A study of monoethanolamine-methanol hybrid solvents for carbon dioxide capture by absorption.

摘要

Climate change and the production of greenhouse gases (GHGs) have become important issues in many countries around the world. There has been a heightened awareness that carbon dioxide (CO2) emission from fossil fuel combustion is the primary contributor to this phenomenon. One of the potential solutions to reducing CO2 emissions is CO2 capture, a process whereby CO2 is separated and collected from industrial gas streams, such as Clue gases. Currently, there are many capture technologies for carbon dioxide. Among them, gas absorption into chemical solvents is the most promising technology due to its capacity to handle a large volume of flue gas. One of the keys to successful operation of CO2 chemical absorption processes is the use of effective solvents. Aqueous solutions of alkanolamines are the most commonly used solvents for CO2 and others acid gas removal. Nevertheless, aqueous alkanolamines do have shortcomings that make the process costly. Firstly, it quickly becomes chemically saturated, and secondly, significant energy is required for solvent regeneration. Therefore, hybrid solvents can play a significant role in improving process efficiency.;This thesis also proposed a model that can predict the mass transfer coefficient. The model was established on the basis of film theory. The model not only can evaluate overall mass transfer coefficient, but also can compute parameters involved based on film theory. From the model's parameters, it can be shown that methanol in MEA hybrid solvent can enhance the mass transfer coefficient of CO2 absorption. Improvement of mass transfer coefficient of MEA hybrid solvent resulted from the increase of physical liquid phase mass transfer coefficient and interfacial loading.;In this thesis, Henry's constant was used to describe the solubility of MEA aqueous and hybrid solvent. The enhancement factor was calculated by applying Henry's constant value to the parameter E/H from the mass transfer coefficient model. The kinetics of the reaction of CO 2 with MEA in aqueous and hybrid solvents were investigated using a stirred cell absorber with a gas-liquid interface. The absorption rate data under the fast reaction regime were analyzed in terms of the zwitterion mechanism. The reaction rate of each step and the order of reaction with respect to CO 2 and MEA were calculated and compared among solutions.;Finally, this research also describes a carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopic method to determine the concentrations of various ionic species that are formed in the liquid phase of the CO 2-MEA aqueous and hybrid system, namely, carbonate (CO 32-), bicarbonate (HCO3-), and carbamate (MEACOO-) ions.;This thesis serves to extend the knowledge of CO2 absorption using hybrid MEA solvents. The performance of CO2 absorption by MEA aqueous solution, MEA in methanol, and MEA in water-methanol 1:1 was measured using a bench-scale gas absorption column with structured packing. The obtained data were compared as a variable of process parameters, including type of solvent, inlet CO2 partial pressure, inert gas flow rate, inlet CO, loading, and solvent flow rate. The results show that MEA in methanol solution showed significantly higher performance for CO2 absorption than MEA in aqueous solution.