Investigation of water kinetics in zeolite Linde‐Type‐A crystals by a concentration‐swing frequency response

Abstract

A new concentration‐swing frequency response system was developed to evaluate water kinetics in non‐binder containing zeolite Linde Type A (LTA) crystals with frequencies up to 1 Hz. For commercial micron‐sized 3A crystals, the mass transfer rate is too fast to be determined accurately due to reduced sensitivity near the system limits. Larger LTA crystals (~15 μm) were synthesized in house and ion exchanged to three potassium concentrations (0, 48, and 77 wt%) to aid in the accurate determination of mass transfer mechanism and rates. Micropore diffusion with parallel sites, not a surface barrier, described all the data well, consistent with the bimodal distribution of crystal sizes from scanning electron microscope images. The transport diffusivity for water in zeolite 3A crystals near saturated loadings at 25°C is about 1 × 10−12 m2/s, 10 times slower than 4A crystals around 10−11 m2/s, both supporting fast micropore diffusion time constants >1 s−1 for micron‐sized crystals.