The offshore process of natural gas dehydration is of crucial importance in meeting the required specifications and avoiding the formation of hydrates when transporting rich gas by pipeline. Monoethylene glycol or triethylene glycol, molecules with a high affinity for water, are generally used as desiccants. After dehydration, the absorbent is regenerated by heating it to a high temperature. Unfortunately, it would seem that successive regenerations gradually alter the desiccant capacities of the two glycols.
This master thesis therefore focuses on the degradation of MEG and TEG glycols used as absorbents for natural gas dehydration. Through a series of experiments and analyses, we have tried to better understand the functioning of this degradation.
For different temperatures, MEG and TEG were heated in the presence of oxygen for three weeks. Samples were regularly taken, inerted and stored in cold. These samples were then analysed by ion chromatograph, pH-metric titration, and spectroscopy. These analyses enabled us, among other things, to identify certain degradation products of the two glycols, to understand the influence of time and temperature on the composition of the degradation products, to highlight the differences in the behaviour of MEG and TEG or to quantify the acids present among the degradation products.
Surplus to the experimental work, the first steps towards simulation of the degradation was taken but comparing predictions of different physical and thermodynamic property models in Aspen Plus. To this end, the calculated values of certain physical and thermodynamic properties were compared with experimental values found in the scientific literature. It was found that the appropriate model is highly dependent on the choice of the used desiccant.