Publication: Selective conversion of purified crude glycerol to lactic acid using mixed strontium and calcium oxide as solid base catalyst
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Date
2022-07-01
Authors
Abdullah, Rozaini
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Abstract
The growths of global biodiesel and oleochemical industries have led to the generation of excess crude glycerol which can be classified as an essential renewable feedstock for lactic acid (LA) production. This study has been carried out to synthesize mixed strontium (Sr) and calcium oxide (CaO) as a solid base catalyst for the selective conversion of purified crude glycerol into LA. Firstly, the performance of each metal oxide was conducted by using the batch reactor with constant reaction temperature (280 'C) and time (2 hours). CaO presented a higher yield of LA (34.3±2.97 %) compared to strontium oxide (SrO) and its selectivity(34.91±3.17 %) at 20 wt. % of catalyst loading. Meanwhile, SrO performed the best at 25 wt. % catalyst loading resulting in yield and selectivity of LA of 33.77±3.57 % and 36.94±5.32 %, respectively. SrO exhibit more selective compared to CaO at higher catalyst loading. Based on this data, both metal oxides were mixed and the ratio of SrO to CaO was screened based on weight percent between both metals as well as comparing between two different preparation methods, wet impregnation (WI) and co-precipitation (CP). At ratio SC30/70-WI showed the yield and selectivity of LA were 38.28±2.77 % and
44.93±5.00 %, respectively. In the meantime, SC30/70-CP exhibit a higher LA yield and selectivity, 43.28±1.92 % and 50.40±5.87 %, respectively. The effect of reaction
parameters was then screened using a 2-level factorial design in Design Expert Software version 11 to determine the significant parameters in terms of obtaining high yields and selectivity of LA. The result of ANOVA presented the R2 (98.56 %), which were the highest conversion of glycerol (91.54 %), yield (47.64 %) and selectivity (57.54 %) of LA at 10 % catalyst loading at 240'C for 3 hours reaction. The screening process indicated that three parameters were interrelated with significant parameters affecting conversion of glycerol, yield and selectivity of LA where P-value less than 0.05. Due to good curvature and ANOVA analysis, these screening data was used to be augmented towards the optimization reaction conditions. The synthesised catalyst was also characterised by using SEM-EDX, XRD, FTIR, TGA, TPD and acidity determination by titration method. The catalyst's properties were then correlated with its catalytic activity in conversion glycerol to LA. Later, the kinetic study was performed, and the reaction followed the first law order. Lastly, the SC30/70-CP catalyst was recycled four times in a batch reactor where the stability of the synthesized catalyst was decreased after the third cycle. The results suggested that mixed SrO and CaO could be potentially applied for the selective conversion of purified crude glycerol into LA.