Abstract:
An apparatus is disclosed for the generation of hydrogen peroxide. The apparatus is designed to allow for a greater range of tolerances in its manufacture. The apparatus provides for the production of a large scale volume of hydrogen peroxide by the generation of a liquid bearing bubble cloud. The bubbles are generated with a tiny volume before flowing over the reactor bed to generate the hydrogen peroxide.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a division of copending application Ser. No. 10/837,773, filed on May 3, 2004, which is a continuation-in-part of application Ser. No. 10/418,589, filed Apr. 17, 2003, now granted as U.S. Pat. No. 7,192,562, and which are both incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the invention is a gas mixing apparatus. In particular, this invention relates to the mixing of gases with compositions that can result in combustible mixtures. 
       BACKGROUND OF THE INVENTION 
       [0003]    Currently the most widely practiced industrial scale production method for hydrogen peroxide is an indirect reaction of hydrogen and oxygen employing alkylanthraquinone as the working material. In a first catalytic hydrogenation step, the alkylanthraquinone, dissolved in a working solution comprising organic solvents (e.g. di-isobutylcarbinol and methyl naphthalene), is converted to alkylanthrahydroquinone. In a separate autooxidation step, this reduced compound is oxidized to regenerate the alkylanthraquinone and yield hydrogen peroxide. Subsequent separation by aqueous extraction, refining, and concentration operations are then employed to give a merchant grade product. 
         [0004]    Overall, this indirect route to H 2 O 2  formation, whereby a carrier medium is reduced and then oxidized, adds complexity and requires high installation and operating costs. One notable drawback is the significant solubility of the alkylanthraquinone in the aqueous extraction medium used to separate the hydrogen peroxide product. This promotes loss of working solution and leads to contamination of the hydrogen peroxide product with organic species that, when the hydrogen peroxide is concentrated to levels suitable for transport, are reactive with it. A second problem relates to the solubility of the aqueous extraction solution in the alkylanthraquinone working solution. When wet working solution is separated from the aqueous phase for recycle to the indirect oxidation stage, residual aqueous phase “pockets” within the organic solution provide regions for hydrogen peroxide product to concentrate to the extent of becoming hazardous. A third problem relates to the usage and recovery of an organic compound when small amounts of hydrogen peroxide are needed without the organic contamination in an aqueous stream. 
         [0005]    Considerably more simple and economical than the alkylanthraquinone route is the direct synthesis of hydrogen peroxide from gaseous hydrogen and oxygen feed streams. This process is disclosed in U.S. Pat. No. 4,832,938 B1 and other references, but attempts at commercialization have led to industrial accidents resulting from the inherent explosion hazards of this process. Namely, explosive concentrations of hydrogen in an oxygen-hydrogen gaseous mixture at normal temperature and pressure are from 4.7-93.9% by volume. Thus the range is extremely broad. 
         [0006]    It is also known that dilution of the gaseous mixture with an inert gas like nitrogen scarcely changes the lower limit concentrations, on an inert gas-free basis, of the two gases. Within normal ranges of pressure variation (1-200 atmospheres) and temperature variation (0-100° C.) the explosive range is known to undergo little change. Furthermore, even when these reactants are brought together in a ratio that, in the homogeneous condition, would be outside the flammability envelope, the establishment of homogeneity from pure components necessarily involves at least a temporary passage through the flammability envelope. For these reasons, the explosion risks associated with the direct contacting of hydrogen and oxygen are not easily mitigated. 
         [0007]    In the area of directly contacting hydrogen and oxygen, some efforts have also been made to contain the reaction in a liquid phase. For example, U.S. Pat. No. 5,925,588 B1 discloses the use of a catalyst having a modified hydrophobic/hydrophilic support to provide optimum performance in an aqueous liquid phase. Also, U.S. Pat. No. 6,042,804 B1 discloses dispersing minute bubbles of hydrogen and oxygen into a rapidly flowing acidic aqueous liquid medium containing a catalyst. Unfortunately, however, the hydrogen and oxygen reactants are only slightly soluble in the aqueous reaction solvents disclosed in these references. 
         [0008]    Other references, namely U.S. Pat. No. 4,336,240 B1 and U.S. Pat. No. 4,347,231 B1 disclose two-phase reaction systems with a homogeneous catalyst dissolved in an organic phase. As mentioned in the former of these two references, homogeneous catalyst systems in general suffer from drawbacks that are a deterrent to their commercial use. The adverse characteristics include poor catalyst stability under reaction conditions, limited catalyst solubility in the reaction medium, and low reaction rates for the production of hydrogen peroxide. In addition, a gaseous H 2 /O 2  containing environment above the two-phase liquid reaction system maintains the equilibrium concentrations of these reactants dissolved in the liquid phase. Therefore, this gaseous atmosphere above the reaction liquid must necessarily be outside the flammability envelope, thus greatly restricting the range of potential reactant mole ratios in the liquid phase. 
         [0009]    There are two types of reactors for making hydrogen peroxide in water. The first is a slurry reactor in which the gas bubbles and catalyst are dispersed in a flowing liquid phase. While this is advantageous for mixing and provides good heat and mass transfer, this method requires a large amount of expensive catalyst, in addition to catalyst recovery and recycle methods. The second reactor is a trickle bed reactor in which the gas and liquid flow over a packed bed of catalyst. The main drawback to the trickle bed reactor is the gas is a continuous phase and therefore requires a small channel size, and hence small particle size to prevent the hydrogen and oxygen from entering a dangerous regime. 
         [0010]    It would be useful to have a device and process for making hydrogen peroxide large quantities, on an as-needed basis, without the need of extra chemicals for an environmental safer method, and without generating a waste product stream. 
       SUMMARY OF THE INVENTION 
       [0011]    One method to overcome the drawbacks of the current methods of hydrogen peroxide production is to generate a large amount of hydrogen and oxygen gas mixture in a dispersed phase of small bubbles in a liquid. The present invention provides an apparatus for generating a mixture of hydrogen and oxygen as tiny gas bubbles. The present invention comprises a pair of plates where the first plate has a main channel and a plurality of smaller channels defined in the first plate for carrying a first gas, and the second plate has a main channel and a plurality of smaller channels defined in the second plate for carrying a second gas. The first plate secondary channels have a portion that extends through the plate and have an outlet in fluid communication with the second plate secondary channels. The plates when stacked provide for mixing of the first and second gas streams in the smaller channels of the second plate, and where the gas mixture exits as small bubbles into a liquid stream. This embodiment of the invention provides a design to allow for greater tolerances in manufacturing the apparatus. 
         [0012]    In an alternate embodiment, the apparatus comprises a pair of plates where the first plate has a main channel and a plurality of smaller secondary channels defined in the first plate for carrying a first gas. In addition, the first plate has at least one tertiary channel in fluid communication with the secondary channels wherein the tertiary channel extends through the plate and has an outlet on the opposite side of the plate as the primary and secondary channels. The apparatus further comprises a second plate having a main channel and a plurality of smaller secondary channels defined in the second plate for carrying a second gas. The second plate secondary channels are in fluid communication with the outlet for the first plate tertiary channels and provide for mixing of the first gas and second gas in a section of the second plate secondary channels. 
         [0013]    Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description. 
         [0014]    Additional objects, embodiments and details of this invention can be obtained from the following detailed description of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a design of a first plate for the mixer; 
           [0016]      FIG. 2  is a design of a second plate for the mixer; 
           [0017]      FIG. 3   a  is schematic of a secondary channel in the first plate of the mixer; 
           [0018]      FIG. 3   b  is a schematic of a secondary channel in the second plate of the mixer; 
           [0019]      FIGS. 3   c  and  3   d  show potential positions of the secondary channels when the first and second plate are stacked; 
           [0020]      FIG. 4  is a design of a fourth embodiment of the first plate for the mixer; and 
           [0021]      FIG. 5  is a cross-sectional view of the fourth embodiment of the first plate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The present invention is an apparatus for large scale mixing of hydrogen and oxygen in water for reaction to generate hydrogen peroxide (H 2 O 2 ). A problem with scale up of hydrogen peroxide production is the generation of quantities that will create large volumes of a mixture of hydrogen and oxygen. This is a potentially dangerous situation. It is therefore desirable to generate a large quantity of mixed hydrogen and oxygen, but in a dispersed phase of small bubbles in water, or other solvent, for the rapid dissolution in the solvent and reaction in the liquid phase to produce hydrogen peroxide. A new design of a mixer suitable for large scale use is presented. 
         [0023]    Although this apparatus is described for use with the production of hydrogen peroxide, it is not limited to hydrogen peroxide production but can be used for the mixing of any gases, and it is especially useful for mixing gases that pass through a combustibility envelope. This apparatus is amenable to a convenient scale up for the large scale mixing of gases, and especially providing large scale mixing of hydrogen and oxygen. A new design is presented that enables more flexibility in the manufacturing of the apparatus, and therefore reducing the cost of production of the apparatus. 
         [0024]    The invention is a gas sparger with narrow channels and is made by stacking plates in an alternate manner to create an apparatus having at least two gas inlets and a plurality of gas outlets for generating small gas bubbles in a liquid. The apparatus has narrow channels for the gas to create a gas mixture. By using narrow channels, the mixing of gases can be done safely when the mixture is in the combustion envelope. However, the narrow channels on the plates must be aligned to allow for gas to flow through a first set of channels and into a second set of channels to mix the gas flowing from the first set of channels with the gas in the second set of channels. The alignment can present a costly setup and manufacturing process to produce the tight tolerances needed. This invention presents a design for producing the gas sparger that allows for greater tolerance variances in the manufacture of the plates and during the assembly of the apparatus. 
         [0025]    The apparatus for mixing gases includes at least two plates, a first plate and a second plate. Each plate has a first side and a second side, and has a series of channels defined in the plate. The first plate  10 , as shown in  FIG. 1 , includes a main channel  12  defined in the first side of the plate  10  and has an inlet  14  for receiving a first gas, and a plurality of outlets  16 . The first plate  10  also includes a plurality of secondary channels  18 , with each secondary channel  18  having an inlet in fluid communication with a main channel outlet  16  and an outlet  20 . The secondary channels  18  are defined in the first side of the first plate and have outlets  20  extending through to the second side of the first plate  10 . The outlets  20  of the secondary channels  18  have an elongated appearance on the second side of the first plate  10 . The outlets  20  are preferably elongated to have a length at least three times greater than the channel width producing outlets with aspect ratios of at least three, although smaller aspect ratios will work for designs with a dense concentration of secondary channels. The aspect ratio of the channel outlets is the ratio of the length, or major axis, of the outlet cross-section to the width, or minor axis, of the outlet cross-section. 
         [0026]    The second plate  30 , as shown in  FIG. 2 , of the apparatus includes a main channel  32  defined in the first side of the second plate having an inlet  34  for receiving a second gas, and a plurality of outlets  36 . The second plate  30  also includes a plurality of secondary channels  38 , with each secondary channel  38  having an inlet in fluid communication with a main channel outlet  36  and an outlet  40 . The secondary channel outlets  40  are located along one edge of the plate  30 . The secondary channels  38  of the second plate  30  have, in general, three sections. A first section beginning at the main channel outlets  36 , where the first section extends to a distance about where the outlet  20  from the secondary channels  18  of the first plate  10  are when the first  10  and second  30  plates are stacked. A second section extends from the end of the first section, at an angle relative to a line continuing from the first section between about 1 degree and about 89 degrees. A third section extends from the end of the second section to the secondary channel outlets  40  and in a direction generally parallel to the first section. 
         [0027]    The first and second plates  10 ,  30  when stacked position a portion of the first plate secondary channel outlets  20  in fluid communication with the second plate secondary channels  38 . This provides a section of the second plate secondary channels  38  as a mixing region for the first gas and second gas. The plates  10 ,  30 , when stacked, are positioned such that a portion of the secondary channels  38  of the second plate  30  is oriented to be non-parallel to the elongated outlets  20  of first plate secondary channels  18 . 
         [0028]    A first embodiment of this design entails plates that have channels in a generally rectangular configuration with the channels in the second plate  30  having secondary channels  38  with a section of the channel  42  configured at an angle between 1 degree and 89 degrees with respect to the general direction of the channel  38 . Preferably the second section of the channel  42  is configured at an angle between 30 degrees and 60 degrees. The outlets  20  from the secondary channels  18  of the first plate  10  are elongated such that a portion of the outlet  20  overlaps with the section  42  of the second plate secondary channel  38 . An individual channel  18  and outlet  20  of the first plate is shown in  FIG. 3   a , and example of a possible secondary channel  38  in the second plate  30  is shown in  FIG. 3   b . With this design, when the plates  10 , are overlaid, the positioning allows for a greater variance, and two cases are shown for slightly misaligned plates in  FIGS. 3   c  and  3   d.    
         [0029]    In the present embodiment, the main channels  12 ,  32  are sized to a width of approximately 50 mm and a depth of approximately 0.5 mm, providing a cross sectional area of 25 mm 2 . The smaller channels  18 ,  38  are sized to a width of approximately 0.2 mm and a depth of approximately 0.2 mm, providing a cross sectional area of 0.04 mm 2 . A good distribution of the gas from the main channels to the smaller channels is achieved by maintaining a ratio of the cross sectional area of the main channel to the sum of cross sectional areas of the smaller channels to be at least 3. In the present embodiment, the current channel sizes allow for about 208 smaller channels to each main channel. The use of small channel dimensions for the smaller channels provides lamellar mixing of the gases and has been shown to be a safe and effective way of mixing hydrogen and oxygen without combustion. 
         [0030]    While the specific design of the smaller channels  18 ,  38  for this embodiment have an effective diameter of about 200 micrometers (0.2 mm), the channel shape and design of the smaller channels  18 ,  38  are only constrained based upon the composition of the gases to be mixed by the sparger. In the instant case of the mixing of hydrogen and oxygen, the smaller channels  18 ,  38  have an effective diameter of less than about 300 micrometers (0.3 mm) and preferably less than about 200 micrometers (0.2 mm). 
         [0031]    While the design of this invention is for use of mixing hydrogen and oxygen for the production of hydrogen peroxide, the invention is not limited to these gases, but to the contrary, any lamellar mixing of gases may be performed with this invention. 
         [0032]    A second embodiment of this invention is that the secondary channels  18 ,  38  of the plates  10 ,  30  have a generally rectangular configuration, with the major axis of the outlets  20  of the first plate secondary channels  18  formed at an angle between 1 degree and 89 degrees with respect to the general direction of the secondary channels  18  such that at least a portion of the outlets  20  will overlap at least a portion of the secondary channels  38  of the second plate  30 . The angle chosen will depend on the density of secondary channels  18 ,  38  and the aspect ratio of the outlets  20 . 
         [0033]    A third embodiment of this invention is that the secondary channels of the first plate have a generally rectangular configuration and the secondary channels of the second plate are oriented at an angle between 1 degree and 89 degrees relative to the first plate when the plates are stacked. The angle chosen for the relationship between the secondary channels of the first plate and second plate depends on, but is not limited to, the density of secondary channels  18 ,  38 , the aspect ratio of the first plates secondary channel outlets  20 , and the angle of the outlets  20  major axis relative to the direction of the secondary channels. This relative orientation can be achieved by forming the secondary channels in the second plate at the desired angle, or by rotating the second plate during the assembly of the apparatus when the plates are stacked. In an alternative, the secondary channels of the second plate have a generally rectangular configuration with the secondary channels of the first plate oriented at an angle between 1 degree and 89 degrees relative to the second plate. 
         [0034]    The apparatus when assembled forms a device with at least one inlet for a first gas, at least one inlet for a second gas, and a plurality of outlets for a mixture of the first and second gases. 
         [0035]    In an alternate embodiment, the outlets from the first plate secondary channels can be oriented to be non-parallel to the second plate secondary channels. The elongated shape of the outlets will provide for a greater range of positions of the first plate relative to the second plate with at least a portion of the outlets of the first plate secondary channels in fluid communication with the second plate secondary channels. This also includes having the outlets from the first plate secondary channels being oriented non-parallel to the first plate secondary channels. 
         [0036]    There can be a plurality of first and second plates stacked in an alternating sequence of first plates and second plates. The plates are bonded together such that the channels formed in the plates are enclosed channels. Plates having channels in an exterior face are covered with a solid plate to form enclosed channels for that plate. Additionally, the apparatus can have additional plates with channels for carrying liquids, or for carrying additional gases to be mixed. 
         [0037]    The requirement for the design is to allow for more flexible tolerances in the manufacture of each plate, such that when the plates are assembled the outlets of the secondary channels of the first plate are in fluid communication with the secondary channels of the second plate. This allows for a savings and reduced waste in the manufacture of each plate and the assembly of a stack of plates. To that end, a fourth embodiment of the apparatus includes a long transverse channel that encompasses a plurality of the outlets of the secondary channels in the first plate  10 . This embodiment comprises a first plate  10  that has a main channel  12  and a plurality of secondary channels  18 , similar to the embodiments described above. The secondary channels  18  have inlets in fluid communication with the main channel  12 . This embodiment further comprises at least one tertiary channel  50 . The tertiary channel  50  has at least one inlet  52  in fluid communication with the secondary channel outlets  20 . The tertiary channels  50  extend through the plate  10  to the second side and have an elongated outlet  54 , such that when the first plate  10  is stacked on top of the second plate  30 , the outlet  54  is in fluid communication with a plurality of second plate secondary channels  38 . 
         [0038]    In a specific example of this embodiment, as shown in  FIG. 4 , the first plate  10  has one tertiary channel  50 . The tertiary channel  50  has a plurality of inlets that are in fluid communication with the secondary channel outlets  20 . The tertiary channel  50  is oriented substantially perpendicular to the secondary channels  18  and intersects all of the secondary channels  18  at the secondary channel outlets  20 . While the tertiary channel  50  is oriented perpendicular to the secondary channels  18 , it is not required to be perpendicular, only that the tertiary channel  50  intersects one or more secondary channels  20 , and that orientation is only limited by design considerations. The tertiary channel  50  extends through the plate  10 , as shown in  FIG. 5 , such that a gas can flow into the main channel  12 , distribute to the secondary channels  18 , enter the tertiary channel  50  and exit the tertiary channel outlet  50  on the opposing, or second, side of the plate  10 . The gas exiting the tertiary channel outlets  54  will enter the secondary channels  38  of the second plate  20  where the gas will mix with a gas in the second plate secondary channels  38 . The effective width of the tertiary channel is less than about 300 micrometers (0.3 mm) and preferably less than about 200 micrometers (0.2 mm). 
         [0039]    In this embodiment, the second plate  30  can be designed as described above, or the second plate  30  can be designed as in U.S. Pat. No. 7,192,562. The flexibility of the design of the first plate  10  in this embodiment allows for a greater variation in designs of the second plate  20 . 
         [0040]    While the invention has been describe with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various modifications and equivalent arrangements included within the scope of the claims.