Oxygen Depletion Cathode Gas Recycling in Chlor-Alkali Electrolysis
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Solution Overview
Problem
Existing methods for recycling excess oxygen in oxygen-consuming cathodes during electrolysis of aqueous solutions of hydrogen chloride or alkali chloride face challenges due to hydrogen concentration above the explosion limit, leading to costly and inefficient oxygen supply requirements.
Innovation Solution
Implementing a gas separation device to separate oxygen-rich and oxygen-poor fractions from the excess oxygen-containing gas discharged from the cathode half-element, allowing for partial recycling of the oxygen-rich fraction back to the cathode, thereby reducing the need for fresh oxygen supply and minimizing trace gases like hydrogen and argon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If excess oxygen-containing gas is discharged into exhaust air without recycling, then hydrogen concentration risk is avoided, but oxygen supply cost increases and resource efficiency decreases
Solution Approach 1:
The patent recovers oxygen from the exhaust gas stream by separating it from other gases (particularly hydrogen and argon) and recycling it back to the cathode half-element. This prevents oxygen loss while implementing safety controls for hydrogen management
Solution Approach 2:
The patent extracts and removes hydrogen and argon gases from the oxygen-containing exhaust stream through separation processes (such as catalytic oxidation for hydrogen and fractional condensation or adsorption for argon). This purification enables safe recycling of the oxygen component
2Reliability
If catalytic oxidation is used to remove hydrogen from exhaust gas, then hydrogen safety is improved, but argon concentration increases requiring more fresh oxygen supply
Solution Approach 1:
The patent segments the exhaust gas treatment into multiple sequential steps: first catalytic oxidation for hydrogen removal, then additional separation processes (such as adsorption or condensation) for argon removal. This multi-stage approach addresses both hydrogen safety and argon accumulation problems
Solution Approach 2:
The patent employs a composite treatment system combining catalytic converters with additional separation media (such as molecular sieves, activated carbon, or condensation chambers) to simultaneously or sequentially remove multiple unwanted gases (hydrogen and argon) from the oxygen stream
3Use of energy by moving object
If pure oxygen is supplied to maintain sufficient oxygen excess at cathode, then oxygen availability is improved, but cost increases
Solution Approach 1:
The patent recovers and recycles oxygen from the cathode exhaust stream, reducing the need for continuous fresh oxygen supply. This significantly lowers operational costs while maintaining adequate oxygen availability for the oxygen-consuming cathode reaction
Solution Approach 2:
The system essentially serves itself by capturing and reusing its own oxygen consumption, creating a partially closed loop that reduces external oxygen supply requirements and associated costs
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the cost of oxygen supply by enabling more frequent recycling of oxygen while maintaining safe hydrogen levels below the explosion limit, improving the efficiency of the electrolysis process.
Implementation Method 1
the oxygen-containing gas is separated into an oxygen-rich and an oxygen-poor fraction
Implementation Method 2
electrolysis of an aqueous solution of hydrogen chloride or alkali chloride in an electrolytic cell
Implementation Method 3
oxygen-consuming cathode
Implementation Method 4
a cation exchange membrane for the electrolytic separation of anode half-element and cathode half-element
Data Source
Figure 1
AI summary
In a process for chlorine-alkali electrolysis, use is made of an oxygen depletion cathode. The process is run with a high excess of oxygen. The oxygen needed for this is provided for a device of the gas separation, for example a VPSA plant or an air fractionation plant. The large quantities of oxygen produced lead to considerable costs of the process. According to the invention, the oxygen-rich atmosphere remaining after passing through the process is fed back into the device for gas separation as input gas. The device the gas separation is therefore operated with an oxygen-rich input gas and therefore produces a larger quantity of oxygen-rich gas, which in turn is fed to the oxygen depletion cathode. As a result of the circulation of the gas, the economy of the overall process is increased considerably.