Highly carbon dioxide-philic liquid oligomers and phase change-solvents for the absorption of carbon dioxide

The overall objective of this work is to identify the most CO2-philic compounds from three classes of compounds made up of C, N, O, and H intended to be used in the carbon capture process associated with the IGCC plant. The three classes of compounds in question are low volatility CO2-philic oligomers, volatile organic solvents, and solid CO2-philic compounds that are capable of melting in the presence of CO2.;Phase behavior experiments have been carried out in order to construct phase diagrams for each solvent and CO2. These diagrams quantify the miscibility of CO2 in each solvent which helps determine the best possible solvent for absorbing CO2 from a mixed gas high pressure stream in a typical counter-current absorption column. The higher the miscibility of CO2 in the absorbent, the lower the pressure of phase separation will be throughout the phase behavior diagram.;Several solvents classified as low volatile CO2-philic oligomers were tested with CO2. A mixture of low volatility CO2-philic oligomers known as poly(ethylene glycol) di-methyl ether, PEGDME, is the current solvent of choice in the IGCC capture process. Poly(dimethylsiloxane), PDMS, and poly(propylene glycol) di-methyl ether, PPGDME, are potentially better solvents, compared to PEGDME, in this process due to their limited miscibility or immiscibility with water, a constituent in the fuel stream, and their low viscosity, an important property for gas transport in and out of the liquid phase solvent.;Volatile organic solvents, while not prevalent in the IGCC capture process, are very widely used as solvents for a range of separation applications and are used extensively in CO2 capture primarily in the sweetening process of natural gas. Commercial scale sorbents including methanol and propylene carbonate have been in use for years under the proprietary names of Rectisol(TM) and the Fluor process. Several organic solvents were examined in this study in binary mixtures with CO2. It was determined that acetone is the best solvent on a weight basis due to its small spherical size and shape and the CO2-philic ketone functionality. It cannot be used commercially however due to its high vapor pressure that would cause significant evaporative losses in practice. The best solvents compared on a molar basis include 2-(2-butoxyethoxy)ethyl acetate, 2-methoxyethyl acetate, both discovered in this work, and methyl acetate. Overall the best solvents on a weight or molar basis are those that are highly oxygenated compounds, rich in carbonyl and/or ether groups that favor Lewis acid:Lewis base interactions with CO2.;CO2-philic solids are from the last group of potential solvents examined with CO2 and were found in the past by our group and two others. Originally investigated to be valuable as sand binders, these solids' unique ability to melt and then mix with CO2 has great potential value in energy savings and initial capital equipment cost savings. This potential stems from these solvents' ability to release all CO2 absorbed at a moderate pressure, approximately 5 MPa as opposed to a liquid solvent that releases CO2 at 0.1 MPa.;Lastly, higher molar mass PDMS solvents were examined and compared to PEGDME (molar mass = 310) at elevated temperatures. These PDMS solvents are all substantially larger than the PDMS hexamer tested in conjunction with the other hexamers and oligomers tested. The major benefit these higher molar mass solvents have is that they allow the capture step to be carried out at higher temperatures. Additionally these PDMS solvents are completely immiscible with water up to 68.95 MPa and 393 K. This change in the capture process allows for the elimination of heat exchangers needed to lower the temperature of the fuel gas stream, and also eliminates a condenser step that is typically needed to eliminate much of the water out of the fuel stream for the hydrophilic PEGDME solvent. (Abstract shortened by UMI.)...