Membrane technology and supercritical fluids: chemical engineering for coupled processes

The purpose of this study is to present a review of new ideas recently proposed in the field of supercritical fluid (SCF) and membrane coupled processes. The first item concerns CO2 recovery by membranes during a supercritical fluid extraction process. The aim is here to enhance the extraction process in lowering the energy required for the CO2 recycling. Then, supercritical CO2 extraction coupled with nanofiltration separation is also described, and applications are proposed in order to purify low molecular weight compounds. This new process has been proposed as an environment safeguarding solution that would normally allow a high permeate, a good control of the whole extraction/separation process and a reduced energy consumption. All these advantages have been checked on model solutions and natural products. Cross-flow filtration applied to viscous liquids fluidified with supercritical carbon dioxide constitutes another interesting example. The basic idea of SCF assisted ultrafiltration is to reduce liquid viscosity at ordinary temperature by injecting a gas (CO2) in supercritical conditions before filtration. These works, as well as other examples involving new membrane contactor or reactor types and supercritical fluids as solvents, bear testimony of the main interest to use such hybrid techniques regarding performance and environmental constraints.

The review proposed in this article shows clearly that the use of a membrane in the presence of a supercritical fluid makes possible the design of very attractive and powerful processes, to improve transfer or reaction, to set in contact phases, to fluidify highly viscous liquids. Overall the major interest of all the processes thus created is to be safeguarding for environment and products, which is in particular essential when these ones are of biological nature. The principal effort requested from the researcher is a whole effort of imagination, and serious in further investigation with appropriate knowledge of membranes and supercritical fluid technologies.