Abstract

The solubility of carbon dioxide, nitrous oxide, methane and ethane in a physical solvent, triethylene glycol monomethyl ether (TEGMME) were recently measured by Henni and Mather (1.2.3.4) at 40, 70 and 100 °C at pressures up to 10.9 MPa. TEGMME was found to be the best solvent for CO2 removal among physical solvents used in the gas processing industry. In order to compare these solubility data with those of other polar solvents, a literature search was done to gather solubility data in solvents with a wide range of dielelectric constants. The solubility data compiled were for pressures higher than atmospheric pressure. The Peng-Robinson (1976) ISI equation of state was used to correlate the data for the solubility of CO2 in the polar solvents. The Henry's constants are then derived using the Kritchevsky-Kasarnovsky(6) or the Kritchevsky- Illenskaya equation m. The results show that ethyl acetate and propyl acetate are the two solvents that absorb CO2 the most. But, among the best solvents for CO2 removal, TEGMME has the lowest boiling point. Dimethyl ether is among the best solvents for CO2 absorption is also among solvents that absorbs methane the most. Diethyl ether has the highest capacity for methane absorption. The study confirms the fact that the best physical solvents for absorbing acid gases have the disadvantage of absorbing the largest amounts of ethane. The solubility data in the CO2, N2O, CH4 and C2H6 systems were generally well-correlated by the Peng-Robinson equation of state even for those systems that are highly nonideal.

Introduction

The Government of Canada has been an active participant in the development of international agreements and protocols for emissions reduction. It has committed the country to meeting national emission caps for anthropogenic air emissions. Just how these national targets will be met is a critical question to provincial governments but also to oil, coal and utility companies in Canada. As carbon dioxide is a major contributor to the global warming phenomena, the process of carbon dioxide removal from coal-fired power plants and its utilisation as a flooding agent for enhanced oil recovery (EOR) is the focus of a lot of attention. The CO2 captured will generate revenues and help reduce emissions that contribute to the greenhouse effect.

Zawacki et al. (1981)(8) have screened more than 100 solvents for their potential of removing acidic gases (CO2, H2S). The dimethyl ether of tetraethylene glycol (DMETEG) was chosen as one of two most promising solvents. In an attempt to provide the industry with better physical solvents, a study was initiated to test new solvents. Triethylene glycol monomethyl ether [TEGMME, c.A. Registry No. 112-35-6] belongs to the same family as DMETEG but it costs four times less. In order to combine the advantages of both physical and chemical solvents, mixed solvents have been proposed. This combination allows for a higher CO2 loading, a low solution circulation rate and regeneration energy.

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