Study On Succinic Acid Produced By Fermentation From Stalk

Succinic acid (SA) is an important four carbon compounds in industry, which could used to synthesis other organic chemicals directly. It has a wide range of application, such as raw materials, specialty chemicals and intermediates in pesticide production, food additives, dyes and production of biodegradable plastic. Development fermentative technology of succinic acid production using agricultural waste straw as raw material has a very important practical significance, due to providing a new way of succinic acid production from cheap raw materials and promoting the re-use of agricultural waste. In this paper, pretreatment condition of different straw, preparation of the fermentative broth from pretreated stalk (pre-straw) directly, and both extraction methods of using the calcium succinate percipitation and organic solvent extraction were mainly investigated. The results were as follows:Comparing three different concentration of alkali pretreatment of straw showed that when corn, wheat and rice stalks were pretreated with 1.0% NaOH concentration at 120℃for 2 h, its rates of both lignin removal and cellulose-hemicellulose remained were reach the maximum(more than 85%). In the conditions of cellulose and cellobiase added with fermentation were performed 72 h by Actinobacillus sucinogenes F3-21 in 150-mL flask, 30.74 g/L, 24.98 g/L and 26.57 g/L SA were achieved using the corn, wheat and rice pretreated stalks as stuff, respectively. While in a 5-L stirred bioreactor, SA concentration were obtained 40.21 g/L, 30.06 g/L and 39.07 g/L in 72 h, and its yields of each per gram of pretreated stalks reached 0.50 g, 0.38 g and 0.49 g correspondingly.The corn straw is the best straw in producing SA.Using the corn straw as raw material, the concentration of substrate, types of cellulase and xylanase loading were studied. Results showd that was the substrate concertration of 90 g/L, the amount of cellulase, cellobiase and xylanase were 20 FPU/g pre-straw, 10 CBU/g pre-straw and 150 U/g pre-straw, the concertration of SA was reached 47.71 g/L with 0.53 g SA by per gram pre-straw in 5-L stirred bioreactor.Extracting SA from the corn straw fermentation broth with calcium succinate percipitation was studied. The optimization process were as follows: firstly the broth enriched to the succinic acid concentration of 80 g/L by boiling after centrifugation; then according to the total fermentation acid, adding 60% CaCl₂ solution slowly with a roatio of acid to CaCl₂ 1:1.3(mol/mol) and calcified in 80℃; Aacid-olysis were performed adding 60% concentrated sulfuric acid and 0.8% activated carbon. After ion-exchange purification and concentration, the total succinic acid extraction rate was 69.05% befor crystallization and a succinic acid crystallization of 99.98% purity was obtained.Extracting SA from the corn straw fermentation broth with trioctylamine extractant consisting of n-octanol was studied. The results showed that: extractant trioctylamine: octanol = 7:3(V/V), 25℃, pH=2, the broth:extractant =1:1(V/V), extraction time 30 min, 1:1, the rate of extraction of succinic acid reached 86.52%; using 1.5 mol/L Na₂CO₃ solution as anti-extractant, the extraction phase: the anti-extractant = 2:1(V/V), 30 min, the extraction yield of succinate reached 86.07%, and the concentration of succinate salt reached 65.09 g/L. The total succinic acid extraction rate was 58.53% befor crystallization rate, and a succinic acid crystallization of 99.99% purity was obtaine. The organic solvent could be re-used after anti-extractionBoth the Calcium succinate percipitation method and the solvent extraction method were compared in the extraction yield, cryatallization. The energy consumption of the solvent extraction method was lower than that of calcium succinate percipitation method, suggesting that the solvent extraction method may be a feasible way for extracting succinic acid from corn straw fermentation broth.