Solubility apparatus

“The physical solubility of N2O in aqueous amine solutions was measured using the apparatus described in Gondal et al. (2015a). The apparatus consisted of a 1L jacketed Büchi glass reactor, a 1L gas holding vessel and a condenser placed at the top of the reactor. The pressure in the reactor and in the gas holding vessel was recorded by the pressure transmitter PTX5072 with a pressure range of 0–6 bar (FS ± 0.04%). In addition, a second pressure transmitter (PTX7517-1) was mounted to the reactor to cover the pressure range of 0–2 bar (FS ± 0.1%). Gas and liquid temperature were recorded by Pt-100 thermocouples (uncertainty ± 0.1 °C).

For each experiment, the reactor was evacuated, fed with a known amount of solution (around 450 g) and evacuated again at room temperature (25 °C) for around one minute. To minimise the risk of solvent loss during evacuation, the temperature of the condenser was maintained at 4 °C. After degassing, the solution was stirred at 500 rpm and heated to 30, 40, 50, 60, 70, 80 and 90 °C. Equilibrium was established at each temperature and a temperature-pressure profile before addition of N2O was obtained. The establishment of equilibrium was automatically determined according to a set of criteria. The criteria were that the variance in reactor pressure and liquid/gas temperature, in a period of one minute, were less than 0.5 kPa, 0.015 °C and 0.025 °C, respectively, and that the difference between gas and liquid temperature was less than 0.1 °C. These conditions were typically fulfilled within 3–4 hrs.

After equilibrium was established at 90 °C, N2O was added from the gas holding vessel to the reactor and the system was again left to equilibrate. Then, the temperature was gradually decreased, and equilibrium was established at each temperature. This resulted in a temperature-pressure profile after the addition of N2O.

The data obtained from this experiment allowed for the calculation of the Henry’s law constant, HN2O, (Eq. (19)).(19)HN2O=pN2OcN2O

In the equation, PN2O is the partial pressure of N2O and cN2O is the concentration of N2O in the amine solution at a given temperature. PN2O was calculated as the difference between the total pressure in the reactor after addition of N2O, Pafter addition ofN2O, and the total pressure in the reactor before the addition of N2O, Pbefore addition ofN2O, (Eq. (20)).(20)pN2O=Pafter addition ofN2O-Pbefore addition ofN2O

cN2O was calculated as given in Eq. (21) where the amount of N2O added from the gas holding vessel, nN2Oadded, and present in the gas phase of the reactor, nN2Og, was calculated using the Peng-Robinson equation of state (Peng and Robinson, 1976).(21)cN2O=nN2Oadded- nN2OgVL

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