Membrane Separation Vapor Recovery Unit

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Membrane separation vapor recovery units utilize organic vapor-selective polymer composite membranes that exploit differences in permeation rates between various gas molecules under pressure-driven conditions to efficiently separate hydrocarbons (VOCs) from air (nitrogen and oxygen). Hydrocarbon molecules preferentially permeate through the membrane to form a concentrated vapor stream for recovery, while air is retained and discharged as clean exhaust.

The technology can operate standalone but is more often integrated with condensation, adsorption, and absorption processes to form multi-stage integrated vapor recovery systems, achieving recovery rates ≥99% and ultra-low emissions ≤10g/m³.

2.1 Fundamental Principle of Membrane Separation

The core of membrane separation vapor recovery lies in the selective permeation difference between organic vapors and air through high-performance composite membranes. The composite membrane consists of an ultrathin selective rubbery top layer and a porous support layer - the top layer performs the separation while the porous support provides mechanical strength.

Membrane permeation rate for organic vapors is 10–100× that of air

Driving force: vapor pressure difference across the membrane (feed compression or permeate-side vacuum)

Permeate side (low pressure): enriched hydrocarbons → recovered or recycled upstream

Retentate side (high pressure): purified air → compliant emission

2.2 Membrane Materials & Modules

Industrial membrane modules typically employ spiral-wound elements that are space-efficient and low-cost. The membrane material is a thin film composite with an elastomeric selective top layer that exhibits high permeability for various hydrocarbon vapors and low permeability for oxygen and nitrogen.

2.3 Typical Two-Stage Process Flow

The membrane separation process typically consists of two steps: compression-condensation and membrane vapor separation.

3.1 Core Advantages

Concentration-independent efficiency - separation efficiency remains constant regardless of whether vapor concentration drops from 30% to 3% to 0.3%

Ambient/moderate pressure operation - no refrigeration or high-temperature heating required

No secondary waste - purely physical separation, generates no hazardous waste such as spent carbon or waste solvents

Minimal moving parts - core is static membrane modules, high reliability, low maintenance

Long membrane life - typical membrane module service life 3–8 years

Small footprint - systems are significantly smaller than carbon adsorption units of similar capacity

3.2 Limitations

Membrane modules are overloaded when treating high-concentration vapor alone, affecting efficiency and service life

Single-stage membrane separation alone cannot achieve ultra-low emissions (e.g. <10g/m³)

High-performance composite membrane manufacturing has high technical barriers, mastered by only a few manufacturers globally

Conclusion: Hybrid systems are the inevitable technical direction. A single vapor recovery method cannot meet increasingly stringent emission standards - the integration of multiple recovery processes has become the mainstream trend both domestically and internationally.

4.1 Condensation + Membrane

Process Positioning：

Condensation performs "rough separation" - treating high-concentration vapor and liquefying most hydrocarbons into product oil; membrane separation performs "fine polishing" - treating residual low-concentration tail gas after condensation for deep purification to meet emission standards.

Process Flow Diagram：

Technical Advantages：

Compared to standalone condensation (requiring temperatures below -95°C), the hybrid system's condensation stage only requires -20°C ~ -30°C - energy consumption dramatically reduced

Membrane separation compensates for condensation's low efficiency on dilute tail gas

Overall recovery rate reaches 95%–99.9%

4.2 Membrane + Adsorption

Process Positioning：

Membrane upfront - removes most vapor, drastically reducing activated carbon loading; adsorption downstream - deep-polishes to ultra-low emissions.

Technical Advantages：

Since most vapor is recovered before entering the activated carbon adsorption unit, the load on the adsorption unit is greatly reduced, lowering capital and maintenance costs.

Adsorber volume can be reduced 30–50%, adsorbent life significantly extended.

Real-World Examples：

Adsorption-membrane hybrid has achieved significant commercial success in Europe for recovering organic compound vapors from waste gases

Suitable for gas stations, chemical storage tanks, and other small-to-medium VOCs treatment scenarios

4.3 Triple Cascade: Condensation + Membrane + Adsorption

Process Positioning：

Three-stage cascade treatment - each stage leverages its strengths for complementary advantages. This is currently the most mature and widely applied three-stage hybrid solution.

Technical Advantages：

Recovery ≥99%

Emission concentration ≤10g/m³, far superior to national standards

The "condensation + membrane + adsorption" approach is energy-efficient, highly effective, and relatively cost-effective.

Real-World Examples：

Shanxi Lu'an 180 Demonstration Project : Condensation + membrane + adsorption hybrid; treatment efficiency ≥99% with significant economic benefits

Refinery small-product road loading project : Adopted "condensation + membrane + adsorption" triple cascade process

Hohhot Petrochemical vapor recovery retrofit : Adopted "low-temperature gasoline absorption + membrane + adsorption + vacuum desorption" hybrid; emission concentration仅为 1/40 of national standard

4.4 4-/5-Stage Cascade: Compression + Condensation + Membrane + Adsorption + Combustion

Process Positioning：

The top-tier configuration for large throughput and ultra-low emission requirements.

Process Flow：

Technical Advantages：

Closed-loop condensation + membrane design: membrane permeate (enriched gas) re-enters the condensation system for recovery, fully leveraging membrane separation's low energy consumption advantage; through continuous enrichment of low-dew-point components, they ultimately condense in the condensation system.

Extremely high recovery efficiency, meets the strictest emission standards.

Treated exhaust meets national standards for hazardous components (especially benzene series and gasoline compounds).

4.5 Absorption + Membrane + Adsorption

Process Positioning：

Absorption upfront - uses absorbent to capture some hydrocarbons under compression, while creating favorable high-pressure differential operating conditions for membrane separation; membrane mid-stage - further concentration; adsorption downstream - deep purification.

Technical Advantages：

Compression creates favorable high-pressure differential for membrane separation.

Three-stage treatment ensures ultra-low emissions, fully meeting the stringent NMHC standard of ≤120 mg/m³.

Verified in gasoline tank farm VOCs recovery and emission reduction.

Research demonstrates that hybrid membrane/condensation systems possess advantages over either separation technique alone. Each hybrid configuration has its applicability depending on specific decision preferences.

Regardless of the hybrid configuration, membrane separation plays an irreplaceable core role in the overall system:

Mid-stage hub : takes effluent from upstream processes (condensation/absorption) and provides "load-reduced" feed to downstream processes (adsorption/combustion).

Concentration-adaptive : maintains stable separation efficiency regardless of vapor concentration

Key to closed-loop recycling : in condensation+membrane hybrids, membrane permeate recycles upstream for "continuous enrichment and complete recovery".

Reduces downstream load : membrane upfront drastically reduces adsorption unit loading, extends adsorbent life, and reduces equipment size.

systems range in capacity from 1 to 700 standard cubic feet per minute and can be configured for a wide range of feed flow rates and compositions. Systems feature skid-mounted, pre-assembled design - available as standardized layouts or tailored to specific site requirements.

Typical system dimensions (MTR fuel gas recovery system): 30 ft (L) × 10 ft (W) × 14 ft (H) , weight 80,000 lb.

Gas station Stage III vapor recovery

Oil depot truck loading / tank breathing

Refinery process off-gas

Petrochemical plants (PE/PP degassing)

Marine / terminal ship loading

Chemical park centralized VOCs treatment

Pharmaceutical industry solvent recovery

Petroleum transformation industries have applied membrane processes for solvent and hydrocarbon recovery as an economic alternative to reduce emissions and reuse evaporated components.

Membrane systems are increasingly attractive for midstream applications due to lower energy consumption and reduced operational complexity. The membrane-based vapor recovery market is projected at CAGR of 7.4%.

10.1 International Standards Compliance.

Compliant with EPA (US) standards.

Compliant with EU BImSchV (German Federal Emission Control Act).

Compliant with ASME, ANSI, PED, TEMA, NEC, IEC and other international codes.

Explosion-proof rating ExdeibmbⅡCT4Gb.

Multi-stage integration : increasing integration, reducing energy consumption, improving recovery efficiency, optimizing process flow

Continued membrane advancement : as membrane technology progresses, the application cost of membrane hybrid systems will further decrease

Intelligent control : PLC/DCS fully automatic control, remote monitoring, and IoT centralized platforms already realized

Ultra-low emission drivers : increasingly stringent environmental standards (e.g. NMHC ≤ 10g/m³) are driving more enterprises toward multi-stage hybrid systems

Membrane separation technology, with its core advantages of wide concentration adaptability, low energy consumption, zero secondary waste, and small footprint, has become an indispensable key component in vapor recovery hybrid systems.

Whether it's "Condensation+Membrane" , "Membrane+Adsorption" , or the "Condensation+Membrane+Adsorption" triple cascade, membrane separation plays the core role of deep purification, load reduction, and efficiency enhancement. As environmental requirements become increasingly stringent and membrane technology continues to advance, membrane hybrid systems will become the most competitive technology pathway in the vapor recovery sector.

We provide comprehensive services from technical consultation, site assessment, system design, equipment manufacturing, installation & commissioning, to after-sales maintenance. Customized membrane separation and hybrid vapor recovery solutions are available based on specific operating conditions (gas composition, concentration, flow rate) and emission standard requirements.

Turning Every Drop of Vapor into Value

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