In this work a thermodynamic model has been developed based on electrolyte-NRTL model within Aspen Plus framework using the binary parameters obtained form literature (Hilliard, 2008) to predict the vapor-liquid equilibria of CO2 in aqueous piperazine (PZ) solutions. The model is validated with the experimental VLE data generated in this work and literature data. The VLE data of CO2 in aqueous PZ were measured over the temperature range of 298 313 K and CO2 partial pressure range of 1-140 kPa using 0.2M, 0.4M, and 0.8M aqueous PZ solutions. The experimental data for the aqueous PZ system are used to regress the electrolyte-NRTL parameters using the maximum likelihood principles of the Aspen Plus software. The model predicted VLE of CO2 in aqueous PZ is in very good agreement with the experimental data.
Keywords: Carbon dioxide, Electrolyte NRTL, Piperazine, Aspen Plus®, VLE
[...] * miγ m 1000 ln km = ln K + i ln x γ * = ln K + ln M i w i i 5 Due to chemical reaction in the liquid phase of the PZ-H2O-CO2 system, carbon dioxide is dissolved predominantly in non volatile, ionic form (Kamps et al., 2003). The fallowing chemical reactions are considered in the liquid phase: the autoprotolysis of water the formation and dissociation of bicarbonate the protonation and diprotonation of piperazine R5) and the formation of piperazine carbamate, piperazine dicarbamate R7). [...]
[...] Carbon dioxide pure) used for the VLE measurements were obtained from Chemtron Science Pvt. Ltd., India Apparatus A VLE experimental setup with thermostated stirred equilibrium cell similar to the one used by Park and Sandall (2001), was used in this work. A detail schematic of the experimental setup is presented in Figure 1. The VLE system consists of a ~ 1.2 L stainless steel cylindrical cell connected to a calibrated external gas buffer vessel and a magnetic stirrer is used for liquid phase agitation. [...]
[...] Chemical Engineering Progress, 32- Danckwerts, P.V. (1979). The reaction of CO2 with ethanolamines. Chemical Engineering Science 443–446. Derks, P.W.J., Dijkstra, H.B.S., Hogendoorn, J.A., and Versteeg, G.F., (2005). Solubility of carbon dioxide in aqueous piperazine solutions. AIChE J 2311–2327. Derks, P.W.J, Kleingeld, C., van Aken, C., Hogendoorn, and J. A., Versteeg, G. F., (2006). Kinetics of absorption of carbon dioxide in aqueous piperazine solutions. Chemical Engineering Science 6837–6854. Samanta, A. (2008). Absorption of carbon dioxide into piperazine activated alkanolamine. PhD dissertation. [...]
[...] Electrolyte-2 a b c d (1994) molecule Water-electrolyte - 8477.711 - DIPPR databank Electrolyte-water 4 From the ENRTL model, the infinite dilution activity coefficient of PZ can be represented by the equation as presented by Cullinane (Cullinane and Rochelle, 2003) 19779 ln γ PZ = 318.1 44.42 ln T ( K ) T ) Data in the form of total pressure which measures the solubility of CO2 into aqueous piperazine solution as a function of molality and temperature were used to adjust the activity coefficients of CO2 in piperazine and water for the simultaneous regression of the binary interaction parameter in the E-NRTL model with representation of the following equation for equilibrium total pressure data * P = xPZ γ PZ PPZ + xH2Oγ H 2O PH 2O + xCO2 γ CO2 H CO H 2O At this stage neglecting the vapour phase piperazine concentration and accounting for the vapour pressure of water, the above expression reduces to equation * PyCO2 = xCO2 γ CO2 H CO H 2O Adjustable binary parameters were determined by DRS within Aspen Plus® utilizing the maximum likelihood principle of Britt and Luecke (1973) through minimization of the following objective function: n ( P P U n f = WU k k ,adj 2 k ,obs + WPk k ,adj 2 k ,obs k σUk σ Pk k Where the measurable variables, Uk, are the state variables (that is and property variables, Pk, are vapour pressure depression and heat capacity Results and discussion In the present work, the VLE data of CO2 in aqueous PZ solutions were generated over the temperature range of 298 313 K and CO2 partial pressure range of 1-140 kPa and presented in Table 3 and fig 2 and compared with available literature data. [...]
[...] Newman and J. M. Prausnitz. (1978). Vapour-liquid equilibria in multicomponent aqueous solution of volatile weak electrolytes. AIChE J 966-976 Ermatchkov, V., A. P. S. Kamps, and G. Maurer, (2003). Chemical equilibrium constants for the formation of carbamates in ( CO2 + piperazine + water) from 1H-NMR spectroscopy. J. Chem. Thermodynamics 1277-1289. Hilliard, M. D. (2008). A predictive thermodynamic model for an aqueous blends of potassium carbonate, piperazine, and monoethanolamine for carbon dioxide capture from flue gas. PhD Dissertation, The University [...]
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