Carbon Dioxide Capture with Amine-Grafted Activated Carbon

There are several possible methods by which amine groups can be grafted on the surface of activated carbon (AC) to improve their capacity for CO₂ adsorption. Ethylenediamine and diethylenetriamine were selected as amino compounds for anchoring on the surface of an oxidized AC. Oxidation of AC was carried out by concentrated nitric acid. For each amino compound, two “in-solvent” and “solvent-free” methods with a number of grafting times were studied. Nitrogen adsorption–desorption at 77 K and proximate and ultimate analysis were used to determine physical and chemical characteristics of the samples. Temperature-programmed (TP) CO₂ adsorption test from 30°C to 120°C were performed to investigate the effect of modification on CO₂ capture. The modification clearly had a negative effect on the textural characteristics of the samples, so the samples showed a less CO₂ uptake at lower temperatures. However, the decrease of capture capacity with increasing temperature is to somewhat softer for amine-grafted samples, so that they have a capacity comparable to the parent sample or even more than that at elevated temperatures. This property may give the new adsorbents this opportunity to be used at flue gas temperature with a higher efficiency. CO₂ capture capacity per unit surface area of all the amine-modified samples, however, was significantly improved, compared to the parent sample presenting a great influence of amino groups on the CO₂ capture capacity. Moreover, the used amine compounds and grafting methods were compared in terms of adsorbent characteristics and CO₂ uptake curves. Cyclic adsorption–desorption tests showed a satisfactory regeneration for the modified samples.