Adsorption of Linear and Cyclic Siloxanes via Regenerable Mesoporous Copper Oxide-Functionalized Activated Carbon for Biogas Purification

Volatile methyl siloxanes in biogas pose significant challenges to energy conversion systems due to silica deposition upon combustion. This study presents a novel mesoporous copper oxide-functionalized activated carbon adsorbent for the efficient removal and regeneration of linear and cyclic siloxanes from biogas. The adsorbent was synthesized with varying copper oxide loadings (10–70 wt %) and characterized using powder X-ray diffraction (PXRD), Brunauer–Emmett–Teller (BET), scanning and transmission electron microscopy (SEM/TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The 50 wt % mesoporous mixed-phase Cu(I)/Cu(II) oxide-activated carbon formulation demonstrated optimal performance, achieving a D4 adsorption capacity of 488 mg/g and outperforming commercial adsorbents under both dry and humid (30% RH) conditions. This work establishes a clear structure–function relationship, showing that Cu2O–CuO incorporation further enhances the adsorption of siloxanes through charge-transfer interactions. Optimized mesoporous CuO-activated carbon composite demonstrates resilience under humid conditions (30% RH) and retains ∼45% of its initial capacity after five mild thermal regeneration cycles, outperforming typical activated carbon regeneration cycles reported under extreme conditions or with oxidants. This synergistically enhanced Cu(I)/Cu(II) oxide-activated carbon adsorbent system offers a sustainable and scalable solution for industrial biogas purification.