Ultrathin porous amine-based solid adsorbent incorporated zeolitic imidazolate framework-8 membrane for gas separation

Abstract

A novel gas separation approach is proposed in this work by combining an amine-based solid adsorbent with a zeolitic imidazolate framework-8 (ZIF-8) membrane. This was achieved by incorporating the amine-based solid adsorbent during the fabrication of the ZIF-8 membrane on a macroporous substrate. An amine-based solid adsorbent was prepared using porous ZIF-8-3-isocyanatopropyltrimethoxysilane (IPTMS) and N-[(3-trimethoxysilyl)propyl]diethylenetriamine (3N-APS) amine compounds. The as-prepared porous amine-based solid adsorbent (denoted as ZIF-8-IPTMS-3N-APS) possessed excellent adsorptive CO₂/N₂ and CO₂/CH₄ separation performances. As the adsorbent needs to be regenerated, this could indicate that the CO₂ adsorption separation process cannot be continuously operated. In this work, an amine-based solid adsorbent was applied during the preparation of the ZIF-8 membranes owing to the following reasons: (i) gas separation by the membrane can be operated continuously; (ii) the amino group provides a heterogeneous nucleation site for ZIF-8 to grow; and (iii) the reparation of surface defects on the macroporous substrate can be performed prior to the growth of the ZIF-8 membrane. Herein, the ZIF-8 membrane was successfully fabricated, and it possessed excellent CO₂/CH₄, CO₂/N₂, and H₂/CH₄ separation performances. The 0.6 μm ultrathin ZIF-8 membrane demonstrated a high CO₂ permeance of 4.75 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 35 °C and 0.1 MPa, and ideal CO₂/N₂ and CO₂/CH₄ selectivities of 4.67 and 6.02, respectively. Furthermore, at 35 °C and 0.1 MPa, the ideal H₂/CH₄ selectivity of the ZIF-8 membrane reached 31.2, and a significantly high H₂ permeance of 2.45 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹.