Experiment and model for surface tensions of 2‑diethylaminoethanol‑N‑(2‑aminoethyl)ethanolamine, 2‑diethylaminoethanol‑N‑methyl‑1,3‑propane‑diamine and 2‑diethylaminoethanol‑1,4‑butanediamine aqueous solutions

https://doi.org/10.1016/j.molliq.2019.111031Get rights and content

Highlights

  • Surface tensions of DEAE and AEEA/MAPA/BDA aqueous solutions were measured.

  • Experiments were modeled satisfactorily by using a thermodynamic equation.

  • Surface thermodynamics including surface enthalpies and entropies were determined.

  • Effects of temperature and mass fraction on surface properties were illustrated.

Abstract

The surface tensions of 2‑diethylaminoethanol (DEAE)‑N‑(2‑aminoethyl)ethanolamine (AEEA), DEAE‑N‑methyl‑1,3‑propane‑diamine (MAPA) and DEAE‑1,4‑butanediamine (BDA) aqueous solutions have been measured by using the BZY-1 surface tension meter. The mass fractions of DEAE and AEEA/MAPA/BDA respectively ranged from 0.300 to 0.500 and 0.050 to 0.150. The temperature ranged from 303.2 K to 323.2 K. A thermodynamic equation was proposed to model the surface tension and the calculated results agreed well with the experiments. The effects of temperature and mass fraction of amines on the surface tension were demonstrated on the basis of experiments and calculations. The surface thermodynamics including surface enthalpy and surface entropy of blended amine aqueous solutions were also determined, and their temperature and mass fraction dependences were analyzed.

Introduction

Carbon dioxide (CO2), a primarily greenhouse gas, has caused global warming and climate change in recent years. The reduction of CO2 has attracted increasing attentions [1,2]. CO2 capture via efficient processes has become a major technological challenge. Among the available separation technologies including absorption, adsorption, membrane and hydration, alkanolamine-based absorption technology is considered to be the most suitable one and gaining more and more attention in CO2 capture process [[3], [4], [5]]. Conventional amines such as primary amine monoethanolamine (MEA), secondary amine diethanolamine (DEA), teriary amine N‑methyldiethanolamine (MDEA) and sterically hindered amine 2‑amino‑2‑methyl‑1‑propanol (AMP) have been extensively applied for CO2 removal [[6], [7], [8], [9]]. However, the drawbacks of high energy cost and low absorption capacity when using traditional primary and secondary amine aqueous solutions lead to operational difficulties and economic infeasibility. Moreover, amine degradation and foaming lead to loss of CO2 absorption capacity, reduction of mass transfer and carryover of amine solutions [10]. Compared with traditional primary and secondary amines, the tertiary amine takes advantages of high absorption capacity and low energy cost in regeneration.

Recently, 2‑diethylaminoethanol (DEAE) has attracted increasing attention in the development of new absorbent for the removal of CO2. Many previous works showed that DEAE has good application potential for CO2 capture and can be good alternatives to traditional tertiary amine like MDEA [3,11,12]. Chowdhury et al. [11] investigated absorption characteristics of CO2 in different kinds of new tertiary amine absorbents and compared with those in MDEA absorbent. Their results showed that DEAE had higher absorption rates and cyclic capacities and lower or comparable heats of reaction than MDEA. Puxty et al. [3] showed that the trend of initial CO2 absorption rate in DEAE absorbent was higher than that in MDEA absorbent. Although the tertiary amine aqueous solutions take advantages of high absorption capacity and low energy cost, they have slower reaction rate with CO2 because they act only as a weak base to produce free OH [12]. Addition of activators like MEA, DEA or piperazine (PZ) into DEAE aqueous solution can overcome the aforementioned drawbacks because the blended amines preserve the advantages of both activators and DEAE [[13], [14], [15]].

Besides MEA, DEA and PZ, new amines like N‑(2‑aminoethyl)ethanolamine (AEEA), N‑methyl‑1,3‑propane‑diamine (MAPA) and 1,4‑butanediamine (BDA) can also accelerate the CO2 absorption in DEAE aqueous solutions and lower the energy requirement in regeneration [[16], [17], [18], [19]]. Xu et al. [16] investigated the cyclic loading and cyclic capacity of various concentration of BDA and DEAE. Their results showed that the blends of 2 M BDA/4 M DEAE had the best absorption performance, with 46% higher cyclic loading, 48% higher cyclic capacity and 11% higher cyclic efficiency than the blends of 5 M MEA/4 M DEAE. Kierzkowska-Pawlak et al. [17] showed that the observed enhancement factors in DEAE-AEEA aqueous solutions were at least twice higher than those in DEAE aqueous solutions. Arshad et al. [18] investigated the equilibrium total pressures and equilibrium CO2 partial pressures in aqueous solutions of DEAE-MAPA. Their results showed that the blends gave fairly good cyclic capacities and CO2 absorption capacity. Monteiro et al. [19] showed that MAPA had similar volatility as PZ but less volatility than MEA.

Thermophysical property like surface tension of blended amine aqueous solution is an important property required in the design of contacting equipment including packed columns and membrane contactors for CO2 absorption, because it affects the hydrodynamics and transfer rates, e.g., decrease of surface tension can lead to a reduction in the bubbles size [[20], [21], [22], [23]]. Moreover, in the packed column for CO2 absorption, surface tension was found to be one of the most sensitive parameter influencing the effective mass transfer area. Decreasing surface tension can trigger an elevated capability of spreading, and help to increase the useful area of the packing [20,21]. In addition, the Marangoni effect resulting from surface tension gradient was found to affect the mass transfer performance in packed–bed absorber [22]. In membrane contactors, values of surface tension are necessary to estimate the breakthrough pressure of the solution through the pore of the membrane. In bubbling reactors, surface tension can modify the size of bubbles. Lower surface tension can allow the achievement of higher interfacial areas [23]. In recent years, there are many experimental and models concerning the surface tension of blended amine aqueous solutions [[24], [25], [26], [27], [28], [29], [30], [31]]. However, experimental and theoretical works concerning the surface properties of DEAE-MAPA, DEAE-AEEA and DEAE-BDA aqueous solutions are rare, and the effects of temperature and mass fraction of amines on surface properties have not been well documented so far.

The main purposes of this work are to (1) measure and model the surface tensions of DEAE-AEEA, DEAE-MAPA and DEAE-BDA aqueous solutions; (2) demonstrate the effects of mass fraction of amine and temperature on the surface thermodynamics. To this end, the surface tension was measured at the temperature from 303.2 K to 323.2 K. The mass fraction of DEAE and AEEA/MAPA/BDA respectively ranged from 0.300 to 0.500 and 0.050 to 0.150. Besides experimental work, thermodynamic equations were used to model the surface tension. Surface enthalpy and surface entropy of blended amine aqueous solutions were also determined, and their temperature and mass fraction dependences were analyzed.

Section snippets

Materials

DEAE, MAPA, AEEA and BDA were used without further purification. The samples in this work are shown in Table 1. Aqueous solutions of DEAE-MAPA, DEAE-AEEA and DEAE-BDA were prepared by adding doubly distilled water (Electrical resistivity >15 MΩ cm at 298 K) which was obtained from the Heal Force ROE-100 apparatus. The uncertainly of the electronic balance is ±0.1 mg.

Apparatus and procedure

The surface tension was measured by using the BZY-1 surface tension meter produced by Shanghai Hengping Instrument Factory. The

Surface tension

The experimental results of the surface tensions of DEAE-MAPA, DEAE-AEEA and DEAE-BDA aqueous solutions are respectively shown in Table 2, Table 3, Table 4. It seems the temperature and the mass fractions of both DEAE and MAPA/AEEA/BDA can affect the value of surface tension. For the surface tensions of a certain blend with given mass fractions, their temperature dependence can be expressed as γ = K1 + K2 T, K1 and K2 can be determined by using the experimental data. For example, to formulate

Conclusion

In this work, the surface tensions of DEAE-AEEA, DEAE-MAPA and DEAE-BDA aqueous solutions were measured and modeled. The effects of temperature and mass fraction of amines on the surface tension were demonstrated. The surface enthalpy and surface entropy were calculated and their temperature and mass fraction dependences were also illustrated. Our results show that:

(1) The surface tensions of DEAE-AEEA, DEAE-MAPA and DEAE-BDA aqueous solutions decrease with increasing wAEEA/wMAPA/wBDA and

Acknowledgements

The authors appreciate the financial supports by the National Natural Science Foundation of China (No. 51776072), the Fundamental Research Funds for the Central Universities (No. 2018MS116), the Natural Science Foundation of Hebei Province (No. E2018502062) and the Beijing Natural Science Foundation (No. 3194060).

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