Figure 1

The schematic diagram of 4-step TSA process (a) and thermodynamic cycle established (b). The Clapeyron diagram has been widely applied in research on physical adsorption technology, such as adsorption refrigeration cycle²⁷, which is also suitable for research on adsorption carbon capture technology like the 4-step TSA technology. As shown in the (a,b), step 1–2 is the pre-cooling process, in which the temperature of the adsorption reactor decreases from T₁ (T_ad) to T₂ with no adsorbed amount changed. Step 2–3 is the adsorption process, the adsorbed amount increases with the CO₂ partial pressure is P_ad in the atmosphere condition, and the adsorption heat is taken away by cooling fluid (such as cold water in T_ad). Step 3–4 is the pre-heating process, in which the reactor bed is heated from T₃ (T_ad) to T₄ with no adsorbed amount changed. And step 4-1 is the desorption process, the adsorbed amount decreases in this process with the CO₂ partial pressure is P_de in the atmosphere condition, and the adsorption reactor is heated by heating fluid (such as hot steam in T_de) continuously to T₁(T_de), then a new cycle starts. With characteristics of different adsorbents, the temperature in the end of pre-cooling process might be higher or lower than that in the end of pre-heating process as shown in the Fig. 2-b. The assumptions of the cycles researched are unrolled as follows: 1. The adsorbed CO₂ is treated as looping fluid in this cycle. 2. The adsorbed amount of N₂ is much lower than that of CO₂ in the adsorbent, which can be neglected. 3. The temperature of adsorbent-adsorbate pair in the adsorption column is assumed as uniform. 4. The adsorption capacity of the adsorbent can be fully utilized in the whole thermodynamic cycle. e. The specific heat capacity of adsorbate is neglected for that is small enough as researched in refs^28,29.