Design, synthesis and characterisation of new absorbents (Ionic Liquids) for the biotreatment of hydrophobic VOC – ILABio

The main steps of the project are:
• the design, the synthesis and the characterisation of ionic liquids dedicated to absorb hydrophobic VOC (for example imidazolium, phosphonium, ammonium, or pyrrolidinium families);
• the study of the absorption in the selected ionic liquid of a single hydrophobic VOC, as well as mixtures of VOC;
• the study of VOC mass transfer from the organic to the aqueous phase containing microorganisms, followed by VOC biodegradation in the aqueous phase or at the liquid/liquid interface;
• the study of the coupling of the above steps in order to propose some useful considerations to design the whole process.

The scientific program of this project can be divided into four steps: (1) the choice, the synthesis and the characterisation of the organic phase; (2) the investigation of VOC biodegradation in an emulsion of water and the selected organic phase; (3) the third step concerns the validation of the first reactor of the integrated process, the gas-liquid contactor; (4) and the last step deals with the optimisation of the two-phase partition bioreactor (TPPB), allowing to propose useful considerations tracks to design the whole process.

A complete literature review on the properties of ionic liquids was used to select a number of structures to explore. Thirty ILs have been synthesized without particular difficulties, in sufficient quantities for the study (a few milliliters). These ILs were evaluated according to several criteria :
- Cytotoxicity : a family of ILs, the isoquinoliniums proved cytotoxic at µM range for 8 cell lines.
- Toxicity towards microorganisms present in the bioreactor : no bacterial toxicity has been demonstrated , but an increase in the acclimation time of microorganisms in the presence of some ILs containing functional groups such ethers was emphasized.
- Release of fluoride ions can cause toxicity to aquatic organisms : no significant release except in the case of ILs functionalized by fluorinated chains were found .
- Biodegradability : no IL is biodegradable after 28 days of contact with microorganisms contained in activated sludge.
- Viscosity : measured values are high, but are acceptable in the project insofar as the element « absorption column «design is optimized (< 650 cP). For example, the column packing used in the part may be designed specifically for viscous fluids. It will nevertheless ensure that these viscosity values do not excessively alter the diffusion of the liquid VOC. Measurements of diffusion coefficients are being conducted to verify this.
- Partition coefficients quantifying the absorbency of toluene: better performances were observed in comparison with some existing systems (silicone oil) , and a very strong absorption of the VOC in the aromatic ILs could be demonstrated .

Halfway through, some families of LI seem to be suitable for the proposed process. The viscosity remains an obstacle but not a must lock. Diffusion coefficients will be measured to quantify the influence of the high viscosity of the mass transfer precisely.
Moreover, once the LI has been selected, tests will be carried out in semi-continuous small-scale (and not at the pilot scale since quantities needed to pass this step are important) in order to verify the feasibility of the process.

1. QUIJANO G., COUVERT A., AMRANE A., DARRACQ G., COURIOL C., LE CLOIREC P., PAQUIN L., CARRIE D. 2013. Ionic Liquids as New Absorbents for the Removal of Hydrophobic Volatile Organic Compounds. Wat. Air Sol Pollut. 224: 1528-1536.

2. GUIHENEUF S., RODRIGUEZ CASTILLO A.S., PAQUIN L., BIARD P.-F., COUVERT A., AMRANE A. 2014. Potential of ionic liquids for hydrophobic organic pollutants absorption and biodegradation in multiphase systems. Pages 305-337. In «Production of biofuels and chemicals with ionic liquids«, Z. Fang R.L. Smith Jr., X. Qi ed. Springer.

3. GUIHENEUF S., PAQUIN L., BAZUREAU J.-P., RODRIGUEZ CASTILLO A.S., QUIJANO G., BIARD P.-F., AMRANE A., COUVERT A., 2013. Conception, synthesis and characterisation of new absorbents for hydrophobic VOCs biotreatment in two-liquid phase system. International Congress on Ionic Liquids (COIL-5), 21/04-25/04, Vilamoura (Portugal).

4. PAQUIN L. October 2013. Ionic liquids: a toolbox for organic synthesis, extraction and/or trapping VOCs. Groupes De Recherche Liquides Ioniques et Polymères. Lyon (F).

Patent in progress: Use of a specific ionic liquid for the treatment of hydrophobic Volatile Organic Compounds

The proposed research project consists in the design and development of new absorbents (Ionic Liquids) for implementation in a process designed to treat hydrophobic VOC (volatile organic compound). This project deals therefore with environmental considerations and its main scientific issues are: (i) the design, synthesis and characterisation of a ionic liquid (IL) displaying firstly high absorption potentialities towards the targeted hydrophobic VOC and secondly an absence of biodegradability and toxicity facing bacteria contained in activated sludge in view of its regeneration using a biological treatment; (ii) the implementation of the IL in an integrated process coupling VOC absorption and their biodegradation. Whereas they have not been already implemented in environmental applications (air treatment, and especially VOC removal), IL appear especially promising owing to their high absorption capacity towards hydrophobic compounds and their low volatility (saturated vapour pressure close to zero), as well as the possibility of IL tailoring, allowing a fine-tuning of their physicochemical properties, leading to a wide range of products with various characteristics. Their non-biodegradability also argues in favour of their use in the innovative combined treatment process likely to be developed in this project, an absorption contactor and a two-phase partitioning bioreactor.