Composition of coke

Table IX. Mass % Composition of Cokes Produced by the Wet Oxidation Process at 285°C...

Petroleum coke is the residue left by the destructive distillation (thermal cracking or coking) of petroleum residua. The coke formed in catalytic cracking operations is usually nonrecoverable because of adherence to the catalyst, as it is often employed as fuel for the process. The composition of coke varies with the source of the crude oil, but in general, is insoluble on organic solvents and has a honeycomb-type appearance. 

As already stated, it is evident that coke, like the ooal itself, will exhibit considerable difference, both in the nature and per centage of its constituents, A glanoe at the analytical tables, submitted at page 80, will show the causes of this difference. It will, therefore, be unnecessary to transcribe here analytical to-sultB of the composition of coke, further than may be sufficient to indicate the usual qualities supplied to the manufacturer. Of those, nineteen analyses are subjoined —... 

The temperature determines for a large part the coking rate and the composition of coke. This can be related to the influence of this parameter on ... 

Composition of coke formed from propene. (From reference 13). 

The composition of coke was determined for various coke contents. With all zeolites the H/C ratio and R, the yield of solubilization of the coke components in methylene chloride (after dissolution of the zeolite in a hydrofluoric acid solution), decreased when the coke content increased. For low coke contents H/C was greater than 1 and R equal to 100%, for high contents H/C was smaller than 1 and R below 100% (e. g. HUSY, Figure 1). 

For similar coke contents the composition of coke depended very much on the zeolite, which confirmed that coking is a shape-selective process (9-10). At low coke contents, the major components were alkylbenzenes in the case of HZSM-5 and HERI, while they were polyaromatic compounds with HUSY and HMOR. At high coke contents the coke components were polyaromatic with all zeolites. However, the size and the shape of coke molecules were different ... 

The composition of coke varies with the source of the crude oil, but in general, large amounts of high molecular weight complex hydrocarbons... 

Composition of coke Concentration of coke Temperature Pressure... 

Composition of coke. The catalyst deposit is predominantly carbon but also contains a substantial proportion of hydrogen and minor pro-... 

Coking, Aging and Regeneration of Zeolites Xtl- Composition of Coke Formed on USHY during Phenol Alkytation with Methanol-Mode of Formation M. GuisneL I. Neves, F. R. Ribeiro, C. Canaff, P. Magnoux and G, Perot... 

Fig. 2. Composition of coke. Proportion (X) of the compounds of the A, B, C, [) families versus the percentage of coke determined a by MS b) by GC.

The composition of coke depends both on time-on-stream (hence on the coke content) and on the zeolite [8]. With all the zeolites carbonaceous compounds are initially formed inside the zeolite pores and, except for mordenite, are soluble in methylene chloride after dissolution of the zeolite in a hydrofluoric acid solution. The yield in soluble coke decreases with increasing coke content. The analysis of the soluble part of coke by GC/MS shows that the size and the degree of aromaticity of the coke components increase with coke content (see for example in Table 3 the change in the amount of the various coke families found with HZSM5 as a function of coke content). 

Coke deactivation on Pt/Al203 catalysts have been studied intensively in the literature. Previous works have focused on the kinetics of catalyst deactivation [7] the influence of additives on coke formation [8] the coke deposition on different morphologic surfaces [9] the structure [10] and chemical composition of coke [11]. Deactivation by coke deposition on niobia supported catalysts, or even on other reducible supports which promote SMSI effect has not been studied. 

The composition of coking gases is similar to that of cracked gases, but coking gases are richer in butane and heavier constituents. 

Five-ring naphthenes are more toxic than 6-rings, for example, cyclopentane is particularly toxic, probably because it is a precursor for the conversion of cyclopentadiene into polyaromatics by Diels-Alder chemistry. This reaction appears to have similar structure-sensitivity to hydrogenolysis and sulphiding.52 Barbier considers that there is electron transfer from Pt —> S. The composition of coke appears to be independent of feed composition.53... 

We show here that a deep change in the composition of coke and on its effect on the zeolite acidity and activity can occur even for treatment under nitrogen flow at relatively low temperatures (250°C). A USHY zeolite was chosen for this study, coke being formed during m-xylene transformation through isomerization and disproportionation at 250 C. 

The composition of coke was determined at different coke contents through the method develop in our laboratory [4], i.e., dissolution of the zeolite in a hydrofluoric acid solution then recovery and GC/MS analysis of the part of coke soluble in methylene chloride. In this case, all the coke components are soluble in methylene chloride. It should be emphasized that practically no coke could be recovered in this solvent through a direct... 

The composition of coke depends very much on time-on-stream (TOS), hence on coke content. At short TOS, coke is mainly constituted by methyl aromatic compounds with one to three aromatic rings. At 75 minutes (C wt% = 7.3), polyaromatic compounds with 4 to 7 rings appear at the expense of the primary coke components (Table 1). 

Figure 3, Composition of coke oven gas during coking cycle.

The major difficulty in the determination of the mode(s) of coking and of deactivation is to establish the composition of coke. Indeed coke is a complex mixture which is very difficult to separate from the zeolite. A critical review of the methods used for characterizing coke will constitute the first part of this paper whereas the second part will show how the composition of coke as function of various parameters varies. 

The methods can be classified into two categories. Certain methods give information on the chemical nature of the coke components only, others define the composition of coke i.e. the quantitative... 

More information was obtained by direct analysis of the coke components recovered after dissolution of the zeolite in hydrofluoric acid solutions. Thus during cyclohexene conversion on USHY at 350 C the coke was totally soluble in methylene chloride and composed of alkyl pyrenes and alkylnaphtenopyrenes [8]. At 450 0 only 40 % of coke was soluble in methylene chloride, 60 % appearing as black particles constituted of highly polyaromatic compounds. Soluble coke contained alkylcyclopentapyrenes and alkylindenopyrenes. The composition of coke formed from propene [7] in the same conditions was practically identical. In contrast the coke formed from 1-hexene on HZSM5 at 320°C contained mainly alkylindanes and alkylnaphtalenes [42]. 

The rate of coke formation on HZSM5 was much lower than on USHY (10 times at 450 C) and the composition of coke was different. At 450 C, (1.6 wt % coke) all the coke components were soluble with methyl-pyrenes as major components [49]. 

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