Liquid purification or separation – Particulate material type separator – e.g. – ion exchange or... – Spaced beds
Reexamination Certificate
1999-03-22
2001-02-06
Langel, Wayne (Department: 1754)
Liquid purification or separation
Particulate material type separator, e.g., ion exchange or...
Spaced beds
C210S681000, C210S683000
Reexamination Certificate
active
06183638
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The invention relates to a process for the preparation of an ultrapure hydrogen peroxide solution and to a plant for the implementation thereof.
(ii) Description of the Related Art
The use of hydrogen peroxide for advanced technology applications or applications in the food industry, in hygiene or health requires increasingly pure products which must meet a growing number of increasingly tight specifications. In particular, the demands of users are turning towards hydrogen peroxide solutions in which the content of each metal impurity is less than one part per billion (ppb) and preferably less than 500 parts per trillion (ppt). In the following account, such solutions will be known as ultrapure hydrogen peroxide solutions.
It is well known, according to the prior art, that it is possible to remove certain impurities by passing the solution through a bed of ion-exchange adsorbents. Mention may be made, for example, of functionalized polymers of polystyrene/divinylbenzene type, silicas or aluminosilicates, in particular the varieties containing controlled micropores, such as zeolites, or active charcoals; these solids carry functional groups capable of complexing either cations or anions. Mention may be made, as examples of functional groups capable of complexing cations, of the carboxylic, sulphonic, phosphonic, hydroxide, amine oxide or phosphine oxide groups or alternatively of cyclic or open polyoxaalkyls, such as, for example, ethylene oxide polymers. Mention may be made, as examples of functional groups capable of complexing anions, of the quaternary ammonium or phosphonium groups. These adsorbents can also be obtained by polymerization of a monomer carrying a functional group, for example poly(methacrylic acid)s, phosphonic acids, polyvinylpyridines, polyvinylpyrrolidones, poly(vinyl alcohol)s, saponified polylactones and copolymers containing these units. The adsorbents which are the most often described are polystyrene gels or crosslinked polystyrenes possessing sulphonic —SO
3
H or trimethylammonium (CH
3
)
3
N
+—
functional groups.
Many combinations have been provided, such as, for example, anionic resin followed by cationic resin or cationic resin followed by anionic resin or alternatively anionic resin followed cationic resin followed by cationic+anionic “mixed bed”. Additions to the inner-stage phases are also described, such as, for example, the addition of acid in order to modify the pH or the addition of chelating agents, such as aminomethylenecarboxylic or aminomethylenephosphonic derivatives.
It is well known to the person skilled in the art that the use of anion-exchange adsorbents presents great difficulties when employed for the purification of hydrogen peroxide. In particular, the hydroxide form, under which these products are generally available industrially, cannot be used directly because of it excessively high basicity, resulting in significant decomposition of hydrogen peroxide. Many publications describe the use of adsorbents exchanged by carbonate or bicarbonate ions, which are less basic, in order to limit the decomposition of hydrogen peroxide, without, however, eliminating it completely.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The subject of the present invention is a process for the preparation of an ultrapure hydrogen peroxide solution, characterized in that it comprises at least one sequence which includes successively passing the solution to be purified through at least one bed of cation-exchange adsorbents (CEA) and at least one bed of anion-exchange adsorbents (AEA) and characterized in peroxide the beds of adsorbents each exhibit a height to diameter ratio of greater than 3.
The subject of the present invention is in particular a process as defined above, in which the said ratio is, in particular, between 5 and 10 and, more particularly, approximately 6.
The hydrogen peroxide solution throughputs, expressed as volume of solution/hour passed per volume of bed of adsorbent, can vary between 0.5 and 100, preferably from 1 to 50 and more particularly from 10 to 30.
The hydrogen peroxide solution to be purified according to the present invention is a technical aqueous solution having a concentration of 1 to 70% by weight and preferably of 5 to 50% by weight. The adsorbents are chosen from those which are described above.
The anion-exchange adsorbents will preferably be fed in an upward mode, whereas the cation-exchange adsorbents will preferably be fed in a downward mode. It is possible to define the geometries of the beds so that the true space velocities and/or throughputs in each adsorbent are optimized. It is also possible to operate under pressure. Preferably, a working pressure of less than 5 atm above atmospheric pressure will be chosen.
The temperature of the solution to be purified according to the process as described above is less than or equal to 30° C. and preferably between −10° C. and +10° C.
In a preferred alternative form of the process, at least one bed of anion-exchange adsorbents contains carboxylate ions of formula R—COO
−
in which R represents a hydrogen atom, an aryl radical containing from 6 to 10 carbon atoms or an alkyl radical containing from 1 to 4 carbon atoms, the said aryl and alkyl radicals being either unsubstituted or substituted by one or more fluorine atoms. Carboxylate ion of formula R—COO
−
is understood to mean in particular the trifluoroacetate ion or the benzoate ion, the formate ion, the acetate ion or the fluoroacetate ion, and preferably the acetate ion.
In an alternative form of the process as defined above, it comprises, upstream or downstream of sequences for passing the solution to be purified through the beds of ion-exchange adsorbents, one or more purification stages, such as, for example, distillation, liquid extraction, crystallization, absorption, filtration, ultrafiltration, nanofiltration or reverse osmosis. If appropriate, the starting solution is brought beforehand to the desired assay and then purified. Depending on the degree of purity and of dilution of the hydrogen peroxide solution to be purified, one or more of these additional stages is/are employed.
In a first preferred alternative form of the present invention, the technical hydrogen peroxide solution to be purified, which is at a concentration of 30% to 70% by weight, is distilled and brought to the desired assay beforehand and then purified through at least two beds of ion-exchange adsorbents, according to the sequence which is the subject of the present invention.
According to a second alternative form of the purification process which is the subject of the present invention, a hydrogen peroxide solution of technical quality or of so-called “food” quality, having a concentration of approximately 50 to 70% by weight, is subjected to the following pretreatment: a first distillation/concentration stage, in order to obtain a condensate having a concentration of greater than 83%, plus a first purification by low-temperature crystallization and the removal of the supernatant. The crystals collected are washed, superficially dried and then melted and the solution obtained is diluted to 30 or 35% with deionized water of ultrapure electronic quality.
In a third preferred alternative form of the present invention, in particular if the carbon content of the hydrogen peroxide solution is a constraint forming an integral part of the required specifications, a second bed of anion-exchange adsorbent can be added to the purification line in order to retain the carboxylate ions released by the complexation of the metal impurities in the first bed of anion-exchange adsorbent.
It is thus possible very easily to obtain from an ordinary technical quality hydro peroxide solution, a hydrogen peroxide solution of “electronic” quality containing less than 200 ppt of each of the metal cations from groups IA to VIIA (with the exception of oxygen) and from groups IB to VIII of the table of the Periodic Classification of the Elements.
Mention
Devos Christine
Ledon Henry
Burns Doane Swecker & Mathis L.L.P.
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Langel Wayne
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