Abstract
It was investigated the lactic acid (LA) production from glycerol in alkaline medium (NaOH) employing platinum (0.5 wt% PtO2) catalysts supported on Al2O3, ZnO and MgO in continuous flow reaction system over a period of 30 h. Besides the effect of catalyst supports, it was studied the influence of the temperature/pressure and NaOH/glycerol molar ratio. The catalysts were prepared by incipient wetness method and characterized by XRF, XRD, N2 adsorption–desorption, TPR, TPD-CO2 and the dispersion of platinum was determined by H2 chemisorption. The reactions were performed at 200–260 °C, 20–46 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. The results of the catalytic tests showed that the main liquid products are lactic acid and 1,2-propanediol (1,2-PDO). Using the Pt/ZnO catalyst at 240 °C/35 atm and NaOH/glycerol molar ratio = 1, it was obtained the highest lactic acid selectivity (∼80%) and yield (∼68%). However, in this reaction, the lactic acid yield decreases to around 25% if NaOH/glycerol molar ratio is reduced to 0.5. The highest yield to 1,2-propanediol (18.5%) was obtained with Pt/Al2O3 catalyst that was associated with the acidity of the catalyst. The catalysts showed excellent stability without evidence of deactivation over the evaluated period.
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