Hydroxyl Free-Radical-Assisted Synthesis of the ZSM-58 Zeolite Membrane for CO2/CO Separation

Abstract

Capturing and recovering CO₂ from steel industry gases is essential for environmental preservation since it lowers greenhouse gas emissions and raises CO concentrations. Because of its high selectivity, energy efficiency, and continuous operation, membrane separation technology has a lot of potential for CO₂ separation. In the present work, a hydroxyl free radical (^•OH), generated by the addition of a small amount of sodium persulfate to the precursor solution, was introduced for the first time to induce the synthesis of the ZSM-58 crystals and membranes. Hydroxyl free radicals can promote the depolymerization and condensation of silica sources during the synthesis process, thereby accelerating nucleation and crystallization. Compared with the precursor solution without sodium persulfate, the synthesis time of the membrane can be reduced by 30%, the resulting zeolite membrane exhibits a CO₂/CO separation factor of 16 and a high CO₂ permeance of 1.5 × 10^–7 mol m^–2 s^–1 Pa^–1. In addition, CO₂/N₂ and CO₂/CH₄ separation performances were also tested to evaluate the membrane quality. The separation factor of the equimolar CO₂/N₂ and equimolar CO₂/CH₄ mixtures reached 28.6 and 248.3 at 298 K at 0.1 MPa, accompanying the corresponding CO₂ permeance of 1.3 × 10^–7 mol m^–2 s^–1 Pa^–1 and 1.5 × 10^–7 mol m^–2 s^–1 Pa^–1, respectively. This research presents an innovative and effective method for fabricating zeolite membranes.