The Research On Separation And Purification Of Citric Acid From Fermentation Broth

Citric acid, a widely used acid with grert market demand, is an important part of organic acids. This thesis focuses on the separation and purification of citric acid from fermentation broth by solvent extraction. Considering the extraction rate and back extraction ratio as main research indexes, the composition of extraction system, extraction, back extraction, decoloration process conditions are optimized. The whole citric acid production procedure is designed and the economic benefit is evaluated.Complexing agent and phase modifier in the extraction system are studied. Considering extraction rate, back extraction ratio and impurity content of stripping solution, including pigment, total sugar, protein, as the examination indicators, complex formulation of extractant 1 and extractant 3 are selected as complexing agent, n-decanol as phase modifier and kerosene as diluent. The volume fraction of 30% extraction 1+40% extraction 3+10% n-decanol+20% kerosene are optimized as the best extraction system formula. The complex structure is determined by double logarithmic method and IR spectroscopy analysis, indicating that extraction reaction of complex agent with citric acid occurs through ion association and hydrogen bond, n-decanol does not participate in chemical reaction.Through single factor and orthogonal test, the best extraction conditions are optimized as follows: the initial fermentation broth p H 1.70, extraction temperature 30℃, speed 500 r/min, phase ratio 2:1, reaction time 10 min. Under the optimal conditions, 6 stages countercurrent extraction are carried out, the results show that extraction rate keeps steady at 99% and citric acid concentration in fermentation broth reaches 1.0 g/L. The extraction reaction molar enthalpy is-7.366 k J/mol by studying thermodynamics, which belongs to the exothermic reaction.The optimal conditions of back extraction process are as follows: temperature 80℃, speed 400 r/min, phase ratio 1:1, reaction time 8 min. After 11 stages countercurrent back extraction, the back extraction ratio keeps steady at 90% and citric acid concentration in stripping solution reaches 128 g/L. After regeneration, the organic phase recycled in extraction process, the extraction rate is almost unanimous compared with the new organic.Regarding the optimization of different adsorbents for decolorizing stripping solution, activated carbon is selected for its higher decoloration rate and lower citric acid loss rate. Through single factor and orthogonal test, the best decoloration conditions are optimized as follows: activated carbon concentration 24 g/L, temperature 30℃, speed 400 r/min, time 55 min. The adsorption thermodynamics results show that the adsorption molar enthalpy is 7.5657 k J/mol, belongs to physical adsorption. The adsorption process fits the Langmuir adsorption model.A 10,000 tons/year of citric acid production process is designed using reciprocating sieve plate extraction column as extraction equipment, and the production process parameters are calculated by raw material and extractant solvent flow. The process chart is drawn and technical and economic analysis is studied on the citric acid production, providing the reference data in practice.