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.