Amine-functionalisation of Ni-DOBDC MOF for CO2 adsorption

Abstract

Biogas is a sustainable energy source substitute for fossil fuels. However, biogas possesses a relatively high carbon dioxide content (CO2) to methane (CH4), which is undesirable as it can damage the engine through corrosion and deposition. Adsorption techniques have been widely employed to extract CO2 from biogas using Metal-Organic Frameworks (MOFs) modified with polar groups such as amines to increase their capacity for CO2 adsorption. Hence, the aim of this study is to investigate how ethylenediamine (EDA) modification affects the CO2 adsorption performance of Ni-based MOF. Ni-DOBDC was synthesised using hydroxylated terephthalic acid (2,5-dihydroterephthalic acid, DOBDC) as ligand and post-synthetically modified with 15 % w/w EDA. Ni-DOBDC and its EDA-modified form were characterised using XRD, FTIR, N2-physisorption, SEM-EDX, and CO2-TPD to investigate the physicochemical properties, which were then employed as CO2 adsorbent in CO2/CH4/N2 (30:60:10) biogas model. The CO2 adsorption test results showed that EDA-modified Ni-DOBDC exhibits an improved adsorption capacity (11.80 mmol/g) compared to pristine Ni-DOBDC (8.71 mmol/g), with highest selectivity towards CO2 when imposed to biogas model at 70 °C. Analysis on the adsorption isotherm, kinetics, and reusability test were also conducted to understand the stability and adsorption mechanism of CO2 within MOF.