(222e) Prediction of VOCs Adsorption Equilibria Under Supercritical Carbon Dioxide Conditions By Using Pure Component Data

Recycle of the supercritical carbon dioxide (scCO₂) is essential in terms of preventing CO₂ emissions and reducing running cost for industrial uses of the solvents. We have focused on adsorption processes du e to its removal capability of dilute solutes such as VOCs (Volatile organic compounds) in scCO₂ solution.  In this paper, measurements and prediction of VOCs adsorption equilibria on activated carbon in scCO₂ were studied for designing the processes.

Experimental data of VOCs (Acetone, n-Hexane, Toluene, n-Decane, Methanol) adsorption equilibria in scCO₂ were measured by a fixed bed method in the pressure range of 4.2 - 15.0 MPa at 313 - 353 K [1, 2]. The Dubinin-Astakhov (DA) equation [3] and the ideal adsorbed solutions theory (IAST) [4] were applied to predict the adsorption equilibria by using pure component adsorption isotherms, that were also measured with a gravimetric method.

The DA-IAST model provided a good prediction of experimental results in the cases of non-polar substance like n-hexane and at lower pressure conditions.  On the other hands, relatively large deviations occurred in the cases of polar substances like methanol and also at higher pressure conditions. These results could be caused by large non-ideality in the adsorbed phase in polar and high pressure conditions.  Therefore, more suitable model for scCO₂ systems must be developed with consideration of the strong non-ideality. 

References

[1] I. Ushiki et al., Fluid Phase Equilib., 344, 101 (2013).

[2] I. Ushiki et al., J. Chem. Eng. Jpn., 45, 931 (2012).

[3] M. M. Dubinin, V. A. Astakhov, Adv. Chem. Ser., 102, 69 (1971).

[4] A. L. Myers, J. M. Prausnitz, AIChE J., 11, 121 (1965).