Figure 6. Enthalpy contour map in the reactor wherein the leading edge of the subsurface layer has a tapered shape that corresponds to the angle of cross-bars in the top-most layer so that fluids from the bulk flow path are not trapped beneath the top-most layer.
The methanol conversion results are presented in Figure 7 for the reactor wherein the volume occupied by the catalyst supported on a mesoporous matrix plus the volume of bulk flow path that is adjacent to the catalyst supported on a mesoporous matrix defines the volume of reaction chamber. All microchannel experiments are conducted with a certain fixed geometry. For the purposes of summarizing heat transfer performance for these devices, the length-to-diameter ratio, typically the channel length divided by the hydraulic diameter is a very useful metric [63, 64]. Boiling heat transfer characteristics of a microchannel can also be enhanced by applying a porous coating or in some means engineer porous or grooved structures on the wall surfaces of a microchannel. For unit operations, including homogeneous chemical reactions and heat exchangers, interaction of the bulk flow species with the active surface feature wall is advantageous to transfer heat to an adjacent heat transfer chamber. Unlike the prior micromixers, it is desirable to move the bulk stream near and past the wall and not necessarily completely and uniformly mix the bulk flow stream. An active surface feature wall that moves more fresh fluid near and past the active surface will be preferential over a design that primarily mixes the bulk stream. For these applications, performance is enhanced with higher Reynolds numbers as opposed to disadvantaged at higher Reynolds numbers because the high momentum streams are moved into a repeating rotating flow pattern that winds the bulk flow past the active surface features and does not substantially stop the flow rotation and try to turn it back in an opposing direction. Once the flow has started to turn in a fixed direction within the active surface features, it continues in the same direction thus demonstrating a high vorticity such that the fluid is replenished against the active surface feature walls. As the momentum is increased at higher Reynolds numbers, the relative vorticity or angular force to spin the fluid also increases and thus the number of contacts or collisions with or near the active surface feature walls is also increased. For these cases, however, vorticity alone is not the only element [65, 66]. Patterns that merely spin the fluid in the bulk flow path, such as that created by a single angular diagonal feature groove across the width of a microchannel wall do not do a good job of pulling the center flow stream into the active surface features. In the present invention, the geometry of the active surface feature wall pattern may be designed to enhance contact, as defined to a molecule breaking the plane of the active surface feature groove and entering into the recessed and angled groove, with active surface features. The preferable active surface features have more than one angle across the width of at least one wall of the microchannel. The feature is preferably contiguous such as a chevron or zig-zag; but in some embodiments a surface feature having at least one angle could be discontinuous if the elements of the feature are aligned so that, except for a gap, the recesses or protrusions would connect, an example is a chevron with a missing apex. The catalyst may be directly wash-coated on the interior walls of the process microchannels, grown on the walls from solution, or coated in situ on a fin structure. The catalyst may be in the form of a single piece of porous contiguous material, or many pieces in physical contact. The catalyst may be comprised of a contiguous material and has a contiguous porosity such that molecules can diffuse through the catalyst. The catalyst may comprise a porous support, an interfacial layer on the porous support, and a catalyst material on the interfacial layer. The interfacial layer may be solution deposited on the support or it may be deposited by chemical vapor deposition or physical vapor deposition.