Reforming kinetics deactivation

The general mathematical description for determining reforming kinetics is shown below for hydrocarbon conversion and deactivation rates, respectively,... 

The elements of range in value from 0 to 1 and are the ratio of the reformer kinetic constants at time on stream t to the values at start of cycle. At any time on stream t, the deactivation rate constant matrix K(a) is determined by modifying the start-of-cycle K with a. From the catalytic chemistry, it is known that each reaction class—dehydrogenation, isomerization, ring closure, and cracking—takes place on a different combination of metal and acid sites (see Section II). As the catalyst ages, the catalytic sites deactivate at... 

Complete reforming kinetics have been developed for several commercial catalysts, including those used in Mobil reformers. Since KINPTR affects Mobil s business strategy, the complete reforming kinetics are proprietary. However, as an example, KINPTR C6 kinetics will be presented for UOP s R16H platinum-rhenium-alumina catalyst. Both the hydrocarbon conversion and the deactivation equations [Eqs. (36), (40)] can be directly applied to the C6 system. For the C6 hydrocarbon conversion, Eq. (40) becomes... 

STEAM REFORMING KINETICS, CATALYST DEACTIVATION AND REACTOR DESIGN... 

Figure 5 Profiles of reforming kinetic relative to deactivation, k /b, as a function of S C for various temperatures...

C, 0.356—1.069 m H2/L (2000—6000 fU/bbl) of Hquid feed, and a space velocity (wt feed per wt catalyst) of 1—5 h. Operation of reformers at low pressure, high temperature, and low hydrogen recycle rates favors the kinetics and the thermodynamics for aromatics production and reduces operating costs. However, all three of these factors, which tend to increase coking, increase the deactivation rate of the catalyst therefore, operating conditions are a compromise. More detailed treatment of the catalysis and chemistry of catalytic reforming is available (33—35). Typical reformate compositions are shown in Table 6. 

While the 13 hydrocarbon lumps accurately represent the hydrocarbon conversion kinetics, they must be delumped for the deactivation kinetics. In addition, delumping is necessary to estimate many of the product properties and process conditions important to an effective reformer process model. These include H2 consumption, recycle gas H2 purity, and key reformate properties such as octane number and vapor pressure. The following three lump types had to be delumped the C5- kinetic lump into Cl to C5 light gas components, the paraffin kinetic lumps into isoparaffin and n-paraffin components, and the Cg+ kinetic lumps into Cg, C9, C10, and Cn components by molecular type. 

The experiments were carried out at a pressure of 1.5 bar and a flow rate of 80-270 Ncm3 min-1. At 200 °C no deactivation of the catalyst was observed. As the rate of reaction was found to show a linear dependence on the residence time, differential conditions were assumed for the measurements. Because of the determined high activation energy of 5 6 kj mol-1, mass transport limitations were excluded. A power law kinetic expression of the following form was determined for methanol steam reforming ... 

Although the above-discussed studies have defined sulfur-poisoning tolerances for conventional nickel catalysts used in steam reforming of natural gas and naptha, they have not considered in sufficient detail the kinetics of poisoning at above-threshold concentrations nor the effects of catalyst and/or gas compositions on rate of deactivation and tolerance level. Nor is there any previous report on the effects of sulfur on product distribution (i.e., relative rates of production of H 2, CO, CH4) in steam reforming of hydrocarbons. 

Deactivation of light naphtha aromatization catalyst based on zeolite was studied, by kinetic analysis, micropore volume analysis and model reactions. Coke accumulates at the entrance of zeolite channel, blocks it and hinders reactant molecule to access active sites in zeolite channel. Our own stabilization technique passivates coke-forming sites at the external surface of the zeolite. This minimizes the coke formation at the entrance of zeolite channel and increases on-stream stability. The stabilized catalyst enabled us to develop a new light naphtha aromatization process using an idle heavy naphtha reformer that is replaced by CCR process. 

The objective of this book is to serve as a practical reference work on testing for the main hydrocarbon-conversion processes applied in oil refineries catalytic cracking, hydroprocessing, and reforming. These fields were combined because of the clear analogies and congruence between the areas, such as deactivation of active sites by coke, mass-transfer phenomena of hydrocarbons into solid catalysts, hydrocarbon chemistry and reaction kinetics, and downscaling of commercial conditions to realistic small-scale tests. 

J.N. Beliramini and R. Datta, React. IQnetics and Catalysts Ijetters, in press. J.N, Beltramini, T.J. Wessel, and R. Datta, Kinetics of Deactivation of FVAtaOg-Cl catalysts by Coking During Methylcyclopentane Reforming, submitted for publication. 

Although the deactivation of Industrial catalysts is often due to two or more different causes, the modeling of simultaneous deactivation phenomena has not been widely studied (refs. 1, 2). The occurrence of two different deactivation processes not only adds another level of complexity to the determination of the intrinsic kinetic behavior but also complicates the interpretation of the experimental results. In our previous studies regarding the thloresistance of naphtha reforming catalysts (refs. 3, 4) we have shown that the activity decay caused by the presence of sulfur compounds in the feed is often accompanied by coking. In this situation, the thioresistance cannot be obtained in a simple way from the deactivation curves. The characteristics of the sulfur poisoning have to be deduced from the overall deactivation rate. 

Goud et al.141 studied the kinetics of deactivation of Pd/Zr02 catalyst in the steam reforming of n-hexadecane. A first-order kinetic model, with first-order deactivation rate, was used to obtain the best fit values for the reaction rate constant and the deactivation rate constant as a function of S/C ratio, temperature, and sulfur loading. They noticed that the reaction rate was enhanced by an increase in temperatures and S/C ratios, but decreased by the presence of sulfur. The catalyst deactivation was more rapid in the presence of sulfur, at low S/C ratios and at lower temperatures. 

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