Catalyst deactivation benzene hydrogenation

Blount and Falconer [54] further examined the photocatalytic oxidation of toluene using TPH. During TPH analysis of used catalyst samples, the strongly bound intermediates observed by Larson and Falconer [43] were reported to be hydrogenated and desorbed predominantly as toluene, along with smaller quantities of benzene. This indicated that the intermediate species responsible for apparent catalyst deactivation during toluene photooxidation retained an aromatic ring structure. 

Theoretical and experimental results on deactivation have been summarized in two reviews by Butt (.1,2). Previous work of particular interest to the present study has been done by Blaum (3) who used a one-dimensional two-phase model to explore the dynamic behavior of a deactivating catalyst bed. Butt and cowotkers (b,5,6)have performed deactivation studies in a short tubular reactor for benzene hydrogenation for both adiabatic and nonadiabatic arrangements. They experimentally observed both the standing (6) and travelling (4) deactivation wave. Hlavacek... 

Zeolites have been used as (acid) catalysts in hydration/dehydration reactions. A pertinent example is the Asahi process for the hydration of cyclohexene to cyclo-hexanol over a high silica (Si/Al>20), H-ZSM-5 type catalyst [57]. This process has been operated successfully on a 60000 tpa scale since 1990, although many problems still remain [57] mainly due to catalyst deactivation. The hydration of cyclohexanene is a key step in an alternative route to cyclohexanone (and phenol) from benzene (see Fig. 2.19). The conventional route involves hydrogenation to cyclohexane followed by autoxidation to a mixture of cyclohexanol and... 

Naphthas with different initial and final boiling points were compared by pilot reactor testing. The pilot reactor unit consisted of isothermal, once-through reactors with on-line GCs for full product analysis and octane number determination. Octane numbers, reformate yields and composition as well as gas yields were measured as a function of reaction temperature at 16 bar reaction pressure and a molar Hj/HC ratio of 4.3. Catalyst deactivation was studied over two weeks periods at high severity conditions, i.e. 102.4 RON and a Hj/HC ratio of 2.2. Test results, with emphasis on the yields of benzene and other aromatics, reformate and hydrogen yields as well as catalyst deactivation, are presented. 

Theoretical equations, which predict the loss of catalyst activity due to sulfur poisoning in hydrogenation reactions, are presented in this paper. The integration of the partial differential equations resulting from a consideration of sulfur poisoning, hydrogenation, and a catalyst active site balance leads to an analytical solution. When these equations were applied to deactivation data obtained for commercial benzene hydrogenation catalysts, conversions measured experimentally as a function of time were fit quite well by these equations. 

Fig. 16. Reaction of methylcyclopentane to Ce-ring hydrocarbons (benzene + cyclohexane), and to hydrogenolysis products, on dual-component mixed catalyst, when platinum component is progressively deactivated by hydrogen sulfide.

This work deals with the study of the coke formation on H-mordenite during the benzene transalkylation with C9 aromatics, under several reaction conditions, in order to evaluate the condition which results in the lowest catalyst deactivation for industrial purposes. It was found that coke was produced in all samples but it was maintained around 4% (weight) without damage to activity and selectivity to toluene and xylenes. The coke was hydrogenated and could be easily removed. The soluble coke was mostly constituted by aliphatic hydrocarbons, while the insoluble coke was amorphous. These results were explained by the mordenite structure as well as by the presence of hydrogen. The best condition to perform the reaction depends much more on the selectivity to toluene and xylenes rather than on coke production. 

T. L6pez, A. Lopez-Gaona, and R. Gomez, Deactivation of Ruthenium Catalysts Prepared by the Sol-Gel Method in Reactions of Benzene Hydrogenation and n-Pentane Hydrogenolysis, Langmuir, 6, pp. 1343-46, 1990. 

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