WO2005033379A1

WO2005033379A1 - Microreactors and methods for generating hydrogen peroxide

Info

Publication number: WO2005033379A1
Application number: PCT/US2004/032526
Authority: WO
Inventors: William Stuart Trimmer; Robert Steven Sears
Original assignee: Azalea Way Consumer Products Llc
Priority date: 2003-10-03
Filing date: 2004-09-30
Publication date: 2005-04-14
Also published as: GB0608317D0; US20070023294A1; GB2422377A

Abstract

Microreactors (10) and methods for generating hydrogen peroxide are disclosed. More specifically, microreactors (10) and methods are provided for the batchwise generation of hydrogen peroxide in which respective hydrogen and oxygen electrolysis chambers, and a hydrogen peroxide reaction chamber is fluid-connected to and positioned physically between, the electrolysis chambers. In specially preferred embodiments, the hydrogen peroxide microreactor (10) of the present invention will be in the form of a silicon chip reactor body having a pair of electrolysis channels (14-1, 14-2), reactant channel (14-3) positioned between the electrolysis channels, and at least one (preferably several) connector channel(s) (14-4) which fluid-connect(s) the pair of electrolysis channels (14-1, 14-2) with said reactant channel (14-3). A pair of electrodes (16-1, 16-2) is provided so that each is in operative association with a respective one of the electrolysis channels (14-1, 14-2). A catalyst for forming hydrogen peroxide is also provided so as to be in operative association with the reactant channel (14-3).

Description

MICROREACTORS AND METHODS FOR GENERATING HYDROGEN PEROXIDE

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority benefits under 35 USC §119(e) from U.S. Provisional Application Serial No. 60/508,235 filed October 3, 2003, the entire disclosure of which is expressly incorporated hereinto by reference.

FIELD OF THE INVENTION The present invention relates to the devices and methods for generating hydrogen peroxide (H₂0₂). In especially preferred forms, the present invention is embodied in micro hydrogen peroxide generators and methods which find use in a number of end-use applications (e.g., as a means to generate hydrogen peroxide on site for cosmetic, dental or general household cleansing devices).

BACKGROUND AND SUMMARY OF THE INVENTION Hydrogen peroxide has many advantageous uses and applications. For example, hydrogen peroxide is use to clean wounds, whiten teeth, bleach items such as hair and textile products, and sterilize surgical instruments. Unfortunately, hydrogen peroxide is difficult to transport and store due to its relatively chemical instability. Specifically, hydrogen peroxide has a propensity to decompose to form oxygen gas and water. Such instability and resulting decomposition can be advantageously used as a source of oxygen and or as a means to effervesce a variety of items for the purpose of cleaning, sterilization and the like.

The relative difficulty associated with the transportation and storage of hydrogen peroxide has therefore limited its use in some applications and has made the manufacture of products containing hydrogen peroxide more difficult. In this regard, because of the difficulty in shipping hydrogen peroxide, it is often necessary to manufacture the product at a location which is physically close to its distribution area. Thus, for example, products containing hydrogen peroxide are usually not exported for sale. The difficulty associated with the storage of hydrogen peroxide also means that products containing the same have a relatively short shelf life. Microreactors are known generally and typically refer to microstructured reactors with fluidic paths under 1 millimeter (mm). A number of entities around the world are involved in microreactor research to produce on a micro scale a wide variety of chemicals, including hydrogen peroxide. The driving force behind such research is not only the small size of the microreactors, but also the benefits achieved from relatively fast heat transfer and mass transfer as compared to more conventional plant-size facilities. Moreover, the small amounts of reactants involved typically results in a more safe reaction environment.

It would therefore be highly desirable if microreactors for forming hydrogen peroxide could be provided. It is towards fulfilling such a need that the present invention is directed.

Broadly, the present invention is embodied in microreactors and methods for generating hydrogen peroxide. More specifically, in accordance with the present invention, microreactors and methods are provided for the batchwise generation of hydrogen peroxide. In this regard, the present invention will necessarily require respective hydrogen and oxygen electrolysis chambers, and a hydrogen peroxide reaction chamber which is fluid-connected to, and positioned physically between, the electrolysis chambers. Water, preferably including a suitable electrolyte (e.g., NaOH), may thus fill each of the chambers and the interconnecting fluid passageways therebetween. In especially-preferred embodiments, the hydrogen peroxide microreactor of the present invention will be in the form of a silicon chip reactor body having a pair of electrolysis channels, a reaction channel positioned between the electrolysis channels, and at least one (preferably several) connector channel(s) which fluid-connect(s) the pair of electrolysis channels with said reaction channel. A pair of electrodes is provided so that each is in operative association with a respective one of the electrolysis channels. A catalyst for forming hydrogen peroxide is also provided so as to be in operative association with the reaction channel. The reactor body most preferably comprises top and bottom silicon chips, wherein the electrolysis channels, the reaction channel and the at least one connector channel are etched into said bottom silicon chip, the hydrogen and oxygen from the electrolysis channels diffuse through the connector channel(s) and into the reaction channel. The reaction channel is positioned between the electrolysis channels such that the ratio of hydrogen and oxygen atoms diffused into the reaction channel is approximately one to one.

These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Reference will hereinafter be made to the accompanying drawings, wherein like reference numerals throughout the various FIGURES denote like structural elements, and wherein;

FIGURE 1 is a greatly enlarged schematic perspective representation of a presently preferred microreactor for generating hydrogen peroxide in accordance with the present invention;

FIGURE 2 is an exploded perspective view of the component parts of the microreactor shown in FIGURE 1 ;

FIGURE 3 is an exploded perspective view of the component parts of the microreactor similar to FIGURE 2, but shown with the electrodes and catalyst strips inoperative associate with their respective reaction channel; and FIGURE 4 is a greatly enlarged view, partly sectioned, showing the relationship between the electrode and catalyst strips and their associated channels.

DETAILED DESCRIPTION OF THE INVENTION In general, the present invention is embodied in microreactors and methods for the batchwise generation of hydrogen peroxide. More specifically, the present invention will necessarily require respective hydrogen and oxygen electrolysis chambers, and a hydrogen peroxide reaction chamber which is fluid-connected to, and positioned physically between, the electrolysis chambers. Water with or without a suitable electrolyte (e.g., NaOH) may thus fill each of the chambers and the interconnecting fluid passageways therebetween.

Oxygen and hydrogen gases are thus generated in the respective oxygen and hydrogen electrolysis channels by applying an electrical potential (e.g., 1.5 volts or greater) through the electrodes. Oxygen atoms will therefore be generated at the anode while hydrogen atoms will be generated at the cathode, the anode and cathode being in respective operative association with the oxygen and hydrogen electrolysis chambers. The concentration of the oxygen and hydrogen atoms will therefore diffuse through the fluid connectors from each of the oxygen and hydrogen electrolysis chambers towards the hydrogen peroxide reaction chamber. Over time, there will exist a concentration of oxygen and hydrogen in the reaction chamber which will react in the presence of a suitable catalyst to form hydrogen peroxide. The hydrogen peroxide in the reaction chamber may therefore be extracted for use. Following generation of hydrogen peroxide, the microreactor may be refilled with water (with or without a suitable electrolyte) and resealed for further use or more simply discarded.

Electrolysis produces from water (H₂0) two hydrogen atoms for every one oxygen atom. If a ratio of two hydrogen atoms to one oxygen atom was present in the reaction chamber, the extra hydrogen would poison the reaction and thus little hydrogen peroxide (H₂0₂) would be generated. Therefore, a ratio of one hydrogen atom to one oxygen atom should be present in the reaction chamber. By positioning the reaction chamber further from the electrolysis chamber in which hydrogen is formed as compared to its position with respect to the electrolysis chamber in which oxygen is formed, it is possible to allow less hydrogen to diffuse through the connection channel(s) and into the reaction chamber. That is, because the connecting channel(s) between the hydrogen electrode chamber and the reaction chamber is longer than the connecting channel(s) between the oxygen electrode chamber, fewer of the hydrogen atoms diffuse into the reaction chamber, and the ratio therein is approximately one to one.

It is also well known that relatively small tubes and channels withstand higher pressures than relatively larger channels. As a result, a small or micro hydrogen peroxide reactor such as provided by the present invention can withstand higher pressures than a similarly designed larger "plant scale" reactor. The higher pressures that the microreactor therefore allows an increase in the reaction rate to be achieved thereby converting hydrogen and oxygen into hydrogen peroxide. A further understanding of this invention will be achieved by reference to the accompanying drawings. In this regard, FIGURE 1 shows one exemplary microreactor 10 for generating hydrogen peroxide in accordance with the present invention. In this regard, the microreactor 10 is generally comprised of a top and bottom silicon chips 12, 14, respectively, it being understood that reference to top and bottom is for mere identification purposes only and is not intended to be limiting to any particular orientation thereof.

As is perhaps shown more clearly in FIGURES 2-4, the bottom chip 14 includes a series of elongate channels 14-1 , 14-2 and 14-3 which, when covered by and sealed with the top chip 12 form the hydrogen electrolysis chamber, the oxygen electrolysis chamber and the hydrogen peroxide reaction chamber, respectively. Each of the channels 14-1 , 14-2 and 14-3 are fluid interconnected with one another by means of connection channels, a representative few of which are identified by reference numeral14-4 in FIGURES 2 and 3, which are substantially transverse to the channels 14-1 , 14-2 and 14- 3. The channels 14-1 through 14-4 may be formed using conventional photolithography and silicon etching techniques well known to those in the art. In this regard, each of the channels 14-1 through 14-4 most preferably forms a substantially V-shaped trough.

Respective cathode and anode strips 16-1 , 16-2 are positioned operatively with respect to the channel 14-1 (hydrogen chamber) and the channel 14-2 (oxygen chamber) as shown more specifically in FIGURE 3. A catalyst strip 16-3 is operatively positioned with respect to the channel 14-3 (hydrogen peroxide reaction chamber). Suitable cathode and anode materials include virtually any electrically conductive material. Preferably, the anode and cathode strips are formed of copper, but may also be formed of platinum or palladium.

Virtually any suitable catalyst conventionally employed for the catalyzed reaction of hydrogen and oxygen to form hydrogen peroxide may be employed as the catalyst strip 16-3. Suitable catalysts include, for example, platinum, palladium, iridium, copper, manganese and iron, most preferably, platinum. It should be noted that reference has been made to "strips" for the electrodes 16-1 and 16-2, as well as for the catalyst 16-3. While such structures may be in the form of physical strips, they may likewise be simply a layer coating on the underside of the top silicon chip 12 and/or a layer coating on an elongate portion of the respective channels 16-1 , 16-2 and 16-3. The top chip 12 includes entrance ports 20-1 , 22-1 and discharge ports 20-2, 22-1 which are in fluid communication with respective end regions of the hydrogen and oxygen channels 14-1 , 14-2 formed in the bottom chip 14. The inlet ports 20-1 , 22-1 allow water to be introduced into the channels 14-1 , 14-2 (and hence also the channel 14-3 via connector channels 14-4) so as to initially fill such channels prior to use and to allow purging of the reactor contents following use (e.g., should it be desired to reuse the microreactor 10 for subsequent hydrogen peroxide generation). The top chip 12 also includes ports 24-1 , 24-2 in fluid communication with the hydrogen peroxide reaction channel 14-3 to thereby allow hydrogen peroxide to be withdrawn following reaction therein to form hydrogen peroxide. Additionally, the ports 24-1 , 24-2 could allow water to be introduced into the reaction channel 14-3 to purge reactants therefrom and assist in the refilling of the microreactor 10 with water for reuse.

As shown schematically in FIGURE 1 , the ports 20-1 , 20-2, 22-1 , 22-2, 24-1 and 24-2 described above and formed in the top chip 14 are fluid connected to respective fluid lines 26-1 , 26-2, 28-1 , 28-2, 30-1 and 30-2, respectively. Each such fluid line is further schematically depicted as including a valve means 32-1 , 32-2, 34-1 , 34-2, 36-1 and 36-2, respectively, to allow fluid control into and out of the microreactor 10. In this regard, the fluid lines and valve means may collectively be embodied in a microstructure in which the fluid lines and various valving structures are formed. Alternatively, the fluid lines may be flexible microtubing that can be pinched for closing fluid flow by a suitable electroactuator. Advantageously, computer control can be exercised over such valve means to allow opening and closing and thereby control the discharge of hydrogen peroxide therefrom and/or the introduction of water therein.

Although the methods of the present invention may be embodied in larger "refinery scale" structures, as noted above, it is preferred that the reaction methods be embodied in a microreactor, one presently preferred embodiment thereof being above-described above. Advantageously, the top and bottom chips 12, 14 may each be substantially square having side dimensions of between about 1 to about 5 mm, preferably about 3 mm. The thickness of the wafer may typically be between about 0.1 to about 1.5 mm, usually about 0.5 mm. The lengthwise and depth dimensions of the channels 14-1 , 142- and 14-3 may be virtually any desired dimension so as to accommodate the volume of water and hence reactants necessary to form the hydrogen peroxide. However, exemplary lengthwise dimensions of the channels 14-1 , 14-2 and 14-3 may be between about 0.5 to about 4.5 mm, and usually about 2.5 mm, with exemplary widthwise dimensions of between about 0.05 to about 0.5 mm, advantageously about 0.03 mm. The length of the connector channels 14-4 are of course sufficient to fluid-connect the channels 14-1 , 14-2 and 14-3 and most preferably have a widthwise dimension of between about 0.0025 to about .05 mm, and preferably about 0.01 mm. The depth of the channels 14-1 through 14-2 may be selected based on the other dimensions to achieve the desired volumes therein. Advantageously, however, the depth of the channels 14-1 through 14-2 may be between about 0.010 to about 0.400 mm, and preferably about 0.200 mm.

In use, the microreactor 10 is filled with water. That is, the channels 14-1 through 14-4 of the microreactor 10 may be filled with water by introduction through the ports 20- 1 , 2-2 and optionally 24-1. Thereafter, the ports may be sealed, for example by applying a suitable sealing structure and/or closure of the valve means. Once sealed, the electrodes may be connected operatively to a source of electrical energy so as to conduct electrolysis within the channels 14-1 and 14-2 and generate hydrogen and oxygen atoms therein, respectively. The pressures generated by gas evolution in the microreactor 10 are sufficient to facilitate the catalytic reaction of oxygen and hydrogen to form hydrogen peroxide in the reaction channel 14-3. In this regard, the microreactor 10 is sized and configured so as to allow for internal pressures of between about 500 to about 2000 psi, preferably at least about 1000 psi. Following elapse of a predetermined time (which time is dependent upon the channel size and amount of water contained therein subject to electrolysis), the hydrogen peroxide may be extracted from the channel 14-3 via ports 24-1 and/or 24-2.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS: 1. A hydrogen peroxide microreactor comprising a silicon chip reactor body having a pair of electrolysis channels, a reaction channel positioned between said electrolysis channels, and at least one connector channel which fluid-connects said pair of electrolysis channels with said reaction channel, a pair of electrodes each in operative association with a respective one of said electrolysis channels, and a catalyst for forming hydrogen peroxide in operative association with the reaction channel.

2. The microreactor according to claim 1 , wherein said reactor body comprises top and bottom silicon chips, wherein said electrolysis channels, said reaction channel and said at least one connector channel are etched into said bottom silicon chip.

3. The microreactor according to claim 1 , further comprising a plurality of ports in fluid communication with said electrolysis and reaction channels.

4. The microreactor according to claim 2, wherein said electrolysis and reaction channels are elongate linear channels etched in said bottom silicon chip.

5. The microreactor according to claim 4, wherein said at least one connector channel is an elongate linear channel etched in said bottom silicon chip substantially transverse to said electrolysis and reaction channels

6. The microreactor as in claim 5, wherein said reaction channel is positioned closer to one of said electrolysis channels as compared to the other of said electrolysis channels.

7. The microreactor as in claim 6, wherein the reaction channel is positioned about one-third of the total distance between said electrolysis channels from said one electrolysis channels.

8. The microreactor as in claim 5, wherein said electrolysis and reaction channels are substantially V-shaped.

9. The microreactor as in claim 1 , wherein said electrodes and said catalyst are in the form of strips operatively associated with said electrolysis channels and said reaction channel, respectively..

10. A method for making hydrogen peroxide comprising: (i) providing a sealed water-filled microreactor formed of a silicon reactor body having a pair of electrolysis channels, a reaction channel positioned between said electrolysis channels, and at least one connector channel which fluid-connects said pair of electrolysis channels with said reaction channel, a pair of electrodes each in operative association with a respective one of said electrolysis channels, and a catalyst for forming hydrogen peroxide in operative association with the reaction channel; (ii) applying an electrical potential to said electrodes so as to generate hydrogen from an anode thereof, and oxygen from a cathode thereof; (iii) allowing the hydrogen and oxygen generated according to step (ii) to diffuse into the reaction chamber to cause a catalytic reaction therebetween to form hydrogen peroxide; and (iv) withdrawing the hydrogen peroxide from the reaction chamber.

11. The method of claim 10, wherein step (iii) is practiced at a pressure of about 1000 psi or greater.

12. A method of making a microreactor for generating hydrogen peroxide, comprising: (a) etching into a silicon chip a pair of electrolysis channels, a reaction channel positioned between said electrolysis channels, and at least one connector channel which fluid-connects said pair of electrolysis channels with said reaction channel; (b) providing a pair of electrodes each in operative association with a respective one of said electrolysis channels, and a catalyst for forming hydrogen peroxide in operative association with the reaction channel.

13. The method according to claim 12, wherein said reactor body comprises top and bottom silicon chips, and wherein step (a) is practiced by etching said electrolysis channels, said reaction channel and said at least one connector channel into said bottom silicon chip.

14. The method according to claim 13, further comprising etching a plurality of ports in said top silicon chip which are in fluid communication with said electrolysis and reaction channels etched into said bottom silicon chip.

15. The method according to claim 13, wherein step (a) is practiced so as to etch aid electrolysis and reaction channels in the form of elongate linear channels in said bottom silicon chip.

16. The method according to claim 15, wherein step (a) is practiced so as to etch said at least one connector channel in the form of an elongate linear channel in said bottom silicon chip substantially transverse to said electrolysis and reaction channels

17. The method as in claim 16, wherein step (a) is practiced so that said reaction channel is positioned closer to one of said electrolysis channels as compared to the other of said electrolysis channels.

18. The method according to claim 17, wherein step (a) is practiced so as that the reaction channel is positioned about one-third of the total distance between said electrolysis channels from said one electrolysis channels.

19. The method according to claim 12, wherein step (a) is practice such that said electrolysis and reaction channels are substantially V-shaped.

20. The method according to claim 12, comprising providing said electrodes and said catalyst are in the form of strips operatively associated with said electrolysis channels and said reaction channel, respectively.