Study On The Crystallization Process Of L-valine

As an essential amino acid, L-valine (CAS No.72-18-4), C5H11NO2, is widelyused in the high added value industries, such as food industry, pharmaceuticalindustry, and cosmetic industry, instead of the traditional feed additives. Systematicstudies have been performed to resolve the problems occurred in the home industrialmanufactures of L-valine, especally in the products quality of domestic L-valine, i.e.purity, crystal shape and particle size distribution, etc. The crystallization andseparation process of L-valine were studied systematically. The results that served asthe essential basic data and heplful technological supports for developing a novelcrystallization process of L-valine with independent intellectual property rights andpromoting the products quality were achived.The solubility of L-valine in five pure solvents (water, ethanol,N,N-dimethylformamide, isopropyl alcohol and acetone) and four binary mixedsolvents of water+(ethanol, N,N-Dimethylformamide, acetone, isopropyl alcohol)was experimentally measured by the synthetic method. Then, the solubility wascorrelated by the Apelblat equation, λ equation, and the (CNIBS)/Redlich–Kisterequation, which provides basic data for the crystallization control and processoptimization.The induction period time (tind) of L-valine in the ethanol–water mixed solventswas investigated experimentally by an intensity of scattered light method. The effectsof the supersaturation on the induction period was discussed． Based on the classicalhomogeneous nucleation theory, the solid-liquid interfacial tension and surfaceentropy factor were calculated from the induction period data．The values of thesurface entropy factor implied that the interface of the L-valine crystals grown fromthe ethanol–water mixed solvents system would be rough and a continuous growth.Based on the research results of the crystallization thermodynamics and growthmechanism, the crystallization process of L-valine was optimized. The effects ofdifferent crystallization pattens, seeds, addition rates of anti-solvents, etc, on the products quality were experimentally studied in details. The optimum operationschedule for the dilution crystallization of L-valine has been determined, and theproduct crystal purity was more than98.7%, the medium size was2times than thecrude L-valine.