## 1 Introduction
The goal of this study is the development of a gel system which reduces the desorption temperature of CO\({}_{2}\) without affecting the CO\({}_{2}\) adsorption capacity of the thermo-responsive gels with LCST polymer network. The factors available for controlling the LCST in the thermo-responsive polymer gels are: the composition of the backbone polymers [12], ionic group contents [13], control of ionic groups ionisations [14], solvent [15], molecules [16], and additives [17], according to the Flory-Huggins-Tanaka's theory [18]. In the development of CO\({}_{2}\) chemisorption-based separation and recovery process, it is important to evaluate the performance of the separation with a slurry system because of its process simplicity, adaptability to existing infrastructure and processing capacity. The key process is a gas-liquid reaction in the slurry system, and the efficiency of the gas-liquid reaction depends on the interface area between the gas and liquid, which can be improved by various configurations of equipment (design of contacts) and operations of the processes in the slurry system. In a previous study, the influence of the solvent composition and NaCl, which reduce the LCST of the thermo-responsive gels, on the desorption temperature and the cyclic capacity for CO\({}_{2}\) was investigated using a slurry system with a well-crushed, cross-linked thermo-responsive N-isopropylacrylamide-N-3-dimethylaminopropylacrylamide copolymer hydrogel as the CO\({}_{2}\) adsorbent. Alcohol is known to absorb CO\({}_{2}\) better than water, and the CO\({}_{2}\) solubility decreases in higher alcohols [19; 20; 21; 22]. Adding 10%-30% of ethanol, 2-propanol, 2-butanol, _tert_-butanol, and dimethylsulfoxide to the slurry reduced the desorption temperature of CO\({}_{2}\), as was intended; however, the addition caused a significant reduction in the cycle capacity for CO\({}_{2}\)[23]. The addition of NaCl resulted in a decrease in both CO\({}_{2}\) solubility and the adsorption capacity of the gel with the increase of its concentration (0.01-0.1 M) in the slurry [23]. Hydration becomes difficult when the polymer becomes hydrophobic due to the LCST events in aqueous systems. The ionisation of the amines immobilized in the polymer network increases the hydrophilicity of the polymer and works to swell (stretch) the polymer chains. The hydrophobic polymer chains require more protons than the hydrophilic polymer chains to ionise the amines required to swell the hydrophobicised polymer chains. This means that the p\(K_{\text{a}}\) of the immobilized amines becomes relatively small in the hydrophobic polymer chains, since the dissociation equilibrium of the amine groups shifted to a relatively low pH region in the polymer with the hydrophobic chains [10]. Therefore, in the polymers with amine groups, which exhibit a large hydrophobic-hydrophilic change in response to the temperature change, significant p\(K_{\text{a}}\) change will be induced, which results in effective adsorption/desorption of the gels for CO\({}_{2}\). In this study, thermo-responsive amine gels with series of hydrophobicity of polymer networks were prepared using N-isopropylacrylamide (NIPA, LCST of polymer = 306 K in aqueous system), N-_tert_-butylacrylamide (NTBA, LCST < 273 K), and N-3-dimethylamino-propylacrylamide (tertiary amine). The temperature swing adsorption/desorption tests for CO\({}_{2}\) were performed using slurries with the series of gels to understand the effect of the hydrophobsisation of the polymer network on both the desorption behaviour of CO\({}_{2}\) and the cyclic capacity of the gels for CO\({}_{2}\). The adsorption/desorption operation was performed by repeating the temperature swing of the gel slurries under an atmosphere of CO\({}_{2}\)-N\({}_{2}\) gas. An equilibrium adsorption model for the gel slurry system was developed based on the phenomenological observations occurring during the CO\({}_{2}\) adsorption/ desorption process to understand the mechanism of the CO\({}_{2}\) recovery in the gel system.