Selective Encaging of N2O in N2O–N2 Binary Gas Hydrates via Hydrate-Based Gas Separation

• Published in: Environmental science & technology Vol. 51; no. 6; pp. 3550 - 3557
• Main Authors: Yang, Youjeong, Shin, Donghoon, Choi, Seunghyun, Woo, Yesol, Lee, Jong-Won, Kim, Dongseon, Shin, Hee-Young, Cha, Minjun, Yoon, Ji-Ho
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.03.2017
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.6b05978

The crystal structure and guest inclusion behaviors of nitrous oxide–nitrogen (N2O–N2) binary gas hydrates formed from N2O/N2 gas mixtures are determined through spectroscopic analysis. Powder X-ray diffraction results indicate that the crystal structure of all the N2O–N2 binary gas hydrates is identified as the structure I (sI) hydrate. Raman spectra for the N2O–N2 binary gas hydrate formed from N2O/N2 (80/20, 60/40, 40/60 mol %) gas mixtures reveal that N2O molecules occupy both large and small cages of the sI hydrate. In contrast, there is a single Raman band of N2O molecules for the N2O–N2 binary gas hydrate formed from the N2O/N2 (20/80 mol %) gas mixture, indicating that N2O molecules are trapped in only large cages of the sI hydrate. From temperature-dependent Raman spectra and the Predictive Soave–Redlich–Kwong (PSRK) model calculation, we confirm the self-preservation of N2O–N2 binary gas hydrates in the temperature range of 210–270 K. Both the experimental measurements and the PSRK model calculations demonstrate the preferential occupation of N2O molecules rather than N2 molecules in the hydrate cages, leading to a possible process for separating N2O from gas mixtures via hydrate formation. The phase equilibrium conditions, pseudo-pressure–composition (P–x) diagram, and gas storage capacity of N2O–N2 binary gas hydrates are discussed in detail.