Process for preparing hydroxylammonium salts

Details Process for preparing hydroxylammonium salts Process for preparing hydroxylammonium salts

1999-04-28

2001-04-24

Langel, Wayne (Department: 1754)

Chemistry of inorganic compounds

Nitrogen or compound thereof

Oxygen containing

C423S388000

Reexamination Certificate

active

06221328

ABSTRACT:

The invention relates to a process for preparing a hydroxylammonium salt through catalytic reduction of nitrate ions with hydrogen in an acid medium in the presence of a palladium and/or platinum catalyst on a carrier.
This type of process is already known from NL-A-7902291. However, a drawback of this process is that, after being conducted for a relatively long time, i.e. longer than a week, the catalysts employed do not show good selectivity. This is particularly disadvantageous in the commercial production of hydroxylammonium salts.
An important application of hydroxylammonium salts is in the preparation of oximes from ketones or aldehydes, in particular the preparation of cyclohexanone oxime from cyclohexanone. A cyclic process is known for the preparation of for example cyclohexanone oxime. Thereafter, the reaction medium is buffered with acid, for example with buffers of phosphoric acid and/or sulphuric acid and the salts derived from these acids, for example alkali and/or ammonium salts.
In the hydroxylammonium synthesis nitrate ions are converted with hydrogen into hydroxylammonium ions; this proceeds according to the following equation:
2 H
+
+NO
3
−
+3 H
2
→NH
3
OH
+
+2 H
2
O
The goal of the invention is now to provide a process in which use is made of catalysts which retain an enhanced selectivity towards hydroxylammonium salt even after prolonged use and exposure to the synthesis conditions.
The goal is surprisingly achieved by incorporation of at least 0.00025 mmol halogen ions per m
2
of palladium and/or platinum surface area of the catalyst employed.
The upper limit for the quantity of halogen ions is at most 0.004 mmol per m
2
of palladium and/or platinum surface area. Preferably the halogen ions are present at a level of between 0.001 and 0.002 mmol halogen ions per m
2
of palladium and/or platinum surface area.
Any of the halogens of iodine, bromine, chlorine and fluorine may be utilised. Preferably use is made of iodine and/or bromine ions. The halogen ions may be applied to the catalyst for example through treatment with a halogen compound. Examples of such halogen compounds are include elemental I
2
, Br
2
, Cl
2
, F
2
, and such compounds as HI, HBr, alkali(ne earth) salts of iodine, bromine, chlorine and/or fluorine, iodinated, brominated, chlorinated and/or fluorinated aliphatic, aromatic, branched or linear hydrocarbons having 1-12 C atoms (for example methyl iodide, ethyl iodide) or mixtures thereof. Preferably use is made of the iodine- and/or bromine-containing compounds.
The catalyst treatment may take place before the (halogen-containing) catalyst is introduced into the reactor. Alternatively this treatment may also be carried out in situ, with the catalyst (whether or not halogen-containing) already being present in the reactor. The aforementioned halogen compound(s) may be used either in pure or in diluted form, optionally being dissolved in a suitable solvent. Preferably the treatment takes place before the catalyst is introduced into the reactor.
The amount of palladium and/or platinum in the catalyst is usually 0.5-20 wt. %, relative to the overall catalyst weight.
If use is made of a catalyst containing both platinum and palladium, the weight ratio of the palladium relative to the platinum will generally be between 6:4 and 9.9:0.1. Preferably the ratio will be between 7:3 and 9.5:0.5.
A solid carrier is generally used for the platinum and/or palladium catalyst. In principle, any material that is stable, i.e. that does not dissolve, pulverize, turn to slime, swell, coagulate or disintegrate in the reaction medium, can be used as the carrier. Examples of suitable carriers include activated carbon or graphite.
The palladium and/or platinum is applied to the carrier in the form of metal particles. The surface area of these metal particles is the palladium and/or platinum area. This area can be determined with the aid of CO adsorption. Usually the palladium and/or platinum area will lie between 0.5 and 20 m
2
per gram of catalyst.
The catalyst is usually activated, as already known from NL-A-7604669, by introduction of the presence of at least one of the metallic elements from the group comprising Cu, Ag, Au, Cd, Ga, In, Tl, Ge, Sn, Pb, As, Sb and Bi including mixtures thereof. Use can also be made of compounds containing the elements concerned, for example oxides, nitrates, phosphates, sulphates, tartrates, oxalates, formiates and acetates thereof. More than one such compound may be utilised in a mixture. The elements or the compounds can either then be applied directly to the catalyst or alternatively they can be added to the reaction medium. A very suitable result can be obtained if 0.01-5 mg of the activating element(s) from the above group is present per gram of palladium and/or platinum.
The activation with one or more of the elements mentioned above can take place both before and after the treatment with the halogen compound(s).
The H
2
pressure at which the catalytic reduction of nitrate ions takes place will generally be between 0.1 and 5 MPa, preferably between 0.5 and 2.5 MPa. The H
2
to be used can be purified beforehand. Purification can take place with the aid of, for example, activated carbon for the purpose of the removal of organic components, with a palladium catalyst for the purpose of the removal of oxygen, and/or with zinc oxide for the removal of sulphur and with a ruthenium compound for the purpose of the conversion of any CO and CO
2
present. Optionally, a different gas can be mixed with the H
2
, for example helium, methane or nitrogen.
The hydroxylammonium salt will usually be prepared at a pH of between 1 and 6, preferably between 1 and 4.
The temperature will usually lie between 20 and 90° C.; preferably a temperature of between 30 and 70° C. is used.
The invention will be further elucidated with reference to the following examples without however being limited thereto.


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patent: 7902291 (1980-09-01), None

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