Experiment and model for the surface tension of carbonated MEA–MDEA aqueous solutions
Highlights
► Surface tensions of carbonated MEA–MDEA aqueous solution were measured. ► Surface tensions of CO2 unloaded and loaded aqueous solutions were modeled. ► The decreasing surface tension is mainly due to increasing MDEA concentration. ► The effects of temperature, amine concentration and CO2 loading were demonstrated.
Introduction
In recent decades, atmospheric levels of CO2 have increased rapidly due to the utilization of great amount of fossil fuel. The reduction of CO2 emissions became a global issue [1], [2]. Aqueous solutions of alkanolamines like monoethanolamine (MEA) and N-methyldiethanolamine (MDEA) are widely used for the removal of CO2 from a variety of gas streams [3], [4], [5], [6], [7], [8].
Among the alkanolamines series, MDEA takes the advantages of high resistance to thermal and chemical degradation, low solution vapor pressure (minimum solvent loss during regeneration), and low enthalpy of absorption (low energy requirement for regeneration). However, compared with other amines like MEA, an MDEA aqueous solution has a lower absorption rate. Adding small amounts of MEA to an aqueous solution of MDEA has found widespread application in the removal of CO2. The mixtures of MEA and MDEA preserve the high rate of the reaction of MEA with CO2, and the low enthalpy of the reaction of MDEA with CO2, hence lead to higher absorption rates in the absorber column, yet lower heat of regeneration in the stripper section [5], [6].
Surface tensions of aqueous solutions are required when designing or simulating an absorption column for CO2 absorption associated with chemical reactions. Until now, there are some experiments concerning the surface tensions of aqueous solutions containing MEA and MDEA [9], [10], [11], [12], [13], [14], [15], [16]. In particular, Vazquez et al. [12] and Alvarez et al. [15] systematically measured the surface tensions of MEA aqueous solutions and MDEA aqueous solutions at temperatures from 298.15 to 323.15 K. They also measured the surface tensions of MEA–MDEA aqueous solutions at temperatures from 298.15 to 323.15 K, with the total mass fraction of amines wMEA + wMDEA = 0.5. However, the surface tensions of MEA–MDEA aqueous solutions at relatively low mass fractions of amines, e.g., wMEA + wMDEA = 0.2, 0.3 and 0.4 are rare. Moreover, the surface tensions of carbonated MEA–MDEA aqueous solutions have been rarely reported, and due to the lack of the experiments and theoretical models, the effects of mass fraction of amines, temperatures and CO2 loading have not been well documented by far.
To demonstrate the temperature, mass fraction of amines and CO2 loading dependence of the surface tensions, the surface tensions of CO2 unloaded (temperature ranging from 293.15 to 333.15 K, wMEA and wMDEA respectively ranging from 0.05 to 0.20, and 0.05 to 0.45) and CO2 loaded (temperature ranging from 293.15 to 323.15 K, wMEA and wMDEA respectively ranging from 0.05 to 0.10 and 0.30 to 0.45, CO2 loading ranging from 0.1 to 0.5) MEA–MDEA aqueous solutions were measured by using the BZY-1 surface tension meter, which employs the Wilhemy plate principle. A model was proposed to correlate the surface tensions of both CO2 unloaded and CO2 loaded solutions.
Section snippets
Materials
Both MEA and MDEA were purchased from HuaXin Chemical Co. The sample description is shown in Table 1. They were used without further purification. Aqueous solutions of MEA–MDEA were prepared by adding doubly distilled water.
Apparatus and procedure
The surface tension was measured by using the BZY-1 surface tension meter produced by Shanghai Hengping Instrument Factory. BZY-1 meter employs the Wilhemy plate principle, i.e., the maximum tensile force competing with the surface tension is measured when the bottom edge of
Results and discussion
Surface tensions of CO2 unloaded MEA–MDEA aqueous solutions at different temperatures and different mass fraction of amines are shown in Table 3. Some of the experimental data are compared with the work of Vazquez et al. [12] and Alvarez et al. [15]. The average relative deviations between our results and those from the work of Vazquez et al. [12] and Alvarez et al. [15] are respectively 0.81% and 0.33%. Surface tensions of the CO2 loaded MEA–MDEA aqueous solutions at series of temperatures,
Summary
In this study, the surface tensions of CO2 loaded and CO2 unloaded MEA–MDEA aqueous solutions were measured and a model was proposed to calculate the surface tensions. The temperature, amine concentration and CO2 loading dependence of the surface tensions were demonstrated. Our results showed that:
- (1)
For both the unloaded and loaded MEA–MDEA aqueous solutions, the increase of amine concentration and temperature tends to decrease the surface tensions.
- (2)
For unloaded MEA–MDEA aqueous solutions, at a
Acknowledgments
The authors appreciate the financial support from the National Natural Science Foundation of China (Nos. 21276072 and 21076070), the Natural Science Funds for Distinguished Young Scholar of Hebei Province (No. B2012502076), and the Fundamental Research Funds for the Central Universities (Nos. 11MG53 and 11ZG10).
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