*3.4. Measurement of TODGA Adsorption from a SC CO2 Solution*

Two approaches to TODGA adsorption measurement in an SC CO2 medium were applied in the work. The first approach had been earlier described by us [31] and consists of direct chromatographic analysis of the solution bulk phase being in a thermodynamic equilibrium with the adsorbent. Based on the system's material balance and the residual TODGA concentration in CO2 determined by the analysis, we calculated the adsorption value by the formula:

$$q = \frac{n\_0^{TODGA} - n^{TODGA}}{m\_0^{ads}} \tag{7}$$

where *nTODGA* <sup>0</sup> is the initial TODGA amount in the solution, *<sup>n</sup>TODGA* is the TODGA amount in the solution after adsorption equilibrium is reached, *mads* <sup>0</sup> is the adsorbent mass.

The alternative approach to adsorption measurement used in the work was the gravimetric method [28,30], calculating the amount of the adsorbed substance by measuring the changes in the adsorbent mass during adsorption in static conditions:

$$q = \frac{\left(m^{ads} - m\_0^{ads}\right)}{m^{ads} \cdot M^{TODGA}}\tag{8}$$

where *mads* is the adsorbent mass after the experiment, *MTODGA* is the TODGA molar mass.

Both approaches were realized simultaneously in the same apparatus. Adsorbent and TODGA samples in a glass vial covered with perforated aluminum foil were placed into the autoclave. The autoclave was sealed and the system was thermostatically controlled. CO2 was pumped into the experimental unit at the rate of about 10 mL/min under the pump head cooling regime. After reaching the target temperature and pressure values, the system was stirred intensively until thermodynamic equilibrium was reached. We then sampled the fluid phase for TODGA SFC analysis. Next, the autoclave was depressurized, the sorbent was taken out of the autoclave and weighed. This allowed us to make a direct comparison of the results obtained in identical conditions applying the two approaches.
