Catalysts pore size

Catalyst circulation coke is a hydrogen-rich coke from the reactor-stripper. Efficiency of catalyst stripping and catalyst pore size distribution affect the amount of hydrocarbons carried over into the regenerator. 

The effect of catalyst pore size on the hydrogenation of 4-tert-butylaniline was examined using catalysts M1081, M1272, M1079, and M1273. The effect on the rate is shown in Table 2. 

Stanislaus, A., Absi-Halabi, M., Khan, Z., Influence of Catalyst Pore Size on Asphaltenes Conversion and Coke-Like Sediments Formation During Catalytic Hydrocracking of Kuwait Vacuum Residues, In Catalysts in Petroleum Refining and Petrochemical Industries. Studies in Surface Science and Catalysis. 1996, Elsevier New York, USA. pp. 189-197. 

The most common process variables are as follows temperature, pressure, concentrations, pH, catalyst pore size, flow rate, stirring rate, etc. In the process of creating a compositional catalyst library the initial steps are as follows ... 

Figure 10. Interaction between catalyst pore size and feed molecular weight in hydrocracking a California solvent deasphalted oil...

Coke deposition alters catalyst pore size distributions significantly and is an effect to be followed in regard to catalyst aging. 

A separate class of experimental evaluation methods uses biological mechanisms. An artificial neural net (ANN) copies the process in the brain, especially its layered structure and its network of synapses. On a very basic level such a network can learn rules, for example, the relations between activity and component ratio or process parameters. An evolutionary strategy has been proposed by Miro-datos et al. [97] (see also Chapter 10 for related work). They combined a genetic algorithm with a knowledge-based system and added descriptors such as the catalyst pore size, the atomic or crystal ionic radius and electronegativity. This strategy enabled a reduction of the number of materials necessary for a study. 

SEM and TEM images give detailed information about the porous structure of a supported heterogeneous catalyst (pore size distribution, typical sizes of the particles, etc.). The information from SEM and TEM images can be used in the reconstruction of porous catalytic medium. In the digitally reconstructed catalyst, transport (diffusion, permeation), adsorption, reaction, and combined reaction-diffusion processes can be simulated (Stepanek et al., 2001a). Parametric studies can be performed, and the resulting dependencies can serve as a feedback for the catalyst development. 

The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions. 

The sizes determined in this work are the apparent molecular sizes and not necessarily the sizes of the asphaltene and maltene molecules at process conditions. Association efforts for asphaltene molecules have been observed for both vapor-phase osmometry molecular weight and viscosity measurements (14, 15). The sizes reported here were measured at 0.1 wt % in tetrahydrofuran at room temperature. Other solvent systems (chloroform, 5% methanol-chloroform, and 10% trichlorobenzene-chloroform) gave similar size distributions. Under these conditions, association effects should be minimized but may still be present. At process conditions (650-850°F and 5-30% asphaltene concentration in a maltene solvent), the asphaltene sizes may be smaller. However, for this work the apparent sizes determined can be meaningfully correlated with catalyst pore size distributions to give reasonable explanations of the observed differences in asphaltene and maltene process-abilities (vide infra). In addition, the relative size distributions of the six residua are useful in explaining the different processing severities required for the various stocks. Therefore, the apparent sizes determined here have some physical significance and will be referred to just as sizes. 

Both asphaltene and maltene molecular size distributions were compared with the pore size distribution of a small pore desulfurization catalyst. Figure 4 shows the Kuwait maltene and asphaltene size distributions along with the catalyst pore size distribution. Most of the maltene molecules are small enough to diffuse into the catalytic pores. In contrast, the Kuwait asphaltenes have a... 

Size characterization measurements have provided useful information on the importance of the hydroprocessing catalyst pore size distribution and on the effects of visbreaking and hydroprocessing on the residua molecular size distributions. It is apparent that asphaltenes and maltenes are not unique entities, but instead have considerable overlap in their size distributions. A complete study of the effects of processing conditions would require consideration of all components of a residuum. 

Influence of Catalyst Pore Size. In the present work, four Ni-Mo/Al203 catalysts with different pore size distributions were used to assess the effect of catalyst pore size on deactivation by coke and metals deposition. Table I summarizes the pore size distribution of the four catalysts used in the present work. The amount of carbon and... 

INFLUENCE OF CATALYST PORE SIZE ON ASPHALTENES CONVERSION AND COKE-LIKE SEDIMENTS FORMATION DURING CATALYTIC HYDROCRACKING OF KUWAIT VACUUM RESIDUES... 

Figure 2. Influence of Catalyst Pore Size on Asphaltene Conversion, Distillate Yield and Sediment Formation.

Coke formation on catalyst pore size distribution and surface area... 

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