Method for generating hydrogen and oxygen from a liquid feed stream - Patent Application 20070122997

Abstract

A method for generating hydrogen and oxygen from a liquid feed stream is achieved by an integrated forward osmosis and electrolysis system, the method comprising the steps of inputting water into an electrolyte solution by forward osmosis and applying a voltage to the electrolyte solution to generate hydrogen and oxygen, the electrolyte solution comprising an electrolyte, an ionic liquid, and a solvent, the amount of the electrolyte being between 1 wt% and 10 wt% of the electrolyte solution, the amount of the ionic liquid being between 1 wt% and 5 wt% of the electrolyte solution, and the amount of the solvent being between 75 wt% and 99 wt% of the electrolyte solution.

Description

[Technical Field]

[0001] The present invention relates to a method for generating hydrogen and oxygen from a liquid feed stream, the liquid feed stream containing water, the method being capable of increasing the production of hydrogen and oxygen from the liquid feed stream containing water under relatively low energy consumption. [Background technology]

[0002] Hydrogen gas is widely used in many fields, including, but not limited to, petroleum refining, methanol production, ammonia production, welding, metal alloying, and electronic manufacturing. Generally, hydrogen gas is produced from fossil fuels or organic materials such as biomass through a thermochemical process that is energy-intensive and produces carbon as a by-product.

[0003] Currently, hydrogen manufacturers use freshwater to produce hydrogen through an electrolysis process, as this method is environmentally friendly and maximizes the use of renewable resources. The electrolysis process uses an electric current to split water (H2O) into hydrogen (H2) and oxygen (O2). Because the process of producing hydrogen and oxygen consumes freshwater, the demand for freshwater as a hydrogen source is increasing.

[0004] In view of the above problems, hydrogen producers are further researching to use other liquid feed streams (e.g., wastewater, brine, seawater, groundwater, tap water, rainwater) as alternative renewable resources to produce hydrogen. However, using liquid feed streams other than freshwater requires additional water purification steps, such as reverse osmosis before feeding it to the electrolysis process or ion exchange to produce hydrogen and / or oxygen. One drawback of reverse osmosis is that filtered water requires a high-pressure pump and pressure vessel.

[0005] From the above, it is clear that conventional methods for generating hydrogen and oxygen from liquid feed streams other than fresh water have their own drawbacks. Therefore, there is a need for a method for producing hydrogen and oxygen from liquid feed streams other than fresh water to increase the yield of hydrogen and oxygen with lower energy consumption. DETAILED DESCRIPTION OF THE INVENTION

[0006] The present invention relates to a method for generating hydrogen and oxygen from a liquid feed stream, the method being achieved by an integrated forward osmosis and electrolysis system, the method comprising the steps of: Water is fed to the electrolyte solution by forward osmosis, pumped from the liquid feed stream in contact with the side of the forward osmosis membrane via an osmotic pressure difference between the liquid feed stream and the electrolyte solution; and • Applying a voltage to the electrolyte solution to produce hydrogen and oxygen, and the electrolyte solution contacts the other side of the forward osmosis membrane; The steps are performed simultaneously, the electrolyte solution contains an electrolyte, an ionic liquid, and a solvent, the amount of the electrolyte used is 1 wt% to 10 wt% of the electrolyte solution, the amount of the ionic liquid used is 1 wt% to 5 wt% of the electrolyte solution, and the amount of the solvent used is 75 wt% to 99 wt% of the electrolyte solution.

[0007] Other aspects, features, and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments of the invention. Abbreviation details Emim.MeSO3: 1-Ethyl-3-methylimidazolium methanesulfonate Emim.Otf: 1-ethyl-3-methylimidazolium trifluoromethanesulfonate H2: Hydrogen KOH: Potassium hydroxide NaCl: Sodium chloride NaOH: Sodium hydroxide NaSc: sodium saccharin Details of the invention Detailed descriptions of preferred embodiments of the present invention are disclosed. However, it should be understood that these embodiments are merely examples of the present invention, and that the present invention can be embodied in various forms. Therefore, the details disclosed herein are not limiting, but should be construed only as a basis for the claims and used to teach the present invention to those skilled in the art. Numerical data or ranges used in the specification should not be construed as limiting.

[0008] The present invention relates to a method for generating hydrogen and oxygen from a liquid feed stream, the liquid feed stream containing water, the method being capable of increasing the yield of hydrogen and oxygen from the liquid feed stream containing water under relatively low energy consumption.

[0009] For purposes of this invention and the appended claims, the term "liquid feed stream" refers to any feed stream that contains water, such as, but not limited to, wastewater, brine, seawater, groundwater, tap water, and stormwater. A first aspect of the present invention is an electrolyte solution comprising: The amount of electrolyte used is 1 wt% to 10 wt% of the electrolyte solution, preferably 8 wt%, and the electrolyte is selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), sodium chloride (NaCl) and mixtures thereof, preferably KOH, The ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (Emim.Otf), 1-ethyl-3-methylimidazolium methanesulfonate (Emim.MeSO3) and mixtures thereof, preferably Emim.Otf, and The amount of solvent used is 75 wt% to 99 wt% of the electrolyte solution, preferably 78 wt%. The solvent is deionized water. The electrolyte solution further contains an additive in an amount of 0 wt % to 10 wt % of the electrolyte solution, preferably 10 wt %, and the additive is saccharin sodium.

[0010] Table 1 shows the chemical components and their compositions used in the electrolyte solution of the present invention. Table 1: Chemical components and their composition used in the electrolyte solution of the present invention

[0011] [Table 1]

[0012] The additive is optional and is used in the integrated process of forward osmosis and electrolysis. If the electrolyte is used in a conventional electrolysis process, it may not contain any additive. The additive has an important effect in the integrated process of forward osmosis and electrolysis, as it increases the osmotic pressure and improves the yield of the target gases (hydrogen and oxygen), and the results are explained in the Examples section below.

[0013] A second aspect of the present invention discusses a method for preparing the electrolyte solution of the present invention, which comprises the following steps: i. Add the electrolyte to the container; ii. adding an ionic liquid via a pump to the vessel of step (i) to form a first mixture; iii. optionally, adding an additive to the first mixture obtained in step (ii) to form a second mixture; and iv. Add the solvent to the second mixture obtained in step (iii) under stirring at 25°C under a pressure of 1 atmosphere for 30 minutes or until the mixture is uniformly dissolved to produce the electrolyte solution of the present invention. Stirrs that can be used include, but are not limited to, a magnetic stirrer, a mechanical stirrer, and a stirrer.

[0014] With reference to the above method, step (ii) should be carried out using a fume hood or suction arm to prevent inhalation of the ionic liquid. A third aspect of the present invention discusses a method for generating hydrogen and oxygen from a liquid feed stream, the method being achieved by an integrated forward osmosis and electrolysis system, the method comprising the steps of:

[0015] Water is pumped from a liquid feed stream in contact with one side of a forward osmosis membrane by forward osmosis due to the osmotic pressure difference between the liquid feed stream and the electrolyte solution and fed to the electrolyte solution; and • Applying a voltage to the electrolyte solution to produce hydrogen and oxygen, and the electrolyte solution contacts the other side of the forward osmosis membrane; The steps are performed simultaneously, the electrolyte solution includes an electrolyte, an ionic liquid, and a solvent, and the electrolyte solution includes an additive.

[0016] The method includes applying a voltage to the electrolyte solution, the applied voltage being in the range of 1.8 V to 2.4 V. The method further includes injecting water into the electrolyte solution through a forward osmosis membrane by forward osmosis, the forward osmosis membrane being wetted with ethanol at a concentration of 99% prior to use in the method.

[0017] The electrolyte solution of the present invention acts as an absorbent in a forward osmosis process, drawing water molecules from a liquid feed stream through the forward osmosis membrane, and simultaneously acts as an electrolyte in an electrolysis process, converting the water molecules into hydrogen and oxygen.

[0018] The osmolality of the electrolyte solution of the present invention is greater than the osmolality of the liquid feed stream. Also, the osmotic pressure of the electrolyte solution of the present invention is greater than the osmotic pressure of the liquid feed stream. Because the osmotic pressure and osmolality of the electrolyte solution of the present invention are greater than the osmotic pressure and osmolality of the liquid feed stream, water molecules pass from the liquid feed stream through the forward osmosis membrane into the electrolyte solution by forward osmosis. It should be understood that the higher the electrical conductivity of the aqueous solution, the higher the permeation molality and permeation pressure.

[0019] The electrolyte solutions of the present invention have a conductivity of at least 36.67 mS / cm, preferably between 36.67 mS / cm and 323.42 mS / cm, and most preferably between 250 mS / cm and 323.24 mS / cm. The liquid feed stream has a conductivity of at least 0.001 mS / cm, preferably between 0.002 mS / cm and 0.01 mS / cm, and most preferably between 0.002 mS / cm and 0.005 mS / cm.

[0020] The conductivity difference between the liquid feed stream and the electrolyte solution of the present invention is at least 36.66 mS / cm, with the electrolyte solution having a higher conductivity than the liquid feed stream, preferably between 36.66 mS / cm and 323.23 mS / cm, and most preferably between 250 mS / cm and 323.23 mS / cm.

[0021] The electrolyte solution in contact with the other side of the forward osmosis membrane is contained in an electrochemical cell. The electrochemical cell includes an anode and a cathode that allow a voltage to be applied to the electrolyte solution. When a voltage is applied to the electrolyte solution, water molecules are converted to hydrogen gas and hydroxide ions at the anode, and the hydroxide ions are converted to oxygen gas and water molecules at the cathode.

[0022] The net reaction converting two water molecules into two hydrogen molecules and one oxygen molecule is:

[0023] [ka]

[0024] The following embodiments are intended to illustrate the present invention in a non-limiting manner. Test results The electrolyte compositions of the present invention are prepared using the methods described in the second aspect of the present invention, using the compositions set forth in Table 1. The methods described in the third aspect of the present invention and the electrolyte solutions of the present invention are used to generate hydrogen gas and oxygen gas from municipal wastewater by-product wastewater.

[0025] Electrolyte composition test results Different electrolytes are evaluated by cyclic voltammetry tests. Cyclic voltammetry tests are used to evaluate the electrochemical potential window of the electrolyte and the corresponding current density at each applied voltage. For the present invention, electrochemical impedance spectroscopy (EIS) tests are performed using 10 milliliters of electrolyte in a small container, employing a three-electrode system. The electrode system used consists of a platinum plate as the working electrode and a counter electrode, and a saturated mercury electrode as the reference electrode. The results for the composite electrolyte show the highest current density recorded for each substance based on response surface methodology (RSM).

[0026] In Table 2, Group 1 refers to a conventional electrolyte solution containing 10 wt% KOH and 90 wt% deionized water. Group 2 represents an electrolyte solution of the present invention, containing 4.29 wt% Emim.Otf, 8.31 wt% KOH, and 97.4 wt% deionized water. Group 3 represents an electrolyte solution of the present invention, containing 4.3 wt% Emim.Otf, 8.31 wt% KOH, 10 wt% NaSc, and 77.39 wt% deionized water.

[0027] Table 2 shows the cyclic voltammetry test results of the electrolytes of the present invention. Table 2: Cyclic voltammetry test results for electrolytes of the present invention

[0028] [Table 2]

[0029] From Table 2, it is clear that Groups 2 and 3 of the present invention can exhibit considerable current density values. It should be understood that the higher the current density, the higher the electrolysis rate and the yield of hydrogen and oxygen. It is also clear that Groups 2 and 3 of the present invention have higher current densities than Group 1, indicating that Groups 2 and 3 of the present invention provide higher hydrogen and oxygen yields during the electrolysis process.

[0030] In Table 3, Group 1 refers to a conventional electrolyte solution containing 10 wt% KOH and 90 wt% deionized water. Group 2 represents an electrolyte solution of the present invention, containing 5 wt% Emim.Otf, 10 wt% KOH, and 85 wt% deionized water. Group 3 represents an electrolyte solution of the present invention, containing 5 wt% Emim.Otf, 10 wt% KOH, 10 wt% NaSc, and 75 wt% deionized water.

[0031] Table 3 shows the results of H2 yield, current density and specific energy consumption of the corresponding electrolyte of the present invention in the electrolysis process. Table 3: H2 yield, current density and specific energy consumption results of the corresponding electrolytes of the present invention during the electrolysis process

[0032] [Table 3]

[0033] According to Table 3, it is clear that Groups 2 and 3 of the present invention have higher current density and H yield under lower energy consumption compared to the conventional electrolyte solution (Group 1), which indicates that Groups 2 and 3 of the present invention are more efficient in producing H than the conventional electrolyte solution (Group 1).

[0034] Test results using the electrolyte solution of the present invention using the method described in the third aspect of the present invention Table 4 shows the amount of hydrogen gas generated under a specific specific energy consumption when using a conventional electrolyte solution containing 10 wt% KOH and 90 wt% deionized water, and an electrolyte solution of the present invention containing 10 wt% KOH, 3.69 wt% Emim.Otf and 86.31 wt% deionized water, obtained by applying the method described in the third aspect of the present invention.

[0035] Table 4: Hydrogen gas generation results under specific energy consumption in conventional electrolyte solution using KOH and the electrolyte solution of the present invention

[0036] [Table 4]

[0037] According to Table 4, the amount of hydrogen gas produced using the electrolyte solution of the present invention under a certain specific energy consumption is higher than the amount of hydrogen gas produced using the conventional electrolyte solution under a certain specific energy consumption, which indicates that energy consumption is reduced by applying the electrolyte solution of the present invention and the method described in the third aspect of the present invention.

[0038] Table 5 shows the water flow rates from wastewater through forward osmosis into an electrolyte solution of the present invention containing 10 wt% KOH, 3.69 wt% Emim.Otf, and 86.31 wt% deionized water, and into a conventional electrolyte solution containing 10 wt% KOH and 90 wt% deionized water.

[0039] Table 5: Water flow rate by forward osmosis from wastewater to KOH in conventional electrolyte solution and in the electrolyte solution of the present invention.

[0040] [Table 5]

[0041] According to Table 5, the water flux from wastewater to the electrolyte solution of the present invention by forward osmosis is higher than the water flux from wastewater to the conventional electrolyte solution by forward osmosis, indicating that the electrolyte solution of the present invention, which is the absorption liquid, increases the efficiency of the forward osmosis process.

[0042] Overall, the method of generating hydrogen and oxygen from a liquid feed stream of the present invention can provide high yields of hydrogen and oxygen through forward osmosis and electrolytic integration process systems with relatively low energy consumption.

[0043] The terms used herein are used only to describe particular exemplary embodiments and are not intended to be limiting. As used herein, the singular forms "one," "one," and "it" can also include the plural unless the context clearly indicates otherwise. The terms "comprise," "including," and "having" are inclusive and thus specify the presence of features, integers, steps, operations, components, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, components, components, and / or groups thereof.

[0044] The method steps, processes, and operations described herein need not be construed as requiring execution in the particular order described or illustrated, unless an order of execution is explicitly identified. It should also be understood that additional or alternative steps may be employed. The use of the phrase "at least" or "at least one" implies the use of one or more elements, as in one embodiment, the use of the phrase may be to achieve one or more desired purposes or results.

Claims

1. A method for generating hydrogen and oxygen from a liquid feed stream, achieved by an integrated forward osmosis and electrolysis system, said method comprising the steps of: Water is fed to the electrolyte solution by forward osmosis, pumped from the liquid feed stream in contact with the side of the forward osmosis membrane via an osmotic pressure difference between the liquid feed stream and the electrolyte solution; and • Applying a voltage to the electrolyte solution to produce hydrogen and oxygen, and the electrolyte solution contacts the other side of the forward osmosis membrane; The steps are performed simultaneously, The electrolyte solution contains an electrolyte, an ionic liquid, and a solvent, and is characterized in that the amount of the electrolyte used is 1 wt % to 10 wt % of the electrolyte solution, the amount of the ionic liquid used is 1 wt % to 5 wt % of the electrolyte solution, and the amount of the solvent used is 75 wt % to 99 wt % of the electrolyte solution.

2. 2. The method of claim 1, wherein the electrolyte solution further comprises an additive, and the additive is used in an amount of 0 wt % to 10 wt % of the electrolyte solution.

3. 2. The method of claim 1, wherein the applied voltage range is between 1.8V and 2.4V.

4. 10. The method of claim 1, wherein the electrolyte solution has a conductivity of at least 36.67 mS / cm.

5. 10. The method of claim 1, wherein the electrical conductivity of the liquid feed stream is at least 0.001 mS / cm.

6. 10. The method of claim 1, wherein the conductivity difference between the electrolyte solution and the liquid feed stream is at least 36.66 mS / cm.

7. 10. The method of claim 1, wherein the voltage is applied to an electrolyte solution in an electrochemical cell including an anode and a cathode.

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