1. Coal-Based Granular Activated Carbon (Briquetted & Crushed) — 8×30 mesh, 1100 iodine, 230 molasses value
1.1 Product Characteristics
Coal-based granular activated carbon (GAC), produced by briquetting → carbonization → activation → crushing, typically features:
- Low ash (≤8%)
- High mechanical strength (≥95%)
- Low floating rate
- A well-balanced pore structure (micropores + mesopores)
This pore distribution allows granular activated carbon to adsorb both small and medium-to-large molecules, making it a common choice in many water treatment systems.
1.2 Main Applications
Suitable for:
- Drinking water deep purification
- Industrial wastewater decolorization
- Municipal water treatment
- Air purification
- Continuous flow systems requiring regeneration
1.3 Decolorization Performance
In the orange pigment solution test (static), it required over 6 hours to reach a noticeable decolorization effect.
1.4 Why the Decolorization Rate is Slower
As a granular activated carbon, it has:
- Smaller contact area with liquid
- Longer internal diffusion path
- Slower mass transfer
Therefore, the decolorization speed is significantly slower compared to powdered activated carbon.
Please watch the video.
2. Coconut Shell Activated Carbon — 8×30 mesh, 1300 iodine
2.1 Product Characteristics
Coconut shell activated carbon has a highly developed microporous structure and typically a high iodine value (1000–1300 mg/g).
This makes it ideal for small-molecule adsorption.
2.2 Main Applications
Widely used in:
- Drinking water purification
- Pharmaceutical & food-grade filtration
- VOC adsorption & air purification
- Gold recovery (Au(CN)₂⁻ adsorption)
- Small molecule organic removal
2.3 Decolorization Performance
Under the same test conditions, the coconut shell carbon showed weaker decolorization for the purple pigment solution compared to coal-based GAC.
2.4 Why the Decolorization Effect is Limited
Reason: Decolorization often involves large molecular pigments, but coconut shell carbon has:
- Highly microporous structure
- Fewer mesopores and macropores
- Lower capacity for large molecules
Therefore, it is not the optimal choice for decolorization applications requiring the adsorption of larger pigment molecules.
3. Wood-Based Powdered Activated Carbon (PAC) — 200 mesh, MB value 20
3.1 Product Characteristics
Wood-based powdered activated carbon is extremely fine (200 mesh) with:
- Very large surface area
- Abundant mesopores (ideal for pigment removal)
- Fast adsorption rate
- High methylene blue value (strong, large-molecule adsorption indicator)
3.2 Main Applications
Commonly used in liquid-phase decolorization, such as:
- Sugar decolorization
- MSG, pharmaceuticals, and oil purification
- Chemical and food processing
- Emergency wastewater treatment
3.3 Decolorization Performance
Under the same test conditions, it achieved significant decolorization within 0.5–2 hours, outperforming granular activated carbon significantly.
3.4 Why PAC Performs the Best
- Massive contact area — powder mixes fully with liquid
- Shortest diffusion distance — pigments quickly reach internal pores
- Mesopore-rich structure — ideal for medium/large pigment molecules
Therefore, powdered activated carbon is the fastest and most efficient option for decolorization.
4. Experimental Results Summary
Decolorization efficiency ranking:
Powdered activated carbon (PAC) > Coal-based GAC > Coconut shell activated carbon
Decolorization speed:
PAC ≫ Granular activated carbon
Reason: differences in particle size, pore size distribution, and diffusion paths — not product quality.
Comparison of the decolorization performance of three types of activated carbon
| Types of activated carbon | Pore characteristics | Decolorization performance | Decolorization speed | Applicable Scenarios |
| Wood powder charcoal | The most abundant central hole | ★★★★★ | ★★★★★ | Food decolorization, pharmaceutical decolorization, emergency wastewater treatment, and high-difficulty decolorization |
| Coal-based granular carbon | Micropores + Mesopores | ★★★★☆ | ★★☆☆☆ | Continuous water treatment, a renewable system, medium-difficulty decolorization |
| Coconut shell granular charcoal | High proportion of micropores | ★★☆☆☆ | ★★☆☆☆ | Small molecule adsorption, air purification, drinking water treatment |
5. The significance of iodine value and methylene blue value in decolorization
A common misconception in decolorization applications is that “the higher the iodine value, the better the decolorization effect.” In fact, the iodine value primarily measures the microporous structure and is suitable for adsorbing small molecules. Decolorization mainly relies on the mesoporous structure.
Therefore, the methylene blue value (MB value) should be more closely monitored, as it more accurately reflects the adsorption capacity of activated carbon for medium to large molecular weight pigments. Coal-based activated carbon, due to its higher proportion of mesopores, has a stronger decolorization ability than coconut shell activated carbon; while wood-based powdered activated carbon has the most abundant mesopores, thus providing the best decolorization effect. A correct understanding of the difference between iodine value and MB value is crucial for process selection and cost control.
6. Recommendations for selecting activated carbon in decolorization applications
When choosing activated carbon for decolorization, please consider the following factors:
6.1 Types of Target Pollutants
Macromolecular pigments → Powdered activated carbon / Mesoporous granular activated carbon
Small molecule organic matter → Coconut shell activated carbon
6.2 Process Requirements
Batch processing → PAC (fastest)
Continuous flow/regeneration system → Coal-based granular activated carbon
6.3 Cost and Operational Considerations
PAC fades the fastest, but it is more difficult to restore.
Granular activated carbon can be regenerated, but the regeneration rate is relatively slow.
Choosing the right activated carbon can significantly improve decolorization efficiency, reduce chemical consumption, and optimize overall operating costs.
7. Common causes of color fading failure and how to solve them
Common decolorization failures include:
selecting activated carbon unsuitable for decolorization (such as using coconut shell activated carbon to treat large molecular pigments),
- insufficient dosage,
- inadequate stirring, too short contact time, solution pH deviating from the optimal range,
- and excessively low temperature, leading to a slower adsorption rate.
- Additionally, if the pore structure of the granular activated carbon does not match the pigment size, it can also result in the pigment not being adsorbed.
Solutions typically include:
- replacing with wood-based powdered activated carbon with well-developed mesopores,
- appropriately increasing the dosage,
- improving stirring efficiency,
- extending the contact time, or adjusting the contact mode in a continuous system to ensure a more complete adsorption process.
Conclusion
The differences in decolorization performance between coal-based activated carbon, coconut shell activated carbon, and powdered activated carbon stem from the characteristics of raw materials, pore distribution, and particle size, rather than quality issues.
- For applications requiring rapid and deep decolorization, powdered activated carbon remains the most effective choice.
- For continuous systems requiring mechanical strength and regeneration capabilities, coal-based granular activated carbon is a reliable option.
Frequently Asked Questions
1. Which type of activated carbon has the best decolorization effect?
Powdered activated carbon (PAC) typically offers the best decolorization performance due to its advantages, such as a large surface area, rich mesoporous structure, and a short diffusion distance.
2. Why does powdered activated carbon work faster than granular activated carbon?
Because PAC mixes directly with the liquid and provides a significantly higher contact area, pigment molecules can reach the internal pores more quickly, thus achieving rapid adsorption kinetics.
3. Can coconut shell activated carbon be used to remove pigments?
It can remove small organic molecules, but its predominantly microporous structure limits its ability to adsorb large pigment molecules. Therefore, it is not the best choice for strong decolorization processes.
4. Why is the decolorization rate of coal-based granular activated carbon relatively slow?
Compared to PAC, granular activated carbon has a longer diffusion path and a smaller contact area, so pigments need more time to enter the internal pores, resulting in a slower decolorization rate.
5. How to choose the right activated carbon for decolorization?
- Macromolecular pigments → Powdered activated carbon
- Continuous flow system → Coal-based granular activated carbon
- Small molecule organic matter → Coconut shell activated carbon
6. Is powdered activated carbon suitable for continuous filtration systems?
Not an ideal choice. PAC is difficult to recycle and is better suited for intermittent processing. Granular activated carbon is better suited for continuous and regenerable systems.
If you require sample testing, technical data sheets, or assistance in selecting suitable activated carbon for your decolorization application, our technical team can provide support based on your specific process conditions.
