In-situ product recovery using membrane-assisted reactive extraction for bio-based 3-hydroxypropionic acid production
Résumé
3-hydroxypropionic acid (3-HP) is a platform molecule of industrial interest targeted by the DoE [1] as a biobased precursor to acrylic acid and polymers. It can be obtained through the bioconversion of biosourced substrates. However, its accumulation in the bioconversion broth can induce a high toxicity toward the producing microorganisms. The production is then limited and the neutralization of the broth is needed to match high concentrations and biocompatible pH, to the detriment of the purification process. In order to overcome these limitations, coupling a bioreactor containing relatively pH tolerant microorganisms with a selective separation process is a promising approach. The studied process is the reactive extraction assisted by a membrane contactor. It consists in extracting the acid through a reversible reaction using an extractant, a hydrophobic amine, diluted in an organic solvent. A strategy to limit the organic phase toxicity toward microorganisms is the use of a membrane contactor providing a high liquid-liquid contact area, thanks to high porosity of the membrane material, while avoiding direct contact with the microorganisms. This integrated process should prevent 3-HP accumulation while performing a primary purification regarding cells, proteins, cations, substrates and coproducts. Trioctylamine is used as the extractant. Long chained alcohols were suitable solvents. Among them, decanol seems to be the best compromise between a low water solubility and good extraction efficiency. The most successful techniques for the renewal of the organic phase were the thermal and the chemical regenerations. For practical reasons, the latter was considered and leads to a total recovery with concentrated 3-HP. The setting-up of the 3-HP production integrated with its extraction and the solvent phase regeneration could allow to reach a stationary state in the production reactor where the 3-HP accumulation stays low. A modelling approach gave driving keys to adjust the process regarding productivities reached with optimized micro-organisms. A productivity of around 2.5 g/L/h (as advised by the DoE and reached by Cargill [2]) would lead to a broth with less than 5 g/L 3-HP whose pH can easily be adjusted with a small amount of base. This study reports original results about the mastery of an extractive bioconversion. It is a potential breakthrough toward the implementation of a robust and intensified biotechnological process at the industrial scale. Further research should be provided concerning membranes aging over long run bioconversions and biocompatibility aspects.
Reference
[1] J.J. Bozell, G.R. Petersen, Technology development for the production of biobased products from biorefinery carbohydrates—the US Department of Energy’s “Top 10” revisited, Green Chem. 2010. 12(4): p. 539-554.
[2] T.W. Abraham, E. Allen, J.J. Hahn, P. Tsobanakis, E.C. Bohnert, C.L. Frank, Recovery of 3- hydroxypropionic acid, US 2016/0060204 A1, 2014.