Patent Publication Number: US-2012040130-A1

Title: Minireactor Array

Description:
PRIORITY 
     The present application claims priority to U.S. Provisional Patent Application No. 61174493, filed 30 Apr., 2009. 
    
    
     BACKGROUND 
     The present disclosure relates to honeycomb structures used as reactors or heat exchangers, or “minireactors” formed into an array, and particularly to methods of joining the structures so as to form channels through the array in a direction perpendicular to the common direction of the honeycomb cells and to the resulting arrays. 
     SUMMARY 
     In forming an array or honeycomb devices for use as a reactor or reactor array, channels may be machined into selected side faces of honeycomb substrates so that when the substrates are joined together one or more high aspect ratio channels are formed through the array in a direction perpendicular to the common direction of the honeycomb cells. Substrates may be joined together using a frit or a cement, or even a compression seal if desired, on selected side faces. 
     According to one embodiment, an array of honeycomb substrates comprises honeycomb substrates, a plurality of which have, for each substrate, substrate cells extending from a first end of the respective substrate to a second end and substrate sides extending from the first end to the second end. The substrates of the plurality are arranged in an array with sides of respective substrates facing one another and cells of respective substrates extending in a common direction. One or more channels are defined between facing substrate sides of two or more substrates of the plurality, and the one or more channels extend in a direction perpendicular to the common direction. 
     According to another embodiment, an array of honeycomb substrates comprises honeycomb substrates, a plurality of which have, for each substrate, substrate cells extending from a first end of the respective substrate to a second end and substrate sides extending from the first end to the second end. The substrates of the plurality are arranged in an array with sides of respective substrates facing one another and cells of respective substrates extending in a common direction. One or more channels are defined along the cells of two or more substrates of the plurality of substrates, and the channels extend from within a first substrate of the plurality through a substrate side thereof into a second substrate of the plurality through a substrate side thereof. The respective sides through which the one or more channels pass may be sealed to each other. 
     According to yet another embodiment of the invention, a method is provided of making an array of honeycomb substrates, the method including providing a plurality of honeycomb substrates having side faces and machining channels into selected ones of the side faces of the plurality of honeycomb substrates, in a direction generally perpendicular to a substrate cell direction, then sealing the channels by sealing the selected of the side faces to other side faces of the plurality of honeycomb substrates. The method may further include machining channels into one or more other side faces of the plurality of honeycomb substrates, in a direction perpendicular to the substrate cell direction, prior to the step of sealing. 
     Among other uses or applications of these embodiments of the present invention is the provision of a very flexible method for incorporating cross-flow heat exchange channels in a large array of substrates, with the cross-flow channels having low pressure drop and a large open frontal area, resulting in large honeycomb-based heat exchangers, or reactors with heat exchange. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a honeycomb substrate being prepared according to one or more embodiments of the present invention; 
         FIG. 2  is a perspective view of the substrate of  FIG. 1  showing further steps according to one or more embodiments of the present invention; 
         FIGS. 3 and 4  are perspective views of the assembly of multiple honeycomb substrates according to one or more embodiments of the present invention; 
         FIG. 5  is a plan view of an assembled minireactor array or honeycomb substrate array according to one or more embodiments of the present invention; 
         FIG. 6  is a perspective view of a honeycomb substrate being prepared according to one or more further embodiments of the present invention; 
         FIG. 7  is a plan view of an assembled minireactor array or honeycomb substrate array according to one or more still further embodiments of the present invention; 
         FIG. 8  is a plan view of an assembled minireactor array or honeycomb substrate array according to one or more yet further embodiments of the present invention; 
         FIG. 9  is a plan view of an assembled minireactor array or honeycomb substrate array according to one or more still further embodiments of the present invention; 
         FIG. 10  is a perspective view of a honeycomb substrate being prepared according to one or more still further embodiments of the present invention; 
         FIG. 11  is a plan view of an assembled minireactor array or honeycomb substrate array according to one or more yet further embodiments of the present invention; 
         FIG. 12  is a perspective view of a honeycomb substrate being prepared according to one or more yet further embodiments of the present invention; 
         FIG. 13  is a plan view of an assembled minireactor array or honeycomb substrate array according to one or more still further embodiments of the present invention; 
         FIG. 14  is a perspective view of a honeycomb substrate being prepared according to one or more still further embodiments of the present invention; 
         FIG. 15  is a plan view of an assembled minireactor array or honeycomb substrate array according to one or more yet further embodiments of the present invention that may use substrates such as that of  FIG. 14 ; 
         FIG. 16  is a perspective view of a honeycomb substrate being prepared according to one or more yet further embodiments of the present invention; 
         FIG. 17  is a perspective view of a honeycomb substrate being prepared according to one or more still further embodiments of the present invention; 
         FIG. 18  is a cross-sectional view of channels of the a substrate of the type shown in  FIGS. 12  and/or  14 ; 
         FIG. 19  is a cross-sectional view of channels of the a substrate of the type shown in  FIG. 16 ; 
         FIG. 20  is a cross section high aspect ratio channels which are an alternative to channels of the types shown in  FIGS. 18  and/or  19  in the various multiple embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A machined channel  12  may be formed on one side face of a rectangular honeycomb substrate  10  as shown in  FIG. 1 . This channel  12  is preferably formed in a green substrate  10  prior to sintering by a simple milling, sawing or belt sanding operation, but it may also be formed on a fully-sintered or partially-sintered substrate  10  if desired. The depth of the machined channel  12  (measured normal to the side face of the substrate  10 ) may be one cell, as shown in the figure, or deeper. Cell walls of the substrate  10  are desirably removed in the area of the channel  12  so that a smooth sidewall surface  14  is formed along the machined channel  12 . The width of the machined channel (measured parallel to the direction of cells of the substrate  10 ) should be less, desirably only slightly less, than the length of the substrate  10 , so that two relatively narrow rows of cells  16 ,  18  remain near each respective end face  20 ,  22 . 
     Next the substrate is sintered (assuming green-substrate channel machining operations). As shown in  FIG. 2 , according to one embodiment of the present invention, after substrate sintering, a frit sealing material  24  is applied to selected side faces of the substrate  26 ,  28 . In additional embodiments, the sealing material may also be a cement  24  or some type of organic adhesive  24 , depending on requirements of the intended use of the resulting array. 
     Frit may be applied via various processes, including doctor-blading, screen-printing, spray application, or by use of frit preforms. By orienting a number of substrates  10  in a row with either end faces or selected side faces touching one another (not shown), the frit may be applied in a continuous process. In general frit application is required on at most two adjacent substrate side faces  26 ,  28 , simplifying the application process since each substrate  10  can rest on a non-frit coated side face  30 ,  32  (not directly visible in  FIG. 2 ) or end face  20 ,  22  (as indicated in  FIG. 1 ) during frit application. 
     End face cells  16 ,  18  directly over or beneath the machined channel are also be plugged, with frit  34 , or with other suitable plug material  34  (shown in cells  18  only) for alternative embodiments. This prevents unintended mixing of fluid flowing in machined channels with fluid flowing in the substrate&#39;s open cells. A frit paste may be applied to plug the cells by first masking those cells which are to remain open, for example. 
     With reference to  FIGS. 3 and 4 , after frit or other sealant is applied, a set  100  of substrates  10  are joined together in an arrayed assembly or array  500 , one embodiment of which is shown in  FIGS. 3 and 4 , showing the set  100  of machined and sealant-coated substrates  10  during assembly into an array  500 . While a regular array  500  of identical shapes is shown, irregular arrays and substrates having various cross sections and shapes may be combined, as one alternative aspect of the various embodiments disclosed herein, if desired. Substrates  10  in the embodiment shown are oriented so that machined channels  12  align with one another to form high aspect ratio channels  102  through the assembled array  500 , shown with one substrate  10  remaining to assemble in  FIG. 4 , in the direction indicated by the arrow  36 . When the substrates  10  are packed together in the array  500  of  FIG. 4 , their fit-coated facing sides come into contact with each other. During subsequent frit sintering, the frit softens and flows to faun a seal with the facing side faces. If desired, the array  500  of substrates  10  may be sintered in a 45 degree V-block (not shown) so that as the frit shrinks on sintering, gravity assists in preventing any gaps from opening between the respective substrates  10 . 
     After frit sintering a substrate array is formed that provides short straight channels in close proximity to a series of high aspect ratio cross-flow channels. The structure of such an array can be used as an efficient large area cross-flow heat exchanger. Overall heat transfer performance depends on thermal conductivity of the substrate material, the substrate channel layout and geometry, and the machined high aspect ratio channel geometry as well as working fluid properties.  FIG. 5  is a plan view of an assembled array  500  with machined channels  102  formed between substrates  10 . 
     In another aspect or alternative embodiment, the substrate channel machining operation can be performed on multiple side faces, as shown in  FIG. 6 , where side faces  11   a  and  11   b  of substrate  10 , adjacent side faces, are machined. Substrates  10  of this type may be joined together in an array  500  having crossed internal channels  102   a  and  102   b  as shown in the plan view of  FIG. 7 . These internal channels  102   a ,  102   b  may optionally be connected to external inlet and outlet feed manifolds, not shown, on the four side faces of the array  500 . 
     By selectively machining high aspect ratio channels into side faces of individual substrates, more complex channel routing configurations may be formed through the array. For example,  FIG. 8  shows a plan view of an array configuration where single feed inlet and outlet channels  104 ,  106  at the array exterior are internally manifolded to an array  108  of high aspect ratio channels  102 . In another configuration shown in plan view in  FIG. 9 , the high aspect ratio channel  102  running between substrates  10  is arranged to form a serpentine  110  in the plane perpendicular to the open cells of the substrates  10 , which serpentine  110  passes near all substrates  10  in the array  500 . 
     The substrate channel machining operation may also be performed on opposite substrate side faces  11   a ,  11   c , as shown in  FIG. 10 . When these substrates  10  are joined together in a substrate array  500  as shown in the plan view of  FIG. 11 , double-wide high-aspect-ratio channels  103  are formed. This embodiment is useful to reduce pressure drop in the high aspect ratio machined channels  103 , especially for configurations where substrate cell dimensions are very small. This may be the case when high heat transfer is required in the open cells via large sidewall surface areas and short mean heat transfer distances from cell center to cell sidewall. Triple or quadruple wide channels and larger may be used if desired, made by machining deeper channels in the substrate side faces. Use of deeper machining and/or double wide or wider channels between substrates my be applied to any high aspect ratio channel layout within a substrate array, including all those shown or otherwise disclosed herein. 
     According to another embodiment of the present invention or according to another aspect which may optionally be applied to various of the embodiments disclosed herein, the substrates that make up the substrate array can have their end faces machined to form U-bend regions so as to form serpentine channels extending up and down along the direction of the cells of the substrate(s), traveling from cell to cell at or near the ends of the substrates and entering and exiting from the side of the substrate(s) or the side of the array, in the direction perpendicular to the open cells. An example of this is shown in  FIG. 12 , where three serpentine channels  112   a ,  112   b ,  112   c  are routed in parallel across a substrate  10 . Channel sidewall holes  114  are drilled into substrate side faces  11   a ,  11   c  to enable fluid transport through the serpentine channels  112   a ,  112   b ,  112   c . The holes  114  at side face  11   a  are within the channel  12  as shown. These substrates  10  may be assembled into a substrate array  500  as shown in  FIG. 13 , where high aspect ratio channels  102  running between substrates  10  distribute fluid to serpentine channels  112  that run through each substrate  10  or through selected ones of substrates  10 . An exemplary cross section showing the U-bends and the resulting serpentine channel is shown in  FIG. 18 . As seen there, the U-bends  116  are formed by a combination of lowered (machined away) sidewalls  118  at the ends of the honeycomb substrate and plugs  120  that do not extend to the lowered sidewalls  118 . 
     It is also possible to fabricate each substrate so only serpentine channels are provided.  FIG. 14  shows such a substrate  10 , with end face machining to create serpentine channel U-bends and channel sidewall holes  114  for serpentine inlet and outlet ports. Such substrates  10  can be coated with frit on two adjacent side faces and assembled into a substrate array  500  as shown in  FIG. 15 . Substrates may be assembled so that side port holes  114  line up with one another, forming long serpentine channels  122  extending from within one substrate  10  to within another substrate  10  within the substrate array  500 , or even extending completely through the array  500  as in the embodiment shown in  FIG. 15 . 
     As an alternative to drilling side face channel holes, the same end face U-bend region machining process illustrated in  FIG. 18  may be used to create U-bend notches  115  that extend to the side face of the substrate as shown in perspective view in  FIG. 16  and in cross section in  FIG. 19 . Substrates  10  such as these may have selected side faces coated with frit, and then a number of substrates may be assembled into a substrate array that similar to the one shown in  FIG. 15 . Similarly to the array  500  in that figure, U-bend notches  115  may be aligned to one another during assembly to create long serpentine channels  122  extending from within one substrate  10  to within another substrate  10  within the substrate array, and even extending completely through the array  500  if desired. 
     Various combinations of side face machined high aspect ratio channels between substrates and end face machined serpentine U-bend channels may be combined together to form integrated manifold structures and channel layouts with optimized pressure drop and heat exchange performance. Other types of channels may also be formed in the substrate instead of U-bend serpentine channels, such as high aspect ratio channels formed by plunge machining operations, such as the high aspect ratio channel  124  depicted in cross-section in  FIG. 20 . Instead of removing merely the ends of side walls as in the embodiments of  FIGS. 18 and 19 , plunge machining or another suitable process is used to remove nearly the entire side wall  118 , in an alternating pattern from alternate ends of the substrate. With plugs  120  closing the substrate above the channel  124  at both ends, a high-aspect-ratio channel  124  is formed. One or more holes  114  may be drilled as shown, or other suitable means may be used, to provide access. 
     As yet another embodiment of the present invention, high aspect ratio channels between substrates may be formed without machined channels or the need to machine substrates. Instead, the high aspect ratio channel regions may be formed by selective deposition of thick frit layers on one or more substrate sidewalls, or by use of shims, as represented in perspective view in  FIG. 17 . Thick frit layers  126 , or shims  126  in an alternative approach, provide the spacing required to form the high aspect ratio channel  12  This approach does not require an additional step for plugging of end face channels directly over or beneath the high aspect ratio channel  12 . A thin frit later  128  is applied on substrate side faces that do not require high aspect ratio channels. If a shim  126  is used, a thin frit may be used on both sides of the shim  126 . After frit application, the substrates  10  are stacked in an array  500  similar to the one shown in  FIGS. 3 and 4  and sintered. All design techniques presented above for arranging machined channels in arrays may be used with such frit-bordered high aspect ratio channels. 
     Within the various embodiments and variations thereof according to the present invention, proximity of high aspect ratio machined channels to short straight channels is easily adjusted by design to meet heat exchange requirements while maximizing open frontal area. Geometry of high aspect ratio channel and short straight channels can also be optimized to balance high heat transfer performance with low pressure drop. The various embodiments, particularly when frit seals are used, allow the short straight open cells of the substrates to operate at high pressures, with frit seals between substrates placed in compression or shear for maximum strength. The frit sealing area on substrate side faces can adjusted, increasing it as needed to increase mechanical strength at the fit-substrate interface. 
     Not as a limiting features, but as one potential benefits, the present invention can allow smaller substrates to be sintered individually in a short sintering cycle, relative to a long cycle required to sinter a single larger body. Even though a subsequent sintering cycle might be required if frit were used to join substrates together, this cycle would also be relatively short. Thus sintering time relative to device cross section may be reduced relative to large cross section honeycomb substrates. Flat side faces allow for simplified interfacing to other devices via bonded ports or O-ring seals. And substrate machining processes are relatively simple when only exterior channel forming operations are used. Such side face channel machining processes could be automated. Various high aspect ratio channels could also be laid out using a “mix and match” approach, where substrates with various side face machining patterns are joined together as needed to form the desired cross-flow heat exchange channel path. 
     Overall, the arrays of the present invention provide significant flexibility, since cross-flow heat exchange channels can be formed in relatively arbitrary sizes, both through side face channel machining as in some embodiments, and/or through internal substrate serpentine or high aspect ratio channels, as in other embodiments, and/or by the use of thick frit or shims and in the embodiment of  FIG. 17 . The methods of the present invention further provide reliable and efficient methods of producing these arrays. 
     The arrays disclosed herein are generally useful in performing any process that involves mixing, separation, extraction, crystallization, precipitation, or otherwise processing fluids or mixtures of fluids, including multiphase mixtures of fluids—and including fluids or mixtures of fluids including multiphase mixtures of fluids that also contain solids—within a microstructure. The processing may include a physical process, a chemical reaction defined as a process that results in the interconversion of organic, inorganic, or both organic and inorganic species, a biochemical process, or any other form of processing. The following non-limiting list of reactions may be performed with the disclosed methods and/or devices: oxidation; reduction; substitution; elimination; addition; ligand exchange; metal exchange; and ion exchange. More specifically, reactions of any of the following non-limiting list may be performed with the disclosed methods and/or devices: polymerisation; alkylation; dealkylation; nitration; peroxidation; sulfoxidation; epoxidation; ammoxidation; hydrogenation; dehydrogenation; organometallic reactions; precious metal chemistry/homogeneous catalyst reactions; carbonylation; thiocarbonylation; alkoxylation; halogenation; dehydrohalogenation; dehalogenation; hydroformylation; carboxylation; decarboxylation; amination; arylation; peptide coupling; aldol condensation; cyclocondensation; dehydrocyclization; esterification; amidation; heterocyclic synthesis; dehydration; alcoholysis; hydrolysis; ammonolysis; etherification; enzymatic synthesis; ketalization; saponification; isomerisation; quaternization; formylation; phase transfer reactions; silylations; nitrile synthesis; phosphorylation; ozonolysis; azide chemistry; metathesis; hydrosilylation; coupling reactions; and enzymatic reactions.