Method of removing organic impurities from aqueous solution of hydrogen peroxide

A method of removing organic impurities from an aqueous solution of hydrogen peroxide, which comprises bringing an aqueous solution of hydrogen peroxide containing organic impurities into contact with a halogen-containing porous resin having a true specific gravity in the wet state of 1.1 to 1.3.

This invention relates to a method of purifying hydrogen peroxide by 
removing organic impurities contained in an aqueous solution of hydrogen 
peroxide. 
Hydrogen peroxide is extensively used, for example, for bleaching and 
chemical polishing. In recent years, its use in the fields of washing 
silicon wafers in the production of semiconductors has increased, and with 
it, there has been a demand for hydrogen peroxide having an extremely high 
purity. 
Presently, a method involving autoxidation is by far most used for hydrogen 
peroxide production. Hydrogen peroxide produced by this method contains 
tiny amounts of organic impurities. Usually, an aqueous solution of 
hydrogen peroxide in a practical concentration of 10 to 70% by weight 
contains 20 to several hundred milligrams/liter of organic impurities as 
the total amount of organic carbon. 
A method known heretofore for removing these impurities from an aqueous 
solution of hydrogen peroxide comprises treating hydrogen peroxide 
containing organic impurities at a temperature of not more than 40.degree. 
C. with a resin having a network molecular structure and containing no ion 
exchange group which is obtained by polymerizing styrene and crosslinking 
the product with divinylbenzene (see Japanese Patent Publication No. 
26095/1971 and U.S. Pat. No. 3,294,488). 
Industrially, however, the use of the conventional adsorbent resin in an 
attempt to remove organic impurities from an aqueous solution of hydrogen 
peroxide gives rise to various problems. For example, since this adsorbent 
resin has a small adsorptive capacity, it must be very often subjected to 
regeneration treatment during use. This is uneconomical, and troublesome 
in operation. In the treatment of removing the organic impurities on an 
industrial scale, it is the general practice to employ a column procedure 
having excellent operability and a high removing efficiency. When the 
above conventional resin is packed in a column and an aqueous solution of 
hydrogen peroxide having a practical concentration of 10 to 70% by weight 
is passed through it as a downward flow, the resin comes afloat in the 
upper portion of the column because the resin has too low a specific 
gravity. As a result, a shortcut flow occurs and the removing efficiency 
is drastically reduced. By passing the aqueous solution of hydrogen 
peroxide as an upward flow, it is possible to inhibit occurrence of short 
circuits to some extent, and increase the removing efficiency. This method 
also has the disadvantage that bubbles occurring at the time of passing 
the aqueous hydrogen peroxide solution are difficult to remove from the 
floating resin in the upper portion of the column. 
It is an object of this invention to provide a novel method of removing 
organic impurities from an aqueous solution of hydrogen peroxide. 
Another object of this invention is to provide a simple and convenient 
method of removing organic impurities from an aqueous solution of hydrogen 
peroxide with a high removing efficiency. 
Still another object of this invention is to provide a method of removing 
organic impurities from an aqueous solution of hydrogen peroxide by 
adsorption with an adsorbent resin having a high specific gravity. 
Further objects of this invention along with its advantages will become 
apparent from the following description. 
According to this invention, these objects and advantages of the invention 
are achieved by a method of removing organic impurities from an aqueous 
solution of hydrogen peroxide, which comprises bringing an aqueous 
solution of hydrogen peroxide containing organic impurities into contact 
with a halogen-containing porous resin having a true specific gravity in 
the wet state of 1.1 to 1.3. 
The resin used in the method of this invention is a halogen-containing 
porous resin which has a true specific gravity of 1.1 to 1.3 in the wet 
state. 
The true specific gravity of the resin in the wet state is measured by a 
pycnometer in accordance with the following method. Deionized water is 
filled in the pycnometer to an indicator line, and the weight (Pw in 
grams) of the water is measured. The pycnometer is then dried, and a 
sample of the resin is accurately weighed (W" in grams) into the dried 
pycnometer. Then, deionized water is filled in this pycnometer to the 
indicator line, and the weight (Pwr in grams) of the water and resin is 
measured. 
The true specific gravity D of the resin in the wet state is calculated in 
accordance with the following equation. 
EQU D=W"/Vw 
where 
W" is the weight (grams) of the resin whose specific gravity D is to be 
measured, and 
Vw is the volume of water which the resin has displaced and is calculated 
from the following equation 
EQU Vw=1/dw(Pw+W"-Pwr) 
in which dw is the density of deionized water, Pw is the weight of 
deionized water, and Pwr is the weight of the resin and water. 
Preferably, the resin used in this invention has a true specific gravity D 
in the wet state of 1.1 to 1.2. Desirably, its true specific gravity in 
the wet state is higher than the specific gravity of the aqueous hydrogen 
peroxide solution to be treated. If, however, this true specific gravity 
of the resin exceeds 1.3, its adsorptive ability generally decreases 
greatly, and liberation of halogen-containing impurities from the resin 
increases greatly. 
The halogen-containing porous resin used in this invention may contain 
halogen in an amount of preferably about 10 to about 40% by weight, more 
preferably 25 to 40% by weight, based on the dry weight of the resin. 
The halogen-containing porous resin has continuous open pores, and its 
porosity corresponds to a specific surface area, measured by the BHT 
method (N.sub.2), of about 200 to about 600 m.sup.2 /g, preferably 400 to 
600 m.sup.2 /g, based on the dry weight of the resin. The continuous open 
pores show a pore volume (dry base), determined by the mercury penetration 
method, of about 0.3 to about 1.0 ml/g. 
Advantageously, the halogen-containing porous resin is used in the form of 
particles having an average particle diameter of about 0.1 to 0.5 mm in 
the method of this invention. The average particle diameter, as used 
herein, denotes the size of openings of a sieve which permit 10% of the 
entire resin to pass through the openings and 90% of the resin to be left 
on the sieve. 
Examples of the halogen-containing porous resin which can be suitably used 
in the invention include halogenation products of crosslinked polymers of 
aromatic monovinyl monomers and aromatic polyvinyl monomers, crosslinked 
polymers of halogenated aromatic monovinyl monomers and aromatic polyvinyl 
monomers, and crosslinked polymers of halogenated aromatic monovinyl 
monomers, aromatic monovinyl monomers and aromatic polyvinyl monomers. 
Styrene and vinyltoluene, for example, are suitably used as the aromatic 
monovinyl monomers. Examples of suitable aromatic polyvinyl monomes are 
divinylbenzene and trivinylbenzene. Examples of suitable halogenated 
aromatic monovinyl monomers are monochlorostyrene and monobromostyrene. 
Illustrative of suitable halogenated products of crosslinked polymers of 
aromatic vinyl monomers and aromatic polyvinyl monomers are, for example, 
chlorinated or brominated products of styrene/divinylbenzene copolymer, 
styrene/trivinylbenzene copolymer, and vinyltoluene/divinylbenzene 
copolymer. Chlorination or bromination may be carried out, for example, by 
reacting the non-halogenated copolymers with molecular chlorine or 
molecular bromine in the presence of a catalyst such as ferric chloride or 
boron fluoride. 
In the method of this invention, a halogenated product of 
styrene/divinylbenzene copolymer is particularly suitably used as the 
halogen-containing porous resin. 
Such a resin is also commercially available For example, a resin obtainable 
under the tradename "SEPABEADS SP207" is a brominated copolymer of styrene 
and vinylbenzene which has a specific gravity of about 1.2. 
The method of this invention is usually practiced by packing particles of 
the halogenated porous resin in a column, and passing an aqueous solution 
of hydrogen peroxide containing organic impurities through the column 
thereby to contact the resin with the aqueous hydrogen peroxide solution. 
The aqueous solution of hydrogen peroxide containing organic impurities may 
have a hydrogen peroxide concentration of about 10% to about 70% by 
weight, or contain organic impurities in a concentration of up to about 
500 mg/liter as the total amount of organic carbon. 
According to the method of this invention, the aqueous solution of hydrogen 
peroxide containing organic impurities may be passed as a downward flow 
through a column packed with the halogen-containing porous resin. Hence, 
the organic impurities can be efficiently removed while maintaining the 
resin in the most closely packed state during the passing of the aqueous 
hydrogen peroxide solution. Any bubbles which may occur by chance in the 
column during passing of the hydrogen peroxide solution can be rapidly 
removed from the resin layer. Accordingly, the treatment of removing the 
organic impurities can be carried out by passing the aqueous hydrogen 
peroxide solution in a stable condition without giving rise to problems 
such as the occurrence of a shortcut flow and the aggravation of the state 
of packing of the resin by bubbles. In addition, the porous adsorbent 
resins used in this invention have markedly increased adsorptive capacity 
as compared with conventional resins. For example, when used to treat the 
aqueous solution of hydrogen peroxide in an amount 1000 times the amount 
of the resin, they still retain a sufficient removing ability. The method 
of this invention, therefore, is very effective for purifying an aqueous 
solution of hydrogen peroxide by removing organic impurities therefrom in 
an industrial operation.

The following examples illustrate the present invention more specifically 
EXAMPLE 1 
Fifty milliliters of SEPABEADS SP207 (a tradename for a brominated 
styrene/divinylbenzene crosslinked copolymer made by Mitsubishi Chemical 
Industry Co., Ltd.) having a true specific gravity in the wet state of 
1.2, a halogen content of 34% by weight, a specific surface area of 400 
m.sup.2 /g, a pore volume of 0.5 ml/g and an average particle diameter of 
0.3 mm was packed in a column having an inside diameter of 10 mm and a 
length of 30 cm. Fifty liters of a 31% by weight aqueous solution of crude 
hydrogen peroxide containing 40 mg/liter, as the total amount of organic 
carbon, of organic impurities was passed through the column as a downward 
flow at a space velocity of 100 hr.sup.-1. During passing of the hydrogen 
peroxide solution, no occurrence of a shortcut flow was observed. Any 
bubbles that formed escaped rapidly from the upper or lower portion of the 
packed resin layer. The effect of removing the organic impurities was such 
that the total amount of organic carbon in the hydrogen peroxide solution 
was 40 mg/liter before the treatment and 5 mg/liter after the treatment. 
COMATIVE EXAMPLE 1 
Example 1 was repeated except that commercial AMBERLITE XAD-2 (made by Rohm 
& Haas Co.; specific gravity 1.0) was used as the porous adsorbent resin. 
During passing of the hydrogen peroxide solution, short circuits formed. 
The removing effect was such that the total amount of organic carbon in 
the aqueous solution of hydrogen peroxide was 40 mg/liter before the 
treatment and 20 mg/liter after the treatment. 
COMATIVE EXAMPLE 2 
Comparative Example 1 was repeated except that the aqueous solution of 
hydrogen peroxide was passed as an upward flow. The state of passing the 
solution was good in the initial stage of the operation. With the passage 
of time, however, bubbles formed and gathered in the resin layer afloat in 
the upper portion of the column to increase resistance, and stable 
treatment became difficult. The removing effect was such that the total 
amount of organic carbon in the aqueous solution of hydrogen peroxide was 
40 mg/liter before the treatment and 15 mg/liter after the treatment. 
EXAMPLE 2 
A resin used in this invention (SEPABEADS SP207) and a conventional resin 
(AMBERLITE XAD-2) were compared in adsorbing amount in the batch method. 
Five milliliters of each resin and 5 liters of a 31% by weight aqueous 
solution of crude hydrogen peroxide were put in a 10-liter polyethylene 
container, and shaken for 12 hours. The resin was separated by filtration, 
and the total amount (mg/liter) of organic carbon in the treated hydrogen 
peroxide solution was measured. For SEPABEADS SP207, it was 40 mg/liter 
before the treatment and 8 mg/liter after the treatment, whereas for 
AMBERLITE XAD-2 it was 40 mg/liter before the treatment and 25 mg/liter 
after the treatment.