Comparison of thermal degradation between fresh and industrial aqueous methyldiethanolamine with continuous injection of H2S/CO2 in high pressure reactor

• Thermal degradation of methyldiethanolamine (fresh and industrial) was compared.
• Organics and heat stable salts were identified with increasing concentration.
• MDEA degradation and formation of organics obeyed first order kinetics.
• Distillation analysis of degraded MDEA identified high boiling degraded products.
• Foaming studies were carried out and compared with both the degraded MDEA.

Thermal degradations of fresh and industrial lean MDEA solvent obtained from the natural gas sweetening unit of GASCO Company (Habshan, Abu Dhabi) were studied for a period of 865 h of continuous operation under CO2 and H2S partial pressures of 0.0675 and 2.025 bars, respectively, at 120 °C. Samples of the degraded solvent were taken out at regular intervals and analyzed using ion chromatography (IC), gas chromatography mass spectrometry (GC–MS), inductively coupled plasma optical emission spectrometry (ICP-OES) and proton-transfer-reaction with quadrupole mass spectrometry (PTR-QMS) instruments. Almost similar degradation compounds like monoethanolamine, diethanolamine, methylethanolamine, triethanolamine, dimethylaminoethanol, dimethylacetamide, etc. were found from both fresh and lean MDEA solvents. The degraded compounds followed first order kinetics and their rate constant values were higher for fresh MDEA than in that of the lean solvent. However, the rate of formation of both formic and acetic acid were higher in lean MDEA than in fresh solvent. Residue content was also almost doubled for lean solvent as compared to fresh after distillation analysis. Finally, iron solubility test (IST) and foaming studies were carried out with both the degraded solvents. Results showed that degraded lean MDEA had higher IST value (292 ppm) and foaming tendency (foam height 235 mm) as compared to freshly degraded MDEA (IST value 119; foam height 94 mm) at constant nitrogen flow rate of 68.3 L/hr.