Gas separation and filtration using thin liquid films

Gas separation or filtration processes refer to techniques used to separate or filter gases, for production or purification purposes. For the production of industrial gases for instance, separation techniques are used to separate atmospheric air into its primary components and produce nitrogen, oxygen, carbon dioxide and sometimes also argon or other rare gases, but also to provide oxygen enriched air for medical applications. In chemical engineering, CO2 removal is a key issue to purify intermediate or final gas products. And for air quality assessment purposes, selective gas separation techniques at very low throughputs are also highly valuable.

Among the various techniques used, the separation of gases by thin membranes is a rapidly growing field. Membranes act as a permeable barrier through which the different gaseous compounds are filtered according to their size, diffusivity, or solubility into the membranes. In this area, liquid membranes have also been studied as they present several advantages such as a high efficiency due to their selectivity, especially when enriched with transport carriers, or their ease to be retreated. In particular dynamic liquid membranes consisting of a liquid flowing on a solid surface have recently proven extremely efficient due to the constant renewal of the liquid membrane, maintaining the dissolved gas concentration steady and increasing the surface devoted to gas exchange.

This project deals with the development of the concept of suspended liquid membrane (SLM), consisting of liquid films supported on a rigid frame to serve as a separation membrane. The aim of this work is to design a new generation of SLM made of a soap film and to assess its efficiency to separate gases in a microfluidic device.

The expected advantages of such a soap film suspended membrane are:

• a larger active surface increasing the throughput of the reaction,
• a chemical composition of the membrane that is kept constant by the flow of the soap forming the film, therefore allowing a steady regime of reaction
• the possibility to easily renew the membrane and decontaminate the exchange surface, by destroying and reforming the film

Different experimental devices are used in the project (see example in figure 1) to address the following questions:

• Can a soap film serve as semi permeable membrane to induce an osmotic flow between 2 different gases?
• What is the role of the film thickness in the process?
• Does the chemical composition of the film modify the dynamics of the reaction?
• Can solid aerosols be filtered without breaking the soap membrane, and if yes, could such a device be used as a sensor to measure the concentration of fine particles in the air?
• Is the efficiency of the gas uptake influenced by the dynamical flow conditions applied to the gases

This project follows the idea that soap films have a real potential in the development of microfluidic devices for air quality measurement, as they are extremely cheap, easy to form and renew, and chemically tunable, thus offering a great flexibility in terms of analysis.