Figure 7. Sherwood number profiles in the exothermic process along the length of the combined parallel plate heat exchanger-reactor.
The Sherwood number profiles in the endothermic process are presented in Figure 8 along the length of the combined parallel plate heat exchanger-reactor. The channels of the group one channel system which have common walls with group two systems but not with other group one channels can be prepared so as to have permeable walls, these group one walls being coated with catalytic material on the inner surfaces for their entire length, part of their length or any combination of lengths desired. Different reactants each composed of one or more components are fed into different channels of the group one channels and there are converted, either catalytically or thermally, into products, then these products permeate through the walls into the channel system wherein they react further with each other resulting in the finally desired product. In this way, short-lived unstable intermediates can be efficiently introduced to each other without the need for going through difficult intermediate isolation steps. In addition, such a system with permeable walls can be used to introduce different reactants in different group one channels to each other in the group two channels in a highly controlled manner such that the different reactant in the different group one channels are not comingled in high concentrations before the desired reaction is allowed to take place between the different reactants. The honeycomb design because of its use of mutually supporting wall design, permits the preparation of very thin walls which would crack due to normally occurring stresses if not mutually supported, namely if exposed or structurally independent. The thin walls and small internal diameters of the channels result in an extremely difficult system for carrying out reactions and transferring heat by giving rise to a high ratio of wall surface area, also referred to a geometric surface area, to reactor volume. The channel walls may be of from 0.5 to 5.0 millimeters in thickness. The channels may be of any length from 10 millimeters up to several meters, for example, 10 meters; however, length intermediate between these extremes is preferred for reasons of handling and also to insure sufficient length for any contemplated reaction or use. Lengths ranging from 2-20 centimeters, preferably 4-8 centimeters, most preferably 6 centimeters are contemplated [41, 42]. The channels should have an internal diameter, calculated by using the hydraulic diameter as a measure [43, 44]. This is to ensure a channel diameter of sufficient dimensions so that heat will have the shortest path possible to migrate to the walls, thereupon to diffuse through the walls into neighboring channels for dissipation and to ensure wall surface area to support sufficient catalyst [45, 46]. The channels of the different systems can be arranged in any pattern desired so long as every channel wall of the group one channel system, also referred to as the reacting channels, is in contact with at least one channel wall of the other channel system, also referred to as the coolant channels [47, 48]. This can be accomplished for example, by surrounding each channel of group one channels with channels of system two. The honeycomb may have any overall diameter so long as this overall diameter is at least 6 times the internal channel diameter as measured by the hydraulic diameter, namely ensuring that every wall of the group one channels is contacted by channels of group two. The channels of the honeycomb may be coated with catalytic material, such as those materials selected from the group consisting of Group VIII, Group VB, Group VIB, Group VIIB, Group IB, metals and oxides from the previously mentioned groups and mixtures thereof.