The present work investigates equilibrium conditions and dissociation enthalpies of semiclathrate hydrates formed from CO 2 + tetra-n-butylammonium chloride (TBACl) + water, CO 2 + tetra-n-butylammonium nitrate (TBANO 3 ) + water, and CO 2 + tetra-n-butylphosphonium bromide (TBPB) + water mixtures. Differential scanning calorimetry (DSC) was used for the determination of hydrate-liquid-vapor (H-L-V) equilibrium conditions in the presence of TBACl, TBANO 3 , and TBPB solutions at ammonium salt mass fractions of 0.3618, 0.3941, and 0.3707, respectively, and at CO 2 pressure in the range of (0.5 to 2.0) MPa. Results reveal that semiclathrate hydrates of TBACl, TBANO 3 , and TBPB are able to incorporate carbon dioxide in their structure and that the resulting mixed hydrates have significantly lower formation pressures than those of pure CO 2 hydrate. The dissociation enthalpies of semiclathrate hydrates of TBACl, TBANO 3 , and TBPB with CO 2 were determined by both DSC and the Clausius-Clapeyron equation. The DSC experiments demonstrate that mixed hydrates of TBANO 3 , TBACl, and TBPB with CO 2 have higher melting enthalpies than single hydrates. From our measurements, it appears that mixed TBPB + CO 2 hydrate has appropriate stability conditions (p, T) and latent heat content for secondary refrigeration applications. DSC measurements combined with the Clausius-Clapeyron equation show that mixed TBPB + CO 2 hydrate can store large amounts of CO 2 and thus could be attractive for gas capture and storage applications.

The phase behavior of simple and mixed semiclathrate hydrates formed from CO2 + tetrabutylphosphonium bromide (TBPB) + water mixtures was investigated by pressure-controlled differential scanning calorimetry (DSC) at TBPB concentrations in the range of 0 to 0.073 mole fraction and at CO2 pressure in the range of (0 to 2.0) MPa. In a previous article we demonstrated that TBPB + CO2 mixed hydrates present high dissociation enthalpies and could be used as phase change material, covering the range of temperature from (284.6 to 289.0) K, for secondary refrigeration applications. The present work investigates a broader domain of compositions, resulting in x–T phase diagrams at atmospheric conditions and at various CO2 pressures. These data are required to model the potential latent heat of hydrate slurries as a function of gas pressure and aqueous phase composition over the whole range of interest for refrigeration purposes. The results presented show that adding TBPB to the water at low concentration (0.0058 mole fraction) decreases the pressure of formation of CO2 hydrates to 0.5 MPa at 281.6 K, instead of 3.5 MPa at the same temperature in the absence of a promoter. Crystallization of CO2 + TBPB hydrate could therefore offer an attractive means of capture for CO2.

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This work investigates the flow properties of CO2 hydrate slurry in dynamic loop in the presence of additives (surfactants, antiagglomerants) for use as two-phase secondary refrigerant. To be considered as suitable for refrigeration systems, the use of hydrate slurries must overcome instability phenomena such as hydrate particle agglomeration. The additives were employed in the present work to prevent this phenomena, and thus to improve the stability and the homogeneity of the fluid. A multicriterion approach was used to select additive and to define the optimal operating conditions for its use. The selected additive was an EO/PO block copolymer. The flow properties of CO2 hydrate slurry in aqueous media in the presence of this additive were then measured in an experimental loop. It was possible to model the rheological behavior of the CO2 hydrate slurry in the presence of EO/PO block copolymer by an Newtonian-type equation. The present results were compared to previous results obtained without additive. This article provides new information on CO2-hydrate slurry rheology, which is important not only in the development of hydrate-based refrigeration systems, but also in the field of flow assurance in oil and gas pipelines or for other applications such as gas purification and storage processes using clathrate hydrates.

The formation of gas bubbles in a liquid is of both academic and industrial interest, and sets the initial conditions for the hydrodynamics, heat and mass transfer as well as chemical reactions from a dispersed gaseous phase to the liquid phase in industrial processes.The literature on bubble formation from a single submerged orifice is large in both Newtonian and non-Newtonian fluids. Despite the numerous theoretical and experimental investigations, the mechanisms of bubble growth and detachment remain far from fully understood. The study of bubble formation at microscale and especially in the presence of a lateral liquid flow field is still very limited. This is the topic for consideration in the present paper. In particular, this study compares both qualitatively and quantitatively the formation of bubbles at microand macroscales. A high-speed digital camera (up to 10 000 images.s -1 ), a micro-Particle Image Velocimetry (µ-PIV) system and also a macro-PIV (PIV) were employed in this work, to measure the velocity flow field at micro-and macroscales. At macroscale, experiments were conducted in a square Altuglas column of 0.1 m filled with water or viscous Emkarox solutions using different orifice sizes and various gas flowrates. A rotating device above the orifice in the column was used to impose a shear flow on the forming bubble at the orifice. At microscale, different sizes of microreactors (600 and 1000 µm) and different microdevices were employed to compare the mechanism of bubble formation. A correlation based on 2 dimensionless numbers was proposed to estimate the formed bubble volume at micro-and macroscales in order to reveal the main factors governing the formation mechanisms.