Submitted to: Bioprocess and Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 18, 2005
Publication Date: April 5, 2005
Citation: Qureshi, N., Hughes, S.R., Maddox, I.S., Cotta, M.A. 2005. Energy efficient recovery of butanol from model solutions and fermentation broth by adsorption. Bioprocess and Biosystems Engineering. 27(4):215-222. Interpretive Summary: Approximately 2.6 billion pounds of butanol, a superior liquid fuel, are produced in the U.S. annually from the depleting petrochemical resources. Butanol can be produced from renewable agricultural crops such as corn and/or agricultural/forest residues by fermentation using selected microorganism/s. However, a major bottleneck in the commercialization of butanol production by this route is the cost intensive product recovery from the fermentation broth by traditional distillation. In an attempt to recover butanol energy efficiently, a number of alternative techniques have been developed. These techniques can be categorized into adsorption, membrane separation, extraction, and gas stripping. In order to evaluate a process, a comparison of energy requirements by these four techniques has been made and it was found that recovery of butanol by adsorption onto silicalite (molecular sieve) is the most energy efficient. This investigation would lead to energy efficient recovery of butanol and hence its commercialization to benefit fermentation industry and the farmers.
Technical Abstract: This is an overview discussing the separation of butanol [also called acetone butanol ethanol (ABE) or solvents] from aqueous solutions and/or fermentation broth by adsorption. Adsorbents such as silicalite, resins (XAD-2, XAD-4, XAD-7, XAD-8, XAD-16), bone charcoal, activated charcoal, bonopore, and polyvinylpyridine have been studied. Use of silicalite appears to be the more attractive as it can be used to concentrate butanol from dilute solutions (5 g/L to 790-810 g/L) and results in complete desorption of butanol (or ABE). In addition, silicalite can be regenerated by heat treatment. The energy requirement for butanol recovery by adsorption-desorption processes has been calculated to be 1948 kcal/kg butanol as compared to 5789 kcal/kg butanol by steam stripping distillation. Other techniques such as gas stripping and pervaporation require 5220 and 3295 kcal/kg butanol, respectively. Use of bone charcoal or charcoal resulted in adsorption of 206-252 mg of butanol/g adsorbent; however, desorption was incomplete. Successful application of polyvinylpyridine has been reported to recover ABE from fermentation broth. The concentration of butanol in the displacer phase (methanol) was reported to be rather low at 30-40 g/L which would require further distillation. However, fermentation parameters were reported to have improved significantly. Results on energy requirements for butanol separation by various processes such as distillation, pervaporation, gas stripping, and extraction are presented.