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CO2 capture experiments

https://doi.org/10.1016/j.cej.2022.138999

“The CO2 capture was performed under isothermal and isobaric conditions in a home-built glass cylinder with a diameter of 56 mm and a height of 300mm fitted with a sintered gas diffuser (16–40 μm) in the bottom. The absorber was charged with 0.150 dm3 of the tested aqueous ammonia solution and was kept at the desired temperature by means of a thermostatic bath (Julabo model F33 MC, accuracy ± 0.1°C). The gas mixture was water-saturated before being injected from the bottom of the absorber through a sintered glass diffuser, with a total flow rate of 12.2dm3h-1 (0.07 6 molCO2h-1 at 23°C). The vent gas from the top of the absorber was dried by flowing in turn through a condenser cooled at -5°C, a concentrated H2SO4 solution and two towers filled with P2O5, before being GC analyzed. The gas chromatograph continuously measured the percentage of CO2 in the treated gas stream. By comparing the percentage of CO2 in the gas mixture before and after the absorption, the capture efficiency is calculated. Measurements of pH and temperature of the solution during absorption were performed with a HI98128 pHep®5 pH & temperature tester (Hanna Instruments, accuracy ± 0.05), calibrated with standard buffer solutions at pH 7.01 and 10.01. A schematic representation of the apparatus used is shown in Fig. 1.

Fig. 1. Schematic diagram of the apparatus for CO2 absorption experiments.

The gas holdup ε is a key hydrodynamic factor to estimate the bubbles diameter. It was measured photographically, through the method of volume expansion, by recording the height of both the static (HS) and aerated liquid (HD), respectively before and after gas injection as follows: ε=(HD – HS)/HD. In order to validate the proposed model and verify its robustness, we conducted three different series of experiments, varying operational parameters such as the NH3 initial concentration of the sorbent (M, mol dm−3) and the system temperature as summarized in Table 1.

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