Electrochemical methods for inducing sustained chain reactions in aqueous solutions

Abstract

The present invention relates to a method for generating at least one persistent free radical using an electrochemical cell, wherein the apparatus has suitable electrode plates, and the method comprises the following steps: passing at least one pair of electrodes through an aqueous solution containing unwanted contaminants, through which a DC current is passed in such a manner that at least one persistent free radical is produced, thereby initiating a sustained, i.e., continuous chain reaction that consumes or destroys any available contaminants, the DC current being controlled so that the potential difference within the electrochemical cell reaches a precise value within a specific time at a controlled rate.

Description

Technical Field

[0001] The present invention relates to an electrochemical method for causing a sustained chain reaction in an aqueous solution, which can be propagated into a water volume without being affected by external influences and can remove various solutes from the water volume. In particular, the present invention can be used in numerous technical fields, including but not limited to: (1) removal of PFAS (perfluoroalkyl and polyfluoroalkyl compounds) from the environment, (2) capture and removal of carbon dioxide from the atmosphere, (3) nutrient salt removal from the environment, (4) wastewater treatment, (5) drinking water treatment, (6) production of organic compounds, (7) perchlorate removal from the environment, and (8) most likely other technical fields that have not yet been identified.

Background Art

[0002] Water is a ubiquitous and very effective solvent. In the above-mentioned technical fields, at a certain point in time, it is necessary to remove foreign substances and contaminants from an aqueous solution to reduce the concentration thereof in said aqueous solution. There are many existing processes that can be and have been used to achieve this, including biological processes, physicochemical processes, incineration processes, thermal processes, advanced oxidation processes, and several electrochemical processes. All of these processes according to the prior art currently available have some, if not all, of the following drawbacks and disadvantages: (1) limited effectiveness, being only capable of removing part of the contaminants present in the aqueous solution; (2) very high capital costs; (3) high energy consumption, resulting in high operating costs; (4) additional increase in already high operating costs due to the consumption of large amounts of chemical substances; (5) the process itself gives rise to another disadvantageous environmental problem; (6) difficulty in control.

[0003] As a result, the environmental challenges posed by pollutants and contaminants in the aforementioned fields remain unresolved. One process considered to address these challenges is electrochemical oxidation, specifically using boron-doped diamond (BDD) electrodes. When an electric current flows through an electrochemical cell containing BDD electrodes, electrochemical oxidation has been shown to reduce the concentration of PFAS dissolved in the electrolyte solution, decrease dissolved carbon dioxide, and destroy organic pollutants with high, nearly 100% current efficiency. However, electrochemical oxidation exhibits significant drawbacks and deficiencies. These drawbacks and deficiencies of electrochemical oxidation include, but are not limited to, the following: (1) When used to regenerate water contaminated with PFAS, this process only achieves partial destruction of certain PFAS, producing short-chain PFAS as a byproduct and generating harmful perchlorates during the reaction. In addition, the reaction rate is very slow, resulting in high energy consumption.

[0004] (2) Although this process is known to reduce dissolved carbon dioxide to carbon monoxide, the reaction rate is very slow, and the continuous supply of energy to the electrochemical cell is large. As a result, this process is not economically viable for carbon dioxide reduction. In addition, harmful perchlorates are produced as byproducts.

[0005] (3) When used to break down organic matter dissolved in wastewater, the reaction rate is slow, resulting in high energy costs, insufficient reaction leading to the generation of undesirable by-products such as perchlorates, and the effectiveness of the process varies depending on the pollutants present in the wastewater.

[0006] (4) In all applications, the mass of contaminants or impurities removed by electrochemical oxidation is directly proportional to the area of ​​the electrode installed. Boron-doped diamond electrodes are expensive, and therefore the capital cost of the process is very high.

[0007] (5) The mass of the contaminants removed is directly proportional to the energy supplied, so a lot of energy is consumed. Clearly, electrochemical oxidation is not a promising solution to the environmental challenges in the aforementioned fields. There is a continuing, and indeed urgent, need for effective and economical means to address not only those described herein, but also many other environmental problems. Simple, cost-effective, and high-performance processes would have a significant impact in addressing the environmental pressures we face today. [Overview of the project] [Means for solving the problem]

[0008] The present invention more than satisfies this need by providing a unique method for destroying unwanted contaminants in an aqueous solution, which involves the electrochemical initiation of a sustained, i.e., continuous chain reaction in the aqueous solution, which is followed by the consumption of the unwanted contaminants with little external influence.

[0009] In particular, the benefits and advantages of this inventive method can be summarized as follows: (1) It non-selectively destroys all organic and targeted inorganic contaminants in aqueous solutions at very low cost; (2) It destroys all PFAS to very low concentrations; (3) It reduces dissolved carbon dioxide in water at low cost; (4) It removes dissolved ammoniacal nitrogen and nitrates in water at low cost; (5) It reduces inorganic and organophosphates from aqueous solutions; (6) It removes numerous inorganic compounds, including but not limited to sulfides and perchlorates, from any water; (7) It generates at least one persistent free radical at low temperature and low pressure, which can be used in other processes that require the generation of free radicals; (8) Once the chain reaction is started, it is not affected by the analytical properties of the aqueous solution; (9) Once the chain reaction is started, it proceeds to completion without requiring substantially any further energy input and without external influence; (10) It has low ownership costs.

[0010] The important objectives, features, and other advantages of the present invention will be apparent to those skilled in the art from the foregoing, the following detailed description, and the accompanying claims, along with the accompanying drawings.

[0011] To better understand the present invention and its novel features and advantages, please refer to the following detailed description, which considers the attached drawings below. [Brief explanation of the drawing]

[0012] [Figure 1] A generalized process flow diagram of a system utilizing this inventive method with various water supply methods for various applications is shown. [Figure 2] This demonstrates how power is applied using the method of the present invention. [Figure 3] This diagram shows the process flow of the equipment used in a series of laboratory tests incorporating the present invention. [Modes for carrying out the invention]

[0013] The diagram above is merely an example and includes various steps that may or may not be present in an actual implementation, depending on the situation. The drawings have been intended to illustrate at least the elements important for understanding various embodiments and aspects of the present invention. However, other method steps may be used to provide a complete processing system for use under a particular set of circumstances.

[0014] Referring here to the drawings, Figure 1 is a generalized flow diagram illustrating the use of this inventive method for treating industrial wastewater. Industrial wastewater 10 containing organic compound solutes, which is the feedwater, is supplied into a storage tank 12. The wastewater is sent to the inlet of a pump 20 and then to the inlet of an electrochemical cell 30. The electrochemical cell 30 includes at least two electrodes made from boron-doped diamond, BDD, which are arranged so that the wastewater flows between the electrodes and comes into contact with these at least two electrodes. In one embodiment, the electrochemical cell 30 includes several pairs of BDD electrodes arranged to form parallel flow paths within the unit. The water is then returned to the storage tank 12. A power supply 40 is connected to the electrochemical cell 30, and at least one supply of DC current is passed through the electrochemical cell 30 according to the power profile shown in Figure 2. A sustained chain reaction in the aqueous solution can be initiated with one power cycle, but multiple cycles can be applied quickly and consecutively. The power is then turned off. The power supply generates at least one type of persistent free radical, which exists in the piping for a few seconds while water flows from the electrochemical cell 30 to the tank 12. Once the water enters the tank 12, the tank can be isolated. A chain reaction then propagates within the tank 12, consuming the available target reactants. The chain reaction terminates when all available reactants have been consumed. The chain reaction typically lasts for several tens of seconds, but can also last for several minutes depending on the concentration of available reactants in the aqueous solution. During this propagation and reaction time in the isolated tank 12, water from one or more additional tanks 13 can be continuously flowed into the electrochemical cell 30, and at least one power cycle as shown in Figure 2 can be applied to rapidly and continuously induce chain reactions in several tanks.

[0015] Figure 2 illustrates a method of supplying power to an electrochemical cell in one embodiment of the present invention. A complete cycle of the applied power sequence shown in Figure 2 can initiate a sustained chain reaction. The essential characteristics of the supplied power sequence can be described as follows: Time T1: A DC current flows through the electrochemical cell, creating a potential difference V within the electrochemical cell. AThis causes [something].

[0016] Time T2: The current flowing through the electrochemical cell is changed to create a specific voltage V in the cell. B The current is raised to a certain point, at which point at least one type of residual free radical is generated, initiating a chain reaction. The rate at which the current is changed is controlled to achieve a specific required rate of increase in the potential difference within the electrochemical cell. B The value of is a specific required value to ensure that the anode voltage of each electrode pair in the electrochemical cell is within the range of approximately 2.3V to 2.9V relative to the SHE (standard hydrogen electrode).

[0017] Time T3:V B When this point is reached, the potential difference within the electrochemical cell or the current flowing through it remains constant for a short period of time. This time can be less than or greater than one second. Time T4: The current is typically, but not necessarily, given the potential difference within the electrochemical cell, and the initial voltage V A It can be changed to decrease to [this state]. The duration of T4 and T1 is not important; it can be less than a few seconds or longer.

[0018] By precisely controlling the power transitions, a chain reaction can be initiated in one pulse or one cycle. To ensure that at least one necessary type of persistent free radical is generated to initiate the desired chain reaction, another power cycle can be rapidly applied in succession, and the polarity can also be reversed. All successive power cycles incorporate time T1-T4 in some way, particularly the voltage rise rate and V indicated in T2 above. B The parameters are precisely controlled.

[0019] In FIG. 3, a generalized flow diagram shows laboratory equipment used for testing various types of water. Water containing contaminants that require removal is provided to a water supply tank 101. The water is then sent to the inlet of a pump 102, and then to the inlet of an electrochemical cell 103. The electrochemical cell 103 comprises four pairs of boron-doped diamond (BDD) electrodes, which are arranged such that water can flow between the electrodes and come into contact with both electrodes of each pair. A DC power supply 105 is connected to the electrochemical cell 103, and a controlled current flows through the electrodes and the water according to the power profile shown in FIG. 2. After exiting the electrode cell 103, the water is returned to the storage tank 101, entering the tank 101 approximately 6 seconds after exiting the electrochemical cell 103. After at least one cycle of the power profile shown in FIG. 2, the power is turned off, and the water is circulated in the system to facilitate mixing while the chain reaction propagates in the storage tank 101. The chain reaction continues for several minutes and terminates when the ultimately available target reactants are consumed.

[0020] Through extensive research and experiments, the present inventors have developed a means for initiating a chain reaction initiated by persistent free radicals in an aqueous solution. Importantly, the inventors have confirmed that such a chain reaction can be propagated and sustained to destroy target contaminants in water and remove them from the system. This is a unique method of water treatment that removes contaminants from the environment at a very low cost, low temperature and low pressure that cannot be achieved by the prior art.

[0021] The method described herein can be implemented in numerous industrial and municipal fields. In many important application fields, the feed water may contain a mixture of organic solutes. The relative concentration of each different solute is uncontrolled, and the overall dissolved organic concentration may be variable. The organic solutes can be removed to any desired final concentration.

[0022] In other fields of application, the feed water may contain PFAS, perfluoroalkyl and polyfluoroalkyl compounds. The inventive method can reduce the overall PFAS concentration from any initial value to a low ppt (parts per trillion) concentration.

[0023] In another field of application of the inventive method, the feed water may contain perchlorate. The method of the present invention can remove perchlorate down to low concentrations. In another field of application of the method of the present invention, the feed water may contain a mixture of ammonia nitrogen, organic phosphoric acid, nitrate and inorganic phosphoric acid. All of the aforementioned solutes are effectively destroyed by the method of the present invention.

[0024] In another field of application of the method of the present invention, the feed water may contain solutes that are effective bactericides, such as CN group-containing compounds and active pharmaceutical ingredients. All such solutes are destroyed by the method of the present invention.

[0025] In other fields of application, the method of the present invention can be used to generate at least one persistent free radical, which can initiate a chain reaction leading to the synthesis of organic compounds.

[0026] Thus, the inventive features of the method disclosed herein are: (1) a single pulse supply of electric power initiates a sustained chain reaction in a small volume of water; (2) once initiated, this chain reaction is maintained while it propagates into a large volume of water; (3) when this chain reaction enters a large volume of water, it propagates and continues without being affected by external influences, and finally terminates when all available reactants are consumed; (4) the method has extremely low cost; (5) the chain reaction can be initiated and propagated in multiple volumes of water using one electrochemical cell, thereby allowing several chain reactions to proceed simultaneously. Examples

[0027] The present invention is described more specifically in the following non-limiting embodiments, which are intended to be illustrative only, as various improvements and modifications will be apparent to those skilled in the art.

[0028] Example 1 In one test, as shown in Figure 3, 8 liters of aqueous solution containing 3,334 ppm of sulfide anions were placed in a tank. The wastewater was circulated in an electrochemical cell at a flow rate of 7 liters per minute. The power applied to the electrochemical cell had the profile shown in Figure 2, and a total of 3 cycles were applied continuously. The total energy consumed was less than 100 joules. The sulfide concentration in the water was reduced to less than 300 ppm. The reaction took approximately 5 minutes to complete and terminate.

[0029] Example 2 In the second test, 20 liters of an aqueous solution containing 3,334 ppm sulfide anions and 2,150 ppm phenol was placed in a tank. The water was circulated in an electrochemical cell at a flow rate of approximately 7 liters per minute. The power applied to the electrochemical cell had the profile shown in Figure 2, and a total of 4 cycles were applied continuously. The total energy consumed was less than 120 joules. The sulfide concentration was reduced to less than 300 ppm, and the phenol concentration to less than 250 ppm. The reaction took approximately 5 minutes to complete and terminate.

[0030] Example 3 In the third test, 8 liters of an aqueous solution containing 4,000 ppm bicarbonate / carbonate anions were placed in a tank. The water was circulated in an electrochemical cell at a flow rate of approximately 7 liters per minute. The power applied to the electrochemical cell had the profile shown in Figure 2 and was applied continuously for a total of 3 cycles. The total energy consumed was less than 150 joules. The carbon dioxide / bicarbonate / carbonate concentration was reduced to less than 2,000 ppm. The reaction took approximately 5 minutes to complete and terminate. The exemplary results of such tests, and in particular the low amount of energy required, the short application time, and the long duration for which the chain reaction continues to remove impurities present in the aqueous solution without further application of power, demonstrate the exceptional efficiency of the unique method of the present invention.

[0031] Thus, the aforementioned objectives are found to be effectively and efficiently achieved, including those revealed above, and it should be understood that the present invention can be implemented in other specific forms without departing from its spirit or essential characteristics, as certain modifications can be made in the execution of the aforementioned methods and in the configuration of appropriate apparatus for executing these methods and producing the desired products described herein. For example, while an exemplary design for treating aqueous solutions by a chain reaction initiated by residual free radicals is shown, other embodiments can also be implemented to realize the results of the principle of the methods disclosed herein. Therefore, it should be understood that the above description of representative embodiments of the present invention is presented for illustrative purposes and to enable understanding of the invention, and is not intended to be exhaustive or restrictive, or to limit the invention to the disclosed forms themselves. Conversely, the present invention is intended to cover all improvements, equivalents, and substitutes that fall within the spirit and scope of the invention as expressed in the supplementary claims. Therefore, the claims are intended to cover not only the methods and structures described herein, but also their equivalents and structural equivalents, as well as equivalent structures or methods. Therefore, the scope of the invention as expressed by the accompanying claims is intended to include variations from the embodiments or equivalents provided and, notwithstanding, described in the broad sense and scope appropriately given to the language of the claims.

Claims

1. A method for initiating and propagating a sustained chain reaction in an aqueous solution within an electrochemical apparatus, wherein the electrochemical apparatus includes at least one electrochemical cell containing an electrode suitable for producing water with a low concentration of a particular solute, (a) To provide a water supply stream which is an aqueous solution containing a solute that includes an organic species or molecule, ammoniacal nitrogen, organic nitrogen, inorganic phosphoric acid, organic phosphoric acid, inorganic sulfide, organic sulfide, nitrate, perfluoroalkyl and polyfluoroalkyl compounds, carbon dioxide, bicarbonate, carbonate, or a combination thereof, (b) Passing the water supply from step (a) through the electrochemical cell so that the water comes into contact with the electrodes contained therein, (c) A direct current is passed through the electrochemical cell to generate at least one persistent free radical that initiates a sustained chain reaction in the aqueous solution, wherein the direct current is varied and controlled to apply a specific power scheme to the electrochemical cell, including at least one cycle or pulse, and the potential difference applied to the cell is increased to a specific value at a precise, controlled voltage rise rate, and once the voltage reaches the specific value, the voltage is reduced. (d) The aqueous solution flows into a larger volume of water containing some or all of the solute described in step (a), so that the sustained chain reaction propagates into the larger volume and the concentration of the solute therein decreases. A method that includes this.

2. The method according to claim 1, wherein once step (d) is completed, steps (a) to (d) are repeated one or more times so that the sustained chain reaction is initiated and propagated in one or more separate additional volumes of water.

3. The method according to claim 1, wherein in step (c), the DC current is changed to increase the potential difference within the electrochemical cell so that the anode potential in each electrode pair within the electrochemical cell reaches a specific value within the range of 2.50 V to 2.85 V relative to a standard hydrogen electrode, SHE, in an elapsed time of 1 second or less.

4. The method according to claim 1, wherein in step (c), the DC current is changed to increase the potential difference within the electrochemical cell so that the anode potential in each electrode pair within the electrochemical cell reaches a specific value within the range of 2.50 V to 2.85 V relative to a standard hydrogen electrode, SHE, in an elapsed time of 1 / 2 second or less.

5. The method according to claim 1, wherein in step (c), the DC current is changed to increase the potential difference within the electrochemical cell so that the anode potential in each electrode pair within the electrochemical cell reaches a specific value within the range of 2.50 V to 2.85 V relative to a standard hydrogen electrode, SHE, in an elapsed time of one-third of a second or less.

6. The method according to claim 1, wherein in step (d), the chain reaction is propagated to synthesize a different organic compound or polymer as a desired product.

Images