Selective Catalytic Reduction process

Schar, C. (2003) Control of a Selective Catalytic Reduction Process, Ph.D. Thesis No. 15221, ETH Zurich. 

In the environmental sector ammonia is used in various processes for removing S02 from flue gases of fossil-fuel power plants. The resulting ammonium sulfate is sold as fertilizer. In the selective catalytic reduction process (SCR) the NOx in flue gases is reduced in a catalytic reaction of the nitrogen oxides with a stoichiometric amount of ammonia [1427] - [1430]. Also noncatalytic reduction is applied with ammonia or urea solutions. 

Lateral transport of heat and reactants across the diameter of the reactor This feature is important when the reaction has a high heat effect or when insufficient mixing of the reactants would have a strong adverse effect on the performance. Examples are selective oxidation processes (highly exothermic), where lateral or radial temperature gradients would decrease the selectivity of the conversion. Another example is the selective catalytic reduction process of nitric oxide with ammonia, where mixing of ammonia with the flue gas is often a point of great concern. Because the void space in a BSR is continuous... 

Monolithic honeycomb have found major application in the selective catalytic reduction process (Fig. 16). The pressure op is about 250-1000 Pa. The SCR reactor asks for a flat velocity profile of the flue gas. Therefore, a layer of dummy honeycombs is installed for flow-straightening purposes. 

With the selective catalytic reduction process by using ammonia as reducing agent, NOx emission can be reduced under diesel engine exhaust gas conditions... 

SCR (selective catalytic reduction) process SNCR (selective noncatalytic reduction) process Wet process Photocata lytic process... 

Also for oxidation reactions, the choice of the alumina support mainly depends on two criteria the stability of the phase at the reaction temperature and the reactivity (or better the lack thereof) toward feed components and products. For example, ethylene oxychlorination to ethylenedichloride is performed at approximately 220-250° C and 5-6 atm in the presence of a y-Al203-supported catalyst, which has a surface area of from 100 to 200 m and contains 10wt% CUCI2 and 3 wt% KCl, (423,424). Another example is a process called ammonia selective oxidation (ASO, or also selective catalytic oxidation, SCO), which converts small amounts of NH3 from waste gases to N2 at reaction temperatures of 150—300 °C. The process is used to abate the ammonia sHp after a selective catalytic reduction process with ammonia or urea in diesel-engine-exhaust after-treatment (425). The patented catalyst consists of Y-AI2O3 (60—300 m g ) loaded with 0.5-4 wt% platinum and 0.5—4 wt% vanadia and is coated onto the surface of a ceramic or metallic monoftthic structure (426). 

Chen J P, Buzanowski M A, Yang R T, Cichanowicz J E (1990) Deactivation of the Vanadia Catalyst in the Selective Catalytic Reduction Process. J Air Waste Manage Assoc 40 1403-1409... 

Park J-H, Park HJ, Baik JH et al (2006) Hydrothermal stability of CuZSM5 catalyst in reducing NO by NH3 for the urea selective catalytic reduction process. Journal of Catalysis 240 47-57... 

Koebel M, Elsener M, Madia G (2001) Reaction Pathways in the Selective Catalytic Reduction Process with NO and NO2 at Low Temperatures. Industrial Engineering Chemistry Research 40 52-59... 

Koebel M, Elsener M (1998) Oxidation of Diesel-Generated Volatile Organic Compounds in the Selective Catalytic Reduction Process. Ind Eng Chem Res 37(10) 3864-3868... 

Selective Catalytic Reduction Processes on Metal Oxides... 

The aim of the project is to evaluate the perspective of a modified selective catalytic reduction process to reduce NO emissions from flue gas. In a previous study the activity of the equimolar NO/NO2 reduction was found to be higher then the NO reduction. The modified process is based on the equimolar NO/NO2 reduction. NO being the predominant NO component in flue gas from stationary sources, must then be partly oxidized to NO2. A desk study is carried out to review the literature on methods for flue gas composition modification with respect to the NO/NO2 ratio. The evaluation of the modified SCR process also requires more knowledge about the increase in catalytic activity of the equimolar NO/NO2 reduction as compared to the NO reduction and about the effect of catalyst composition on the reaction rate. In order to investigate these aspects, an experimental programme is carried out, using four different catalyst materials two commercial preparations and two self-prepared vanadium-titaniumdioxide catalysts. The results of activity measurements for NO, NO2 and the equimolar NO/NO2 reduction are reported, under conditions relevant for large scale applications. From these results some prehminary conclusions can be drawn with respect to the perspective of the modified process. 

In the selective catalytic reduction process, NO, in flue gas is selectively reduced to nitrogen and water vapor by reaction with HH3 in the presence of a catalyst. The SCR process is described by the following overall chemical reactions (Blair et al., 1981) ... 

Investigations to develop base metal catalysts have led to the use of selective catalytic reduction processes with supported vanadium pentoxide catalysts... 

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