Experiments and model for the surface tension of DEAE-PZ and DEAE-MEA aqueous solutions

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Highlights

  • The surface tensions of DEAE and amine-DEAE aqueous solutions were measured.

  • The experiments were modelled satisfactorily by using a thermodynamic equation.

  • MEA and PZ have close ability to decrease the solution surface tension.

  • The temperature dependence of the surface tension was illustrated.

  • The effects of the mass fractions of amines and DEAE were demonstrated.

Abstract

The surface tension (γ) of 2-diethylaminoethanol (DEAE), DEAE-monoethanolamine (MEA), and DEAE-piperazine (PZ) aqueous solutions was measured by using the BZY-1 surface tension meter. The temperature ranged from 303.2 K to 323.2 K. The mass fraction of DEAE, MEA and PZ respectively ranged from 0.30 to 0.50, 0.05 to 0.15 and 0.025 to 0.075. An 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.

Introduction

Climate change and environmental problems caused by the emissions of carbon dioxide (CO2) have attracted increasing attention worldwide and the reduction of CO2 has become a global issue [1], [2]. Post combustion CO2 capture using amine as absorbent is one of the mature technologies for reducing CO2 emissions from coal-fired power plants [3], [4], [5], [6], [7]. Conventional amines such as primary amine monoethanolamine (MEA), secondary amine diethanolamine (DEA), tertiary amine N-methyldiethanolamine (MDEA), and diamine piperazine (PZ) have been extensively applied to remove CO2 from a variety of industrial processes [8], [9]. Among these amine series, the major drawback of primary and secondary amines aqueous solution is the high energy consumption in regeneration process [10], [11], [12]. Tertiary amines take advantage of high absorption capacity and low energy cost for regeneration, however, the CO2 reaction rate is relatively slow. Previous work [13], [14], [15] shows that addition of small amount of activators like MEA, DEA or PZ into tertiary amine aqueous solution can significantly enhance the absorption rate of CO2.

Recently, DEAE has attracted increasing attention in the development of new absorbent for CO2 capture. As it has a good application potential for the removal of CO2 and can be prepared from renewable resources [16], [17], it is considered to be a good alternative to MDEA. Chowdhury et al. [18] investigated the absorption characteristics of 24 kinds of tertiary amine absorbents and compared their performances with those of MDEA. Comparison shows DEAE has better chemical stability, higher CO2 loading capacity, higher cyclic capacity yet lower heat of reaction. By far, there are many studies [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32] concerning both the kinetics and thermodynamics for the absorption of CO2 in DEAE aqueous solution and its blends with MEA and PZ. In particular, very recently, Fu et al. [29], [30] measured the absorption capacity of CO2 in DEAE-PZ and DEAE-MEA aqueous solutions, and the viscosities for both CO2-unloaded and CO2-loaded DEAE-PZ and DEAE-MEA aqueous solutions. Their work showed that DEAE has better absorption capacity than MDEA, and the addition of MEA and PZ can significantly enhance the absorption rate of CO2. Moreover, they also illustrated the effects of mass fraction and temperature on the absorption capacity and the effects of temperature, mass fraction and CO2 loading on viscosities. Besides absorption capacity and viscosity, surface tension is also important to the design and simulation process for CO2 capture. It can significantly affect the absorption efficiency because both the penetration of CO2 molecules from the gas phase to the liquid phase and the enhancement of the absorption closely relate to the surface tension, thus the knowledge of surface tension is required when designing or simulating an absorption column. In recent years, there has been some experimental and theoretical work concerning the surface tension of aqueous solutions containing amines and their blends [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45]. The surface tension of DEAE aqueous solutions within the temperature range 283.15 K to 303.15 K has been reported by Lampreia et al. [46]. However, experimental and theoretical studies on the surface tension of DEAE-MEA and DEAE-PZ aqueous solutions are rare so far.

The main purpose of this work is to determine experimentally the surface tension of DEAE, DEAE-MEA and DEAE-PZ aqueous solutions and model the surface tension, and then demonstrate the effects of temperature and mass fractions of amines on the surface tension. To this end, the surface tension was measured within the temperature range from 303.2 K to 323.2 K. The mass fraction of DEAE, MEA and PZ respectively ranged from 0.3 to 0.5, 0.05 to 0.15 and 0.025 to 0.075. Besides experimental work, an equation is proposed in this work to model the surface tension.

Section snippets

Materials

The samples used in this work are detailed in Table 1. Purities are as stated by the supplier, and no further purification was carried out. The water contents (in mass fraction) of DEAE, MEA and PZ are respectively 0.04%, 0.06% and 0.05% (determined by using the Karl Fischer method, as stated by the supplier). The uncertainty of the analytical balance is ±0.1 mg, however, taking the purities and water content into account, the uncertainties of the mass fractions of DEAE, MEA and PZ are

Results and discussion

To verify the reliability of the equipment, the surface tension of water was measured at T = 298.2 K. The obtained value is 71.9 mN·m−1. This value is compared to that (72.0 mN·m−1) presented in the work of Fu et al. [39] and Vázquez et al. [44], and the deviation is 0.14%. Moreover, the surface tension of pure DEAE and DEAE aqueous solutions was measured and then compared with those reported in the work of Lampreia et al. [46]. For pure DEAE, the surface tension values at 283.2 K, 293.2 K and 303.2 K

Conclusions

In this work, the surface tension of DEAE, DEAE-MEA, and DEAE-PZ aqueous solutions was measured by using the BZY-1surface tension meter and modelled by using a thermodynamic equation. The effects of temperature and mass fraction of amines on the surface tension were demonstrated. Our results show that:

  • (1)

    The increase of temperature and the mass fraction of DEAE, MEA and PZ tend to decrease the surface tension;

  • (2)

    Within the investigated ranges of temperature and mass fractions of amines, the surface

Acknowledgments

The authors appreciate the financial support from the National Natural Science Foundation of China (No. 21276072) and the Fundamental Research Funds for the Central Universities (No. 13ZD16).

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