Abstract
In recent years, the rapid swift increase in world biodiesel production has caused an oversupply of its by-product, glycerol. Therefore, extensive research is done worldwide to convert glycerol into numerous high added-value chemicals i.e., glyceric acid, 1,2-propanediol, acrolein, glycerol carbonate, dihydroxyacetone, etc. Hydroxyl acids, glycolic acid and lactic acid, which comprise of carboxyl and alcohol functional groups, are the focus of this study. They are chemicals that are commonly found in the cosmetic industry as an antioxidant or exfoliator and a chemical source of emulsifier in the food industry, respectively. The aim of this study is to selectively convert glycerol into these acids in a single compartment electrochemical cell. For the first time, electrochemical conversion was performed on the mixed carbon-black activated carbon composite (CBAC) with Amberlyst-15 as acid catalyst. To the best of our knowledge, conversion of glycerol to glycolic and lactic acids via electrochemical studies using this electrode has not been reported yet. Two operating parameters i.e., catalyst dosage (6.4–12.8% w/v) and reaction temperature [room temperature (300 K) to 353 K] were tested. At 353 K, the selectivity of glycolic acid can reach up to 72% (with a yield of 66%), using 9.6% w/v catalyst. Under the same temperature, lactic acid achieved its highest selectivity (20.7%) and yield (18.6%) at low catalyst dosage, 6.4% w/v.
Highlights
Glycolic and lactic acids are hydroxyl acids consisting of carboxyl and alcohol groups
Previous studies demonstrated that glycolic and lactic acids can be synthesized from a glycerol oxidation process (Kumar et al, 2008; Zhou et al, 2008; Lakshmanan et al, 2013; Purushothaman et al, 2014)
In view of the work carried out by Lux et al, a single compartment electrochemical process is presented in this study in order to convert lactic acid from glycerol in a single step reaction
Summary
Glycolic and lactic acids are hydroxyl acids consisting of carboxyl and alcohol groups. The product variation is extremely reliant on the catalyst structure, especially the porosity of the catalyst support, and the type of metal catalyst and its particle size Reaction conditions such as reaction temperature, the acidity or basicity of the medium and mole ratio of metal to substrate are key factors that could influence the product selectivity (Katryniok et al, 2011; Bagheri et al, 2015; Wang et al, 2015). From the study carried out by Lux et al, lactic acid was produced through a hybrid process of combining the electrochemical and catalytic process. In view of the work carried out by Lux et al, a single compartment electrochemical process is presented in this study in order to convert lactic acid from glycerol in a single step reaction
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