Recovery of Butanol from ABE Fermentation Broth with Hydrophobic Functionalized Ionic Liquids as Extractants

Biobutanol has a high energy density, good miscibility with gasoline, and a low environmental impact; therefore, it is a possible substitute or additive for gasoline. Because biobutanol is typically obtained through so-called ABE fermentation, the effective separation of butanol from the product mixture is important. Ionic liquids (ILs) have been used as extractants, and tailoring the IL structure to promote hydrogen bonding with butanol could improve the extraction performance. In the present work, an amine group was added to the imidazole cation of an IL, paired with bis(trifluoromethylsulfonyl)imide as the anion. Hydroxyl groups were added to the 1,8-diazabicyclo-[5.4.0]-undec-7-ene cation, and an imidazolium-based IL was produced by combining hydroxyl with imidazole. The structures of these three ILs were verified by H-1 nuclear magnetic resonance and Fourier transform infrared spectroscopic analyses. The binding energies between these substances and butanol, acetone, and ethanol were calculated using the Gaussian software package based on density functional theory. The results indicated that the interaction energies between N,N-bis(2-hydroxypropyl)octan-1-aminium hydroxide imidazole ([C(8)DIPA][Im]) and butanol, acetone, and ethanol are greater than that with water. These ILs were examined as extractants for the separation of butanol, acetone, or ethanol with water, and the [C(8)DIPA] [Im] exhibited the best performance. Effects of extraction time, extraction temperature, and IL proportion on extraction rate were assessed, and this IL extracted 78%, 34%, and 6% of the three components, respectively. This performance remained stable after 10 recycling trials, and [C(8)DIPA][Im] was also used to separate the products in an actual ABE fermentation mixture.