Article pubs.acs.org/jced
Measurement and Correlation of the Solubility of Carbon Dioxide in the Mixtures of Aqueous Monoethanolamine Solution and Benzoic Acid Hyun Seung Lee, Myoung Do Seo, Jeong Won Kang, and Dae Ryook Yang* Department of Chemical and Biological Engineering, Korea University, 1 Anamdong 5Ga, Seongbukku, Seoul 136-713, Republic of Korea ABSTRACT: The solubility of CO2 in the mixture of aqueous monoethanolamine (MEA) with benzoic acid was measured and correlated using a reaction-phase equilibrium model. The solubility of CO2 in 15 wt % aqueous MEA solution was measured at a temperature of 313.2 K and pressures up to 200 kPa. Also, the solubility of CO2 in the mixtures with various weight ratios of benzoic acid, MEA, and water were measured at a temperature of 313.2 K and pressures ranging from (1 to 250) kPa. The weight ratios (acid/MEA/water) were 1:15:85, 2:15:85, 10:15:85, 15:15:85, 1:14:85, 2:13:85, and 5:10:85. Reaction equilibrium constants of the Kent−Eisenberg model were used for the CO2−MEA−water mixture, and new equilibrium constants involving benzoic acid were estimated using experimental data. The concentration of species in the liquid phase was estimated as a function of CO2 loading, and the effect of adding benzoic acid can be predicted within reasonable accuracy using the proposed model.
1. INTRODUCTION
2. EXPERIMENTAL SECTION 2.1. Materials. MEA and benzoic acid were purchased from Dae Jung Co., Korea (w > 0.99) and used without further purification. CO2 gas (w > 0.9999) was purchased from Sambo Co., Korea. The purity of MEA was confirmed by measurement and comparison of density with a literature value7 as shown in Table 1. Also, the aqueous solutions were prepared with tripledistilled water. 2.2. Apparatus and Procedure. The experimental procedure and apparatus used in this study are similar to the previous work of Kim et al.8 for measuring the solubility of CO2 in ionic liquids, and they are briefly discussed here again. As shown in Figure 1, the apparatus consists of an equilibrium cell (1), a CO2 reservoir (2), a CO2 cylinder (3), a solution reservoir (4), a vacuum pump (5), a circulator (6), a water bath (7), a pressure gauge (8), a temperature indicator (9), and valves (V1, V2, V3). Prior to each measurement, the entire system was cleaned and evacuated with vacuum pump to remove contaminants. After the evacuation step, the CO2 reservoir was filled with pure CO2 by opening the valve (V1) from gas cylinder. Weighted MEA solution or benzoic acid and MEA solution was placed in solution reservoir (4). Then V2 was opened, and the solution was introduced by vacuum state of equilibrium cell. Finally, V3 was opened, and CO2 was introduced in equilibrium cell as well. After 3−4 h of the equilibration period, the final partial
Chemical absorption is a useful and economic technology for capturing CO2 in postcombustion capture systems from a power plant.1−3 The CO2 capture technologies using amines have been the focus of many research papers and are available commercially. However, the amine-based absorption still requires a considerable amount of energy and capital cost in the solvent regeneration step. To reduce capital and energy costs in the process, researchers have tried to improve the process. Recently, there are studies in which an organic acid solution is added to emit CO2 from the amine absorbent in the amine scrubber by decreasing the CO2 solubility.4,5 Then, the amine solvent and the acid would be separated by a liquid− liquid or solid−liquid phase split. In this study, the effects of adding acid on the solubility of CO2 in amine solution and chemical equilibrium model are presented. MEA (monoethanolamine) was used as amine solvent, which is widely used commercially due to its high solubility of CO2 and low solvent cost. Also, benzoic acid was chosen among acid candidates (benzoic acid, fumaric acid, and oxalic acid) as the organic acid because it can form a solid phase in amine solution and can be separated by energy-efficient reaction crystallization.6 The solubility of CO2 in amine solution with varying amounts of benzoic acid were measured and correlated using the reaction-phase equilibrium model based on the Kent−Eisenberg model. New reaction constants involving benzoic acid were estimated to fit experimental data. The measured data and proposed model can be used for process development of postcombustion CO2-capture system. © 2012 American Chemical Society
Received: September 14, 2012 Accepted: November 8, 2012 Published: November 16, 2012 3744
dx.doi.org/10.1021/je301009d | J. Chem. Eng. Data 2012, 57, 3744−3750
Journal of Chemical & Engineering Data
Article
Table 1. Comparison of Experimental Density, ρ, of Monoethanolamine at 298.15 K ρ/g·cm−3
a
compound
source
mass fraction purity
monoethanolamine
Dae-Jung Co.
