Integrated process for preparing isocyanates

• US 20040024244A1
• Filed: 08/27/2002
• Published: 02/05/2004
• Est. Priority Date: 08/02/2002
• Status: Active Grant

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Walsdorff, Christian, Harth, Klaus, Fiene, Martin, Deberdt, Filip, Strofer, Eckhard, Jacobs, Jan D.
• Granted Patent: US 6,916,953 B2
• Time in Patent Office: Days
• US Class Current: 560/347
• CPC Class Codes: B01J 23/462 Ruthenium
• CPC Class Codes: C01B 7/04 Preparation of chlorine from hydrogen chloride
• CPC Class Codes: C07C 263/10 by reaction of amines with carbonyl halides, e.g. with phosgene
• CPC Class Codes: C07C 263/20 Separation; Purification
• CPC Class Codes: C07C 265/14 containing at least two isocyanate groups bound to the same carbon skeleton
• CPC Class Codes: Y02P 20/10 Process efficiency

Abstract

Process for preparing organic isocyanates, which comprises the steps

(a) making available a first partial amount of chlorine, with the chlorine of this first partial amount having a content of free and bound bromine and iodine of <400 ppm;

(b) making available a second partial amount of chlorine;

(c) reacting the first and second partial amounts of chlorine with carbon monoxide to form phosgene;

(d) reacting the phosgene from step (c) with one or more primary amines to form the corresponding isocyanates and hydrogen chloride;

(e) separating off and, if necessary, purifying the isocyanates formed in step (d);

(f) separating off and, if necessary, purifying the hydrogen chloride formed in step (d);

(g) catalytically oxidizing at least part of the hydrogen chloride separated off in step (e) by means of oxygen to form chlorine;

(h) separating off the chlorine formed in step (g) and using at least a partial amount of the chlorine which has been separated off as second partial amount of chlorine in step (b).

Claims

1. A process for preparing organic isocyanates, which comprises the steps

(a) making available a first partial amount of chlorine, with the chlorine of this first partial amount having a content of free and bound bromine and iodine of <

400 ppm;

(b) making available a second partial amount of chlorine;

(c) reacting the first and second partial amounts of chlorine with carbon monoxide to form phosgene;

(d) reacting the phosgene from step (c) with one or more primary amines to form the corresponding isocyanates and hydrogen chloride;

(e) separating off and, if necessary, purifying the isocyanates formed in step (d);

(f) separating off and, if necessary, purifying the hydrogen chloride formed in step (d);

(g) catalytically oxidizing at least part of the hydrogen chloride separated off in step (e) by means of oxygen to form chlorine;

(h) separating off the chlorine formed in step (g) and using at least a partial amount of the chlorine which has been separated off as second partial amount of chlorine in step (b).

2. A process as claimed in claim 1, wherein the chlorine of the first partial amount of chlorine is obtained by electrolysis of a solution containing chloride ions.

3. A process as claimed in claim 1, wherein the chlorine of the first partial amount is depleted in bromine and/or iodine in a purification stage.

4. A process as claimed in claim 1, wherein essentially the total amount of the chlorine separated off in step (h) is used as second partial amount of chlorine in step (b), and the first partial amount of chlorine is calculated so that the sum of first and second partial amounts remains constant.

5. A process as claimed in claim 1, wherein the second partial amount of chlorine makes up at least 70% of the sum of first and second partial amounts of chlorine.

6. A process as claimed in claim 1, wherein the chlorine of the first partial amount has a content of free and bound bromine and iodine of <

100 ppm.

7. A process as claimed in claim 1, wherein the hydrogen chloride oxidation (e) is carried out in the presence of a heterogeneous catalyst.

8. A process as claimed in claim 7, wherein the hydrogen chloride oxidation is carried out over a catalyst comprising ruthenium oxide on a support selected from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide, zirconium dioxide and mixtures thereof.

9. A process as claimed in claim 1, wherein the primary amine or amines is/are selected from the group consisting of the isomeric, monomeric and oligomeric diphenylmethanediamines, isomeric toluenediamines, isophoronediamine and hexamethylenediamine.

10. A process as claimed in claim 1, wherein the hydrogen chloride oxidation is carried out in a fixed-bed or fluidized-bed reactor.