Direct CO2 capture from air using char from pyrolysis of digestate solid

Digestate solid is a waste produced by biogas plants. It has a promising potential for the application of direct capture of CO2 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 N2-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 (CO), 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 CO2 capture first increased and then decreased. In addition, when the adsorption temperature increased, the capacity of CO2 capture further decreased.