Carbon burn-off

Carbon Burn-off (%) DR plot (carbon dioxide at 273 K) Nitrogen displaced by nonane... 

Fig. 4. Comparison of the total surface areas derived from BET and SAXS measurements versus the carbon burn-off.

Samples On Caibmi Particle size fAl Ratio of carbon burning off... 

Thermogravimetric and Differential Thermal Analysis has been performed on Cat D. The TG and DTA profiles in Fig 2 show three different steps. The first one is the evaporation of hydrocarbons up to 200 °C with a moderate endotherm. The second step is the oxidation reaction of metal sulfides to oxides (most of the Mo sulfide, and part of the Co sulfide), starting around 200-250 °C. The third step around 350-450 °C is strongly exothermic, due to carbon burn-off as well as the remaining of sulfides oxidation. The carbon bum-off reaction finishes around 500 °C in this experiment performed on a dynamic mode at the heating-up rate of 5 °C/min. 

Periodic catalyst regeneration or carbon burn off is required to maintain the activity of the catalyst. Typical cycle time is reported to be at least 8 hr, with 7 hr of process time and 1 hr of regeneration time. For continuous operation, various furnace modules can be operated such that, for example, seven operate in the process mode while one is in the regeneration mode. Fig. 13 shows a schematic diagram of a STAR process unit. ... 

These workers also draw attention to the afterglow phenomenon associated with slow carbon burn-off. 

As mentioned earlier, the reactivity of a prepared coal char is often measured with the sole purpose of char classification and compsu ison to known samples. Because of its simple determination, the CO2 reactivity is measured fi om an isothermal TGA experiment (e.g., at 1000 °C) [62]. The reactivity, as shown in Equation (3.22), is calculated where the carbon burn-off under a CO2 atmosphere is X = 0.5. 

Figs. 1 to 4 show the presence of LPH, its magnitude being dependent on the carbon burn-off in spite of the fact that the... 

CO oxidation catalysis is understood in depth because potential surface contaminants such as carbon or sulfur are burned off under reaction conditions and because the rate of CO oxidation is almost independent of pressure over a wide range. Thus ultrahigh vacuum surface science experiments could be done in conjunction with measurements of reaction kinetics (71). The results show that at very low surface coverages, both reactants are adsorbed randomly on the surface CO is adsorbed intact and O2 is dissociated and adsorbed atomically. When the coverage by CO is more than 1/3 of a monolayer, chemisorption of oxygen is blocked. When CO is adsorbed at somewhat less than a monolayer, oxygen is adsorbed, and the two are present in separate domains. The reaction that forms CO2 on the surface then takes place at the domain boundaries. 

No. 41 or 541 filter paper. Wash the precipitate first with warm, dilute hydrochloric acid (approx. 0.5M), and then with hot water until free from chlorides. Pour the filtrate and washings into the original dish, evaporate to dryness on the steam bath, and heat in an air oven at 100-110 °C for 1 hour. Moisten the residue with 5 mL concentrated hydrochloric acid, add 75 mL water, warm to extract soluble salts, and filter through a fresh, but smaller, filter paper. Wash with warm dilute hydrochloric acid (approx. 0.1M), and finally with a little hot water. Fold up the moist filters, and place them in a weighed platinum crucible. Dry the paper with a small flame, char the paper, and burn off the carbon over a low flame take care that none of the fine powder is blown away. When all the carbon has been oxidised, cover the crucible, and heat for an hour at the full temperature of a Meker-type burner in order to complete the dehydration. Allow to cool in a desiccator, and weigh. Repeat the ignition, etc., until the weight is constant. 

The reduction is avoided by first charring the paper without inflaming, and then burning off the carbon slowly at a low temperature with free access of air. If a reduced precipitate is obtained, it may be re-oxidised by treatment with sulphuric acid, followed by volatilisation of the acid and re-heating. The final ignition of the barium sulphate need not be made at a higher temperature than 600 800 °C (dull red heat). A Vitreosil or porcelain filtering crucible may be used, and the difficulty of reduction by carbon is entirely avoided. 

A more steadily performing catalyst, requiring less attention and less frequent replacement, could permit a reduction in the semivariable costs for manning and maintenance stores. In the case of a catalyst system requiring frequent regeneration by burning off, a decrease in the carbon laydown (and consequent decrease in necessary burn-off frequency) may both increase throughput and reduce conversion costs. 

Group 2 Coke imbalance. This grouping considers malfunctions leading to a difference between the rate at which coke accumulates on the catalyst and the rate at which it is burned off. A coke imbalance is associated with a reduction of oxygen, which can be caused by a loss of combustion air or through an increase in the conradson carbon in the gas oil feed to the unit. 

Fat is only an energy storage form (Fig. 17-4). Fat cannot be converted to carbohydrate equivalents. This is a very important point. Remember it The reason for this is a bit subtle. The carbon skeleton of fatty acids is metabolized to acetyl-CoA only. Glucose precursors such as oxaloacetate can be synthesized from acetyl-CoA by going around the TCA cycle. However, acetyl-CoA has 2 carbon atoms. Going around the TCA cycle burns off 2 carbon atoms (as C02). The net number of carbon atoms that ends up in oxaloacetate is then zero. No carbohydrate can be made from fat.5... 

Fixed beds are the main interest of this Section. Usually it is adequate to assume that the fluid and solid are at the same temperature at a point. There are cyclic processes, however, where the solid is first heated with flue gases or by burning off carbon before contacting the reacting fluid for a time. A moving bed of heated pebbles (Phillips pebble heater) has been used for the production of olefins from butane and for the fixation of atmospheric nitrogen. A fluidized sand cracker for the production of olefins functions similaiiy, with burning in a separate zone. 

There is a routine procedure to form the transport pores in catalysts catalyst is mixed with some additive, which can be burned off after preparation. Consider the catalyst with true density pc = 3.3 g/cm3 and the additive (carbon black) with true density of pA= 1.2 g/cm3. Calculate the amount of additive necessary to form the interlinked system of transport pores. 

The last point is worth considering in more detail. Most hydrocarbon diffusion flames are luminous, and this luminosity is due to carbon particulates that radiate strongly at the high combustion gas temperatures. As discussed in Chapter 6, most flames appear yellow when there is particulate formation. The solid-phase particulate cloud has a very high emissivity compared to a pure gaseous system thus, soot-laden flames appreciably increase the radiant heat transfer. In fact, some systems can approach black-body conditions. Thus, when the rate of heat transfer from the combustion gases to some surface, such as a melt, is important—as is the case in certain industrial furnaces—it is beneficial to operate the system in a particular diffusion flame mode to ensure formation of carbon particles. Such particles can later be burned off with additional air to meet emission standards. But some flames are not as luminous as others. Under certain conditions the very small particles that form are oxidized in the flame front and do not create a particulate cloud. 

One good method of exploring the effects of variables on kiln performance is to prepare performance maps of appropriate subspaces of the kiln performance space. The most widely used map for this application was a graph of catalyst circulation rate versus carbon burned. Temperature and bum-off constraint curves were used to define the operating region given as shaded areas in Fig. 14. The conditions for the kiln used in Fig. 14 are given in Table IV. 

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