Equilibrium conditions for semi-clathrate hydrates formed with CO2, N2 or CH4 in the presence of tri-n-butylphosphine oxide

We measured the thermodynamic stability conditions for the N, CO, or CH semiclathrate hydrate formed from the aqueous solution of tri-n-butylphosphine oxide (TBPO) at 26 wt %, corresponding to the stoichiometric composition for TBPO·34.5HO. The measurements were performed in the temperature range 283.71-300.34 K and pressure range 0.35-19.43 MPa with the use of an isochoric equilibrium step-heating pressure-search method. The results showed that the presence of TBPO made these semiclathrate hydrates much more stable than the corresponding pure N , CO, and CH hydrates. At a given temperature, the semiclathrate hydrate of 26 wt % TBPO solution + CH was more stable than that of 26 wt % TBPO solution + CO, which in turn was more stable than that of 26 wt % TBPO solution + N. We analyzed the phase equilibrium data using the Clausius-Clapeyron equation and found that, in the pressure range 0-20 MPa, the mean dissociation enthalpies for the semiclathrate hydrate systems of 26 wt % TBPO solution + N, 26 wt % TBPO solution + CO, and 26 wt % TBPO solution + CH were 177.75, 206.23, and 159.00 kJ·mol, respectively

Propriétés rhéologiques d'un écoulement de coulis d'hydrates de CO2 en présence d'additifs

International audienceThis 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 ofCO2 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

Bubble formation at an orifice: A multiscale investigation

International audienceThe 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 micro-scale 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 micro- and macro-scales. A high-speed digital camera (up to 10,000 images s(-1)), a micro-Particle Image Velocimetry (mu-PIV) system and also a macro-PIV (PIV) were employed in this work, to measure the velocity flow field at micro- and macro-scales. At macro-scale, 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 micro-scale, different sizes of micro-reactors (600 and 1000 mu m) and different micro-devices were employed to compare the mechanism of bubble formation. A correlation based on dimensionless numbers was proposed to estimate the formed bubble volume at micro- and macro-scales in order to reveal the main factors governing the formation mechanisms

Characterization of mixed CO2 + TBPB hydrates for refrigeration applications

International audienceThe present work investigates the use of semiclathrate hydrates, formed from CO2 + tetra-nbutylphosphonium bromide (TBPB) + water mixtures, as appropriate media for cold storage and distribution in refrigeration applications. Previous studies show that these hydrates are able to trap molecules of carbon dioxide resulting in mixed hydrates. Calorimetry devices were used for determining the dissociation enthalpies of mixed CO2 + TBPB hydrates under various stability conditions (P, T) and salt concentrations. The results reveal that mixed CO2 + TBPB hydrates can be considered as good candidates for air-conditioning, due to positive melting temperatures (between 282 to 289 K) at moderate CO2 pressures (between 0.5 to 2 MPa). A hydrate solid fraction model was developed based on a CO2 mass balance taking into account CO2 solubility in aqueous tetrabutylphosphonium salt solution. The salt effect parameter was evaluated in order to estimate the influence of TBPB on the CO2 solubility. Finally, in order to characterize the flow behavior of mixed CO2 + TBPB hydrate slurries, a rheological study was carried out in a dynamic loop and an Ostwald-de Waele model was obtained