Oxidation reactions coke burning

GO Combustion. The combustion products leaving the coke-burning site consist of both CO2 and CO, typically at a CO2/CO mole ratio of 1.0. The CO formed can then be further oxidized. When a CO combustion promoter is present, the reaction of CO and O2 to form CO2 occurs readily in... 

First, a blast of hot air causes coke, a form of carbon, to burn, producing CO2 and heat. Limestone, CaC03, which is mixed with the iron ore in the furnace, decomposes to form lime (CaO) and more carbon dioxide. The carbon dioxide then oxidizes the coke in a redox reaction to form carbon monoxide, which is used to reduce the iron ore to iron. The process is outlined here and illustrated in Figure 16.9. 

The vapor-phase conversion of aniline to DPA over a soHd catalyst has been extensively studied (18,22). In general, the catalyst used is pure aluminum oxide or titanium oxide, prepared under special conditions (18). Promoters, such as copper chromite, nickel chloride, phosphoric acid, and ammonium fluoride, have also been recommended. Reaction temperatures are usually from 400 to 500°C. Coke formed on the catalyst is removed occasionally by burning. In this way, conversions of about 35% and yields of 95% have been reported. Carba2ole is frequently a by-product. 

The reduction of iron oxide takes place in several stages in different temperature zones within the fiimace. The reducing agent is CO produced from burning coke. Here are the key reactions ... 

Ash, as determined by the standard test method (ASTM D-3174), is the residue remaining after burning the coal and coke and differs in composition from the original inorganic constituents present in the coal. Incineration causes an expulsion of all water, the loss of carbon dioxide from carbonates, the conversion of iron pyrites into ferric oxide, and other chemical reactions. In addition, the ash, as determined by this test method, will differ in amount from ash produced in furnace operations and other firing systems because incineration conditions influence the chemistry and amount of the ash. 

Particle Temperature Overshoot. The temperature of the burning char particles will run hotter than that of the bed by amounts that depend upon particle size, reactivity, bed temperature. It is determined in part by the heat released at the particle surface due to reaction and in part to the additional heat released by carbon monoxide oxidation near the particle surface (54-58). Measurements for 1.8 to 3.2 millimeter size coke particles burning in a fluidized band of sand at 1173 K increased from the bed temperature at low oxygen concentrations to values 150 to 200 K above the bed temperature for oxygen concentrations approaching that of air (72). Estimation of this temperature rise is important for purposes of evaluating the NO/C reaction and also for prediction of the burnout times of fines. 

The regeneration of Y-zeolite catalysts used in isobutane alkylation with C4 olefins was studied. The coke formed on these catalysts during this reaction needs temperatures higher than 500°C to be burnt off with air. Ozone was used in this study to eliminate most of the coke at a much lower temperature. After a treatment at 125 C with ozone, the small amount of coke remaining on the catalyst can be removed with air at 250°C. The ozone not only eliminates coke from the catalyst, but also modifies its burning characteristics as measured by Temperature Programmed Oxidation, shifting the peak to lower temperatures. This allows a combined treatment with ozone at 125°C followed by air at 250°C to restore the activity and stability of Y-zeolite catalysts for isobutane alkylation. 

---