Solid–Liquid Equilibria of a 30 wt % Aqueous Monoethanolamine Solution Containing Urea and Monoethylene Glycol

The solid–liquid phase boundaries on new innovative solvents for the carbon capture and storage (CCS) technology have been measured in this work. The solvents have been formulated with vapor reduction additives (VRAs) also known as water lean solvents. The solid–liquid equilibrium (SLE) data will create better prediction models for the CCS technology and prevent precipitation in process equipment and thereby reduce the risk of costly shutdowns.

The presented SLE data cannot be used in the prediction of solid formation in the condenser as it would require knowledge of the vapor–liquid–solid equilibria. The SLE of the systems urea–H2O, urea–monoethanolamine (MEA)–H2O, and monoethylene glycol (MEG)–H2O has been determined using the methods freezing point depression (FPD) and SLE by FPD.

A total of 61 new SLE data points are listed of 0 < w(urea) < 60% and 0 < w(MEG) < 20%. It is the first time that the ternary systems have been measured. The eutectic temperatures were found at −8 °C for urea–H2O and −27 °C for urea–MEA–H2O. Highly concentrated urea solutions freeze completely upon mixing water with MEA due to the endothermic reaction.

Solubility data of MEG–MEA–H2O were found for t > −40 °C. All SLE points for MEG in 30 wt % aqueous MEA freeze below −15 °C. To avoid clogging from urea precipitation, it is recommended to use urea below 30 wt %.