Abstract:
A device and process is presented for producing hydrogen peroxide on an as needed basis is disclosed. The process and device produces hydrogen peroxide on a small scale without the addition of chemicals and disposal of waste streams.

Description:
FIELD OF THE INVENTION 
   This invention relates to the production of hydrogen peroxide. Specifically, an apparatus for the production of hydrogen peroxide in an acidic solution, and the subsequent separation and recycle of the acid from the hydrogen peroxide. 
   BACKGROUND OF THE INVENTION 
   The production of hydrogen peroxide is currently produced by a chemical process that is sufficiently complex that it requires large scale production to economically produce it. The most common method for hydrogen peroxide is the industrial scale production through 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. 
   The direct production of hydrogen peroxide directly from oxygen and hydrogen is another route. However, these methods involve working with gases in a combustible range, or with liquids having low concentrations of hydrogen and oxygen dissolved in the liquid phase. 
   The production of hydrogen peroxide on a small scale as needed would be beneficial as the user of the hydrogen peroxide would not need to store it. In order for methods of small scale production of hydrogen peroxide to be useful, the process and apparatus should be sufficiently self contained as to remove the need for adding additional chemicals, or for operating under conditions that can produce a potentially dangerous situation. 
   SUMMARY OF THE INVENTION 
   The present invention is an apparatus that provides for the production of hydrogen peroxide under conditions that can be operated in a home environment and without the continuous addition of chemicals. The apparatus comprises an electrolyzer for generating an oxidizing agent, a hydrolyzing reactor for reacting the oxidizing agent and water to generate hydrogen peroxide, a separation unit for separating the hydrogen peroxide, and a condensing unit. This apparatus can produce hydrogen peroxide in either a continuous or batch mode. 
   In one embodiment, the invention is a self-contained device that recirculates an oxidizing agent, and produces hydrogen peroxide from water. The apparatus includes a housing, or shell, that has a plurality of zones wherein an electrolyzer, a hydrolyzer, and a condensing unit are disposed within the housing, and wherein different zones are operated at different temperatures. By recirculating the oxiding agent through the invention, hydrogen peroxide is formed and separated from the oxidizing agent for use on an as-needed basis. 
   Additional objects, embodiments and details of this invention can be obtained from the following detailed description of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a first embodiment of the invention; 
       FIG. 2  is a diagram of a second embodiment of the invention; and 
       FIG. 3  is a diagram of a third embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The production of hydrogen peroxide in an aqueous solution and free from other chemical reactants is important for many applications. In addition, it would be preferable to produce the hydrogen peroxide on an as needed basis for use in bleaching and sanitizing removing the need to store hydrogen peroxide, or the need to process other chemicals that require special handling. 
   The present invention provides for an apparatus to generate hydrogen peroxide with only the addition of water and air. In a first embodiment, the invention comprises an apparatus for the continuous generation of hydrogen peroxide. The apparatus, as shown in  FIG. 1 , comprises an electrolyzer  10  for generating an oxidizing agent, a hydrolyzing reactor  20 , an air stripping and separation unit  30 , and a condensing unit  40 . While an air stripping unit  30  is contemplated, other gases can be used in the air stripping unit  30 , and it is understood that when using the term air, any gas can be used, unless otherwise specifically stated. The electrolyzer  10  includes an inlet  12  for admitting a solution including an oxidizable compound, an outlet  14  for a solution including an oxidizing agent, and electrodes for supplying the electrical energy to convert the oxidizable compound to the oxidizing agent. Electrolyzers  10  are well known in the art, and are especially known for the use in dissociating water into hydrogen and oxygen. Electrolyzers  10  are also of use for facilitating chemical reactions where the reaction is for the oxidation of an already oxidized compound. In the present invention, the preferred oxidizable compound is sulfuric acid, and is oxidized to the oxidizing agent of persulfuric acid. Persulfate production in an electrolytic cell is demonstrated in U.S. Pat. No. 4,144,144, which is incorporated by reference in its entirety. While other oxidizable compounds and oxidizing agents are contemplated, for the sake of convenience, the preferred oxidizable compound is sulfuric acid, and the preferred oxidizing agent is persulfuric acid, and will be used interchangeably herein. 
   The electrolyzer is operated at a temperature from about 20° C. to about 40° C. The temperature is controlled to prevent the electrolyzer from getting too hot, wherein the persulfuric acid would begin to break down. An aqueous solution of persulfuric acid is drawn off from the electrolyzer  10  and directed to a hydrolyzing reactor  20 . The hydrolyzing reactor  20  is preferably a tubular reactor and sized to provide sufficient residence time to drive the reaction to equilibrium. This comprises designing a tubular reactor of sufficient length. The reactor  20  is heated to drive the equilibrium toward the production of hydrogen peroxide and forming a solution comprising hydrogen peroxide and sulfuric acid. The reactor  20  is heated to a temperature between about 40° C. and about 85° C., with a preferred operating temperature from about 60° C. to about 70° C. 
   The solution of hydrogen peroxide and sulfuric acid is passed to an air stripping and separation unit  30 . The solution and air are mixed and enter the separation unit  30  where there is further heating of the solution to transfer hydrogen peroxide and water to the gas phase. The sulfuric acid is concentrated as a liquid when the water and hydrogen peroxide evaporate. The sulfuric acid is collected and cooled in a cooling tank  50  before redirecting the sulfuric acid to the electrolyzer  10 . In addition, water  52  is added to the cooling tank to replenish the water lost in the production of hydrogen peroxide. 
   The air stripping unit  30  is operated such that during the separation process wherein the hydrogen peroxide is transferred to the gas phase, virtually all of the sulfuric acid is retained in the liquid phase, and some of the hydrogen peroxide can be retained in the liquid phase. While this does not recover all of the hydrogen peroxide, the operation is such that the sulfuric acid is substantially completely recycled and the further addition of sulfuric acid is only periodically needed to make up for minor losses. 
   The stripping unit  30  can use gas, or air, that has been preheated to facilitate the evaporation of hydrogen peroxide and water from the liquid hydrogen peroxide solution. This could entail an inline heating unit (not shown) for the gas inlet to the stripping unit  30 , or some other means known in the art for heating a gas. 
   The stripping unit  30  can further include a means for creating a mist from the hydrogen peroxide/sulfuric acid solution. By creating a mist of the solution in the stripping/separation unit  30 , mass transfer is facilitated to enhance the rate at which hydrogen peroxide and water are evaporated into the vapor phase. Means for creating a mist include spray nozzles sized to generate a fine mist, and nebulizers for mixing the gas with the liquid and forming a mist. 
   While the preferred embodiment comprises an air stripping unit  30  for the separation unit, other separation units are contemplated by this invention, including but not limited to a distillation unit, or an adsorption separation unit. 
   In one embodiment, the hydrolyzing reactor  20  is coiled around the air stripping unit  30  where heating of both the reactor  20  and stripping unit  30  is integrated. 
   The gas in the air stripping unit  30  is passed through a mist eliminator  32  to remove residual droplets that can have sulfuric acid in them. The gas containing hydrogen peroxide and water is cooled and condensed, and in one embodiment, the gas is passed through a condensing coil  40  with the liquid condensate collected in a storage tank  60 . The storage tank  60  includes an air vent  62 , to release the air added to the system in the air stripping unit  30 . The mist eliminator  32 , preferably, will remove all droplets having a diameter greater than 0.05 micrometers. 
   In a second embodiment, as shown in  FIG. 2 , the apparatus is contained within a single shell  100 . The shell  100  is divided into at least two sections, an electolyzer section  10  and an evaporator/separator section  30 . Within the evaporator/separator section  30 , is a hydrolyzing coil  20 . The electrolyzer  10  generates a stream comprising persulfuric acid, and is directed to the hydrolyzing coil  20 . In one embodiment, the means for directing the persulfuric acid stream to the hydrolyzing coil  20  is through a pump  22 . The pump  22  is used to drive the fluids through the apparatus, and in a preferred embodiment, only one pump is needed to circulate the liquid phase within the apparatus. The hydrolyzing coil  20  is heated, and the persulfuric acid reacts with water in the hydrolyzing coil  20  to generate a solution comprising hydrogen peroxide and sulfuric acid. 
   The hydrogen peroxide solution generated in the hydrolyzing coil  20  is mixed with air creating a vapor liquid mixture, and enters the heated evaporation/separation section  30 . The mixture separates into liquid and vapor phases as the mixture travels down the separation section  30 . The hydrogen peroxide with some water is evaporated to the vapor phase, while the sulfuric acid is retained in the liquid phase, as the mixture travels through the heated section  30 . The vapor phase passes through a demister, to remove liquid droplets that comprise sulfuric acid, and is directed to a condensing coil  40 . The liquid sulfuric acid solution is collected at the bottom of the separator section  30  and passed through a cooling section  50  and returned to the electrolyzer  10 . Water is added to the cooling section  50  to dilute the sulfuric acid and to make up for water losses from the reaction and carried out through the vapor phase. The added water also provides the benefit of reducing the viscosity of the sulfuric acid solution passing to the electrolyzer  10 . The electrolyzer  10  includes a vent  12  for any gases generated during the electrolysis reaction. 
   The condensing coil  40  is wrapped around the electrolyzer  10 , and both are located in a cooling section of the vessel  100 . The hydrogen peroxide and water vapor are condensed and collected in a section  60  of the vessel  100  for storage, where it can be accessed as needed. The storage section  60  includes a vent  62  to vent air that is blown into the vessel  100  in the evaporator/separator section  30 . 
   In this embodiment, the apparatus  100  is a self-contained unit wherein the operation requires the input of water, air, and electrical power, and generates an output of an aqueous hydrogen peroxide solution and air that is vented. 
   In another embodiment, the apparatus is operated in batch mode. As shown in  FIG. 3 , the apparatus includes an electrolyzer  10  for generating a solution comprising an oxidizing agent. In this specific embodiment, the oxidizing agent is persulfuric acid. The electrolyzer  10  is operated at a temperature between 10° C. and 40° C. Preferably the temperature is from about 20° C. to about 40° C. The electrolyzer  10  is operated continuously to generate the persulfuric acid product, and the product is stored in a separate compartment to build up a supply of persulfuric acid. The compartment is vented to the atmosphere through a suction breaker. 
   The persulfuric acid solution is periodically drawn off from the electrolyzer  10  and directed to a hydrolyzing reactor  20  in the form of a coil of tubing and is disposed around an evaporator/separator unit  30 . The acid solution is drawn off at a predetermined time, or when the storage compartment reaches a predetermined level. Level controllers and timers are well known in the art, and not discussed here. The hydrolyzing reactor is heated to a temperature between about 40° C. to about 85° C., with the temperature preferably between about 60° C. to about 70° C. The length of the coil is sized to provide sufficient residence time for the hydrolysis reaction and to allow the reaction to go to a desired conversion, generating a solution having hydrogen peroxide and sulfuric acid. In one embodiment, the desired conversion is substantially to equilibrium. 
   The hydrogen peroxide solution is fed into the evaporator/separator  30  heated to a temperature between about 60° C. and 85° C., and supplied with air by a blower  34 . In an alternative, the air can be supplied from any compressed air source. The air and hydrogen peroxide solution are mixed and fed into a packed bed  36 , where hydrogen peroxide and water transfer to the gas phase. The vapor and liquid phases exit the top of the packed bed  36  and the liquid and vapor are separated in the evaporator/separator  30 . The vapor phase, containing hydrogen peroxide and water pass through a mist eliminator  38 , and then the vapor is passed to a condensing unit  40  wherein a liquid hydrogen peroxide solution is collected. The mist eliminator  38  recovers substantially all entrained liquid droplets that have sulfuric acid in them. Air and uncondensed hydrogen peroxide and water vapor can be vented through a vent located in the condensing unit  40  or in a separate storage section  46 . The separate storage section  46  may be a part of the condensing unit  40 , or a separate tank. The peroxide solution can be stored in a part of the condensing unit  40 , or can be stored in a separate unit (not shown) for uses wherein a larger storage is desired. Controllers, timers, and other devices can regulate the flow of peroxide solution from the hydrogen peroxide storage, and are well known in the art and not further discussed here. 
   The liquid phase in the evaporator/separator  30  comprises sulfuric acid, and is collected and returned to the electrolyzer  10 . During the process, water is evaporated from the liquid phase, and the sulfuric acid solution becomes more viscous. Water can be added to dilute the sulfuric acid, and to reduce the viscosity of the liquid phase. Water is also added to replace water lost in the process of generating the hydrogen peroxide. The sulfuric acid is pumped from the separator  30  to the electrolyzer  10 , and the pump  42  is used to maintain the pressure needed to circulate the fluids through the system. 
   In one embodiment, the apparatus further includes an adsorbent bed  44 , comprising a material for removing contaminants that may enter the system. The adsorbent bed  44  is preferably designed to remove any metal impurities in the sulfuric acid. The adsorbent bed  44  may also include a cooling means to cool the sulfuric acid to the temperature of the electrolyzer. Cooling means includes cooling coils running through the adsorbent bed  44 , or cooling jackets on the conduits transferring the sulfuric acid to the electrolyzer  10 , or any other means known in the art for cooling a liquid. 
   In one embodiment, the hydrolyzer coil  20  is wound around the evaporator/separator  30 . Both the hydrolyzer  20  and the separator  30  are heated and combining the two units provides for the ability to heat both in a single heating zone. In another embodiment, the hydrolyzer coil  20  is disposed within the evaporator/separator unit in a similar manner as shown in  FIG. 2 . 
   In general, the electrolyzer  10  and condensing unit  40  are situated in cooling zones of the apparatus, while the hydrolyzer  20  and the evaporator/separator  30  are situated in the heating zones of the apparatus. 
   While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.