Electrodispersion for supercritical CO2-water phase contact

Supercritical carbon dioxide is a preferred solvent substitute in the chemi cal process industries, but processing that requires contact between CO2 an d an aqueous phase has been hindered by the inefficient phase contact and h igh capital cost of conventional contactors. We examine the phase-contact p erformance of an electrodispersion contactor in this service. We have dispe rsed droplets of aqueous phases into supercritical CO2 using pulsed, high-i ntensity electric fields. Using small-angle laser light scattering, we char acterized the mean droplet size as a function of operating conditions (liqu id flow rate, field strength, frequency, temperature, and pressure) and obs erved operating regions that yield submicron-sized droplets. The effects of temperature and pressure on droplet size were correlated with the interfac ial tension. Then, using the extraction of ethanol from a water-ethanol sol ution as a test system, we attempted to characterized mass transfer perform ance, but under maximum CO2 flow rate conditions of the downstream liquid c ondensers, mass transfer was equilibrium-limited in all cases. Because of t he small droplet size and high interfacial area, the electrodispersion cont actor offers the potential for achieving excellent mass transfer performanc e. The submicron-sized droplets were efficiently coalesced electrostaticall y, and negligible entrainment was observed. We anticipate that initial comm ercial applications might arise in the processing of small volumes of high- value substances in aqueous media such as might be found, for instance, in the pharmaceutical industry.