Methods for production of L-methionine and related products

1. A method comprising:

(a) enzymatically processing an O-acetylhomoserine (OAHS) fermentation liquor to produce a processed liquor comprising L-methionine and an acetate source;

(b) separating at least a portion of said L-methionine from at least a fraction of said acetate source to form separated L-methionine and a residual liquor comprising an acetate-source; and

(c) recovering at least a portion of said acetate source from said residual liquor as recovered acetate,

wherein said separating comprises at least two crystallizations, and wherein isolated crystallized methionine from a second crystallization is dissolved and recycled into a processed liquor of step (a).

2. The method according to claim 1 , further comprising using said recovered acetate as a reagent in at least one member selected from the group consisting of:

(i) adding said reagent to OAHS fermentation liquor;

(ii) adding said reagent as an ingredient in a fermentation medium; and

(iii) incorporating said reagent a in a fermentation product.

3. The method according to claim 2 , wherein said fermentation product is selected from the group consisting of carboxylic acids and amino acids.

4. The method according to claim 1 , comprising implementing at least one process selected from the group consisting of water removal, active carbon treatment, addition of a solute, pH adjustment, ion-exchange, membrane filtration and contacting with at least one water-soluble organic solvent during a purification process.

5. The method according to claim 1 , wherein said residual liquor comprises an ammonium salt.

6. The method according to claim 1 , wherein said separating comprises crystallizing, which comprises the use of: a C1-C4 alcohol; a crystal habit modifier; or L-methionine seed crystals.

7. The method according to claim 6 , wherein crystalline L-methionine resulting from said crystallizing is characterized by at least one characteristic selected from the group consisting of:

(i) purity greater than 95%;

(ii) containing less than 1% acetate source;

(iii) OAHS content greater than 1 PPB;

(iv) content of at least one particular impurity is greater than 10 PPM;

(v) less than 2% of D-methionine; and

(vi) carbon-14 to carbon-12 ratio of at least 2.0×10 −13 .

8. The method according to claim 1 , wherein said separating comprises at least two crystallizations, and wherein crystalline L-methionine resulting from the second crystallizing is characterized by at least one of:

(i) containing less than 0.1% acetate source; and

(ii) containing at least 1 PPB of OAHS.

9. The method according to claim 1 , wherein said residual liquor is characterized by:

(i) a methionine concentration of at least 15 g/1;

(ii) an acetate concentration of at least 100 g/1;

(iii) total solids of at least 20%;

(iv) specific gravity in the range of 1.05 to 1.25;

(v) ammonium sulfate concentration of at least 60 g/l; and

(vi) OHAS content of at least 1 PPB.

10. The method according to claim 1 , wherein said recovering comprises:

(a) contacting the residual liquor with at least one acidulant selected from the group consisting of (i) a strong acid, (ii) CO 2 under pressure, and (iii) a cation-exchanger that is at least partially in free acid form to form a residual liquor comprising free acetic acid; and

(b) separating said free acetic acid.

11. The method according to claim 10 , wherein said recovering comprises at least one of:

(i) distilling free acetic acid from said residual liquor and

(ii) contacting said residual liquor comprising free acetic acid with an extractant to form an acetic acid-comprising extract and an acetic acid depleted residual liquor.

12. The method according to claim 11 , comprising contacting said acetic acid-comprising extract with a base to form recovered acetate salt of said base.

13. The method according to claim 1 , wherein said residual liquor further comprises an ammonium source, which is recovered from said residual liquor as recovered ammonium.

14. The method according to claim 13 , comprising at least one of:

contacting said residual liquor with a calcium base to form free-base ammonia and a calcium salt;

crystallizing an ammonium salt from said residual liquor to form crystalline ammonium salt and separated ammonia-depleted residual liquor; and

distilling ammonia and acetic acid from said residual liquor to form ammonia-depleted residual liquor.

15. The method according to claims 13 , comprising adding at least a fraction of said recovered ammonium to a fermentation media.

16. A method according to claim 1 , wherein said separating produces L-methionine with a purity ≧98%.

17. A method according to claim 1 , wherein said separating produces L-methionine with a bulk density of at least 50 g/dl.

18. A method according to claim 1 , wherein said separating produces L-methionine as thin plate crystals.

19. A method comprising:

(a) enzymatically processing an O-acetylhomoserine (OAHS) fermentation liquor to produce a processed liquor comprising L-methionine and an acetate source;

(b) separating at least a portion of said L-methionine from at least a fraction of said acetate source to form separated L-methionine and a residual liquor comprising an acetate-source; and

(c) recovering at least a portion of said acetate source from said residual liquor as recovered acetate;

wherein said separating comprises at least two crystallizations, and wherein isolated crystallized methionine from a second crystallization is dissolved and recycled into a processed liquor of step (a), and wherein said separating produces thin plate L-methionine crystals with a purity >98% and a bulk density of at least 50 g/dl.

20. The method of claim 1 or 19 , wherein crystalline L-methionine resulting from the second crystallization is characterized by purity greater than 75%.