Adsorptive gas dehydration with supported ionic liquids

在2015年11月完成的dfg项目中，离子液体（ILs）已经成功地研究了它们通过吸收（气体洗涤）用于气体干燥的用途。结果发现，IL [EMIM][MeSO3]是目前用于工业气体干燥的三乙二醇（TEG）的合适替代品，并且在重要的性能特征上优于TEG：与TEG相比，所需的吸附柱高度较低；由于它的蒸气压很低，所需的再生温度也低得多，因此避免了再生步骤中蒸发造成的损失；此外，它抗氧化的稳定性使IL再生与空气作为剥离剂；相反，TEG对氧气很敏感。基于这些结果，首次使用负载离子液体（[EMIM][MeSO3]在二氧化硅上）的测量表明，这种系统也可以用于气体干燥。与常用的吸附剂如硅胶或沸石相比，其主要优点是再生温度低得多。在申请的新研究项目（申请继续资助）中，应继续对气体干燥的负载型ILs进行研究，以便更好、更深入地了解新的吸附系统。（注：严格地说，蒸汽是在离子液体中被吸收的，离子液体是在多孔固体载体上被吸收的，但这里使用吸附这个术语，因为与离子液体中的吸收平行，固体载体上也可能发生真正的吸附，该过程在固定床上进行，通常用于吸附。）除了已经（部分）表征的IL [EMIM][MeSO3]外，还有两种有前途的离子液体[EMIM][醋酸盐]和[EMIM][Cl]值得详细研究。首先，重点确定剩余两种液体的气体干燥重要物化数据（H2O活度系数、蒸汽压）；此外，还必须进行有关h2o吸附热力学（吸附等温线）的系统测量。根据这些测量结果，将决定IL和多孔支撑的哪种组合最适合在固定床吸附器中进行进一步研究。因此，为了确定传质（孔隙扩散）对吸附动力学的影响，必须改变孔隙填充程度以及颗粒大小。这将分别通过对突破曲线和传递区高度的分析进行实验探讨。在这些实验中，固定床吸附过程的建模是至关重要的，无论是在单个颗粒的水平上还是在整个固定床上。因此，必须求解单粒子（扩散、吸附）和固定床的微分方程；通过与实验数据的比较，验证了吸附器模型的正确性。

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.