activated carbon specifically for biogas treatment
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Iodine-impregnated activated carbon (most commonly used and most efficient)
Working principle: Iodine acts as a catalyst to catalytically oxidize H₂S into elemental sulfur (S) or sulfuric acid (H₂SO₄) under normal temperature and aerobic conditions.
Chemical formula: H₂S + ½O₂ → S + H₂O or H₂S + 2O₂ → H₂SO₄
Advantages
High sulfur capacity: It has a very strong ability to carry sulfides and a long service life.
Quick activation: It can quickly achieve efficient removal effects.
Strong adaptability: Not sensitive to fluctuations in temperature and humidity.
Applicable scenarios: The vast majority of biogas projects, especially those with high H₂S concentrations (>1000 ppm) or requiring extremely low outlet concentrations (<50 ppm).
2. Alkaline impregnated activated carbon (such as KOH/NaOH impregnated)
Working principle: Through a chemical neutralization reaction, H₂S reacts with an alkali to form sulfide salts.
Chemical formula: H₂S + 2NaOH → Na₂S + 2H₂O
Advantages
It has a very good initial removal effect on high-concentration H₂S.
It can simultaneously remove part of the carbon dioxide (CO₂) and increase the calorific value of biogas.
Disadvantage
The sulfur capacity is usually lower than that of iodine-impregnated carbon because the reaction products can clog the channels.
In a humid environment, alkali may be washed away.
Applicable scenarios: It is suitable for working conditions where the concentration of H₂S fluctuates greatly and the acidity of biogas is strong.
3. Metal oxide-impregnated activated carbon (such as Fe₂O₃, ZnO
Working principle: Stable metal sulfides are generated through chemical reactions.
Chemical formula: H₂S + ZnO → ZnS + H₂O
Advantages: The reaction is irreversible and the removal accuracy is high.
Disadvantages: The active components are non-renewable, the sulfur capacity is limited, and the cost is relatively high.
Applicable scenarios: Mainly used for fine desulfurization, and relatively less applied in the biogas field.
Ii. Key Selection Indicators
When choosing activated carbon, the following physical and chemical indicators need to be comprehensively considered:
1. Pore structure (crucial)
Give priority to activated carbon with well-developed mesopores (mesoporous pores). The products of H₂S catalytic oxidation reaction (elemental sulfur or sulfuric acid) have a relatively large molecular volume and require sufficient mespores (2-50 nm) as "reaction sites" and "transport channels". Macropores (>50 nm) are conducive to the diffusion of reactants and products.
Avoid using activated carbon mainly composed of micropores. Micropores (<2 nm) are prone to being clogged by reaction products, leading to rapid deactivation of activated carbon.
2. Mechanical strength
High-strength activated carbon must be selected. In a fixed-bed adsorption tower, activated carbon is subjected to the pressure from the upper layer of materials and the friction caused by gas flow. Low-strength activated carbon is prone to pulverization, which leads to increased bed resistance (elevated pressure drop), and may even clog pipelines and damage back-end equipment.
Key indicators: Hardness of the ball disc ≥ 95%. This is a very important industrial indicator.
3. Carbon tetrachloride adsorption value (CTC value) or iodine adsorption value
For impregnated carbon, the CTC value or iodine value is no longer the primary indicator, as its core work is chemical catalysis rather than physical adsorption.
An activated carbon with a medium CTC value (such as 50%-70%) but well-impregnated and with well-developed mespores has a desulfurization performance far superior to that with a high CTC value but not impregnated or with well-developed micropores.
4. Moisture content
Biogas is usually saturated with water vapor A certain level of humidity is beneficial for catalytic oxidation reactions because water molecules serve as the medium for the reaction.
However, the moisture content of activated carbon at the time of leaving the factory should be controlled reasonably (such as less than 5%) to avoid unnecessary weight and transportation costs.
5. Bulk density
The bulk density affects the filling volume and equipment design. Under the premise of meeting other performance requirements, a moderate heap density is sufficient.
6. pH value
For impregnated carbon, the pH value is usually determined by the impregnating substance (iodine-impregnated carbon may be neutral or weakly acidic, while alkaline impregnated carbon is strongly alkaline).
Summary and selection suggestions
Feature recommendation selection (preferred) : Alternative solutions are not recommended
Type: Iodine-impregnated activated carbon, alkali-impregnated activated carbon, common unimpregnated activated carbon
The mesopores are well-developed, the structure of medium and macropores is reasonable, and micropores are dominant
High mechanical strength (ball disk hardness ≥95%), medium strength, low strength, prone to powdering
The core indicators, sulfur capacity (request this data from the supplier), CTC value and pH value, only look at the iodine adsorption value
The final advice for you
Contact the activated carbon supplier directly and clearly inform them that your application is "biogas desulfurization".
Ask them if they have a special "iodine-impregnated activated carbon for biogas desulfurization".
Request the technical parameter table of the product from the supplier, with a focus on: iodine impregnation amount, sulfur capacity, mechanical strength (ball disk hardness), and pore structure description.
Working condition matching: At the same time, inform the supplier of your specific working conditions, such as the inlet concentration of H₂S in biogas, the expected outlet concentration, gas flow rate, temperature and pressure. They will provide you with the most suitable model and dosage suggestions.
By following the above guidelines, you can select efficient, economical and durable activated carbon products in a very targeted manner to ensure the stable operation of the biogas desulfurization system.
