Bio-butanol downstream processing: regeneration of adsorbents and selective exclusion of fermentation by-products

Abstract

Due to the decreasing availability of fossil resources and the negative effects on the global climate, an alternative to the petrochemical industry for the production of chemicals and fuels has to be developed. Bio-butanol is one of the most promising substitutes for gasoline and platform chemicals. However, the economical production of butanol by fermentation is limited by several factors. Since butanol is toxic for the cells, only low concentrations can be achieved in the fermentation broth. A recovery of butanol by distillation consumes more energy than the purified product contains and therefore is uneconomic. As an alternative, the purification of butanol by adsorption is a promising energy efficient technique. In this work adsorption isotherms for the resin SP-207 and the activated carbons AC 207C and CAL TR were determined for butanol solutions and synthetic fermentation broths at pH 4 and 5. The specific loading for butanol in the synthetic fermentation broth with pH 4 was decreased up to 53% at a butanol concentration of 4 g L− 1 compared to the pure butanol–water solution. The reduction was mainly caused by a replacement of butanol by butyric and acetic acid. To prevent the replacement, a selective pre-separation of the acids by the anion exchange resin MP 62 WS was tested. The resin showed affinity for the acids only, no solvent adsorption was observed. A pH shift of the medium from 4 to 5 led to a strong increase of the butanol adsorption. Furthermore, a screening test for the thermal regeneration of the three adsorption materials showed a drop of the butanol loading after the first cycle for the activated carbons, but not for the resin and allowed a pre-selection for further desorption tests.