Maximum coke content

Contrary to the findings for water, the relative change of the absolute values of Ti and of its frequency dependence is much more pronounced for n-heptane, which possesses a high affinity for the surface coke. One of the steps in the dispersion function can be interpreted as being related to the onset of full coverage of the surface. Because the maximum coke content corresponds to an average layer... 

The effectiveness factors and n, defined as the ratios of the actual reaction rates at time 0 to the maximum reaction rates on a clean catalyst, are obtained nEmerically from equations [4] -[9]. An explicit finite difference method was used to solve the partial differential equations without further simplifications. Densities, porosities and clean catalyst pore diameters were measured experimentally. The maximum coke content is assumed to be that which fills the pore completely. The tortuosity is taken as 2.3, as discussed by Satterfield et al. (14). 

Coke content kg-coke/kg-catalyst, QM maximum coke content... 

For a coarse-grained (particle containing) graphite, the system depicted in Figure 1 is typical. The nin-of-kiln coke is brought in on railroad cars and emptied into pits where the coke is conveyed to an elevator. The elevator feeds a second conveyor that empties the coke into any one of a number of storage silos where the coke is kept dry. The manufacturer usually specifies a maximum moisture content in the incoming coke at about 0.1—0.2% to ensure that mix compositions are not altered by fluctuations in moisture content. 

Chen and co-workers have studied the role of coke deposition in the conversion of methanol to olefins over SAPO-34 [111]. They found that the coke formed from oxygenates promoted olefin formation while the coke formed from olefins had only a deactivating effect The yield of olefins during the MTO reaction was found to go through a maximum as a function of both time and amount of coke. Coke was found to reduce the DME dilfusivity, which enhances the formation of olefins, particularly ethylene. The ethylene to propylene ratio increased with intracrystal-line coke content, regardless of the nature of the coke. 

The effect of the H2/oil ratio on the coke content of a NtV/SiOj catalyst (low HDS activity, thermal coke predominates) is shown in Figure 6. The distinct maximum of the coke deposited with the H2/oil ratio is apparent from both experiment and theory. Detailed analysis of the model output indicates that at low gas rates the VGO feedstock is mainly in the liquid phase throughout the reactor, whilst at the highest gas rates the reactor is operated in the gas phase already at the reactor inlet. In both limits the amount of coke deposited is modest. Intermediate gas rates (1000 Nl/kg), however, lead to much higher rates of coke... 

The aluminum industry consumes about 0.45 lb. of anode carbon for each pound of aluminum produced. The ideal carbon should have a moderately-isotropic structure with minimum oxidant-accessible surface of low, uniform reactivity, and a maximum ash content, excluding bath salts, of a few tenths of one percent. Industrial anode carbon is a baked composite usually made of calcined petroleum coke filler with a binder of coal-tar pitch coke. While there is no shortage of calcined petroleum coke, the quality is not very good and likely to become worse. Also, coke binders are subject to variability in both quality and supply. 

For all three samples of ZSM-5 a band appears at ca. 1780 cm 1 when coke in ZSM-5 is exposed to air at conversion temperatures and above (see Fig. 1 (a-c)). This is accompanied by the loss of some IR bands due to coke between 1700 and 1300 cm, especially at temperatures above 500°C. This band is stable up to 450°C and at conversion temperatures takes a few hours to reach maximum intensity. Heating above 550°C produces a clean spectrum of the zeolite which only contains a pair of bands at 3740 and 3610 cm"1 due to the hydroxyl groups of the zeolite. The rate of growth of the 1780 cm"1 band is independent of zeolite aluminium content for similar coke contents. 

Fig. 9, in which y is essentially clock time, shows how a maximum in the rate of the main reaction develops from a certain degree of coking onwards, as a consequence of the opposing effects on of the descending profiles of coke content and concentration of A. This maximum in rA travels down the bed with time ... 

The maximum number o carbon atoms considered was taken to be 21 this figure although arbitrary, is similar to the number of carbon atoms observed in coke species deposited inside Y zeolites during the transformation of n-heptane [3]. In fact, the amount of compounds with 21 (or more) carbon atoms was taken as the coke content of the catalyst. 

Coke content of Pt(h,500)AVZ run at 250 °C and of WZ run at 200 °C (both with hydrogen) are 0.49% and 0.32 %, respectively, but the latter is much more condensed. Consequently there is not a direct relation between the amount of coke and its maximum burning temperature. This result is also an indication of the importance ofPt in the generation of a less polymerized coke its hydrogen dissociation capacity reduces polymerization reactions that favor the formation of a more condensed coke. From the point of view of regeneration procedures, the degree of coke polymerization is sometimes more important than the amount of coke. 

---