Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2002-02-04
2003-03-18
Davis, Brian (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S301000
Reexamination Certificate
active
06534681
ABSTRACT:
The present invention relates to a process for the preparation of high-purity, stabilized hydroxylamine solution (HA solutions) in which an aqueous hydroxylamine starting solution is treated with an anion exchanger in order to remove anions.
High-purity, concentrated, aqueous hydroxylamine solutions are used, inter alia, in the electronics industry, for example for the pre-cleaning of printed circuit boards. For use in the electronics industry, concentrations of impurities, for example anions, of less than 10 ppm are usually required in the starting materials employed, such as solutions, substances and other agents. Starting materials of such high purity are referred to as “electronics grade” products. However, the aqueous hydroxylamine solutions currently commercially available contain impurities from production, for example sodium sulfate, in the 30 ppm range.
One way of purifying aqueous hydroxylamine solutions is described in U.S. Pat. No. 5,872,295, in which the hydroxylamine solution is passed firstly over at least one strongly acidic ion exchanger which has been treated in advance with dilute hydrochloric acid and then over at least one strongly basic anion exchanger which has been pretreated or regenerated using a non-metallic amino or hydroxide base solution. The HA solution obtained in this way, which has been subjected to double exchange treatment, is then mixed with a stabilizer. The resultant HA solution is thus post-stabilized. Apart from the additional effort associated therewith, this gives rise to the problem that the stabilizer contains metal ions, in particular sodium, in relatively large amounts—about 1 ppm—from its preparation process. Since E grade chemicals must be primarily free from metal ions, post-stabilization of this type is ruled out since sodium ions would be re-introduced thereby.
U.S. Pat. No. 5,788,946 discloses a similar process for the purification of hydroxylamine which results in a significant reduction in respect of the content of cations and anions. In this process a solution of hydroxylamine is passed through at least one strongly acidic ion exchanger bed which has been treated in advance with a dilute hydrochloric acid, and subsequently through at least one bed of a strongly basic anion exchanger resin. The aqueous hydroxylamine solution obtained in this known process is not stabilized. If the hydroxylamine solution were to be post-stabilized, the problems already mentioned above would again occur.
U.S. Pat. No. 4,147,623 discloses a process for the removal of hydroxylamine from an aqueous hydroxylammonium salt solution; the solution contains cation salts whose respective corresponding free bases have dissociation constants of >10
−7
. These salts also include the above-mentioned sodium sulfate. In accordance with this known process, the starting solution employed is firstly adjusted to a pH of from 6 to 11, subsequently passed through a bed of a strongly ionic exchanger resin, which can be a cation exchanger resin or an anion exchanger resin. Under these conditions, the majority of the hydroxylamine ions are transformed into electrically neutral hydroxylamine molecules, whereas the other salts present in the solution are essentially unaffected. If the solution is thus passed through the cation or anion exchanger, the electrically uncharged hydroxylamine is retained in the exchanger resin, while the salts are the first to leave the column in the eluate. The solution obtained in accordance with this prior art is likewise not stabilized and would have to be post-stabilized as already mentioned above. Thus, the problems already discussed above would again arise here.
PCT/EP99/00993 describes the preparation of essentially metal ion-free hydroxylamine solutions by treatment with an acidic cation exchanger.
Another purification method is distillative work-up of hydroxylamine solutions as described in U.S. Pat. No. 5,472,679. However, it must be ensured during the distillation that a temperature of 65° C. is not exceeded since the onset temperature, i.e. the temperature at which recognizable decomposition begins, is about 70° C. in the case of a 50% strength hydroxylamine solution. Alternative distillation methods are described in WO 97/22551 and WO 98/57886, the latter giving “electronics grade” hydroxylamine. A distillation, in particular at low temperatures and pressures, is associated with corresponding effort and time consumption. Accordingly, salt-free aqueous hydroxylamine solutions in electronics grade purity prepared in this way are correspondingly expensive and thus restricted in their use to a few areas of application.
It is an object of the present invention to provide a process for the preparation of stabilized, aqueous, high-purity hydroxylamine solutions which meet the requirements of electronics grade purity. In addition, the process should be less expensive than the process usual in the prior art. Finally, it should be possible to carry out the process without the risk of decomposition of the hydroxylamine.
We have found that this object is achieved by a process in which high-purity, stabilized hydroxylamine solutions are prepared by treating an aqueous anion-containing hydroxylamine starting solution with an anion exchanger loaded with a hydroxylamine stabilizer in order to remove the anions.
For the purposes of the present invention, the term “high-purity HA solutions” is taken to mean HA solutions whose content of anions, in particular sulfate ions, is below the quantitative detection limit, i.e. for example below 10 ppm. Preference is given to HA solutions whose content of cations (metal ions, in particular alkali metal ions, such as sodium ions) is less than 1 ppm, in particular less than 0.1 ppm.
The hydroxylamine starting solution used is generally an HA solution whose content of anions is up to 50 ppm, in general from 20 to 40 ppm of anions, in particular sulfate ions. The content of cations is generally up to about 50 ppm, in particular up to 30 ppm. The hydroxylamine concentration of such solutions is generally in the range from 1 to 70% by weight, in particular from 5 to 60% by weight. The preparation of HA solutions of this type is known to the person skilled in the art and is described, for example, in WO 97/22551 and U.S. Pat. No. 5,472,679.
Suitable anion exchangers are weakly basic, but preferably strongly basic anion exchangers. Suitable anion exchangers are, for example, the Amberlite, Duolite and Purolite resins from Rohm & Haas, such as Amberlite IRA-400, IRA-402, IRA-904 and preferably IRA-92 and IRA-93, Duolite A-109 and Purolite A-600, A-400, A-300, A-850 and A-87, and the Lewatit resins from BAYER AG, such as Lewatit M 511. The base form of the anion exchanger can be generated using conventional bases, such as sodium hydroxide or potassium hydroxide, or ammonia.
In accordance with the invention, use is made of anion exchangers which have been loaded with a stabilizer. The anion exchangers are used in the hydroxyl form having a pH in the range from 8 to 14. In the case of a weakly basic anion exchanger, the pH is in the range from 8 to 12, in particular from 8 to 11, while in the case of a strongly basic anion exchanger the pH is in the range from 12 to 14, in particular from 13 to 14. Suitable stabilizers are those which are bound by an anion exchanger. These are, for example, thioglycolic acid, hydroxyanthraquinones, hydroxyquinolines, hydroxyquinaldines, the salts of ethylenediaminetetraacetic acid or N-hydroxylethylethylenediaminotriacetic acid, hydroxanoic acids, dipyridyl compounds, aminoquinolines or phenanthrolines.
Preferred stabilizers are the compounds of the formula
R
1
R
2
N—A—NR
3
R
4
(I)
where
A is alkylene, alkenylene, alkynylene, cycloalkylene, cycloalkenylene, arylene, o-, m- or p-xylylene, a 5- or 6-membered saturated or unsaturated heterocyclic ring containing a nitrogen atom, where said radicals may have 1, 2 or 3 substituents selected, independently of one another, from alkyl, alkoxy or hydroxyl, or is
X&Brketopenst;NR—B&Brketclosest;
n
where
B and X are —CH
Watzenberger Otto
Wilfinger Hans Jörg
BASF - Aktiengesellschaft
Davis Brian
Keil & Weinkauf
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