High-pressure gas adsorption on activated carbons from pomegranate peels biochar: A promising approach for biogas purification

Abstract

Biogas is a promising bioenergy source and its composition is based on methane (55–70% vol) but contains impurities such as CO2 (30–45% vol). Various technologies are available to purify biogas and produce biomethane that can be injected into the existing natural gas network. In this work, the effectiveness of activated carbons (ACs) obtained by chemical activation from industrial food waste for CO2 removal by adsorption was investigated. ACs with better textural development were obtained at higher activation temperature and dose of the activating agent (BET surface area and total pore volume up to 1446 m2/g and 0.589 cm3/g, respectively). The adsorbents exhibited a microporous character (micropore volume up to 0.472 cm3/g). The ACs were tested in high-pressure gas adsorption tests (CO2, CH4 and H2 up to 3, 8 and 4 MPa, respectively). All of them showed high, medium and low selectivity against for the adsorption of CO2, CH4 and H2, respectively, although with different efficiencies. The adsorbent obtained under the most aggressive activation conditions (900 °C, 1:1 wt ratio) showed the greatest textural development and the maximum adsorption capacity for CO2 (at 3 MPa) and CH4 (at 8 MPa) (495 mgCO2/g and 126 mgCH4/g). Despite the porosity of the materials, all showed a very low affinity for hydrogen adsorption at 4 MPa (up to 3.71 mgH2/g). Taking the above into account, these activated carbons could be used in the purification of biogas and in the separation of CO2/H2 mixtures to produce pure H2 and obtain hydrogen-free CO2 for capture and storage.