Process for the production of cyclohexanone oxime

Details Process for the production of cyclohexanone oxime Process for the production of cyclohexanone oxime

2003-08-28

2004-07-06

Solola, Taofiq (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

Reexamination Certificate

active

06759556

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This application is the National Phase of International Application PCT/NL01/00428 filed May 31, 2001 which designated the U.S., and which further claims priority to European application No. 00201970.1, filed Jun. 5, 2000, both of which are hereby incorporated in their entirety by reference.
The invention relates to a process for the production of cyclohexanone oxime in which a phosphate-containing aqueous reaction medium is cycled from a hydroxylammonium synthesis zone to a cyclohexanone oxime synthesis zone and back to the hydroxylammonium synthesis zone, in which hydroxylammonium synthesis zone hydroxylammonium is formed by catalytic reduction of nitrate with hydrogen, and in which cyclohexanone oxime synthesis zone hydroxylammonium is reacted with cyclohexanone in the presence of an organic solvent to form cyclohexanone oxime.
Oximes can be produced in a process in which a buffered, aqueous reaction medium containing buffer acids or acidic salts, for example phosphate buffers, and buffer salts derived from these acids, is continuously recycled between a hydroxylammonium synthesis zone, in which nitrate ions are catalytically reduced with molecular hydrogen to hydroxylammonium, and an oxidation zone where a ketone, e.g. cyclohexanone, is converted to an oxime. Before the aqueous reaction medium is passed into the hydroxylammonium synthesis zone, it may be enriched with the required nitrate ions by addition of nitric acid or by absorption of nitrous gases in the aqueous reaction medium in which instance nitric acid is formed in situ. After having been enriched in hydroxylammonium in the hydroxylammonium synthesis zone, the aqueous reaction medium is then passed to the oxime synthesis zone, where the hydroxylammonium reacts with a ketone,e.g., cyclohexanone, forming the corresponding oxime. The oxime can then be separated from the aqueous reaction medium which is recycled to the hydroxylammonium synthesis zone.
The net chemical reactions occurring during the process can be represented by the following equations.
1) Preparation of the hydroxylammonium:
2H
3
PO
4
+NO
3
−
+3H
2
→NH
3
OH
+
+2H
2
PO
4
−
+2H
2
O
2) Preparation of the oxime
3) Supply of HNO
3
to make up the depletion of the source of nitrate ions after removal of the oxime formed
H
2
PO
4
−
+HNO
3
→H
3
PO
4
+NO
3
−
The catalyst used in the reduction of the nitrate ions is generally palladium and/or platinum on a carrier material of carbon or alumina, the carrier material being loaded with from 1 to 25% wt. of palladium and/or platinum. The activity of the catalyst is adversely affected by the presence of organic contaminants, such as the ketone and oxime, in the recycled stream.
A number of techniques have been developed to address this problem of the recycled stream containing high amounts of contaminants that poison the catalyst U.S. Pat. No. 3,940,442 describes that poisoning of the catalyst is prevented by heating the aqueous reaction medium being recycled from the cyclohexanone oxime synthesis zone to the hydroxylammonium synthesis zone to an elevated temperature in the range of 50° C. to 106° C. GB-A-1,283,894 and U.S. Pat. No. 3,997,607 describe that heat treating the aqueous reaction medium in the presence of nitrous acid, respectively nitrous gases reduce the extent of catalyst poisoning.
It has now been found that an increased phosphate concentration in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone results in a decrease of the concentration of the organic contaminants in the aqueous reaction medium which is recycled from the cyclohexanone oxime synthesis zone to the hydroxylammonium synthesis zone.
Therefore, the invention provides a process for the production of cyclohexanone oxime in which a phosphate-containing aqueous reaction medium is cycled from a hydroxylammonium synthesis zone to a cyclohexanone oxime synthesis zone and back to the hydroxylammonium synthesis zone, in which hydroxylammonium synthesis zone hydroxylammonium is formed by catalytic reduction of nitrate with hydrogen, and in which cyclohexanone oxime synthesis zone hydroxylammonium is reacted with cyclohexanone in the presence of an organic solvent to form cyclohexanone oxime, characterized in that the phosphate concentration in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone is higher than 3.0 mol/l. The invention also provides a process for the production of cyclohexanone oxime in which an aqueous reaction medium containing hydroxylammonium, phosphate and nitrate is fed into a cyclohexanone oxime synthesis zone, in which hydroxylammonium is reacted in the presence of an organic solvent with cyclohexanone to form cyclohexanone oxime, characterized in that the phosphate concentration in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone is higher than 3.0 mol/l.
Using the process according to the invention it is possible to decrease the amount of organic contaminants which poison the catalyst, in particular residual cyclohexanone and/or cyclohexanone oxime, entering the hydroxylammonium synthesis zone under further equal circumstances. According to the invention it is also possible to omit steps for the removal of organic contaminants or to lessen the extent to which such steps are carried out, for instance by using smaller equipment, the increased phosphate concentration avoiding or mitigating an increase of the amount of organic contaminants entering the hydroxylammonium synthesis zone. According to the invention, it is also possible to increase the concentration hydroxylammonium in the aqueous reaction medium entering the cyclohexanone oxime systhesis zone, the increased phosphate concentration avoiding or mitigating an increase of the amount of organic contaminants entering the hydroxylammonium synthesis zone.
According to the invention, the phosphate concentration in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone is higher than 3.0 mol/l. As used herein, the phosphate concentration denotes the sum concentration of all phosphates, irrespective of the form in which they are present, expressed in mol per liter of aqueous reaction reaction medium. Preferably, the phosphates are present as PO
4
3−
, HPO
4
2−
, H
2
PO
4
−
, H
3
PO
4
, salts of PO
4
3−
, HPO
4
2−
, H
2
PO
4
−
, and/or combinations thereof.
Preferably, the phosphate concentration in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone is higher than 3.3 mol/l, more preferably higher than 3.4 mol/l, in particular higher than 3.5 mol/l, more in particular higher than 3.7 mol/l. Increasing the phosphate concentration results in a further decrease of the concentration of the organic contaminants exiting th cyclohexanone oxime synthesis zone. There is no specific upper limit for the phosphate centration. Preferably, the phosphate concentration is chosen such that no crystallization occurs, which depends, inter alia, on the temperature and the concentration of other components in the aqueous reaction medium. Generally, the phosphate concentration in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone is lower than 8 mol/l, preferably lower than 5 mol/l, more preferably lower than 4.5 mol/l.
There is no specific lower limit for the concentration hydroxylammonium in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone. Preferably, the concentration hydroxylammonium in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone is higher than 0.8 mol/l. An increased concentration of hydroxylammonium is advantageous, since the conversion of hydroxylammonium in the cyclohexanone oxime synthesis zone may then be increased. Furthermore, the amount of cyclohexanone oxime produced per unit of time can be increased by increasing the concentration hydroxylammonium in the aqueous reaction medium entering the cyclohexanone oxime synthesis zone. Prefera

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