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This review includes the current state of the art understanding and advances in technical developments about various fields of gas hydrates, which are combined with expert perspectives and analyses.

Tetra-n-butylammonium bromide forms the title semi-clathrate hydrate crystal, C16H36N+.Br-.38H2O, under atmospheric pressure. The cation and anion lie at sites with mm symmetry and seven water molecules lie at sites with m symmetry in space group Pmma. Br- anions construct a cage structure with the water molecules. Tetra-n-butylammonium cations are disordered and are located at the centre of four cages, viz. two tetrakaidecahedra and two pentakaidecahedra in ideal cage structures, while all the dodecahedral cages are empty.

Equilibrium conditions of CH 4 , CO 2 , and C 3 H 8 hydrates confined in small pores of porous glass were determined. The dissociation temperature of each hydrate at a given pressure shifted lower than that for bulk hydrate; the largest shift for CH 4 hydrate was -12.3 K ( 0.2 K for 4-nm-diameter pores and the shift decreased to only -0.5 K for 100-nm pores. CH 4 hydrate experiments at temperatures lower than the quadruple point of 270.6 K in 30-nm porous glass showed no shift of the equilibrium line. All temperature shifts were fitted by the Gibbs-Thomson equation; the best fits for CH 4 , CO 2 , and C 3 H 8 hydrates predicted hydrate-water interfacial energies of 1.7(3) × 10 -2 J/m 2 , 1.4(3) × 10 -2 J/m 2 , and 2.5(1) × 10 -2 J/m 2 , respectively. Both type-I hydrates of CH 4 and CO 2 had interfacial energies within 20% of each other but significantly smaller than the type-II hydrate of C 3 H 8 . Ice formation in the same porous glass fit the Gibbs-Thomson relation with an interfacial energy of 2.9(6) × 10 -2 J/m 2 , which is in good agreement with established values. The estimated interfacial tensions between gas hydrates and water were found to be only weakly affected by the kinds of gas. This indicated that the pore effect on the phase equilibrium was mainly due to the water activity change. The wide range of experiments on pore size, temperature, and the kind of gas allowed us to evaluate the validity of previous model predictions for pore effects on gas hydrate stability.