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Digestate solid is a waste produced by biogas plants. It has a promising potential for the application of direct capture of CO 2 from the air. In this study, digestate soild was carbonised under different temperatures to obtain digestate char. The carbon capture performance using the produced digestate char was further explored. Firstly, the structural properties of the prepared digestate char were characterised by N 2 -adsorption/desorption, X-ray diffractometry (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and ultimate analysis. It was revealed that the addition of the carbonisation temperature from 400 to 800 °C led to the increase of specific surface area and total pore volume. When the carbonisation temperature increased, the degree of the molecular cleavage increased, and the content of graphite-C (C–C) increased, while the digestate char formed more carbonyl (C O), phenol, alcohol, or ether group (C–O). Furthermore, the effects of carbonisation temperature, gas flow rate and the adsorption temperature on the carbon capture performance of the digestate char were evaluated. The results showed that the carbon capture ability increased with the increase of carbonisation temperature, and with the increase of gas flow rate, the capacity of CO 2 capture first increased and then decreased. In addition, when the adsorption temperature increased, the capacity of CO 2 capture further decreased. • The structural changes of digestate char with pyrolysis temperatures were systematically studied. • Digestate char shows good CO 2 capture performance during direct air capture. • CO 2 capture ability of digestate char is affected by carbonisation temperature, adsorption temperature and gas flow rate. [ABSTRACT FROM AUTHOR]

This study used Camellia oleifera cake to prepare activated carbon (AC) for nickel removal from aqueous solutions. After carbonization at 700 °C for 2h, activation was subsequently carried out with four different activators (Na 2 CO 3 , KOH, NaOH, H 3 PO 4). The results showed that the four ACs had well-developed microporous structures. The AC with NaOH activation had the highest specific surface area of 512.18 m2 g−1, and the largest pore volume of 0.356 cm3 g−1. The adsorption of Ni(II) on the ACs showed that the removal ratio of Ni2+ reached 95.7% at 25 °C on AC with Na 2 CO 3 activation when the input amount was 5 g L−1, while AC with NaOH as activator had the highest Ni2+ removal ratio of 86.75% when the input amount was 1g L−1 at 25 °C. In addition, the adsorption capacity of AC was increased when the temperature rose between 25 and 60 °C. Compared to pseudo-first-order (PFO) model, the adsorption of Ni2+ on ACs is better suited by pseudo-second-order (PSO) model, and the ion precipitation in chemical adsorption is proved as adsorption mechanism. [Display omitted] • Small molecule gases produced in activation process are favorable for pore forming. • The activated carbon prepared by NaOH and KOH has better physical properties. • Ion precipitation is the form of nickel ion adsorption. • The adsorption mechanism of nickel ion is monolayer chemisorption. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2) capture is critical for emission reduction. Biochar is a promising adsorbent for CO 2 capture. In this work, the effect of relative humidity and biochar activation with steam or KOH treatment on CO 2 capture was investigated. The results demonstrate that the biochar sample activated by KOH has a high CO 2 capture capacity (50.73 mg g−1). In addition, the biochar after 1.0 h of steam treatment showed a carbon capture capacity of 38.84 mg g−1. The results also show that the capture ability of biochar decreased as CO 2 concentration decreased from 100% to 15%. The relative humidity had a negative impact on CO 2 capture over biochar. The CO 2 capture capability of biochar materials treated by steam decreased by a range of 31.38%–62.89% as the relative humidity rose from 8.8% to 87.9%. Furthermore, the lifetime of biochar samples at various relative humidity shows that increased relative humidity had a negative impact on CO 2 adsorption due to water molecules occupying active sites. • KOH activated wood pellet biochar has a CO 2 capture capacity of 50.73 mg g−1. • CO 2 capture performance of Chemical activated biochar outperforms physically activated biochar. • High relative humidity has a negative effect on CO 2 adsorption of biochar. • Biochar shows higher stability under dry conditions than moisture conditions. [ABSTRACT FROM AUTHOR]

Auto thermal biomass gasification produces syngas more energy-efficiently by utilizing the heat released from the reaction between CaO and CO 2. The auto thermal gasification process also reduces CO 2 emissions and gasification temperature. However, the high temperature required for the regeneration of spent CaO consuming large amounts of energy is a challenge for this process. This paper investigated the effect of steam on the regeneration of spent CaO during biomass gasification from an energy-saving perspective. The modelling results indicated that the regeneration temperature could be lowered with the introduction of steam while maintaining the same 60% CaCO 3 calcination efficiency. For example, the introduction of 10 ml h−1 of steam can reduce the regeneration temperature by 50 °C compared to the regeneration under air environment. In addition, SEM and BET analysis confirmed that the steam flow rate needs to be precisely controlled to prevent it from diminishing the surface area of the sorbent and reducing the adsorption capacity of the regenerated CaO. • Steam addition was investigated for spent CaO regeneration. • 60% CaCO 3 calcination efficiency can be obtained at lower temperature via adding more steam. • Calcination temperature can be reduced by 50 °C with 10 ml h−1 of steam. • Optimal steam flow rate should be considered. [ABSTRACT FROM AUTHOR]