The Versatile Purifier: Coal Based Activated Carbon

From water filtration to air purification and beyond, activated carbon is an incredibly useful material with a wide range of applications. But what exactly is activated carbon, and why is coal such an important source for its production? Let's take a closer look at this highly porous, uniquely purifying substance.

What is Activated Carbon?

Activated carbon is a form of carbon processed to have an exceptionally high surface area due to its extensive internal pore structure. Just one gram can have a surface area in excess of 500 square meters, all located within a microscopic maze of tiny pores and crevices.

It's this tremendous surface area that gives activated carbon its amazing adsorptive properties. Adsorption is the ability to attract and trap molecules and particles from gases, liquids, or dissolved substances through chemical attraction and binding them to the carbon's porous surfaces.

This makes activated carbon extremely effective at removing a wide variety of contaminants including volatile organic compounds (VOCs), chlorine, odors, heavy metals, and more. As liquids or gasses pass through, the activated carbon acts like a selective molecular sieve and filter.

Producing Activated Carbon from Coal

While activated carbon can be manufactured from various carbon-rich precursor materials like wood, coconut shells, and even olive pits, coal is one of the most commonly used sources. Its natural abundance, low cost, and high carbon content around 90% make coal an ideal feedstock.

There are two main methods of deriving activated carbon from coal - physical activation and chemical activation.

The physical activation process involves two main steps. First, the raw coal is heated to extremely high temperatures around 600-900°C in the absence of oxygen, which drives off any volatile components and non-carbon impurities. This leaves behind char consisting of the coal's concentrated carbon content.  

Next, this char is re-heated and exposed to an oxidizing gas stream like carbon dioxide, steam, or air. This selectively burns away some of the carbon atoms creating the highly porous activated carbon structure.

For chemical activation, the raw coal is first mixed with dehydrating agents like phosphoric acid or potassium hydroxide. The mixture is heated to around 450-900°C in an inert environment which chemically etches the internal surfaces to create pores. This single step combines both carbonization and activation in one process.

Potential Environmental Benefits

In addition to its wide-ranging purification uses, producing activated carbon from abundant coal sources can offer environmental advantages compared to other precursor materials like coconut shells which have to be grown and shipped from tropical regions.

Many coal-based activated carbon manufacturers are also looking at ways to incorporate waste coal products from mining operations into their processes. This gives new value to coal residues that would have otherwise been discarded.

Applications of Coal Activated Carbon

Activated carbon derived from coal is deployed across numerous sectors to remove contaminants and purify liquids and gasses:

- Drinking water and wastewater treatment to remove chlorine, pesticides, herbicides and other organic matter

- Air filtration (homes, vehicles, industrial facilities) to control odors and toxic emissions

- Food and beverage processing, from purifying sugars to decaffeinating coffee and tea 

- Metal and chemical processing, such as removing mercury from industrial waste streams

- Environmental remediation, like vapor extraction of contaminated soils and groundwater

With its ability to be highly tuned and optimized based on the raw coal feedstock and specific activation process, coal based activated carbon continues to find new applications as a versatile, cost-effective purification solution.