The Purification Of γ-Aminobutyric Acid By Ultrafiltration And Electrodialysis Techniques

Gamma-aminobutyric acid (GABA) is a natively existing non-protein amino acid. It is helpful to lower blood pressure, to improve brain function, to enhance long-term memory, to enhance liver and renal function and so on. It exists widely in nature, but with very low content. Early chemical synthesis of GABA has a high cost and a low production rate. Furthermore, it can not be used in food industry on reason of dangerous solvents used in the synthesis. The production of GABA with biological methods has the advantages of lower cost, higher content and better safety. Thus it can be widely used in food industry. The separation and purification of fermentation broth is the key process for the industrial production of GABA. Membrane separation has many advantages, such as no phase change, lower energy consuming, more facile operations and better selectivity. It is naturally the first choice for the separation of fermentation broth.This research aims to use the Ultrafiltration (UF) and electrodialysis (ED) to separate and purify GABA fermentation, in order to obtain high purity and high recovery of the GABA product. The research is composed of three aspects:After a pretreatment of high speed centrifugation, a UF membrane with a MWCO value of 45000 is used to separate GABA fermentation broth. The effect of pressure difference and circulation velocity on separation are investigated, the best operation conditions are required:a pressure difference of 0.1MPa and a circulation velocity of 1.15m/s. The effect of concentrate rate on UF flux and GABA recovery at such pressure and flow velocity are also studied. According to the SEM observation and the flux curve, combined with recovery requirement, a concentrate ration of 10 is acquired. Research result indicates that high speed centrifugation and UF can separate more than 60% protein, making the purity of GABA increase from 3.19% to 6.20%. The recovery of GABA is 88.60%.With different NaCl concentrations, the effects of liquid concentrations and flow velocity on limited current density in electrodialysis are investigated. Experiment results show that high concentration and high flow velocity are good for the limited current density. The effect of adding amino acid with pI on the limited current density of NaCl salt solutions shows that the adding amino acid brings in the decrease of limited current density as it increases the liquid concentration. But the difference is small as the adding amino acid doesn't directly participate in the transmission of electric current. On the basis of modified Wilson empirical equation, the effects of liquid concentration and flow velocity on the limited current density are analyzed.The effects of technique parameters of ED are investigated to require good ED...