Cycling coke materials

During this carbonization cycle, the cross-linked polymeric chains do not break down and, unlike coke materials, do not go through a mesophase. The carbonization of phenolic polymers follows a similar pathJ i... 

Sepiolite has been made exchangable by chemical treatments and Mg2+ at the border of the channels has been substituted by Al3+. In this way sepiolite with mild acidity, controlled mesopore, and improved stability has been obtained. This material is active for gasoil cracking, giving a good bottom conversion, and light cycle oil products without excessive gas and coke formation. Meanwhile, it is active for vanadium passivation. 

The catalyst, which may be an activated natural or synthetic material, is employed in bead, pellet, or microspherical form and can be used as a fixed bed, moving bed, or fluid bed. The fixed-bed process was the first process to be used commercially and uses a static bed of catalyst in several reactors that allows a continuous flow of feedstock to be maintained. Thus, the cycle of operations comprises (1) flow of feedstock through the catalyst bed, (2) discontinuance of feedstock flow and removal of coke from the catalyst by burning, and (3) insertion of the reactor on stream. The moving-bed process uses a reaction vessel (in which cracking takes place) and a kiln (in which the spent catalyst is regenerated) and catalyst movement between the vessels is provided by various means. 

Recycling to extinction is uneconomic because polycyclic aromatics concentrate in the cycle gas oil and these compounds are not only hard to crack but are converted largely to coke and gaseous products. On the other hand, partial recycling is commonly practiced. In the United States, cycle gas oil constitutes, on the average, about 20% of the total feed to catalytic cracking (16,257). The material recycled may be a portion of... 

A principal factor governing the operating cycle of ethylene steam crackers (ESC) is coke formation on the inside surfaces of the radiantly heated pyrolysis tubes. Steam is used as the carrier for the hydrocarbon feedstock as it is known empirically to minimise this coking. It is probable that the observed deposition is a net process representing the difference between formation and removal, primarily by thermal oxidation. A fundamental requirement of any detailed understanding of the overall processes involved, therefore, is knowledge of the oxidation behaviour of such deposits. Although several studies have been undertaken on various carbons considered to simulate ESC pyrolysis tube coke (e.g. ( )) no relevant information has been published for plant material. To provide these data, therefore, the oxidation behaviour of a coke formed on an ESC tube has now been examined in water vapour. 

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