Impregnated Activated Carbon
Specialized H₂S removal carbons are created through impregnation—a process where the activated carbon is treated with alkaline chemicals that react with hydrogen sulfide, converting it into stable, non-volatile compounds that remain trapped in the carbon structure.| Common Impregnation Chemicals | ||||
| Type | Sodium Hydroxide (NaOH) | Potassium Hydroxide (KOH) | Potassium Carbonate (K₂CO₃) | Potassium Iodide (KI) |
| Mechanism | 2NaOH + H₂S → Na₂S + 2H₂O | 2KOH + H₂S → K₂S + 2H₂O | K₂CO₃ + H₂S → K₂S + H₂O + CO₂ | Catalytic oxidation of H₂S to elemental sulfur |
| Loading content | 5-15% by weight | 6-18% by weight | 8-20% by weight | 1-5% by weight |
| Advantages | Cost-effective, high reactivity, widely available | Higher capacity than NaOH, faster kinetics | Good moisture resistance, stable performance | Catalytic action, very high efficiency |
| Best for | Medium H₂S concentrations (500-3,000 ppm) | High H₂S concentrations (>3,000 ppm) | High humidity biogas streams | Ultra-low H₂S requirements (<1 ppm outlet) |
This type of activated carbon has been specially processed to have a high specific surface area and microporous structure. It is designed for efficient removal of H₂S and can be used for H₂S-containing waste gas treatment in sewage treatment plants, smelters, etc. And it is especially suitable for sulfide control in biomethane plants, with a removal efficiency 40-50 times that of ordinary activated carbon.
Original Activated Carbon
For effective VOC removal in biogas applications, we recommend pellet activated carbon with an iodine number ≥800 mg/g, with premium products offering ≥1,000 mg/g.Higher iodine numbers correlate with:
• Greater micropore volume for capturing small VOC molecules
• Larger total surface area for maximum adsorption sites
• Enhanced capacity for aromatic compounds (benzene, toluene, xylene)
• Better retention of esters, ketones, and organic acids
4mm Cylindrical Pellet Activated Carbon is our primary recommendation for biogas VOC removal due to its optimal balance of performance and practicality.
| Size | 4± 0.5 mm | |||
| Iodine Number | 900-1,100 mg/g | |||
| Surface Area | 1,000-1,200 m²/g | |||
| Hardness |
≥95% |
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| Ash content | ≤8% (coal-based) or ≤3% (coconut shell) | |||
| Moisture | ≤5% | |||
Optimal Design and Loading Strategy
For maximum efficiency and cost-effectiveness, we recommend loading the adsorption vessel in two distinct layers, with each layer targeting a specific contaminant group.
Recommended Vessel Configuration |
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| ⬇ GAS INLET (Contains H₂S + VOCs) | ||||
| UPPER LAYER: High Iodine VOC Carbon 4mm Cylindrical Pellets | Iodine ≥900 mg/g Removes: Siloxanes, BTEX, Esters, Organic Acids Typical Bed Depth: 400-800 mm |
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LOWER LAYER: H₂S Removal Carbon |
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| ⬇ CLEAN GAS OUTLET (H₂S <4 ppm, VOCs <5 mg/Nm³) |
Why this Configuration Works Best
The sequential two-layer loading strategy offers several critical advantages:H₂S Removal First (Bottom Layer)
Gas enters the vessel and immediately contacts the H₂S removal carbon in the lower section. The alkaline impregnated carbon chemically reacts with hydrogen sulfide, converting it to stable sulfide salts (Na₂S, K₂S) that remain trapped in the carbon structure. This prevents H₂S from reaching the upper VOC carbon layer.
VOC Removal Second (Top Layer)
After H₂S removal, the partially cleaned gas flows upward into the VOC removal carbon layer. Here, the high-surface-area carbon physically adsorbs organic compounds through van der Waals forces and pore trapping. This layer handles siloxanes, aromatics, and other volatile organics.
Protection of VOC Carbon
By removing H₂S first, we prevent it from occupying adsorption sites in the VOC carbon, allowing the VOC carbon to work exclusively on organic compounds. This maximizes the utilization of both carbon types.
Independent Replacement
The two-layer system allows monitoring and replacement of each carbon type based on its individual saturation rate, rather than replacing all carbon when only one component breaks through. Based on dynamic adsorption capacity calculations, H₂S adsorption usually reaches saturation faster and requires priority monitoring. If the activated carbon treatment effect alone is insufficient, it can be combined with a pre-alkaline scrubber (to remove acid gases) or a back-end catalytic oxidation (to decompose residual VOCs) to form a multi-stage purification system.
Conclusion
At Zhulin Carbon, we've dedicated over two decades to developing and supplying activated carbon solutions specifically engineered for biogas purification challenges. For specific questions about your biogas purification challenges, contact our engineering team atinfo@zhulincarbon.com or call +86-19949132731.RFQ:
Can customers purchase a single activated carbon that treats both Volatile Organic Compounds (VOCs) and Hydrogen Sulfide (H₂S)?Activated carbon mainly relies on the pores to absorb different gases, so one type of activated carbon can adsorb both gases at the same time. However, the ability of original activated carbon for H2S removal is very small. If clients want better results, it is recommended to purchase two types of activated carbon for adsorption.
