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A direct experimental scale-up method is presented for steam cracking of hydrocarbon feedstocks. It is based on the “severity” concept but uses two severity indices instead of one to unambiguously characterize the product yields for a given feedstock. Reaction path analysis suggests that the combination of the ethylene/ethane yield ratio and the methane yield characterizes the complete product spectrum. Simulation results for n-butane cracking in a pilot plant reactor, a Lummus SRT-1 reactor, and a 4-2-1 split coil reactor confirm that the same product spectrum is obtained for identical values of both indices in the different reactor geometries although the process conditions differ strongly. The soundness of the approach is further corroborated by experimental results obtained from a pilot plant reactor and a small scale Uno-Quattro coil. This approach is only valid when similar feedstocks are used. A rule of thumb is that the highest PIONA weight fraction for a feedstock cannot deviate by more than 5% of the corresponding value for the reference feedstock. Stronger deviations in feedstock composition lead to larger differences between the product spectra.

A kinetic model for the transalkylation of methylamines over amorphous silica/alumina is presented. The experimental data obtained at temperatures ranging from 623 to 683 K and pressures ranging from 0.2 to 2 MPa were described adequately. Transalkylation reactions occur between ammonia/methylamine adsorbed on an acid site and ammonia/methylamine adsorbed on a neighboring base site. In all reaction paths, the surface reaction between adsorbed species was assumed to be rate determining. At all pressures, the fraction of free acid sites as calculated by the model is very low. The fraction of free base sites is low at high pressures only. Models derived from other mechanisms were rejected based on a statistical analysis, mechanistic considerations, and physicochemical interpretation of the parameters. An industrial transalkylation reactor was simulated. To enhance the rate of dimethylamine formation, a mixture with an excess of monomethylamine and a deficit of ammonia and trimethylamine is recommended as the inlet composition for a transalkylation reactor. Decreasing the inlet partial pressure of ammonia results in a reduced amount of catalyst required to obtain the equilibrium concentration of dimethylamine.

The deposition of stoichiometric V2O5films for abrasion‐resistant V2O5/TiO2anatase catalysts was investigated. Direct current magnetron sputtering from ceramic oxide targets in an argon/oxygen atmosphere was chosen as the deposition technique. Layers were prepared with different oxygen mole fractions in the plasma and the influence upon electronic and optical properties was investigated. Surface XPS measurements showed that stoichiometric layers are obtained for low oxygen flows, whereas for higher oxygen contributions reduced vanadium species are increasingly present. This departure from stoichiometry is ascribed to active re‐sputtering of the deposited layer by O−ions, due to the higher sputter yield of oxygen compared with vanadium. Polycrystalline V2O5layers were obtained at elevated substrate temperatures. Optical absorption coefficients in the visible region were found to correlate well with the layer stoichiometry, as deduced from the XPS lineshape analysis. Copyright © 2002 John Wiley & Sons, Ltd.

The adsorption of benzene on Pt(111) was analyzed using first-principles density functional theoretical cluster and periodic slab calculations. The preferred adsorption site at low coverage is the bridge(30) site with an adsorption energy of 117 kJ/mol. At the bridge(30) site, two of the C pz orbitals are well aligned for overlap with the metal dz^{2 and dyz orbitals, leading to a strong C−Pt bond and a strong adsorption energy. The molecule's second important site is the hollow(0) site with an adsorption energy of 75 kJ/mol. Comparing calculated and experimental vibrational frequencies confirms the preference for the bridge site at low coverage and also indicates that adsorption at the hollow(0) site becomes preferred at higher coverage. Adsorption at the hollow(30), the bridge(0) and at the atop sites was found to be unfavorable.}

A pilot unit for steam cracking equipped with a transfer line heat exchanger (TLE) that allows for the study of coke deposition in both the reactor and the TLE is presented. The reactor and TLE are made of Incoloy 800HT. The duration of a coking run typically amounts to 32.4 ks. The influence of different dimethyl disulfide (DMDS) addition procedures, i.e., continuous addition, presulfidation and presulfidation followed by continuous addition, on CO production and on coke deposition in the reactor and in the TLE during naphtha cracking is investigated. Presulfidation reduces CO production. However, to obtain a low and stable CO production, continuous addition of sulfur is required. The influence of sulfur addition on coke formation in the reactor can strongly differ from its influence on coke formation in the TLE. In the reactor, as well as in the TLE, the observed influence of sulfur addition is complex and strongly depends on the technique used. The optimal operating conditions for reducing CO production and minimizing coke formation consist of presulfidation followed by continuous dosing.