A simple kinetic model has been used to simulate catalytic naphtha reformers. The model idealises naphtha to three constituents, namely, paraffins, naphthenes and aromatics, with average properties assigned to each class. Out of the many reactions the mixture can undergo, four major reactions have been considered for which the kinetic parameters have been estimated using plant production data. The reactor model is validated against two different sets of plant data. The agreement between predicted results and observations is generally good. A sensitivity analysis of operating parameters on reactor performance revealed that, while temperature affects the aromatics production significantly, the effect of pressure is negligible.Un modtle cinttique simple a Ctt utilisC pour simuler des reformeurs de naphta catalytiques. Dans ce modtle, le naphta est represent6 par trois composants, soit les paraffines, les naphtenes et les aromatiques, avec des proprittts moyennes attributes ? i chacun des groupes. Outre les nombreuses rtactions que le mtlange peut subir, quatre rtactions principales ont ttt considtrtes pour lesquelles les paramktres cinttiques ont ttt estimts en utilisant des donntes de production d'une installation. Le modkle de rtacteur est valid6 en confrontant deux stries diffdrentes de donntes de production. L'accord entre les rtsultats prtdits et les observations est gtntralement satisfaisant. Une analyse de sensibi-lit6 des effets des parametres optratoires sur la performance du rtacteur rtvkle que l'effet sur la pression est ntgligeable, alors que la temptrature exerce un effet important sur la production des aromatiques.
The inclusion of Re in Pt-Re-AlzO3 reforming catalysts to improve the lifetime is known, but how rhenium functions and how it is disposed in the catalyst remain unclear. These fundamental questions have been attempted in this study by the use of proton-induced X-ray emission and Rutherford backscattering spectrometry (together with electron microscopy and chemisorption studies) to characterize a commercial like catalyst for dehydrogenation of methylcyclohexane. Catalysis is one of the most intensely pursued subjects in chemical engineering and related disciplines, primarily because of its economic importance. The development of modern surface science has made possible studies of the catalyst surface at the molecular level, leading to a better understanding of its role in determining catalytic activity. In situ measurements by infrared spectroscopy (Eischens and Pliskin, 1958;Blyholder, 1968; Force and Bell, 1975a,b), Mossbauer spectroscopy (Dumesic and Topsoe, 1977), electron spin resonance (Lunsford, 1972) and X-ray diffraction (Srivastava et al., 1982) have enabled chemical engineers to broaden their thinking beyond the semiempirical reaction parameters, and relate them to structural aspects of the catalyst, thus leading to a more comprehensive and integrated modeling of chemical reactors.In spite of the applications of advanced instrumental techniques in catalysis, there have been great difficulties inherent in studying the structure and composition of surface atoms in dispersed high area systems such as Pt-Re-AlzO3, the industrial reforming catalyst. Platinum-rhenium-alumina catalysts contain an amount of rhenium comparable to the amount of platinum present (about 0.3 wt. % of each). The addition of rhenium provides greater stability; however, the reasons for the promotional effect of rhenium are unclear, despite some 25 reported studies. It is important to understand how rhenium functions if alternate and better catalyst systems are to be developed. The impact of the research in this bimetallic catalyst area is likely to increase over the next few years. For example, the MTH (methylcyclohexane-toluene-hydrogen) system using methylcyclohexane as a hydrogen carrier, which requires the catalytic (Pt-Re-AlzOs) production of hydrogen from an on-board reactor, is commercially exploited for automotive application (Cresswell et al., 1984).The application of proton-induced X-ray emission analysis (PIXE) and Rutherford backscattering spectrometry (RBS) can provide a significant insight into the near surface elemental composition. Both these techniques were designed originally for research in nuclear physics, and tended to be temperamental and complicated. Most accelerators are now designed for material analysis; however, the full potential of PIXE and RBS techniques in catalyst research has not yet been exploited.In this investigation, results are postulated using the techniques of proton-induced X-ray emission and Rutherford backscattering spectrometry with complementary data from electron microscopy and chemisorptio...
Reforming of naphtha over Pt–Sn/Al2O3 and Pt–Re/Al2O3 catalysts has been investigated. Addition of nitrogen accelerated the catalyst deactivation process, enabling the study of activity decline and subsequent regeneration. Effect of presulfiding on the activity, selectivity and regeneration capacity of the catalyst was also examined. Presence of nitrogen promoted the dealkylation of C7 hydrocarbons, resulting in a higher initial benzene yield which declined with loss in catalyst activity. Sulfiding lowered the aromatics yield by blocking some of the active sites but deactivation rate declined, prolonging catalyst life between regenerations. Performance of Pt–Sn catalyst was similar to that of Pt–Re catalyst except that the aromatics yield was somewhat higher in the latter case.
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