Showing papers on "Selective catalytic reduction published in 1990"

Method for reduction of nitrogen oxides with ammonia using promoted zeolite catalysts

Abstract: A method comprising passing through a zeolite catalyst, a gaseous stream containing nitrogen oxides, ammonia and oxygen to selectively catalyze the reduction of nitrogen oxides and, if excess or unreacted ammonia is present, to oxidize the excess of unreacted ammonia with oxygen to hydrogen and water The method includes the use of a zeolite catalyst composition which comprises a metal (eg, iron or copper) promoted zeolite, the zeolite being characterized by having a silica to alumina ratio of at least about 10 and a pore structure which is interconnected in all three crystallographic dimensions by pores having an average kinetic pore diameter of at least about 7 Angstroms Promoted zeolites of the above type have demonstrated high tolerance for sulfur poisoning, good activity for the selective catalytic reduction of nitrogen oxides with ammonia, good activity for the oxidation of ammonia with oxygen, and the retention of such good activities even under high temperature operations, eg, 400°C or higher, and hydrothermal conditions

Staged metal-promoted zeolite catalysts and method for catalytic reduction of nitrogen oxides using the same

Abstract: A zeolite catalyst composition is provided in which a first or upstream zone of the catalyst has a lower metal (e.g., iron or copper) promoter loading than the metal promoter moter loading of the second or downstream zone of the catalyst. The first zone may contain from none up to about 1 percent by weight of the promoter and the second zone may contain from about 1 to 30 percent by weight promoter. The zeolite may be any suitable zeolite, especially one having a silica-to-alumina ratio of about 10 or more, and a kinetic pore size of about 7 to about 8 Angstroms with such pores being interconnected in all three crystallographic dimensions. The method of the invention provides for passing a gaseous stream containing oxygen, nitrogen oxides and ammonia sequentially through first and second catalysts as described above, the first catalyst favoring reduction of nitrogen oxides and the second catalyst favoring the oxidation or other decomposition of excess ammonia.

Deactivation of the Vanadia Catalyst in the Selective Catalytic Reduction Process

Abstract: Results are summarized of a comprehensive study of the effects on the SCR process of all major possible poisons encountered in the combustion gases from U.S. coals. A general rule evolved from this study Is that the effect of the additive on the catalyst activity Is directly related to the basicity of the additive; poisoning Is caused by the basicity. Quantitative effects are presented, while a qualitative summary is given as follows: strong poisons-alkali metal oxides; weak poisons-oxides of alkaline earth metals, arsenic, lead phosphorus and chlorides of strong alkaline metals. SO2 is a promoter due to its acidity. HCI, although acidic, reacts with both NH3 (forming NH4CI) and V2O5 (forming VCI2 and VCI3) and consequently strongly deactivates the SCR reaction. A summary is also given for a theoretical and experimental study of the monolithic honeycomb reactor using both undoped and poison-doped catalysts. The results showed that the reactor performance can be predicted directly from the intrinsic cataly...

Chapter II.3 Catalytic Decomposition of Nitrogen Monoxide

Abstract: The exhaust gases from vehicle engines and industrial boilers contain considerable amounts of harmful nitrogen monoxide (NO). To remove NO, catalytic reduction processes using NH 3 , CO or hydrocarbons have been applied, but several problems remain to be solved. It is suggested that a catalytic decomposition process be used for NO removal. The present states and the problems with various processes, including reduction, adsorption and decomposition, are outlined and then the catalytic performance of copper ion-exchanged zeolites for NO decomposition is summarized. Finally, a reaction mechanism is suggested on the basis of IR, ESR, phosphorescence, temperature-programmed desorption and kinetic data.

Cold selective catalytic reduction of nitric oxide for flue gas applications

Abstract: Commercial selective catalytic reduction (SCR) processes for the reduction of NO to N 2 by NH 3 require temperatures above 300°C. Significant SCR activities have been measured for transition metal sulfates as the catalysts, at temperatures as low as 30°C. Under commercial SCR throughput and gas composition conditions, a 10% NiSO 4 /Al 2 O 3 catalyst exhibited NO x conversion of over 50% in the temperature range 50-120°C and another activity peak at 200-250°C with nearly 80% NO x conversion. The low-temperature SCR activity was attributed to the Bronsted acidity of the surface. The Bronsted acidity, and hence the SCR activity, decreased upon the adsorption of water and increased with the presence of SO 2 in the gas phase

Catalytic methods for lowering the amount of nitrogen oxides in exhaust gases on combustion of fuel

Abstract: The catalytic methods for reducing the amount of nitrogen oxides in exhaust gases on combustion of different types of fuel are analysed: the catalytic combustion method and the method involving the selective catalytic reduction of nitrogen oxides by ammonia. The bibliography includes 187 references.

Catalyst for removal of nitrogen oxides and method for removal of nitrogen oxides by use of the catalyst

Abstract: A honeycomb catalyst for effecting catalytic reduction and removal of nitrogen oxides in waste gas in the presence of ammonia, which homeycomb catalyst (I) contains a catalytically active substance comprising 60 to 99.5% by weight of a binary oxide containing titanium and silicon and 40 to 0.5% by weight of the oxide of at least one metal selected from the group consisting of vanadium, tungsten, molybdenum, copper, manganese, cerium, and tin, (II) possesses an opening ratio in the cross section of said catalyst in the range of 80 to 90%, (III) has a thickness of partition walls separating through holes in the range of 0.2 to 0.8 mm, and (IV) possesses pores comprising substantially two independent pore groups each of a uniform pore diameter, such that the pore volume occupied by one pore group having a pore diameter in the range of 0.01 to 0.03 μm accounts for a proportion in the range of 50 to 80% of the total pore volume and the pore volume occupied by the other pore group having a pore diameter in the range of 0.8 to 4 μm accounts for the proportion of the range of 10 to 30% of the total pore volume.

Process for removing carbon-containing or nitrogen oxide-containing pollutants in flue gases

Abstract: A process for the removal of carbon-containing or nitrogen oxide-containing pollutants in low-dust flue gases by catalytic reduction, which is characterized in that a reducing agent is injected through nozzle(s) into the intermediate space of one stage of the economizer, said reducing agent is mixed with the low-dust flue gas in the tube bundles of the economizer, and the resultant reduction flue gas mixture passes catalyst layers located downstream of the economizer at a local velocity greater than 6.5 m/s.

A process for the removal of nitrogen oxides from offgases from turbines.

Abstract: Nitrogen oxides can be removed from turbines by a selective catalytic reduction (SCR) with ammonia with greater efficiency than by prior art technique if the ammonia needed for the reduction of the nitrogen oxides is added before the turbine, preferably in a stoichiometric excess compared to the contents of nitrogen oxides in the exhaust gas. One can employ well-known SCR catalysts and advantageously the exhaust gas after the turbine is passed through a layer of SCR catalyst followed by a layer of a combustion catalyst. The latter expediently consists of metal oxides, preferably selected from copper oxide, manganese oxide and chromium oxide, deposited on aluminum oxide, magnesium oxide, silicon oxide or mixtures thereof.

Ammonia recovery from purge gas

Abstract: A continuous process for recovering ammonia from a purge gas of an ammonia synthesis system wherein the purge gas is scrubbed by an aqueous liquid solution in counter-current flow with continuous cooling which is controlled to maintain temperature levels safely above the freezing point and to produce an aqueous solution of high ammonia concentration which is mixed with an anhydrous ammonia product of the ammonia synthesis system to form a blended ammonia product with a minimum water concentration high enough to provide corrosion protection to carbon steel storage equipment and a maximum water concentration low enough to meet a maximum design specification for the concentration of water in the blended ammonia product.

Process for producing a catalyst for denitration by catalytic reduction using ammonia

Abstract: A catalyst for denitration by catalytic reduction using ammonia capable of preventing catalyst deterioation due to vapors of heavy metal compounds contained in exhaust gases and having a high strength and a superior resistance to poisons and a process for producing the catalyst are provided, which catalyst comprises TiO2, oxide(s) of at least one of V, Cu, Fe and Mn and oxide(s) of at least one of Mo, W and Sn, the total of the mol number(s) of the oxide(s) of at least one of Mo, W and Sn falling within a range of 2×10-6 to 20×10-6 mol/m2 per the unit specific surface of the catalyst, and which process comprises having oxide(s) of at least one of Mo, W and Sn adsorbed and supported onto a composition comprising TiO2 prepared in advance and oxide(s) of at least one of V, Fe, Cu and Mn so as to give the above-specified total of the mol number(s) of oxide(s) of at least one of Mo, W and Sn.

Treatment of waste combustion gas

Abstract: PURPOSE: To efficiently remove the NOx, SOx and CO 2 in the waste combustion gas by removing the NOx in the gas with ammonia, then removing the SOx by the lime-gypsum process and further bringing the gas into contact with an amine-based compd. CONSTITUTION: The NOx in the waste combustion gas are removed in a denitrator 3 by the selective catalytic reduction process with ammonia as a desulfurizing agent. The SOx in the gas are then removed in a desulfurizer 7 by the lime-gypsum process. The gas is successively brought into contact with at least one kind of material among an amine-based compd. (e.g. monoethanolamine), potassium carbonate and sodium carbonate in a decarbonator 9 to remove CO 2 . Consequently, the NOx, SOx and CO 2 in the waste combustion gas such as a boiler waste combustion gas are comprehensive ly and effectively removed. COPYRIGHT: (C)1991,JPO&Japio

Process for the recovery of ammonia from flue gases

Abstract: For reducing nitrogen oxides in the flue gases of a firing plant, fresh ammonia water, i.e. an aqueous solution of ammonia (NH3), is introduced into the flue gas flow. For achieving a high degree of separation of the nitrogen oxide a superstoichiometric addition of ammonia (NH3) is necessary. Most of the excess ammonia is washed out in the wet washer (6). A liquor, e.g. milk of lime (Ca(OH)2), is dosed into the wash water in a connecting line (10) to a stripping column (11), so that a pH-value above 9.5 is obtained. The now physically dissolved ammonia (NH3) is desorbed from the wash water in the stripping column (11). The steam/ammonia mixture passing out of the stripping column (11) is condensed in a condenser (17) and the condensate in the form of ammonia water is admixed to the fresh ammonia water in feed line (3). As a function of the nitrogen oxide reduction, approximately 10 to 50% of the fresh ammonia water can be saved.

Mechanism of the reduction of NO on oxide catalysts

Abstract: When a mixture of NO with CO (H 2 , CH 4 ) is in contact with metal oxides, in addition to the catalytic reaction between these substances they also interact with the catalyst. The observable rates of interaction with the catalyst differ from the rates of the reduction and reoxidation of the catalyst as a result of the presence of adsorbed molecules of the reagents or fragments of them on its surface. The reaction of catalytic reduction of NO on oxide catalysts proceeds primarily according to an associative mechanism

Catalytic reduction of dinitrobenzenes using a noble metal catalyst and iron or iron salts

Abstract: There is provided an improved process for the reduction of optionally substituted dinitrobenzenes to the corresponding nitroanilines with high yields which comprises contacting the dinitrobenzene with hydrogen in an acidic medium in the presence of a catalytic amount of a combination of a noble metal hydrogenation catalyst, and iron or an iron salt Isomer specific reductions may be achieved with those compounds containing suitable directing substituents The 2-halo-5-nitroanilines which may be produced in this process may be converted via a multi-step synthesis to useful 1-aryl-4-substituted 1,4-dihydro-5H-tetrazol-5-one herbicides

Process for catalystically removing nitrogen oxides from exhaust gases by means of reducing agent

Abstract: A method for the removal of nitrogen oxides contained in exhaust gases of an optionally fluctuating composition with a temperature of 0 DEG -600 DEG C. by means of catalytic reduction at a preselected stoichiometric ratio between the concentration of reducing agent and the concentration of nitrogen oxide in which the reducing agent is dosed in a pulsed manner.

Removal of nitrogen oxide from flue gas by selective reduction

Abstract: PURPOSE: To obtain a catalyst having activity and selectivity free from being affected even in the presence of sulfur dioxide by carrying a vanadium (III) compound on a SiO2 carrier and converting the vanadium (III) into V2 O5 . CONSTITUTION: In the production of the catalyst used for a ammonia catalytic reduction method of nitrogen oxide, the V (III) compound is applied on the SiO2 carrier material and is converted to V2 O5 . At the same time, titanium (III) is converted to titanium (IV). The resultant catalyst obtained in the manner exhibits excellent activity and selectivity for the reaction of nitrogen oxide with ammonia and the oxidation of ammonia for forming nitrogen molecule at a higher temp.

Reduction of oxides of nitrogen in diesel exhaust with addition of partially decomposed ammonia.

Abstract: A chemical process capable of reducing nitric oxide from the diesel engine exhaust is studied. In this process, an amidogen (NH2) -containing ammonia gas is mixed with the exhaust gas to ensure destruction of NO by NH2 at a relatively low temperature level. Theoretical predictions based on the rate-controlled partial equilibrium method show that the addition of only a small amount of NH2 may effectively reduce nitric oxide in the exhaust gas. The feasibility of the proposed process is demonstrated on a miniature system consisting of an NH2 producer and a mixing chamber into which a part of exhaust gas from a diesel engine is introduced. Results show that a significant reduction of nitric oxides is achieved at a mixing-chamber temperature higher than 750 K. Furthermore, the practical feasibility in controlling NOx is compared with that of the cianuric-acid method proposed by Perry and Siebers.

Zeolite catalyst accelerated stepwise by metal and catalytic reduction process for nitrogen oxide using said catalyst

Abstract: PURPOSE: To efficiently reduce NOx by treating a gas contg. the NOx and ammonia with a zeolite catalyst contg. =1 wt.% iron or copper. CONSTITUTION: A compd. of individual iron and copper and/or the both is carried on zeolite by =1 wt.% (expressed in terms of metal) for the wt.% of the zeolite to prepare a 2nd catalyst. A gaseous stream contg. NOx and ammonia is passed through the 1st catalyst zone to reduce and decrease the NOx and then, the steam is passed through the 2nd catalyst zone to reduce and remove the NOx in the stream.

Method of vanadium catalysts preparation on oxidative carriers

Abstract: The solution concerns the preparation method for vanadium catalysts applied by means of direct interaction of V2O5 with the oxide carrier, while the reaction is induced by highly intensive grinding in mechano-chemical activators. This simple method, not requiring usage of liquid or gaseous impregnation agents, enables preparation of catalysts suitable especially for the reaction of selective catalytic reduction nitrogen oxides. The so prepared catalysts are comparable to catalysts prepared by former, technologically more complicated methods.

Production of n-benzylpyrrolidine derivative or its salt

Abstract: PURPOSE:To obtain the title substance which is nseful as a medicine, agrochemical or a starting substance in the pure form simply, economically in high yield by catalytic reduction of a pyrrolidine or its salt and benzaldehyde in the presence of a metal catalyst such as Raney nickel. CONSTITUTION:A compound of formula I (X is 1-3C alkyl, hydroxyl, halogen, H) or its salt and benzaldehyde are stirred in the presence of a metal catalyst in a hydrogen atmosphere of normal pressure to 10-kg/cm at 20 to 100 deg.C for 1 to 100 hours to give a compound of formula II. The metal catalyst is Raney nickel, platinum oxide, Rh catalyst. Ru catalyst, Pd catalyst, preferably Raney cobalt, Raney nickel or Raney copper. In the reaction, an acid such as hydrochloric acid, p-toluenesulfonic acid or a dehydrating agent such as anhydrous sodium sulfate may be added in an amount of 0.01 to 1 equivalent to the compound of formula I.

Low temperature catalytic reduction of nitrogen oxides

Abstract: Commercially viable processes of the SCR type for converting nitrogen oxides to nitrogen with ammonia: (a) in the presence of an iron, cobalt, nickel, or other transition metal sulfate with Bronsted activity; (b) at a temperature of not more than 250° C.; and (c) preferably in a dry environment if room or near room temperatures are employed. The process may be used to eliminate nitrogen oxides from flue gases, other exhaust gases, and the like and in other applications in which the reduction of a nitrogen oxide is wanted. Excess ammonia and/or sulfur dioxide may be maintained in the reaction mixture to promote process efficiency. The catalysts have appreciable Bronsted activity even at ambient temperatures and are capable of effecting NO x conversions with efficiencies of at least 50 percent in even demanding applications at temperatures below the 250° C. maximum. They can be unsupported or supported on a porous support. If of the latter type, the catalyst can be prepared by impregnating the support with an aqueous solution of a selected transition metal salt and then drying the impregnated support. Also, if the salt is not a sulfate, the salt is calcined and the resulting oxide reacted with a compound such as sulfur dioxide to generate the sulfate.

Method of removing nitrogen oxides from combustion exhaust gas

Abstract: A method of removing nitrogen oxides formed in an exhaust gas of a combustion apparatus and reducing the residual ammonia concentration, which comprises spraying an aqueous urea solution having controlled hydrogen ion concentration into a combustion chamber or an exhaust passage of the combustion apparatus in accordance with the combustion state of the apparatus. The nitrogen oxides can be removed appropriately in the combustion state of a relatively low temperature by controlling the hydrogen ion concentration of the aqueous urea solution and the quantity of the generated residual ammonia can be minimized.

Photoacoustic NH3 Monitoring with Waveguide CO2 Lasers

Abstract: Ammonia is not a natural constituent of fossil fueled power plant emission, but nitrogen oxides and sulphur dioxide are. In various schemes for denitrification and desulphurization, ammonia is introduced either as a reducer of NOX as in the Selective Catalytic Reduction (SCR) process or as a neutralizer for acids developed in the denitrification, as in the corona based CORONOX process. In either case one wants to monitor the efficiency of the process and to be able to document compliance with NH3 emission limits. Thus, there is an increasing need for ammonia measurements in smoke stacks, and the monitor needs to be: moderately sensitive, corresponding to 1 ppm detection limit; very selective, so as to monitor NH3 regardless of known and unknown components in the smoke; automatic; moderately fast, corresponding to 1 measurement per 10 minutes for normal monitoring, and 1 per minute for reactor characterization and process optimization.