Recovery of N₂O: Energy-Efficient and Structure-Driven Clathrate-Based Greenhouse Gas Separation

Abstract

N2O has 300 times more global warming potential than CO2 and is also one of the main stratospheric ozone-depleting substances emitted by human activities such as agriculture, industry, and the combustion of fossil fuels and solid waste. We present here an energy-efficient clathrate-based greenhouse gas-separation (CBGS) technology that can operate at room temperature for selectively recovering N2O from gas mixtures. Clathrate formation between α-form/β-form hydroquinone (α-HQ/β-HQ) and gas mixtures reveals guest-specific and structure-driven selectivity, revealing the preferential capture of N2O in β-HQ and the molecular sieving characteristics of α-HQ. With a maximum gas storage capacity and cage occupancy of 54.1 cm3 g–1 and 0.86, respectively, HQ clathrate compounds including N2O are stable at room temperature and atmospheric pressure and thus can be easily synthesized, treated, and recycled via commercial CBGS processes. High selectivity for N2O recovery was observed during β-HQ clathrate formation from N2O/N2 gas mixtures with N2O concentrations exceeding 20%, whereas α-HQ traps only N2 molecules from gas mixtures. Full characterization using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, solid-state nuclear magnetic resonance, and compositional analysis and the formation kinetics of HQ clathrates was conducted to verify the peculiar selectivity behavior and to design the conceptual CBGS process. These results provide a new playground on which to tailor host–guest materials and develop commercial processes for the recovery and/or sequestration of greenhouse gases.

Temperature-Dependent Structural Characteristics and Guest Occupation Behavior of CO2-Loaded Hydroquinone Clathrates

“…To observe the reactivity of CO 2 toward HQ molecules, the formation kinetics of HQ clathrates with pure CH 4 , N 2 , and CO 2 gases at 293 K and 4 MPa were measured and compared for 5000 min by determining the number of consumed gases during β-HQ clathrate formation (Figure ). In previous works, , the HQ clathrate formation mechanisms involve two steps: the reaction takes place at the surfaces of the gas−α-HQ and α-HQ−β-HQ clathrate, which is then followed by migration of the gas molecules across the shells of β-HQ clathrate. As shown in Figure , the formation kinetics using N 2 exhibits a very slow and small consumption of gases, which indicates that the formation of β-HQ clathrates does not occur and only diffusion of N 2 is observed in α-HQ.…”

Excellent capture of N2O functioning at RT and lower pressure by utilizing an NaCaA-85 zeolite

“…7,[10][11][12][13][14]16 It is the NaCaA-85 sample that exhibits the highest adsorption amount reported to date for a temperature of around 300 K. [7][8][9][10][11][12][13][14][15][16] Recently, quite different and attractive N 2 O adsorption systems have also been reported, although the material demonstrates its high activity under relatively higher pressure conditions. 17 It is well known that vibrational bands in n 1 and n 3 modes for a free N 2 O molecule represent allowed transitions and are observed at 1285 and 2223 cm À1 , respectively. 18 To clarify the particular N 2 O adsorption phenomenon observed for the NaCaA-85 sample, we performed mid-IR measurements at RT for the NaCaA-85 sample evacuated at 723 K, followed by exposure to N 2 O under various equilibrium pressures from 0.1 to 4.9 Torr at RT under the in situ condition.…”

“…7,10–14,16 It is the NaCaA-85 sample that exhibits the highest adsorption amount reported to date for a temperature of around 300 K. 7–16 Recently, quite different and attractive N 2 O adsorption systems have also been reported, although the material demonstrates its high activity under relatively higher pressure conditions. 17…”