Clathrate hydrates: recent advances on CH₄ and CO₂ hydrates, and possible new frontiers

Abstract

Gas hydrates continue to attract enormous attention throughout the energy industry, as both a hindrance in conventional production and a substantial unconventional resource. Scientists continue to be fascinated by hydrates because of their peculiar properties, including the ability of sequestering large amounts of hydrophobic gases, unusual thermal transport properties, and unique molecular structures. From a technological point of view, clathrate hydrates offer potential advantages in applications as diverse as natural gas production, carbon sequestration, water desalination and natural gas storage. The communities interested in hydrates span traditional academic disciplines, including earth science, physical chemistry, and petroleum engineering. The studies on this field are equally diverse, including field expeditions to attempt the production of natural gas from hydrate deposits accumulated naturally on the seafloor, to lab-scale studies to attempt to exchange CO2 for the CH4 present in hydrate deposits; from the scale up of water desalination plants to the testing of compounds used to prevent the formation of large hydrate plugs in pipelines; from theoretical studies to understand the stability of hydrates depending on the guest molecules, to molecular simulations to probe nucleation mechanisms. This review highlights a few fundamental questions faced by the research community, with focus on knowledge gaps representing some of the barriers that must be addressed to enable growth in the practical applications of hydrate technology, including natural gas storage, water desalination, CO2-CH4 exchange in hydrate deposits, and prevention of hydrate plugs in conventional energy transportation.

Structural Stability of the CO2@sI Hydrate: a Bottom‐Up Quantum Chemistry Approach on the Guest‐Cage and Inter‐Cage Interactions

“…The revPBEÀ D3(0) and revPBEÀ D3(BJ) results are found to underestimate both interaction and cohesive energies for the D and T sI cages. All functionals under study predict that the interaction energies are larger for the T cage than the D one, indicating that CO 2 @5 12 6 2 configurations are more stable than the CO 2 @5 12 , in accord with previous studies. [26,47,48,69] In turn, we also examined the structures corresponding to the two-adjacent DT, TT(6) and TT(5) sI cages (see lower-right panel in Figure 1) of 39, 42 and 43 water molecules, respectively.…”

“…CO 2 has been mainly found to form sI type clathrate hydrates. The sI host lattice contains six individual tetrakaidekahedral (5 12 6 2 or T) cages, which are arranged to form two interstitial dodecahedral (5 12 or D) cages (see lower-left panel in Figure 1). A non redundant arrangement of such cages is presented in the top panel of Figure 1, while combinations between D and T adjacent cages are depicted in the lower-right panels.…”

“…Thus, we first considered the D and T individual sI cages (see lower-left panel in Figure 1) in a cubic supercell, and we explored interaction energies and cohesive energies of the CO 2filled and empty sI cages, respectively. In Figure 2 we display the interaction energies obtained using the indicated revPBE, PW86PBE and B3LYP DFT/DFTÀ D functionals, that were found to perform best in estimating the binding energies of the CO 2 @5 12 and CO 2 @5 12 6 2 , together with cohesive energies of the empty T and D cages (see Table S1 in supporting information). The reference DF-MP2/CBS energies for both CO 2 -filled and empty D and T individual sI cages are also displayed [26,27] (see vertical dashed and long-dashed lines in Figure 2, respectively).…”

“…[2] Investigations on clathrate hydrates are largely motivated by the growing need for new energy sources, such as methane and hydrogen clathrates, [5][6][7][8][9][10] while more recently mixed-binary clathrates, combining CO 2 and CH 4 as guest gases, have also generated tremendous interest, as possible byproduct storage media and new fuel sources. [7,11,12] CO 2 clathrate hydrates have been mainly found in the sI crystal structure, although some evidence of the CO 2 @sII type, and so far binary CO 2 @sH clathrates have also been reported. [2,[13][14][15][16][17][18] The stability of these clathrates relies on the nature of the guest molecule/s and its interactions with the hydrogen-bonded water network.…”

“…[30][31][32][33][34][35][36] In this work, through reliable electronic DF-MP2 and DFT/ DFTÀ D calculations for isolated finite-size clathrate-like clusters the structural stability of the CO 2 @sI cages is investigated. We evaluate the guest-host and inter-cages (cage-cage and guest-guest) effects for the individual building block cages D (small or 5 12 ) and T (large or 5 12 6 2 ) of the CO 2 @sI clathrate, as well as twoadjacent aperiodic DT and TT cages, from a bottom-up approach. The impact of the DF-MP2 and different DFT/DFTÀ D approaches on the interaction and binding of such clathratelike systems is checked.…”