Process for the purification of an aqueous stream coming from the fischer-tropsch reaction

Patent metadata

Field	Value
Publication number	US-9067806-B2
Application number	US-201013147119-A
Country	US
Kind code	B2
Filing date	Jan 28, 2010
Priority date	Jan 30, 2009
Publication date	Jun 30, 2015
Grant date	Jun 30, 2015

Abstract

Process for the purification of an aqueous stream coming from the Fischer-Tropsch reaction comprising a treatment with at least one inorganic base, an evaporation treatment, a distillation and/or stripping treatment and a treatment with at least one organic base. The process allows at least a part of the aqueous stream coming from the Fischer-Tropsch reaction to be used as process water in the production plant of synthesis gas subsequently sent to a Fischer-Tropsch plant for the production of hydrocarbons.

First claim

The invention claimed is:

1. A process for purifying an aqueous stream (i) coming from a Fischer-Tropsch reaction containing organic acid(s) comprising:
adding at least one inorganic base to the aqueous stream (i),
feeding the aqueous stream (i) after addition of the at least one inorganic base to an evaporator and obtaining a vapor stream (ii) and an aqueous stream (iii):
wherein the vapor stream (ii) exits a head of the evaporator and comprises alcohols having from 1 to 20 carbon atoms and optionally other volatile compounds and is subsequently condensed thus forming an aqueous stream (iia);
wherein the aqueous stream (iii) exits a bottom of the evaporator and comprises alcohols having from 1 to 20 carbon atoms, organic acids, and salts of organic acids that are formed upon the addition of the at least one inorganic base to the aqueous stream (i) and is subsequently fed to a distillation column;

separating aqueous stream (iii) in the distillation column into an aqueous stream (iv) which emerges from a head of the distillation column and an aqueous stream (v) which emerges from a bottom of the distillation column:
wherein the aqueous stream (iv) exiting from the head of the distillation column comprises alcohols having from 1 to 20 carbon atoms and comprises less than or equal to 2% by weight of organic acids having from 1 to 8 carbon atoms with respect to the total weight of the aqueous stream (iv), and optionally comprises other volatile compound(s), and
wherein the aqueous stream (v) exiting from the bottom of the distillation column comprises a portion of the salts of organic acids present in said aqueous stream (iii);

adding to the aqueous stream (iv) exiting from the head of the distillation column at least one organic base having a pKa, measured at 25° C. in water, greater than or equal to 7; and combining the aqueous stream (iv), after addition with the at least one organic base, with the aqueous stream (iia) to obtain an aqueous stream (vi); routing the aqueous stream (vi) and a process gas to a saturator and producing a gaseous stream (vii) from a head of the saturator; and feeding the gaseous stream (vii) from the saturator to a synthesis gas production plant; and, optionally, routing a drain stream (viii) from a bottom of the saturator into aqueous stream (i); and, optionally, routing the aqueous stream (v) exiting from the bottom of the distillation column to further treatment in order to obtain purified water.

2. The process according to claim 1 , wherein said inorganic base has a pK a , measured at 25° C. in water, greater than or equal to 6.5.

3. The process according to claim 1 , wherein said aqueous stream (iv) comprises organic acids in an amount of from 0.01% by weight to 1.2% by weight with respect to the total weight of said aqueous stream (iv).

4. The process according to claim 1 , wherein said organic base has a pK a , measured at 25° C. in water, ranging from 7 to 12.

5. The process according to claim 1 , wherein said gaseous stream (vii) that is fed to the synthesis gas production plant undergoes catalytic steam reforming.

6. The process according to claim 1 , wherein said aqueous stream (iia) has a concentration of alcohols greater than or equal to 1% by weight with respect to the total weight of said aqueous stream (iia).

7. The process according to claim 6 , wherein said aqueous stream (iia) has a concentration of alcohols ranging from 2% by weight to 5% by weight with respect to the total weight of said aqueous stream (iia).

8. The process according to claim 1 , wherein said aqueous stream (iii) has a concentration of salts of organic acids greater than or equal to 0.05% by weight with respect to the total weight of said aqueous stream (iii).

9. The process according to claim 8 , wherein said aqueous stream (iii) has a concentration of salts of organic acids ranging from 0.2% by weight to 10% by weight with respect to the total weight of said aqueous stream (iii).

10. The process according to claim 1 , wherein said aqueous stream (iv) has a concentration of alcohols greater than or equal to 0.5% by weight with respect to the total weight of said aqueous stream (iv).

11. The process according to claim 10 , wherein said aqueous stream (iv) has a concentration of alcohols ranging from 1% by weight to 10% by weight with respect to the total weight of said aqueous stream (iv).

12. The process according to claim 1 , wherein said aqueous stream (v) comprises a quantity of salts of organic acids greater than or equal to 80% by weight with respect to the total weight of the salts of organic acids present in the aqueous stream (iii) fed to the distillation column.

13. The process according to claim 12 , wherein said aqueous stream (v) comprises a quantity of salts of organic acids ranging from 90% by weight to 99.9% by weight with respect to the total weight of the salts of organic acids present in the aqueous stream (iii) fed to the distillation column.

14. The process according to claim 1 , wherein said inorganic base is selected from at least one of an alkali metal hydroxide, an alkali metal oxide, an alkaline earth metal hydroxide and an alkaline earth metal oxide; or mixtures thereof.

15. The process according to claim 14 , wherein said inorganic base is selected from sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, lithium hydroxide, or mixtures thereof.

16. The process according to claim 15 , wherein said inorganic base is selected from sodium hydroxide, potassium hydroxide, or mixtures thereof.

17. The process according to claim 1 , wherein adding at least one inorganic base to the aqueous stream (i) comprises adding 0.70 to 1.50 molar equivalents of the at least one inorganic base in proportion to the organic acid content of aqueous stream (i).

18. The process according to claim 17 , wherein adding at least one inorganic base to the aqueous stream (i) comprises adding 0.90 to 1.20 molar equivalents of the at least one inorganic base in proportion to the organic acid content of aqueous stream (i).

19. The process according to claim 1 , wherein said inorganic base is added to the aqueous stream (i) in a quantity such that the pH of the aqueous stream (iii) coming out from the bottom of the evaporator is greater than or equal to 6.5.

20. The process according to claim 19 , wherein said inorganic base is added to the aqueous stream (i) in a quantity such that the pH of the aqueous stream (iii) coming out from the bottom of the evaporator is ranging from 7 to 11.

21. The process according to claim 1 , wherein said evaporator operates at a temperature ranging from 90° C. to 160° C. and at a pressure ranging from 0.5 ata (atmospheres absolute) to 4 ata (atmospheres absolute).

22. The process according to claim 1 , further comprising releasing salts of organic acids from a bottom of the saturator as a drain stream (viii).

23. The process according to claim 22 , wherein said drain stream (viii) is fed to the distillation column, after having been combined with the aqueous stream (i) coming from the Fischer-Tropsch reaction.

24. The process according to claim 1 , wherein said saturator operates at a temperature ranging from 160° C. to 200° C. and at a pressure ranging from 30 bara (bar absolute) to 60 bara (bar absolute).

25. The process according to claim 1 , wherein said organic base has a boiling point ranging from 70° C. to 200° C.

26. The process a

Assignees

• Carnelli Lino
• Eni Spa

Inventors

• Carnelli Lino
• Locatelli Lino

Classifications

• C02F1/048

  Purification of waste water by evaporation · CPC title

• C02F2101/32

  Hydrocarbons, e.g. oil · CPC title

• C02F9/00

  Multistage treatment of water, waste water or sewage · CPC title

• C02F1/04 Primary

  by distillation or evaporation · CPC title

• C02F3/286

  including two or more steps · CPC title