Aspen plus modelling of CO2 absorption using DEEA

“In the Aspen Plus database, DEEA can be found as component. However, its cation was not found in the database and was added. The components, DEEA and DEEAH+, together with their interaction with water, carbon dioxide and ions need to be fitted. The experimental data used to fit and validate the developed model are listed in Table 1.

Table 1. Sets of parameters used for fitting and validation of the simulation model presented in this work.

Data [DEEA] Temperature (°C) Loading (mol CO2/mol DEEA) Points References
CO2 Partial pressure 2 M 40, 60, 80 0.02–0.888 43 [20]
CO2 Partial Pressure 5 M 40, 60, 80 0.005–0.398 42 [20]
Total Pressure 2 M 80 0.71–1.02 9 [20]
Total Pressure 5 M 80 0.25–0.67 9 [20]
Heat of mixing 0.0472–0.9011 (Molar Fraction) 25 0 18 [23]
Total Pressure 5 M 40 0.039–1.038 44 [24]
CO2 Partial Pressure 5M 40, 80 0.038–0.990 68 [24]
Density 0–1 (Molar Fraction) 20–70 0 106 [25]
Density 2 M 20–70 0.14–0.79 36 [25]
Density 5 M 20–70 0.14–0.42 20 [25]
Density 0-1 (Molar Fraction) 20–40 0 96 [29]
Density 0–1 (Molar Fraction) 25–45 0 78 [28]
Vapour pressure 1 5–45 0 31 [20]
Vapour pressure 1 60–176 0 13 [30]
Vapour pressure 0.0015–0.5611 (Molar Fraction) 50–95 0 44 [15]
Water vapour pressure 0 49–144 0 7 [26]
Water vapour pressure 0 34–100 0 50 [27]

Firstly, the vapour pressure of DEEA was regressed with Aspen Plus using data from Hartono et al. [15] and for water using information from NIST (National Institute of Standards and Technology) [26] and Kim et al. [27]. New values are presented for the Antoine’s equation for both pure components, DEEA and H2O (Table 6). Then, the binary system DEEA-H2O was regressed using experimental data [15] and new interaction parameters were obtained. Additionally, the excess enthalpy was fitted using data from Mathonat et al. [23].

For loaded DEEA solutions, the partial pressure of CO2 and total pressure data were used to fit physical solubility of CO2 by regression. The new interaction parameters of the electrolyte pairs were obtained. Due to the high number of parameters to be fitted, the regression was improved with some final modifications by trial and error, using the CO2 partial pressure and total pressure data [20][24] as outputs to be fitted.

Knowledge of densities is important for several applications within the absorption process: power required for pumping the unloaded and loaded solutions, influence in mass transfer, absorption rate and subsequently the efficiency of the entire process. The prediction of densities must be taken into account in order to obtain proper values in the calculation of the process. The densities of unloaded and loaded DEEA solutions were regressed in this work using the Racket model with Aspen Plus. New value for the Racket parameter (ZRA) was obtained and results were validated with experimental data for DEEA-H2[25][28][29] and DEEA-H2O-CO2 systems [25].

In this work, the errors are reported by the parameter AARD, averaged absolute relative deviation (Eq. (1)).(1)AARD(%)=1N∑i=kN100|nk−φk|φk

The critical parameters as well as the acentric factor and compressibility factor are listed in Table 2.

Table 2. Pure physical properties of DEEA, H2O and CO2 [31].

Empty Cell DEEA H2O CO2
PC (kPa) 3180 7374 22060
TC (K) 592 304.13 647.3
VC cum/kmol 0.401 0.0939 0.0559
Zc 0.259 0.274 0.229
Acentric factor 0.782 0.225 0.344

The dielectric constant of DEEA was approximated to the value of trimethylamine due to the similarities in their structure. Values are included in Table 3, together with the values for H2O.

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