Hydrogen cross-flow

De Vos, R., Smedler, G., and Schoon, N.-H., Selectivity aspects of using the cross-flow catalyst reactor for liquid phase hydrogenations. Ind. Eng. Chem. Process Des. Dev. 25, 197-202 (1986). 

Catalytic Hydrogen Combustion 3 [CHC 3] Combined Mixer/Cross-flow Com-bustor/Heat Exchanger for Determination of the Kinetics of Hydrogen Oxidation... 

Catalytic Hydrogen Combustion 4 [CHC 4] Cross-flow Combustor/Heat Exchanger lor Hydrogen Oxidation... 

Catalytic cross-flow reactor Calcium aluminum silicate H2 diffusion in liquid-filled pores Hydrogenation of p-nitrobcnzoic acid Pd-coated monolith wall 60 ... 

The key problem of the cross-flow reactor is not how to construct an effective separation of the two flowing phases. It is instead connected with how to design the porosity and location of the catalytic active zones of the separating walls so that the transport resistance across the wall does not limit the conversion and the selectivity of the chemical reactions. Palladium-alloy membranes, or thin films of these alloys on porous ceramic tubs, seem to have the potential to be good solutions of the separating-wall problem for cross-flow reactors used for hydrogenation reactions. 

Deactivation of the catalyst is always an industrially important problem. For fixed-bed reactors, to which class the cross-flow reactors also belong, catalyst poisoning is a particularly delicate matter, since the reactivation is often complicated and expensive. Some poisoning effects may be difficult to explain and understand, and this of course causes extra uncertainty. One example of such poisoning was the observation by Amor and Farris [33] that a special deactivation effect appeared in liquid-phase hydrogenation of toluene using a spiral tubular membrane reactor. Toluene was not hydrogenated at all over the palladium foil used. This phenomenon and reactivation of the catalyst have recently been studied by Ali et al. [56]. 

The yield of cis- (equatorial) and trans- (axial) l,4-di-/er/-butylcyclohexane was of interest to compare in slurry hydrogenations using ground cross-flow catalyst with the cross-flow reactor hydrogenation. It was found from this comparison that the selectivity of cis to trans at high conversion was equal to about 10 in slurry experiments, but increased to between 28 and 322 in comparing experiments with the cross-flow reactor. 

The hydrogenation of l,4-di-/m-butylbenzene may be described with the complex reaction scheme in Fig. 12. Due to this complexity, an attempt to explain the different results of the two hydrogenation series was performed only by mathematical simulation, based on different sets of parameter values of the rate equations describing the reaction network and of the effective diffusivities. The result of this simulation showed that it was quite possible to find a reasonable set of parameter values that can explain the great selectivity differences between slurry and cross-flow experiments. The mathematical simulation also included a calculation of the concentration profiles of the different compounds... 

A simulation of trickle-bed hydrogenations was also performed, giving almost the same high selectivity as in the cross-flow case. This shows that the high selectivity is primarily a pore transport effect and not a result of the addition of the arene and hydrogen to opposite sides of the porous plate. 

One, which is available commercially [12.16] appears to use a cross-flow reactor containing sand-sized limestone, believed to be 2 to 6 mm in size. With a contact time of about 0.5 sec., at least 85 % of the hydrogen fluoride is removed. The pressure drop is reported to be about 0.3 kPa. 

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