CO2 Capture Using Ternary Amine-based Deep Eutectic Solvents

Abstract

The global energy demand is in continuous increase, and as a result, the dependence on burning fossil fuels to meet the energy demands is causing substantial rise in CO2 emissions, which is considered as one of the greenhouse gases that are believed to increase global warming. Post combustion carbon capture technology is one of the commonly used processes in capturing CO2 and reducing its amounts in the atmosphere. For many years, this technology has been utilizing aqueous amine solutions as absorbents for the capture of CO2. However, aqueous amine solutions have several drawbacks such as, solvent degradation, high regeneration energy, and negative environmental impacts. Consequently, a new class of green solvents termed as deep eutectic solvents (DESs) has emerged in recent years to replace aqueous amines. Based on the wise choice of their constituents, many of the DESs are cheap, easy to prepare, biodegradable, non-toxic, and have negligible vapor pressure, making them viable solvents for several industrial processes. Nonetheless, most of DESs have very high viscosities, which impede their use in many applications. Therefore, this MSc. thesis investigates the effect of the addition of water, as a low viscous ternary component, to amine-based deep eutectic solvents during the preparation step, on the physicochemical properties, thermal stability, CO2 absorption capacity and heat of absorption. In addition, the effect of HBA:HBD molar ratio, water content, type of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) on the aforementioned parameters was investigated. Moreover, the effect of temperature and pressure on the CO2 absorption capacity of the DESs was predicted using COSMO-RS. COSMO-RS was also used to predict the CO2 solubility in the DESs and the results were compared to the experimental values. The results revealed that the addition of small quantities of water, e.g. 5% and 10% by weight during the preparation step, is capable of decreasing the viscosity of the resulting DESs significantly, up to 25% at room temperature, while maintaining high CO2 absorption capacity and high thermal stability. The MEA based ternary DESs exhibited high CO2 absorption capacity ranging from 0.155 – 0.17 (g CO2 / g DES). Furthermore, an increase in the heat of absorption upon the inclusion of water was noticed; therefore, a compromise between the viscosity and the heat of absorption should be considered. The ternary DESs proved to be thermally stable with an onset degradation temperature of 125 °C which promotes the use of such solvents in post-combustion capture processes. Finally, COSMO-RS was found to be an appropriate tool to be used in qualitatively predicting the CO2 solubility in DESs and demonstrating the trends associated with the effect of varying factors such as temperature, pressure, molar ratio, water content, HBD and HBA on the CO2 solubility.

Date of Award	Dec 2021
Original language	American English