Solubility of dilute sulfur dioxide in binary mixtures of ethylene glycol and tetraethylene glycol dimethyl ether
Introduction
Sulfur dioxide (SO2), one of the most significant contaminants, is the main causes of several environment problems, e.g., acid rain, polluted rivers, corroded architectures, and human health problems. Especially, it plays an important role in the formation of particulate matters 2.5 (PM 2.5), which has spread across China in the past few years [1], [2]. Nowadays, the control of SO2 emission has become a serious problem.
The most effective way to control the SO2 in flue gas emitted from combustion of fossil fuels is flue gas desulfurization (FGD). The conventional flue–gas desulfurization (FGD) technique is based on limestone. However, there are some inherent drawbacks, such as high capital investment and operating cost, useless byproducts (CaSO4 and CaSO3), and waste water [3], [4]. Considering that SO2 is a kind of useful chemical material, regeneration of the SO2 after absorption is desirable. Thus, organic solvents [5], [6], ionic liquids (ILs) [7], [8], [9], [10], [11], and SO2-binding organic liquids [12], [13], [14], which can be regenerated by reducing pressure or increasing temperature, turn to be alternatives to the conventional method.
Due to the favorable absorption and desorption properties of acid gases and their excellent fluid properties, organic solvents, including alcohols, amines, amides, sulfoxides, and ethers, have caught the attention of researchers for many years [4], [6], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]. Ethylene glycol (EG) and its aqueous solutions are considered to be a kind of promising absorbent for SO2 because of their advantages such as reversible absorption, low price, and non-toxic. Our previous work demonstrated that the absorption of SO2 in EG is a physical absorption process, so the absorbent can be regenerated by either reducing pressure or increasing temperature [29], [30]. However, the absorption capacities of dilute SO2 in pure EG and its aqueous solutions are rather low, so an improvement is still required. Tetraethylene glycol dimethyl ether (TEGDME) is a polar solvent which has been applied in acid gases removal [19], [28]. To the best of our knowledge, few solubility data of SO2 in pure TEGDME and binary mixtures of EG and TEGDME can be found in literature.
In this work, we determined the solubilities of SO2 in EG, TEGDME and their mixtures at temperatures from 293.15 K to 313.15 K under a constant pressure of 122.7 K to investigate the effect of the mixture composition on SO2 absorption. In addition, further thermodynamic parameters, including Henry’s law constants (H′), enthalpy changes (ΔH), entropy changes (ΔS) and Gibbs free energies (ΔG), were also calculated to investigate the mechanism of the absorption processes.
Section snippets
Materials
Ethylene glycol (EG) and tetraethylene glycol dimethyl ether (TEGDME) were purchased from Beijing Yili Fine Chemical Co., Ltd. and Alfa Aesar, respectively. All reagents were obtained in the highest purity grade possible, and directly used as received without further purification. (see Table 1) The standard dilute gas of SO2 in N2 ( = 8 × 10−3) employed in determination of gas–liquid equilibrium data of EG and TEGDME mixtures was supplied by Beijing Gas Center, Peking University.
Solubility of SO2
All GLE data of SO2 in binary mixtures were listed in Table 2 and plotted in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 at different temperatures. In Table 2, w1 is mass fraction of TEGDME in the mixture, is the partial pressure of SO2 in GLE system, and denotes the molarity of SO2 in the liquid phase.
As shown in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, the solubility plots are similar to those in literature [32]. The results show that the solubility of SO2 in each mixture increases
Conclusion
In this work, isothermal GLE data of dilute SO2 in EG, TEGDME and their mixtures were measured at temperatures from 293.15 K to 313.15 K under a total pressure of 122.7 kPa. The absorption processes of dilute SO2 obeys Henry’s law at the investigated pressure. Based on these isothermal GLE data, thermodynamic parameters of SO2 absorbed in these liquids were obtained, which indicates that the absorption of SO2 is enthalpy driving and exothermic at the given conditions. Furthermore, the mixture with
Acknowledgment
This work was supported by Boyuan Hengsheng High-Technology Co., Ltd., Beijing, China.
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