Enzymatic Esterification under High-pressure CO 2 Conditions for in situ Recovery of Butyric Acid from Anaerobic Ferment
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pISSN 1226-8372 eISSN 1976-3816
RESEARCH PAPER
Enzymatic Esterification under High-pressure CO2 Conditions for in situ Recovery of Butyric Acid from Anaerobic Fermenters Jaesung Chun and Byoung-In Sang
Received: 22 May 2020 / Revised: 27 May 2020 / Accepted: 27 May 2020 © The Korean Society for Biotechnology and Bioengineering and Springer 2020
Abstract Butyric acid, a short chain carboxylic acid with diverse usages, is produced by Clostridia fermentation. In the industrial scale production of butyric acid, its separation and recovery from fermentation broth requires energyintensive processes. To reduce the product recovery costs, it is necessary to convert butyric acid into a chemical with a much higher partition coefficient in the hydrophobic extractants than butyric acid. Butyl butyrate, with an excellent partition coefficient to tetradecane, can be produced by the enzymatic conversion of butyric acid via esterification. Moreover, butyl butyrate can be used as a valuable fuel source and additive in the food, cosmetic, and pharmaceutical industries. Novozyme 435, Candida antarctica lipase B immobilized on acrylic resin, and tetradecane were used as the enzyme and extractant, respectively. A high-pressure CO2-facilitated reactor was used to temporarily drop the pH of the fermentation broth so that the enzymatic reaction could be activated. The in situ removal of butyric acid and simultaneous production of butyl butyrate were processed continuously during fermentation. To optimize the enzymatic reaction, it was necessary to maintain a temperature of 40°C at 50 bar and an optimal molar ratio of substrate. In the extractive fermentation, 11.6 g/L butyl butyrate was produced with a productivity of 0.77 g/L/h from butyrate produced through fermentation. This process is expected to be able to extract carboxylic acids with more diverse carbon lengths in ester form. Keywords: Clostridium tyrobutyricum, butyric acid, butyl butyrate, extraction process, carbon dioxide
Jaesung Chun, Byoung-In Sang* Department of Chemical Engineering, Hanyang University, Seoul 04763, Korea Tel: +82-2-2220-2328; Fax: +82-2-2220-4716 E-mail: [email protected]
1. Introduction Short chain carboxylic acids (SCCAs), including butyric acid, have the potential to be promising platform chemicals for the production of many chemicals and biofuels [1-3]. Through catalytic reactions, butyric acid can be converted into hydrocarbons that can be used for vehicle fuels, such as gasoline, diesel, and jet fuel, and for various applications in the fragrance, cosmetic, paint, solvent, and coating industries [4,5]. Although butyric acid is usually produced via petrochemical routes, bacterial fermentation can be an alternative method for butyric acid production [6,7]. Clostridium tyrobutyricum, Clostridium acetobutyricum, and Clostridium butyricum are some of the most generally investigated and industrially used strains [8,9]. Among them, C. tyrobutyricum is known to have high tolerance and efficient productivity of butyric acid. Repeated fedbatch ferment
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