Note: Descriptions are shown in the official language in which they were submitted.
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Procedure for cleaning filter
The present invention relates to a procedure for cleaning
a filter, and particularly for a sinter used in filtering
metal catalyst suspension. The present invention is par-
ticularly well suited for cleaning a filter unit consis-
ting of a plurality of sinters and contaminated by mat-
ter, from catalytic hydrogenation of anthraquinone or a
derivative thereof, i.e. for the purification treatment
of the primary filter unit of a hydrogen peroxide plant.
Hydrogen peroxide can, as is known in the art,
be produced by the so-called anthraquinone process. In
said procedure, an anthraquinone derivative is dissolved
in an organic solvent consisting of one or more com-
ponents. A solution thus produced, called generally a
working solution, is first conducted into a hydrogenation
step. At the hydrogenation step part of the anthraquinone
derivative is with the aid of hydrogen gas reduced in the
presence of a catalyst to the corresponding anthra~uinone
derivative. Prior to the next step, i.e. oxidation, the
catalyst is separated from the working solution. The sep-
aration of the catalyst is most often carried out by fil-
tering. At the oxidation step the anthraquinone deriva-
tive is oxidized with air or oxygen, whereby it reverses
to the state preceding hydrogenation, i.e., to the an-
thraquinone derivative. At the same time, hydrogen pero-
xide is produced. The hydrogen peroxide thus produced is
removed from the working solution by extracting it with
water. After the extraction the working solution is dried
and conducted back to the hydrogenation. The aqueous sol-
ution of the hydrogen pero~ide obtained at the extraction
step is purified and concentrated (Kirk-Othmer, En-
cyclopedia of Chemical Technology, 3. painos, Vol. 13,
pages 16-21).
For separating a suspension catalyst taking place by fil-
tering, for instance ceramic or metal sinter filters
(Chemical Processing, January 1982, page 24), as well as
carbon filters (DE-PS-1 272 292) can be used. In con-
tinuous action filtering, the filters become gradually
blocked in spite of the backflushing systems used.
Thus, the object of the present invention is to provide a
procedure for cleaning a metallic or ceramic sinter used
for filtering a metal catalyst suspension of a finely
powdered metal catalyst entered into its pores more ef-
ficiently than before.
Cleaning metal sinter filters takes in general place so
that they are removed from the cover plates of a primary
filter unit and taken into wash basins in which they are
submerged separately into washing solutions. The washing
process comprises several manual steps and is therefore
both cumbersome and time consuming.
Another purpose of the present invention is therefore to
provide a procedure for cleaning a filter unit consisting
of a plurality of sinters and contaminated by matter,
from catalytic hydrogenation of anthraquinone or a deri-
vative thereof, without detaching individual sinters from
the cover plate of the filter unit. Therefore, the inven-
tion is well appropriate for cleaning filters used for
separating noble metal catalysts, and in the production
process of hydrogen peroxide especially appropriate for
cleaning filters used for filtering noble metal catal-
ysts.
The main characteristic features become obvious in the
accompanying claims.
In the procedure of the invention a metallic or ceramic
porous sinter is treated with an aqueous solution of hyd-
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rogen peroxide for displacing the metal catalyst present
in the pores of the sinter with the aid of a gas gener-
ated by the decomposition of the hydrogen peroxide caused
by the metal catalyst until the formation of gas ceases
indicating that no substantial quantities of the metal
catalyst are left in the sinter.
The procedure of the present invention is therefore high-
ly selective because the gas generation caused by the
decomposition of the hydrogen peroxide is concentrated
particularly into those pores in the filter which contain
said metal catalyst. The forming gas "blows" efficiently
the finely powdered metal catalyst out from the pores of
the sinter. An advantage of the procedure is that the
formation of gas ceases when no significant quantities
of the metal catalyst are left in the pores of the sin-
ter, which easily leads to the conclusion that the sinter
is clean enough.
The procedure of the invention is especially appropriate
for cleaning a filter unit consisting of a plurality of
sinters, and contaminated by matter, from catalytic hyd-
rogenation of anthraquinone or a derivative thereof,
whereby the individual sinters need no longer be detached
from the cover plate of the primary filter unit. Here-
with, the treatment of separate sinters is avoided and at
the same time, the risk is minimized that individual sin-
ters are damaged. With the present design, also the need
to seal filters diminishes substantially. By the aid of
the invention, also such advantageous design, from the
point of view of work hygiene, is obtained when the in-
dividual sinters need no longer be detached from the fil-
ter unit.
According to the invention, the filter unit flushed with
a solvent used for dissloving anthraquinone or a derivat-
ive thereof and released thereafter from the solvent by
steaming is treated with 5 to 50 per cent aqueous sol-
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ution of hydrogen peroxide so long and so many times that
substantially no more gas generates, whereafter the fil-
ter unit is washed with water and dried at the end.
A particularly preferable measure is to treat the filter
unit with diluted, 5 to 15 per cent, for instance 10 per
cent, aqueous solution of hydrogen peroxide.
The filter unit washed with water may once more be washed
with a warm aqueous solution of an acid dissolving the
metal catalyst, prior to renewed hydrogen peroxide treat-
ment, water washing and final drying for a more thorough
removal of the metal catalyst from the sinters of the
filter unit. The purification efficiency may further be
intensified by washing the filter unit after the solvent
flushing and steaming with a warm alkaline aqueous sol-
ution prior to the actual hydrogen peroxide treatment.
The cleaning treatment may further be intensified by
treating the ilter unit prior to the washing with the
warm alkaline aqueous solution with an aqueous solution
of hydrogen peroxide and by washing with water there-
after.
For the aqueous solution of an acid, a 10 to 50 per cent
aqueous solution of nitric acid at 20 to 800C temperature
can be used. Particularly advantageously a 25 to 35 per
cent, e.g. 30~ aqueous solution of nitric acid is used,
this being at 60 to 70C temperature, e.g. about 65C.
For the aqueous solution of an alkaline, a 1 to 20 per
cent, preferably about 5%, aqueous solution of sodium
hydroxide at a temperature of over 20C, preferably 70 to
90C, for instance about 80C, can be used.
In the present context all percentages are indicated as
volumetric percentages, unless otherwise noted.
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The procedure of the invention is especially appropriate
for cleaning ceramic or metallic porous sinters, said
sinters being used for filtering noble metal catalysts,
particularly Pd black.
The US patent publication print No 4,113,613 discloses
that it is known in the art to condition fixed-bed fil-
ters made from granular substance, such as sand filters,
by generating gas bubbles catalytically in the bed. The
gas bubbles catch the granular filter material, whereby
the filter becomes more permeable in the manner of a dry
filter. Said reference has no mention concerning cleaning
of sinters, instead, it does give a mention of improving
the filter characteristics of a bed consisting of gran-
ular matter.
The invention is described below in detail, reference
`~ being made to the accompanying drawing presenting a
schematical, cross-sectional vertical image of a washing
equipment appropriate for implementing the procedure of
the invention.
In the accompanying figure is shown a washing unit for
cleaning metallic primary filters of a hydrogen peroxide
plant. The actual washing tank is generally indicated by
reference numaral 1, and it consists of an upper part 4
and a lower part 5, wherebetween the cover 2 of the fil-
ter unit with sinters 3 is tightly disposable. The metal
sinters 3 are elongated filter elements closed at the
lower ends, their open upper end being tightly connected
to an aperture in the cover 2 located at an equivalent
point so that the streams between the upper and the lower
side of the cover pass through said apertures and through
the walls of the sinters 3 joined thereto.
To the upper part 4 of the tank 1 drying air is conducted
in a tube 4, whereto a heat exchanger 12 has been at-
tached for heating the dr~ing air with the aid of steam
13', this being let out from the heat exchanger 12 as
condensate 15'. To the upper part 4, steam can be also
conducted directly from the pipeline 13. Reference num-
eral 17 refers to an outlet pipe connected to the upper
part 4. In addition, an aqueous solution of hydrogen per-
oxide is conducted from the container 6 along the tube
16. Thus the aqueous solution of hydrogen peroxide flows
from the upper part 4 into the sinters to their so-called
clean side, and through the sinters into the lower part
5, that is, to the so-called dirty side of the sinters 3,
in other words, to the opposite direction than the metal-
lic catalyst suspension had flown during the filtering of
the metal catalyst in the catalytic hydrogenation of an-
thraquinone or a derivative thereof. This assists in a
particularly effective manner the release of the metal
catalyst caught in the pores of the sinters 3 because it
is easier to remove the metal catalyst in the direction
from which it came. Viz., when hydrogen peroxide decom-
poses, water and oxygen gas are produced, increasing the
pressure on the clean side of the sinters to the extent
that differential pressure is formed between the clean
side and the dirty side of the sinters 3, forcing the
metal catalyst caught in the pores of the filter elements
3 out from the pores in the same direction as they had
entered said pores.
The washing unit comprises further containers for aqueous
solution of nitric acid 7, aqueous solution of lye alka-
line 8 and water 9, these being alternately supplied
along the tube 11 to the lower part 5 of the washing con-
tainer 1, whereby also the pipeline 11 is provided with a
heat exchanger 12 for heating said flows indirectly with
the aid of steam 13.
In the upper part of the lower part 5 of the washing con-
tainer 1 is also connected a discharge pipe 18 and a pipe
20 for letting out washing solutions from the lower part
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5 as an overflow in order to return these into their res-
pective containers 6,7,8 or 9 through a discharge pipe 19
connected to the bottom of the lower part 5 of the wash-
ing container 1 and the filter 10 joined to each con-
tainer 6,7,8 and 9. The pore size of the filters 10 must
be smaller than the pore size of the metal sinters 3 for
preventing solid impurities from entering the containers
6,7,8 and 9. It goes without saying that said fresh sol-
ution is added into the containers 6,7,8,9 if needed.
The invention is described also below in detail with the
aid of examples.
Example 1
As shown in the figure, the so-called short washing pro-
gramme was carried out in the washing unit of a hydrogen
peroxide plantO
The cover 2 of one filter unit with the sinters 3 (Pall
Filters PSS, Pall Corporation, Great Britain) was lifted
into a washing tank 1 after the filter unit had been
backflushed with a solvent component (aromatic hydrocar-
bon) of a working solution. In the upper part 4 of the
washing tank 1, i.e. the so-called clean side, filtered
steam 13 (aty 2 to 2.5 aty 135 to 140C) was conducted,
the steam was allowed to exit through a breather tube 18
of the dirty side, while a small amount of condensate was
left in the washing tank 1. After the steaming, preheated
ion exchanged pure water 9 was pumped through a heat ex-
changer 12 (65C) and through a tube 11 to the dirty side
of the filter element 3 for about 15 minutes. From the
dirty side the water was conducted from the lower part 5
of the washing tank 1 as overflow 20 through the filter
10 back to the water tank 9. Next, for about 20 minutes
diluted (10%) H202) aqueous solution of hydrogen peroxide
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at room temperature (20C) was pumped through the filter
elements 3 from the clean side to the dirty side from the
tank 6. The hydrogen peroxide treatment was followed by
flushing with water (as before, 65C, 15 mins). Prior to
the final drying the sinters 3 were heated by conducting
steam 13 on their clean side for about 5 mins, the uncon-
densed steam was conducted into the breather tube 18 and
the condensate at the end of the steaming into the water
tank 9. Finally, the drying of the sinters 3 was carried
out by conducting filtered, hot (105C) pressurized air
14 on their clean side for about 20 mins, and the air was
discharged through the breather tube 18 of the dirty
side.
Example 2
As shown in Fig. 1, the so-called medium length washing
programme was carried out in the washing unit of a hydro-
gen peroxide plant.
The cover plate 2 of one filter unit with the sinters 3
(Pall Filter PSS) was lifted into the washing tank 1.
Prior to the transfer, the sinters 3 had been flushed
with an organic solvent. First, into the upper part 4 of
the washing tank l, to the so-called clean side, steam 13
(2 to 2.5 aty 135 to 140C) was conducted, the steam was
allowed to exit through the breather tube 18 of the dirty
side, and the little amount of the condensate thus gener-
ated was left in the washing tank 1. Subsequent to the
steaming, pure, ion exchanged water 9 was pumped through
a heat transfer means 12 (65c) on the dirty side of the
sinters 3 for about 15 mins. From the dirty side of the
washing tank 1 the water was conducted as overflow 20
through the filter 10 back into the water tank 9. Next,
for about 20 minutes diiuted (10%) aqueous solution of
hydrogen peroxide 6 at room temperature (20C) was pumped
through the sinters 3 from the clean side to the dirty
side. The hydrogen peroxide treatment was followed by
flushing with water (as before, 65C, 15 mins). After
flushing with water, preheated nitric acid solution 7
(30%) was pumped through the heat transfer means 12 into
the washing tank 1 at about 65C, again on the dirty side
of the sinters 3. From the dirty side of the washing tank
1 the solution of nitric acid was conducted as overflow
20 through the filter 10 back into the nitric acid tank
7. After the acid treatment, flushing with water (65~,
lS mins) was carried out. Prior to the final drying, the
sinters 3 were heated by conducting steam 13 on their
clean side for about 5 mins, the uncondensed steam being
conducted into the breather tube 18, and the condensate
at the end of the steaming step into the water tank 9.
Finally, the drying of the sinters 2 was carried out by
conducting filtered, hot (105C) pressurized air 14 on
their clean side for about 20 mins, and the air exited
through the breather tube 18 of the dirty side.
~mE~
As shown in the figure, a so-called long washing pro-
gramme was carried out in the washing unit of the hydro-
gen peroxide plant.
The cover plate 2 of one filter unit with the sinters 3
(Pall Filters PSS) was lifted into the washing tank 1. In
the upper part 4 of the washing tank l, on the so-called
clean side, filtered steam 13 (2 to 2.5 aty, 135 to
140C) was conducted, the steam being allowed to exit
through the breather tube 18 of the dirty side, and a
small amount of the condensate thus produced was left in
the washing tank 1. Preheated lye solution 8 (5% NaOH)
was pumped through a heat transfer means 12 at about 80C
along the tube 11 into the washing tank for about 30
minutes. From the washing tank 1 the lye exited as over-
flow 20 through the filter 10 back into the lye container
8. The catalyst released during the steaming and the lye
wash was separated with the filter 10 of the lye cycle.
After the lye wash, the solution was discharged from the
washing tank through a tube 19. After the lye wash, pure,
ion exchanged water 9 was pumped through the heat trans-
fer unit 12 at about 65C to the dirty side of the sin-
ters for about 15 mins. From the dirty side the water was
conducted as overflow 20 through the filter 10 back into
the water tank 9. Next, for about 20 minutes diluted
(10%), aqueous hydrogen peroxide solution 6 at room tem-
perature (20C) was pumped through the sinters 3 from the
clean side to the dirty side. The hydrogen peroxide
treatment was followed by flushing with water (as before,
65C, 15 mins). Next, preheated nitric acid solution 7
(30%) was pumped through the heat transfer unit 12 and
the tube 11 into the washing tank at about 65C, again on
the dirty side of the sinters 3. From the dirty side of
the washing tank 1, the nitric acid solution was con-
ducted as overflow 20 through the filter 10 back into the
nitric acid container 7. After the acid treatment, flush-
ing with water (65OC, 15 mins), hydrogen peroxide treat-
ment (10% H2O2, 20C, 20 mins) and flushing with water
(65C, 15 mins) were carried out. Prior to the final dry-
ing, the sinters 3 were heated by conducting steam 13 on
their clean sides for about 5 mins, the uncondensed steam
being conducted into the breather tube 18, and the con-
densate after terminating the steaming into the water
tank 9. Finally, the drying of the sinters 3 was carried
out by conducting filtered, hot (105C) pressurized air
on their clean side for about ~0 minutes, and the air
exited through the breather tube 18 of the dirty side.
Using the washing programmes of the present invention, a
particularly successful end result is obtained compared
with a treatment in which the filter unit is merely
treated with the aqueous hydrogen peroxide solution.
