| सारांश: | Glycerol generated from biodiesel manufacture is a beneficial waste that can be
potentially used to synthesize valuable products via the low-cost and simple setup
method, namely electrolysis. This waste can produce oxygenated and reduced compounds
through electrooxidation and reduction reactions, respectively. This work aims to study
the reaction mechanisms of glycerol electroreduction in the cathode region using
inexpensive activated carbon-based electrodes. The experiments were divided into three
sections. The first part is to synthesize the activated carbon composite (ACC) electrodes
with various activated carbon compositions. The influence of different activated carbon
percentages (60%, 70%, 80%, and 90%) of the total weight in the ACC electrodes on the
physicochemical and electrochemical properties was explored by field emission scanning
electron microscopy and energy-dispersive X-ray spectroscopy (FESEM-EDX), cyclic
voltammetry (CV), and chronoamperometry (CA) analyses. Results indicated that high
activated carbon content portrayed a dominant role in controlling an electroactive surface
area (EASA), and the electrons transfer process which eventually improved the
electrocatalytic activity. 80ACC outperformed other ACC electrodes by generating
Amberlyst-15 anionic radicals (A-15•-
) with the highest EASA (36.7 cm2
) and current
density (-0.2018 A/cm2
) at low potential. A-15•-
served as the electron-donor for the
homogeneous redox reaction with glycerol in delivering highly reactive glycerol radical
for further intermediates development and generated 1,2-propanediol. Meanwhile, the
low activated carbon percentage preferred diethylene glycol formation. Acetol and
ethylene glycol were subsequently suggested as the intermediates for 1,2-propanediol and
diethylene glycol formation, which were produced from the dissociation of glycerol either through the C-C bond or C-O bond cleavage, respectively. Hence, in the second part, the
proposed intermediates were employed as the glycerol substitutes to elucidate the overall
reaction mechanisms of glycerol electroreduction on the 80ACC electrode. Data proved
80ACC in Amberlyst-15 redox mediator solution demonstrated a superior activity for
acetol electro-hydrogenation into 1,2-propanediol. At 80 °C, 1,2-propanediol selectivity
(with 59.8 C mol% yield) reached 77.3% at the 7
th hour using 3.0 M of acetol and 0.28
A/cm2
current density. Whereas diethylene glycol was acquired through intermolecular
dehydration of ethylene glycol in the Amberlyst-15 solution without electricity. Besides,
H
+
ions from Amberlyst-15 are advantageous in facilitating glycerol conversion to a
selective acetol. Lastly, the preliminary experiments for glycerol electroreduction to study
the effects of reaction temperature (27-106.5 °C), initial glycerol concentration (0.3-4.35
M), and current density (0.07-0.28 A/cm2
) on the reaction were carried out. Findings
revealed the generation of acetol, and ethylene glycol intermediates was profoundly
controlled by the temperature where a mild value is needed to maintain a selective acetol 1,2-propanediol route. Additionally, a moderate glycerol initial concentration reduced the
hydrogen formation and indirectly improved 1,2-propanediol yield. A medium current
density raised the conversion rate and minimized the intermediates growth. At 80.0 °C
and 0.21 A/cm2
, glycerol (3.0 M) electroreduction to 1,2-propanediol reached the
maximum yield of 42.3 C mol%. The experimental value obtained was close to the
predicted yield (41.8 C mol%) from the polynomial model developed using response
surface methodology (RSM) and analysis of variance (ANOVA).
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