METHOD FOR CRYSTALLIZING AMINO ACID

Abstract: This invention relates to a method for crystallizing an amino acid characterized by adding a surfactant and/or an alcohol to an amino acid solution.

Description: Field of the Art The present invention relates to a method for the crystallization of amino acids, more particularly to a method for improving crystal shape by the crystallization operation of amino acids. Background Art As conventional methods for crystallization of amino acids, there have been proposed a method for crystallization which comprises concentrating an aqueous solution of an amino acid under reduced pressure, a method which comprises neutralization for crystallization, a method which comprises crystallization with a solvent while adding a lower alcohol or a ketone to the aqueous solution in large quantities, and so on (cf. Japanese Patent Application Laid-Open Nos. 59-39857, 59-45898, etc.). Among these methods, in the method for crystallization which comprises concentration under reduced pressure, fine amino acid crystals precipitated tend to include bubbles in the crystals and cause bumping so that care is required in the concentrating operation. Furthermore, according to the method which comprises neutralization for crystallization, crystals tend to float on the upper layer of the solution and the crystals do not grow as expected and in most cases, therefore, the solid-liquid separation is time consuming. On the other hand, the method which comprises crystallization of an amino acid by adding a lower alcohol or a ketone requires a separate equipment for recovering the organic solvent, which not only leads to a complicated process but is also economically disadvantageous, because it is impossible to completely recover the solvent. JP-B1-46 019 610 discloses a method for the crystallization of DL-methionine produced by the hydantoin method according to which the foaming of the system and consequently the floatation of the crystals is prevented by adding a surface active agent in amounts of preferably 50 to 500 ppm. Accordingly, there is a need in the art to provide a method for crystallization of amino acids having a high purity, in a simple manner using simple apparatuses. Disclosure of the Invention The present invention relates to a method for crystallizing an amino acid selected from the group consisting of phenylalanine, tryptophan, serine, isoleucine, valine, threonine and leucine in the presence of a surfactant wherein the concentration of said surfactant is 500 to 5000 ppm based on the weight of said amino acid in the solution. The method of preparation of these amino acids is not particularly limited but the amino acids may be any one prepared by fermentation, chemical synthesis, enzymatic method and other processes. In general, the present invention is applied to the crystallization of the above L-amino acids but may also be applicable to D- or DL-amino acids and to amino acid derivatives. The surfactants which can be used in the present invention are as follows. As anionic surfactants, there are effectively used those of the fatty acid salt type, sulfate salt type, alkylallylsulfonate salt type and phosphate salt type. Specific examples include sodium oleate, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, lecithin, etc. As cationic surfactants, there are effectively used those of the quaternary ammonium salt type, aliphatic amine type and pyridinium type. Specific examples include SANISOL (manufactured by Kao Atlas Co., Ltd.), laurylamine, lauryl hydrogensulfate pyridinium, etc. As nonionic surfactants, there are effectively used those of the polyoxyethylene ether type, sorbitan alkyl ester type, esters of polyvalent alcohols and fatty acids and fatty acid ethanolamide type. Specific examples include Brij (manufactured by Atlas Co., Ltd.), Tween (manufactured by Atlas Co., Ltd. ), glycerol monostearate, etc. In the practice of the present invention, the additive described above is dissolved in an acid or alkali solution of the amino acid and then an alkali or acid is added to the solution to effect crystallization by neutralization. Alternatively, after the additive described above is dissolved in an amino acid aqueous solution, the aqueous solution is concentrated to crystallize the amino acid. In this case, however, since some of the additive is foaming, it is recommended to use such an additive that hardly foams, for example, glycerol monostearate, etc. Alternatively, the amino acid aqueous solution in which the above additive is dissolved may be cooled as it is to cause crystallization. As stated above, the present invention is applicable, irrespective of the method of crystallization of the amino acid. In this case, the concentration of the amino acid may be any concentration as long as crystals are precipitated. Furthermore, the amino acid composition is not particularly limited. It may also be of the system containing other impurities. The concentration of the additive in the present invention greatly affects the crystal mode and in some occasion, it is considered that crystal growth might be inhibited. Therefore, the optimum concentration has been previously determined by experiment. The concentration is 500 to 5000 ppm, based on the weight of the amino acid in the solution. When the present invention is applied as described above, the hydrophobic property of the amino acid on the crystal surface is improved, its crystals form a stable suspension state without being isolated from the aqueous solution and, the substrate in the solution is continuously supplied to the crystal surface so that crystals grow to a large size without causing superfluous fine crystals. Accordingly, the crystals float on the surface of the aqueous solution only with difficulty and hence, the crystals can be readily concentrated, without including foam and generating foam. The crystals further grow to a larger size and thus, solid-solution separation also becomes easy and the volume of the mother liquor adhered can be reduced. In this case, the crystallization mode varies in various fashions depending upon kind or concentration of the additive and method for crystallization. In general, however, the crystals tend to be aggregated by crystallization through concentration and in the case of crystallization by neutralization or cooling, tend to grow in a single crystal. As stated above, the present invention has established a technology for the crystallization of certain amino acids in a high purity, by the addition of a surfactant. Hereafter the present invention is explained in more detail, by referring to the examples. Example 1 To 1 liter of a crude solution of pH 1.5 containing L-phenylalanine (L-Phe) in a concentration of 150 g/liter were added 1000 ppm each (based on the weight of L-Phe) of the additives shown in Table 1. After crystals were precipitated by neutralizing at 60°C to pH of 6.0, the system was cooled to 40°C to grow the crystals. The obtained crystals were isolated for evaluation under definite conditions using a desk centrifuging machine. For the purpose of comparison, the same operation was performed in the case where no additive was added. The results are shown in Table 1. Additive Purity of Water Shape of Crystal (size) Crystal Adhered Sodium laurylsulfate 97.2% 1.9% Aggregate of several single crystals (40-80 µm) Span 20 (manufactured by Atlas) 94.4% 3.9% Aggregate of large, thick crystals (100-200 µm) TL-10 (manufactured by Japan Chemicals) 88.3% 7.6% Aggregate of fine crystals (containing in part fine crystals) (20-40 µm) Glycerol monolaurate 87.8% 8.9% Aggregate of fine crystals (containing in part fine crystals) (10-40 µm) Fatty acid sucrose ester 82.6% 10.8% Aggregate of fine crystals (containing in part fine crystals) (20-50 µm) None 70.9% 21.2% Aggregate of fine crystals (10-20 µm) Example 2 To 5 liters of an aqueous solution containing L-tryptophan (L-Trp) in a concentration of 6 g/liter, which had been obtained by fermentation, were added 2000 ppm each (based on the weight of L-Trp) of the additives shown in Table 2. After the aqueous solution was concentrated under reduced pressure at 60°C, it was cooled to 40°C to precipitate the crystals of L-Trp. The obtained crystals were isolated for evaluation under definite conditions using a desk centrifuging machine. For the purpose of comparison, the same operation was performed in the case where no additive was added. The shape of crystals and suspension state in this case are shown in Table 2. Additive Water Adhered Shape of Crystal and Suspension State Glycerol monostearate 38.1% Somewhat large size, good deposition, no foaming Softazolin (manufactured by Kawaken Fine Chemicals) 45.2% Aggregate of spherical crystals, foaming only with difficulty TL-10 (manufactured by Japan Chemicals) 48.4% Scaly crystals, foaming only with difficulty None 57.3% Fine scaly crystals easy to float, foaming Example 3 To 2 liters of an acidic solution obtained by dissolving crude L-isoleucine (L-Ile) crystals in a concentration of 250 g/liter at 50°C, were added 500 ppm each (based on the weight of L-Ile) of the additives shown in Table 3. After crystals were fully dissolved, 6N-NaOH aqueous solution was dropwise added to the solution for neutralization to recrystallize. The crystals were isolated by filtration for evaluation under definite conditions. For the purpose of comparison, the same operation was performed in the case where no additive was added. The shape of crystals and suspension state in this case are shown in Table 3. Additive Water Adhered Shape of Crystal and Suspension State Lauryl hydrogensulfate pyridinium 15.8% Scaly, hard to float, Good suspension state is obtained. Laurylamine 17.5% Scaly Span 20 (manufactured by Atlas) 20.3% Scaly, foaming only with difficulty Brij 35 (manufactured by Atlas) 22.3% Aggregate of fine crystals, somewhat foaming Lecithin 22.9% Aggregate of fine crystals None 26.7% Fine scaly crystals, easy to float Industrial Applicability According to the present invention, the operability for isolating amino acid crystals can be improved and at the same time, crystals having a higher purity can be prepared at low costs. Therefore, it is expected to practice the present invention on an industrial level.

Claims: A method for crystallizing an amino acid selected from the group consisting of phenylalanine, tryptophan, serine, isoleucine, valine, threonine and leucine from its aqueous solution in the presence of a surfactant wherein the concentration of said surfactant is 500 to 5000 ppm based on the weight of said amino acid in the solution. A method for crystallizing an amino acid according to claim 1, wherein said surfactant is at least one of an anionic surfactant of fatty acid salt type, sulfate salt type, alkylallylsulfonate type and phosphate salt type; a cationic surfactant of quaternary ammonium salt type, aliphatic amine type and pyridinium type; a nonionic surfactant of polyoxyethylene ether type, sorbitan alkyl ester type, ester of polyvalent alcohols and fatty acid and fatty acid ethanolamide type.

Inventors: SAEKI MASARU C O KYUSYU PLANT, SHIROSHITA YOSHINARI C O KYUSY, TOYOMASU RYUTA C O KYUSYU PLAN, SAEKI, MASARU, C/O KYUSYU PLANT, SHIROSHITA, YOSHINARI, C/O KYUSYU PLANT, TOYOMASU, RYUTA, C/O KYUSYU PLANT
Applicants: AJINOMOTO KK, AJINOMOTO CO., INC.
Application year: 1990
Main classification: C07C229
IPC codes: C07C227, C07D209