Poisoning catalytic combustion

One of the common limitations of catalytic-combustion-type analyzers is the poisoning of the filament by silicon, sulfur, chlorinated compounds, or lead compounds. A variety of filament protection means have been added to increase the poison resistance of the sensors. Life expectancies are usually defined in terms of exposure concentration hours. One high-concentration exposure of a poison has been known to knock out a sensor therefore, nonpoisoning techniques should be considered when poisoning is an issue. 

Catalytic combustion Combustible 1000 > 1 <95 L None Contaminants could poison catalyst... 

Catalytic total oxidation of volatile organic compounds (VOC) is widely used to reduce emissions of air pollutants. Besides supported noble metals supported transition metal oxides (V, W, Cr, Mn, Cu, Fe) and oxidic compounds (perovskites) have been reported as suitable catalysts [1,2]. However, chlorinated hydrocarbons (CHC) in industrial exhaust gases lead to poisoning and deactivation of the catalysts [3]. Otherwise, catalysts for the catalytic combustion of VOCs and methane in natural gas burning turbines to avoid NO emissions should be stable at higher reaction temperatures and resists to thermal shocks [3]. Therefore, the development of chemically and thermally stable, low cost materials is of potential interest for the application as total oxidation catalysts. 

The Influence of Phosphorus Poisoning. - Catalytic oxidation using noble metal catalysts has been used to reduce the concentration of unburned hydrocarbons, carbon monoxide pollutants released from internal combustion engines, and similar applications. It is well known that contaminants arising from lubricants, (P, Ca, and Zn) deactivate these catalysts. Phosphorus compounds in printing processes are the source of decay of noble metal catalysts used to control these emissions. 

As a preventive solution to the problem of NOx emissions, catalytic combustion has come to the forefront during the last two decades. The focus of major interest here is its application in gas turbines for power generation and for transportation by road, water or air. Any catalyst for catalytic combustion, however, has to face extreme demands above 1000°C in the presence of oxygen and steam, in uninterrupted operation for at least one year also, resistance to impurities or poisons in the fuel and to severe thermal and mechanical shocks. Promising developments in catalytic supports, washcoats and active materials are reviewed briefly. 

Sulfur poisoning in catalytic combustion of industrial waste... 

The objective with the present work was to study catalytic combustion and the poisoning effect of sulfur in the catalytic combustion of gasified industrial waste over palladium and platinum catalysts on different support materials. 

Conventional combustion processes generally proceed at high temperatures and lead to formation of undesired nitrous oxides. Combustion catalysts are intended to achieve fast total combustion of the fuel at lower temperatures. Catalytic combustion of methane in a gas turbine has already been developed by a company in lapan, where a research society for catalytic combustion has also been established. However, the complex metal oxide catalysts do not yet have sufficient temperature stability and resistance to catalyst poisons. 

It has been published that hydrophobic-activated carbons can be suitable supports for noble metal species active for total oxidation. The catalytic behaviour of platinum and palladium supported on carbon-based monoUths was studied in the low temperature catalytic combustion of benzene, toluene and m-xylene, and compared with the corresponding behaviour of Pt-supported on y-Al203 coated monoliths. Carbon-based monoliths showed much better catalytic performance, which was ascribed to the fact that the carbon surface is more hydrophobic than the y-Al203, and the poisoning effect of water molecules produced during the combustion was... 

Other fuel quality parameters include limits on the heteroelements sodium, potassium, sulfur, phosphorus, calcium, and magnesium. The presence of these heteroelements can also negatively influence combustion and poison catalytic exhaust emissions controls as well as contribute to the formation of sediments when storing the fuel. These elements can arise in biodiesel as remaining transesterification catalysts, carry over from feedstocks such as animal fats having had contact with other animal parts such as meat and bones or sulfur-containing glucosinolates in rapeseed. 

Catalytic Oxidation. Catalytic oxidation is used only for gaseous streams because combustion reactions take place on the surface of the catalyst which otherwise would be covered by soHd material. Common catalysts are palladium [7440-05-3] and platinum [7440-06-4]. Because of the catalytic boost, operating temperatures and residence times are much lower which reduce operating costs. Catalysts in any treatment system are susceptible to poisoning (masking of or interference with the active sites). Catalysts can be poisoned or deactivated by sulfur, bismuth [7440-69-9] phosphoms [7723-14-0] arsenic, antimony, mercury, lead, zinc, tin [7440-31-5] or halogens (notably chlorine) platinum catalysts can tolerate sulfur compounds, but can be poisoned by chlorine. 

The mechanism of poisoning automobile exhaust catalysts has been identified (71). Upon combustion in the cylinder tetraethyllead (TEL) produces lead oxide which would accumulate in the combustion chamber except that ethylene dibromide [106-93-4] or other similar haUde compounds were added to the gasoline along with TEL to form volatile lead haUde compounds. Thus lead deposits in the cylinder and on the spark plugs are minimized. Volatile lead hahdes (bromides or chlorides) would then exit the combustion chamber, and such volatile compounds would diffuse to catalyst surfaces by the same mechanisms as do carbon monoxide compounds. When adsorbed on the precious metal catalyst site, lead haUde renders the catalytic site inactive. 

This is because the heat capacity of a wall of finite thickness is several orders of magnitude higher than that of the hot combustion products. However, some researchers did observe a small effect of the properties of the wall [17] on the quenching distance. This was interpreted in terms of some residual catalytic activity of the wall surface, poisoned by the combustion products from the preceding experiments [18]. With respect to this explanation, the surface of any material moistened through the condensation of the water vapor produced in the reaction is supposed to have very similar, low activity. 

Heterogeneous catalysts are the active ingredients in automobile catalytic converters. When combustion occurs in an automobile engine, side reactions generate small amounts of undesired products. Some carbon atoms end up as poisonous CO rather than CO2. Another reaction that takes place at the high temperatures and pressures in automobile engines is the conversion of N2 to NO. Furthermore, the combustion process fails to bum all the hydrocarbons. Hydrocarbons, CO, and NO all are undesirable pollutants that can be removed from exhaust gases... 

The highway police, the air quality monitoring services or the meteorological stations do not measure the levels of these compounds. Although no reports on the amounts of the above aromatics in the exhaust gases are available, experts assert that complete combustion of these compounds in an engine is impossible. The combustion products therefore pollute the air to a degree that makes the common CO and CO2 pleasant air fresheners. No catalytic converter will help. Rather, it will be poisoned prematurely. 

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