Overview
Methane below the lower flammability limit of 5 % cannot be burned. Thermal flow-reversal reactors need at least 0.2–0.3 %; most catalytic and biological oxidizers need around 500 ppm. Coal mine ventilation air holds 0.1–1 %, dairy barn exhaust holds 5–100 ppm, and passive landfill vents hold 3–12 %. The energy is present, the climate impact of capturing it is large, and no technology takes it.
ARBOK-METRAP treats that threshold as a design parameter rather than a physical constant. The stream is concentrated on TEG by rapid-cycle adsorption with vacuum regeneration, without heat input, up to the level at which existing utilization equipment becomes operable.
The distinguishing point is not the cycle, which is well known, but the sorbent. Zeolites and carbon molecular sieves lose capacity irreversibly to the moisture and hydrogen sulfide present in every real stream, which is why conventional schemes carry a drying and desulfurization stage that dominates their economics. TEG is hydrophobic and chemically inert, so that stage is removed.
Applications
Coal mine ventilation air; dairy, pig and poultry housing exhaust; passive vents and weak gas at closed municipal landfills; stripped gas from vacuum degassing of anaerobic effluent; biogas upgrading. The same unit and cycle also address hydrogen sulfide, ammonia, volatile organic compounds and exhaust-air deodorization.
Operating Principle
The feed passes through a TEG bed. Methane is retained on the surface while nitrogen and oxygen pass through. On saturation the chamber is isolated and switched to vacuum desorption, and the enriched methane is withdrawn. Multiple chambers operate in a continuous rotation — adsorbing, regenerating, and equalizing pressure in turn — so the treated flow is continuous and part of the compression work is recovered between chambers.
A vacuum exhaust step preceding the main desorption clears residual air from the interstitial volume, raising the methane fraction in the product without changing the adsorption or desorption pressures. Without it the product is diluted by the free volume of the vessel.
Regeneration is by vacuum only. At cycle times of tens of seconds thermal regeneration is physically impossible, which is what ties METRAP to the rest of the vacuum platform.
Key Parameters
| Parameter | Value |
|—|—|
| Process temperature | ambient — no heat supplied, no setpoint |
| Desorption pressure | Deep vacuum (sub-atmospheric) |
| Bed pressure drop, design limit | Low, set by mine ventilation regime rather than by energy |
| Cycle time | Tens of seconds |
| Fan energy penalty | 0.8 % of the thermal power carried by the stream |
| Adsorption heat load | ≈ 200 kW at 40 kmol/h, removed by the graphite matrix |
| TEG working surface | 2,400–3,600 m²/g (4–12× hard carbon, 2–4× activated carbon) |
| TEG particle | 3–5 million separated single-atom graphene layers |
| TEG stability | hydrophobic; to 450 °C; inert to sulfur and nitrogen compounds |
| TEG filtration | up to 98 % of particles below 0.2 µm; regenerable up to 30 times |
| TEG production | mobile units up to 1 t/h, diesel or gas, 8-foot container, 1–3 kWh/kg |
| Form factor | 20-foot container, 15–30 m², two operators, no consumables |
| Product concentration target | below the 5 % lower flammability limit, with automatic diversion above 4 % |
Architecture and Components
Dust removal and droplet separation on the inlet; multiple parallel adsorption chambers with blocked TEG sorbent and straight channels; switching valve manifold; vacuum pump set, liquid-ring preferred as intrinsically spark-free; product line with flame and detonation arresters; continuous methane, oxygen and bed-temperature monitoring; full bypass of the ventilation stream in under 30 s.
Advantages
Takes streams nothing else takes. The 5–100 ppm range of livestock exhaust has no competing technology; a 2025 review in the Journal of Dairy Science states this explicitly.
Removes the pretreatment stage. Hydrophobicity and chemical inertness eliminate the drying and desulfurization that govern the cost of conventional adsorptive upgrading.
Removes the heat problem. The graphite matrix carries away the ≈ 200 kW of adsorption heat within the cycle, which a packed carbon bed cannot.
Costs almost nothing to push air through. Macroporous structure keeps the fan penalty at 0.8 % of the stream's thermal power — decisive at 83 m³/s.
Shares the site's existing vacuum loop. Where ZWD or AZOW is already installed, methane recovery is an addition to an existing loop rather than a standalone plant.
Sorbent made on site. Mobile TEG production removes the supply chain from the operating model.
Integrations
ARBOK-NaTEG · Arbok-ZWD Gasification · Arbok Zero-Organic-Waste (AZOW) · ARBOK-Gas · Arbok-STEC · landfill leachate · Ammonia Trap
One vacuum loop serves the whole site. ZWD runs under deep vacuum, where water boils at ambient temperature, at 1 kWh/t with heat recovery to 98 %, water recovery to 99.98 % and separation below 30 nm. AZOW applies the same physics to organic effluent. Vacuum degassing of anaerobic effluent removes up to 94 % of dissolved methane and 88 % of hydrogen sulfide. METRAP runs under its own deep-vacuum desorption regime. The difference between applications is only what is fed to the module.
Typical integrated configurations:
- Landfill — ZWD on leachate, METRAP on passive vents, enriched gas to heat returned into the same loop
- Livestock — METRAP on exhaust ventilation with simultaneous ammonia and H₂S capture, closing the odor and permitting question
- Coal mine — mine water and ventilation methane on one manifold
- Anaerobic treatment — METRAP as a second stage behind a vacuum degasser
Deployment & Operation
Containerized module mounted on concrete in the open air, connected to the ventilation duct, the vent well or the degasser outlet. Modular scaling at 50,000–100,000 m³/h per module. Two operators, no consumables. Inlet dust below 1 mg/m³ and droplet separation are mandatory; bed pressure drop is monitored as the fouling indicator.
At landfill scale, where gas flows are two to three orders of magnitude below mine scale, a mobile execution is possible: arrive, work the site, move on.
TRL
Not assigned. The process scheme, material parameters and mass and energy balances are prepared; no pilot has been run under this name.
Market Potential
The biomethane potential of EU manure alone is about 23 billion m³ per year with less than 3 % realized. The unused 22.3 billion m³ carries 799 PJ — the heating demand of 14.8 million European homes — and represents 476 million tons of CO₂ equivalent annually.
Per site: a single mine ventilation shaft at 300,000 m³/h and 0.5 % methane yields 5,140 t of methane per year, 153,000 t CO₂-eq avoided and 9 MW of recovered thermal power. Livestock is the open niche; landfills are the compact, mobile-execution segment; biogas upgrading is a mature market entered through the removal of pretreatment rather than through product purity.
Typical Project Economics
CAPEX and OPEX are not fixed at the technology level — they are calculated per site.
Site-level anchors: a landfill treating 100,000 t of leachate per year returns roughly €240,000 from water and salts through ZWD, with the gas line added on top without separate infrastructure. On farms the feedstock price is negative — manure disposal is paid at about $20/t, digestate $15/t, municipal sludge up to $100/t — so margin is taken at both ends. At farm and landfill sites the driver is regulatory penalty rather than revenue, and the two together are reported to give roughly three times the result assumed on entry.
Risk Factors
The methane isotherm on TEG under process vacuum at near-ambient temperature is the parameter that decides the equipment volume, and it is the least commonly measured; it must be determined experimentally before design. Kinetics at 30–60 s cycles will fall below equilibrium capacity. Working capacity after 10⁴–10⁵ cycles with accumulated dust and moisture is unknown. Siloxanes and halogenated organics at landfills are the components that historically destroy landfill-gas equipment. The 5–15 % explosive window makes the product concentration a regulatory decision rather than an optimization one. The container size for TEG production is recorded as 8 ft here and 10 ft in ARBOK-NaTEG — one of the two is stale.
Related Technologies
ARBOK-NaTEG · Arbok-ZWD Gasification · Arbok Zero-Organic-Waste (AZOW) · ARBOK-Gas · Arbok-STEC · Ammonia Trap · ARBOK-Arctic