Process for preparing chromium(III) oxide

Patent metadata

Field	Value
Publication number	US-9580333-B2
Application number	US-201113991516-A
Country	US
Kind code	B2
Filing date	Dec 7, 2011
Priority date	Dec 8, 2010
Publication date	Feb 28, 2017
Grant date	Feb 28, 2017

Abstract

Process for preparing chromium(III) oxide, which comprises the steps:
a) reaction of sodium monochromate with gaseous ammonia, in particular at a temperature of from 200 to 800° C., b) hydrolysis of the reaction product obtained in step a) with the pH of the water for the hydrolysis being reduced before the hydrolysis or that of the alkaline mother liquor being reduced during or after the hydrolysis, to a value of from 4 to 11, preferably from 5 to 10, by means of an acid, c) isolation of the hydrolysis product which has precipitated in step b), preferably at a pH of from 4 to 11, in particular from 5 to 10, and optionally washing and optionally drying and d) calcination of the hydrolysis product obtained in step c) at a temperature of from 700 to 1400° C., in particular from 800 to 1300° C.

First claim

The invention claimed is:

1. A process for preparing chromium(III) oxide, the process comprising:
reacting gaseous ammonia with sodium monochromate to produce a reaction product;
hydrolyzing the reaction product in the presence of water to form a resultant mixture of a precipitate and a mother liquor, wherein the hydrolyzing comprises lowering the pH of at least one of:
the water before the hydrolysis,
the mother liquor during the hydrolysis, and
the mother liquor after the hydrolysis,

by the addition of an acid to the at least one of the water and the mother liquor so that the resultant mixture has a pH of 4 to 11;
separating the precipitate from the resultant mixture having the pH of 4 to 11; and
calcining the precipitate to form chromium(III) oxide product.

2. The process according to claim 1 , further comprising reacting the sodium monochromate and gaseous ammonia at a temperature of 200° C. to 800° C. in an indirectly heated reactor.

3. The process according to claim 1 , wherein for reacting the gaseous ammonia with sodium monochromate the sodium monochromate is in the form of one of:
solely sodium monochromate; or
sodium monochromate in admixture with at least one other Cr(III)- and/or Cr(Vl)-containing compound.

4. The process according to claim 1 , wherein the sodium monochromate is in the form of solely sodium monochrornate.

5. The process according to claim 1 , wherein the sodium monochromate is in the form of sodium monochromate in admixture with at least one of chromium(III) oxide, sodium chromite, sodium ammonium chromate double salt, ammonium monochromate, ammonium dichromate and sodium chromichromate.

6. The process according to claim 1 , wherein the pH is adjusted during and after the hydrolysis by adding at least one of carbon dioxide, formic acid, and acetic acid to the mother liquor.

7. The process according to claim 1 , further comprising calcining the precipitate at a temperature of 700° C. to 1400° C.

8. The process according to claim 7 , further comprising one of:
washing the calcined product at least once with water, and subsequently drying the washed product;
milling the calcined product;
washing the calcined product at least once with water, subsequently drying the washed product, and milling the washed calcined product.

9. The process according to claim 1 , further comprising adding 0.01% by weight to 3.0% by weight of at least one of:
alkali metal halides, ammonium halides, alkaline earth metal halides, alkali metal hydroxides, and chromic acid
to the precipitate before calcining the precipitate.

10. The process according to claim 1 , further comprising adding 0.02% by weight to 1.0% by weight of at least one of:
alkali metal halides, ammonium halides, alkaline earth metal halides, alkali metal hydroxides, and chromic acid to the precipitate before calcining the precipitate.

11. The process according to claim 1 , further comprising adding 0.02% by weight to 1.0% by weight of at least one of:
fluorides, chlorides, bromides, iodides or hydroxides of sodium,
fluorides, chlorides, bromides, iodides or hydroxides of potassium,
fluorides, chlorides, bromides or iodides of ammonium, and
chromic acid,
to the precipitate before calcining the precipitate.

12. The process according to claim 1 , wherein:
the sodium monochromate and gaseous ammonia are reacted at a temperature of 200° C. to 800° C.; and
the precipitate is calcined at a temperature of 700° C. to 1400° C.

13. The process according to claim 12 , wherein:
for reacting the gaseous ammonia with sodium monochromate the sodium monochromate is in the form of one of:
solely sodium monochromate; or
sodium monochromate in admixture with at least one other Cr(III)- and/or Cr(VI)-containing compound; and

the pH is adjusted by adding acid to the at least one of the water and the mother liquor.

14. The process according to claim 13 , wherein:
the sodium monochromate and gaseous ammonia are reacted at a temperature of 300° C. to 600° C.;
the pH is adjusted to 5-10 during and after the hydrolysis by adding carbon dioxide to the mother liquor; and
the precipitate is calcined at a temperature of 800° C. to 1300° C.

15. The process according to claim 14 , wherein:
the sodium monochromate and the gaseous component are reacted in a rotary tube furnace or fluidized bed; and
the process further comprises:
washing the precipitate at least once with water, and subsequently dried;
adding 0.02% by weight to 1.0% by weight of at least one of:
fluorides, chlorides, bromides, iodides or hydroxides of sodium,
fluorides, chlorides, bromides, iodides or hydroxides of potassium,
fluorides, chlorides, bromides or iodides of ammonium, and chromic acid,

 to the washed and dried precipitate before calcining the precipitate;
washing the calcined product at least once with water, and subsequently drying the washed product; and
milling the washed calcined product.

16. A process for preparing chromium(III) oxide, the process comprising:
reacting gaseous ammonia with sodium monochromate at a temperature of 200° C. to 800° C. to produce a reaction product;
hydrolyzing the reaction product in the presence of water to form a resultant mixture of a precipitate and a mother liquor, wherein the hydrolyzing comprises maintaining a pH of 4-11 of the resultant mixture at least during and after the hydrolyzing;
separating the precipitate from the mother liquor; and
calcining the precipitate at a temperature of 700° C. to 1400° C. to form chromium(III) oxide.

Assignees

• Friedrich Holger
• Boll Matthias
• Ortmann Rainer
• Lanxess Deutschland Gmbh

Inventors

• Friedrich Holger
• Boll Matthias
• Ortmann Rainer

Classifications

• C01G37/00

  Compounds of chromium · CPC title

• C09C1/346

  Chromium oxides · CPC title

• C01G37/033 Primary

  Chromium trioxide; Chromic acid · CPC title

• C01P2006/80

  Compositional purity · CPC title