Experiment and model for the viscosity of carbonated 2-amino-2-methyl-1-propanol-monoethanolamine and 2-amino-2-methyl-1-propanol-diethanolamine aqueous solution
Introduction
The greenhouse effect and acid rain caused by the emission of CO2 from industrial processes and coal-fired boilers seriously impacted the sustainable development of the economy. Development of affordable yet technically feasible separation technologies for reducing CO2 emission has attracted global attention. Chemical absorption is one of the most effective approaches for CO2 capture because CO2 can be satisfactorily removed and the absorbents can be well regenerated by heating. Currently, aqueous solutions of alkanol amines have been widely used for the removal of CO2 from a variety of gas streams [1], [2], [3], [4], [5], [6], [7]. Among the alkanol amine series, N-methyldiethanolamine (MDEA) takes the advantages of large absorption capacity, high resistance to thermal and chemical degradation, low solution vapor pressure, and low enthalpy of absorption. However, MDEA has a low absorption rate. Adding small amount of primary and secondary amines to an aqueous solution of MDEA has found widespread application in the removal of CO2 [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18].
Besides MDEA, the sterically hindered amine, e.g., 2-amino-2-methyl − 1-propanol (AMP), is also considered to be an attractive solvent for the removal of CO2 due to its absorption capacity, absorption rate, selectivity and degradation resistance advantages [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]. Compared with MDEA, AMP has the same absorption capacity for CO2 (1 mol of CO2 per mol of amine) but much higher reaction rate [23]. When the aqueous solutions of AMP are used to absorb CO2, as AMP only forms bicarbonate and carbonate ions, the regeneration energy costs are relatively low. Adding small amount of primary and secondary amines to an aqueous solution of AMP is also helpful to promote the absorption of CO2 [24], [25]. For similar relative composition, the rates of absorption of CO2 in AMP–MEA and AMP–DEA aqueous solutions are higher than those in MDEA–MEA and MDEA–DEA aqueous solutions.
The viscosities of alkanol amine aqueous solutions are required when designing or simulating an absorption column for CO2 absorption. In particular, solution viscosity is important to the mass transfer rate modeling of absorbers and regenerators because these properties affect the liquid film coefficient for mass transfer. By far, there are some experiments concerning the viscosities of aqueous solutions containing AMP–MEA and AMP–DEA [30], [31], [32]. In particular, Mandal et al. [30] measured and modeled the viscosities of both AMP–MEA and AMP–DEA aqueous solutions. However, the experiments and theoretical work for the viscosities of CO2-loaded AMP–MEA and AMP–DEA aqueous solutions are rare.
The main purpose of this work is to investigate the viscosities of carbonated AMP–MEA and AMP–DEA aqueous solutions experimentally and theoretically, so as to demonstrate the temperature, mass fractions of amines and CO2 loading dependences of the viscosities. To this end, the viscosities of carbonated AMP–MEA and AMP–DEA were measured at temperatures from 303.15 K to 323.15 K, with the total mass fractions of amines and the CO2 loading respectively ranging from 0.3 to 0.4 and 0.1 to 0.5. The modified Grunberg–Nissan equation [33] was used to model the viscosities of carbonated aqueous solutions.
Section snippets
Materials
AMP, MEA and DEA were purchased from Huaxin Chemical Co. The sample description is shown in Table 1. They were used without further purification. Aqueous solutions of AMP–MEA and AMP–DEA were prepared by adding doubly distilled water. The uncertainty of the electronic balance is ± 0.1 mg.
Apparatus and procedure
The carbonated AMP–MEA and AMP–DEA aqueous solutions were prepared according to the methods mentioned in the work of Amundsen et al. [34], Weiland et al. [36] and Fu et al. [37], [38], [39], [40]: CO2-unloaded
Results and discussion
The viscosities of carbonated AMP–MEA and AMP–DEA aqueous solutions at different temperatures, CO2 loadings and amine mass fractions are shown in Table 2, Table 3.
Besides experiments, models that can correctly correlate and predict the viscosities are also important. Among the widely used equations [33], [36], [41], the Eyring [41] equation can only quantitatively describe the temperature dependence of viscosity. The Grunberg–Nissan equation [33] can well describe the temperature and amine
Summary
The viscosities of carbonated AMP–MEA and AMP–DEA aqueous solutions have been measured. The experiments have been satisfactorily modeled by using a modified Grunberg–Nissan equation. The effects of temperature, mass fractions of amines and CO2 loading on the viscosities of carbonated solutions have been demonstrated based on the experiments and calculations. Our results showed that:
(1) The modified Grunberg–Nissan equation can correctly describe the viscosities of carbonated AMP–MEA and AMP–DEA
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 (No. 13ZD16).
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