The Fundamental Researches And Process Optimization And Contamination Control Of The Glutamate Continuous Crystallization

The major extracting technology of glutamic acid in mono-sodium glutamate industry in China is batch iso-electric crystallization, however, this technology has two obvious defects: on one hand, many tiny crystals will be produced because the degree of supersaturation during the crystallization process which is difficult to be controlled. Meanwhile, the quality of product of each batch is different. On the other hand, it cannot effectively deal with increasing high acid concentration of fermentation broth. In this study, the process optimization of continuous crystallization of glutamic acid was mainly carried out, and was expected to provide some theoretical guidance for the industrial production.The effects of different pH regulation modes, feed flowing methods, temperature, stirring intensity on the crystal size distribution(CSD), and the effects of different operation conditions on the crystal agglomeration degree were also studied, which were done as basic research for continuous crystallization process. Results have shown that the optimized pH regulation mode that adjusted to the change of degree of solution supersaturation and the method feeding in the turbulent region are more favorable for the crystallization process. On the base of inhibiting theβ-type crystal being produced, an appropriate increase in crystallization temperature helps to improve the crystal size and uniformity. When the stirring Reynolds number was less than 300,β-type crystals were produced due to the poor mixing condition.While, when the stirring Reynolds number was surpassed 600, the average crystal size demonstrated a decreasing tendency with the stirring intensity and time. Lower stirring intensity and higher acidification speed will increase the degree of crystal agglomeration and reduce the quality of product as well as crystal form.The comparison of the crystallization effectiveness between the conventional crystallizer and optimized new crystallizer was firstly studied, and the technological conditions such as residence time, feed concentration, crystal suspension density in continuous crystallizer were investigated and optimized. The crystal nucleation and growth kinetics in continuous crystallization was then established. Experimental results suggested that the optimized new crystallizer can increase crystal size and improve the CSD obviously. The quality of glutamate crystals obtained in continuous crystallization were relatively better when the temperature was 30℃, residence time was 12h, feeding concentration was 8%, crystal slurry suspension , respectively. The two kinetic equation could be used to explain the influence mechanism of supersaturation, crystal slurry suspension density and temperature on the crystallization of glutamate, so as to provide important theoretical basis for the process controlling in the continuous crystallization of glutamic acid.The wild yeast strain isolated from the contaminated continuous crystallizer of L-glutamic acid production was preliminary identified, and the results showed that the yeast is Candida. The growth characteristics of Candida was investigated and the possible approaches preventing its contamination were consequently studied in this paper. It was found that the proliferation of the wild yeast will be gradually inhibited with the drop of pH, but maintaining the pH at a low value 3.22 could not preventing the contamination effectively. The temperature has a more significant effect on the growth of the wild yeast, once it exceed 50℃, the wild yeast's growth will be almost ceased. However, high temperature above 50℃is detrimental to the extraction of glutamic acid. By adjusting the residence time in continuous crystallization to less than 9.12h which is the doubling time of the wild yeast, the wild yeast will be washed out from the crystallizer gradually, since its specific growth rate is lower than the critical dilution rate. Through this way, the contamination problem in the crystallization process can be effectively solved, thus the loss of the main product of glutamic acid during the extraction process can be cut down.