Reactive extraction of bio-based 3-hydroxypropionic acid : towards an integrated process of a membrane-assisted extractive bioconversion
Résumé
3-hydroxypropionic (3-HP) is a promising building-block for renewable polymers and chemicals like acrylic acid, acrylates, acrylamides and bioplastics. As such, it has been referred by the DoE as one of the “Top 10” value-added chemicals to produce from biomass (1). A large variety of bio-sourced substrates to feed biotechnological processes have been investigated successfully to produce 3-HP like glycerol for wild strains or glucose, xylose and even CO2 for genetically modified micro-organisms (2,3). However, rather low product concentration and productivity have been observed due to strong inhibitions from 3-HP and other metabolites, for example for glycerol bioconversion with L. reuteri (3). A solution to overcome this problem is called in situ product recovery. It consists in removing the product from the bioconversion broth while it is produced. The process we chose is the reactive liquid-liquid extraction assisted by a hollowfiber membrane contactor. Very hydrophilic acids such as 3-HP cannot be recovered efficiently through simple liquid-liquid extraction without using a huge amount of solvent. The aqueous phase containing 3-HP is then brought into contact with an organic phase containing a hydrophobic aliphatic amine. Both molecules can selectively interact with each other through acid-base interactions leading to the formation of a complex mainly soluble in the organic phase. The use of a micro-porous membrane between the two phases keeps the micro-organisms away from the organic phase potentially avoiding a high toxicity and stabilizes the interface preventing both phases from mixing and emulsifying while providing a high specific surface area when compared to traditional processes. Several reactive liquid-liquid extraction assisted by a hollow fiber membrane contactor have been performed and parameters like the nature of the solvent and the concentrations of the aliphatic amine and 3-HP have been tested. We provide equilibrium and kinetics results and propose a chemical model taking into account the complex formation, the influence of the solvent, the acid dissociation, the acid partitioning between the two phases and the leak of amines in the aqueous phase to predict extraction yields. This is the first step for a deep understanding and the implementation of an integrated process of extractive bioconversion for 3-HP production from biomass. References
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