Chunfei Wu

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CO2 absorption - solvent - Amine-based - Influence of process conditions - Amine concentration - Temperature - Type of amine

Vapor–liquid equilibrium using nonaqueous 10 wt % Diisopropylamine

https://doi.org/10.1021/acs.energyfuels.0c00880

“Figure 3 shows the vapor–liquid equilibrium results obtained for solutions containing mixtures of different diluents and 10 wt % of diisopropylamine, at both 40 and 80 °C. These data can also be found in the Supporting Information together with its uncertainties.”

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“Figure 3. Vapor–liquid equilibrium data for solvents containing 10 wt % diisopropylamine.”

“The blue-colored datapoints refer to values obtained under operation at 40 °C and clearly indicate heavy depression of chemical reaction in the NMP–diisopropylamine blend (◇ markers). This is evidenced by the almost entirely linearly dependent set of VLE data obtained at both 40 and 80 °C, typical of physical absorption behavior (i.e., Henry’s law). Conversely, H2O–diisopropylamine and MEG–diisopropylamine have VLE curves commonly observed for chemical solvents, hallmarks of which are little dependence of CO2 solubility on partial pressure up to near the stoichiometric limit (α = 1 mol CO2·mol amine–1) and, afterward, a sharp dependency of solubility on pressure.

We have not been able to obtain reliable data with aqueous diisopropylamine 10 wt % at 80 °C due to excessive volatilization of the solvent. This volatilization led to the formation of a rock-solid white precipitate in some key parts of the calorimeter apparatus, including around the pressure transducer. Consequentially, the pressure readings of these experiments had to be completely discarded. In fact, aqueous diisopropylamine 10 wt % presents issues even before loading began. A close inspection of the unloaded solution inside a transparent bottle reveals separation between a light organic phase and a heavy aqueous phase.
Conversely, phase separation has not been observed for mixtures of diisopropylamine with either N-methyl-2-pyrrolidone or ethylene glycol. As a preliminary result, this indicates that shifting from water to an organic diluent enables the utilization of diisopropylamine for CO2 absorption/desorption in conditions otherwise impractical in aqueous solvents.
Figure 4 shows the integral heat of absorption obtained for solutions containing mixtures of different diluents and 10 wt % diisopropylamine only at 40 °C. Data for the heat of absorption at both 40 and 80 °C can be found in the Supporting Information together with its uncertainties.”

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