Abstract
In this work, a highly selective and active gold-based catalyst for the oxidation of high concentrated monoethylene glycol (MEG) in aqueous solution (3 M, 20 wt%) is described. High glycolic acid (GA) selectivity was achieved under mild reaction conditions. The optimization of the catalyst composition and of the reaction conditions for the oxidation of MEG in semi-batch mode under alkaline conditions led to a GA yield of >80% with a GA selectivity of about 90% in short reaction time. The bimetallic catalyst 0.1 wt% AuPt (9:1)/CeO2 showed very high activity (>2000 mmolMEG/gmetalmin) in the oxidation of MEG and, contrary to other studies, an extremely high educt to metal mole ratio of >25,000 was used. Additionally, the gold–platinum catalyst showed a high GA selectivity over more than 10 runs. A very efficient and highly selective process for the GA production from MEG under industrial relevant reaction conditions was established. In order to obtain a GA solution with high purity for the subsequent polymerization, the received reaction solution containing sodium glycolate, unreacted MEG and sodium oxalate is purified by a novel down-stream process via electrodialysis. The overall GA yield of the process exceeds 90% as unreacted MEG can be recycled.
Highlights
The oxidation of alcohols to aldehydes or carboxylic acids has been actively investigated for more than 100 years
The optimization of the catalyst composition and of the reaction conditions for the oxidation of monoethylene glycol (MEG) in semi-batch mode under alkaline conditions led to a glycolic acid (GA) yield of >80% with a GA selectivity of about 90% in short reaction time
GA opens up a wide field of applications, ranging from cosmetic to food industries and the possibility to serve as a building block for the degradable polymer polyglycolic acid (PGA)
Summary
The oxidation of alcohols to aldehydes or carboxylic acids has been actively investigated for more than 100 years. The biotechnical oxidation of MEG achieves high GA selectivity of >90%, but in comparison to the chemical route low productivities (90% at mild reaction conditions can be achieved [6]. Drawbacks of this MEG production route are the use of low concentrated solutions and the low educt to catalyst ratio, i.e., MEG.
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