Scale fixed bed

In initial experiments carbon nanomaterial-supported catalysts showed acceptable activities and comparatively high selectivities toward higher hydrocarbons. Nevertheless, the applicability of these new materials in large-scale fixed bed reactors is limited due to their powdery appearance. Concerning this challenge research has already started, and hopefully carbon nanomaterial pellets will... 

In general, large industrial fixed beds operate under near-adiabatic conditions, whereas small laboratory-scale fixed beds may approach isothermal operation (Ruthven, 1984). Especially, for most environmental applications, for catalytic, adsorption, and ion-exchange operations, the species to be removed are in such low concentrations that the operarion is nearly isothermal. Thus, the heat transfer to the external fixed-bed wall is often of minimal importance. 

Dynamic Behavior of an Industrial Scale Fixed-Bed Catalytic Reactor... 

Studies of the Fischer-Tropsch synthesis on nitrided catalysts at the Bureau of Mines have been described (4,5,23). These experiments were made in laboratory-scale, fixed-bed testing units (24). In reference 5, the catalyst activity was expressed as cubic centimeters of synthesis gas converted per gram of iron per hour at 240°C. and at a constant conversion of 65%. Actually, the experiments were not conducted at 240°C., but the activity was corrected to this temperature by the use of an empirical rate equation (25). Conditions of catalyst pretreatment for one precipitated and two fused catalysts are given in Table IV. 

Generally, an amount of coke on the catalyst increases from the entrance to the exit of the fixed bed reactors in residue hydroprocessing (1, 6, 7). Tamm et al. showed the highest remained catalyst activity at the outlet of the bench-scale fixed-bed reactor after a constant desulfurization operation (1), while Myers et al. found the highest catalyst deactivation rate in the last stage of three-stage pilot-scale expanded-bed reactors after a 60 - 70% vacuum residue conversion operation (7). These results from two typical reactor operations support that the catalyst deactivation in a lower... 

According to this concept, Masuda et al. [75] studied the catalytic cracking of the oil coming from a previous thermal pyrolysis step of polyethylene at 450°C in the bench-scale fixed-bed reactor shown in Figure 3.11. The catalysts employed were different zeolite types REY (rare earth exchanged zeolite Y), Ni-REY (nickel and rare earth... 

Figure 3.11 Bench-scale fixed-bed reactor used for the catalytic reforming of products coming from the thermal degradation of polyethylene [75]. (Reproduced with permission from Elsevier)...

Small scale gasification [1] This protocol will be used for small-scale, fixed bed, engine based systems. The working group decide that a method similar to that used for sampling PAHs in stack gas would be appropriate. 

Pure hydrocarbons (benzene, n-pentane and n-heptane) and a mixture 70% n-pentane and 30% cyclohexane were used as feed in bench scale, fixed bed flow reactors provided with on-line chromatographic analysis. 

Wang et al. " compared the model predictions to experimental data on the desulfurization of simulated coal gas from a laboratory-scale fixed-bed reactor and from a process development reactor operated on actual coal gas. The solid reactant was formed from cylindrical pellets of zinc and titanium oxides. Data from six experiments using different temperatures, pressures, feed gas flow rates, and feed gas H2S concentrations were available. Product gas concentrations were measured as a function of time, and the axial distribution of sulfur within the reactor was determined at the conclusion of the test. 

There were basically two approaches, which were used in the past for HDT process development studies using catalyst in the commercially applied size and shape. The first one, which was followed 30-40 yr ago in various industrial research and development centers, was to test the commercial catalyst in large pilot plants. The second approach was to use a smaller pilot plant and simulate the data generated in these units, applying a suitable hydrodynamic model to predict the performance of a commercial unit. These are generally known as small-scale TBRs. Because of the presence of a liquid phase, the problems in these small TBRs are more complex as compared to those present in other small-scale fixed-bed catalytic reactors handling only vapor phases. 

Moving from a fixed to a fluidised operation also required a new catalyst. The selected VAM catalyst was an Au/Pd mix in the form of very fine spheres, so miniscule that they seem to flow almost as liquid, prepared in collaboration with the leading catalyst manufacturer Johnson Matthey. Hence, gold-based nanocatalysts are already being used for this process on an industrial scale. Fixed bed processes based on Au/Pd catalysts have been operated for some time by companies such as Celanese and Dupont. 

Due to the cooling requirement, the industrial scale fixed bed reactors used for this process are normally constructed based on the multi-tube design. 

This paper outlines the OXCO chemistry and process concept and presents methane conversion and product selectivity data obtained in a small-scale fixed-bed reactor. The implications of these results for the design of a large-scale OXCO reactor are then briefly discussed. 

Fig. 3 Performance of a lab-scale fixed-bed bioreactor simulation with and without an...

The setup for testing of catalysts has to be as close as possible to the technical conditions of catalyst application. Therefore, powder catalysts for liquid and gas-liquid reactions are usually tested in slurry reactors, which can be operated continuously, under semibatch conditions (constant pressure of the reaction gas, compensation of gas uptake) or in the complete batch mode (no compensation of gas uptake, record of pressure drop of the gas phase). In contrast, catalysts for continuous fixed-bed applications have to be tested in continuous lab-scale fixed-bed reactors. The latter can be operated under either steady-state or non-steady-state (transient) conditions. 

Steady-State Reactors for Testing Fixed-Bed Catalysts Lab-scale fixed-bed reactors for catalyst testing usually reveal diameters between 5 and 15 mm. Steady-state reactors are operated in either an integral or a differential mode. 

The plates had microchannels with different dimensions so as to give different reaction volumes for SS and Ti microchannels. Figure 10.3 shows the comparison between a laboratory-scale fixed-bed reactor and a microchannel reactor. Studies were... 

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