Publication: Selective oxidation of glycerol to lactic acid using zirconia supported catalysts
Date
2023-03-01
Authors
Noraini Binti Razali
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Abstract
Glycerol is a promising raw material for the synthesis of useful chemicals, one of them is lactic acid. Homogeneous catalytic conversion suffers from severe conditions and unfriendliness to the environment. Alternatively, a supported solid catalyst was explored to significantly favor the formation of lactic acid. Hence, a potential supported solid catalyst was screened using CeO2, alkaline earth metal oxide (MgO, BaO, CaO) and support material (Al2O3, MgO, ZrO2). The CaOCeO2/ZrO2 catalysts exhibited the highest activity with 96.4±3.0 % of glycerol conversion and 39.8±0.4 % yield of lactic acid. Then, the CaOCeO2/ZrO2 catalyst preparation was evaluated at different methods (co-precipitation and impregnation), and calcination temperatures (500-900 ℃). The reaction condition was maintained at a 250 ℃ for 2 h with the presence of O2 and 20 wt.% of catalyst loading. The co-precipitation method with 800 ℃ calcination temperature produced the highest lactic acid yield of 40.8±2.2 % and glycerol conversion at 90.9±1.7 %. To explore the physicochemical of CaOCeO2/ZrO2 catalyst, the correlation of the characteristic analysis from the surface analyzer, XRD, XPS, CO2-TPD, TGA, TEM, and SEM-EDX was evaluated as well as basicity analysis. Further, the best condition of the catalytic activity was examined using the one factor a time method. The reaction parameters studied were at different ratios of xCaO:yCeO2 loading (x:y = 1:1, 2:1 and 1:2), the ratio of CeO2 loading (x:y =1:0.5-1:3 wt./wt. %), catalyst towards glycerol loadings (5-35 wt. %), reaction temperature (210-290 ℃) and reaction time (0.5-2.5 h). The best reaction conditions were identified at a ratio xCaO:yCeO2 of 1:2 with 30 wt.% of catalyst loading at 2.5 h of reaction at 270 ℃ of temperature reaction. The highest conversion 95.6% and 44.7 % yield of lactic acid resulted. The stability and reusability of the 30wt%CaOCeO2/ZrO2 catalyst were found to maintain at two times recyclability. Changes in the catalyst structure were investigated by analysis of XRD, SEM and EDX. The amount of Ca dropped from 5.29 to 1.44 wt. % and the amount of Ce dropped from 12.86 to 3.65 wt.%. The kinetic study was performed using the Arrhenius equation. The kinetic model calculated data against experimental data were well fitted indicated the precision of the model. To conclude, 30wt.%1CaO2CeO2/ZrO2 supported catalyst possesses was high basicity, well developed morphology, is able to form active sites to facilitate the reaction mechanism of glycerol to lactic acid is highly recommended as a promising and alternative supported solid catalyst to produce lactic acid from glycerol.