Oxidative thermal degradation of Monoethylene Glycol (MEG) in water lean solutions at 110–150 °C

• Experimental verification of MEG oxidation rate: 1–6 mg/kg/h at 110–150°C . • Data supports estimation of MEG degradation and loss in regeneration units, heat exchangers , and other high-temperature equipment. • Development of a dedicated experimental setup for accurate measurement of oxidation rates. • Introduction of a method to estimate dissolved oxygen concentration in MEG–water solvent mixtures. • Identification of temperature-dependent oxidation products : ○ Formic acid/formate dominates at temperatures up to 110°C . ○ Glycolic acid/glycolate becomes predominant at 140–150°C This work investigates the oxidation behaviour of monoethylene glycol (MEG) used as a hydrate inhibitor, with a focus on oxygen consumption and the formation of oxidation products under conditions relevant to MEG recovery. MEG solutions containing up to 10 wt% water and up to 2 mg/kg dissolved oxygen (DO) were heated to temperatures between 110 and 150 °C. Under these conditions, the DO consumption rate—determined using flow-based measurements—ranged from 1 to 6 mg/kg/h for solutions prepared with high-purity glycol. Carboxylic acids and iron, which are common contaminants in MEG and may also undergo oxidation under these conditions, were included in the experimental scope. The presence of 100–300 mg/kg of formate and acetate, or 25 mg/kg of ferric iron, had no measurable effect on the oxygen consumption rate under the conditions investigated. At 140–150 °C, glycolate was identified as the primary oxidation product when neutral or alkaline MEG reacted with DO at concentrations between 0.1 and 2 mg/kg. At 110 °C, formate was the dominant product in high-purity MEG, while both formate and glycolate were formed in technical-grade MEG. Acetate concentrations did not increase during oxidation; on the contrary, when acetate was added to the solution, its concentration decreased over the course of the experiments. These findings provide insight into the oxidative stability of MEG under regeneration and reclamation conditions and offer guidance for the design and operation of MEG recovery systems in hydrate management applications.