Process for removing NO.sub.x from combustion zone gases by adsorption

A process for removing NOX from combustion gases by adsorption includes the step of desorbing the NOX when the adsorbent is saturated to create an effluent. The effluent is mixed with a reducing gas and passed over a reduction catalyst which reduces the NOX to water and elemental nitrogen. The resultant harmless gas is discharged to the atmosphere.

BACKGROUND OF INVENTION 
There has been great activity in the field of removing NO.sub.x from 
combustion zone gases. Much of the work has been done on the removal of 
SO.sub.x and NO.sub.x from a gas stream derived from coal and residual oil 
burning furnaces of electric power generating stations. There are many 
examples of this process stream being purified of the SO.sub.x and 
NO.sub.x, but that is not a part of the present invention. When both 
SO.sub.x and NO.sub.x are present, many of the schemes handle the SO.sub.x 
in one reactor and NO.sub.x in a second reactor, after SO.sub.x has been 
removed. This process and its many variations are not particularly 
pertinent to the present invention. 
U.S. Pat. Nos. 4,182,745 and 4,282,115 are of interest to the present 
invention. U.S. Pat. No. 4,182,745 issued to Nishida, et al. describes a 
typical method used for removal of nitrogen oxide by selective conversion 
by reaction of the nitrogen oxide with ammonia in the presence of oxygen. 
This process is described and other background information given in column 
1, lines 10 through 51. 
The uniqueness of the Nishida et al. catalysts is stated also in column 1, 
lines 53 through 65. The catalysts which are useful in this process are 
the heteropolyacids and their salts are also identified as being 
applicable, those are enumerated in column 2, lines 28 through 54. 
There are many points of difference between the Nishida et al. process 
reference (known broadly as the SCR process) and the process of the 
present invention. First is that the present invention uses no ammonia, 
whereas, the SCR process uses ammonia as a selective reducing agent. The 
second point of difference is that the catalyst and adsorbent of the 
present invention operate at less than 300.degree. C., which is a typical 
commercially economic condition. The catalyst in question in the SCR 
process, must operate above 350.degree., and the single example shows it 
operating at 400.degree. C., thus entailing a substantial commercial 
liability for heating the flue gas or heat exchanging after the reduction. 
In this process the permissible space velocity is 3,000 to 8,000 whereas 
in the present invention the space velocity is 12,000 to 18,000 making for 
lower capital costs. 
U.S. Pat. No. 4,282,115 issued to Atsukawa, et al. as described in the 
abstract, uses ammonia as a reducing agent for the reduction of the 
nitrogen oxides. The novel feature of this patent is that a unique 
support, calcium silicate, is used and is purported to provide improved 
resistance to sulfur poisoning. Thus, the thrust of this patent is one of 
an improved support. Column 3, lines 47 through 67 and column 4, lines 1 
through line 66 list prior art. 
These SCR cases describe the prior art as it pertains to the use of ammonia 
as a selective reducing agent for the nitrogen oxide in the presence of 
oxygen. Other reducing gases such as hydrogen, methane and carbon monoxide 
are mentioned as not being as selective as ammonia. One of the major 
problems, however, with the use of ammonia, is the high temperature that 
is required and the fact that the nitrogen oxide is removed only to the 
extent of 75 to 95% and not the 100% removal accomplished in the present 
invention. Furthermore, the ammonia may not be completely reacted with the 
result that it would, itself be discharged to the atmosphere where it 
would produce harmful pollution. 
A further prior art is a paper which was presented by Shell research of 
Amsterdam (the Netherlands) as a part of the proceedings of the 1989 joint 
EPA-EPRI Symposium on stationary combustion NO.sub.x control. This paper 
discloses that the catalyst is sensitive to sulfur and, as shown on page 2 
of the paper, the NO.sub.x conversion is only 60% to 80%. It also is of 
note that the catalyst is very susceptible to moisture content with the 
result that moisture tends to deactivate the catalyst. All flue or exhaust 
gases would contain 10 or more percent of moisture from the inlet air as 
well as the combustion of the fuel. 
The foregoing prior art all are processes which are very closely related to 
the general process SCR which is the abatement of NO.sub.x using ammonia 
as the reducing gas. Various prior art show the problems with the process 
and through it is very different from the present process, are referred to 
because of the fact that it does remove nitrogen oxide but by a process 
which is vastly inferior and is substantially different from the process 
of this invention. 
A further prior art of this same process is given in Industrial and 
Engineering Chemical Research. Issue 29 in the 1990 volume, pg. 1985-1989: 
This process as described in the introduction on page 1985-1989: This 
process as described in the introduction on page 1985 is very similar to 
the two patented processes previously described, except that amorphous 
chromia is used as catalyst instead of the lanthanum and titanium oxides 
of the previous references. Furthermore, in this test, there is some very 
serious doubt thrown on the validity and commercial utility of the data 
because the gases that are used in the denitrogenation are all anhydrous, 
whereas any commercial process except in very rare cases, would have water 
vapor in it. 
Other types of nitrogen oxide abatement process will be referred to herein. 
The first is one entitled "Enhancement Effect of Magnesium Plus Two Ions 
Under Direct Nitrate Oxide Decomposition Over Supported Palladium 
Catalyst". This is presented in Applied Calalysis 65, 1990, Letters, pg. 
11-Letters page 15. The process is briefly described and superiority is 
claimed in the introduction on page L11. In describing prior work, certain 
precious metals catalyst were described but then it was shown that they 
were not active until temperatures exceeded 500.degree. C. and, 
preferably, were in the range of 700.degree.-800.degree. C. The 
superiority of the catalyst presented and described in this reference, 
which is a magnesium promoted material, is indicated by the fact that it 
will operate at a temperature in excess of 650.degree. C. The process does 
not use ammonia, but the conversion of nitrogen oxide and abatement of 
nitrogen oxide at 550.degree. C. does not exceed 23% and at 650.degree. C. 
does not exceed 50%. These data are shown in table 1 on page L-13. It is 
clear that this process is both expensive from the standpoint of 
temperature requirements and reheat fuel, furthermore is very poor from 
the standpoint of nitrogen oxide abatement. 
A further process, described as the NOXOL process, was briefly described in 
the "Chemical and Engineering News" in their science technology 
concentrates, Oct. 21, 1991, pg. 20. In this process, activated alumina 
granules impregnated with sodium carbonate were used to adsorb both 
nitrogen oxide and sulfur dioxide. The nitrogen oxide was further 
processed by desorbing from the adsorbent, and recycling to the furnace to 
which was added a small amount of methane (natural gas) under which 
conditions the amount of nitrogen oxide abatement increases from 
approximately 6% to approximately 90%. This process is under investigation 
at a commercial installation of the Ohio Power Company at a location which 
was not identified. The efficacy of this process is not given since the 
degree to which the nitrogen oxide is removed from the gases by the sodium 
carbonate alumina adsorbent is not given. The degree to which these 
nitrogen oxides are regenerated from the sodium carbonate is also not 
given, but it would be expected that for good removal, very high 
temperatures would be involved, that is above 600.degree. C. It is not 
stated, but it would be expected that if the sulfur dioxide is adsorbed by 
the sodium carbonate, sodium sulfite would be formed which would, in the 
presence of the oxygen in the gas stream, be converted to sulfate and 
regeneration would be essentially impossible except at extremely high 
temperatures, probably above 1,000.degree. C. No report has recently been 
received of the performance at this commercial site, probably because it 
is too early to get any indication of performance. 
A still further procedure for NO.sub.r abatement is given in "Industrial 
Engineering Chemistry Product Research and Development" of 1983, 21, pg. 
405-408. This process also has serious shortcomings one of which is that 
the test was made with no oxygen in the gas stream, which, of course, 
immediately brings into question its capability of removing nitrogen 
oxides in an atmosphere containing oxygen. Furthermore, temperatures of 
operation and testing were in the range of 600.degree.-700.degree. C. The 
information just quoted is given in the introduction to the paper on page 
405, whereas the temperature of operation is given in the second column on 
page 406. Also, at the bottom of this column, the statement is made to 
have a high conversion when oxygen is present, the temperature must be 
raised to 750.degree. C. From the standpoint of a practical commercial 
operation, this is economically unsound. 
A still further reference is to a paper in "Industrial Engineering 
Chemistry Product Research and Development", 1983, line 21 pg 56-59. This 
process is described in the introduction and comprises a catalyst either 
nickel oxide or cobalt oxide, supported on activated carbon. The activated 
carbon was used for the reduction. A description of the process is given 
briefly in the abstract on page 56 and in the introduction on pages 56 and 
57. This process is one in which a catalyst is consumed in the course of 
the removal of the nitrogen oxide. The NO.sub.x reacts with the carbon 
forming carbon-dioxide, and, simultaneously, the catalyst is being 
destroyed. It is obviously a very poor solution to the problem and its 
commercial development has obviously not been achieved since it has been 
ten years since it was originally proposed in the periodical. 
A further reference is given in "Energy and Fuels", 2989, Vol. III, pg 
740-743. The title of the paper is "Control of NO.sub.x Emissions by 
Selective Catalytic Reductions With Hydrogen Over Hydrophobic Catalysts", 
by L. Fu and K. T. Schuang. The process is described both in the abstract 
and in the introduction, with the basic concept being that a hydrophobic 
support, which in this case is di vinyl-benzene-styrene resin, and the 
catalytic metals, are platinum, platinum plus ruthenium, palladium, 
ruthenium alone, and gold. The conversion in this process was reported to 
be 60-80%, but, in the presence of oxygen, this was sharply reduced. 
SUMMARY OF THE INVENTION 
The present invention relates to a process whereby nitrogen oxides 
generally identified as NO.sub.x are removed from exhaust gases also 
containing oxygen, such as those from gas powered turbines and electric 
power generating stations. These gases contain nitrogen oxide either 
derived from the fuel or from the extremely high temperatures to which 
nitrogen and oxygen in the flue gas are simultaneously heated. The 
NO.sub.x, content may be in the range of 50 to 1000 parts per million and 
the O.sub.2 from 0 to 21%. 
The process of the invention is unique in that it utilizes an adsorbent 
comprising primarily manganese oxides, potassium carbonate, potassium 
permanganate, potassium chromate and dichromate, ceria and alumina which 
will remove the nitrogen oxides over a long time period by a rapid and 
compete adsorption process. The adsorbed nitrogen oxides, after a period 
of adsorption, are removed from the adsorbent by regeneration for reuse of 
the adsorbent. The adsorbent will remove the nitrogen oxides to the extent 
of 100% at a space velocity exceeding 15,000 and a temperature in the 
range of 150.degree.-300.degree. C. or above. The nitrogen oxides can be 
quickly reduced in situ or be evolved from the adsorbent as a concentrated 
stream by passing a gas containing N.sub.2 plus 0.5 to 10% hydrogen at a 
temperature of 300.degree. to 350.degree. C. over the saturated adsorbent. 
The nitrogen oxides in the concentrated stream are reduced to nitrogen and 
water at this temperature. This reduction of NO.sub.x is also 100% 
complete over a catalyst comprising, for example, chromium, copper, cobalt 
or nickel oxides supported on gamma alumina or even the same composition 
as the adsorbent. The adsorbent can be utilized repeatedly in the 
adsorption-desorption cycle without loss of effectiveness. Both the 
catalyst-adsorbent and reducing catalyst are resistant to small quantities 
of SO.sub.x which may be in the exhaust stream. The process is unique 
because it can be utilized for adsorption over a period of hours in a gas 
stream containing oxygen and can readily be regenerated for reuse. 
To one skilled in the art it would be evident that desorption of NO.sub.x 
from the saturated adsorbent could be effected by high temperature 
steaming or displacement with CO.sub.2 or other gas or by evacuating of 
the NO.sub.x from the adsorbent at pressures lower than that of 
adsorption. 
In recent tests it has been possible to design the catalyst bed and/or the 
adsorption catalyst and to effect reduction of the NO.sub.x during 
desorption thus eliminating entirely the catalyst and facilities required 
for a down-stream reduction vessel

DETAILED DESCRIPTION 
This invention provides a procedure whereby NO.sub.x can be removed from a 
gas stream containing oxygen to the extent of essentially 100%. The 
process consists of first adsorbing the nitrogen oxide on a highly 
efficient adsorbent at approximately 200.degree. C., then desorbing the 
nitrogen oxide at a slightly higher temperature using a gas stream which 
contains hydrogen, water vapor and nitrogen, but no oxygen. The nitrogen 
oxide can be simultaneously desorbed and reduced to nitrogen and water 
vapor either by the adsorbent itself acting as a reducing catalyst, or by 
a separate reactor and catalyst type downstream from the adsorbent which 
reduces the nitrogen oxide to elemental nitrogen and water vapor. 
FIGS. 1-2 illustrate reactors which could be used in the practice of this 
invention. With respect to FIG. 1, instead of using individual reactors, 
the desorption reactor can be eliminated by placing the reduction catalyst 
downstream from the adsorbent in the adsorption reactor. In FIG. 2 the 
designation 1 is the pathway for the adsorption step where the inlet gas 
is NO, N.sub.2, O.sub.2, H.sub.2 O and the outlet gas is N.sub.2, O.sub.2, 
H.sub.2 O. The designation 2 is the pathway for the desorption-reduction 
step where the inlet gas is N.sub.2, H.sub.2 and the outlet gas is 
N.sub.2, H.sub.2 O. It is noted that there is an N.sub.2, H.sub.2 addition 
before the second reactor. 
FIG. 3 is a block diagram depicting the complete scheme of NO.sub.x 
abatement from a large volume of gas containing low concentration of 
NO.sub.x and also containing O.sub.2. The designation X is used to 
indicate the control valves directing and controlling flow through the 
system. 
Certain of the catalyst-adsorbent materials are resistant to sulfur 
dioxide, but the catalyst is most efficient in the absence of sulfur 
dioxide in the gas from which the nitrogen oxides are to be removed. The 
most effective agent for the adsorption is manganese and aluminum oxide 
co-precipitated to produce a 50/50 mixture of finely divided mixed 
manganese and aluminum oxides powder. This powder is milled in a ball mill 
to produce a paste comprising water, the aluminum oxide-manganese oxide 
powder and some colloidal cerium oxide to act as strengthening agent for 
the dried milled paste. After the paste has been dried, the granules are 
derived by crushing and screening the dried paste. The granules are 
further treated by adding a solution of potassium carbonate which, on 
drying, leaves the potassium carbonate completely covering the interior 
and exterior of the granules. 
These granules are placed in the adsorption reactor shown in FIG. 1 which 
is heated by an external furnace. The gas containing oxygen, nitrogen 
oxides, water vapor and the remainder nitrogen, is passed through the 
catalyst in the furnace at approximately 200.degree. C. The exit gas is 
free of detectable nitrogen oxides and remain so for a period of more than 
nine hours of testing. 
The adsorbent now containing more than 0.2% NO.sub.x by weight is 
regenerated for reuse by passing a gas containing from .05 to 10% hydrogen 
in nitrogen; both carbon dioxide and water vapor can also be present. The 
catalyst and reactor are heated to 300.degree. C. and the aforementioned 
gas is passed through, simultaneously either reducing the nitrogen oxide 
in situ on the adsorbent and/or passing it downstream to a different 
catalyst in the process system. The reduction catalyst can either be in 
the downstream portion of the same reactor or in a separate downstream 
reactor, as shown in FIG. 2. Economics favor the single reactor. 
After regeneration, the catalyst can be used for adsorption and experience 
indicates that the amount of nitrogen oxide removed in the second use of 
the catalyst can exceed the nine hours previously reported for the first 
use. 
Inasmuch as the regeneration scheme requires that the adsorbent catalyst be 
made available for the regeneration scheme, it is obvious that a second 
reactor in parallel would be required while the first was being 
regenerated. The scheme is shown in its entirety in the FIG. 3. 
As previously stated, one of the most effective adsorbent catalysts is a 
50% manganese oxide 50% aluminum oxide co-precipitated from the nitrate. 
However, all the ratios of manganese to alumina can be used with good 
performance being obtained from 20% manganese oxide to 80% of the aluminum 
oxide, and 80% manganese oxide and 20% aluminum oxide. 
Although manganese oxides appear to be relatively unique as being the most 
effective, adequately effective materials can also be made by substituting 
for the manganese oxide such oxides as iron, nickel, cobalt, zinc, copper 
and molybdenum and tungsten, combinations of these oxides plus manganese 
oxides also are very effective and also have some tolerance to SO.sub.x in 
the gas stream from which the nitrogen oxides are being removed. In 
addition to or as a substitute for the alumina one can use silica, thoria, 
magnesia, calcia, strontia, titania, zirconia, stania or baria or their 
mixtures or the lanthanides. 
Although potassium carbonate is preferred, the alkali carbonate can be that 
of sodium, rhubidium or cesium. Potassium permanganate, potassium chromate 
or dichromate or their mixture can also be used and have some advantages. 
The quantity of alkali can vary from 5 to 50% of the total weight of the 
adsorbent. 
The second stage catalysts that are effective for the reduction of the 
concentrated nitrogen oxide stream are oxides of nickel, cobalt, iron and 
tin combined with chromium oxide, gadolinium oxide supported on alumina, 
silica, titania, ceria, zirconia and others. Many other hydrogenation 
catalysts are effective including the precious metals and the moderated 
precious metals. 
Although the temperature of adsorption is described above as approximately 
200.degree.the temperature can be varied from approximately 100.degree. to 
500.degree.. The reduction can be conducted at 200.degree.to as high as 
500.degree.. Problems may be encountered when the adsorption is at too low 
or too high a temperature, and also the reduction of the nitrogen oxide 
may be adversely influenced (may form a small amount of NH.sub.3) if the 
reduction is conducted at temperatures in excess of 350.degree. C. 
Instead of or in addition to the use of a second (reduction) reactor one 
can recycle the effluent from the reducer or the adsorber itself, and 
small quantities of NO.sub.x to the high temperature combustion zone or 
the incoming flue gas to the adsorber for elimination by either of these 
three means. 
The present invention, differs importantly from the SCR process in that no 
ammonia is used in the reduction of the NO.sub.x. Ammonia is objectionable 
because it may in itself produce nitrogen oxides or it may be incompletely 
reacted in the course of the nitrogen oxide abatement, and, as a 
consequence, produce adverse atmospheric affects. Further points of 
difference are that the adsorbent-catalyst has a uniquely high capacity, 
in that it will function for long periods of time experimentally 
determined to be over nine hours. The regeneration of this catalyst can be 
accomplished in as short a time as twenty minutes, by choosing the proper 
gas type and temperature conditions. This makes it possible for the 
process to be operated on a cycling basis, with high efficiency of 
NO.sub.x adsorption, and high efficiency of reduction of the nitrogen 
oxide so the gas streams involved can, after adsorption and also after 
reduction, be exhausted to the atmosphere as pure gases. 
A third point of difference is that the temperatures employed are all 
either relatively low or a very small volume of gas is heated to the 
350.degree.-500.degree. C. range. This is in contrast to the 
aforementioned background processes at which the gas may be heated as high 
as 800.degree. C., and in huge volume. Always, in the background 
processes, the heating or secondary heat recovery is performed on the 
entire gas stream, whereas in this invention , it is a small stream used 
for the regeneration process. This gas stream may be from 1-3% of the 
volume of the gas from which the nitrogen oxide is removed. 
The temperature used for the adsorption in the present invention, 
200.degree. C., is very close to if not equal to the temperature at which 
the gas would be exhausted from a boiler or compressor. This means that it 
would be unnecessary to heat or reheat large volume of gas because the low 
temperature of adsorption is essentially identical to that of the flue gas 
exhaust. As for the reduction gas, as pointed out previously, this is of 
such low volume that the cost of heating it to the 300.degree.-400.degree. 
C. desired is economically of little concern. 
EXAMPLES 
The following examples demonstrate the procedure for manufacturing first 
the adsorbent, second the reduction catalyst for reducing the nitrogen 
oxide and last the testing procedure whereby the catalyst and adsorbents 
were evaluated. The extent of the examples is such that they demonstrate 
the procedures and materials used, but it should in no way limit the 
extent to which this concept can be extended. Example 1 is as follows: 
The Adsorbent 
1. An aqueous solution is made consisting of 1 ltr. of distilled water and 
0.5 mole of manganese nitrate, anhydrous, and 0.5. mole aluminum nitrate 
nonahydrate. 
2. The solution is adjusted to a temperature of 30.degree. C. and is 
rapidly, agitated with a paddle type agitator. 
3. With the agitator operating, a 10% solution of potassium carbonate is 
added until a pH of 6.8-7.0 is attained. 
4. With carbon dioxide constantly bubbling through the slurry, the slurry 
is agitated at 30.degree. C. for a period of 1 hour after the correct pH 
is attained. 
5. After this period of supplemental carbon dioxide addition, the slurry is 
filtered and separated from the supernatant liquid. 
6. The filter cake is dried at 150.degree. C. and then is calcined for 2 
hours at 400.degree. after the temperature reaches 400.degree. C. 
7. The powder is ball milled for 18 hours with sufficient water to make a 
thin slurry. 
8. The slurry is removed from and washed out of the ball mill into a large 
beaker and is washed by decantation using a solution of 0.10% of ammonium 
bicarbonate. The purpose of which is to ion exchange out the alkali ion 
and replace it with ammonium ion. The ammonium ion is volatilized and 
removed from the adsorbent during subsequent heating. 
9. After the washing by decantation and removal of the potassium to less 
than 0.10%, the slurry is filtered and washed on the filter. 
10. The washed filter cake is dried at 150.degree. C. 
11. The washed and dried cake is next ball milled with sufficient water to 
produce a relatively thin slurry in which is included sufficient colloidal 
cerium oxide to result in a 3% content in the dried milled paste. The 
milled paste is dried at 150.degree. C. 
12. After drying, the cake is crushed and granulated to produce a screen 
size distribution preferred in the subsequent test. This range is usually 
8 to 14 mesh. 
13. The granules are now impregnated with a solution of K.sub.2 CO.sub.3 in 
such volume and concentration to give K.sub.2 CO.sub.3 content of 50% of 
the total weight of the dry adsorbent Instead of 50% the percentage can be 
varied from 10 to 90% but the 50% content has proved to be optimum. 
Instead of K.sub.2 CO.sub.3, Na.sub.2 CO.sub.3, Rb.sub.2 CO.sub.3 or 
Cs.sub.2 CO.sub.3 can be used or the bicarbonates of the alkali metals. 
14. The adsorbent is now dried and after drying is ready for use. 
Description of the Preparation of the Reduction Catalyst 
The reduction catalyst is made by the following procedure: 
1. A solution is made containing 0.5 mole of nickel nitrate hexahydrate and 
0.5 mole of chromium nitrate. Sufficient distilled water is used in this 
step to produce a total of a one molar solution. 
2. The solution is heated to 30.degree. C. and a concentrated solution of 
ammonium bicarbonate is added to reach a pH of 6.8 to 7.0. 
3. At the completion of precipitation, the slurry is agitated for an 
additional one hour, during which time carbon dioxide in finely divided 
bubbles, is bubbled through the slurry to attain a high carbonate level in 
the precipitate. 
4. The slurry is filtered and washed then the filter cake is dried at 
150.degree. C. 
5. After drying, the reduction catalyst is calcined at 400.degree. C. for 
two hours after reaching 400.degree.. After performing 5, the procedure 
becomes the same as items 6 through 12 of the instructions for the 
adsorbent in the initial part of this example. 
The next section of this example 1 is evaluating the adsorbent and the 
reduction catalyst as subsequently described. 
Evaluation of the Adsorbent and Reduction Catalyst 
1. Two reactors are set up in sequence, with the first reactor and the 
second reactor being essentially identical in all respects. The reactors 
in question comprise a quartz tube 7/8" in diameter by 24" long, which is 
placed in a split furnace, enabling the heating of the reactor to a chosen 
temperature from 100.degree. C. to 500.degree. or greater, as is required 
for the test in question. The reactors are each equipped with a means of 
introducing gas at the top of the reactor and removing the gas at the 
bottom of the reactor. Thermocouples are placed in such locations that the 
temperature of the furnace and the interior of the catalysts bed and the 
upstream portion just above the catalyst bed, can be determined and 
controlled. The gases entering the reactors are heated and controlled by 
suitable control equipment. 
The evaluations are conducted as follows in the previously described 
equipment: 
1. The adsorbent is placed in the first reactor and is situated in such a 
way that a vertical column of the adsorbent, at least 3 reactor diameters 
high, (Ca. 3 inches) is present in the reactor with the thermocouples in 
locations where temperature can be indicated and controlled. The reactor 
is heated to 180.degree. C. and a gas flow, comprising 400 parts per 
million of nitrogen oxide, 3% oxygen 12%-15% water vapor and the remainder 
nitrogen, is passed over the catalyst at a space velocity of from 3,000 to 
20,000. At this temperature and at this flow, the gas is measured exiting 
the unit and an analysis indicated zero parts per million of NO.sub.x in 
the gas exit stream. 
2. Flow is continued for a total of nine hours and, during this period, 
analyses are made on twenty minute intervals until the end of the nine 
hour period. During this period, removal of NO.sub.x is 100% complete. 
3. At this point, the nitrogen oxide on the adsorbent must be removed in 
order to prepare it for further use as an adsorbent. To accomplish this, a 
gas stream comprising nitrogen, 0.5 to 5% hydrogen and 8-12% water vapor 
is passed over the catalyst at a space velocity of 3,000-12,000 and at a 
temperature of 300.degree.-325.degree. C. 
4. A temperature rise of approximately 50.degree. C. is noted in the 
catalyst bed as the nitrogen oxide is removed and simultaneously reduced. 
5. Reduction is continued for two hours during which time the nitrogen 
oxide being desorbed totals approximately 22% of that which had been 
originally adsorbed, with the remainder, which is not amenable to 
analysis, being converted to elemental nitrogen and water vapor before or 
during desorption in the H.sub.2 containing gas stream. 
6. At the conclusion of two hours, the adsorbent has been regenerated for 
reuse. 
7. While the adsorbent is being regenerated, the nitrogen oxide which is 
contained in the effluent, is passed through the second reactor at a 
temperature of 300.degree.-325.degree. C. In this reactor, 100% of the 
nitrogen oxide remaining is converted to water vapor and nitrogen. 
8. The temperature in the adsorbent portion of the two reactors can be 
changed from as low as 100.degree. C. to as high as 500.degree. C., the 
optimum being approximately 180.degree.-200.degree. C. but is dependent on 
space velocity. Furthermore, the temperature in the reducing vessel can be 
changed to 250.degree.-500.degree. C. with the optimum being approximately 
300.degree. C. Further, the two reactors can be combined in such a way 
that the adsorbent is in the top stage of a single reactor, and the 
reductant catalyst in the bottom stage of the same reactor, and the 
temperature can be varied to accomplish both the adsorption stage at 
200.degree. C. and the reduction stage at a higher temperature. If the 
temperature at this point is raised to approximately 325.degree. C., the 
adsorbent will perform two desirable things, one of which is the adsorbed 
nitrogen oxide can be removed totally in about twenty minutes and 
approximately 80% of the nitrogen oxide is reduced to water vapor and 
elemental nitrogen during this desorption stage. The decision as to 
whether two reactors should be used versus one, is dependent upon the 
conditions of an individual system, which decisions are made on the basis 
of economics and industrial/commercial factors. 
After the regeneration, the adsorbent was again used and was examined for 
adsorption characteristics and these proved to be at least as effective as 
the initial test. The adsorbent and reduction catalyst were used, reused 
and regenerated for a total of 12 cycles with little to no deterioration 
in performance. 
Instead of the manganese alumina mixture used in the adsorption, many other 
types can be used as discussed and shown in the subsequent examples. The 
same variation in composition can be made in the reducing portion of the 
catalyst beds with the result that a large number of candidates are 
suitable for this service. Many of these will be identified in the 
abbreviated examples presented in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Abbreviated Presentation of Examples 2 through 17 
__________________________________________________________________________ 
Abreviated Ingredient 
Example Atomic Hardening 
NO.sub.x 
Time 
Number 
Composition 
Ratio Precipitant 
Agent Removed % 
Hours 
__________________________________________________________________________ 
2 MnO.sub.x /Al.sub.2 O.sub.3 
50/50 K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
99 6 
Colloidal 
3 MnO.sub.x /Al.sub.2 O.sub.3 
50/50 K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
100 4 
4 MnO.sub.x Al.sub.2 O.sub.3 
50/50 K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
100 3 
5 BaOAl.sub.2 O.sub.3 
50/50 K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
25-50% 2.5 
6 CaOAl.sub.2 O.sub.3 
50/50 K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
5-40% 2 
7 MgOAl.sub.2 O.sub.3 
50/50 K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
25-40% 2 
8 MnO.sub.x CaOAl.sub.2 O.sub.3 
25/25/50 
K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
78-93% 4.5 
9 MnO.sub.x MgOAl.sub.2 O.sub.3 
25/25/50 
K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
62-99% 6 + 6 
10 Same as Test 9 92-100 7 
11 MnO.sub.x MgOAl.sub.2 O.sub.3 
25/25/50 
K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
80-96% 6.5 
12 MnO.sub.x SiOAl.sub.2 O.sub.3 
50/25/25 
K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
50-80% 3.5 
13 MnO.sub.x MgOAl.sub.2 O.sub.3 
50/25/25 
K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
70-90% 3.5 
14 MnO.sub.x ZrOAl.sub.2 O.sub.3 
25/25/50 
K.sub.2 CO.sub.3 
3% C.sub.e O.sub.2 
70-96% 6.5 
15 NiOAl.sub.2 O.sub.3 
50/50 K.sub.2 CO.sub.3 
5% 100% 5.5 
colloidal 
SiO.sub.2 
16 NiOAl.sub.2 O.sub.3 
32/18/50 
K.sub.2 CO.sub.3 
5% SiO.sub.2 
100% 4.0 
17 Commercial 
100% -- None 99% 1.0 
MnO.sub.x 
MnO.sub.x Necessary 
18 See below, following Note 2. 
__________________________________________________________________________ 
Abreviated NO.sub.x Reduced 
Example 
Adsorption 
Time 
Regeneration 
During Promoter 
Number 
Temperature 
Hours 
Temperature 
Regeneration 
Alkali 
__________________________________________________________________________ 
2 195-210 
2 205-305 
56% K.sub.2 CO.sub.3 
3 180-225 
2 205-330 
75% K.sub.2 CO.sub.3 
4 170-206 
2 293-312 
75% K.sub.2 CO.sub.3 
5 185-229 
None None 
6 191-227 
None None 
7 191-227 
None None 
8 191-215 
None None 
9 195-210 
3 hours 
310-340 
70% K.sub.2 CO.sub.3 
10 197-211 
3 hours 
310-350 
75% K.sub.2 CO.sub.3 
11 198-276 
3 hours 
310-345 
29% 
12 205-265 
13 178-268 
14 181-250 
15 250 C. 1.5 400.degree.-500.degree. C. 
Not K.sub.2 CO.sub.3 
determined 
16 300.degree. C. 
0.16 
400.degree. C. 
Not K.sub.2 CO.sub.3 
determined 
17 250.degree. C. 
2.0 300.degree. C. 
Not K.sub.2 CO.sub.3 
determined 
18 
__________________________________________________________________________ 
Note 1 to first 17 Examples 
The foregoing 17 examples portray individual tests of most significance but 
many other tests were made to determine the optimum CeO.sub.2 content as 
hardener (range 1 to 15%), MnO.sub.x /Al.sub.2 O.sub.3 ratio (10/90 to 
90/10) and the preferred alkali, both type and quantity, (50% K.sub.2 
CO.sub.3); Na.sub.2 CO.sub.3, Cs.sub.2 CO.sub.3, and Rb.sub.2 CO.sub.3 
were compared to K.sub.2 CO.sub.3. A range of 10 to 75% on the basis of 
total weight of the catalyst were evaluated and 50% of K.sub.2 CO.sub.3 
was preferred. The preferred precipitant was KHCO.sub.3. 
Note 2 
Although elements as oxides other than MnO.sub.x were evaluated, the best 
adsorbent was either all MnO.sub.x and alumina or a composition in which 
MnO.sub.x was still a significant component. 
Example 18 
This example is a summary of fabrication procedures and component 
identification for useful NO.sub.x reduction catalysts. These catalysts 
are to be used in that portion of the abatement system represented by the 
next to the last block of the block diagram of FIG. 3. As explained herein 
before, if the two reactors are combined into a single reactor this 
reduction catalyst would be in the down-stream portion of that reactor. 
Thus the reduction catalyst, e.g. NO.sub.x +H.sub.2 &gt;H.sub.2 O+N.sub.2 and 
its possible components are much broader than for the catalyst adsorbent. 
Examples of the preferred reduction catalyst are given in Example 1 and 
are comprised of copper oxide and chromia or probably some copper 
chromite. This catalyst is preferred because it has little if any, 
tendency for the formation of NH.sub.3. However, with proper selection of 
operating conditions, temperatures, space velocity, reducing gas 
composition and catalyst calcining condition, many other elements can be 
substituted for both the copper and chromium. As examples but not limited 
to are Al, Fe, Ti, Zr and Sn. These ingredients as soluble salts, 
preferably nitrates, are processed as described in Example 1 to produce a 
granular product. The ingredients can also be impregnated onto and into a 
support such as alumina, silica, silica alumina, activated carbon, silicon 
carbide, and others well known to the art. The form of the supports can be 
granules, cylinders, rings, honey combs, rods, spheres and others also 
known to the art. These same forms are suitable also for the adsorbent.