The CO 2 absorption properties of monoethanolamine (MEA) solutions containing varying amounts of surfactant were examined using different experimental apparatus: a packed column, a stirred reactor, a wetted wall column, and a bubble column. The carbon capture efficiency in the packed column was improved by the addition of surfactant. Surface tension measurements of the different solutions were taken over a range of CO 2 loadings, and the addition of surfactant was seen to lower the surface tension of the amine solvent. However, the improvement in carbon capture efficiency could not be fully correlated to the surface tension depression. The addition of surfactant improved CO 2 absorption in the packed and bubble columns, while the surfactant inhibited absorption in the stirred reactor and wetted wall column experiments. Visual inspection of solvent flowing down a packed column revealed the gas to be bubbling through the liquid, which increases the gas−liquid interfacial area and thus the overall level of mass transfer of carbon dioxide into solution.
■ INTRODUCTIONThere is growing concern about the emission of carbon dioxide into the atmosphere and the associated environmental impact. 1 As a result, reducing CO 2 emissions is of global interest. Significant progress in this area might be made by reducing carbon dioxide emissions from large, stationary point sources such as power plants. 2 For this purpose, carbon capture and storage (CCS) using aqueous amine solvents is well understood and can be implemented at these point sources. 3,4 In this report, we discuss some of our work on improving the absorption of CO 2 by amines for such applications.Absorption of carbon dioxide by an amine solvent consists of the gaseous CO 2 being absorbed into the liquid and the subsequent chemical reaction with the amine. Thus, there are both physical and chemical limitations to this process. The physical aspects of absorption (dissolution of CO 2 into the liquid and product and reactants diffusing to and from the gas− liquid reaction interface) are dependent on the CO 2 , product, and amine concentration gradients and localized mixing. 5 In this work, we focus on lowering the physical resistance to CO 2 absorption by using a surfactant. Surfactants in aqueous systems have been proposed to increase gas−liquid interfacial turbulence (Marangoni instability) and thereby increase the level of mass transfer, 6−8 though it is not clear that this instability is present in systems that feature a rapid chemical reaction such as the CO 2 −aqueous amine system. 9 In fact, there are numerous other reports that say the opposite; i.e., surfactant additives decrease the level of mass transfer of gases (N 2 , CO 2 , and O 2 ) into aqueous amine solutions and pure water. 10−15 One consideration when evaluating these contradictory results is the surfactant itself. Shorter hydrophobic chain lengths (≤10 carbons) were shown to enhance mass transfer at low concentrations, 6−8 whereas surfactants with longer hydrophobic chain lengths (>10 carbons) re...