Hydrocracking suppression

Hydrocracking, 30 48-52 behavior, thermal, 29 269 catalytic, 26 383 deethylation, 30 50 demethylation, 30 50 metallocarbene formation, 30 51-52 of f -decane, 35 332-333 primary coal liquids, 40 57 procedure, 40 66-67 product distribution, 30 49 reactions, over perovskites, 36 311 suppression by sulfur, 31 229 zeolite-supported catalysts, 39 181-188... 

The reverse reaction of carbenium ions with molecular hydrogen, can be considered as alkylation of H2 through the same pentacoordinate carbonium ions that are involved in C—H bond protolysis. Indeed, this reaction is responsible for the long used (but not explained) role of H2 in suppressing hydrocracking in acid-catalyzed... 

That sulfur is responsible for suppressing hydrocracking of organic molecules on Pt is consistent with the work of Fischer and Kelemen (88) showing that bonding of benzene on Pt(100) is sufficiently modified by preadsorbed sulfur to enable an increasing fraction of the adsorbed benzene to desorb at elevated temperatures rather than to dehydrogenate. 

Combination of Pt and Ir, though not widely exploited commercially, has attracted attention. It has many similarities to Pt. Pure Ir metal is inactive for isomerization, but more active than Pt for hydrocracking. Ptir catalysts have gained importance in naphtha reforming Dees and Ponec and Rice and Lu report that PtIr catalysts have higher activities than Pt catalysts. Rasser et al." claim that the main function of Ir is the suppression of surface carbiding. 

The reason for the low alkylate yield in the reaction in 2-methyl-butane was most likely the high reaction temperature. High reaction temperatures favored side reactions, reducing the selectivity of alkylate. Indeed, C5-C7 hydrocarbon products formed in high selectivity in the high temperature reaction conducted in supercritical 2-methyl-butane. It is possible that hydrocracking occurred as a side reaction at the same site where the alkylation reaction proceeded. The temperature of the reaction with propane was low and the side reactions were effectively suppressed. The deactivation of this reaction is probably due to the poor extraction capacity of the propane medium, especially at the low reaction temperature used here. The low solubilities of catalyst poisons in supercritical propane at these reaction conditions deactivated the catalyst. 

A major drawback of all the thermal processes of the day was the production of low valued coke. Alternative process routes were being developed to address this issue. One development pursued was hydrocracking which suppresses coke formation by the circulation of high pressure hydrogen. However, the route successfully pioneered by Houdry led to an eventual refinery configuration with the FCC centered as the primary means of conversion in today s modem refinery. Houdry s route appeared to preempt hydrocracking. Table I provides an overview of the major milestones of FCC (4, 5, 6, 7). 

This is very similar to pyrolysis, but in this process the mixed plastic waste (MPW) is heated with hydrogen. As the molecules are cracked (the process is often termed hydrocracking), they are saturated with the hydrogen molecules to produce a saturated liquid and gaseous hydrocarbons. The synthetic crude oil produced is of a very high quality. It is necessary to keep the pressure of the hydrogen sufficient to suppress repolymerisation or the generation of undesirable by-products. 

The deposits usually accumulate in the downstream separators, heat exchangers, and fractionating towers, and foul the transfer lines, eventually causing unit shutdown. Equipment fouling by the coke-like sediments formed in residual oil hydroconversion or the hydrocracking process can lead to enormous financial burdens in terms of increased costs of operation, maintenance, and shutdown. The refiners often use chemical and mechanical treatments to remove the deposits from the equipment Some refiners use antifoulant chemical additives to the feed to suppress the formation of sediments. 

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