Coke formation Subject

Temperature ramps were applied for testing, which were set to 300, 325 and 350 °C and held for 1 h each for low-temperature shift. For high-temperature shift testing, the temperature ramps were set to 350,375 and 400 °C for the same duration. These low reaction temperatures compared with industrial conditions for high-temperature shift (up to 450 °C) were applied because mostly precious metal catalysts were tested in the screening protocol, which are subject to coke formation at higher reaction temperatures. 

The objective of the symposium is to promote a scientific approach of the phenomenon of catalyst deactivation which will contribute to the development of catalysts less subject to structural transformations and more resistant to poisons and coke formation. 

KEYWORDS catalyst deactivation, coke formation, kinetics of coke formation, diffusional limitations, chemical reactors subject to catalyst deactivation. 

Kinetic studies of catalyst deactivation by coke formation are not simple. It should be clear by now that the kinetics of the coking reaction(s) are also needed and this calls for techniques which are less familiar than those applied in the kinetic study of reactions not subject to deactivation. 

In this work we report the kinetic behavior of a bifimctional catalyst based on a M/H-MFI zeolite with unique shape selectivity and active for enhancing gasoline octane number. As a test reaction the n-octane transformation was used. The catalyst showed to be subject to inhibition as well as deactivation effects other than the effects of coke formation. To test these effects, the presence of inhibitors and poisons in the feedstock, was also studied [9]. 

Deactivation of catalysts, particularly by coke deposition (the main means of reversible FCC catalyst deactivation) has been the subject ofintensive study over the past 50 years (2-4). Initially, the loss of activity was correlated with the time on stream, but it is now generally accepted that a more appropriate approach to understanding the effect of deactivation by coke is to relate deactivation to the deposited coke concentration (5). Furthermore, few studies on the effect of catalyst formulation on both the product distribution and coke formation have appeared in the open literature. 

For fired heaters subject to creep problems, make sure that the tube metal temperature was considered in materials selection, hi the absence of better information, assume the fireside temperature is 100°F (38°C) higher than the process temperature. (If tube-side fouling is anticipated [e.g., coke formation], assume the tube metal temperature is 150°F [85°C] higher than the process temperature.) If necessary, make a note on the template to ensure that creep is accommodated during design of heater tubes, in accordance with API 530 [23]. 

Heavy oils and residues contain substantial amounts of asphaltenes, which preclude the use of these residues as fuel oils or lubricating stocks. Subjecting these residues directly to thermal cracking is economically advantageous, since, on the one hand, the final result is the production of lower-boiling fractions on the other hand, asphaltenes in the residue are regarded as coke-forming constituents and may even promote coke formation from the compounds of the residue. 

Equations (4-147) and (4-148) describe the conversion and coke profiles in an isothermal reactor subject to deactivation by coke formation via a parallel mechanism. Derive the corresponding equations for deactivation via a series mechanism. 

Coke formation [911-915] is a very important phenomenon in most hydrocarbon conversions on zeolites. Also, reactions of olefins on zeolites (in particular isomerization and oligomerization) were frequently subject of in-situ IR experiments [916-919] and theoretical treatment [740, 920], in many cases because of the close relation to coke formation, for instance, during isomerization and alkylation reactions [835,916,917]. Further examples are presented in... 

In recent years, fuels of higher molecular weight and reforming reactions, which have higher tendency toward coke formation such as dry reforming, have been the subject of investigations in the field of membrane reformer development. 

The hydrogen content of the liquid product is a useful operational control variable. Though subject to interpretation, generally the lower the hydrogen content of the liquid product the more severe the cracking and the closer the operation is to excessive coke formation. 

An obvious advantage of partial oxidation is that only an air feed is required, apart from the fuel. This makes the system simpler because evaporation processes, as required for steam reforming, are avoided. On the other hand, the amount of carbon monoxide formed is considerably higher compared with steam reforming. This puts an additional load onto the subsequent clean-up equipment, but only where CO-sensitive fuel cells are cormected to the fuel processor. When fuels are converted by partial oxidation, some total oxidation usually takes place as an undesired side reaction [46]. In practical applications, an excess of air is fed to the system and consequently even more fuel is subject to total oxidation. The water formed by the combustion process in turn gives rise to some water-gas shift. Another typical byproduct of partial oxidation is methane, which is formed according to reaction (3.5). Coke formation is a critical issue (see Sections 4.1.1 and 4.2.11). Coke may be formed by reaction of carbon monoxide with hydrogen ... 

Only when there are no diffusion limitations will this ratio of fluxes equal the ratio of chemical reaction rates, represented in what follows by, the deactivation (or activity) function. The coke formation itself may also be subject to deactivation, expressed as... 

Coking kinetics has been the subject of various researches reported in the literature, with special emphasis on the mechanism of coke formation, interconversion of the solubility class components during conversion, role of these components in coke formation, influence of structural properties on coking rate and yields, development of correlations, among others. 

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