## 1 Introduction
In this sense, capital costs for large-scale units operating at these conditions could be unacceptable. More representative operating conditions (adsorption temperatures of 45 and 60 \({}^{\circ}\)C, and gas residence times of 16-17 s) were considered in the study by [PERSON] et al., [15], in which CO\({}_{2}\) adsorption capacities of 0.57 and 0.47 mmol g\({}^{-1}\) (at 45 and 60 \({}^{\circ}\)C, respectively) were reported for a granular palm shell-derived N-doped AC. The three above-mentioned studies, however, were conducted under dry conditions. Given that the real flue gas contains a certain amount of moisture (which is unavoidable in practice), the effect of water vapor on the CO\({}_{2}\) adsorption capacity and CO\({}_{2}\)/N\({}_{2}\) selectivity under dynamic conditions should also be assessed. In this regard, there are relatively few experimental studies available in the literature that have explored the performance of biomass-derived ACs under humid conditions. Among them, it is worth mentioning the study by [PERSON] et al., [16], where the performance of a commercial coconut shell-derived AC was tested during a vacuum swing adsorption (VSA) cycle under humid conditions. In the experiment conducted by [PERSON] et al., the adsorption step was conducted at an absolute pressure of 120 kPa, at a bed temperature of 60 \({}^{\circ}\)C, and using a feed gas steam composed of CO\({}_{2}\) (12 vol. %), water (4.8 vol. %), and air (balance). Surprisingly, the authors reported an almost identical recovery and purity of CO\({}_{2}\) in the presence of water as compared to the dry condition. However, this study did not assess the performance of the tested adsorbent over sequential adsorption/desorption cycles. [PERSON] et al., [17] investigated the ability of a pine sawdust-based AC to selectively adsorb CO\({}_{2}\) from wet biogas under dynamic conditions (at an absolute pressure of 135 kPa, 30 \({}^{\circ}\)C, and using a quaternary gas mixture of CH\({}_{4}\)/CO\({}_{2}\)/N\({}_{2}\)/H\({}_{2}\)O\({}_{(\
u)}\) with a relative humidity of 55%). The authors observed that, under humid conditions, the CO\({}_{2}\) uptake and breakthrough time decreased in comparison with those measured during the breakthrough experiments under dry conditions. In fact, the breakthrough time was reduced by a factor of 1.85 for a molar ratio CO\({}_{2}\)/CH\({}_{4}\) of 30/70 in the feed gas mixture. However, as a remarkable finding, [PERSON] et al., [17] stated that the presence of water vapor on the bed can promote the CO\({}_{2}\) adsorption over CH\({}_{4}\), leading to a more efficient separation with respect to the dry case. The specific aim of the present study is to explore the feasibility of using biomass-derived physically activated biochars as cost-effective adsorbents for CO\({}_{2}\) capture from humid postcombustion flue gas. The performance of physically activated carbons based on vine shoots as well as wheat straw pellets was assessed via cyclic breakthrough experiments under dry and severe humid conditions (relative humidity of 100%). Both biomass sources were selected on the basis of their potential sustainability, since they are agricultural wastes (residual biomass) that do not compete with food, feed or timber production either directly or indirectly within a specific area.