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Carbon activation deposition

As in the fixed bed process, carbon is deposited on the surface of the catalyst and covers the active sites. This deposit lowers the activity very rapidly. [Pg.19]

Carbon formation/deposition is a difficult deactivation mechanism to characterize on cobalt-based FTS catalysts. This is due to the low quantities of carbon that are responsible for the deactivation (<0.5 m%) coupled with the presence of wax that is produced during FTS. Furthermore, carbon is only detrimental to the FT performance if it is bound irreversibly to an active site or interacts electronically with it. Hence, not all carbon detected will be responsible for deactivation, especially if the carbon is located on the support. [Pg.65]

In addition, the catalyst appeared very stable under the reaction conditions little carbon was deposited on the spent catalyst. Other supported metals were less active. The activity order, Ru Rh > Ni > Ir > Co > Pt > Pd > Fe, is very comparable to that measured for the steam reforming of methane. Of all the supports tested, Y203 and Zr02 gave the best results for the Ru-catalyzed steam reforming of glycerol. [Pg.250]

The carbon deposition reaction causes the thermodynamic activity of carbon at the interface between FejC and deposited carbon to be reduced to unity. Since iron carbide is unstable at unit carbon activity, it would begin to dissociate by the reaction,... [Pg.130]

Scaling occurs if a dissolved salt exceeds its saturation point. Most cooling systems can tolerate a slight degree of supersaturation of (for example) calcium carbonate for short periods however, the degree of scaling and rate of deposition are dependent on a number of critical factors. The primary factors are degree of supersaturation, residence time, temperature, active deposition sites, pH, and the DCA product employed. [Pg.401]

It is also of interest to compare the number of carbon atoms deposited per M0S2 stab. Table 2 shows large numbers of carbon atoms deposited per M0S2 slab for a 10 wt % C loading. Thus the mode of deactivation of both components is notably different. While it can be suggested that metal deposits deactivate the catalyst by contamination or promoter substitution of the NiMo sulfide active... [Pg.152]

Fig. 17 shows that a large amount of carbon was deposited without loss of much catalytic activity. The conversion of both ethane and propane declined gradually to a similar degree, possibly indicating that some encapsulated carbon was forming in parallel with weakly or non-deactivating filamentous carbon (Fig. 18). At higher steam-to-carbon ratios under otherwise similar conditions, the conversion curves are almost stable, indicating that carbon was the main cause of deactivation. Fig. 17 shows that a large amount of carbon was deposited without loss of much catalytic activity. The conversion of both ethane and propane declined gradually to a similar degree, possibly indicating that some encapsulated carbon was forming in parallel with weakly or non-deactivating filamentous carbon (Fig. 18). At higher steam-to-carbon ratios under otherwise similar conditions, the conversion curves are almost stable, indicating that carbon was the main cause of deactivation.
An alternative method of preparation of zeolite-carbon adsorbents is the treatment of mixtures clay mineral with hard coal and waste carbon deposits. The treatment consists of several physicochemical processes i.e. formation, carbonization, activation and crystallization, presented in this paper. The adsorbents prepared with this procedure are not a simple mixture of two components but strongly dispersed material resulting fi om thermochemical transformation, thus fecilitating the surface structure. [Pg.500]

One of the causes of catalyst deactivation is coking of the active phase or the support. The coke may even block the catalyst pores if large quantities are formed. Figure 7.22 represents the cross-section of a hydrotreatment catalyst sphere recovered from an industrial plant, A carbon-rich deposit with a thickness of approximately 10-20 pm forms an extremely dense barrier that prevents the reagents from reaching the active sites. This coke barrier , which could be produced during abnormal operation of the plant, explains the significant deactivation of this catalyst. [Pg.148]

Holland and Zimmermann, 2000). The latter authors do accept, however, that there is generally lower dolomite abundance in carbonate sediments deposited during the past 200 Myr. These qualihcations notwithstanding, a number of previously described parameters (Sr/Ca, Mg/ Ca, aragonite/calcite, possibly dolomite/calcite, and frequency of ooids and iron ores) appear to be related in some degree to sea-level stands, the latter at least in part a reflection of plate tectonic activity during the Phanerozoic. [Pg.3864]

On this process, carbon is deposited on the catalyst surface and causes the deactivation. However, the high activity of CO2 reduction was sustained over 60 h examined. The weight of Ni/SiOj catalyst increased from 0.4 to 2.04 g after CO2 reduction for 60 h. The molar amount of carbon deposited on catalysts was 200 times larger than that of supported Ni. SEM observation and XRD analysis suggest that the formed carbon on the catalyst surface was a filament shaped graphite. Figure 4 shows the TEM photograph of the... [Pg.150]

C. Conversions increased with alkali content indicating that the potassium cation was involved in the active sites for the reaction. Carbon was deposited on the catalyst and the conversion increased in proportion to the amount of carbon deposited. The carbon was steamed off subsequently and the rate of gasification with steam increased with K content, confirming the promoting effect of K on the steam-carbon reaction (see Figure 10). A linear relationship... [Pg.67]


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See also in sourсe #XX -- [ Pg.59 ]




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