Catalytic combustion of hydrocarbons

The detoxification of hydrocarbon pollutants is one of the global environmental challenges [531-533]. The complete catalytic oxidation of hydrocarbons to carbon dioxide and water has received much attention in order to reduce their emission from motor vehicles and processing plants [531,533,534]. 

The high activities observed for CnOj, and CrOj, were assigned to the intrinsically high methane oxidation capability of these oxides themselves [38,127]. 

Since in the Kr/Xe enrichment steps, the hydrocarbons would enrich as well and would form an explosive mixture, they have to be removed first. This is done by combustion to water and CO2 in an exothermal reaction with oxygen on a Pd- or Pt-catalyst at a temperature of about 400-500 °C. To this end the cryogenic liquid 

The residual concentration of hydrocarbons after the combustion is small and typically 1 ppm. However in subsequent steps, hydrocarbons will be enriched again. Thus, depending on the purities required, hydrocarbons may have to be further separated in the downstream rectification. 

N2O is also converted on the catalyst into oxygen and nitrogen, whereas the thermally stable greenhouse gases CF4, C2F5 and SFg are only partially decomposed. 

The hot gas from the catalyst s outlet is being cooled and its water and CO2 content, resulting from the combustion, is removed in an adsorber. 

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Fomi, L. and Rossetti, I. Catalytic combustion of hydrocarbons over perovskites. Appl. Catal, B Environmental, 2002, Volume 38, Issue 1,19-211. 

Oxidation is extremely important both from a scientific and a practical point of view. Without oxidation life would not exist. In the chemical industry, too, oxidation is probably the most important process. A major example is the combustion of fossil fuels. This process is usually uncatalyzed, but sophisticated catalytic processes do exist. Examples in the inorganic industry are the oxidation of sulphur dioxide and ammonia in the manufacture of sulphuric acid and nitric acid, respectively. In the petrochemical industry many catalytic synthesis processes are carried out, for example the production of ethylene and propene epoxide, phthalic acid anhydride. An example which has recently also become important is the catalytic combustion of hydrocarbons in flue gases. Table 5.2 gives a list of examples of oxidation catalysis in industry [93]. 

Catalytic combustion of hydrocarbons on ceria has been studied for a long time. Both paraffins and unsaturated hydrocarbons are totally oxidised on ceria between 300°C and 500 C. Previous results of Morooka and co-workers have clearly evidence the catalytic properties of ceria compared to other oxides in total oxidation of acetylene, ethylene, propene, isobutene and propane [39]. They noted... 

Since its foundation the Department of Chemical Engineering and Industrial Chemistry of the V.U.B. acquired considerable experi-eice in the field of high temperature processes, -with studies on steam-reforming of natural gas, pyrolysis of hydrocarbons and catalytic combustion of hydrocarbons. The Department conducted fundamental studies as well as contract work for industry, e.g. in the domain of fluidized bed techniques, incinerator grate mechanisms and small waste-fed boilers. An assessment on current thermal disposal techniques was prepared on behalf of E.E.C.[ 5 57958] ... 

Fig. 6.26. Temperature for 50% conversion in the catalytic combustion of hydrocarbons lwt% Pd/AbOs and Pt/ApOs were prepared by IMP. 1 19 Au/support catalysts were prepared by CP and calcined in air at 673 K. (I) 1 wt% Pd/Al203 (II) lwt% Pt/ApOa (III) 10wt% Au/Fe203 (IV) 10wt% Au/ZnFe204 (V) 10wt% Au/NiFe204 (VI) 10 wt% AU/C03O4. (A) Methane (B) propene (C) trimethy-lamine (D) propane. The concentrations of reactant gases in air was CH4 0.25 vol% CaHs and CsHe 0.1 vol% (CH3)3N 0.05 vol% balanced with air to 1 atm SV 2 X 10" ml g th (based on [535])...

Temperature resistant oxide supports for catalytic active phases are necessary for the catalytic combustion of hydrocarbon pollutants in the field of environment as well for energy production through hydrocarbon clean combustion. Four commonly used pure support oxides in catalysis silica, alumina, titania, and zirconia were synthesised by the sol-gel and aerogel methods and, in parallel, the same oxides were doped with yttria. Pure yttria aerogel was also made and characterised. Heat treatments were performed from ambient up to 1200°C and BET surface areas and XRD patterns were recorded after heat treatments at 300, 600, 900 and 1200 °C for pure and doped oxides, respectively. 

In considering the pressure oxidation of hydrocarbons with oxygen to form alcohols and aldehydes, it will be well to review some of the phenomena connected with the non-catalytic combustion of hydrocarbons under pressure, since the literature regarding the oxidation to form oxygenated products is very meagev. J... 

Elimination of toxic emissions [using new catalysts] An example is the catalytic combustion of hydrocarbons such as methane to obviate the formation of NO,. By developing catalytic systems capable of reducing the flame temperature from 1800°C to 1300°C, it is possible to reduce the NO, level from 200 ppm to less than 1 ppm, an amount which will meet all anticipated future regulations. ... 

The E and K0 Values for Catalytic Combustion of Hydrocarbons over Various Catalysts... 

It is known that the catalytic combustion of hydrocarbons exhibits ignition-extinction phenomena which depend on feed composition [3]. The ignition experiments reported in this study were performed with inlet fuel concentration comprised in the region of surface flammability, in which hysteresis effects occur typical values were ycH4 0.04, yc3H8 0.02, y o 0.03. The superficial velocity (u) of the reactant gas was between 1 and 5 cm/s. 

In this work we wish to report an application of the gel supported precipitation procedure, originally developed for the disposal of nuclear waste [10], to the preparation of zirconia spheres (0.01-2 mm). In addition to the controlled geometric form and the relatively large dimensions, this process allows to obtain large surface area materials starting from inexpensive salt precursors. As a preliminary test of their properties, these materials have been checked in the preparation of Pt catalysts for the low temperature catalytic combustion of hydrocarbons. This modified sol-gel technique is quite general and suitable for the preparation of a variety of materials of interest for catalytic applications. 

The catalytic combustion of hydrocarbon fuels becomes more difficult the lower the number of carbon atoms that are present in the fuel molecule. Platinum and... 

A second catalytic combustion of hydrocarbons downstream of the krypton and xenon enrichment... 

Rossetti, I. and Fomi, L. (2007) Oxide nanomaterials for the catalytic combustion of hydrocarbons, in Synthesis, Properties and Applications of Oxide Nanomaterials (eds JA. Rodriguez and M. Fernandez-Garcia), Wiley Interscience, New Jersey, pp. 563-602. 

Tembile, D., Trovarelli, A., de Leitenburg, C., Primavera, A., and Dolcetti, G. Catalytic combustion of hydrocarbons with Mn and Cu-doped ceria-zirconia solid solutions. Catal. Today 1999, 47, 133-140. 

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