New adsorbents from maize cob wastes and anaerobic digestate for H2S removal from biogas

Two activated carbons (ACs) were prepared by physical activation of Maize Cob Waste (MCW) with CO2, during 2 and 3 h (MCW(PA)2h and MCW(PA)3h, respectively). Two other ACs were prepared by chemical activation: a) MCW(LD) - MCW was impregnated with anaerobic liquid digestate (LD) and carbonized under N-2 atmosphere; and b) CAR-MCW(LD) - previously carbonized MCW was impregnated with LD and carbonized under N-2 atmosphere. All ACs were fully characterized for textural and chemical properties, and then used in dynamic H2S removal assays from real biogas samples. Regarding H2S removal, the ACs that were physically activated behaved much better than the impregnated ones: MCW(PA)3h and MCW(PA)2h showed H2S uptake capacities of 15.5 and 0.65 mg g(-1), respectively, while MCW(LD) and CAR-MCW(LD) showed values of 0.47 and 0.25 mg g(-1), respectively. This may indicate that textural properties (surface area and microporosity) are more important than mineral content in H2S removal. Effectively, both surface area and micropore volume were much higher for the samples of MCW(PA)3h (S-BET = 820 m(2) g(-1), and V-micro = 0.32 cm(3) g(-1)) and MCW(PA)2h (S-BET = 630 m(2) g(-1) and = 0.21 cm(3) g(-1)) than for the ACs that were chemically activated (S-BET = 38.0 m(2) g(-1) and V-micro = 0.01 cm(3) g(-1) for MCW(LD); S-BET = 8.0 m(2) and V-micro = 0.01 cm(3) g(-1), for CAR-MCW(LD)). High oxygen content in MCW(PA)3h favoured the catalytic oxidation reaction of H2S, promoting its removal. The use of MCW as precursor and LD as activating agent of the ACs may contribute for the integrated management of maize wastes and to diversify the applications of anaerobic digestate. (C) 2019 Elsevier Ltd. All rights reserved.