Activated Carbon for Gas Treatment: Mercury, H₂S, VOC & More

Q: What type of activated carbon is used for gas purification?

Coal-based pellet activated carbon (3–4 mm diameter) is the standard for most gas purification. Pellet form provides low pressure drop and uniform gas distribution. For mercury removal, the carbon is sulfur-impregnated. For H₂S, KOH or KI impregnation is standard.

Q: Can activated carbon remove mercury from natural gas?

Yes. Sulfur-impregnated carbon (10–15% sulfur) is the standard mercury guard in LNG plants. Mercury forms stable HgS in the pores, achieving outlet levels below 0.01 µg/Nm³. Beds last 3–10 years.

Q: How does activated carbon compare to iron sponge for gas treatment?

Iron sponge is cheaper per ton but has lower capacity, creates pyrophoric waste, and can't handle mercaptans. Impregnated activated carbon has higher capacity, non-hazardous waste, and multi-contaminant capability. Above 100 Nm³/hr, carbon typically has lower total cost.

Q: How long does activated carbon last in gas treatment?

Mercury guard beds: 3–10 years. H₂S removal: 6–18 months. VOC adsorbers with regeneration: 3–5 years. Biogas H₂S: 6–12 months. Higher concentrations and flow rates shorten bed life.

Q: Is pellet or granular activated carbon better for gas treatment?

Pellet is generally preferred for gas-phase applications due to predictable pressure drop, better gas distribution, and less dust. Granular is used where higher surface area per volume is needed, like BTEX guard beds.

Activated carbon is used in natural gas processing at multiple stages — from wellhead gas cleanup to pipeline-quality polishing. Each stage targets different contaminants and requires different carbon specifications.

This guide covers the main gas treatment applications, the carbon types and specs for each, and how to specify carbon for your gas processing project.

What Activated Carbon Removes from Gas Streams

Industrial gas treatment with activated carbon targets these contaminant groups:

Contaminant	Sources	Why It Must Be Removed	Carbon's Role
H₂S	Natural gas, biogas, syngas	Toxic, corrosive, poisons catalysts	Catalytic oxidation (impregnated carbon) or adsorption
Mercaptans (R-SH)	Natural gas, LPG	Odor, corrosion	Physical adsorption + catalytic oxidation
Mercury (Hg⁰)	Natural gas (0.01–5,000 µg/Nm³)	Poisons aluminum heat exchangers in LNG plants, environmental hazard	Chemisorption on sulfur-impregnated carbon
BTEX	Natural gas, associated gas	Contaminates glycol, causes emissions	Physical adsorption in micropores
Siloxanes	Biogas, landfill gas	Forms abrasive SiO₂ deposits in engines	Physical adsorption
VOCs	Process vents, tank emissions, fugitive sources	Emissions compliance, health hazard	Adsorption with optional thermal desorption

Contaminant

Sources

Why It Must Be Removed

Carbon's Role

H₂S

Natural gas,

biogas, syngas

Toxic, corrosive,

poisons catalysts

Catalytic oxidation

(impregnated carbon)

or adsorption

Mercaptans

(R-SH)

Natural gas, LPG

Odor, corrosion

Physical adsorption +

catalytic oxidation

Mercury

(Hg⁰)

Natural gas

(0.01–5,000 µg/Nm³)

Poisons aluminum

heat exchangers in LNG

plants,

environmental hazard

Chemisorption on

sulfur-impregnated

carbon

BTEX

Natural gas,

associated gas

Contaminates glycol,

causes emissions

Physical adsorption

in micropores

Siloxanes

Biogas,

landfill gas

Forms abrasive SiO₂

deposits in engines

Physical adsorption

VOCs

Process vents,

tank emissions,

fugitive sources

Emissions compliance,

health hazard

Adsorption with optional

thermal desorption

Natural Gas Processing Applications

1. Mercury Removal for LNG Production

Mercury in natural gas, even at trace levels (µg/Nm³), destroys the aluminum brazed heat exchangers used in LNG cryogenic processing. A single mercury excursion can cause liquid metal embrittlement that costs millions in repairs and months of downtime.

Sulfur-impregnated activated carbon is the standard mercury guard in LNG feed gas treatment. The sulfur reacts with elemental mercury to form mercuric sulfide (HgS), a stable and non-volatile compound trapped permanently in the carbon pores.

Specifications:

Carbon type: coal-based pellet (3–4 mm) or granular (4×10 mesh)
Impregnation: elemental sulfur, 10–15% by weight
Mercury capacity: 10–20% of carbon weight (theoretical); practical capacity depends on inlet concentration and contact time
Operating temperature: 20–60°C
EBCT: 5–15 seconds for guard beds
Outlet target: <0.01 µg/Nm³ mercury

Mercury removal beds are non-regenerable — the carbon is replaced when capacity is exhausted. Bed life ranges from 3–10 years depending on inlet mercury levels.

2. H₂S and Mercaptan Removal

For natural gas with H₂S levels below 1,000 ppm, impregnated activated carbon provides a simpler alternative to amine systems. This is common for small-to-medium gas fields, marginal wells, and gas gathering stations where installing an amine plant isn't economical.

For a comprehensive guide to H₂S removal with activated carbon — including biogas, natural gas, and refinery applications — see our detailed article on activated carbon for sulfur removal.

Key specs for gas sweetening:

Carbon type: coal-based pellet, 3–4 mm
Impregnation: KOH (5–10%) for H₂S; virgin carbon or NaOH-impregnated for mercaptans
H₂S capacity: 0.15–0.25 g/g (KOH) or 0.20–0.40 g/g (KI)
Pressure: systems must be rated for pipeline operating pressure

3. BTEX Removal from Glycol Dehydration

Triethylene glycol (TEG) dehydration systems absorb BTEX along with water from natural gas. When the glycol is regenerated, BTEX is released — creating an emission source that may require control under environmental regulations.

An activated carbon bed on the glycol regeneration vent captures BTEX before it enters the atmosphere. The carbon can be thermally regenerated or replaced periodically.

Specifications:

Carbon type: coal-based granular, 4×10 or 8×30 mesh
Surface area: ≥900 m²/g
CTC activity: ≥50% (indicates good capacity for medium-weight hydrocarbons)
Moisture resistance: low ash, hydrophobic surface preferred
Regeneration: thermal (steam or hot nitrogen) at 150–200°C

4. VOC Emission Control

Gas processing plants, compressor stations, and storage facilities produce VOC emissions from process vents, tank breathing losses, and fugitive sources. Activated carbon adsorption is the standard control technology when:

VOC concentrations are too low for thermal oxidation (below 25% LEL)
The VOC stream is intermittent or variable
Solvent recovery makes economic sense

Fixed-bed carbon adsorbers with two beds in alternating adsorption/regeneration cycles are the standard configuration. The regenerated VOCs can be recovered as liquid or routed to a flare.

Specifications:

Carbon type: coal-based pellet (3–4 mm) for low pressure drop, or granular (4×10) for higher capacity
CTC activity: ≥60% (higher CTC = more VOC capacity per bed volume)
Butane activity: ≥25% for general VOC applications
Working capacity: depends on specific VOC and regeneration conditions
Regeneration: steam at 120–150°C, or hot nitrogen

5. Biogas and Landfill Gas Upgrading

Biogas upgrading to biomethane (renewable natural gas) requires removal of H₂S, siloxanes, and VOCs before the gas enters membrane or PSA upgrading systems. Activated carbon handles all three contaminant groups, often in a multi-stage configuration:

Stage 1: KOH-impregnated pellet carbon for bulk H₂S removal
Stage 2: Virgin or specialty carbon for siloxane and VOC removal

For detailed biogas and landfill gas treatment specifications, see our sulfur removal guide.

Carbon Type Selection by Gas Treatment Application

Application	Target	Carbon Form	Impregnation	Key Spec	Bed Life
LNG mercury guard	Hg⁰	Pellet 3–4 mm	Sulfur (10–15%)	Hg capacity, low pressure drop	3–10 years
Natural gas H₂S	H₂S	Pellet 3–4 mm	KOH or KI	H₂S cap ≥0.15 g/g	6–18 months
Mercaptan odor	R-SH	Granular 4×10	NaOH or virgin	Iodine ≥900	12–24 months
BTEX from glycol	BTEX	Granular 4×10	None	CTC ≥50%, SA ≥900	6–12 months (regenerable)
VOC emission control	Mixed VOCs	Pellet 3–4 mm	None	CTC ≥60%, butane ≥25%	3–5 years (regenerable)
Biogas H₂S	H₂S + siloxanes	Pellet 3–4 mm	KOH	CTC ≥60%, pH 9–11	6–12 months

How to Specify Activated Carbon for Gas Treatment

When sourcing carbon for gas treatment, provide your supplier with:

Gas composition — full analysis including target contaminants, moisture, CO₂, and hydrocarbon content
Flow rate and pressure — Nm³/hr and operating pressure (bar/psi)
Target outlet levels — what contaminant concentrations must you achieve?
Operating temperature — ambient or elevated?
Vessel constraints — if retrofitting existing equipment, the diameter and bed height are fixed
Regeneration capability — do you have steam or hot gas available for regeneration?

Huamei Carbon produces coal-based pellet activated carbon for gas treatment applications, including H₂S removal, mercury guard beds, VOC control, and biogas upgrading. We offer virgin, KOH, KI, NaOH, and sulfur-impregnated grades in pellet diameters from 0.9 mm to 8 mm.

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Frequently Asked Questions

What type of activated carbon is used for gas purification?

Coal-based pellet activated carbon (3–4 mm diameter) is the standard for most gas purification applications. Pellet form provides low pressure drop and uniform gas distribution in fixed-bed vessels. For mercury removal, the carbon is impregnated with sulfur. For H₂S removal, KOH or KI impregnation is standard.

Can activated carbon remove mercury from natural gas?

Yes. Sulfur-impregnated activated carbon (10–15% sulfur loading) is the standard mercury guard bed in LNG and gas processing plants. Mercury reacts with sulfur to form stable HgS trapped in the carbon pores. These beds typically last 3–10 years and achieve outlet levels below 0.01 µg/Nm³.

How does activated carbon compare to iron sponge for gas treatment?

Iron sponge is cheaper per ton but has lower H₂S capacity per volume, creates pyrophoric waste, and can't handle mercaptans or other contaminants. Activated carbon — especially impregnated grades — has higher capacity, produces non-hazardous waste, and can be specified for multi-contaminant removal. For operations above 100 Nm³/hr, activated carbon typically has lower total cost of ownership.

How long does activated carbon last in gas treatment?

It depends on the application and contaminant loading. Mercury guard beds: 3–10 years. H₂S removal (KOH-impregnated): 6–18 months. VOC adsorbers with regeneration: 3–5 years. Biogas H₂S: 6–12 months. Higher inlet concentrations and higher flow rates shorten bed life.

Is pellet or granular activated carbon better for gas treatment?

Pellet carbon is generally preferred for gas-phase applications because the uniform cylindrical shape provides more predictable pressure drop and better gas distribution than irregularly-shaped crushed granular carbon. Pellet carbon also generates less dust during loading and operation. Granular carbon is used where higher surface area per volume is needed, such as BTEX guard beds on glycol systems.

Activated Carbon for Mercury Removal from Flue Gas

Mercury is a regulated hazardous air pollutant. Power plants, cement kilns, waste incinerators, and industrial boilers all emit mercury in flue gas — and most jurisdictions now require treatment before discharge.

Activated carbon is the dominant technology for mercury capture from flue gas. Two approaches exist: powdered activated carbon (PAC) injection directly into the flue gas duct, and fixed-bed granular/pellet activated carbon adsorbers downstream of particulate control. This guide covers both methods, the carbon specifications that determine performance, and how to select the right product for your plant.

Mercury Emission Regulations: Where Things Stand

Regulation	Scope	Mercury Limit	Status
U.S. EPA MATS (2012)	Coal- and oil-fired EGUs >25 MW	1.2 lb/TBtu (existing coal units)	In effect; 2024 amendments repealed Feb 2026
EU Industrial Emissions Directive (IED) / BREF	Large combustion plants, waste incineration	1–10 μg/Nm³ (varies by sector)	In effect; BAT-AELs under periodic review
Minamata Convention on Mercury	All signatory countries (140+)	BAT/BEP for new sources; national plans for existing	In force since 2017; phase-down obligations tightening
China GB 13223-2011	Thermal power plants	0.03 mg/Nm³	In effect; ultralow emission standard even stricter in some provinces

Regulation

Scope

Mercury Limit

Status

U.S. EPA MATS (2012)

Coal- and oil-fired EGUs >25 MW

1.2 lb/TBtu

(existing coal units)

In effect; 2024 amendments

repealed Feb 2026

EU Industrial Emissions

Directive (IED) / BREF

Large combustion plants,

waste incineration

1–10 μg/Nm³

(varies by sector)

In effect; BAT-AELs

under periodic review

Minamata Convention

on Mercury

All signatory

countries (140+)

BAT/BEP for new sources;

national plans for existing

In force since 2017;

phase-down

obligations tightening

China GB 13223-2011

Thermal power plants

0.03 mg/Nm³

In effect; ultralow emission

standard even stricter

in some provinces

Even in jurisdictions where enforcement has relaxed — for example, the U.S. EPA repealed the 2024 MATS amendments in February 2026 — the original 2012 MATS rule remains in effect. Most coal-fired plants that already installed mercury control equipment continue operating it. And internationally, the trend is toward stricter limits, not looser ones: the EU's BAT-AELs and China's ultralow emission standards both push mercury limits below what MATS requires.

How Mercury Exists in Flue Gas

Mercury in flue gas takes three forms, and the form determines which removal technology works best:

Mercury Form	Symbol	Characteristics	Removal Method
Elemental mercury	Hg⁰	Gaseous, insoluble in water, not captured by scrubbers or ESPs	Activated carbon adsorption (PAC or fixed bed)
Oxidized mercury	Hg²⁺	Water-soluble, captured by wet scrubbers and ESPs	Wet FGD scrubbers, ESPs, or activated carbon
Particulate mercury	Hg(p)	Bound to fly ash particles	Particulate control (ESP, baghouse)

Mercury Form

Symbol

Characteristics

Removal Method

Elemental mercury

Hg⁰

Gaseous, insoluble in water,

not captured by

scrubbers or ESPs

Activated carbon adsorption (PAC

or fixed bed)

Oxidized mercury

Hg²⁺

Water-soluble, captured by

wet scrubbers and ESPs

Wet FGD scrubbers,

ESPs, or activated carbon

Particulate mercury

Hg(p)

Bound to fly ash particles

Particulate control

(ESP, baghouse)

Elemental mercury (Hg⁰) is the hardest to capture — it passes through conventional pollution control equipment (scrubbers, ESPs) without being removed. This is exactly where activated carbon becomes essential. Activated carbon adsorbs Hg⁰ from the gas stream, either through physical adsorption or chemical reaction on the carbon surface.

The ratio of Hg⁰ to Hg²⁺ in flue gas varies by fuel type: bituminous coal produces more Hg²⁺ (easier to capture with existing equipment), while subbituminous and lignite coals produce more Hg⁰ (requires activated carbon injection for compliance).

PAC Injection: The Most Common Approach

Powdered activated carbon injection is the most widely deployed mercury control technology for coal-fired power plants. The process is straightforward:

PAC is pneumatically injected into the flue gas duct, upstream of the particulate control device (ESP or baghouse)
Mercury adsorbs onto the carbon surface during the 1–3 second residence time in the duct
The mercury-laden carbon is collected along with fly ash in the ESP or baghouse
Spent carbon/fly ash mixture is disposed of or managed as solid waste

Key Design Parameters for PAC Injection

Parameter	Typical Range	Notes
PAC injection rate	1–10 lb/MMacf	Higher rates for Hg⁰-dominant flue gas (subbituminous/lignite)
Particle size (d₅₀)	10–25 μm	Finer particles = faster adsorption kinetics but more ESP penetration risk
Injection point	Upstream of ESP or baghouse	Baghouse provides longer contact time and better performance
Flue gas temperature	250–400°F (120–200°C)	Lower temperatures favor adsorption; above 400°F performance drops sharply
SO₃ concentration	<5 ppm preferred	High SO₃ competes for adsorption sites and degrades performance

PAC injection with a downstream baghouse consistently delivers >90% mercury removal. With an ESP only, removal rates are typically 50–80%, because the shorter gas-carbon contact time (seconds vs. minutes in a baghouse filter cake) limits adsorption.

Standard PAC vs. Brominated PAC

Standard (untreated) PAC works well for Hg²⁺ capture and for flue gas from bituminous coal, which naturally produces more oxidized mercury. For subbituminous and lignite coals — where elemental mercury (Hg⁰) dominates — brominated PAC is often needed.

Brominated PAC contains bromine compounds that oxidize Hg⁰ to Hg²⁺ on the carbon surface, making it adsorbable. This allows injection rates 40–60% lower than standard PAC for the same removal efficiency. The tradeoff: brominated PAC costs more per ton, and the bromine content can affect fly ash quality for concrete recycling.

Fixed-Bed Activated Carbon for Mercury Control

For waste incinerators, cement kilns, and industrial boilers, fixed-bed activated carbon adsorbers offer an alternative to PAC injection. These systems use granular (GAC) or pelletized activated carbon in a packed bed or moving bed configuration.

Advantages over PAC injection:

Higher mercury removal efficiency — contact times of seconds to minutes vs. milliseconds for PAC injection, achieving >95% removal
Multi-pollutant capture — a single fixed bed can simultaneously remove mercury, dioxins/furans, and heavy metals
No fly ash contamination — mercury-laden carbon is separate from fly ash, simplifying waste management
Lower carbon consumption — the carbon bed is used more efficiently than dispersed PAC particles

Disadvantages:

Higher capital cost (vessel, ductwork, carbon inventory)
Pressure drop across the bed
Periodic carbon replacement required

Fixed-bed systems are standard practice in European waste incineration plants, where they're often combined with lime/calcium reagent injection to also capture acid gases (HCl, SO₂).

What Carbon Specs Matter for Flue Gas Mercury

Standard activated carbon specifications (iodine number, BET surface area) do not directly predict mercury removal performance. The critical factors are:

1. Impregnation Chemistry

For elemental mercury (Hg⁰) capture, impregnated activated carbons significantly outperform unimpregnated carbon. Common impregnants:

Impregnant	Mechanism	Best Application
Sulfur (S)	Hg⁰ reacts with S to form HgS (cinnabar) — stable, non-leachable	Natural gas processing, LNG, industrial flue gas
Bromine (Br)	Oxidizes Hg⁰ to Hg²⁺ for enhanced adsorption	Coal-fired power plants (PAC injection)
KI (Potassium Iodide)	Hg⁰ reacts with KI to form HgI₂	Waste incinerators, low-temperature gas streams
Chloride (HCl, CaCl₂)	Promotes Hg⁰ oxidation on the carbon surface	Enhanced performance in low-chloride coals

Impregnant

Mechanism

Best Application

Sulfur (S)

Hg⁰ reacts with S to form

HgS (cinnabar) — stable,

non-leachable

Natural gas processing,

LNG, industrial flue gas

Bromine (Br)

Oxidizes Hg⁰ to Hg²⁺ for

enhanced adsorption

Coal-fired power

plants (PAC injection)

KI (Potassium Iodide)

Hg⁰ reacts with KI

to form HgI₂

Waste incinerators,

low-temperature gas streams

Chloride (HCl, CaCl₂)

Promotes Hg⁰ oxidation

on the carbon surface

Enhanced performance

in low-chloride coals

Sulfur-impregnated carbon is the most widely used for fixed-bed mercury removal because HgS is thermally stable and passes TCLP leaching tests. For PAC injection in coal plants, brominated carbon dominates because of its lower injection rate requirement.

2. Carbon Form Factor

PAC (powdered, <75 μm): for duct injection systems; maximum surface-to-volume ratio for fast kinetics in short contact time
Pelletized (1.5–4 mm cylinders): for fixed-bed adsorbers; low pressure drop, high mechanical strength, low dust generation
GAC (granular, 4×8 to 8×30 mesh): for fixed-bed or moving-bed systems; balance of contact efficiency and pressure drop

3. Base Material

Both coal-based and coconut shell-based carbons are used for mercury applications. Coal-based pelletized carbon is more common in fixed-bed flue gas systems because of its broader pore size distribution (better for large Hg-impregnant complexes) and higher mechanical strength at the larger pellet diameters needed for low pressure drop.

4. Operating Temperature

Mercury adsorption on activated carbon is strongly temperature-dependent. Below 300°F (150°C), adsorption capacity is highest. Above 400°F (200°C), physical adsorption weakens, and even chemisorption (with impregnants) becomes less efficient. If your flue gas is above 350°F, consider gas cooling before the carbon treatment stage.

Mercury + Dioxin: Combined Removal in One System

Waste incinerators and some industrial boilers must control both mercury and dioxins/furans (PCDD/F). Activated carbon is effective for both pollutants, and a single fixed-bed system can handle both simultaneously.

Dioxins adsorb onto activated carbon through a similar mechanism to mercury — surface adsorption driven by van der Waals forces. The key difference: dioxin adsorption favors carbons with high mesopore volume (pores 2–50 nm), because dioxin molecules are large and need accessible pore structures.

For combined mercury + dioxin removal:

Use sulfur-impregnated pelletized carbon (handles mercury) with sufficient mesopore development (handles dioxins)
Design EBCT for dioxin removal first (typically the limiting factor at ≥2 seconds gas residence time)
Mercury removal will typically exceed 95% if the system is designed for adequate dioxin removal

European waste incineration BAT/BREF guidelines typically specify activated carbon injection rates or fixed-bed contact times sufficient for both mercury and dioxin compliance in a single treatment step.

Huamei Activated Carbon for Flue Gas Mercury Control

Huamei manufactures pelletized activated carbon and powdered activated carbon for gas-phase applications. For mercury removal from flue gas:

Fixed-bed mercury adsorbers: HME-AC pelletized activated carbon (coal-based, steam activated, 1.5–4 mm diameter). Available with sulfur impregnation (S-HME-AC) or KI impregnation for enhanced Hg⁰ capture. CTC 20–100%, ash ≤12%.
PAC injection systems: wood-based or coal-based powdered activated carbon. Available in standard and brominated grades for different coal types and flue gas chemistries.
Combined mercury + dioxin systems: pelletized impregnated carbon designed for waste incineration flue gas treatment meeting EU IED requirements.

We supply activated carbon to power plants, cement kilns, and waste incinerators in more than 40 countries. If you're planning a mercury control upgrade or building a new treatment system, send us your flue gas composition data — temperature, Hg speciation (if available), SO₂/SO₃ levels, particulate loading — and we'll recommend the appropriate carbon grade and estimate consumption rates.

Frequently Asked Questions

What type of activated carbon is best for mercury removal from flue gas?

For PAC injection in coal-fired power plants, brominated powdered activated carbon delivers the best performance at the lowest injection rate, especially for subbituminous and lignite coals with high elemental mercury (Hg⁰). For fixed-bed systems in waste incinerators and industrial applications, sulfur-impregnated pelletized activated carbon is the standard choice because it forms stable HgS that passes leaching tests.

How much mercury can activated carbon remove from flue gas?

PAC injection with a downstream baghouse typically achieves >90% mercury removal. PAC injection with an ESP only achieves 50–80%. Fixed-bed activated carbon adsorbers can exceed 95% removal when properly designed with adequate contact time and appropriate impregnation chemistry.

Does activated carbon remove dioxins from flue gas too?

Yes. Activated carbon adsorbs both mercury and dioxins/furans (PCDD/F) from flue gas. A single fixed-bed activated carbon system can be designed to handle both pollutants simultaneously, which is standard practice in European waste incineration plants. The carbon should have sufficient mesopore development to accommodate the large dioxin molecules.

What is the difference between standard PAC and brominated PAC for mercury?

Standard PAC relies on physical adsorption to capture mercury. Brominated PAC contains bromine compounds that chemically oxidize elemental mercury (Hg⁰) to oxidized mercury (Hg²⁺) on the carbon surface, making it much easier to adsorb. Brominated PAC typically requires 40–60% lower injection rates than standard PAC for the same mercury removal efficiency, especially in flue gas from subbituminous and lignite coals.

Is mercury-laden spent activated carbon hazardous waste?

It depends on the mercury concentration and local regulations. In the U.S., spent mercury-laden carbon must pass the TCLP (Toxicity Characteristic Leaching Procedure) test. Sulfur-impregnated carbons form HgS (cinnabar), which is highly stable and typically passes TCLP, allowing disposal as non-hazardous waste. Untreated spent carbon with high mercury loading may fail TCLP and require hazardous waste management. Always test spent carbon before disposal and follow local environmental regulations.

Planning a mercury control system? Send us your flue gas data and compliance targets. We'll recommend the right activated carbon — PAC, pelletized, or impregnated — and provide samples for testing.