Gas diffusion and adsorption capacity enhancement via ultrasonic pretreatment for hydrothermal synthesis of K-KFI zeolite with nano/micro-scale crystals

Abstract Small-pore zeolites have been a research hotspot in the field of gas adsorption and separation. Despite the high adsorption levels of these zeolites, the slow adsorption and desorption rate as well as desorption hysteresis are detrimental to the industrial applications. In this work, nano/micro-scale (~500 nm) K-KFI zeolite crystals were synthesized via hydrothermal and ultrasound-assisted (US) methods. The US-K-KFI zeolites obtained were characterized by means of X-ray diffraction, scanning electron microscopy, and nitrogen adsorption-desorption isotherms at 77 K. The effect of the ultrasonic treatment time on zeolite formation was investigated. The results revealed that the ultrasonic time had a significant effect on the morphology of the K-KFI zeolite, and the particle size was reduced from 1.5 μm to 500 nm. Furthermore, the sample ultrasonically treated for 3 h and crystallized for 1 day (US-K-KFI-3h/1d) exhibited the same high level of crystallinity as the sample hydrothermally crystallized for 3 days without ultrasonic treatment (HT-K-KFI-0h/3d). Compared with large-crystal (3 μm) zeolite (HT-K-KFI-0h/3d) at a given pressure, nano/micro-scale (500 nm) zeolite (US-K-KFI-10h/1d) was characterized by a shorter adsorption equilibrium time and exhibited enhanced mass transfer due to its shorter diffusion path. Moreover, compared with that of HT-K-KFI-0h/3d, the adsorption capacity of US-K-KFI-10h/1d for CO2, CH4, N2, and O2 was 31%, 24%, 18%, and 26% higher, respectively, at room temperature (298 K) and 1 bar. The results of this work showed that the ultrasound-assisted method represents a rapid and controllable means of synthesizing nano/micro-scale zeolites.