CO2 capture using SAPO zeolite and influence of temperature and pressure

https://doi.org/10.1039/D2SC00702A

“Pure CO₂ adsorption isotherms of SAPO-35_x samples were measured at 273, 283 and 298 K, respectively, to evaluate the CO₂ adsorption abilities of SAPO-35 zeolites with different Si contents and acidity. As shown in Fig. 2 and Table 1, the CO₂ uptakes of these SAPO-35 samples decrease with increase in temperature, and are always in the order SAPO-35_0.14 > SAPO-35_0.22 > SAPO-35_0.08 at 273, 283, and 298 K and 100 kPa whether in the low-pressure area or in the high-pressure area. The results clearly show that Si contents regulated by the template and the enhanced acidity could strengthen the CO₂ adsorption capacity of SAPO-35 zeolites. Compared with other pure AlPO zeolites and SAPO zeolites, SAPO-35_0.14 (4.76 mmol g⁻¹ at 273 K and 100 kPa) appears to be one of the best AlPO/SAPO zeolite adsorbents for CO₂ adsorption (Table S2†), which is superior to aluminosilicate zeolites with the same topology (Na-LEV)²⁸ and most of the SAPO zeolites, proving the potential of SAPO-35 zeolites in CO₂ adsorption.”

“Fig. 2 CO₂ adsorption of (a) SAPO-35_0.08, (b) SAPO-35_0.14, and (c) SAPO-35_0.22 at 273, 283 and 298 K. (d) Isosteric heat of adsorption (Q_st) for the SAPO-35_x samples.”

“Obviously, the framework Si content of SAPO-35 zeolites plays an essential role in governing the CO₂ adsorption behaviour of this structure type of small-pore zeolites. To further explore the relationship between CO₂ adsorption properties, Si content and acidity in SAPO-35_x zeolites, the isosteric heats of CO₂ adsorption (Q_st) for SAPO-35_x zeolites were calculated by fitting the CO₂ adsorption isotherms at 273, 283 and 298 K to the virial equation (Fig. S5†). As shown in Table 1 and Fig. 2d, the Q_st at zero coverage for SAPO-35_0.14 (29.3 kJ mol⁻¹) is the highest among the three SAPO-35_x samples. The result indicates that increased acidity could strengthen the interaction between the CO₂ adsorbate and the inorganic framework. The regeneration of the adsorbent is one of the most important parameters for practical application. One way to estimate the regeneration of an adsorbent is the determination of the energy released during the adsorption process by means of Q_st. Excessive Q_st of aluminosilicate zeolites will be against the desorption of CO₂, thus leading to low regenerability and high-energy cost.^4a SAPO-35 zeolites possess medium Q_st and relatively high CO₂ adsorption, which are beneficial to the application for CO₂ adsorption/desorption.”