Adsorptive gas dehydration with supported ionic liquids

在2015年11月完成的DFG项目过程中，离子液体（IL）已经成功地研究了其用于通过吸收（气体洗涤）干燥气体的用途。结果，已经发现IL [EMIM][MeSO 3]是目前用于工业气体干燥的三甘醇（TEG）的合适替代物，并且在重要性能特征上超过TEG：与TEG相比，所需的吸附塔高度较低;由于其非常低的蒸气压和所需的低得多的再生温度，避免了再生步骤中由于蒸发而造成的损失;此外，其抗氧化的稳定性使得能够用空气作为汽提剂再生IL;相反，TEG对氧敏感。基于这些结果，用负载型离子液体（在二氧化硅上的[EMIM][MeSO 3]）进行的首次测量表明，这种系统也可用于气体干燥。主要优点是与常用的吸附剂如硅胶或沸石相比，再生温度低得多。在新的应用研究项目（申请继续资助）中，应继续对气体干燥用离子液体进行研究，以便更好地深入了解新的吸附系统。（备注：严格地说，蒸汽被吸收在离子液体中，离子液体负载在多孔固体上;然而，这里使用术语吸附，因为与离子液体中的吸收平行，真实的吸附也可以在固体载体上发生，并且该过程通常在用于吸附的固定床中进行。除了已经（部分）表征的IL [EMIM][MeSO 3]之外，另外两种有前途的离子液体[EMIM][乙酸盐]和[EMIM][Cl]对于详细研究是有意义的。首先，重点在于气体干燥的重要物理化学数据（H2O的活度系数，蒸汽压）的其余两个离子液体的测定;此外，系统的测量方面的H2O吸附热力学（吸附等温线）必须进行。基于这些测量，将决定哪种IL和多孔载体的组合是最好的，用于在固定床吸附器中的进一步研究。因此，必须改变孔填充度以及颗粒尺寸，以确定传质（孔扩散）对吸附动力学的影响。这将分别通过分析穿透曲线和转移区的高度进行实验探索。沿着这些实验，固定床中吸附过程的建模在单个颗粒以及整个固定床的水平上都是至关重要的。因此，必须求解考虑单个颗粒（扩散、吸附）和固定床中的过程的微分方程;通过将模拟中获得的数据与实验数据进行比较，可以证明吸附器模型。

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.