Selective Electrochemical Conversion of Glycerol to Glycolic Acid and Lactic Acid on a Mixed Carbon-Black Activated Carbon Electrode in a Single Compartment Electrochemical Cell

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.

An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au

“…reported that strong alkali can promote this deprotonation step, since glycerol behaves as a weak acid in a strong alkaline solution whose pH is close to the pKa of glycerol (14.15). Once chemisorbed, a second deprotonation from the carbon atom occurs, which oxidizes glycerol into glyceraldehyde or DHA [19] . As in alkaline conditions OH exists in the electrolyte, Pt‐OH(ads) (reportedly produced at 0.5 V–0.6 V vs RHE [20] ) can subsequently oxidize the chemisorbed glyceraldehyde into glyceric acid or glycerate.…”

“…An overview of these hypotheses and controversies is therefore timely, and should be used to direct the future works. It is an area that has not yet been emphasized in previously published reviews [19–21] . The reaction mechanism of GEOR was partially reviewed by Gomes et al [22] .…”

A review of recent developments on kinetics parameters for glycerol electrochemical conversion – A by-product of biodiesel

“…The mechanism pathways and reaction kinetics can be infl u enoed by overpotential, glycerol conversion, selectivity and yield of desired products, which could alter reaction parameters like activation energy barrier to stimulate fast molecular collision and surmount the binding energies of the reactants. For instance, an increase in temperature from 27 °C to 80 °C could accelerate the C C bond breakage, hence, converting glycerol into glycolic acid (Lee et al, 2019a). Lee et al (2019a) reported high glycolic acid yield (66.1%) with a selectivity of 72% after 6 h of reaction at 80 °C.…”

“…For instance, an increase in temperature from 27 °C to 80 °C could accelerate the C C bond breakage, hence, converting glycerol into glycolic acid (Lee et al, 2019a). Lee et al (2019a) reported high glycolic acid yield (66.1%) with a selectivity of 72% after 6 h of reaction at 80 °C. Besides, the glycerol/catalyst molar ratio is a crucial param eter to attain high glyoerol conversion and products selectivity (Kim et al, 2017a).…”

“…Since this study used the one pot electrochemical reactor, lactic acid may be formed through a direct electro reduction from pyru vie acid and glycolic acid obtained from direct glycerol electro oxidation (Lee et al, 2019a). It is important to know that the uti lization of heterogeneous catalysts is capable to control product selectivity and has better separation from the obtained products (Nakagawa et al, 2018).…”