Adsorptive gas dehydration with supported ionic liquids

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In the course of the DFG-project, which was completed in November 2015, ionic liquids (ILs) have been successfully studied with regard to their use for drying of gases by absorption (gas scrubbing). As a result, it has been found that the IL [EMIM][MeSO3] is a suitable alternative to triethyleneglycol (TEG) currently used for industrial gas drying and surpasses the TEG in important performance features: The required height of the adsorption column is lower compared to TEG; losses due to evaporation in the regeneration step are avoided because of its very low vapor pressure and the much lower regeneration temperatures needed; furthermore its stability against oxidation enables regeneration of the IL with air as stripping agent; in contrast, TEG is sensitive to oxygen. Based on these results first measurements with supported ionic liquid ([EMIM][MeSO3] on silica) have shown that such a system can be also used for gas drying. A main advantage is the much lower regeneration temperature compared to commonly used adsorption agents such as silica gel or zeolites. Within the applied new research project (application for continuation of funding), this research on supported ILs for gas drying should be continued in order to get a better and deeper insight into the new adsorption system. (Remark: Strictly speaking, steam is absorbed in the ionic liquid, which is supported on porous solid; nevertheless, the term adsorption is used here, because parallel to the absorption in the IL a real adsorption may also take place on the solid support and the process is conducted in a fixed bed typically for adsorption.) In addition to the already (partly) characterized IL [EMIM][MeSO3], two other promising ionic liquids, [EMIM][acetate] and [EMIM][Cl], are of interest for detailed investigation. At first, the focus lies on the determination of the important physicochemical data for gas drying (activity coefficient of H2O, vapor pressure) of the remaining two ILs; in addition, systematic measurements with regard to the thermodynamics of H2O-adsorption (adsorption isotherms) have to be conducted. Based on these measurements, the decision will be made which combination of IL and porous support is the best for further studies in a fixed-bed adsorber. Thereby, the pore filling degree as well as the particle size has to be varied in order to determine the influence of mass transfer (pore diffusion) on the kinetics of adsorption. This will be experimentally explored by the analysis of breakthrough curves and the height of the transfer zone, respectively. Along with these experiments, modelling of the adsorption process in the fixed-bed is crucial, on both the level of a single particle as well as the entire fixed-bed. Therefore, the differential equations considering the processes in a single particle (diffusion, adsorption) and in a fixed-bed have to be solved; by comparison of the data gained in the simulations with the experimental data, the adsorber model can be proven.