Optimizing spatial pore-size and porosity distributions of adsorbents for enhanced adsorption and desorption performance

• A method is proposed to optimize the spatial structure of adsorbents.
• A uniform spatial structure is proven to be the preferred one.
• The average porosity of adsorbents is optimized.
• The method is relevant to PSA processes, where the effect of the adsorption/desorption cycle period is considered.

This paper shows that a uniform spatial distribution in meso/macroporosity of adsorbents maximizes their adsorption and desorption performance. It highlights the importance of optimizing porosity and pore diameter, not only at the nanoscale but also at larger length scales. The effects of spatial pore size and porosity distributions on mass transfer in adsorbents are studied by using a continuum approach. These effects are evaluated by comparing the adsorption/desorption performance of adsorbents subjected to a square wave concentration perturbation with a wide range of cycle period (10–100,000 s) for the adsorption of n-pentane on 5A zeolite adsorbents. The uniformly distributed pore size and porosity is the preferred structure, which is confirmed by using four empirical tortuosity–porosity relations. Further optimization of the uniform structure shows that its optimal average porosity is in the range of 0.4–0.6 when the perturbation cycle period is between 100 s and 2000 s and the volume-averaged pore diameter is between 10 nm and 150 nm. The relationships between optimal average porosity, cycle period and volume-averaged pore diameter are determined and explained. These results should serve to guide the synthesis of adsorbents.