SK287595B6 - Process for the isolation of cystine - Google Patents

Abstract

Method of isolation of cystine crystals in the cell suspension in which the crystals contained in the suspension are centrifuged in a decanter centrifuge having a speed ranging from 1000 to 4000 g.

Description

The invention relates to a method of isolating crystalline cystine from a cell suspension.

BACKGROUND OF THE INVENTION

The amino acid cystine is usually obtained by acid hydrolysis from keratin waste, such as human hair, and purified by precipitation. The development of an efficient process for the fermentative production of cystine (EP 0885962 A1) also necessitates the development of an efficient method of purification of this product.

Several processes have already been proposed for the treatment of fermentation-produced products which are sparingly soluble in the fermentation broth. US 5547858 describes the selective elimination of amino acid or nucleic acid crystals from a fermentation broth using a hydrocyclone. A disadvantage of this process is that only low product yields are achieved at high sensitivity.

WO 96/40758 discloses a process in which sequential densification by membrane filtration, solvent addition solubilization, and repeated membrane filtration to separate cells is used to isolate water-insoluble compounds from the fermentation broth. However, due to the very poor solubility of cystine in almost all organic solvents, application of this procedure is practically impossible for cystine.

WO 95/08620 uses a sequence of steps in which the microorganisms are solubilized, for example by heat treatment in acids or bases, and then the insoluble product is isolated by centrifugation. However, in the case of cystine, this method also cannot be used, since although cystine is soluble in acids and bases, it is not thermostable in bases.

In principle, the classically used method for purifying cystine, precipitating from acids or bases can be used. However, due to the strong buffering effect of the fermentation broth, the direct adjustment of the pH in the fermentation broth also does not lead to the target.

SUMMARY OF THE INVENTION

The object of the invention was to find a method of isolating crystalline cystine from the fermentation broth in such a way as to obtain a significant primary enrichment at high yield, thereby obtaining a product with a high cystine content and low residual moisture.

SUMMARY OF THE INVENTION The present invention provides a method for isolating cystine crystals from a cell suspension, wherein the crystals are separated by centrifugation in a decanter centrifuge, wherein the centrifuge acceleration is between 1000-4000 g and the quotient of linear flow rate and centrifuge acceleration in the centrifuge body 10 to 50 g.min.cm ¹ .

The cell suspension is primarily a fermentation broth.

The isolated cystine is preferably L-cystine.

Conventional decanting centrifuges are suitable for centrifugation; decanting decantation cenrtrifuges.

During centrifugation, cystine crystals are separated even in a very wide range of grain sizes due to their high density until the cells are removed with an overflow.

Operating parameters of the decanter centrifuge

- number of drum rotations,

- permeability,

- the sludge height (control flap diameter) is adjusted so that a product with a high cystine and dry matter content is obtained following the recommended parameters.

The drum speed is set so that the centrifuge acceleration is between 1000 and 4000 g, preferably between 1500 and 3000 g.

The throughput is set so that the quotient calculated from the linear flow rate and centrifuge acceleration in the centrifuge body is in the range of 10 to 50 g.min.cm ^-1 , the range of 15 to 35 g.min.cm ^-1 is most preferred.

The linear flow rate is calculated from the volumetric flow rate and flow area A in the circular-shaped centrifuge drum, which is determined by the radii r and r, (Fig. L). The radius r _(corresponds to the internal diameter of the drum of the centrifuge, the radius r ₂ to the internal diameter of the liquid ring in the drum. The liquid ring was determined by application of control valves. Surface A is then calculated as (η ₃ ² -Γ ²⁾ π.

In order to increase the cleaning effect, the product obtained can be washed once more in water and centrifuged again in a decanter centrifuge.

The amount of water can vary widely. Preferably, the concentration of solids in the slurry formed is in the range between 5 and 50% by weight, with the range between 7.5 and 30% by weight being most preferred.

The operating parameters of the decanter centrifuge are adapted to the increased solids concentration so that if the solids content of the suspension is doubled, the quotient of the linear flow rate and the centrifuge acceleration in the centrifuge body also approximately doubles.

The following examples serve to further illustrate the invention. A TS 210 FK type decanter centrifuge from Siebtechnik GmbH was used in all experiments.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

240 liters of fermentation broth containing 34.01 g / l of undissolved cystine with a flow rate of 150 l / h were centrifuged in a decanter centrifuge. According to the number of revolutions of the drum, the centrifuge speed was set to 1500 g. A flow area of 38.5 cm ² resulted in a linear flow rate of 64.9 cm / min. and thus the quotient of the linear flow rate and centrifuge acceleration in the centrifuge body equal to

23.1 g.min.cm ' ¹ . The speed difference was set to 7. After a one-volume treatment of 49 L, the product collector was replaced. The final product obtained (9.9 kg) had a dry matter content of 68.8% and a cystine content (calculated as dry matter) of 92.4%. This corresponds to a yield of 6.29 kg (77%) of pure cystine.

Example 2

230 liters of fermentation broth containing 31.7 g / l of undissolved cystine with a flow rate of 300 to 330 l / h were centrifuged in a decanter centrifuge. According to the number of revolutions of the drum, the centrifuge speed was set to 2380 g. A flow area of 38.5 cm ² resulted in a linear flow rate of 136.4 cm / min. and thus the quotient of the linear flow rate and centrifuge acceleration in the centrifuge body

17.5 g.min.cm ^-1 . The speed difference was set to 7. The final product obtained (10.87 kg) had a dry matter content

70.2% and cystine content (calculated on dry weight) 94.0%. This corresponds to a yield of 7.17 kg (98.7%) of pure cystine.

Example 3

244 liters of fermentation broth containing 30.9 g / l of undissolved cystine with a flow rate of 250 Vh were centrifuged in a decanter centrifuge.

According to the number of revolutions of the drum, the centrifuge acceleration was set to 1880 g. From flow area size

38.5 cm ² resulted in a linear flow rate of 108.2 cm / min. and thereby a quotient of a linear flow rate and centrifuge acceleration in the centrifuge body equal to 17.4 g.min.cm ^-1 . The speed difference was set to 7. The final product obtained (9.93 kg) had a dry matter content of 69.5% and a cystine content (calculated on dry matter) of 94.2%. This corresponds to a yield of 6.50 kg (86.3%) of pure cystine.

Example 4

9.76 kg of the unpurified product of Example 1 (cystine content 6.21 kg) were mixed in 70 1 H ₂ O and centrifuged in a decanting centrifuge at a flow rate of 75 L / h. According to the number of revolutions of the drum, the centrifuge speed was set to 1500 g. A flow area of 38.5 cm ² resulted in a linear flow rate of 32.5 cm / min. and thus a quotient of the linear flow rate and centrifuge acceleration in the centrifuge body equal to 46.2 g.min.cm ^-1 . The speed difference was set to 7. The final product obtained (7.65 kg) had a dry matter content of 73.4% and a cystine content (calculated as dry matter) of 96.0%. This corresponds to a yield of 5.39 kg (86.8%) of pure cystine.

Claims (8)

Method for isolating cystine crystals from a cell suspension, characterized in that the cystine crystals contained in the suspension are separated by centrifugation in a decanter centrifuge, wherein the center of the fugitive acceleration is in the range of 1000 to 4000 g and the quotient calculated from centrifuge acceleration and linear flow rate in the body centrifuges are in the range of 10 to 50 g.min.cm ^-1 . Method according to claim 1, characterized in that the cell suspension is a fermentation mixture. Method according to either of Claims 1 and 2, characterized in that the isolated cystine is L-cystine. Method according to one of Claims 1 to 3, characterized in that in the case of a decanting centrifuge, a sludge decanting centrifuge is used. Method according to one of Claims 1 to 4, characterized in that the decanter centrifuge runs at a number of drum revolutions at which the centrifuge acceleration reaches 1000 to 4000 g. 5 Method according to one of Claims 1 to 5, characterized in that the throughput of the decanter centrifuge is adjusted such that the quotient calculated from the centrifuge acceleration and the linear flow rate in the centrifuge body is between 10 to 50 g.min.cm ¹ . Method according to one of Claims 1 to 6, characterized in that the product obtained is repeatedly washed in water and again centrifuged by decanting centrifuge. The process according to claim 7, characterized in that the amount of water for washing the product is determined such that the concentration of solids in the formed suspension is in the range of from 5 to 50% by weight.