Bio-butanol separation by adsorption on various materials: Assessment of isotherms and effects of other ABE-fermentation compounds

In the general effort to produce chemicals and fuels from renewable resources there is new interest in the biotechnological route to produce butanol. Acetone-Butanol-Ethanol (ABE) fermentation leads to low product yield because butanol is toxic to microorganisms. Selecting an efficient technology to recover butanol from low concentration butanol (about 2%) solutions is key to a successful implementation of this butanol production process on an industrial scale. Adsorption has been suggested as a potential technology for butanol recovery. This paper reports a systematic investigation of the adsorption of the metabolites that are typically present in the ABE fermentation broth: acetone, butanol, ethanol, acetic acid, butyric acid, yeast extract. The effect of glucose as a carbon source for the ABE fermentation was also investigated. Three adsorbents were characterized: Amberlite XAD-4, Amberlite XAD-7 and Zeolite Y. Batch tests under a wide interval of operating conditions were carried out for the assessment of the adsorption capacities of the three adsorbents. The selectivity of the three adsorbent materials towards the main components of ABE broths was also investigated. These tests were carried out using both dilute model solutions and real fermentation broths. The tests show that Amberlite XAD-7 has the highest affinity for butanol adsorption. The co-presence of all the metabolites in the solution - synthetic broth and real broth - changes the distribution in the adsorbed phase remarkably. The distribution of the concentration of the adsorbed components can be affected by pH. The presence of glucose does not affect butanol adsorption. Amberlite XAD-7 has a great potential as an adsorbent in ABE fermentation coupled with in situ recovery product removal techniques.