3, ZnO and MgO in continuous flow reaction system was investigated. The catalysts were prepared by impregnation method and characterized by XRF, XRD, N2 adsorption–desorption, TPR, and TPD-CO2 and the dispersion of copper was determined by N2O oxidation. The reaction was carried out at 240 °C, 35 atm, with space velocity (WHSV) of 2 h− 1, 10 vol.% glycerol solution and NaOH/glycerol molar ratio of 0.5, 0.75 and 1.0. All catalysts showed high conversion of glycerol with yield and selectivity to lactic acid in the range of 80 and 90%, respectively, when the reactions are performed with NaOH/glycerol molar ratio of 1.0.

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