PREPARATION OF CAPROLACTAM FROM 6-AMINO CAPROIC ACID OBTAINED IN A FERMENTATION PROCESS

Abstract

The invention relates to a method for preparing caprolactam comprising recovering a mixture containing 6-aminocaproic acid, from a culture medium comprising biomass, and thereafter cyclising the 6-aminocaproic acid in the presence of superheated steam, thereby forming caprolactam, wherein the weight to weight ratio carbohydrate to 6-aminocaproic acid in said mixture is 0.03 or less.

Claims

1. Method for preparing caprolactam comprising recovering a mixture containing 6-aminocaproic acid from a culture medium comprising biomass, which culture medium comprises more than one carbohydrate, and thereafter cyclising the 6-aminocaproic acid in the presence of superheated steam, thereby forming caprolactam, wherein the weight to weight ratio of total carbohydrate to 6-aminocaproic acid in said mixture is 0.03 or less.

2. Method according to claim 1, wherein the mixture comprises less than 5 g/l.

3. Method according to claim 1, wherein the mixture comprises less than 2 g/l carbohydrates.

4. Method according to claim 1, wherein the mixture comprises less than 0.5 g/l carbohydrates.

5. Method according to claim 1, wherein the 6-aminocaproic acid is prepared microbiologically, which microbiological preparation is at least ended under carbon-limited conditions.

6. Method according to claim 1, wherein the 6-aminocaproic acid is prepared microbiologically, which microbiological preparation is at least ended at a total carbohydrate concentration in the culture medium of less than 5 g/l.

7. Method according to claim 1, wherein the 6-amino caproic is separated from biomass by at least one technique selected from the group of tangential flow filtration, microfiltration, other forms of filtration, and centrifugation.

8. Method according to claim 1, wherein the recovery of the mixture comprises separating 6-aminocaproic acid and one or more polymers.

9. Method according to claim 8, wherein the 6-aminocaproic acid is separated from one or more polymers by ultrafiltration.

10. Method according to claim 1, wherein the mixture is subjected to a water removal step prior cyclising 6-aminocaproic acid.

11. Method according to claim 1, wherein the cyclisation is carried out at a temperature in the range of from 250 to 400° C.

12. Method according to claim 1, wherein the cyclisation is carried out at a pressure in the range of from 0.3 to 2 MPa.

13. Method for purifying caprolactam, comprising performing the method according to claim 1 and subjecting the caprolactam to at least one distillation step, thereby obtaining a fraction enriched in caprolactam.

14. Method according to claim 13, wherein one or more compounds having a lower boiling point than caprolactam and one or more compounds having a higher boiling point than caprolactam are separated from caprolactam by distillation, thereby obtaining a fraction enriched in caprolactam, and subjecting said fraction to a crystallisation step, thereby obtaining caprolactam crystals.

15. Method for preparing a polymer, comprising performing the method of claim 1 and polymerising the caprolactam.

16. Method according to claim 1, wherein the 6-aminocaproic acid is prepared microbiologically, which microbiological preparation is at least ended at a total carbohydrate concentration in the culture medium of less than 2 g/l.

17. Method according to claim 1, wherein the 6-aminocaproic acid is prepared microbiologically, which microbiological preparation is at least ended at a total carbohydrate concentration in the culture medium of less than 0.5 g/l.

18. Method according to claim 8, wherein said one or more polymers is selected from the group of polysaccharides, polypeptides and proteins.

19. Method according to claim 15, wherein the polymerizing is in the presence of one or more further polymerisable compounds.

Description

COMPARATIVE EXAMPLE A

[0039] Fermentation broth was obtained from a fermentation process with E. coli for production of a commercial enzyme. Biomass was removed from the broth by microfiltration. Bio-polymers, including the target product, then were removed by ultrafiltration. By adding 6-ACA to the remaining fermentation broth, a model fermentation broth for a 6-ACA fermentation process was prepared, wherein 6-ACA is obtained at a titer of 150 g/l. The total carbohydrate content in this mixture was 6.3 g/l (i.e. the carbohydrate to 6-ACA weight ratio was 0.042). The resulting product mixture was concentrated under vacuum in a forced circulation evaporator at 40° C. The concentrated mixture contained 48.3 wt. % water, 42.1 wt. % 6-ACA, 1.8 wt. % carbohydrates and 7.8 wt. % of other broth components (organic acids, inorganic ions, etc.).

[0040] 1 Kilogram of the thus obtained concentrated product mixture was fed to a 2 liter stirred tank reactor. The reactor was closed and the contents were inertized by flushing with nitrogen. The reactor pressure controller in the vapour exit line in top of the reactor was kept at 1.2 MPa during the entire experiment. After starting the stirrer at 1000 r.p.m. the reactor contents were gradually heated up during approximately 25 minutes to about 315° C., using electric wall heating. During this period the water present in product mixture gradually evaporated and was condensed in a vapour cooler present in the vapour exit line. The recovered condensate fraction was weighed and analysed using HPLC for 6-ACA, CAP and the linear and cyclic oligomers thereof. When the reactor content reached the target temperature of about 315° C. a water feed was started and controlled at a rate of between 400 and 800 g/hr. This water was fed via a feed pipe beneath the stirrer where steam was formed in situ when the water came in contact with the hot reactor contents. Steam and steam-stripped products left the reactor via the vapour exit line at the top of the reactor. The condensed fractions were weighed and analysed by HPLC for content of CAP, 6-ACA and the linear and cyclic oligomers thereof. In this way it took approx. 5 hours to complete the reaction. The caprolactam yield obtained in this experiment was 67 mol % (calculated as the total of caprolactam analysed in the recovered product condensates relative to the overall amount of 6-ACA that was fed to the reactor originally).

EXAMPLE 1

[0041] A fermentation broth was prepared in a similar way as described in comparative example A, with the only difference that the original fermentation was prolonged for sufficient time so as to obtain a lower residual carbohydrate content in the fermentation broth. In this way a similar model fermentation mixture was prepared as in comparative example A, but now the carbohydrate concentration of this model broth was 1.3 g/l and the carbohydrate to 6-ACA weight ratio was 0.0087. Using the same procedure for 6-ACA conversion to caprolactam as described in comparative example A, the caprolactam yield finally obtained was 85 mol %.

EXAMPLE 2

[0042] Example 1 was repeated, with the difference that the residual carbohydrate concentration in the finally obtained model fermentation broth was even further reduced to 0.3 g/l (by prolonging the fermentation time); the carbohydrate to 6-ACA weight ratio was thereby reduced to 0.0020. Using the same procedure for 6-ACA conversion to caprolactam as described in comparative example A, the caprolactam yield finally obtained was 94 mol %.

[0043] Above examples show that high caprolactam yields are achievable if the carbohydrate to 6-ACA weight ratio in the fermentation broth is reduced to a low value.