High Efficient Methods Of Separating Butyric Acid From Anaerobic Fermentation Broth

Butyric acid is an important chemical material and has various applications in industry, agriculture, medicine, etc. It can be produced with both chemical methods and biological methods. With the consideration of low productivity, low concentration of butyrate in the final product and a complicated, expensive isolation process, biotechnological production of butyric acid is not commercially competitive with chemical production. However, butyric acid fermentation is a typical process of anaerobic process with low energy consumption, and hydrogen can be produced at high yield as one future clear energy. Besides, microbial fermentation is a better method due to the increasing consumer demands for natural food ingredient. Therefore, many efforts have been paid to improve the bioproduction of butyric acid nowadays. Correspondently, it is very demanding to develop novel strategies of separating butyric acid from the fermentation broth efficiently.To explore the proper methods for butyric acid separation from fermentation broth, in the present work, three methods (ion exchange, extraction and salt out) was studied.The weakly basic anion ion exchange resin D301 was screened out as the suitable resin for separating butyric acid from fermentation broth. Adsorption dynamics, effect of initial pH of static adsorption, the breakthrough and elution condition of dynamic adsorption were studied, then proper operation conditions were determined as follows:initial pH value of the solution was 2.0, adsorption flow rate 2 BV·h-1, elution flow rate 2 BV·h-1,1 M Na2CO3 solution as eluent.In order to extract butyric acid effectively, TBP was selected as the extractant and sulfonated kerosene as the solvent. The extract and reextract process were optimized, and finally the suitable conditions were determined as follows:Initial pH was adjusted to 2.0, while TBP and sulfonated kerosene with volume ratio 1:1 was used as extractant and 1M Na2CO3 solution was used as reextractant. Extraction and reextraction were operated both at 25℃with phase ratio 1. The recovery ratio could attain up to 99.33% after four-time repeated extraction. It was also showed that the extractant had a good regeneration performance. On the basis of previous study, two-component mixture of butyric acid and acetic acid was extracted by this process. Fermentation broth was further employed to test the above process. In the present work, one novel separation methodology was developed with aide of "salt out" effect. Calcium chloride was screened out from different salts (potassium chloride, sodium chloride, magnesium chloride). In the butyric acid-water-calcium chloride system, the higher were butyric acid and calcium chloride concentrations, the stronger was the salt out effect. In the two phase formed by salt out effect, butyric acid was enriched in the upper phase with maximum concentration approximately 900 g/L, whereas most of calcium ions contained in the lower phase. Further study showed that "salt out" effect could be used to separate butyric acid with the repeated separation procedure. The effect of calcium chloride on acetic acid solution and the two-component mixture was also studied. Phenomenon of phase split was not observed when 50 g/L-200 g/L calcium chloride was added in 100 g/L-500 g/L acetic acid solution at 25℃; phase split was observed when calcium chloride was added in the simulated solution which consisted of butyric acid and acetic acid. Comparing with the initial concentration ratio, the final concentration ratio of butyric acid and acetic acid in the upper phase could be improved significantly due to the difference of distribution coefficient. It indicated that salt out effect not only enriched butyric acid efficiently but also separated butyric acid and acetic acid in some extend.