Note: Descriptions are shown in the official language in which they were submitted.
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PEROXIDE TREATMENT PROCESS
The invention relates to a process for the purification of
hydrogen peroxide and to an apparatus for production of
purified hydrogen peroxide.
Hydrogen peroxide is a clear, colourless liquid with a
slight pungent odour. It dissolves completely in water.
When used, it has minimal environmental impact because it
decomposes to only water and oxygen. Peroxide is an
efficient oxidiser and bleaching agent, which makes it
useful in many industrial processes.
Peroxide is commonly sold to industry as solutions of 35%,
50%, 60% or 70% by weight in water (by comparison,
peroxide sold in a pharmacy for domestic use is generally
3 to 5% by weight aqueous solution).
The major and fastest growing use of peroxide is bleaching
of wood pulp, in the paper and pulp industry. It is
particularly effective in the bleaching of high yield
pulps to higher brightness. High yield pulping is
becoming increasingly important in today's global economy
and a significant factor in the development of the
Australasian Pulping industry. Hydrogen peroxide is also
growing in chemical pulping and waste paper repulping.
In gold mining, peroxide is used to enhance bleaching and
to destroy excess cyanide in the extraction process.
The textile and wool industry relies on peroxide to bleach
many products.
Many chemicals and plastics are made using peroxide in the
production process.
In waste water treatment, peroxide reduces odour in
sewerage streams.
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The food industry employs peroxide to sterilise packaging
materials and to bleach certain foods.
S It is known in the prior art to produce hydrogen peroxide
by autoxidation of an organic compound such as
anthraquinones, isopropyl alcohol or hydrazobenzene.
In the case of anthraquinones such as 2-alkylanthraquinone
the process involves a preliminary step of catalytic
reduction. The anthraquinone is dissolved in an organic
solvent and is hydrogenated using a catalyts to produce
the corresponding anthraquinol which is then oxidized with
oxygen, typically simply by aerating the mixture, to form
the anthraquinone and simultaneously produce hydrogen
peroxide. The anthraquinone is commonly called the
reaction carrier or working material whereas the organic
mixture of the anthraquinone and solvent in which the
hydrogen peroxide is formed is known as the working
solution.
The hydrogen peroxide in the working solution is then
extracted with water generally in an extractor vessel.
Whilst such a process for preparing hydrogen peroxide is
efficient, the hydrogen peroxide so formed does contain
small, but significant, amounts of contaminants including
organic contaminants remaining from the autoxidation
process.
It is known in the prior art to utilise various processing
steps to improve the purity of the crude peroxide stream.
However, such processes are highly expensive and
significantly increase the cost of a new hydrogen peroxide
manufacturing plant. The presence of organic contaminants
in the hydrogen peroxide significantly reduce its
stability and poses a signif cant safety risk. Contact
between organic material and concentrated hydrogen
peroxide, particularly at hydrogen peroxide concentrations
WO9S/04702 ~ ~ 6 91 ~ 8 PCT/AU94/~S
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of 50% by weight or more, poses a serious risk of fire or
explosion. For many applicangs peroxide concentrations of
50 to 70% are desirable and are produced by vaporization
of more dilute solutions. The safety risks posed by
contamination are increased during vaporization and
severely reduce the efficiency with which vaporization can
be carried out.
Typically the quality of hydrogen peroxide is measured in
relation to pH, strength, turbidity, total carbon content,
colour, smell and general apperance, such as the presence
or otherwise of free floating material. It would be a
significant advance in the art if a hydrogen peroxide
could be produced of improved quality, but without the
attendant costs and risks associated with the prior art.
Accordingly it is an object of the present invention, to
overcome, or at least alleviate, one or more of the
difficulties related to the prior art.
Accordingly, in a first aspect of the present invention
there is provided a process for the purification of
aqueous hydrogen peroxide, which process includes
providing a source of crude hydrogen peroxide
including organic contaminants;
introducing the hydrogen peroxide into a
separation means wherein the separation means includes at
least one hydrocyclone; and
collecting a purified hydrogen peroxide product
therefrom.
The source of hydrogen peroxide may be an aqueous solution
of hydrogen peroxide from an extractor vessel. The
extractor vessel may typically be a sieve plate type
liquid extraction column. In the extractor vessel, a
distribution co-efficient in favour of the aqueous phase
allows the hydrogen peroxide to be concentrated, typically
to a concentration of approximately 25% to 45% in the
WO9S/04702 2 I 6 3 I 5 8 PCT/AU94/00~5
aqueous phase. The aqueous solution of hydrogen peroxide
may be collected from the bottom of the extractor vessel.
The aqueous solution of hydrogen peroxide may contain
small amounts of entrained working solution, including
organic contaminants, as well as other contaminants
including non-organic contaminants.
In a preferred embodiment the invention is utilized in
purification of peroxide manufactured by autoxidation,
particularly autoxidation of an anthraquinone. In this
embodiment the contaminants will generally be derived from
the working solution and may include an anthraquinone and
an organic solvent in which the anthraquinone is
preferably soluble and which solvent is typically water
immiscible. The working liquor may then be extracted with
water following the autoxidation process to provide the
crude aqueous hydrogen peroxide which is introduced to the
hydrocyclone. Typical examples of organic solvents used
in the working solution are hydrocarbons such as
distillate or kerosene.
The separation means includes a hydrocyclone. Typical
hydrocyclones are described in Australian Patent Numbers
521482 and 559530, the entire disclosures of which are
incorporated herein by reference.
The hydrocyclones may be typically conocylindrical bodies
in which the mixture to be separated is fed tangentially,
preferably with an involute inlet, under pressure to
create a vortex resulting in separation of components of
the mix via an underflow and a light phase outlet of the
hydrocyclone(s) (generally the overflow).
The hydrocyclones according to this aspect of the present
invention may be characterised by having a relatively
large length to diameter ratio (L/D), preferably in excess
of approximately 10, and a relatively small overflow
orifice to diameter ratio (Do/D) ratio, preferably less
WOg5/04702 21~ g 15 ~ PCT/AU94/00465
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than approximately 0.2, wherein L is the length of the
hydrocyclone, D is the major cyclone diameter and Do is
the orifice diameter of the port by which the lighter
contaminant is removed (ie the overflow orifice
diameter). Preferably this port is located towards the
inlet end of the hydrocyclone. More preferably L/D is at
least 15 and, although a wide range of ratios may be used
a convenient upper limit is 30. More preferred Do/D
ratios are in the range of from 0.01 to 0.1.
The light organic phase contaminants removed from the
hydrocyclone may be stored or redistributed via process
units such as vessels, pumps etc. Typically the light
organic phase flow is less than approximately 10% of the
total feed volume, more typically less than approximately
5% more preferably less than 3%. Preferably at least 0.5%
of the total feed will be light organic phase.
Such hydrocyclones are particularly useful in removal of
small residual organic materials, for example working
solution, which may be free phase or dissolved, as well as
removal of other non-organic contaminants. Such
hydrocyclone systems are particularly applicable for the
removal of small amounts of lower density material from a
continuous aqueous phase. For example, the concentration
by volume of such light contaminant material may be less
than approximately 2%, more typically less than
approximately 100 ppm by volume. Such contaminants may
further include small amounts of gas and solids present in
the aqueous phase.
It has been found that separation of contaminants using
the hydrocyclone is particularly efficient when the crude
hydrogen peroxide is introduced to the hydrocyclone at a
temperature of 20 to 50C and more preferably 30 to 50C.
Increases of as little as 10C within the range 20 to 50
can result in as much as a 25-30% improvement in
contaminant removal.
WO9S/04702 PCT/AU94/00465
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The hydrocyclones may be placed in the crude peroxide
stream at any point between the extractor outlet to the
final storage tank prior to shipment or further treatment.
The separation means preferably includes a plurality of
hydrocyclones which may be arranged in parallel, the crude
hydrogen peroxide feed being split using a manifold.
Alternatively or in addition to using hydrocyclones in
parallel two or more hydrocyclones may be arranged in
series. Two types of series are possible. In the
preferred type of series the contaminant depleted
underflow of one or more hydrocyclones, containing
primarily an aqueous phase, is fed into one or more
secondary cyclone to provide further removal of
contaminants. In the alternative type of series the
contaminant enriched overflow of one or more hydrocyclones
is fed into one or more secondary cyclones for further
separation of aqueous hydrogen peroxide from the organic
phase.
Additional process units or items of equipment may be
placed upstream, downstream, or in parallel with the
hydrocyclones to facilitate enhancement of the quality of
the hydrogen peroxide. Enhanced quality includes reduced
total carbon (TC), lower turbidity, lighter colour,
increased stability, consistency and less odour.
In a further aspect of the invention there is provided an
apparatus for treating crude aqueous hydrogen peroxide
comprising organic contaminants the apparatus including a
seive plate solvent extraction column and at least one
hydrocyclone to which the aqueous phase from the
extraction column is fed.
The present invention will now be more fully described
with reference to the accompanying drawings and examples.
It should be understood, however, that the description
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following is illustrative only and should not be taken in
any way as a restriction on the generality of the
invention described above.
Figure 1 is a flow chart illustrating a process and
apparatus for the purification of hydrogen peroxide
according to one embodiment of the present invention.
Figure 2 is a flow chart illustrating a process and
apparatus for purification of hydrogen peroxide according
to another embodiment of the invention.
Hydrogen peroxide is formed in a mainly organic mixture
commonly called a "working solution". In accordance with
Figure 1 the working solution flows into an extractor
vessel (1) via working solution inlet (2) towards the
bottom of the extractor vessel (1). In the extractor, a
distribution co-efficient in favour of the aqueous phase,
which enters towards the top (4) of the extractor vessel,
allows the hydrogen peroxide to be concentrated to
typically 25% to 45% in the aqueous phase. This
extraction of hydrogen peroxide from the working solution
into the aqueous phase is done in the extractor vessel
which is typically a sieve plate liquid extraction column.
Towards the top of the extractor vessel the working
solution, with some entrained aqueous phase but depleted
of hydrogen peroxide, leaves the extractor vessel via
working solution outlet (3).
Towards the bottom of the extractor vessel the aqueous
phase, now concentrated with hydrogen peroxide but
containing some small amounts of entrained working
solution and other contaminants, leaves the extractor
vessel via aqueous phase outlet (5). This stream is often
referred to as a "crude peroxide stream".
This crude peroxide stream is then subject to one or more
W095/04702 w~l~ 91 5 8 PCT/AU941~465
further process steps. These process steps are prior to
the crude peroxide stream being concentrated and/or
stabilised and stored ready for shipment. The aim of the
steps is to remove small residual organic material (e.g.
working solution) which may be free phase or dissolved;
and also, these steps may remove other non-organic
contaminants. The crude peroxide stream (5) is fed
preferably via a pump and/or a primary separator (6) to a
hydrocyclone t7). The crude peroxide stream (5) is fed
tangentially into the hydrocyclone (7) which has an
involute inlet and dimensions listed in Example 1 below to
produce an underflow (7a) which is an aqueous hydrogen
peroxide stream reduced in organic contaminants and an
overflow stream (7b) which is enriched in organic
contaminants. The apparatus may be provided with a line
(8) for bypassing the hydrocyclone which bypass line (8)
may include one or more parallel treatment means (9) for
separation of contaminants.
The underflow (7a), in addition to any by-pass line feed
(10), is fed to a storage vessel (11). The purified
underflow stream of the hydrocyclone (7) may be provided
with a recycle line (10) to allow recycle of a portion,
preferably 10 to 70%, of the underflow for processing with
the crude peroxide stream (5). A separation vessel (12)
is provided for receiving the enriched organic phase of
the hydrocyclone (7). The separation vessel (12) may
allow gravity separation of organic and aqueous phases and
be provided with means for recycling the aqueous phase to
the crude peroxide stream.
Referring to Figure 2 there is shown a further embodiment
of a hydrogen peroxide purification apparatus comprising
an extractor vessel (13) (as described with respect to the
extractor vessel (1) of Figure 1), a solvent scrubber (15)
for receiving crude aqueous hydrogen peroxide, a
multiplicity of hydrocyclones (16) (preferably four
hydrocyclones) arranged in parallel for receiving the
WOgS/04702 ~ 1~91 ~ 8 PCT/AU94/00465
crude aqueous phase from adjacent the base the scrubber
(lS) via transfer pump (17), organic crude recovery tank
(18) for receiving the overflow from the hydrocyclones
which overflow is enriched in the organic phase and a
recycle line (19) for enabling a portion of the underflow
of the hydrocyclones (7), which has reduced contamination,
to be recycled and admixed with the crude hydrogen
peroxide. Further downstream processing of the underflow
is provided by an aqueous hydrogen peroxide filter (20)
before the purified hydrogen peroxide is fed to a storage
tank (29). The purified hydrogen peroxide may be
concentrated in an evaporator (not shown) to provide a
hydrogen peroxide concentration of 50-70% by weight.
In the purification process the working solution
containing hydrogen peroxide generated as a result of
anthraquinone autosidation in a hydrocarbon solvent is fed
into the extractor (13) adjacent the bottom and fresh
water is introduced adjacent the top. Counter current
extraction of the peroxide into the aqueous phase results
in a crude hydrogen peroxide solution containing from 25
to 35% by weight of hydrogen peroxide which is fed from
the bottom of the extractor (13) to a counter-current
scrubber (15) adjacent the top. It is particularly
preferred that the crude hydrogen peroxide line (14) is
provided with a heat exchanger (21) which maintains a
temperature in the range of about 30 to 45C. In contrast
conventional hydrogen peroxide purification processes
generally cool the crude peroxide stream to less than
20C. The crude hydrogen peroxide line (14) may also be
provided with a valve (14a) to regulate flow.
Organic phase liquid, preferably a hydrocarbon, is
introduced to a scrubber (15) toward the bottom so that
counter current of the lighter organic phase and aqueous
phase results in partial extraction of impurities from the
aqueous phase. The aqueous hydrogen peroxide phase is fed
from adjacent the bottom of the counter current scrubber
W095/04702 PCT/AU94/00465
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(15) to hydrocyclones (16) via a pump (17). The
hydrocyclones are arranged in parallel and crude hydrogen
peroxide is introduced via manifold (22). The dimensions
of the hydrocyclones are preferably as described in
Example 1 below. The overflows of the hydrocyclones (16)
are combined in overflow outlet manifold (23) and fed to
organic crude recovery tank (18) which allows the aqueous
and organic phases to separate. The aqueous phase which
separates in the organic crude recovery tank (18) may be
recycled from adjacent the base of the tank (18) via pump
(24) and valve (25) to be mixed with the crude aqueous
hydrogen peroxide in crude hydrogen peroxide line (14).
The organic phase which separates in the organic crude
recovery tank (18) may be delivered via an overflow (26)
for reuse or further processing.
The underflows of the hydrocyclones (16) are combined in
underflow outlet manifold (27) and are fed to a filter
unit (20) to remove at least part of any remaining traces
of organic phase in the aqueous hydrogen peroxide. The
filter unit (20) preferably includes glass wound filter
elements. At least part of the underflow, preferably from
10 to 70%, from the hydrocyclones is recycled via recycle
line (19) and combined with the crude aqueous hydrogen
peroxide transferred from the solvent scrubber (15). The
inclusion of a recycle has been found to significantly
increase the efficiency of contaminant removal.
The traces of oil removed at the filter (20) may be
transferred to the organic crude recovery tank (18) via
transfer time (28). The purified aqueous hydrogen
peroxide has a concentration of about 25 to 35~ and may be
fed to a storage tank and/or vaporized to further
concentrate the hydrogen peroxide. The use of the
hydrocyclones (16) significantly improve product quality
by increasing the efficiency of removal of organic
contaminants. As a result the product has high stability
and concentration of the hydrogen peroxide may safely be
W095/04702 ~9 1~ PCT/AU94/00~5
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carried out by vaporization of the purified product to
provide a concentration of, for example from 50 to 70% by
weight.
5 The removal of contaminants improve the quality
performance and marketability of the manufactured hydrogen
peroxide. Some of the typical measures used to assess the
quality of hydrogen peroxide include, pH, strength,
turbidity, total carbon content, colour, smell and general
appearance such as the presence or otherwise of free
floating material.
EXAMPLE 1
Test HYdrocYclone
The test hydrocyclone had the following dimensions:
D = 38 mm = Major hydrocyclone diameter
Do = 1.5 mm = Orifices diameter for light phase unit
L = 1016 mm = Hydrocyclone length
Therefore
L = 26.7 Do = 0.039
D D
Test Confiquration
This configuration was as depicted in Figure 1 and there
was no process units other than pump (6) between the feed
to the hydrocyclone and the crude peroxide outlet (5).
Bypass line (8) and recycle line (10) were not used so
that all flow passed directly through the hydrocyclone
(7). The feed strength was approximately 35% with the
temperature of about 45C.
Typical results were:
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Feed inlet to hydrocyclone : 16. 4 NTU turbidity
211 mg/l total carbon
Treated outlet of hydrocarbon : 2.1 NTU turbidity
192 mg/l total carbon (TC)
The dissolved Total Carbon (TC) was 176 mg/l.
The hydrocyclone was operated with a light phase flow of
less than 3% of the total feed flow to the hydrocyclone.
The process according to the present invention thus
results in a reduction in total carbon (TC) of
approximately 54%.
EXAMPLES 2 AND 3
Test HYdrocYclones
Primary dimensions as for the test program.
Test Confiquration
For this test configuration there was 3 main process units
upstream of the hydrocyclone.
There was a packed solvent scrubbing vessel of the type
described with respect to Figure 2 [solvent scrubber
(15)]; a further vessel to allow gravity separation of
organic solvent immediately downstream of the solvent
scrubber and a process pump to feed the hydrocyclone and
final filter.
Typical results were:
Feed inlet to hydrocyclone : 45.5 turbidity (NTU)
220 mg/l total carbon
Treated outlet at 9 typically : 0.7 turbidity (NTU)
163 mg/l total carbon
wo gs/ 470z 216 ~ 15 8 ~CTIAU941~0465
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The dissolved TC was 145 mg/l.
The process according to the present invention thus
results in a reduction in total carbon (TC) of
approximately 76~.
Finally, it is to be understood that various other
modifications and/or alterations may be made without
departing from the spirit of the present invention as
outlined herein.
