(780f) A Generic Approach of Hybrid Membrane / Condensation Process : Potentialities and Limitations

In numerous industrial applications, gaseous streams containing an inert gas and a condensable compound have to be treated by a separation process. A direct condensation strategy is often applied for that purpose, but it requires in certain cases a cryogenic operation (e.g. a liquid nitrogen cold box), typically when the target condensor temperature is lower than –30 C. This situation occurs for low boiling compounds and/or when a low residual concentration of the condensable compound is necessary. In that event, an alternative approach based on hybrid membrane condensation process can be proposed: the principle consists to achieve a pre-concentration of the condensable compound by membrane separation (vapor permeation), in order to enable condensation to occur on the permeate side of the membrane at a higher temperature. This concept has been already succesfully applied for Volatile Organic Compounds (VOC’s) recovery from air [1-4], where increasingly stringent regulatory requirements make recovery of VOC’s of utmost importance. Nevertheless, the hybrid membrane condensation concept could possibly be of interest for other industrial applications such as drying of natural gas, hydrocarbon removal from hydrogen purification, ammonia recovery or carbon post combustion capture [5].

In this study, a generic approach of a hybrid membrane/condensation process has been developped and will be compared to a direct condensation strategy, taken as the baseline. It will be shown that, based on only two key parameters, namely the condensable compound solubility parameter and the membrane selectivity, the potential interest of the hybrid approach can be rapidly evaluated. The Hildebrand solubility parameter includes indeed the cohesive energy of the condensable compound and its molar volume; this property can be related to the condensation temperature, the heat of condensation or the solubility of a compound in an elastomeric membrane.

A large range of solubility parameter data, covering gases (CO₂, NH₃), VOC’s (hexane, dicholoroethane, acetone or vinyle chloride) and water has been investigated through a series of simulations of the hybrid process. The influence of different membrane process parameters, e.g., recovery ratio, pressure ratio, stage cut has been carried out. The condensation temperature has been evaluated for each set of conditions and each compound, and, from this, the corresponding overall energy requirement of the process is estimated.

As a major outcome of this study, a generic process selection map will be presented. Based on the solubility parameter and membrane selectivity, the potentiality of the hybrid membrane/condensation process to achieve attractive performances comparing to the standalone condensation process is analysed. Heuristic rules and recommandations leading to an increased energy efficiency of the hybrid membrane condensation process covering diffrents solvent/inert/membrane systems will finally be proposed.

References

[1] Richard W. Baker, Noriaki Yoshioka, Judith M. Mohr, Amy J. Khan, Separation of organic vapors from air, Journal of Membrane Science, Volume 31, Issues 2–3, May 1987, Pages 259-271.

[2] H. Paul, C. Philipsen, F.J. Gerner, H. Strathmann, Removal of organic vapors from air by selective membrane permeation, Journal of Membrane Science, Volume 36, 1988, Pages 363-372.

[3] K. Kimmerle, C.M. Bell, W. Gudernatsch, H. Chmiel, Solvent recovery from air, Journal of Membrane Science, Volume 36, 1988, Pages 477-488.

[4] M. Leemann, G. Eigenberger, H. Strathmann, Vapour permeation for the recovery of organic solvents from waste air streams: separation capacities and process optimization,  Journal of Membrane Science, Volume 113, Issue 2, 15 May 1996, Pages 313-322.

[5] B. Belaissaoui, D. Willson, E. Favre, Membrane gas separations and post-combustion carbon dioxide capture: Parametric sensitivity and process integration strategies, Chemical Engineering Journal 211–212 (2012) 122–132.