CO2 separation and capture by clathrate hydrate crystallization is a non-conventional way of trapping and storing gas molecules from flue gases. Clathrates hydrates are non-stoichiometric ice-like crystalline solids consisting of a combination of water molecules and suitable guest molecules. Mixed hydrates of cyclopentane (CP) + gas have been studied in one national project (FUI ACACIA) and a European program (iCAP). Cyclopentane is an organic additive which forms mixed hydrates of CP + CO2 + N2 at low pressure and moderate temperature. The equilibrium pressure is decreasing up to 97 % (relative to the equilibrium pressure without cyclopentane). CO2 selectivity in hydrates is enhanced and gas storage capacity approaches a roughly constant value of 40 m3gas (STP) /m3hydrate. Crystallization of CP + CO2 mixed hydrates seems limited by gas diffusion through the gas / liquid interface, which gets in the way of the determination of the intrinsic kinetic constants of crystallization. Experimental studies have also been investigated in presence of a Focused Beam Reflectance Measurements (FBRM) probe in stable emulsion of CP in water. FBRM probe can successfully identify hydrate nucleation. The sharp change in the mean chord length and the spread of Chord Length Distribution (CLD) are related to the progressive disappearance of the CP droplets in favor of the CP + CO2 mixed hydrates formation. The change in the mean chord length distribution is not only related to the agglomeration phenomenon of the particles but also to the occurrence of the shrinking core crystallization of the CP droplets.
