A photodriven energy efficient membrane process for trace VOC removal from air: First step to a smart approach

[Display omitted] •Proof of concept by experiment and modeling of a novel photodriven membrane process.•Efficient trace VOC removal.•No compression, no vacuum pumping required.•Intensification of photocatalytic reaction and limitation of potential by-products.•Hybrid process with high energy efficiency and suitable to work with solar source. The VOC removal from air is a major concern both in the context of occupational and domestic exposure. Membrane processes are often presented as unsuitable for the removal of low concentrated VOCs mainly due to a too low driving force leading to high-energy costs. The aim of the work presented in this paper is to investigate the original combination of a dense membrane separation process and a photocatalytic oxidation process implemented in the permeate compartment of the system for the intensification of the separation and the decomposition of toxic compounds. An unpublished modeling of this coupled processes completed by a robust experimental study integrating the main operating parameters (flow rates, pressures, membrane materials, catalyst mass, concentration, light irradiance) is presented in this work. This exploratory study shows that for a test compound, n-hexane, this approach significantly intensifies the separation of a low-concentration VOC (i.e. 1 to 25 ppm) with a low-energy cost. The model developed here allows designing more enhanced system such as hybrid plug-flow module operating with a thin polydimethylsiloxane membrane and sweep-gas on the permeate compartment. This configuration seems particularly relevant for an efficient VOC separation and limits greatly the presence of potential by-products in the treated effluent, such as formaldehyde, acetaldehyde or carbon monoxide well-known intermediates identified in photocatalysis. From a reaction position, this hybrid process leads to the VOC photocatalytic oxidation advantageously increased compared to a single plug-flow reactor especially for low light irradiances (≈3 W m−2). This process is suitable to work with the solar irradiance.