Do N-doped activated carbons truly outperform N-free activated carbons for CO 2 separation in humid conditions?
Abstract
This study aims to evaluate whether N-doping of activated carbons (ACs) can improve CO 2 separation in a real-world post-combustion scenario. A high-surface-area, N-free AC was synthesized and subsequently N-doped by blending it with urea and subjecting it to heat treatment at 623 K in air. The potential of this N-doped AC for environmental gas separation was assessed, focusing on its CO 2 capture performance in the presence of increasing relative humidity (RH) levels. High-pressure adsorption isotherms for CO 2 and N 2 were obtained and fitted, using the Dual-Site Langmuir model to calculate selectivity. The results indicate that the N-doping post-treatment with urea reduces the AC textural properties, particularly affecting larger micropores and mesopores. Despite this, N-doping enhances CO 2 selectivity, and dynamic breakthrough simulations for CO 2 /N 2 separation suggest that N-doped AC can perform better than undoped samples under dry conditions due to their increased tap density.
However, N-doping also increases water affinity, which may be undesirable for applications involving undried flue gas streams. The pristine AC exhibited a nearly stable CO 2 adsorption capacity up to 40% relative humidity (RH), whereas the CO 2 capacity of the N-doped AC progressively decreased from 10% RH.