PREPARATION OF CAPROLACTAM FROM 6-AMINO CAPROIC ACID OBTAINED IN A FERMENTATION PROCESS
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.
1 . Method for preparing caprolactam comprising recovering a mixture containing 6-aminocaproic acid from a culture medium comprising biomass, which culture medium may comprise one or more carbohydrates, 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, preferably less than 2 g/l, and more preferably less than 0.5 g/l carbohydrates.
3 . Method according to claim 2 , wherein the mixture comprises less than 2 g/l carbohydrates.
4 . Method according to claim 3 , 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, preferably less than 2 g/l, and more preferably less than 0.5 g/l carbohydrates
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, such as one or more polymers selected from the group of polysaccharides, polypeptides and proteins.
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 according to claim 1 in which the product comprising caprolactam is further purified by 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 according to claim 1 , in which the caprolatam obtained is further polymerized, optionally in the presence of one or more further polymerisable compounds.