SO2 oxidation reaction

Figure 13.2 Dependence of the intrinsic kinetic constant kc ofde-NO, and SO2 oxidation reactions (full squares and circles, respectively) on the V content of the catalyst. T = 350 °C, fede-NO, (Nmh ) fesOi-SOi (s )- Adapted from ref. [28]...

E Tronconi, A Beretta, A.S. Elmi, P Forzatti, S Malloggi, A. Baldacci, A complete model of SCR monolith reactors for the analysis of interacting NO, reduction and SO2 oxidation reactions, Chem Eng Sci. 49 4277 (1994). 

Sulfur Dioxide to Sulfur Trioxide Process. The manufacture of sulfuric acid involves the oxidation of elemental sulfur to SO2, followed by the catalytic oxidation of SO2 to SO3 over vanadium pentoxide. The next step involves the absorption of SO3 with water to form H2SO4. The SO2 oxidation reaction to... 

This new method of SO2 oxidation is based on a periodic reversal of the direction of the reaction mixture flow over the catalyst bed. The process was developed by Dr. Matros at the Institute of Catalysis of the former USSR. Basically, a large bed of catalyst is used both as a reversing, regenerating heat exchanger and as a catalytic reactor for the SO2 oxidation reaction. 

For the SO2 oxidation reaction to take place, it is considered essential that the reactants are highly soluble, and that trace metal catalysts or strong oxidising agents are present. The presence of ammonia is helpful but not essential. 

To obtain significant and reproducible data for both SO2 oxidation and NO conversion in the laboratory, the catalyst must be conditioned. Starting from a fresh catalyst, the NO conversion is typically seen to increase with time until a steady-state level is approached. Likewise, the SO3 concentration at the reactor exit is nil at time zero and increases with time on stream (36). Catalyst conditioning in the laboratory requires typically few hours in the case of NO reduction but it may take up to 70-80 h in the case of the SO2 oxidation reaction. 

In a companion paper (117), the dynamic model of Reference (116) has been completed with account of the SO2 oxidation reaction. For this purpose transient SO2 conversion data were collected over a commercial V-W/Ti02 honeycomb catalyst during SO2 oxidation experiments, involving step changes in temperature, area velocity, and feed composition (SO2, O2, H2O and NH3) with respect to typical DeNOx conditions. Characteristic times of the system response were of a few hours, and peculiar SO3 emission peaks were noted upon step increments of reaction temperature and H2O feed content. All the data could be successfully fitted by a dynamic kinetic model based on the assumption that buildup-depletion of surface sulfate species is rate controlling (see eg. Figure 17). Finally, it was shown that the dynamic model of the SCR monolith reactor in Reference... 

V2O5 Oxides. - Supported V2O5 oxides are extremely important industrial catalysts for environmental pollution control, and are used in catalytic scrubbers for SO2 oxidation and NO reduction. During the operation of the catalyst (usually at 400-600 °C) in the SO2 oxidation reactions, pyrosulfate melts are formed in the pores of the catalysts, and V2O5 can dissolve in these melts forming vanadium oxo-sulfate complexes ... 

The oxidation reaction between butadiene and oxygen and water in the presence of CO2 or SO2 produces 1,4-butenediol. The catalysts consist of iron acetylacetonate and LiOH (99). The same reaction was also observed at 90°C with Group (VIII) transition metals such as Pd in the presence of I2 or iodides (100). The butenediol can then be hydrogenated to butanediol [110-63-4]. In the presence of copper compounds and at pH 2, hydrogenation leads to furan (101). 

Direct conversion processes use chemical reactions to oxidize H2S and produce elemental sulfur. These processes are generally based either on the reaction of H2S and O2 or H2S and SO2. Both reactions yield water and elemental sulfur. These processes are licensed and involve specialized catalysts and/or solvents. A direct conversion process can be ii.scd directly on the produced gas stream. Where large flow rates are encoLui tered. ii is more common to contact the produced gas stream with a chemical or physical solvent and use a direct conversion proce.ss on the acid cas liberated in the regeneration step. 

SO2 oxidation to H2SO4 on aerosols, in cloud droplets, and by gas phase reactions following attack by OH. 

The vanadium content of some fuels presents an interesting problem. When the vanadium leaves the burner it may condense on the surface of the heat exchanger in the power plant. As vanadia is a good catalyst for oxidizing SO2 this reaction may occur prior to the SCR reactor. This is clearly seen in Fig. 10.13, which shows SO2 conversion by wall deposits in a power plant that has used vanadium-containing Orimulsion as a fuel. The presence of potassium actually increases this premature oxidation of SO2. The problem arises when ammonia is added, since SO3 and NH3 react to form ammonium sulfate, which condenses and gives rise to deposits that block the monoliths. Note that ammonium sulfate formation also becomes a problem when ammonia slips through the SCR reactor and reacts downstream with SO3. 

The catalyst must be designed to handle the abrasive environment where catalyst hnes are always present in the flue gas yet still perform with a low pressure drop typically below 5 inches of water column. It must also maintain activity continuously for a 5 year cycle, yet be selective enough to limit undesirable reactions like SO2 oxidation. The catalyst must also be able to withstand periodic blasts of steam or pressurized air coming from the soot blower system found in many of the newer FCCU SCR units. 

Horiuti s results (there was a war ) analyzed the SO2 oxidation case. Both Horiuti and Boreskov assumed that all reaction steps, except one of them, are reversible and fast. These steps are not obligatory adsorption steps. One reversible step, i.e. rate-determining one, is much slower than the rest of other steps. Using SO2 oxidation as an example and assuming power low kinetic expressions for the reaction rates, Boreskov showed that... 

For typical one-route linear mechanisms all the Horiuti numbers can be selected to be equal to 1. This is not necessarily true for non-linear reaction mechanism, e.g. for SO2 oxidation mechanism... 

The difficulties created by stopcocks and valves can usually be minimized. However, it is occasionally necessary to completely eliminate these sources of leakage and contamination by the use of break-seals and vacuum seal-offs. Typical situations in which sealed tube techniques are widely used are quantitative hydrolysis and oxidation reactions which require elevated pressures and temperatures, precise physical measurements on highly reactive organometallic compounds, long-term storage of reactive samples, and nonaqueous reactions under high pressure (for example, SO2 or NH3 at room temperature). Each piece of apparatus must be constructed to meet a specific need, so it is not possible to outline an apparatus which is of general use. Nevertheless, several examples will be presented here which serve to indicate the approach. 

Sulfated catalyst activity was determined with the S02 free feedstream in the absence of water The light-off temperatures reported in Fig 3a for propene oxidation show that sulfation by SO2 induces the same effects on catalyst activity than SO2 in the feedstream in the course of the oxidation reaction (Fig 1b). Thus Pt-Rh catalyst activity is not affected by sulfation while monometallic platinum catalysts are far less active after sulfur storage with 20 ppm SC>2 We must note also that a small inhibiting effect appears after sulfur storage with 4 ppm SO2. 

Most likely the changes in IEP value, as well as in PCD potential, during the enzymatic treatment of wool are the result of enzyme-initiated oxidation reactions. As can be seen from the XPS results specified below (Table 1), a slight increase in SO2, SO3, SO4 groups concentration, from 0.248% (0.248%= 11.8% of 2.1% of total elemental concentration) for untreated sample to 0.314% (0.314% = 19.6% of 1.6% of total elemental concentration) can be observed. 

An important feature of a reactor operating with reversing flows is a gradual decrease of temperature of the packed bed outlet that allows for higher conversion in an adiabatic catalyst bed than for steady-state performance of an exothermic reversible reaction such as SO2 oxidation or ammonia synthesis. Conventional operation can provide only the temperature rise along the adiabatic catalyst bed. 

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