Cu-ZSM-5 as a regenerable adsorbent for removal of low-concentration methyl mercaptan

Abstract

Regeneration of desulfurizer is a difficult topic because the bond is strong between the adsorptive site and the S-containing gas. This work synthesized a regenerable desulfurizer by dispersing Cu into ZSM-5, which removed 8.84 mg·g⁻¹ of methyl mercaptan by Cu²⁺ and CuO sites. Both N₂ and H₂ were feasible to regenerate the used adsorbent at 500 °C. N₂ was a better choice since the adsorptive capacity maintained at 6.23−6.40 mg·g⁻¹ even after five-cycle regenerations. On the contrary, the adsorptive capacity was decreased to 4.58 mg·g⁻¹ after three H₂-regeneration cycles. H₂ regeneration reduced the Cu²⁺ sites, which were oxidized to CuO after being exposed to air. Methyl mercaptan was inclined to be oxidized to SO₄²⁻ on CuO during the thermal regeneration. CuO sites were thus occupied by SO₄²⁻, which decreased the adsorptive capacity. Residual S content was increased to 3.74 wt.% after the forth H₂ regeneration. In comparison, the S content was only 1.26 wt.% after the sixth N₂ regeneration. Therefore, this work put forward a regenerable desulfurizer together with a regeneration method, which is in favor of sustainable adsorption of refractory sulfur-containing odorous gas.