Valorization of spent disposable wooden chopstick as the CO(2) adsorbent for a CO(2)/H(2) mixed gas purification

A series of activated carbons (ACs) derived from spent disposable wooden chopsticks was prepared via steam activation and used to separate carbon dioxide (CO(2)) from a CO(2)/hydrogen (H(2)) mixed gas at atmospheric pressure. A factorial design was employed to investigate the effects of the activation temperature and time as well as their interactions on the production yield of ACs and their CO(2) adsorption capacity. The activation temperature exhibited a much higher impact on both the production yield and the CO(2) adsorption capacity of ACs than the activation time. The interaction of both parameters did not significantly affect the yield of ACs, but did affect the CO(2) adsorption capacity. The optimal preparation condition provided ACs with a desirable yield of around 23.18% and a CO(2) adsorption capacity of 85.19 mg/g at 25 °C and 1 atm and consumed the total energy of 225.28 MJ/kg AC or 116.4 MJ/g-mol CO(2). A H(2) purity of greater than 96.8 mol% was achieved from a mixed gas with low CO(2) concentration (< 20 mol%) during the first 3 min of adsorption and likewise around 90 mol% from a mixed gas with a high CO(2) concentration (> 30 mol%) during the first 2 min. The CO(2) adsorption on the as-prepared ACs proceeded dominantly via multilayer physical adsorption and was affected by both the surface area and micropore volume of the ACs. The adsorption capacity was diminished by around 18% after six adsorption/desorption cycles. The regeneration of the as-prepared chopstick-derived ACs can be easily performed via heating at a low temperature and ambient pressure, suggesting their potential application in the temperature swing adsorption process.