Gas to liquid transfer enhancement during hydrate crystallization: Case study of CO₂ hydrate for cold storage and transport

Secondary refrigerants, like ice slurries, are already used for industrial application, but their generation requires mechanical processes (scraping or brushing surface exchangers). CO₂ hydrates slurries were classically obtained in a stirred reactor, by gaseous CO₂ dissolution inside liquid water and cooling process. In the present work, an original set up was developed in order to measure in real time and in situ the dissolved CO₂ amount in the liquid phase during crystallization process thanks to the FTIR-ATR measurements. Results on this device allowed to quantify crystallization driving force, related to supersaturation, and to focus on the crystallization limiting step, in particular to determine whether or not it is gas to liquid diffusion. Some parameters were tested as stirrer type (propeller, Rushton turbine with and without hollow shaft) or stirring speeds. The increase of stirring speed or hollow shaft stirrer choice enhanced significatively gas/liquid transfer and thus strongly attenuated or even eliminated under certain conditions the limiting factor at the vapor-liquid interface.