Oxygenates /hydrocarbons, reduction

Other Oxygenated Hydrocarbons Reductants. Other oxygenated hydrocarbons— 2-propanol, ethanol, methanol, iso-butanol, ethyl ether—were also tested. The inlet carbon atom concentration of these hydrocarbons was calculated to be equal to that of acetone in the tests reported above, e.g., equivalent to 1,300 ppm acetone. The NO conversion at steady state for each reductant is shown in Table II. All reductants showed 100% selectivity to N2. Since the carbon concentration of all reductants was the same, the activity of the reductants can be compared by comparing the NO conversion. The only reductant with activity close to acetone is 2-propanol with 31% conversion. Others showed much less activity than acetone. Specifically, methanol showed negligible NO reduction activity. It is speculated that the NO selective reduction activity is closely related to the ability of hydrocarbons to form oxygenated surface intermediates at these reaction conditions. This is being investigated further. 

Montreuil and Shelef [81] studied the SCR reaction over ZSM-5/AI2O3 supported on a cordierite monolithic substrate. Various oxygenated hydrocarbons, such as methanol, ethanol, propanol, acetaldehyde, acetone, methyl ethyl ketone, and 1,4-dioxane were used as reductant at 755 K [81]. The reaction extent with the various organic compounds was compared with that obtained when using propene as reductant. Propene was the superior reductant. Methanol as a reductant showed a very low NO conversion, whereas propanol showed the highest activity, albeit lower than that of propene. Upon adding oxygen to the feed the difference between propanol and propene vanishes. 

NOx removal under lean-bum conditions has not yet been fiilly demonstrated although Pt based catalysts show considerable promise. However, very little detailed information is available on the nature of the active sites, the reaction mechanism or the effectiveness of different hydrocarbon reductants. This paper presents a detailed kinetic analysis of the reaction between NO and CjHe or CbH under lean-bum conditions and provides a rationalisation for the differences between hydrocarbons which compete successfully and unsuccessfully with oxygen for adsorption sites on the catalyst. 

An oxygenated hydrocarbon enhancer was also tested by co-injecting it with the urea-based chemical The co-injection resulted in 15% additional NOx reduction at lower temperatures (816-927 C or 1,5(X) - 1,7(X) F). Particulate measurement at the ESP showed that the urea-based SNCR had no effect on total particulate load or its collection efficiency. 

In situ FTIR and diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) studies deal mainly with photocatalytic oxidation or reduction of nitric oxide (NO) as important pollutant and green house gas as well as the depollution or selective oxidation of organics such as olefinic, aliphatic, aromatic, and oxygenated hydrocarbons. 

Bowers WE (1988) Reduction of nitrogen-based pollutants through the use of urea solutions containing oxygenated hydrocarbon solvents. US Patent 4,719,092... 

Hamada, H. Selective reduction of NO by hydrocarbons and oxygenated hydrocarbons over metal oxide catalysts. Catal. Today 1994, 22, 21 0. 

Enhancers Used Typically oxygenated hydrocarbons to increase reagent utilization, increase NO, reduction efficiency, widen temperature range, vary optimum reaction temperature, and reduce ammonia slip. Not often used. Hydrogen to extend effective temperature range. Not often used. No enhancers are injected. 

In some installations, small amounts of proprietary chemicals called enhancers (typically oxygenated hydrocarbons) may be injected to increase utea utilization, increase NO, reduction efficiency, widen the reaction temperature range, vary the optimum reaction tempera-... 

The overall outcome of the comhustion reaction is the partial loss of electrons from both carbon and hydrogen (their oxidation) in CH and their partial gain by oxygen (its reduction) in O2. Thus, the combustion of methane, and by extension, of any hydrocarbon, is a redox reaction in which the hydrocarbon is oxidized and oxygen is reduced. 

Both CI2 and HCl have been shown to chlorinate hydrocarbons on fly ash particles. Pilot-scale data involving the injection of fly ash from municipal waste combustion (33) show that intermediate oxygen concentrations (4—7%) produce the highest levels of PCDD and PCDF. These data also show significant reductions in PCDD and PCDF emissions with the upstream injection of Ca(OH)2 at about 800°C. 

Reduction of Aldehydes and Ketones to Hydrocarbons. Deep hydrogenation of aldehydes and ketones removes the oxygen functionahty and produces the parent hydrocarbons. 

Fire refining, the final smelting operation, removes further impurities and adjusts the oxygen level ia the copper by air oxidation followed by reduction with hydrocarbons, ammonia, or reformed gas (CO + H2). 

There has been a growing demand for a lean NO catalyst ia order to decrease the relatively low NO emission of the lean bum engine sufftciendy to meet the future standards. Lean NO catalysts have been developed based on 2eolites (see Molecularsieves). Cu-promoted ZSM-5 2eolite has shown ability to reduce NO ia an exhaust having excess oxygen at an efficiency of 30 to 50% (153). Durability is not proven. Research has revealed that certain hydrocarbons are preferred for the reduction of NO, and that CO and H2 apparentiy do not reduce NO over such lean NO catalysts (154). 

In the presence of a proton source, the radical anion is protonated and further reduction occurs (the Birch reduction Part B, Section 5.5.1). In general, when no proton source is present, it is relatively difficult to add a second electron. Solutions of the radical anions of aromatic hydrocarbons can be maintained for relatively long periods in the absence of oxygen or protons. 

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