Solubility of Nitrogen Gas in Aqueous Solution of Tetra-n-Butylammonium Bromide

Semiclathrate hydrates are water-based host-guest compounds formed from aqueous solutions of ionic guest substances. These materials can greatly moderate formation pressures and temperatures from canonical gas hydrates. This is a significant advantage for industrial applications such as gas separation and storage. N ₂ gas is a major component contained in various flue gases and is usually mixed with CO ₂. Semiclathrate hydrates can separate these gases under moderate thermodynamic conditions. Tetra-n-butylammonium bromide (TBAB) is a widely used ionic guest substance. To develop the application technologies and their theoretical models, solubility data of N ₂ gas in TBAB aqueous solutions are required. In this study, we report N ₂ gas solubility measured by an absolute gravimetric method for the semiclathrate hydrate formation system of TBAB + H ₂O + N ₂. The measurement pressures, temperatures and TBAB mass fractions were 3 MPa, 5 MPa and 7 MPa, 292.15 K, 302.15 K and 307.15 K, and 0 (pure water), 0.10, 0.20, 0.32 and 0.40, respectively. The uncertainties were 0.056 MPa, 0.44 K and 0.00012 in mole fraction. Although the technical difficulty lays on measurements of small N ₂ gas solubility by the absolute gravimetric method, our data implied the unique gas dissolution property of aqueous TBAB solution depending on the TBAB concentration. The aqueous TBAB solutions with mass fractions of 0.10 and 0.20 had similar N ₂ gas solubility as that in pure water. With higher mass fractions, 0.32 and 0.40, the N ₂ gas solubility slightly increased from that in pure water, which implies the salting-in effect of TBAB.