Thermal degradation kinetics of morpholine for carbon dioxide capture

Abstract

Deterioration of amines under process operating conditions for sour gas treatment is a severe problem. New amines are being investigated to replace conventional amines which face operational, economic and environmental challenges. Morpholine (MOR) is an understudied amine for carbon dioxide (CO2) capture which comes with good CO2 capture characteristics like CO2 absorption rate, CO2 solubility etc. This study investigates the stability of aqueous morpholine under stripper conditions. Effect of CO2 loading and temperature have been investigated on the degradation kinetics of MOR. CO2 loading is varied from 0 to 0.48 mol CO2/mol alkalinity and temperatures is varied 135–190 °C. Thermal degradation experiments were conducted using 316 stainless steel cylinders, closed with Swagelok® endcaps. The degraded samples were analyzed by using Gas Chromatography-Mass Spectrometry (GC–MS), Gas Chromatography-Flame Ionization Detector (GC-FID) and Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry (LC-QToF-MS) for morpholine concentration and identification of degradation products. Morpholine demonstrated higher stability up to 150 °C. However, higher degradation rate is found at temperatures 175 °C and above. Degradation rate increases with CO2 loading. Identified degradation products are tabulated in the text and reaction mechanisms for formation of some of the key degradation products are also provided. A kinetic model for the rate of degradation of morpholine is proposed, which shows a decent agreement with experimental data. Comparison shows that morpholine is thermally more stable compared to monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA) and piperazine (PZ).