Note: Descriptions are shown in the official language in which they were submitted.
- ~ 21 92a69
WO 95/33682 - 1 - PCT/~P95/01935
Process and filter for preparing NO2-free nitrogen mon-
oxide using sulfur-cnnt~n;ng polymers
The invention relates to a process for preparing
nitrogen-dioxide-iree gases and liquids and a filter for
the selective removal of nitrogen dioxide irom gases and
liquids.
Nitrogen ~ gas or ni~rogen n~ gas mixtures
which are free of nitrogen dioxide are required in
exhaust gas metrology for the calibration of measurement
and analysis systema.
Recently, the medical use of nitrogen nYide (NO) has
attained particular importance. In patients having
serious pulmonary symptoms, addition of NO to the
breathing air can decrease the blood hypertension in the
pulmonary circulation. In combination with the broncho-
dilatory action of NO, an improved aeration of diverse
lung sections and thus also ; ~ ~v~ gas exchange occurs.
The colorless nitrogen monoxide (NO) rapidly reacts with
molecular oxygen to form brown nitrogen dioxide (NO2). In
the presence of air or on the admission of air, NO2 is
therefore formed from NO. NO2 - owing to the ubiquitous
oxygen - is therefore an inherent impurity of NO.
Especially in the event of a medical use of NO, owing to
its toxicity, the content of NO2 must be very low. There
has therefore been no lack of attempts to selectively
absorb or convert to NO the NO2 once formed.
The catalytic conversion of NO2 to NO in the presence of
oxygen according to:
2 N02 \- 2 hO ~ ~2
21 9206~ 2 -
at a Cu, Mo or Ni catalyst at temperatures of ~ 220~C is
possible. This method is employed in the separate deter-
mination of NO and NO2 by the chemoluminescence method
(see operation and maintenance instructions for the NOy
mea~ul~ t instrument CSI 1600 from Columbia Scientific
Industries, Austin~ Texas, 1980). Disadvantages in this
process are the high temperature required and the possi-
bility of recombination of NO + ~2 to give NO2 after the
gas stream has cooled.
It is further known that NO2 dissolves very readily in
~nr~ntrated inorganic acids such as HNO3 or H2SO4. NO can
therefore be very readily purified by the abovementioned
acids using a gas scrubber (A. Golloch, Anorganisch-
chemische Praparate [Inorganic Chemical Preparations],
Walter de Gruyter Verlag 1985, pp. 232 ff.). A disad-
vantage in this case is the relatively high expenditure
in terms of safety and chemical engineering.
Further methods are the frArtion~l c~n~Pnast;~n and
distillation to remove NO2 from NO. A summarizing presen-
tation of the purification processes for NO is found in:G. 3rauer, ~an~hn~h der praparativen anorganischen Chemie
[Handbook of preparative inorganic chemistry], volume 1,
pp. 470 ff., 3rd edition (1975), Verlag E. Enke.
The object is to find a simple process and a filter for
the selective removal of NO2 from NOx-containing gases or
liquids.
It has been shown that a selective removal of NO2 from NO
or No-c~nt~;n;ng media such as gases or liquids can be
carried out highly efficiently by contacting them with a
sulfur-containing polymer, preferably poly(arylene
thioether), in particular poly(phenylene sulfide).
The invention therefore relates to a process for pre-
paring NO-containing gases or liquids which are free of
NO2, which comprises contacting an NOx-c~nta;n;ng gas or
~~ ~
~ 21 ~2069 3 -
an NOx-containing liquid with a material which cnnt~;n~
a sulfur-~nt~in;ng polymer; NO2 i8 preferably removed
from an NO-~on~;n;ng gas mixture.
The expression ~Ifree of NO2" means that the content of
NO2 in a medium is les6 than l ppm.
NOX is used aE a collective term for nitrogen oxide6 NO,
NO2 and N2O and al60 includes mixtures of these oxides.
.. . .
Sulfur-~ntA;n-ng polymers are, for example, linear or
branched polyaryl systems (mean molecular weight, Mw:
4000-200,000) having the repeating unit of the formula
which contain at least one thioether group,
-[(Ar1)n-X]m-[(Ar2)i-Y~j-[(Ar3) k-Z] 1- [ (Ar4)O-W]p- (I)
where Ar1, Ar2, Ar3, Ar4, W, X, Y and Z, independently of
each other, are identical or different. The indices n, m,
i, j, k, l, o and p are integers from 0 to 4, where their
6um must be at lea6t 2. Arl, Ar2, Ar3 and Arq are in the
formula (I) simple or directly para-, meta- or ortho-
linked aryl systems having 6 to 18 carbon atoms. W, X, Y
and Z are linking groups, selected from the group con-
sisting of -SO2-, -S-, -SO-, -O-, -CO-, -CO2-, alkyl and
alkylidene group~ having 1-6 carbon atoms and -NR1-
groups, where R1 is alkyl or alkylidene groups having 1-6
carbon atoms. The aryl systems of the formula (I), in the
context of the invention, ~PpPn~;ng on their chemical
structure can further additionally contain, independently
of each other, one or more usual functional groups, e.g.
alkyl radicals, halogens, sulfonic acid, amino, nitro,
cyano, hydroxyl or carboxyl groups. In addition, block
copolymers of units of the formula (I) may also be used.
The ;ntPr~rt;~n of the sul~ur-~nt~;n;ng polymers such as
poly(arylene thioether) with NO is negligibly small in
comparison to the interaction with NO2, therefore separa-
tion of NO2 from an NOx -c~nt~;n;ng gas stream is poss-
219206~ - 4 -
ible.
Preferred sulfur-~nt~;n;ng polymers are polyarylenes
having repeating units of the formulae (II-VI) whose
syntheses are described, e.g., in Chimia 28(9), 567:
~ ~ S ~3 S ~3 5 ~ I - ( I I )
~) _
-- C --
~ S ~ 3 S ~ 1' - (III)
1, _
~ ,_ I
~5~5~~- (IV)
- n -
- _~ 5 ~3 - ( V )
5 ~3 S ~3 ~ - (\/ 1 )
and p,ly~arylene th;o~th~rs) having repeating units of
the formula (VII) which are described, e.g., in
US-A-4,016,145.
21 92069 5 _
o
~ S ~ (VI I )
Particularly Freferred sulfur-cnnt~;n;ng polymers are
poly(phenylene 6ulfides) (PPS) having the repeating unit
of the formula (VIII), whose preparation process is des-
cribed, e.g., in the patent documents US 3,919,177,
US 4,038,262 and US 4,282,347.
~ S - ( V I I I )
PPS of the ~ormula (VIII) can also have, up to a content
of 50 mol percent, a 1,2- and/or a 1,3-linkage at the
aromatic nucleus. PPS is taken to mean both the linear
and also the crosslinked material. In addition, the PPS
of the iormula (VIII) can contain, per aryl unit, in-
dependently of each other, 1 to 4 ~lnrt;nn~l groups, e.g.
alkyl radicals, halogens, sulfonic acid, hydroxyl, amino,
nitro, cyano or carboxyl groups.
If poly(arylene th;reth~rs) according to the invention
are used, in general poly(arylene thioethers) are
suitable which have a mean molecular weight of 4000 to
200,000, preferably 10,000 to ~50,000, in particular
25,000 to 100,000 (determined by gel permeation chroma-
tography).
The sul~ur-cnnt~in;ng polymers can be used as powder,
fiber, nonwoven web, woven fabric, film, sintered
material, molding or as a coating or impregnation of
support materials. Moldings having a particularly large
surface area may be produced by suitable processes, e.g.
. ~; ' ;-
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having a grating or honeycomb structure. The powders
have, e.g., commercial particle sizes, granules also
being usable. It i8 important in this case that the gas
to be treated or the liquid can be paYsed without ob-
struction through the polymer material, for example inthe form of a powder flxed bed. If the polymers are ubed
as fibers, these are used as staple iibers, needle-felt,
'~nonwoven" material, carded sliver or woven fabric. Films
or film shreds can also be used in suitable form.
.
~oatings of support materials with sulfur-r~nt~;n;ng
polymer such as poly(phenylene sulfide) can be obtained
by applying solutions of the sulfur-c~nt~in;ng polymer to
the support material. Impregnations are made e.g. by
impr~r,n~t;ng an absorbent support mater~al. Support
materials which are used are generally inorganic sub-
stances such as glass, silica gel, alumina, sand, ceramic
compositions, metal and organic substances such as
plastics.
F.g. metals, in particular noble metals and transition
metals, or metal oxides such as transition metal oxides,
can also be applied to the sulfur-r~nt~;n;nr, polymers,
for example by superimpregnation, which metals or metal
oxides are then present e.g. in the form of small
clusters.
The process ~rrr,rd;nr~ to the invention can be carried out
at any temperature which lies beneath the softening point
of the polymers used. The application temperatures
generally lie in the range from minus 30 to +240~C,
pre~erably minus 25 to +220'C.
Nitrogen dioxide is generally removed quantitatively, the
~ reaction times dPp~nd;ng on the fl,w velocity, the
surface o~ the purification material, the geometry of the
absorber and the temperature. Generally, the time of
contact of the sulfur-containing polymer with the medium
to be purified is in the range from 0.001 seconds to 10
~ ~ 21 92069 7 _
minutes, preferably 0.01 seconds to 5 minutes. However,
the times can also be ~ d
In the removal of N02 irom ~0 -containing gas or
N0y-~nt~;n;ng liquid, no volatile products are formed
from the polymer.
The sulfur-c~nt~;n;ng polymer, e.g. poly(arylene thio-
ether), can generally be used as llnhl~n~P~ material.
However, addition of conv~rt;~n~1 fillers such as chalk,
talc, clay, mica, and/or fibrous reinforcements, such as
glass fibers and/or carbon fibers, whiskers and other
conventional additives and processing aids, e.g. lubri-
cant8, release agents, antioxidants and W stabilizers is
also possible.
The process according to the invention can be employed
with Nox-c~rt~;n;ng gas streams and liquids. The process
operates e.g. with gases having an N0 content in the
range from 60% by volume to 1 ppb, preferably 50% by
volume to lO ppb and in particular 40~ by volume to
50 ppb. The N02 content which can be separated off is in
the range from 50~ by volume to l ppb, preferably 20% by
volume to lO ppb and in particular from 10% by volume to
10 ppb. The ratio between N0 and N02 in the gases or
liquids to be treated can in this case be from
l,000,000:1 to 1:1,000,000, preferably from lO,000:1 to
~5 l:lO,000 and in particular from lO00:1 to l:lO00.
In the process according to the invention, the removal of
N02 can be effected e.g. by using a filter which contains
a sulfur-~nt~;n;ng polymer. The removal of N02 from
liquids or gases can also be performed for example by
swirling up a powder which contains sulfur-containing
polymer. This can be effected by stirring a powder in a
liquid. The process for removing N02 from liquids or
gases, as is the case with other conventional adsorption
processes for purifying gases or liquids or as is the
case with separation processes which are based on an
~ 2192~69 - 8 -
adsorption process, can be carried out in a batch or
column process.
The invention further relates to a filter for removing
N02 from N0x-~nntcinin~ gases or N0x-~n~t~inin~ liquids,
which filter cnnt~inc a sulfur-cnntA;ning polymer.
The specifications for the sulfur-cont~;n;ng polymer
which were given in connection with the process according
to the invention correspondingly apply to the filter.
The filter can also be operated in combinacion with other
filter materials, e.g. dust filters.
The filter which cnntc;nc a sulfur-cnnt~ining polymer can
contain the filter material e.g. in the form of a powder
packed bed, a n~ v~n web, a nonwoven web/powder
mixture, a grating structure or honeycomb structure.
~owever, the powder can also be in~ oldted into non-
woven webs of other materials.
The process and the filter are particularly suitable for
producing N0 test gases, in which case e.g. an N0 crude
gas which is contaminated by N02 and nontcinc a high N0
concentration is passed through the filter and is puri-
fied in the course of this and is then diluted to the
desired rnn~ntration using an oxygen-free gas. The
dilution and filtration steps can also be carried out in
parallel or in reverse order.
The process and the filter ~ccnr~ing to the invention can
further be used in medical t~hnnl ngy, Thus, for example,
in a treatment using N0 uptake via the lung, the
N0-containing gas and the added air can be combined
upstream o~ or in the filter and thus breathing in of an
N02-free gas mixture can be achieved. The filter can
comprise ~or example a breathing mask in the intake
stream of which is inserted the filter cnnt~ining the
sulfur-~nnt~;n;ng polymer.
~ 2 t 920 69 - 9 -
The filter according to the invention car. be used to
generate N02-free nitrogen ~P/nitrogen/air mixtures
for trPat;ng IRDS (IRDS - Infant Respiratory Distress
Syndrome), ARDS (= Acute ResFiratory Distress Syndrome,
also = Adult Respiratory Distress Syndrome), lur.g
~ailure, migraines, persistent pulmonary hypertonia based
on left myocardial insufficiency or for improving lung
function.
Examples:
1.) A so-called N0 crude gas comprising approximately 20~
by volume N0 in nitrogen which was cont~m;n~ted with
795 ppm of Nù2 due to its preparation was passed through
a filter cartridge which was packed with poly(phenylene
sulfide) (Mw: 30,000, melting point Tm: 288~C) in the
~orm of granules (mean particle diameter approximately
1 mm). The absorption section is characterized by the
following parameters:
Internal ~;. tPr2.5cm
Bed height: 32.5 cm
Mass: 100.5 g
Throughput: 100 l/h
At the exit of the absorber bed the gas was analyzed
using an FTIR spectrophotometer (manufacturer: Perkin-
Elmer, ~berli.ngen, Federal Republic of Germany) and an
N0/N02 chemoluminescence measuring instrument (Type
CSI 1600, Columbia Scientific Instruments, Austin, Texas,
USA) for N02 and N0 contents. In the entire period of 4
hours over which measurements were taken, the N02 concen-
tration was beneath the detection limit o~ 100 ppb.
2.) gas mixture o~ 158 ppm of N02 in nitrogen was
passed through a filter cartridge as in Example 1.
Tmm~ tPly at the exit of the filter, the Nû2 content of
the gas mixture was determined by IR spectroscopy. The
N02 cnncpntration was beneath the detection limit.
- ~ 2192069 -lO-
3.) In a similar manner to Example 1, the capacity of the
filter ~ nPd in Example 1 was determined using a gas
mixture of 1~ by volume N02 and 99~ by volume nitrogen.
The gas mixture was passed through the filter until the
N02 content of the gas downstream of the filter increased
above an N02 content of 1 ppm. The amount of gas which
flowed through the filter until the set limit of N02
content was achieved was defined as the absorption
capacity of the filter. At a temperature of 22~C, an
absorption capacity resulted of approximately 2~ by
weight of the filter mass.
. .,
