Suppressing the Competitive Effect of Water Vapor on CO Adsorption over 5A Molecular Sieves via Silanization Hydrophobic Modification

Recently, the investigation of high-efficiency adsorbents for CO adsorption and separation has gradually become a research focus with carbon energy chemistry developing and environmental protection requirement enhancing. The adsorption performance of CO would be devitalized under a humid environment, although the traditional molecular sieves could serve as an effective adsorbent toward CO adsorption under an anhydrous atmosphere. In this work, a strategy of silanization modification was proposed to enhance the performance of CO adsorption by restraining the surface occupied by competitive water molecules due to the hydrophilic nature of silica hydroxyl groups on the 5A molecular sieves. A series of hydrophobic CO adsorbents (X-B-5A) were successfully prepared via impregnation using butyltrichlorosilane (BTS) as a hydrophobic agent, toluene as a dispersion solution, and commercial 5A molecular sieves as a raw material. The effect of different concentrations of BTS in toluene solution on hydrophobicity and CO adsorption performance was investigated. The results showed that the hydrophobicity of X-B-5A was significantly increased after silanization modification. Additionally, the water contact angle of 0.004-B-5A increased from 20° to 154°, and the static water vapor adsorption capacity was reduced from 27.5 to 6.0% at 35 °C. The CO static adsorption capacity of 0.004-B-5A still reached 1.54 mmol/g, which was only 14.6% lower than that of pristine 5A molecular sieves. Additionally, the dynamic adsorption capacity of CO over the as-prepared X-B-5A was significantly enhanced compared to pristine 5A molecular sieves in the presence of moisture. The as-prepared hydrophobic adsorbents exhibited satisfactory CO adsorption performance and high thermal stability in a humid environment. This work presents a novel strategy for the preparation of adsorbents toward CO adsorption employed under a high relative humidity environment.