Note: Descriptions are shown in the official language in which they were submitted.
2 ~ ~ rrj r~
OESTE, Franz Dietrich
Steibergstr. 4
D-6309 Munzenberg 2
Method and apparatus for removing undesirable chemical substances
from gases, exhaust gases, vapors, and ~rines.
The present invention relates to a method and apparatus for
purifying gases, exhaust gases, vapors, and brines, which are
contaminated with undesirable chemical substances or contain high
concentrations of these substances, by means of photocatalytic
reactions occurring on the surface of catalysts.
The catalysts are situated on catalyst carriers in a fixed bed or
in a fluidized bed. In fluidized beds, the catalysts themselves
can serve as catalyst carriers. The substrates to be purified are
fed through a closed system which contains the catalyst carriers
and catalysts.
In the fixed-bed catalytic process, the catalyst carrier/catalyst
system continuously or discontinuously passes through a washing
zone to remove the generated mineralization products.
The reaction is induced by shortwave photons of wavelengths
between 250 and 400 nm.
Endothermic chemical reactions require energy. Energy can be
supplied in numerous ways. Frequently, photons of various
wavelengths are employed.
Since these reactions occur at relatively low temperatures,
catalysts are added to accelerate the reaction.
In the following, this combination of inducing chemical reactions
by photons and increasing the speed of reactions by catalysts will
be referred to as photocatalysis.
Photocatalyzed chemical reactions have been the sub~ect of
increasing attention for some time. Applications have been sought
for these reactions in the area of environmen~al protection.
,
,, . ,
~,
- "~. , '~ ' .
... ..
'.` ' .. ~ :
- 2 - 2~7~
In Environmental Sci. Technol. Vol. 17, No. 10 (1983) 828-31, for
example, a reaction is described in which chloroform is degraded
in an aqueous suspension of titanium dioxide by photoassisted,
heterogeneous catalysis.
Chloroform is a main by-product occurring in the disinfecting
chlorine treatment of drinking water and also, for example, water
in swimming pools.
Chloroform is ascribed carcinogenic characteristics.
This method is applicable ~o aqueous suspensions with high
particle content, known as slurries. A disadvantage of this method
is the production of hydrochloric acid, which must be removed from
the system.
European Patent Application 89100265.1 discloses a method and
apparatus for the removal of hydrogen sulfide from exhaust gases
using a titanium dioxide catalyst applied on the surface of a
honeycomb support of activated charcoal, and ultraviolet
radiation.
The activated charcoal adsorbs odorous compounds, such as H2S and
scatoles, which are degraded by ultraviolet light. The method is a
selective method and has the disadvantage that only part of the
total surface can be utilized for the reaction.
In DOS 40 23 995.0, a method is disclosed in which pollutants are
photocatalytically mineralized by a fixed-bed catalyst which is
moved relative to the photon source.
Compared to other methods for the destruction of pollutants, such
as incineration, this method has the advantage that it does not
create additional environmental pollutants. These occur in
incineration when auxiliary fuel is required, which usually
results in the production of carbon dioxide.
The method described in the cited DOS patent does not require
auxiliary fuel, even when the pollutant occurs in v~ry low
concentrations, and is carried out at relatively low temperatures.
Liquid or solid mineralization products such as phosphoric and
arsenic acid, however, can accumulate on the photocatalyst if
pollutants are continually employed which, in addition to carbon,
hydrogen, oxygen, and nitrogen, contain, e. g., halogens, sulfur,
phosphorus, or arsenic, as well as pollutants and other wastes
~' ,
.: , : ;
2 ~
3 --
consisting solely of these latter elements. The low reaction
temperature, generally below 50C, does not allow these substances
to evaporate. As a result, the photocatalytic function is
increasingly inhibited, and the reaction finally s~ops completely.
There are several known methods for removing pollutants and
contaminants from exhaust gases and other media in which they are
undesirable.
These include purely physical methods such as adsorp~ion or
absorption, or purely chemical methods such as chemisorption or
incineration.
These methods, however, are frequently unsuitable for minerali~ing
or removing complicated chemical compounds, such as sulfur
hexafluoride, by economically or ecologically acceptable means.
These methods have other disadvantages as well. Physical sorption
methods are limited by sorbent capacity. The loaded sorbent must
either be disposed of, frequently as hazardous waste, or be
desorbed, a process requiring large amounts of energy.
The alternative incineration methods, on the other hand,
frequently lead to high expenditures for cleaning the exhaust
gases of the pollutants and of the auxiliary fuel. The normally
high incineration temperatures result in extremely high energy
expenditures if the incineration warmth is not utilized.
All of the stated methods and apparatus in the art have certain
disadvantages in their scope of application, service life, and the
resulting total space-time yield, significantly reducing their
cost-effectiveness.
Taking the shortcomings of other methods into consideration, it is
the object of the present invention to provide a method and
apparatus for carrying out the invention which circumvent the
stated disadvantages, are more universally applicable, allow the
resulting products to be easily removed from the system, and allow
the mineralization of even difficult chemical substances, such as
inert halogen-carbon compounds, halogenated hydrocarbons, or SF6.
The object of the present invention is realized by a method for
the purification of gases, exhaust gases, vapors, and brines,
`, , '. . : ''
' ' ' ' ' , ~ ' " '
_ 4 _ 2~
contaminated with or containing undesirable chemical substances,
by means of photocatalytic reactions occurring on the surface of
catalysts, wherein the substrate to be purified is fed through a
physically closed system consisting of:
a) a catalyst carrier with a high specific surface relative to the
material used, which is long-term resistant to chemical corrosion
and shortwave light, and which shows the mechanical stability
needed for mobile mechanical parts;
b) a catalyst applied to the catalyst carrier and consisting of at
least one oxide and/or mixoxide with semiconductor behaviors
mixed and/or loaded with a metal of the platinum series of the
VIII group of the periodic table of chemical elements;
c) a catalyst applied to the catalyst carrier and consisting of at
least one element of the lanthanides, actinides,and the IIIb group
of the periodic table of chemical elements;
d) at least one source of shortwave light of wavelength from 250
to 400 nm, as a photon source;
e) at least one washing zone for the catalyst carrier in
accordance with a), on which catalysts are applied in accordance
with b) and c), through which the catalyst carrier is transported
and treated with polar solvents.
The catalyst carriers consist of mats, knitted or comparable
wovens or nonwovens, preferably in packets of stainless steel,
titanium, tantalum, niobium, zirconium, hafnium, or metals of the
VIII group of the periodic table of chemical elements, such as
palladium or platinum. The surface of the catalyst carriers is
roughened in order to increase the surface area and to improve the
adhesion of the applied catalysts. The surface is roughened
mechanically and/or chemically-oxidatively. Examples for chemical
roughening are acidic etching and for oxidative roughening
annealing in an oxidative medium. The catalyst carrier packets or
bundles are fixed in frames, on glass plates or similar apparatus,
- 5 ~
which consist of noncorroding materials and are resistant to
shortwave light.
Porous materials in tubes, for example, can be used as catalyst
carriers as well. The catalyst carriers can consist of thick
porous tubes or porous sheets. The porous sheets can be joined to
form sheet systems as in heat exchangers.
In special cases, particularly in cases of low oxidative media,
the catalyst carrier can consist of porous carbon or carbon
fibers.
Porous ceramics with zeolite structures or closed cell organic or
inorganic polymer- or polycondensation materials can be used as
catalyst carriers as well.
In the method of the present invention, the catalyst carriers
occasionally serve as catalysts themselves, e. g., metals
containing partially oxidized titanium or zirconium or etched
precious metals containing platinum or palladium. Partially
oxidized and etched metals have a very high specific surface and
are therefore surface-active.
Catalysts are applied to the catalyst carriers and consist of
semiconductor oxides mixed and/or loaded with a metal of the
platinum series of the VIII group of the periodic table of
chemical elements.
, The oxides are of the formula:
M20X~ and MlM20 x,where
Ml - elements of the Ia, IIa and IIb group of the periodic table
M2 - Ti, Zr, Hf, V, Nb, Ta, and those of thc IIIb group
such as yttrium and scandium.
The platinum series consists primarily of palladium, platinum,
rhodium, and ruthenium.
x - means a stechiometric or understechiometric value
When chemical compounds are used which are extremely difficult to
degrade, e. g., SF6 or halogen-carbon compounds containing various
halogens, an additional catalytic component is added to the
catalytic system consisting of a salt, usuallyas chlorides of a
lanthanide and/or an actinide element. The chlorides are converted
to oxides and applied to the catalyst carrier.
. . ` '
.
- - 6 ~ 2~ '2~
The degradation reaction employed in the method of the present
invention is induced by shortwave light usually supplied by low-
pressure quartz lamps. Normally, light sources with a wattage
between 200 and 1000 W are used, depending on the size of the
purification apparatus and the geometry of the light sources. The
use of several light sources of low wattage is preferable to the
application of a few light sources of high wattage, mainly to
avoid heat build-up within the purification unit.
The method of the present invention can be employed not only in
fixed-bed but also in fluidized-bed catalytic methods as well. In
fluidized-bed methods, the catalyst is suspended in the reaction
medium.
Fluidized-bed catalysis has the advantage over fixed-bed catalysis
that higher concentrations of catalytic particles per unit of bed
volume can be achieved. The catalytic fluidized bed, however,
requires a relatively constant air or gas flow through the
fluidized particle bed.
Occasionally, the flow rate of the reaction medium may be too
high.
In these cases, particle mobilization is achieved by inducing
vibrations in all or some of the fluidized-bed catalyst carriers.
This is achieved by inducing vibrations inductively or
piezoelectrically and is inde~endent of the direc~ion of flow,
which may be in or against the direction of acceleration under
normal gravitational conditions or in a centrifuge.
To reduce noise emission, the vibrations within the fluidized bed
may also be stimulated by an ultrasonic transmitter.
When the f low is conducted horizontally over or through a particle
bed surface, it is possible to deposit the bed coating as a
continuous surface.
The vibratory bed has an advantage over the fluid-dynamically
stimulated f luidized bed in that the requirements placed on
particle fractionation are less stringent. If the catalytic
particles are at least partially on ferromagnetic catalyst
carriers, moving lines of magnetic flux may be used as an
additional particle stimulation method for mobile beds. The
movement of the lines of magnetic flux forces the particles of the
,
: ', `. . ': ' '.:
`', ~' ,: ' ~. ' `
. , :. . . .. :: .,.:.: .:
. , ' .
- 7 -
catalytic bed to constantly rearrange themselves and,
consequently, continuously present new surface areas to the
photons.
The catalyst carrier and catalytic load are continuously or
discontinuously washed to regenerate the catalysts, as in the
fixed bed catalytic method. Washing is conducted with polar
solvents, preferably with water.
The reactivation of the catalysts is improved if the washing
medium contains oxidizing substances, for example, H202 or ozone.
The catalysts are washed according to various process principles.
For example, the catalyst carriers and catalysts are bathed, or
dipped in a bath, or sprayed, or sprayed and centrifuged.
In most cases, the substances to be removed are highly soluble,
inorganic compounds.
If the mineralization is unfavorable, due to the composition of
the substrate's contaminant, the coating of the catalys~ may be
less soluble. In these cases, but also to generally accelerate
mineralization, an aid, such as water vapor, ammonia, or liquid
ammonia, may be added to the purification substrate.
The washing of fluidized-bed catalysts is best conducted by
exchanging the catalyst batch. Fluidized-bed catalytic methods are
preferably employed when gases occur as sole mineralization
products.
When the substrate gas consists, for example, of pure gas, air,
oxygen-enriched air, and polluted water is sprayed
into the substrate gas, the method becomes a purification method
for liquid substances, in a reversal of the substrate admission in
the purification method of the present invention.
In all, the method of the present invention is the method of
choice for the special requirements of substrates which are to be
purified.
A further object of the present invention was to provide apparatus
with which the method may be carried out.
- '" ~
.~ .
- 8 -
This object was realized by apparatus for carrying out the various
applications of the method as described, the apparatus consisting
of the following principal components:
f) a closed housing of a corrosion-resistant material, equipped
with inlet and outlet nozzles for the substrate and product of the
method, as well as with bearings and clamps for the catalyst
carriérs and catalysts, and with a source of shortwave light;
g) a frame to hold the catalyst carriers and catalysts;
h) an apparatus to move the catalyst carriers and catalysts within
the housing in accordance with f);
and
i) at least one source of shortwave light in the wavelength range
from 250 to 400 nm.
Except for the fluidized-bed method, the housing according to f)
contains a cavity for the bathing liquid, which is equipped with
inlet and outlet nozzles for the bathing liquid.
The catalyst-containing ~arrier is held in a frame, cage, or is
otherwise secured, and moved through the bath in the cavity in
such a way that, as a minimum, the entire carrier passes through
it~
Alternatively, the washing of the catalyst may be conducted by a
spraying method. The spray drips into the cavity, from which it is
removed or returned to the process by re-circulation.
Due to the long-term effectiveness of the catalysts, washing by
bath or spraying may be conducted in intervals.
The frame g) frequently is a cylindrical body with a central axle,
a cavity surrounding the axle, followed by a round container,
which may be subdivided into pockets and which is connected to the
axle on both sides, resulting in a closed container 14 whose outer
62 and inner 63 cylinder casings are constructed in such a manner
.
- . , ,: ~ , ; - :
. - . ~ .. ,;,
:
' ` . '
_ 9 _ 2.~7~
that they are easily permeable for gases and can easily contain
and secure the catalyst carriers and catalysts.
The frame holding the catalyst carriers and catalysts may be
constructed in various geometric forms, for example, a square
object in a packet which ~ravels up and down within the housing in
accordance with g) and is thereby submerged in the washing liquid.
When applying such variations of the method, it must be guaranteed
that the purification process is interrupted during the
washing process or that multiple systems are in service so the
substrate to be purified is fed to an available purification unit
by synchronized switching.
Frames are not required in the fluidized-bed method. The catalyst
carriers and catalysts are suspended within the container and
require a supporting base plate or drum which must be permeable
for gases but impermeable for particulate matter.
The method can be conducted in reductive as well as in oxidative
media, for example, when purifying extremely inert
chlorofluorohydrocarbons. These compounds are best mineralized
under oxygen-free conditions and in the presence of H2S, CS2, COS,
or mixtures thereof. The presence of water and/or ammonia also
promotes the reaction.
Other reductive agents which helps to eliminate halogens, are
for example, dithiols, mercaptans, thiophenols and their alkali
salts, sodium sulfide, and sodium polysulfide, which are
introduced to the process as gases or, for example, as aqueous
solutions.
By reversing these conditions, these sulfur compounds, if
occurring as unwanted pollutants, can be eliminated by the method
of the present invention. This is especially important, since
these compounds are extremely odorous.
Nany gases contain significant amounts of the covalently bound
pollutants as aerosols. In a variation of the method of the
present invention, precipitation of these components can be
promoted by connecting the catalyst fixed bed to a voltage
differential. Depending on the geometry of the fixed bed, the
backplate electrode may be either the housing ~) itself, or
1 0 ~ 3 r~ 7 ~ ~
appropriately positioned wires, or even an additional catalyst
fixed bed, as shown in Fig. 3.
Surprisingly, the new method functions even if the aqueous phase,
the bath or the washing liquid used to spray the catalyst, is
polluted with organochemical substances. The pollutants are
adsorbed from aqueous solution and adhesively bound by the
catalyst carrier and the catalyst.
Even oil films on the surface of the water or substances dissolved
in the aqueous solution, for example, are adsorbed by the catalyst
fixed bed, appear in the gas phase, and are mineralized under the
influence of the photons. This variation shows the applicability
of the method for purifying extremely polluted waste water, which
would be difficult by any other means.
Examples of the apparatus required for carrying out the method are
illustrated in Figures 1 to 7.
Fig. 1. shows a standard apparatus. The hermetic enclosure of
the reaction chamber 11 by the bath 12 and the side wall
of the cylindrical container 14 forces the substrate to travel
through the photon-irradiated 7 catalyst fixed bed 1. This is also
where photocatalytic mineralization of undesirable substrate
components occurs. The purified product leaves the purification
unit 15 via the hollow axle 5.
The catalyst fixed bed and the catalysts are washed in bath 12 and
freed of minerals, which are removed with the washing liquid via
nozæle 10.
.
Fig. 2 shows the same apparatus in a vertical cross section
along the middle axis.
Fig. 3 shows a variation of the apparatus for the purification
of co~alently bound pollutants in aerosols.
Purification is best conducted with an electric field as described
in Example 8.
Fig. 4 shows a variation of the apparatus for pollutants which
; are extremely difficult to eliminate. r~he apparatus is
.
2~rt~
designed such that purification is conducted in two stages. The
first purification stage occurs between chamber areas 34/51, and
the second stage occurs betw~en chamber areas 42/52. The method is
described in detail in Example 5.
ig. 5 shows a vertical cross section of the apparatus of
Fig. 4.
ig. 6 shows a variation of the apparatus in which the washing
liquid is admitted through the same inlet as the
substrate to be purified. The catalyst carrier and catalyst are
washed by spinning off the washing liquid as described in
Example 9.
ig. 7 Shows an apparatus which uses fluidized-bed catalysts.
The applications of this new method are extremely diverse. ~he
fixed-bed catalyst method is used in households for air
purification as well as for flue gas dust collectors. In v~hicles,
it is used for purifying circulated air and exhaust gases. In
public buildings, e. g., schools, parking garages, and hospitals,
it is used for purifying circulated air and emissions.
Fixed- and fluidized-bed catalytic methods are also employed in
several other sectors, for example, in paint factories and paint
shops, in glue factories and in glueing, and in the production of
printing inks and in printing to remove solvent and softener
vapors. They are also used in the chemical and pharmaceutical
industries, in refineries, and in coking plants to remove all
types of pollutants, employing as required a variation of the
method of the present invention~ They are also used for
occupational safety, for example, in welding.
Other applications are the decontamination of ground water and
soil by abandoned pollutants or following accidents.
Further applications are the destruction of
chlorofluorohydrocarbons, PCBs, or other environmental poisons,
dangerous by-products of semiconductor production, such as ASH3,
SiC14, SiHC13, SiH4, SF6, MoF6, the flue gases of viscose
production, which contain CS2 and H2S, the black liquors occurring
in cellulose production, and waste waters in electroplating shop~
tanneries and pesticide pollution.
,
- 12 - 2~7~
The destxuction of gases for chemical warfare, such as LOST, or
nerve gases which contain phosphorus are additional fields of
application.
The method is also called for in clean-room technology, since a
precleaning step would significantly reduce even residual traces
of micro-particles.
The new method is a significant contribution to solving
environmental pollution problems and is extremely energy-saving
and cost-effective.
The following examples will demonstrate some of the capabilities
of the method and its apparatus.
.
Posi~ions-Zahlen-Lis~e LiSl ol relere~3e~n~rnb~rs
A~le casc 1I Sbch~ott - ker--vora I ¦¦ Antnclaet Applicanl
rT-OES ?hotocatalytic method OESTE, Franz Dietr~Ah
Posl 3enennunoiDtSl9nal~on and aDDaratus
i _ 4 9 d~ e t -an s mi s s i on
1 ¦ cata~rs~ ed bed 50 l e~tei i nb- 10CK
51 ¦ ?u-e 3as chamDer, 1st sta3e
3 !!noto- 52 ! ~u~e ~as chamDer, 2nd sba~e
4 !s~-a~ or ~ear disk 53 bath _ _
S !hoiiow a:~le 54 _ _
6 !suDs~,-ate inlet noz~'e 55 h in, ~ig. 4 and 5
7 !sho-~~a~re lamD ~hoton source 56
8 !washin3 }icuid nieb 57 _ _ _
9 !washinb l- luid outlet 58
10 ¦ba~h out'low _ _ 59 ~
ll !gas Dhase chamDer _ 60 su~70rtin~ a~;le
12 Icatal rs ~ashing bath 61 lain bea-in~_
13 llsolat`-3 I'loat _ ____ 62 ou~,er c~rlinder casing
lC ¦c~rlinc-ica7 catal~st `oed ca--ier 63 inner c-~rlinae- cas nb
~5 !a??ara-us hous nb _ 64
16 !DUre roduct ou let noz~le 65 midcle catal~rs~, bed
17 !su`ost-ate to `oe ~urified _ 66 SU`DStrate in_et no_z'e
13 !sa~a~r noz~les _ _ 67 hol ~ ow a;~le _
19 !ca~alrs '-`~cec `oeà, ~i~. 3 _ 6a ^a-balyst Deds _
20 !ca~a"s~, car~io- c~r`~inder 69 aua-tz glass ~'ates
21 IDnobor. source, Fi~,. 3 70 W lam~s
22 !rotatin~ ~ain a:cle _ _ 71 ?ure ~roduct crlamDe-
23 !a?e-ture to 2nd Durif. sta~e 72 ure ?roduct ou~,iet
24 !wasr.i-.- liluid oub' et _ 73 a??aratus outer cas_n~,
~5 Ihousi.~ 3 74 ¦ a~ara-bus bot om
_ _ . _ .
26 !r.e_ati-;e vol a~e source 75 ~asr.ing liauià O~ e-
27 !oosi~, ~;e ~rol~a-e sou-Ao 76 rib-abinb base ?labe
2~ ! aO i a i .. ~las i c sl eeve_ 77 mesh oot~,om_?ia-bes ( '-i~s )_9 !s` i~ ^on_acT 78 catalys ~, fl uid -ed oe~
30 Is ^in~ ^on~ act 79 auarb~ ~lass ?ia~.e_ _
31 !?U"e ?roduct out~ et 80 crude gas inlet
32 ! coc`~ - 'or cqta~rs ~ f :ced ~ed al ?ure as outlet
33 Isu-s t-a~e i n eT _ _ 82 _ _
3 ¦c ube ~-as c:~lq `oer, ist ?uri;`. sta3e 83 1
_ ~
36 1 85 __
37 ~aDerture to 2nd ~urif. sta~e B6
38 Is~_' 87 _
39 IC _ai"ra_ -"asn- n,~- )aTbh 88
40 !-iasn ~ auia inlet ag - _ __ _ _
41 l~asnin~- ~ icu__ ou-let si?non go
42 Ic~uce -_s ^:~la~^.o-r~ ~nc ~urif. staee
43 L~ n--a ii -_tion a c i nlet
44 !s -- n~ ~otor __ _
~ S lonoton ,ou--c e ~ _
~6 l~hoton. sourco
~7 !?U~oT~a~c~ outie~ Attr~rnuy Dr.EriChreimin
48~cente-inb d--ve rol'ers D-7881`Herrlschried,
- 14 -
E x a m p 1 e
Prepara~ion of the cataly3t carrier
A three-dimensional, knitted wire mat of stainless steel with a
layer thickness of 50 mm is cut into strips of 150 mm width and
1000 mm length.
The mesh is ca. 10 mm. The strips are used to form a hollow
cylinder with the following dimensions: outer diameter ca. 30 cm,
inner diameter ca. 20 cm, cylinder height ca. 15 cm.
The mat is held in shape by meshed stainless steel wires.
The cylinder is then blasted with grey cast iron blasting shot,
mesh 0.2 to 0.4 mm, until the surface of the wire mat is well
roughened, recognizable by the delustering of the wires.
Following this pretreatmen~, the diameter of the knitted wires is
ca. 0.2 mm. The wire mesh is then washed and thoroughly dried.
The wire mesh is then dipped into a solution of soluble sodium,
density 1.4 kg/l, and thoroughly wetted.
Short activated charcoal fibers with an average length of 1.0 to
3.5 mm, which are best produced by cutting fibrous webs of
activated charcoal, are added to a 5% aqueous solution of citric
acid. The charcoal fibers sediment completely in the citric acid
solution and are then removed by decanting and filtration. The
fibers are then dried to a constant weight at 70C.
The fibers are shaken through a sieve onto the wire mat, which has
~een wetted with the soluble sodium solution, until the surface of
the wires is covered with the short charcoal fibers as comple~ely
as possible. Prepared in this manner, the wire mat is then sprayed
uniformly with a 5~ aqueous solution of soluble sodium, followed
by a 5% aqueous solution of citric acid. It is then dried to a
constant weight at 110C.
This method produces a thin silicate layer on the flock coating of
charcoal fibers.
Subsequently, the wire mat is repeatedly dipped into a water bath
to remove all soluble salts. The wire mat is then dxied to a
constant wei~ht at 70C.
.
. ~ .
- .,
~;,
..: .; :
- 15 - 2~ 5~
Preparation of the ca~aly~t
A suspension is prepared containing:
5~ titanium dioxide powder, rutile type, mesh smaller than 0.1 mm
10% ethyl ti~anate, 3~ bentone swollen in xylol
0.5~ palladium, metal colloid
0.5~ rhodium, metal colloid and
81.0% xylol
Depositing the catalyst on the catalyst carriex
The catalyst suspension is deposited on the catalyst carrier by
spraying or dipping and is dried at a temperature between 20C and
50C and a relative humidity of 50% to 95%. After the catalyst
carrier and catalyst have been prepared as described, they are
built into the apparatus components shown in Figs. l and 2,
container 14.
Procedure
Container 14 with catalyst carrier and catalyst l is mounted on a
rotatable axle 60 supported by bearings 61 in a closed housing 15.
Catalyst carrier and catalyst form the catalyst fixed bed l.
The cylindrical container 14 is closed on both sides. The flow of
substrate to be purified enters the purification unit (Figs. 1 and
2) of housing 15 via inlet nozzle 6. Since housing 15 is
hermetically sealed, the substrate can reach the hollow axle 5
only by traversing the catalyst fixed bed l. The hollow axle 5 is
also the outlet nozzle through which the substrate lea~es the
purification unit as a purified product.
During the reaction, the catalyst fixed bed 1 is activated by
several 200 W low pressure quartz lamps 7. The cylinder
(container) 14 is continually rotated on cylinder axle 60 during
the work phase. The axle 60 is drtven by motor 3 via hollow axle 5
and strap or gear disk 4.
During the work phase, the rotation dips the complete casing of
the catalyst fixed bed into bath 12, which in this case is a water
bath and is situated in the lower section of housing 15. The wash
water enters the bath by inlet 8 at a rate of ca. 2 to 5 l/h.
,, .
r
'' ~
- 16 -
~ter it is loaded with the mineralization products, it is removed
from the bath via outlet 9.
In the reaction area of the quartz lamps 7, the surface of the
bath is covered with isolating floats 13 to minimize evaporation
and heating. Container 14 is turned at a speed of ca. 0.5 to
1.~ times per hour.
Tap water, but preferably water from an ion exchanger, is used as
the washing liquid.
The process operates as follows:
An air stream is adjusted to a relative humidity of ca. 90% by
feeding it through a tank of cooled water at a rate of 0.3 l/s.
At a rate of Q.l l/s, an additional stream of air is fed through a
2 liter washing flask roughly half-filled with a solution of
various biocide substances. The biocide solution is of the
following composition:
3 n % profenofos (0-ethyl-S-propyl-0-(2-chloro-4-bromphenyl)-
thiophosphate; CllH15BrC103PS),
25~ chlorofos ~0,0-dimethyl-2,2,2-trichloro-1-hydroxy-ethane
phosphate; C4H8C1304P),
5% cacodyl oxide (bis(dimethyl arsyl)oxide; As2(CH3)40),
25~ demeton-S (O,O-diethyl-S-(ethyl thio)ethyl thiophosphate;
C8H1903PS2) l
15% fluoro acetic acid-n-butyl ester (C6H11F02).
The two air streams are mixed with a static mixer and fed through
the apparatus shown in Figs. 1 and 2. A defined aliquot of the gas
stream fed through the catalyst fixed bed is diverted for analysis
and burned in an oxyhydrogen gas flame. The resulting gas is
condensed in a quartz cooler such that the condensate drips from
the cooler into a diluted hydrogen peroxide solution. The
fluoride, bromide, sulphate, phosphate and arsenate content. of the
hydrogen peroxide solution is analyzed at two-hour intervals.
The solution contains hydrogen peroxide and a small amount of
potassium iodide.
;: .,
, :,,,
, '' . ~ .: ' . .:
:. . ,,., ... ;.
- 17 ~
Even after the experiment was conducted continually for two weeks,
none of the ions mentioned abo~e was detected in the hydrogen
peroxide solution.
E x a m p 1 e 2 (Comparative example)
The process is conducted exactly as described in Example 1, except
that the catalyst is not washed. Pollutants were detected in the
emissions after only 24 hours reaction time.
E x a m p 1 e 3
The process is conducted as described in Example 1, but the
catalyst is washed not by bathing but rather by spraying the
catalyst and catalyst carrier from the inside of container 14.
The washing liquid is removed through outlet 10. Container 14 is
rotates at a speed of 300 to 1500 rpm during the washing method.
The washing is conducted discontinuously at intervals of 2 to 24
hours depending on the pollutant content of the substrate to be
purified.
The resulting emissions are of the same quality as in Example 1.
E x a m p 1 e 4
The process is conducted exactly as described in Example 1, except
that the catalyst is washed discontinuously. Bath 12 is filled for
15 minutes every two hours. The washing liquid is then removed.
The same good results were achieved as in Example 1.
E x a m p 1 e 5
Preparation of the catalyst carrier and catalyst
A 20 mm thick, stainless steel knitted mat is cut into strips of
38 cm length and 4 cm width and roughened by corundum streams. The
-, . ' ~ ::' ' .
- ~' :, '
- 18 2~
roughened stainless steel strips are treated with soluble sodium
as in Example 1.
1.5 kg short aluminum oxide fibers with an average length of 1 to
3 mm and a diameter of 0.1 mm are stirred into a solution of 75 g
thorium tetrachloride, 30 g cerium trichloride and lS g yttrium
trichloride in 3 1 of water.
The solution is then neutralized by adding sodium hydroxide. The
chlorides are converted into hydroxides and precipitate on the
surface of the aluminum oxide fibers.
The applied fibers are removed by filtration, neutralized by
washing, and dried.
The dry fibers are fluidized by a vertical air stream and the
stainless steel knitted mat, which was wetted by treatment with
soluble sodium, is flock coated by dipping into the shor~ fiber
fluidized bed.
A high fiber density is achieved by applying a relatively high
voltage of 5 kV to the stainless steel knitted strips during flock
coating.
Immediately thereafter, the coated strips are dried to a constant
weight in a CO2 atmosphere at room temperature. ThPy are then dried
to a constant weight in a nitrogen atmosphere while the
temperature is gradually increased to 400C. This temperature is
maintained for two hours.
.~
The resulting strips are freed of alkali carbonates by washing and
dried.
Subsequently, the prepared catalyst carrier is coated and fixed
with palladium- and rhodium-doped titanium dioxide, as described
in Example 1.
The resulting catalyst carriers and catalysts are mounted in the
64 pockets 32 of the catalyst carrier cylinder 20 as shown in
Figs. 4 and 5. Cylinder 20 is then mounted in housing 55.
Cylinder 20 is mounted in chamber housing 55 such that sections of
the cylinder are simultaneously in both of the chambers while the
cylinder rotates.
;,
, : ~
~, ' ~, '.
_ 19 ~
Cylinder 20 divides each of the two chambers 34/51 and 42/52 into
two sections, the substrate section and the product section.
Cylinder 20 rota~es counterclockwise at a speed of 0.5 rpm and is
driven eccentrically by the interconnected supporting rollers 48.
Procedure
Nitrogen containing lO00 ppm sulfur hexafluoride, 5000 ppm carbon
disulfide, 10000 ppm ammonia, and 20 g/m3 water vapor is fed into
the chamber 34 via substrate inlet nozzle 33 at a rate of 0.3 l/s
and a temperature of 23C.
The quartz lamps 45 and 46 on both sides of the chamber are turned
on.
The photon emission maximum i5 between 300 and 400 nm.
The gas is fed through catalyst bed 62, where practically all
pollutants are converted to elementary sulfur, ammonium fluoride,
and carbon dioxide.
The resulting sulfur and ammonium fluoride remain on the catalyst.
The gas is then fed through aperture 37 into chamber 42 where, at
a temperature of 20C, it is mixed with air which enters ~y inlet
43 at a rate of 0.3 lts and whose relative humidity has been
adjusted to 100% at a temperature of 25C.
The gases are stirred by ro~or 44.
~ithout a change in photon conditions, the gas mixture is fed
through catalyst bed 62 into chamber 52.
The gas reaching chamber 52 does not contain sulfur dioxide or any
other pollutants. Residual pollutants, as well as the elementary
sulfur on the catalyst, are converted to ammonium sulfate and
ammonium hydrogen sulfate in the catalyst fixed bed of chamber
areas 42/52. The purified product is removed from the purification
unit by outlet 47.
The catalyst bed is washed continuously while moving through
bath 63. The washing liquid enters upper section 39 of the bath by
inlet 40 at a rate of 2 l/h, is fed through the catalyst bed where
it removes mineralization products and is collected in lower
section 53 of the bath.
~ '
- - 20 ~
The washing method removes mineralized salts, such as fluorides
and sulfates. The resulting washing liquid is removed from the
purification unit by siphon 41. Leveling locks 50 are regulated by
the height of the siphon.
The ammonia content of the washing liquid is monitored via the pH-
value, which varies between 6.5 and 7.5.
The seals 38 minimize gas leakage between the chambers.
.
- Waste water processing
Milk of lime is added to the waste water. The resulting sulfates
and fluorides precipitate as gypsom and fluorspar.
Subsequently, the waste water is stripped in a packed column using
air in a counterflow system. The stripping air, which contains
ammonia, is recycled via aperture 37 and is reintroduced to the
process in chamber 42.
The precipitated calcium salts are removed by filtration and
disposed of. The filtrate can be used as service water.
In this manner, extremely dangerous chemical substances are
converted to harmless mineral salts.
E x a m p 1 e 6
As in Example 5, but with the following substrate composition:
500 ppm bromtrifluoro methane (halon), 200 ppm difluoro-dichloro
methane instead of sulfur hexafluoride, and 5000 ppm H2S instead of
carbon disulfide.
More than 95~ of the covalently bound halogens are mineralized to
halogenides.
The waste water filtrate cannot be used as service water, since it
contains calcium chloride and bromide.
~ :,...
.
- 21 - 2~
E x a m p 1 e 7
As in Example 5, except that a knitted mat of -titanium wire,
preferably roughened, and of less than 0.5 mm diameter is used
instead of a stainless steel mat.
The knitted mat is annealed in oxygen, resulting in a titanium
dioxide layer on the surface of the wires, which supplies the
required catalytic properties in this process.
Subsequently, the wire mat is dopPd with one or a mixture of the
platinum metals and/or oxidized compounds of the elements or their
mixtures from the lanthanide group or yttrium or the actinide
group, leading to the same good results.
E x a m p 1 e 8
Nany gases contain significant amounts of the covalently bound
pollutants as aerosols. For the precipitation of these components,
it is advantageous to connect the photocatalyst fixed bed to a
voltage differential. Depending on the geometry of the fixed bed,
the bac~plate electrode may be either the housing itself,
appropriately positioned wires, or even an additional catalyst
fixed bed.
Fig~ 3 shows the geometry of three catalyst fixed beds 19, 65,
which rotate around a common axle 22 within housing 25. ~oth
external catalyst beds are connected electrically with conductive
matal axle 22 and, via sliding contact 29, positive voltage source
27.
Central catalyst bed 65 is isolated from metal axle 22 by plastic
sleeve 28 and receives a negative charge via sliding contact 30
from voltage source 26.
Two photon sources 21 are mounted rigidly between rotating
catalyst beds 19, 65.
Spray nozzles 18 enrich the substrate, which enters the
purification unit via 17, with an aerosol of washing liquid.
The rotational speed of the catalyst beds is variable between 10
and 500 rpm.
- 22 ~ 2 ~ 7~ ~
In intervals, rotational speed is increased to maximum to spin off
washing liquid during washing.
Subsequently, the spun-off washing liquid is removed from the
apparatus by outlet 24. ~he purified gas is removed by outlet 31.
5000 to 30,000 V is the ~est voltage range ~or s~ripping aerosols.
The catalyst carriers are prepared according to Examples 1 and 5.
E x a m p l e 9
Fig. 6 shows a further variation of the method using aerosols.
The substrate - polluted gas - is fed through inlet 66, hollow
axle 67, and catalyst beds 68.
Spray nozzle 18 enriches the substrate with an aerosol of washing
liquid. The catalyst beds are mounted between disk-shaped, round
quart~ glass plates 69, which are securely fastened to the hollow
axle.
The hollow axle is permeable for gases in the catalyst bed section
between the quartz glass plates.
The hollow axle and, consequently, the catalyst bed are turned by
a motor and drive unit 4, as in Example 8.
W lamps 70, the photon sources, are located between the catalyst
beds.
The purified substrate is fed into chamber 71 and removed from the
unit as a pure product by outlet 72.
A filled gas washer is mounted downstream of the purification unit
to strip aerosols.
The washing liquid aerosol aggregates and coalesces within the
catalyst fixed bed, is spun to wall 73 of the unit, collects in
bottom section 74, and is removed from the apparatus by outlet 75.
E x a m p l e 10
A variation of Example 9 is to secure the photocatalyst fixed bed
by a tight, transparent housing. The catalyst is secured within
.
.,. ..~ ..
.
- 23 ~ 2~7~
glass capillaries. This is achieved by applying the catalyst to
the glass walls or pores of the capillaries.
When employing wide capillaries with diameters of ca. 1 mm and
larger, the catalyst particles are applied by pouring.
Previous etching improves the adhesion of the catalyst to the
glass surface.
E x a m p 1 e 11
The apparatus can also serve as a waste water purification unit
if, as in Example 9, the spray nozzle is fed with water to be
purified and inlet 66 is fed with clean air~
;' ' '
