Gas separation membranes, leveraging the principle of selective permeation, have become essential technology in modern industry. They are primarily applied in the following critical fields, delivering key benefits including energy savings, environmental protection, efficiency, and cost reduction:

Major Application Areas and Core Functions:

1. Natural Gas Processing:

   • Primary Functions: Dehydration, Acid Gas Removal (H₂S & CO₂), Methane Purification
   • Application Details: Removes water vapor (dehydration using hydrophilic membranes), CO₂, and H₂S (acid gas removal) from raw natural gas. Membrane dehydration is more energy-efficient and environmentally friendly than traditional glycol dehydration. Removing acid gases enhances pipeline gas quality, ensures compliance with standards, and reduces corrosion. Under specific conditions, membranes can also separate nitrogen (N₂) to increase methane concentration. Compared to traditional amine absorption, membrane technology offers greater cost-effectiveness for medium/small-scale operations or gas with specific compositions.

2. Hydrogen Separation and Recovery:

   • Primary Functions: Hydrogen Purification, Tail Gas Recovery
   • Application Details:
     • Refineries: Efficiently separate and recover hydrogen (H₂) from catalytic reformer off-gas, hydrocracker purge gas, and FCC dry gas. The purified hydrogen is recycled back into hydrotreatment processes, significantly reducing costs.
     • Ammonia Plants: Recover hydrogen from purge gas (N₂/H₂ mixture).
     • Chemical Plants: Recover by-product hydrogen from the chlor-alkali industry.
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3. Air Separation:

   • Primary Functions: Production of Nitrogen-Enriched Air (NEA) / Oxygen-Enriched Air (OEA)
   • Application Details:
     • Nitrogen (NEA): Used in food packaging, fruit/vegetable preservation (inhibiting respiration and microbial growth), inert gas blanketing of chemical storage tanks (explosion prevention), electronic component encapsulation, and oil tanker inerting. Membrane-based N₂ generators are compact, easy to operate, and have fast start-up.
     • Oxygen (OEA): Used in healthcare (portable/stationary oxygen concentrators), wastewater treatment (enhancing biological treatment efficiency by increasing O₂ concentration in aeration basins), and oxygen-enhanced combustion (increasing flame temperature, saving fuel, reducing exhaust emissions).

4. Biogas and Landfill Gas Upgrading:

   • Primary Functions: Methane (CH₄) Purification
   • Application Details: Biogas (from anaerobic digestion) and landfill gas primarily consist of methane and CO₂, along with minor impurities. Membrane technology is widely used to remove CO₂ and H₂S, increasing methane purity (e.g., from ~60% to >95%). This enables the upgraded biogas to be injected into natural gas pipelines (meeting pipeline specifications) or used as compressed natural gas (CNG)/liquefied natural gas (LNG) for vehicle fuel or grid electricity generation, enabling resource utilization and reducing greenhouse gas emissions.

5. Volatile Organic Compound (VOC) Recovery:

   • Primary Functions: VOC Recovery, Emission Control
   • Application Details: From process vents (e.g., during tanker truck loading/unloading, oil depot fugitive emissions, chemical tank breathing) in industries like petrochemicals, paint spraying, and printing, membranes selectively permeable to organic vapors (e.g., silicone rubber types) are used to concentrate low-concentration VOCs. The concentrated VOCs are recovered for reuse (e.g., fed back into the process or used as fuel), while clean air is released. This is a vital environmental technology and resource recovery method, helping meet increasingly stringent emission regulations.

6. Carbon Capture, Utilization, and Storage (CCUS):

   • Primary Function: CO₂ Capture
   • Application Details: Separation and capture of CO₂ from flue gases of large emission sources like coal-fired power plants, cement plants, and steel mills (current challenges lie in low CO₂ concentration and massive gas volumes, requiring ongoing improvements in membrane cost and performance). Also used for CO₂ capture in biomass utilization (e.g., fermentation gas) and natural gas purification. Membrane separation is considered a promising CCUS pathway due to its potential for low energy consumption and modular design.

7. Medical & Healthcare:

   • Primary Functions: Medical Gas Production
   • Application Details: Small membrane separators are used in portable or stationary medical oxygen concentrators to provide supplemental oxygen for patients with respiratory conditions. Membrane technology may also serve as a pre-treatment or purification step in the manufacturing of high-purity gases.

8. Industrial Gas Drying and Purification:

   • Primary Functions: Gas Dehydration, Removal of Specific Impurities
   • Application Details: Widely used for dehydration of inert gases (e.g., N₂, Ar), rare gases (e.g., He), and compressed air systems (instrument air). Also employed to remove trace oil vapor or other specific impurities from air streams.

9. Safety Protection and Detection:

   • Primary Function: Detection of Specific Gases
   • Application Details: Membranes with special selectivity are integrated into gas sensors for environmental monitoring (e.g., CO, H₂S alarms) or online detection and concentration alarms for specific gases in industrial process control systems.
     

Summary of Core Functions of Gas Separation Membranes:

1. Selective Separation: The fundamental function. Exploits differences in gas molecule solubility and diffusion rates (permeability differences) within the membrane material to efficiently separate target gas components from mixtures.
2. Energy Savings & Reduced Consumption: Compared to traditional separation technologies like cryogenic distillation, solvent absorption, and pressure swing adsorption (PSA), membrane separation is typically a continuous, physical process without phase changes or complex cycling operations, leading to significantly lower energy consumption (especially for small/medium-scale applications). E.g., membrane dehydration consumes less energy than glycol dehydration.
3. Environmentally Friendly: Reduces solvent use (avoiding pollution) and lowers emissions of greenhouse gases (GHGs) and toxic/hazardous gases (VOCs, H₂S, SOₓ/NOₓ), promoting resource recovery (biogas, hydrogen).
4. Cost Reduction: Lower equipment investment (especially for smaller scales), simple operation and maintenance (no moving parts, high automation), reducing operating and labor costs (H₂ recovery drastically cuts raw gas purchase costs).
5. Process Simplification: Modular design, easy integration into existing processes or capacity expansion, small footprint.
6. High Reliability: Simple operation, good stability, capable of continuous operation.
7. Enhanced Product Purity & Yield: E.g., improved hydrogen purity, methane concentration in natural gas, and methane recovery rates (biogas upgrading).
8. Compact Size & Portability: The compact structure of membrane modules makes them highly suitable for distributed applications (e.g., small biogas sites, remote wellheads) and mobile scenarios (e.g., mobile VOCs recovery units for depots, medical oxygen concentrators).

In conclusion, gas separation membrane technology is extensively applied across numerous fields such as energy/chemicals, environmental protection, healthcare, and food preservation due to its characteristics of high efficiency, energy savings, environmental friendliness, and flexibility. Continued advancements in material science and process design are further expanding and deepening its scope of application.