Note: Descriptions are shown in the official language in which they were submitted.
DEVICE FOR CARRYING OVT PHOTOCHEMICAL REACTIONS
The present invention relates to a device for carrying out
photochemical reactions in liquid and/or gaæeous streams by
irradiation with UV light. This devics is particularly useful fox
the degradation of organic substances, and especially those having
an aliphatic, aromatic and/or heterocyclic structure, which may
optionally have been mono- or poly-substituted with halogen or
contain nitrogen and carbon atoms in the same molecule, said device
consisting of a 10w reactor, one or more UV lamps and inl~t and
outlet conduits.
Photochemical reactions hitherto have been ma~nly employed in
the synthesis of specific organic substances. From the German
Patent DE-PS 909 292 there has been known a device for the
ultraviolet-irradiation of liquids in flow tubes, and especially
of liquid foodstuffs of any kind intended to be sterilized by UV
light and to be enriched with vitamins. There was provided, in
view of the low penetration depth of the W radiation, that the
liquids should ba passed through the device in a turbulent flow in
direct contact with the ultraviolet radiation. For this purpose,
flow pipes were proposed having a cross section changing with the
direction of flow. These devices comprising tubes with diameters
undulating with the direction of flow are difficult to manufacture
and even more difficult to clean. Thus, it is understandable why
these devices have not found acceptance in practice. However, in
the meantime use has been made, especially by Applicant, of the
fact that UV light is suitable to degrade organic substances in
liquid and/or gaseous flows so that, for example, noxious materials
are removed from natural and contaminated ground waters, industrial
waste waters and industrial wasts gases.
Processes of this kind have been proposed, for examples, in
the German Pa-tent Applications 39 03 549.2 and ~O 16 514Ø
It is the object of the present invention to ca~ry out such
photochemical reactions in the best possible way with respect to
flexibility, efficiency and safety, so that these processes can be
used reliably and as universally as possible.
Conventional devices for carrying out photochemical reactions
in ganeral consist of a flow reactor, one or more UV lamps and
inlet and outlet conduits.
One general problem inherent to all photochemical reactions,
including those amploying UV light, consists of that the absorption
of the light by the reaction medium is sub;ect to Lambert-Beer's
Law and, thus, to a major extent depends on the extinction
coefficient of the reaction mixture or the various wavelengths of
the incident ligh-t. If the extinction coefficients are high and
the concentrations are high, the effe-tive penetration path of the
UV light ca be relatively short. At low extinction coefficients
and low concentrations, the light is not absorbed and, thus, the
light rays are emitted unused. While for specifically designed
syntheses of organic substances the dimensional design of the
device, the concentrations of the starting materials to be reacted
and the flow velocity may be adjusted to one another in preliminary
experiments, such a coordination of process parameters is
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substantially more difficult to achieve for a degrada-tion of
organic substances. This applies -to the absorption spectra of the
contaminations to be degraded as well as to the concentrations of
these substances. Nevertheless, for -the economy and reliability
of the process it is extremely important to achieve a light ~uantum
efficiency as high as possible and to assure that the products to
be decomposed are indeed reliably degraded to the degree desired.
The problem can be solved in a surprisingly simple manner by
providing in the reactor an inner surface which is highly
reElective for UV light and by means for generating a turbulent
flow on or in front of this surface.
The turbulent flow generated causes in strongly absorbing
li~uid and/or gaseous flows that the material to be decomposed is
brought close to the region o intensive irradiation, i.e. to the
W lamp. The surface of the reac-tor which is highly reflective for
UV light, causes the unabsorbed UV light to be returned into the
reactor so that it is again available there for reaction.
This embodiment of the invention of the reaction vessel makes
it possible that in the first part of the reaction vessel even
higher concentrations of the substances to be degraded are degraded
rapidly and efficiently and in the last part of the reaction vessel
the remainders thereof still left are exposed to an intensive
irradiation so that a sufficient absorption and a sufficient
degradation may be accomplished.
Thus, the reactor preferably consists of an elongated
stainless steel tube, the inner surface of which has been polished,
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which stainless tube on i-ts inner wall or spaced apart therefrom
comprises baffle means. One or more high performance UV immersion
lamps are inserted in this -tube. The lamp output preferably should
be 100 watts per centimeter of leng-th of the immersion lamp.
Basically, although low-pressure lamps can be used, medium-
pressure and especially high-pressure lamps are more efficient.
It is known that the spectrum of such VV lamps may be limited to
a few narrow partial regions by doping with specific metal salts.
This is certainly useful in the synthesis of specific organic
substances. It will also make sense i~, for e~ample, just one
definite substance having a definite absorption spectrum is
intended to be removed from the water or gas to be purified. If,
however, there are mixtures of contaminants to be removed, then it
is preferable to employ undoped lamps emitting a broad spectrum of
radiation and, thus, to provide for the possibility that a variety
of substances will be enabled to absorb this light effectively and
to be -thus degradedO
The absorption of the UV light by the substances to be
degraded proceeds extremely fast, while the subsequent degradation
reactions may require somewhat more time. Thus, the device
according to the invention preferably comprises elongated stainless
steel tubes in which, if so desired, two immersion lamps may be
inser-ted from both ends thereof.
It has further proven -to be useful to employ UV lamps wherein
a layer of an inert UV-permeable gas has been provided between the
immersed tube and the UV lamp. Particularly suitable ~or this
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purpose is "Nitrogen 5.0" which has a purity of 99.999~ by volume
of N~. A weak flow of this gas may be passed through the
intermediate space, and the effluent gas may be vented without
further purification. The presence of oxygen in this gas results
not only in absorption losses, but, as a major effect, also in the
formation of ozone and nitrogen oxides which should not be allowed
to escape, at least in closed rooms.
It is possible, of course, to provide solid catalysts in -the
inlst and/or outlet conduits and/or on portions of the inner
surfaces, which catalysts would enhance and optimize the
degradation process. These fixed bed catalysts optionally may also
induce or accelerate after-reactions, thereby to significantly
improve the overall result.
The device of to the invention in its inlet conduit may also
comprise a suppl~ port for auxiliary chemicals which, in som0
cases, produce a further improvement in the results. Such
auxiliary chemicals, more particularly, include H202 and 2 which
will oxidize organic compounds to form CO2. Also the humic acids
which are highly absorptive to UV light are decomposed thereby.
Formic acid, ammonia, urea and amine derivatives such as
amidosulfonic acid promo-te the destruction of nitrate and nitrite.
Both have high extinction coefficients for UV light. As a
consequence of the chemical destruction of nitrate and nitrite, a
higher amount of UV light will be available for the degradation of
the other noxious materials. For the degradation of compounds
containing nitrogen and carbon in the same molecule, and especially
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of cyanides and complex cyanides, there is used especially H202 at
high pH values of about 9. The addition of Hz02 may also provide
a catalytic action in the degradation of halogenated hydrocarbons.
~t is basically possible that the gases or water streams, if they
carry high loads, are circulated and are discharged only after
several passage cycles through the device according to the
invention. However, unexpectedly, so far there has not been even
one single case that would have required to take such a measure.
The device according to the invention, due to the combin~tion of
its parts, allows the fast and reliable degradation to be effected
already in one passage of the contaminating substances within a
wide range of concentrations.
The device of to the invention may of course be combined in
any conventional manner with analytical apparatuses, control
recorders, automatic turn-off in the case of immersion-lamp failure
etc. It is even possible to make the whole device, due to its
relatively low weight, mobile so that it may be readily moved to
the site of use. Larger units may be mounted in contain0rs and,
thus, again may be transferred as a whole to the site of use.
The amount of gas or water -to be purified per unit time to a
high degree depends on the amounts of impurities present therein.
Flow amounts of up to 30 m3/hour have in fact been attained in an
apparatus containing a commercially available immersion lamp of
about 110 cm length.
One typical embodiment of -the device according to the
invention is illustrated in the attached Figure 1 wherein the
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reference numerals have the following meanings:
1 Reactor Vessel
2 UV Lamp
3 Outer Wall of the Immersion Tuba
4 Nitrogen Inlet
Nitrogen Outlet
6 Baffles
The liquid or gaseous material to be treated is introduced
into the reaction vessel (1) from the bo-ttom and is discharged
therefrom at the top. The bafles (6) provide thorough mixing and
a turbulent flow of the reaction. The inner surface of the
reaction vessel consists of polished stainless steel and, thus, is
highly capab}e of reflex-reflectin~ UV light.
The device according to Figure 1 has not been drawn to scale.
It is preferred that the devices are more elongated in shape in
order to provide a path as long as possible for the irradiation of
the material to be treated and, thus, a relative long period of
exposure in the reaction vessel. Furthermore, the baffles rnay be
provided as a rernovable insert located close to the surface of the
reaction vessel. This embodiment has the advantage of being easier
to clean.
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