Hydroquinone clathrate based gas separation (HCBGS): Application to the CO2/CH4 gas mixture

Abstract

Hydroquinone (HQ) clathrates have recently been identified as promising candidates for selective gas capture and storage processes. This study evaluates the effectiveness of HQ clathrates in the separation of CO 2 from CO 2 / CH 4 gas mixtures, through direct gas/solid reactions in a fixed-bed reactor. The influence of the process operating parameters (i.e. reaction time, pressure, temperature and feed gas composition) on the CO 2 capture kinetics, selectivity towards CO 2 , and transient storage capacity were investigated. The experiments were performed using either pure HQ or HQ-based composite materials, with temperatures ranging from about 283 to 343 K, pressures from 3.0 to 9.0 MPa, and CO 2 mole fraction in the gas mixture ranging from 0.2 to 1. The experimental results show that over the range of gas composition investigated, the enclathration reaction is selective to CO 2. This preferential CO 2 capture is enhanced at high CO 2 mole fractions, low temperatures and high pressures. Regarding gas capture kinetics, it was confirmed that the composite material is much more efficient than pure HQ crystals. The CO 2 enclathration rate increases with temperature, pressure and CO 2 fraction in the feed gas. For the first time, the feasibility of such gas separation techniques using HQ clathrates was demonstrated at bench scale.

Insights into the Crystal Structure and Clathration Selectivity of Organic Clathrates Formed with Hydroquinone and (CO2 + CH4) Gas Mixtures

“…This comparison might suggest that the clathrate selectivity toward CO 2 becomes much higher than 1 if the clathrate formation pressure largely exceeds the three-phase clathrate equilibrium pressure (in this study, the synthesis pressure is around 30 times higher than the equilibrium pressure). In addition, the SF values in this work were found to be about 3–10 times lower than those obtained by Coupan et al (i.e., SF CO 2 /CH 4 from 10.1 to 18.8 at 293 K) and Lee et al who have also worked with CO 2 + CH 4 gas mixtures. These higher SF values could be explained by the fact that the mixed gas HQ clathrates found by Coupan et al and Lee et al were obtained (i) through a direct gas–solid reaction instead of crystallization from an HQ-saturated solvent, or (ii) through using an intermediate guest-free HQ clathrate (formed by using CO 2 ) identified as being particularly selective toward CO 2 .…”

“…The reactor is pressurized either with pure CO 2 (or CH 4 ) or with a CO 2 −CH 4 gas mixture until the desired pressure of 3.0 MPa is reached. The temperature and pressure used in this work were chosen based on previous studies by the authors, particularly two: the first is a process evaluation of CO 2 /CH 4 separation by HQ clathrate formation in which a temperature of 298 K and a pressure of 3.0 MPa could be a relevant operating point for an industrial production gas separation unit using such a technology; 17 the second presents a wide range of physical and chemical characterization results for (CO 2 −CH 4 )−HQ clathrates obtained at ambient conditions and 3.0 MPa but did not study crystal structures. 24 Both temperature and pressure are maintained constant during crystallization.…”

“…HQ clathrates (denoted by β-HQ), discovered more than 150 years ago and considered for ages as just a fascinating scientific oddity, actually have very interesting properties: (i) these crystals can store large quantities of gases; (ii) can release (or absorb) energy when the guests enter (or exit) the clathrate structure; in the case of some systems, (iii) have a very high stability at ambient conditions that is ideal for applying analytical characterization techniques; and (iv) can exist in a metastable state with no guests present in the lattice structure. , As a result, practical applications based on HQ clathrates have been proposed, including sequestration of hazardous substances, fractionation of organic compound mixtures, hydrogen storage, , and separation of CO 2 from different gas mixtures containing H 2 , N 2 , and CH 4 …”

Terahertz Vibrational Motions Mediate Gas Uptake in Organic Clathrates

“…The pores are formed by hydrogen bonded rings, with the accessible spherical-like cages having diameters of about 4 Å, which may (or may not) be occupied by small guest molecules to form clathrates (Figure b). The guest-free-β-HQ form is highly selective in the guest-capturing kinetics, making it a promising candidate for selective gas separation and storage. , HQ frameworks have also been recognized as being valuable for hydrogen storage , as well as serving as a platform for studying the dynamics of confined guest molecules. , Numerous theoretical and experimental studies have been performed to understand the properties of α- and β-HQ, including the dynamics and kinetics involved in the capture, release, and diffusion of guest molecules, some dating back over 50 years . Methods including X-ray diffraction, Raman spectroscopy, nuclear magnetic resonance spectroscopy, and terahertz spectroscopy have been used for measuring the formation and decomposition rates of various types of HQ clathrates. ,, However, these studies provided little atomic-level insight regarding the specific dynamics involved.…”

Novel Hydroquinone-Alumina Composites Stabilizing a Guest-Free Clathrate Structure: Applications in Gas Processing

“…The results obtained for α-HQ, native alumina particles, and impregnated particles are presented in Figure 10. For the HQ that served as the raw material for the impregnation, the pattern of the α-form of HQ (Figure 10a) is easily identified, with lattice parameters calculated to be a = b = 38.330( 14) Å and c = 5.6450 (22) Å in the space group R3. Concerning the impregnated particles, the analysis was performed 2 years and 6 months later than the first set of analyses, on the same batch of impregnated particles (stored in a closed plastic bag, away from light, under ambient temperature and pressure conditions).…”