Abstract:
Process for purification of aqueous solutions of hydrogen peroxide comprising the steps of adding one or more macroligands to said solution to form a mixture and forcing the mixture through an ultrafiltration membrane.

Description:
This application is a continuation of application Ser. No. 08/950,977, filed Oct. 15, 1997, now U.S. Pat. No. 5,851,402. 
    
    
     BACKGROUND OF THE INVENTION 
     (i) Field of the Invention 
     The present invention relates to a process for the purification of aqueous solutions of hydrogen peroxide in order to remove cations and organic acids therefrom. 
     (ii) Description of Related Art 
     Aqueous hydrogen peroxide has many industrial uses and, in the case of the electronics field, must exhibit a high purity and must therefore be rid of its cations and organic acids. 
     The methods of purification described to date refer to distillation, treatment on ion exchange resins, as in French Patent Application FR 1 043 082, treatment on exchange resins to which chelating agents are added, in French Patent Application FR 2 624 500 and to a reverse osmosis process, as in U.S. Pat. No. 4,879,043. 
     However, these methods are not entirely satisfactory for the removal of some impurities such as especially the ferric Fe +++   or aluminic Al +++   ions. 
     The present invention proposes to remedy these disadvantages. 
     SUMMARY OF THE INVENTION 
     The subject-matter of the invention is a process for the purification of aqueous solutions of hydrogen peroxide, characterized in that one or more macroligands are added to the solution and the resulting mixture is forced through an ultrafiltration membrane. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Aqueous solutions of aqueous hydrogen peroxide are usually employed in electronics assays at from 30 to 35% by weight. The invention can, however, be applied to solutions assaying at up to 75% by weight. Macroligands are added to these aqueous solutions; the subject-matter of the invention is especially a process in which the macroligands contain one or several functional groups chosen from carboxylic, sulphonic and phosphonic groups or nitrogen-containing functional groups such as aromatic or nonaromatic amine functional groups or N-oxidized amine functional groups. 
     Aqueous hydrogen peroxide to which the ligand(s) has (have) been added is then forced under pressure through an ultrafiltration membrane. The membrane is of an oxidation-resistant nature of the fluoropolymer type (PTFE, PVDF, PFA) and with a cut-off threshold adapted to the polymers employed. The working pressure is from 1 bar to a few bars, in general 3 to 4 bars; the subject-matter of the invention is particularly a process in which the ultrafiltration membrane is a membrane made of fluoropolymer, especially of polyvinyl difluoride (PVDF), of polytetrafluoroethylene (PTFE) or of polyfluoroalkoxy (PFA). 
     The results of the tests developed in the examples mentioned below show that results lower than 10 ppb (parts per billion) are obtained for the Fe +++   and Al +++   ions when the macroligands are chosen from the 4-vinylpyridine homopolymer, the styrene/4-vinyl-pyridine 2/8 and 1/9 copolymers, acrylic phosphate/sulphonate copolymers (Mw=500 000), acrylic phosphate copolymer (Mw=500 000) and polyvinylphosphonic acid (Mw=30 000), this choice constituting a preferred alternative form of the present invention. 
     Besides the good results obtained, an advantage of this process consists in it being possible for this method of purification to be used upstream or downstream of other purification stages. 
     Another aspect of the invention is a process for the manufacture of unstabilized ultrapure hydrogen peroxide from the crude product prepared according to the methods known to a person skilled in the art, such as, for example, the autooxidation of anthraquinone or of its derivatives, anodic oxidation of the SO 4   --  /HSO 4   -   couple, cathodic reduction of oxygen or the direct synthesis, optionally including one or more purification stages chosen from distillation, passing over ion exchange resins, passing over a column of adsorbents, especially of zeolites, or reverse osmosis, characterized in that it additionally includes at least one ultrafiltration stage according to the process as defined above. 
     The ultrapure hydrogen peroxide thus produced corresponds to the standards imposed by the users, especially the manufacturers of electronics components. 
     Another aspect of the present invention relates to a plant for the production of unstabilized ultrapure hydrogen peroxide, characterized in that it includes 
     a) a hydrogen peroxide synthesis unit, 
     b) a unit for purification of the crude hydrogen peroxide obtained in stage a), comprising at least one ultrafiltration stage according to the process, and 
     c) a storage vessel for the hydrogen peroxide purified in b), making it possible to absorb the variation in the final user&#39;s consumption, and characterized in that the plant is situated on the same site as the final user of the purified hydrogen peroxide and especially on the site of a factory for the manufacture of electronics components. 
    
    
     The following examples illustrate the invention without, however, limiting it. 
     EXAMPLE 1 
     A 70% strength aqueous hydrogen peroxide of industrial quality originating from the anthraquinone process was diluted to 30% and had added to it 0.25% of acrylosulphonic copolymer of Mw=4500. This solution was then ultrafiltered on a Filtron® mini-ultrasette equipped with a 50 cm 2  polyethersulphone membrane at a rate of 1 dm 3  /min of retentate and 1.3 cm 3  /min of filtrate. Results (in ppb). 
     
         ______________________________________K           Fe     Al      Ni   Cr    Mn   Sn______________________________________30% H.sub.2 O.sub.2   17      123    124   13   22    2    7800Filtrate   8       12     13    &lt;4   5     &lt;0.2 40______________________________________ 
    
     EXAMPLE 2 
     0.25% by weight of polyvinylphosphonic acid of Mw=30 000 is added to a 30% strength by weight aqueous hydrogen peroxide of electronics quality. The solution is then ultrafiltered on a Filtron 3K mini-ultrasette at a rate of 1.5 dm 3  /min of retentate and 0.7 cm 3  /min of filtrate. Results (in ppb). 
     
         ______________________________________          K         Cu______________________________________30% H.sub.2 O.sub.2            0.95        0.94Filtrate         0.45        0.21______________________________________ 
    
     EXAMPLE 3 
     0.25% by weight of 4-vinylpyridine homopolymer is added to industrial aqueous hydrogen peroxide. The resulting solution is ultrafiltered on 1K membrane. Results (in ppb) 
     
         ______________________________________Si           Fe      Al      Cr   P      Sn______________________________________30% H.sub.2 O.sub.2   10 300   127     407   23   22 200 7700Filtrate   1680     3       &lt;9    16   11 600 100______________________________________ 
    
     EXAMPLE 4 
     Operating in a manner similar to Example 3, and employing as macroligands a styrene/4-vinylpyridine 2/8 copolymer and the 1/9 copolymer, following results are obtained: 
     
         ______________________________________   Fe    Al       Cr      P       Sn______________________________________30% H.sub.2 O.sub.2     70      140      17    23 800  7400Filtrate  &lt;4      &lt;9       &lt;4    11 200  &lt;20______________________________________ 
    
     EXAMPLE 5 
     Operating as in Example 1, employing the macroligands cited below, the following results are obtained: 
     
         ______________________________________       K     Fe      Al      Cr    Mg______________________________________30% industrial H.sub.2 O.sub.2         12      56      95    20    50A             &lt;8      16      40    &lt;4    24B             &lt;8      8       &lt;9    &lt;4    14C             &lt;8      3       25    &lt;4    30D             &lt;8      4       15    &lt;4    2______________________________________ 
    
     A: acrylic/sulphonate copolymer 
     B: acrylic/phosphate/sulphonate copolymer Mw=500 000 
     C: acrylic/phosphate copolymer Mw=500 000 
     D: polyvinylphosphonic acid Mw=30 000.