Effect Of Impurities On Crystallization Of L-Glutamic Acid And Purification Of The Glutamic Acid Of Secondary Crystallization Process

L-glutamic acid (L-Glu) is one of the largest output fermentation products all over the world, the output of L-Glu and glutamate reached to 2.2 million tons at 2010, accounting for more than 70% of the world production. L-Glu is produced by fermentation of microorganism, and was extracted from broth by crystallization. A great amount of impurities are contained in the broth, many impurities coexisted with L-Glu may have a significant impact on the crystallization of L-Glu. The influence of L-phentermine (L-Phe), ammonium sulphate, glucose and L-lactic acid on solubility, nucleation, crystallization rate and habit of L-Glu was investigated. No effect of L-Phe was observed on the solubility of L-Glu when temperature was 25℃; L-Phe molecules were absorbed on and incorporated in the crystals, then impacted the crystallization of L-Glu, inhibited the crystallization ofβcrystals and changed the habit ofαcrystals; Solid - liquid surface tension, free energy of nucleation and the critical nucleation radius of L-Glu reduced as addition of L-Phe, while the maximum nucleation rate also reduced as addition of L-Phe, so the nucleation rate of L-Glu reduced as increasing of addition amount of L-Phe. Ammonium sulfate had significant impact on solubility of L-Glu which was called salting-in effect; the addition of ammonium sulfate retarded the nucleation of L-Glu, reduced the rate of crystallization of L-Glu but had no effect on crystal habit; As increasing of concentration of ammonium sulfate, the crystals size reduced sharply; ammonium sulfate could not be incorporated into the crystals lattice, but could be embedded into crystals by absorbing onto crystals surface, formation of inclusion in crystals and voids in agglomerates. Glucose had no effect on solubility of L-Glu during the addition range tested in this study, and glucose had no influence on nucleation, crystal growth, crystal habit, while little impact of glucose on crystal size had been observed; the uptake of glucose in crystals mainly caused by absorbing onto surface and the formation of voids in agglomerates. L-lactic acid had solubilization on L-Glu as ammonium sulphate, and the effect promoted as addition amount increasing; the nucleation and crystal growth inhibited and crystal habit changed by addition of L-lactic acid, the crystals size reduced as increasing of addition of L-lactic acid; L-lactic acid could be incorporated into crystal lattice of L-Glu as solid solution for a carboxy group was is located on theαcarbon which could form hydrogen bond with L-Glu molecule.Purification processes of the glutamic acid of secondary crystallization process (GASCP) were investigated. The method of crystal phase transformation (CPT) was studied first, influencing factors such as temperature, pH, GASCP /water ratio, active carbon on CPT were studied; the results shown temperature, pH, GASCP /water ratio and active carbon had a significant impact on CPT, and based on the researches, the ideal conditions for CPT of GASCP were determined as follow: temperature was 95℃, pH 4.5, the ratio of GASCP/water was 1:2.5, the addition of ratio of activated carbon was 1%. The quality of GASCP increased substantially when treated by method of CPT, but the question of quality of GASCP could not be solved fundamentally. So"acid-dissolution of GASCP and to re-adjust iso-electric of broth process"(ADRAI) was designed to solve the problem. Determination of the concentration of sulphuric acid, selection of a kind of suitable active carbon, solid/water ratio of acid-dissolution, and the addition mount of active carbon were contained in this section. Less new pigment generated when GASCP dissolved in 30wt%, 40 wt % and 50 wt % sulphuric acid, and when 98wt% sulphuric acid was diluted to 30wt%, 40 wt % and 50 wt % by washing mother liquid, less new pigment generated when diluted to 30wt%,and more stable, so the concentration of sulphuric acid was determined as 30wt%. Solid/water ratio of acid-dissolution was determined by theoretical calculations and experimental verification as 1:7(M/V). The carbon made by Tianlun Corporation had the strongest absorption ability of pigments in acid-solution among the seven kinds of active carbon tested in the study, and addition of 0.5wt% of the active carbon could absorb most of pigments in the acid-solution. The addition of ADRAI process to the"L-Glu double crystallization extraction of non-waste process"could solve the question of purification of GASCP perfectly, and made the all process much more perfection.