Membrane processes in ScCO2 medium for economical supercritical processes – MemScCO2

The project covers several aspects:
- Selection of commercial membranes suitable for Sc-CO2 in terms of filtration performance, physical, chemical or mechanical resistance, etc.
- Design of an installation and a membrane filtration cell adapted to the high pressures envisaged, ranging from 100 to 400 bars.
- Measurements of membrane performance during the filtration of pure Sc-CO2 or mixed with oil: productivity and selectivity as a function of Sc-CO2 pressure and temperature conditions.
- Modelling of separation and coupling of separation/extraction with Sc-CO2 to assess material and energy consumption.
- Simplified technical and economic optimisation by simulating the coupling of the two unit operations, enabling energy consumption gains to be made.
- Comparative Life Cycle Assessment of Sc-CO2 extraction and coupled processes to validate the environmental benefits of coupling, which are not limited to the reduction in energy consumption.

In addition to the possibility of using commercial membranes, coupling allows energy consumption to be reduced by more than 90%, thereby removing a barrier limiting the use of these processes on an industrial scale. For example, for the extraction of sunflower oil, the cost of extraction falls from 0.45 €/kg to 0.044 €/kg for a commercial price of ~2 €/kg.
The filtration cell allows continuous operation, limiting the cleaning sequences inherent in membrane filtration. A patent has been filed for it. The coupling is generic and other types of Sc-CO2 process can benefit from it.

With the exception of the task concerning the use of membrane contactors in a supercritical environment, the entire program was covered. It took longer than expected (apart from COVID 19) to develop the installation needed to start up and operate at pressures that are unusual for commercial membranes. During the following thesis, we developed practical aspects of the installation to obtain results more quickly, simply and regularly.
The commercial membranes are satisfactory and it does not seem necessary at present to develop membranes specific to the application studied. However, the choice of membrane for another application where the solutes to be recovered from the Sc-CO2 have different properties to sunflower oil will always be an issue.
The energy crisis in the winter of 2022-23, linked to the war in Ukraine, showed many industries how sensitive they are to energy prices. A number of industrialists have shown an interest in our results at conferences, so the technology transfer appears to be relevant.


From a scientific point of view, the model we have published, which provides a qualitative explanation of the results observed, will have to be compared with an experimental study. It will then be necessary to work with well-known membranes manufactured in the laboratory and to establish collaborations for measuring the structural parameters of polymers in a supercritical environment.
The study was carried out using refined commercial sunflower oil for filtration, and the coupling was carried out numerically. It now seems essential to look at the processing of oil extracted directly from the seeds. This oil is likely to contain other solutes that could lead to membrane clogging. This fouling would mean that cleaning or membrane replacement steps would have to be considered, depending on the time scale/life span of the membranes.

The scientific output includes Dihia Chabni's thesis, 7 oral communications, 2 posters, one article and one patent. The filing process blocks publications that are therefore likely to be published subsequently. The fields covered include membrane processes, supercritical processes and agri-food applications. The last part of the project concerning life cycle analysis (Post Doc by Christopher Hernandez Hernandez) should be published.

Green chemistry principles lead to non-solvent or green solvent processes among which CO2 in sub or supercritical state (ScCO2) has been considered as an excellent choice for its modulable transport properties as density, viscosity diffusivity of compounds in ScCO2 and its good solvent power for non-polar compounds. However, even if use of ScCO2 as a solvent is promising from environmental and safety points of view, the energy costs of using high-pressure CO2 may discourage its use at industrial scale. As an example, the energy cost to recompress the CO2, from atmospheric pressure to 120 bars is around 160 kJ/kg of CO2: this energy is lost during the gas expansion to recover the products at atmospheric pressure. Research and development are thus needed in order to increase the arsenal of solutions to reduce energy and costs associated to the use of high-pressure CO2. The MemScCO2 project presents a strategy to decrease energy costs associated to the use of high pressure CO2 by using membrane processes.
Membrane processes are considered as energy-efficient technologies which allow a high selectivity for separation and allow the achievement of high levels of process intensification. Membrane processes can be used to concentrate the products before the recovery step from the ScCO2 using reverse osmosis or to extract the products from the ScCO2 without decreasing the CO2 pressure using membrane contactors. Purified ScCO2 is then recycled at high pressure allowing a reduction of the compression cost.
The aim of MemSCCO2 is to study the coupling of membrane processes with a ScCO2 extraction in order to evaluate energy gains by taking into account the specificities of both processes with a life cycle assessment approach. In the MemScCO2 project, we propose to extract carotene and lycopene as high added value products and vegetable oil as a low added value product from natural matrices and to couple this extraction to a membrane process in order to obtain a rentable extraction process by decreasing the environmental footprint and the energy consumption.