METHOD FOR RECOVERING SUCCINIC ACID CRYSTALS USING SURFACTANTS DURING CRYSTALLISATION, AND RESULTING CRYSTALS

Abstract

The invention relates to a method for producing succinic acid crystals, comprising double crystallisation and the use of at least one surfactant during the first crystallisation step. The invention also relates to the succinic acid crystals obtained from a fermentation medium, characterised in that they have a colour index b, measured in the reference system L, a, b, that is less than or equal to 1.00, preferably less than or equal to 0.90, and, better still, less than or equal to 0.80.

Claims

1. A process for producing succinic acid crystals from a fermentation medium containing succinic acid, comprising: a) bringing a fermentation medium to a pH of between 1.0 and 4.0, b) crystallizing succinic acid from the fermentation medium resulting from step to form first succinic acid crystals and a first crystallization mother liquor, then separating the first succinic acid crystals from the first crystallization mother liquors and then washing the obtained crystals with water to obtain washed succinic acid crystals, c) dissolving the washed succinic acid crystals in water at a temperature between 30° C. and 70° C. to obtain a solution containing dissolved succinic acid, d) purifying the solution by contacting said solution with activated carbon and on ion exchange resin, e) crystallizing succinic acid contained in the purified solution to form second succinic acid crystals, and a second crystallization mother liquor, separating the second succinic acid crystals from the second crystallization mother liquors and then washing the second succinic acid crystals with water, f) drying the washed, second succinic acid crystals of step e) to a moisture content of less than 0.5% and cooling them to a temperature below 30° C., wherein at least one surfactant is introduced before and/or during step b).

2. The process according to claim 1, wherein said surfactant comprises one of non-ionic surfactants comprising polysorbates having an HLB greater than 15 and alkylene oxide block copolymer based surfactants.

3. The process according to claim 1, comprising bringing the fermentation medium to a pH of between 1.5 and 3.5.

4. The process according to claim 1, wherein the fermentation medium includes one of bacteria comprising bacterial strains of the Mannheimia, Anaerobiospirillum, Bacillus or Escherichia genus, or from fungal strains.

5. The process according to claim 1, further comprising crystallizing succinic acid batchwise or continuously, by cooling.

6. The process according to claim 1, wherein the separating of steps b) and e) is conducted by filtration or centrifugation.

7. The process according to claim 1, wherein washing is carried out with water, at a temperature of between 15° C. and 25° C.

8. The process according to claim 1, wherein a part of at least one of said first and second crystallization mother liquors, and washing water is recycled as a feed to step b).

9. The process according to claim 1, wherein said dissolving provides a dry matter content of between 5% and 50% by weight of the total weight of said solution.

10. The process according to claim 1, wherein the activated carbon comprises powder or granules.

11. The process according to claim 1, wherein all of said second crystallization mother liquid sand washing mother liquors of step e) are recycled to step b).

12. The process according to claim 1, wherein said succinic acid crystals are dried to a moisture content of less than 0.4%, weight of water relative to the dry weight of succinic acid, and cooled to a temperature below 30° C.

13. Fermentation produced succinic acid crystals comprising a color index b, measured in the reference system L, a, b, of less than or equal to 1.00.

14. The succinic acid crystals according to claim 1 having a reducing sugar content of less than 20 ppm.

15. The succinic acid crystals according to claim 14, comprising a sphericity index, as measured according to the Rittenhouse test, at least equal to 0.70.

16. A composition containing succinic acid crystals prepared according to the method of claim 1.

17. Fermentatively produced succinic acid crystals having a moisture content of less than 0.5% by weight, a sphericity of greater than 0.70, and a color index b, measured in the reference system L, a, b, of less than or equal to 1.00.

Description

EXAMPLES

Example 1

Fermentation

[0067] A fermentation medium is prepared under the strict conditions of example 1 of document WO 2011/064151. The only things that differ are the devices used: the pre-culture step is carried out on a Puntbus 6 I reactor, the growth phase on a 7 m.sup.3 fermenter and the production phase on two 70 m.sup.3 fermenters. The fermentation liquor flow rate is then approximately 1.5 m.sup.3/h.

[0068] The separation of the biomass and the fermentation liquor is carried out by microfiltration. The latter is carried out batchwise at a temperature of 80° C., followed by a diafiltration step. The module is equipped with 2 “Kerasep” ceramic casings of 25 m.sup.2, having a porosity equal to 0.1 pm. The mean permeate flow rate is approximately 2 m.sup.3/h with a transmembrane pressure of approximately 1 bar.

Acidification Step a)

[0069] The fermentation liquor is treated on weak cationic resin of Amberlite IRC 747 type at a flow rate of 2 BV/h at 60° C. in order to achieve a divalent ion concentration of less than 5 ppm. The resins are regenerated after having passed over a volume of fermentation liquor of between 30 and 40 times the resin volume.

[0070] The solution obtained is then acidified on an Aqualyzer® EDBM EUR40 BPED (bipolar electrodialysis) module sold by the company Eurodia, at a pH of approximately 3.5.

[0071] The solution is then treated on a strong cationic resin of Purolite C150 type at a flow rate of 2 BV/h and at a temperature of 40° C. in order to achieve a pH of 2.0. The resins are regenerated after having passed over a volume of fermentation liquor of between 15 and 20 times the resin volume.

First Crystallization: Step b)

[0072] The acidified solution is concentrated on a forced-circulation vacuum plate evaporator sold by the company Alfa Laval, to a concentration of 35% by dry matter and at a temperature of 80° C. It is then continuously crystallized by flash cooling on 2 stages each composed of an external-loop vacuum crystallizing dish sold by the company Gea Kestner. The vacuum in the crystallizing dishes is fixed so as to obtain a temperature on the first stage of 40° C. and on the second stage of 20° C. The residence time is approximately 5 h.

[0073] In the case of the use of the surfactant, the latter is continuously introduced by means of a metering pump at a flow rate equal to 1200 ppm relative to the flow rate of solution which feeds the crystallizing dish. The surfactant chosen is Erol 18 sold by the company PMC Ouvrie.

[0074] The crystalline mass is then separated on a batch centrifuge of SC 1200 type sold by the company Robatel in order to recover the succinic acid crystals. During this step, the crystals are washed with demineralized water at 20° C. with an amount equal to 1 kg/kg of crystals.

[0075] Between 0% and 70% by weight of the crystallization and washing mother liquors recovered on the centrifuge are recycled to the top of the evaporator.

Crystal Dissolving Step c)

[0076] The succinic acid crystals are dissolved at a temperature of 45° C. with demineralized water so as to obtain a solution at 10% dry matter content.

Purification Step d)

[0077] The step of treatment on activated carbon is carried out with a granular carbon of Chemviron CPG LF 12×40 type on a column operating as a fixed bed. The flow rate of solution in the column is fixed at 0.5 BV/h and the volume of solution treated before renewal of the bed is variable depending on the operating conditions and the quality desired. It is between 40 and 500 times the volume of carbon of the column.

[0078] The step of treatment on ion exchange resins is carried out at a flow rate of 2 BV/h at 60° C. on a strong cationic resin of Dowex 88 type, then on a weak anionic resin of Lanxess Lewatit S4528 type. The resins are regenerated after having passed over a volume of solution equal to 40 times the resin volume.

Second Crystallization: Step e)

[0079] The purified succinic acid solution is concentrated on a falling-film vacuum evaporator sold by the company Wiegand, to a concentration of 30% by dry matter and at a temperature of 80° C. It is then continuously crystallized by flash cooling on 2 stages each composed of an external-loop vacuum crystallizing dish sold by the company Gea Kestner. The vacuum in the crystallizing dishes is fixed so as to obtain a temperature on the first stage of 40° C. and on the second stage of 20° C. The residence time is approximately 7 h.

[0080] The crystalline mass is then separated on a batch centrifuge of SC 1200 type sold by the company

[0081] Robatel in order to recover the succinic acid crystals. During this step, the crystals are washed with demineralized water at 20° C. with an amount of crystals equal to 1 kg/kg.

[0082] All of the crystallization and washing mother liquors are recovered on the centrifuge and recycled to the top of the evaporator at the level of step b).

Drying Step f)

[0083] The product is dried on a rotary dryer so as to obtain a residual moisture content equal to 0.3% by weight of water relative to the total weight of product, then cooled on a fluidized bed at a temperature of 25° C.

Example 2

Fermentation

[0084] A fermentation medium is prepared under the strict conditions of example 5 of document WO 2011/064151. The only things that differ are the devices used: the pre-culture step is carried out on a Puntbus 6 I reactor, the growth phase on a 7 m.sup.3 fermenter and the production phase on two 70 m.sup.3 fermenters.

[0085] The separation of the biomass and the fermentation liquor is carried out by microfiltration. The latter is carried out batchwise at a temperature of 80° C., followed by a diafiltration step. The module is equipped with 2 “Kerasep” ceramic casings of 25 m.sup.2, having a porosity equal to 0.1 pm. The mean permeate flow rate is approximately 2 m.sup.3/h with a transmembrane pressure of approximately 1 bar.

Acidification Step a)

[0086] The fermentation liquor is then treated on a strong cationic resin of Purolite C150 type at a flow rate of 2 BV/h and at a temperature of 40° C. in order to achieve a pH of 2.0. The resins are regenerated after having passed over a volume of fermentation liquor of between 15 and 20 times the resin volume.

[0087] All of the other steps b) to f) are carried out as described in example 1.

Example 3

[0088] This example corresponds to the performing of tests according to or outside the invention (with or without surfactant), in a double crystallization process.

[0089] Six tests were carried out, so as to evaluate the influence of 2 parameters: the value of the ratio of the volume of solution treated to the volume of carbon in step c) (“Bed Volume” or BV=Volume of solution/volume of activated carbon) and the % of crystallization mother liquors recycled at the level of step b).

[0090] Tests Nos. 1 to 3 are carried out according to the protocol given in example 1 and without surfactant.

[0091] Tests Nos. 4 to 6 are carried out according to the protocol given in example 2 and without surfactant.

[0092] Tests Nos. 7 and 8 are carried out according to the protocol given in example 1, with 1200 ppm of Erol 18 as surfactant.

[0093] Tests Nos. 9 to 11 are carried out according to the protocol given in example 2, with 1200 ppm of Erol 18 as surfactant.

[0094] The measurement of the index “b” is carried out on an average sample: a sample is taken every 12 hours, this being for 15 days, and then all of these samples taken are mixed together.

TABLE-US-00001 TABLE 1 % recycling Total of the mother Index % sugars Tests BV liquors % “b” Yield (ppm) 1 50 0 1.80 81 58 2 100 0 2.50 80 98 3 50 50 4.20 89 158 4 50 0 1.75 80 41 5 100 0 2.10 79 59 6 50 50 3.90 90 157

TABLE-US-00002 TABLE 2 % recycling Total of the mother Index % sugars Tests BV liquors “b” Yield (ppm) 7 300 0 0.71 82 4 8 300 50 0.91 90 16 9 300 0 0.65 81 2 10 300 50 0.87 90 10 11 300 60 0.95 94 16

[0095] The comparison between tables 1 and 2 clearly reveals the positive influence of the surfactant on the values of the index “b”.

[0096] In addition, it is possible to adjust both the value of this index and the yield of the process in terms of succinic acid, through the recycling of all or part of the first-crystallization mother liquors.

[0097] Finally, FIG. 2 reveals the morphology of the crystals obtained without surfactant (test No. 1), which are needles, whereas FIG. 3 (test No. 7) reveals balls, having an index much higher than 0.70. These photos were taken on a Leica EZ4HD microscope. This is particularly surprising insofar as it was known from document WO 01/07389 that the use of surfactants in a succinic acid crystallization process led to the formation of needle-shaped succinic acid crystals. As it happens, successfully achieving such ball-shaped crystals is particularly advantageous since, as previously indicated, the purification of the succinic acid is then improved for various reasons; moreover, these crystals flow better and have less of a tendency to cake. Without being bound by any theory, the applicant explains this fundamental difference in behavior during the crystallization by the impurities of a succinic acid obtained from a fermentation medium, which are different from those of the petroleum-based succinic acid of document WO 01/07389.

Example 4

[0098] This example corresponds to the performing of tests outside the invention (with or without surfactant), in a single crystallization process.

[0099] During the various tests, crystals are sampled before the dissolving step c) in some of the tests of the previous example.

[0100] The crystals are then dried on a Retsch laboratory fluidized bed until a moisture content of 0.3% by weight of water, relative to the total weight of product, is obtained.

TABLE-US-00003 TABLE 3 Tests Index “b” 1a 9.01 7a 5.05 4a 8.27 9a 4.39

[0101] The results of table 3 demonstrate that the processes with single crystallization, optionally in the presence of surfactant, do not result in satisfactory “b” values.

Example 5

[0102] For tests Nos. 1, 4, 8 and 10, the stability of the process was tested by operating the process continuously over several days.

[0103] Samples were taken 24 hours apart for analysis. The “b” values thus determined are reproduced in table 4 below.

TABLE-US-00004 TABLE 4 Days Test 1 Test 4 Test 8 Test 10 1 1.43 1.52 0.97 0.95 2 2.10 1.13 0.96 0.81 3 1.75 1.90 0.82 0.85 4 1.60 2.04 0.97 0.78 5 2.56 1.38 0.82 0.74 6 2.13 1.54 0.78 0.79 7 1.50 1.52 0.85 0.74 8 2.46 1.68 0.82 0.71 9 2.05 1.41 0.89 0.87 10 1.99 1.78 0.92 0.81 11 1.81 1.65 0.78 0.79 12 1.49 1.98 0.75 0.91 13 1.79 2.70 0.82 0.94 14 1.84 2.14 0.89 0.91 15 1.96 1.85 0.91 0.85 Mean value 1.92 1.75 0.86 0.83 Standard deviation 0.37 0.38 0.07 0.08

[0104] This table clearly establishes the stability of the process according to the invention, the measurements being much more reproducible than in the case of the prior art.