Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to improvements ln the
purificatlon of an exhaust or flue gas by removing
environmentally noxious gases therefrom, for example as are
present in flue gases developed during the productlon of nitric
acid or in exhaust gases from internal combustion engines,
including nitrogen oxides, carbon monoxide, hydrocarbons and/or
sulfur oxides.
It is known to remove such environmentally noxious gases as
nitrogen oxides in the gaseous phase by means of catalysts and
additional substances, for example ammonia. Gas purification
installations ~or carrying out such processes are very
expensive to build. In addition, the efectiveness of the
cata}y~ts used in th~se methods i8 llmited 80 that they must be
regenerated every two years, at the latest, to obtain
satisfactory results.
It is an object of this invention to overcome these
disadvantages and to remove 9D-99~ of the environmentally
noxious gases present in flue or exhaust gases, such as oxldes
of nitrogen and sulfur, hydrocarbons and carbon monoxide, in a
; single stage.
We accomplish this and other objects in accordance with the
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I inventlon by intensively mixing the gases with a contact 11quid
containing a catalyst suspended or dissolved in the llquid
I until the gases and liquid have formed a foamt and reactin~ the
~ gase~ with the catalyst in the for~ed foam.
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Useful catalysts include, for example, lnorganic catalysts,
such as Raney nickel or platinum black, or organic catalysts,
~uch as metallic phthalocyanine whose metalllc ato~ is, for
example, copper, iron or cobalt. These catalysts, for example
platinum black or phthalocyanine, are suspended in a carrier
liquid or, for example phthalocyaninesulfonate, are dissolved
therein.
Useful carrler liquids for the catalysts include, for
example, silicon oils and paraffin olls as well as other
chemically inert liquids, such as quinoline, trlch:Lorobenzene
or benzophenonone.
If the contact liquid iæ an aqueous catalyst solution, the
gases are reacted with the catalyst at a temperature of 20C to
150C, preferably 90-100C. If the contact liquid has a hl~h
botling point, the gases are xeacted at a temperature of 20C
to 250C, or up to 500C if the gases are removed from the
exhaust gas of an internal combustion engine.
According to a preferred feature of the present invention,
the contact liquld ls fed downwardly and countercurrently to
the foam phase, a partial stream is branched off, the partial
tream is optionally passed through a heat exchanger and is
then tested for ~ensity of the catalyst contalned t~lerein, and
an amount of catalyst r~quired to attain a desired level of
catalyst denslty i8 added to the stream.
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If oxides of nitrogen are removed fro~ the flue or exhaust
gas, a subst~ate reactive therewith, for example ammonia,
carbon monoxide or hydrocarbons, may be added in stoichiometric
amounts.
The maintenance of an intensive gas-liquid phase contact at
the lowest pressure loss possible enables the method of this
invention to be carried out on an industrial scale. This
effect may be achieved, for example, ln a column comprising
phase contact bottoms which ald in overcoming and controlling
the hydrostatic pressure oE the liquid column resting thereon.
Such an apparatus i9 disclosed ln European patent application
publication No. 73,801, published March 16, 19~3.
_ It i9 known to use metallio phthalocyanines as catalysts
for hydrating carbon monoxide to a Cl - C5 hydrocarbon, and
to use cobalt or iron phthalocyanine on coal for the removal of
oxides o~ nitrogen from cigarette smoke. It is, however,
surprislng to ~ind such catalysts and others suqpended or
dissolved in a carrier llquid to have a great effect in
intensive phase contact with the ga3eous mixtures to be
purified.
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This helghtened activity of the catalyst~ is of
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coneiderable technical lmportan~e. For example, a 90-
e~ficiency can be obtained with powe~ plant exhaust gases
;~ ~ containing about 1000 ppm of oxides of ni~rogen, ~reated with
iron phthalocyanine at a temperature of 150C ~y using about 10
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phase contact boktoms, an increase of the number of contact
bottoms increasing this efficiency up to 99~. When using a
circulating amount of 200 1 carrier liquid, 10 kg of catalyst
are needed.
The above and other ob~ects, advantages and features of the
invention will be more fully described in connection wlth the
following preferred embodiments taken in conjunction with the
accompanying schematic drawing of apparatus useful for carrying
out the method and wherein
FIG. 1 shows an installation using ammonia a~ a reactlon
~ubstrate and
FIG. 2 shows an installation converting the removed oxides
of nitrogen to ammonium nitrate.
Referring now to the drawing and first to FIG. 1, du~t and
sulfur are first removed from the flue gas to be purified by
contacting the flue gas with an ammoniacal solutiQn before ~t
i~ introduced in~o mixing chamber M. Ammonla is
stoichiometrically admixed to the flue gas in the ~ixing
chamber under the control of a measuring probe. The catalyst
suspended or-dls~olved in a carrier llquid, for example water,
paraffin or si~icon oil, is ¢irculated in reaction chamber R,
and is countercurrently brought into intensive phase contact
with the rising gas by means of ouitable contac~ element~ to
form a foam. In thl~ foam phase1 the o~ides of nltrogen react
with the add ~3 to generate nitrogen nd water.
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Residual catalyst is removed from the purified flue gas
with cleaned carrier liquid in gas scrubber W ~nd returned to
reaction chamber R. Sludge is removed from the reaction column
at the bottom thereof.
The concentration of the catalyst is about 1 to 30~, by
weight, of the carrier liquid, preferably about 5~. Depending
on the catalyst, the treatment temperature is in the range of
20C to 5Q0C, preferably about 20-150C.
FIG. 2 shows a like reaction tower u~ed for the production
of ammonium nitrate from the removed oxides of nitrogen. In
this embodiment, the NH3 is not lntroduced into reaction
chamber R but lnto the gas scrubber W.
_ If exhaust gases from stationary Diesel motors are to be
purified, no dust and sulfur need be removed therefrom before
they are treated.
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In the purlfication method of the pre~ent invention, the
degree of removal of nitrogen oxides from flue or exhaust gases
containing up to 10,000 ppm NOX is above 90%.
Consldering increased CO contents ln Diesel motor exhaust
;gases, it ls posslb~e to purify the exhaust gases from Diesel
motor trucks with the use of CO as a reaction substrate, CO
being reacted to generate CO2 and the hydrocarbons being
reacted to generate CO2 and H2O.
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