Wetted Wall Column (WWC) experimental apparatus

Fig. 1 shows the experimental apparatus used in this work and Table 1 presents the instrument list. The Wetted Wall Column allows for counter-current contact between the liquid solvent and a defined gas mixture. CO2 and N2 are supplied by gas bottles with a molar purity of 99.995% and 99.996% respectively. The streams from the bottles are controlled by two Bronkhorst mass flow controllers which determine the composition of the inlet mixture in the chamber. The gas mixture passes through a pre-saturator at ambient temperature and a saturator immersed in a thermostatic bath at the temperature of the experiment. After the saturators, the gas mixture is saturated with water at the same temperature of the thermostatic bath. Between the reaction chamber and the CO2 concentration probe (VAISALA CARBOCAP GMT 221) is positioned a condenser. The saturators and the condenser are necessary in order to have a known amount of water in the gas and consequently determine accurately the amount of CO2 in the gas flow. Before the reaction chamber, in the gas line, there is a bypass valve. The valve allows to measure the carbon dioxide concentration before and after the absorption reactions switching the flow straight to the CO2 probe or to the reaction chamber.

Fig. 1

Fig. 1. Wetted Wall Column set up pictures: (i) on the left the picture depicts the overall Wetted wall Column set up, (ii) on the right the picture shows a focus on the reaction chamber where the absorption reaction takes place.

Table 1. Instrumentation list.

Quantity measured Manufacturer Model Range Uncertainty
N2 Flow [Ndm3/min] Bronkhorst F-201 CV 0–20 [Ndm3/min] 0.005VR+0.001FS
CO2 Flow [Ndm3/min] Bronkhorst F-201 CV 0–2 [Ndm3/min] 0.005VR+0.001FS
Pressure [mbar] Rosmount 2088 0–9900 [mbar] 0.001FS
CO2 concentration [dimensionless] VAISALA GMT 220 0–0.1 [dimensionless] 0.02VR+0.002
Temperature [°C] TC Direct Pt 100 1/3 DIN − 50 °C to 200 °C 0.03VR+0.0005FS
Density [g/cm3] Anton-Paar DMA 4100 0–3 [g/cm3] 5*10−5[g/cm3]
Viscosity [mPa s] Anton-Paar AMV 200 0.001[mPa s]

The thermostatic bath controls the temperature of the reaction chamber and the temperature of the inlet solvent in the reaction chamber. The solvent, prepared with a known NH3 concentration and CO2 loading is charged in a liquid reservoir of 0.7 dm3. A micro pump pushes the liquid with a controlled mass flow into the thermostatic bath and then into the reaction chamber. The reaction chamber consists of a glass tube in which a stainless steel tube is located (dimensions are reported in Fig. 1). The liquid, pushed inside the stainless steel tube, falls down in a thin film around the stainless steel tube. In this way the contact area between the liquid and the gas phase is well defined.

Based on the known contact area between the gas and the liquid, and the amount of CO2 absorbed in the chamber, it is possible to determine the dependence between the CO2 surface flux absorbed by the liquid and the CO2 partial pressure in the gas mixture at a fixed temperature. A clear scheme of the plant layout is available in the Fig. 1 in the second paragraph of the article which describes the experimental data analysis [1].

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