Integrated purification system and method for removing methane impurity in carbon dioxide gas
By using an integrated purification system and multi-stage processing steps, modified alumina and noble metal catalysts are used to convert methane. Combined with multi-stage adsorption towers and online analysis systems, the problem of deep removal of trace methane from carbon dioxide gas is solved, achieving efficient, stable and economical high-purity CO2 preparation, which meets the high purity requirements of semiconductor manufacturing.
Patent Information
- Application Number
- CN202511930623.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-19
- Publication Date
- 2026-04-03
AI Technical Summary
Existing technologies are insufficient for efficiently and stably removing trace methane impurities from carbon dioxide gas. Traditional methods have poor selectivity and high energy consumption, making it difficult to meet the high-purity CO2 requirements of semiconductor manufacturing.
An integrated purification system is adopted, including pretreatment, catalytic oxidation, posttreatment and purification steps. Modified alumina and noble metal catalysts are used to convert methane into CO2 and H2O, and high-purity CO2 is prepared through multi-stage adsorption towers. The operating parameters are optimized by combining online analysis and automatic control system.
It achieves efficient and stable reduction of methane impurities to below 10 ppb, ensuring CO2 gas purity of 99.9999%, reducing energy consumption and equipment investment, and meeting the high purity requirements of semiconductor manufacturing.
Smart Images
Figure CN121775650A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of specialty gas purification technology, specifically to an integrated purification system and method for removing methane impurities from carbon dioxide gas. Background Technology
[0002] In semiconductor manufacturing, high-purity carbon dioxide serves as a crucial and versatile auxiliary gas, primarily used in cutting-edge fields such as supercritical fluid cleaning, deep silicon etching, and cryogenic etching. As an "enabler" and "fine-tuning tool" for achieving nanoscale precision machining, cleaning, and thermal management, it is indispensable for improving chip yield and manufacturing advanced structures. These processes demand extremely high purity CO2 gas, requiring a total impurity content below 1 ppb (parts per billion). Methane (CH4) is one of the common and difficult-to-remove trace impurities in CO2 feedstock gas.
[0003] Currently, traditional CO2 purification technologies (such as adsorption and cryogenic distillation) face significant challenges in removing methane: First, methane and carbon dioxide have similar molecular sizes, boiling points, and chemical properties, resulting in poor selectivity and low separation factors for conventional adsorbents; second, while cryogenic distillation has some effectiveness, it is extremely energy-intensive, requires complex equipment, and has limited efficiency for deep removal below the ppb level. Therefore, developing a purification technology that can efficiently, stably, and deeply remove trace amounts of methane from CO2 is a crucial technological bottleneck that urgently needs to be overcome in this field. Summary of the Invention
[0004] The purpose of this invention is to provide an integrated purification system and method for removing methane impurities from carbon dioxide gas, so as to solve the problems mentioned in the background art.
[0005] To achieve the above objectives, the present invention provides an integrated purification method for removing methane impurities from carbon dioxide gas, characterized in that it includes: S1. Pre-treat the raw material CO2 gas to remove sulfide impurities and obtain pre-treated CO2 gas. S2. The pretreated CO2 gas is heated and injected with a trace oxygen source. Trace methane is catalytically oxidized to CO2 and H2O through a supported noble metal catalyst to obtain the reaction gas. S3. Cool the reaction gas and remove excess oxygen to obtain post-treated gas; S4. The post-treated gas is purified by adsorption of moisture and residual impurities to obtain high-purity CO2 gas with a purity ≥99.9999%.
[0006] Preferably, in step S1, the raw material CO2 gas is pretreated, including: The raw material CO2 gas is passed through a fixed-bed reactor containing modified alumina and ceramic adsorbent under conditions of pressure 0.5-1.0 MPa and temperature 20-40℃. The modified alumina has a specific surface area ≥200m² / g and a pore size distribution of 2-10nm, and is used for selective adsorption of H2S and COS sulfides. The ceramic adsorbent is an active component loaded on a porous ceramic carrier, used to adsorb heavy metals and other organic impurities.
[0007] Preferably, in step S2, heating the pretreated CO2 gas and injecting it into a trace oxygen source includes: The pretreated CO2 gas is heated to the catalytic reaction temperature range of 280-350℃ using an electric heater or heat exchanger, and a trace amount of oxygen source, namely O2 or N2O, is injected into the pretreated CO2 gas through an oxygen source injection device; the amount of oxygen source injected is 105-120% of the stoichiometric ratio of methane; the oxygen source is high-purity oxygen (purity ≥99.999%) or high-purity nitrous oxide (purity ≥99.999%).
[0008] Preferably, in step S2, the trace methane is catalytically oxidized to CO2 and H2O using a supported noble metal catalyst, comprising: The supported noble metal catalyst uses γ-alumina, molecular sieve or activated carbon as a support and supports 0.1-1.0 wt% of palladium, platinum and rhodium noble metals; The catalytic reaction conditions are: temperature 280-350℃, pressure 0.6-1.2MPa, and space velocity 1000-5000h⁻¹; When O2 is used as the oxygen source, the reaction is: CH4 + 2O2 → CO2 + 2H2O; When N2O is used as the oxygen source, the reaction is: CH4 + 4N2O → CO2 + 2H2O + 4N2.
[0009] Preferably, in step S3, cooling the reaction gas and removing excess oxygen includes: The reactant gas is rapidly cooled from 300-350°C to below 40°C using an interstage cooler, and the condensate is separated. The cooled gas enters a deoxygenation reactor containing a palladium-based catalyst, and is heated at a temperature of 40-80℃ and a pressure of 0.5-0.8MPa. If O2 is used as the oxygen source, the palladium-based catalyst will react the excess O2 with hydrogen to produce water, and the deoxygenation depth will make the O2 residue <5ppb. If N2O is used as the oxygen source, moisture is removed by adsorption to obtain post-treated gas.
[0010] Preferably, in step S4, the post-treated gas is purified by adsorption of moisture and residual impurities, including: The post-treated gas first passes through an adsorption tower equipped with 3A molecular sieves, where moisture is removed to <1 ppb at room temperature and 0.3-0.6 MPa. The dehydrated gas is then passed through a highly selective carbon molecular sieve reactor to remove residual nitrogen, hydrogen, and carbon monoxide to <1 ppb. The final high-purity CO2 gas has a total impurity content of <10 ppb and a purity of over 99.9999%.
[0011] Preferably, the method further includes an automatic control step: A first online analyzer is installed at the CO2 gas inlet of the raw material to monitor the methane and sulfide content in the raw material gas in real time. A second online analyzer is installed at the high-purity CO2 gas outlet to monitor the methane, oxygen, and moisture content in the product gas in real time. The monitoring signal is fed back to the PLC or DCS central controller, and the oxygen source injection volume, heating temperature and cooling water volume parameters are dynamically adjusted through the PID control algorithm. A mathematical model of methane conversion rate and oxygen injection rate was established to achieve adaptive optimization control.
[0012] An integrated purification system for removing methane impurities from carbon dioxide gas, comprising: The pretreatment unit, catalytic reaction unit, post-treatment unit, and purification unit are connected sequentially along the airflow direction; The pretreatment unit includes adsorption reactors arranged in parallel. The adsorption reactors are filled with modified alumina and ceramic adsorbent in layers with a layer height ratio of 1:1 to 1:2, which are used to remove sulfide impurities from the raw gas. The catalytic reaction unit includes a heater, a supported noble metal catalyst reactor, and an oxygen source injection device; The heater adopts a zoned temperature control design with a temperature control accuracy of ±1℃; the supported precious metal catalyst reactor adopts a multi-stage catalyst loading structure; the oxygen source injection device has a control accuracy of ±0.5% and a response time of <200ms. The post-processing unit includes a cooler and a palladium-based catalyst reactor; corrosion-resistant materials are used to cool the reaction gas from above 300°C to below 40°C; the palladium-based catalyst reactor is filled with a Pd-Pt bimetallic catalyst. The refining unit includes a 3A molecular sieve adsorption tower and a high-selectivity carbon molecular sieve reactor; the 3A molecular sieve adsorption tower adopts a multi-tower parallel design to achieve continuous operation; the high-selectivity carbon molecular sieve reactor has a pore size distribution of 0.3-0.5 nm.
[0013] Preferably, the system further includes an analysis and control unit, which includes an inlet online analysis system, an outlet online analysis system, a central controller, and a safety interlock system; The imported online analysis system includes a laser methane analyzer and a sulfur chemiluminescence detector; The online analysis system for the outlet includes a gas chromatograph, a trace water analyzer, and a trace oxygen analyzer; The central controller includes a PLC or DCS system; The safety interlock system includes over-temperature, over-pressure, and gas leak alarms, as well as automatic shutdown protection.
[0014] Preferably, the system adopts a modular design, with each unit being an independent skid, facilitating transportation and installation; a standardized interface design enables rapid connection; flexible configuration allows for adjustable processing capacity ranging from 10-100 Nm³ / h; and pre-installed online monitoring and sampling interfaces.
[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. High efficiency and high selectivity: Utilizing catalytic oxidation technology, methane molecules that are difficult to separate physically are converted into CO2 and H2O that are easy to remove, fundamentally solving the separation problem caused by the similar physical properties of methane and CO2. The removal efficiency is extremely high, and methane can be stably reduced to below 10 ppb.
[0016] 2. No secondary pollution: By precisely controlling the amount of oxygen added and implementing multi-stage protection measures (deoxygenation tower, fine adsorption tower), the introduction of excessive oxygen source and byproducts CO or H2 is effectively avoided, ensuring the purity of the final product gas.
[0017] 3. Stability and reliability: The multi-stage coupled process design of "pretreatment-catalytic conversion-deep removal-end purification" has strong resistance to fluctuations in raw gas, long operating cycle, and can stably produce ultra-high purity CO2 that meets semiconductor requirements.
[0018] 4. Relative economic efficiency: Compared with cryogenic distillation technology that requires extremely low temperature and high pressure, the operating conditions of this invention (medium temperature and medium pressure) are more moderate, and the overall energy consumption and equipment investment are expected to be significantly reduced. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the methane deep removal system of the present invention. Detailed Implementation
[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] See Figure 1 The diagram shows an integrated purification system for removing methane impurities from carbon dioxide gas according to the present invention, comprising: a pretreatment unit, a catalytic reaction unit, a post-treatment unit, and a purification unit connected sequentially along the gas flow direction; The pretreatment unit includes an adsorption reactor 1, the inlet of which is connected to the raw material gas inlet, and the outlet is provided with a high-pressure discharge port; the adsorption reactor 1 is filled with modified alumina and ceramic adsorbent in layers, and the layer height ratio of the modified alumina and ceramic adsorbent is 1:1-1:2. The catalytic reaction unit includes a heater 2 and an oxygen source injection device 4, which are respectively connected to the supported noble metal catalyst reactor 3; the inlet of the supported noble metal catalyst reactor 3 is connected to the outlet of the adsorption reactor 1, and the outlet is connected to the cooler 5. The post-treatment unit includes a cooler 5 and a palladium-based catalyst reactor; the inlet of the cooler 5 is connected to the outlet of the supported noble metal catalyst reactor 3, and the outlet is connected to the inlet of the palladium-based catalyst reactor; the outlet of the palladium-based catalyst reactor is connected to the inlet of the 3A molecular sieve adsorption tower; the cooler 5 is respectively provided with a water inlet, a water outlet and a pressure relief port. The refining unit includes a 3A molecular sieve adsorption tower 7 and a carbon molecular sieve reactor 8; the inlet of the 3A molecular sieve adsorption tower 7 is connected to the outlet of the palladium-based catalyst reactor, and the outlet is connected to the inlet of the carbon molecular sieve reactor 8; the outlet of the carbon molecular sieve reactor 8 is provided with a pure gas outlet; the 3A molecular sieve adsorption tower 7 is also provided with a high-pressure discharge port.
[0022] It should be noted that the system also includes an inlet online analysis system, an outlet online analysis system, a central controller, and a safety interlock system. The inlet online analysis system includes a laser methane analyzer and a sulfur chemiluminescence detector, respectively installed at the inlet of adsorption reactor 1. The outlet online analysis system includes a gas chromatograph, a trace water analyzer, and a trace oxygen analyzer, respectively installed at the outlet of carbon molecular sieve reactor 8. The safety interlock system includes temperature sensors, pressure sensors, gas leak alarms, and automatic shutdown control devices installed at each unit. The laser methane analyzer, sulfur chemiluminescence detector, gas chromatograph, trace water analyzer, trace oxygen analyzer, temperature sensors, pressure sensors, gas leak alarms, and automatic shutdown control devices are all connected to the central controller.
[0023] The working principle of this system is as follows: The raw gas first enters adsorption reactor 1, where modified alumina and ceramic adsorbents remove sulfides. Oxygen injection device 4 precisely injects oxygen (with a control accuracy of ±0.5%) based on the methane content measured by the imported online analysis system (laser methane analyzer), ensuring a suitable methane-to-oxygen ratio. The mixed gas enters the zoned temperature-controlled heater 2, where the central controller heats the gas to the target temperature (with a temperature control of ±1℃) according to the catalytic reaction requirements. After heating, the gas enters the multi-stage loaded supported precious metal catalyst reactor 3 to complete the catalytic oxidation of methane (generating CO2 and H2O). During this process, the safety interlock system monitors the temperature and pressure in real time, automatically shutting down for protection when limits are exceeded. The high-temperature gas (above 300℃) after the catalytic reaction enters the corrosion-resistant cooler 5, where the central controller controls the cooler 5 to cool the gas to below 40℃. After cooling, the gas enters the palladium-based catalyst reactor to remove residual trace oxygen (to prevent it from affecting the adsorbent in the subsequent purification unit). Simultaneously, the outlet online analysis system (trace oxygen analyzer) monitors the oxygen content in real time and feeds it back to the central controller to adjust the post-processing parameters. The gas then enters 3A... Molecular sieve adsorption tower 7 removes trace amounts of water from the gas (the water content is monitored by a trace water analyzer at the outlet). The central controller automatically switches between adsorption and regeneration towers to ensure continuous dehydration. After dehydration, the gas enters a high-selectivity carbon molecular sieve reactor 8 (pore size 0.3-0.5nm) to further remove residual trace impurities, ultimately yielding purified CO2. The outlet gas chromatograph monitors the product purity in real time and feeds it back to the central controller, which then adjusts the operating parameters of the preceding units (such as adsorption switching frequency, oxygen injection rate, heating temperature, etc.).
[0024] The import / export online analysis system collects real-time data on gas composition, temperature, and pressure at each node and transmits it to the central controller (PLC / DCS). The central controller dynamically adjusts the operating parameters of each unit (such as adsorber switching, oxygen injection rate, heater temperature, purification tower switching, etc.) according to preset purification indicators. At the same time, the safety interlock system monitors abnormal operating conditions throughout the process, enabling continuous, stable, and safe collaborative operation of each unit, and ultimately outputting qualified purified CO2. Example
[0025] 1.1 Raw gas pretreatment The raw material, CO2 gas (industrial grade, 99.5% purity), first enters the pretreatment unit and passes through a fixed-bed reactor containing modified alumina and ceramic adsorbent under conditions of 0.8 MPa and 30°C. The modified alumina has a specific surface area of 250 m² / g and a pore size distribution of 3-8 nm, specifically designed for adsorbing sulfide impurities such as H₂S and COS. The ceramic adsorbent is a porous cordierite ceramic carrier supporting transition metal oxides, effectively adsorbing heavy metal vapors and other organic impurities. After pretreatment, the sulfide content in the gas decreases from an initial 50 ppm to <1 ppb, and heavy metal impurities decrease to <0.1 ppb, creating favorable conditions for subsequent catalytic reactions.
[0026] 1.2 Catalytic oxidation reaction Pretreated CO2 gas enters the catalytic reaction unit, where it is first heated to the catalytic reaction temperature of 320°C using an electric heater. High-purity oxygen (99.999% purity) is injected via a high-precision mass flow controller, with the oxygen injection rate being 110% of the stoichiometric ratio of methane. The mixed gas then enters a supported noble metal catalyst reactor, with γ-alumina as the catalyst support and 0.5 wt% palladium metal loaded onto it. Under reaction conditions of 320°C, 0.8 MPa, and a space velocity of 3000 h⁻¹, the catalytic oxidation reaction occurs: CH₄ + 2O₂ → CO₂ + 2H₂O.
[0027] 1.3 Post-processing The high-temperature gas (320°C) after the reaction is rapidly cooled to 35°C through an interstage cooler, separating the condensate. The cooled gas then enters a palladium-based catalyst deoxygenation reactor, where excess oxygen reacts with a trace amount of added hydrogen at 60°C and 0.6 MPa to produce water, reducing the residual oxygen to below 3 ppb.
[0028] 1.4 Refined The post-treated gas is sequentially passed through a 3A molecular sieve adsorption tower and a high-selectivity carbon molecular sieve reactor. The 3A molecular sieve removes moisture to 0.5 ppb at room temperature and 0.5 MPa; the carbon molecular sieve removes residual nitrogen and hydrogen to below 0.8 ppb. The final high-purity CO2 gas has a total impurity content of <5 ppb and a purity of 99.99995%. Example
[0029] 2.1 Preprocessing Unit The pretreatment unit employs a parallel design of two adsorption reactors, each with a diameter of 500 mm and a height of 2000 mm. The reactors are layered with modified alumina (lower layer, 800 mm high) and ceramic adsorbent (upper layer, 1200 mm high), with a layer-to-height ratio of 1:1.5. Equipped with a backflushing system and an electrically heated regeneration device, the adsorbent is regenerated online, ensuring continuous and stable operation.
[0030] 2.2 Catalytic Reaction Unit The catalytic reaction unit comprises a tubular heater, a fixed-bed catalytic reactor, and a mass flow controller. The heater employs a three-zone temperature control design with a temperature control accuracy of ±0.5℃. The catalytic reactor has a diameter of 400mm and is filled with three layers of catalyst, each layer being 300mm high, with temperature monitoring points installed between the layers. The mass flow controller has a control accuracy of ±0.3% and a response time of 150ms.
[0031] 2.3 Post-processing unit The post-treatment unit uses a plate heat exchanger for rapid cooling, with a heat exchange area of 15 m² and a cooling rate of 250 °C / min. The palladium-based deoxygenation reactor is filled with a Pd-Pt (0.3%-0.1%) bimetallic catalyst, which has high deoxygenation activity and long service life.
[0032] 2.4 Refining Unit The refining unit comprises two sets of 3A molecular sieve adsorption towers (one in use and one on standby) and a primary carbon molecular sieve reactor. The molecular sieve adsorption towers are equipped with a pressure swing regeneration system, and the carbon molecular sieve reactor uses specially treated activated carbon fibers with precise pore size control.
[0033] Example 3: Operational Case of a 30 Nm³ / h Industrial Plant 3.1 Raw material gas conditions Gas processing capacity: 30 Nm³ / h Raw material gas composition: CO2 99.5%, CH4 500ppm, H2S 10ppm, H2O 200ppm, O2 100ppm Operating pressure: 0.8 MPa Inlet temperature: 25℃ 3.2 Operating parameters of each unit Preprocessing unit: Adsorption temperature: 30℃ Adsorption pressure: 0.8 MPa Airspeed: 1000 h⁻¹ Sulfide removal efficiency: 99.99% Catalytic reaction unit: Reaction temperature: 320℃ Reaction pressure: 0.8 MPa Oxygen-to-hydrocarbon ratio: 2.2:1 (110% of stoichiometry) Methane conversion rate: 99.998% Post-processing unit: Temperature after cooling: 35℃ Deoxygenation temperature: 60℃ Oxygen residue: <3 ppb Moisture content: <50 ppb Refining Unit: Adsorption temperature: 25℃ Adsorption pressure: 0.5 MPa Product gas purity: 99.9999% Total impurity content: <5 ppb 3.3 Product Gas Quality Indicators The final product gas parameters, as determined by the online analyzer, are as follows: CH4 content: <0.5 ppb O2 content: <3ppb H2O content: <0.5 ppb Total sulfur content: <0.1 ppb Total impurity content: <5 ppb Purity: 99.99995% Example 4: Comparison Experiment under Different Process Conditions 4.1 Effect of temperature on methane conversion rate The effect of different temperatures on methane conversion was investigated under the conditions of a pressure of 0.8 MPa and a space velocity of 3000 h⁻¹. Temperature (°C) Methane conversion rate (%) Byproduct CO (ppb) 280 99.5 ＜1 300 99.9 ＜1 320 99.998 ＜0.5 350 99.999 ＜0.5 Experimental results show that 320-350℃ is the optimal reaction temperature range, which can ensure high conversion rate and avoid catalyst sintering.
[0034] 4.2 Effect of oxygen-to-hydrocarbon ratio on product gas quality The effect of different oxygen-to-hydrogen ratios was investigated under the conditions of 320℃ and 0.8MPa: oxygen-hydrogen ratio <![CDATA[CH4 Residue (ppb)]]> <![CDATA[O2 Residual (ppb)]]> degree of side effects 2.0:1 50 ＜1 none 2.1:1 5 3 none 2.2:1 0.5 5 none 2.3:1 0.1 15 slight The preferred oxygen-to-hydrocarbon ratio is 2.1:1-2.2:1, which balances conversion efficiency and product gas quality.
[0035] Example 5: Implementation of an Automatic Control System 5.1 Configuration of Online Analysis System A laser methane analyzer and a sulfur chemiluminescence detector are installed at the feed gas inlet to monitor CH4 (detection limit 0.1 ppb) and total sulfur content (detection limit 0.5 ppb) in real time. A gas chromatograph (detection limit 0.1 ppb), a trace water analyzer (detection limit 0.1 ppb), and a trace oxygen analyzer (detection limit 0.5 ppb) are installed at the product gas outlet.
[0036] 5.2 Implementation of Control Strategies The central controller (DCS system) adopts a feedforward-feedback composite control strategy: Feedforward control: Predicting oxygen demand based on changes in CH4 concentration in the feed gas. Feedback control: Adjust the oxygen injection rate in real time based on the residual CH4 at the outlet. Adaptive control: Automatic optimization of operating parameters based on catalyst activity decay model 5.3 Safety Interlock Protection The system is equipped with comprehensive safety interlock protection: Over-temperature protection: Automatically cuts off heating when the reaction temperature exceeds 400℃. Overpressure protection: Depressurization is activated when the system pressure > 1.2 MPa. Gas leak detection: Multiple gas sensors deployed Emergency shutdown system: Safe shutdown in case of major malfunctions Example 6: Economic Analysis 6.1 Investment Cost Analysis The total investment for a 30 Nm³ / h unit is approximately 3 million yuan, with the main cost components as follows: Catalyst system: 35% Control system: 25% Heat exchange system: 20% Auxiliary equipment: 20% 6.2 Operating Cost Analysis Power consumption: 0.5 kWh / Nm³ Catalyst lifespan: 2-3 years Adsorbent lifespan: 1-2 years Overall operating cost: 0.8 yuan / Nm³ 6.3 Technological and Economic Advantages Compared to traditional cryogenic methods: Energy consumption reduced by 65% Equipment investment reduced by 40% Reduced floor space by 50% Increased automation reduces labor costs The embodiments of the present invention demonstrate that the integrated purification system and method have significant advantages such as high efficiency, stability, and economy, and are particularly suitable for the demand for ultra-high purity CO2 gas in high-end manufacturing fields such as semiconductors and new energy.
[0037] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. An integrated purification method for removing methane impurities from carbon dioxide gas, characterized in that, include: S1. Pre-treat the raw material CO2 gas to remove sulfide impurities and obtain pre-treated CO2 gas. S2. The pretreated CO2 gas is heated and injected with a trace oxygen source. Trace methane is catalytically oxidized to CO2 and H2O through a supported noble metal catalyst to obtain the reaction gas. S3. Cool the reaction gas and remove excess oxygen to obtain post-treated gas; S4. The post-treated gas is purified by adsorption of moisture and residual impurities to obtain high-purity CO2 gas with a purity ≥99.9999%.
2. The method as described in claim 1, characterized in that, In step S1, the raw material CO2 gas is pretreated, including: The raw material CO2 gas is passed through a fixed-bed reactor containing modified alumina and ceramic adsorbent under conditions of pressure 0.5-1.0 MPa and temperature 20-40℃. The modified alumina has a specific surface area ≥200m² / g and a pore size distribution of 2-10nm, and is used for selective adsorption of H2S and COS sulfides. The ceramic adsorbent is an active component loaded on a porous ceramic carrier, used to adsorb heavy metals and other organic impurities.
3. The method as described in claim 1, characterized in that, In step S2, the pretreated CO2 gas is heated and injected into a trace oxygen source, including: The pretreated CO2 gas is heated to the catalytic reaction temperature range of 280-350℃ using an electric heater or heat exchanger, and a trace amount of oxygen source, namely O2 or N2O, is injected into the pretreated CO2 gas through an oxygen source injection device; the amount of oxygen source injected is 105-120% of the stoichiometric ratio of methane; the oxygen source is high-purity oxygen (purity ≥99.999%) or high-purity nitrous oxide (purity ≥99.999%).
4. The method as described in claim 3, characterized in that, In step S2, trace amounts of methane are catalytically oxidized to CO2 and H2O using a supported noble metal catalyst, including: The supported noble metal catalyst uses γ-alumina, molecular sieve or activated carbon as a support and is loaded with 0.1-1.0 wt% of palladium, platinum and rhodium noble metals; The catalytic reaction conditions are: temperature 280-350℃, pressure 0.6-1.2MPa, and space velocity 1000-5000h⁻¹; When O2 is used as the oxygen source, the reaction is: CH4 + 2O2 → CO2 + 2H2O; When N2O is used as the oxygen source, the reaction is: CH4 + 4N2O → CO2 + 2H2O + 4N2.
5. The method as described in claim 4, characterized in that, In step S3, cooling the reaction gas and removing excess oxygen include: The reactant gas is rapidly cooled from 300-350°C to below 40°C using an interstage cooler, and the condensate is separated. The cooled gas enters a deoxygenation reactor containing a palladium-based catalyst, and is heated at a temperature of 40-80℃ and a pressure of 0.5-0.8MPa. If O2 is used as the oxygen source, the palladium-based catalyst will react the excess O2 with hydrogen to produce water, and the deoxygenation depth will make the O2 residue <5ppb. If N2O is used as the oxygen source, moisture is removed by adsorption to obtain post-treated gas.
6. The method as described in claim 1, characterized in that, In step S4, the post-treated gas is purified by adsorption of moisture and residual impurities, including: The post-treated gas first passes through an adsorption tower equipped with 3A molecular sieves, where moisture is removed to <1 ppb at room temperature and 0.3-0.6 MPa. The dehydrated gas is then passed through a highly selective carbon molecular sieve reactor to remove residual nitrogen, hydrogen, and carbon monoxide to <1 ppb. The final high-purity CO2 gas has a total impurity content of <10 ppb and a purity of over 99.9999%.
7. The method as described in claim 1, characterized in that, The method also includes an automatic control step: A first online analyzer is installed at the CO2 gas inlet of the raw material to monitor the methane and sulfide content in the raw material gas in real time. A second online analyzer is installed at the high-purity CO2 gas outlet to monitor the methane, oxygen, and moisture content in the product gas in real time. The monitoring signal is fed back to the central controller, and the oxygen injection volume, heating temperature, and cooling water volume parameters are dynamically adjusted through the PID control algorithm. A mathematical model of methane conversion rate and oxygen injection rate was established to achieve adaptive optimization control.
8. An integrated purification system for removing methane impurities from carbon dioxide gas, characterized in that, include: The pretreatment unit, catalytic reaction unit, post-treatment unit, and purification unit are connected sequentially along the airflow direction; The pretreatment unit includes adsorption reactors arranged in parallel. The adsorption reactors are filled with modified alumina and ceramic adsorbent in layers with a layer height ratio of 1:1 to 1:2, which are used to remove sulfide impurities from the raw gas. The catalytic reaction unit includes a heater, a supported noble metal catalyst reactor, and an oxygen source injection device; The heater adopts a zoned temperature control design with a temperature control accuracy of ±1℃; the supported precious metal catalyst reactor adopts a multi-stage catalyst loading structure; the oxygen source injection device has a control accuracy of ±0.5% and a response time of <200ms. The post-processing unit includes a cooler and a palladium-based catalyst reactor; corrosion-resistant materials are used to cool the reaction gas from above 300°C to below 40°C; the palladium-based catalyst reactor is filled with a Pd-Pt bimetallic catalyst. The refining unit includes a 3A molecular sieve adsorption tower and a high-selectivity carbon molecular sieve reactor; the 3A molecular sieve adsorption tower adopts a multi-tower parallel design to achieve continuous operation; the high-selectivity carbon molecular sieve reactor has a pore size distribution of 0.3-0.5 nm.
9. The integrated purification system for removing methane impurities from carbon dioxide gas as described in claim 8, characterized in that, The system also includes an analysis and control unit, which includes an inlet online analysis system, an outlet online analysis system, a central controller, and a safety interlock system. The imported online analysis system includes a laser methane analyzer and a sulfur chemiluminescence detector; The online analysis system for the outlet includes a gas chromatograph, a trace water analyzer, and a trace oxygen analyzer; The central controller includes a PLC or DCS system; The safety interlock system includes a temperature sensor, a pressure sensor, a gas leak alarm, and an automatic shutdown control device.