(43g) Advanced VSA Setup for CMS Quality Control

As a consequence of the tailored pore structure, carbon molecular sieves (CMS) enable separations of relevant gas mixtures including O₂/N₂, CO₂/CH₄, N₂/CH₄, or CO₂/N₂ by exploiting dissimilarities of mass transfer rates among adsorptives. Thus, PSA/VSA techniques utilize primarily that effect for the efficient production of purified gas streams. However, the rigorous design of those systems requires extended information about the selected adsorbent such as adsorption capacity, selectivity, regenerability, kinetics, and costs.

Commercially manufactured CMS are inhomogeneous due to the fluctuating properties of raw materials originating in natural sources, along with not uniform conditions inside the reactors enabling large production capacities. Therefore, the quality of the product varies within the accepted deviation range for a specific CMS grade. Those quality variations are common not only among different production batches but also within a single production batch. For this reason, to extract representative information about the adsorbent property, the results of experimental methods involving small amounts of the adsorbent shall be analyzed statistically, which might be associated with a notably extended number of tests.

The process-based quality assessment of CMS via PSA/VSA carried out in pilot plants remains the commercial standard and it is considered the most foolproof procedure which directly provides data about the separation effectiveness in authentic operating conditions. In this case, the utilization of relatively large amounts of the material allows for a significant reduction in the number of experiments to extract reliable information. However, those methods are not fully suitable for the fundamental study of mechanisms governing separation processes because the obtained performance results always depend on the interaction of adsorption equilibria, mass transfer kinetics, and adsorber dynamic effects.

To address those issues, an advanced VSA setup for fast and reliable N₂-CMS quality control is constructed, which enables implicit estimation of adsorption capacity, separation selectivity, and adsorbent regenerability at different cycle conditions. The setup functionality as well as collected data using different CMS types are presented and discussed. The developed system can be adapted to different gas mixtures. Conducted experiments are supporting the fabrication of improved adsorbents in favour of PSA/VSA systems exhibiting reduced CAPEX and/or OPEX as well as the design of novel materials.