# Experimental Study on Renewable Porous Carbon Dioxide Adsorbent Materials for Space Shuttles
## 2 Experimental Section
### CO\({}_{2}\) Adsorption in the Solid Amine  
Figure 3a shows the CO\({}_{2}\) adsorption in the solid amine at the temperature range of 20 \({}^{\circ}\)C to 60 \({}^{\circ}\)C and pressure ranging from 0 to 6 bar. The amount of adsorption increased rapidly at low pressure (0-1 bar), then increased slowly at high pressure (1-6 bar) because the CO\({}_{2}\) adsorption in the solid amine was mainly chemical adsorption, as shown in Equation (1). \[2\mathrm{R_{x}NH_{y}+CO_{2}}=\left(\mathrm{R_{x}NH_{y}}\right)_{2}\mathrm{CO_{ 3}}+\Delta H \tag{1}\]  
At low pressure, the chemisorption of CO\({}_{2}\) in the amine-based adsorbent was more dominant over physisorption; the CO\({}_{2}\) molecules interacted with CO\({}_{2}\) to form ammonium carbamate in the dry condition [32; 33]. With an increase in pressure, the amine-CO\({}_{2}\) occupied the CO\({}_{2}\) molecule completely. Little physical adsorption occurred at the micropore. The effect of temperature on the amount of adsorption was inconspicuous at the study temperature range because the chemical adsorption needed a suitable activation energy at a certain temperature. The CO\({}_{2}\) adsorption decreased with increased temperature; at a high temperature, the amine may have been volatile and the adsorption amount at the micropore absorbed by the physical adsorption desorbed, which may be different from refs. [6; 9]. Figure 1: Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analysis of the solid amine. Figure 2: Heat capacity of the solid amine at different temperatures. The isosteric heat of the adsorption decreased with an increase in the adsorption amount, which indicates that the interaction between the adsorbed molecules will become weak with an increase in the adsorption molecule. The shape of the decrease in the isosteric heat of adsorption in the solid amine was convex. Figure 3b shows that the isosteric heat of CO\({}_{2}\) adsorption in the solid amine decreased with an increase in temperature, then decreased and increased again. The minimum value was at 45 \({}^{\circ}\)C under dry conditions, which means that the heat release was at a minimum at this fixed temperature. Parasitic energy is an index to consider desorption condition optimization in the separation process design. This indicator is a measure of power loss caused by the increased carbon capture and storage (CCS) process [34]. For this work, the material with the least parasitic energy was the best material. The total amount of energy required for CCS was the amount of heat required for separation [35]. This consists of two components: (1) the energy required to heat the adsorbent to achieve the desorption conditions (sensible heat); (2) the energy required to remove the adsorption process. For the endothermic process of CO\({}_{2}\) desorption, we need to provide an energy equivalent to adsorption heat \(Q\) in atmospheric pressure. The total thermal energy \(Q_{thermal}\) per kilogram of captured CO\({}_{2}\) (\(m_{CO_{2}}\)) is given by:  
Figure 3: Amount and isosteric heat of CO\({}_{2}\) adsorption in the solid amine. (**a**) Isotherm adsorption in the solid amine. (**b**) Isosteric heat of adsorption in the solid amine. \[Q_{thermal}=\frac{C_{p}m_{adsorbent}\Delta T}{m_{CO_{2}}}+\frac{Qq}{m_{CO_{2}}} \tag{2}\]  
The parameters in the equation are illustrated in Table 2. The first term corresponds to the sensible heat requirement to drive the process by heating the bed. \(C_{p}\) is the specific heat capacity of the adsorbent. \(m_{adsorbent}\) is the total mass of the adsorbent. \(\Delta T\) is the temperature difference between the adsorption and desorption conditions. The second part of heat energy is the energy required for CO\({}_{2}\) desorption, which is composed of working capacity and adsorption heat. Working capacity is defined as the difference between the amount adsorbed under gas conditions (1 bar, 25 \({}^{\circ}\)C) and the remaining amount in the material under desorption conditions.