What is activated Carbon?
Activated carbon is a form of carbon that has been treated to make it extremely porous and thus has a very large surface area available for adsorption and chemical reactions.
It is usually derived from charcoal (also called activated carbon, activated charcoal, or activated coal).
Importance of activated carbon:
Activated carbons are considered to be the most successful adsorbent materials due to:
1- High adsorption capacity for pollutants, e.g., dyes, heavy metals, pharmaceuticals and phenols.
2- They possess a large surface area.
3- They possess different surface functional groups, which include carboxyl, phenol, quinone, lactone and other groups bound to the edges of the graphite as layers.
So, they are considered good adsorbents both in liquid and gas phases.
The most widely used carbonaceous resources for the manufacturing of activated carbons are coal, wood and coconut shell.
These origins are quite expensive and often imported into many countries; later making it necessary for developing countries to find a cheap and available source for the preparation of activated carbon.
The surface area of activated carbon
It is treated physically or chemically to generate micro-fissures that hugely increase its adsorptive surface area.
The great surface area (between 500 and 1500 m2/g) and electrical charge successfully adsorb a wide range of polar combinations, particularly phenols and their derivatives.
Examples of activated carbon applications
1- Drinking water purification
2-Wastewater treatment.
3-Glycerin manufacturing.
4- Dye removal
5-Decolorize wine.
6- Odor control systems.
Deodorizing carbons are valuable in removing mercaptan off-odors, but may also remove desired flavor compounds.
Activated carbon may also give the treated wine an atypical odor.
Additionally, activated carbon has an oxidizing asset.
Although this can be valuable, trials using small wine samples are vital to avoiding undesirable, unexpected effects.
Alternative sources
To reduce the production cost of activated carbons, some green by-products are lately suggested:
1. Olive-waste cakes
2. Cattle-manure compost.
3. Bamboo materials.
4. Apple pulp.
5. Potato peel.
6. Banana peel.
Environmental pollution
Environmental pollution can be defined as the contamination of the physical and biological components of the earth/atmosphere system to such a normal level of environmental processes that are badly affected.
The presence of contaminants in the environment leads to harm to humans or other living organisms.
Environmental pollution is categorized into three main groups:
1- Air pollution.
2-Water pollution.
3-Soil pollution.
Lignocellulosic Bio-mass
Biomass-derived from plants, called lignocellulosic biomass, is the richest and most bio-renewable bio-mass on earth.
The major components of woody plants, as well as grasses and agricultural residues, are three structural polymers:
1- Lignin (10–25%),
2- Hemicellulose (20–30%)
3-Cellulose (40– 50%).
Non-structural components such as:
1- Proteins
2- Chlorophylls
3- Ash
4-Waxes
5- Tannins (in the case of wood)
6- Pectin (in most fibers)
Specifically, lignocellulosic wastes are a low-cost natural carbon source for the production of various materials including activated carbon.
The lignin is considered to be the main sponsor for activated carbons’ productive properties such as the mean pore size versus the specific porous volume achieved by all original components whatever their weight input.
Activated Carbons Production
The production of activated carbons from lignocellulosic materials is a two-stage process:
1- Carbonization at low temperatures (700–800 K), in the absence of oxygen, to eliminate volatile materials.
2-Subsequent activation at higher temperatures (1100–1300 K) to increase the porosity and the surface area of the solid.
Activation Process
The process of activation can be carried out in different ways:
1-Chemical activation uses chemicals such as (KOH, H3PO4, and ZnCl2.
2-Physical / Thermal activation using CO, air, or water vapor.
Advantages of physical activation
The low-cost process with a lower environmental impact.
Advantages of chemical activation
Porosity improvement (adsorption capacity) of the final material.
Pre-treatment process of biomass should follow the following criteria:
1-Low energy and resource consumption.
2-Low water and chemical consumption.
3-Low operation risk and safe to operate.
4-Cost-effective
5-Eco-friendly.
Optimized manufacturing processes allow the production of materials with surface areas ranging up to 3000 m2g-1 and pore volumes up to1.8 cm3g-1, bringing about an immense diversity of applications.
The challenge is to develop adsorbents that are not only cost-effective and environmentally friendly but also have high efficiency, selectivity and regeneration δ rate and cycles.
Factors affecting activated carbon properties
The preparation conditions of carbonaceous materials affect the physicochemical properties of the produced material such as:
1- Surface area.
2- Pore size distribution.
Another critical factor is the physicochemical properties of the origin itself; depending on:
1-Weather conditions.
2-Harvesting methods.
3-The season that it is collected.
4-Initial moisture and oxygen content.
5- Derived components fraction of cellulose, hemicellulose, and lignin.
References
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[13] Moreno-Piraján, J. C., & Giraldo, L. (2011). Activated carbon was obtained by pyrolysis of potato peel for the removal of heavy metal copper (II) from aqueous solutions.Journal of Analytical and Applied Pyrolysis, 90(1), 42-47.
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