Turning Coconut into Charcoal

Another term for activated carbon is activated charcoal. Both of these terms refer to a charcoal material that has been reheated and oxidized (“activated”) to increase porousness. So, one of the necessary steps toward turning a coconut into activated carbon is to turn that coconut into charcoal. How does one do that?

With heat. Lots and lots of heat.

But it’s not enough to simply throw a coconut into the fire. Before heating the coconut, one must empty the coconut’s milk, scrape out the flesh, and ensure that the shell is clean and dry. The exterior part of the coconut will need to be cleaned of fibers, as well.

Charring

Once the shell is cleaned and dried, there are a variety of ways to turn this hard, woody material into charcoal. This process of turning coconut shell into charcoal is also called charring or pyrolysis. Essentially, the coconut shells need to be subjected to very high temperatures (between 300 and 500 degrees Celsius) for several hours in order to break down into charcoal. The vessel in which this process happens may vary.

One of the most popular methods of coconut charcoal production happens in a drum kiln, a lidded tank with a small chimney that creates higher interior temperatures by limiting oxygen flow. The bottom layer of coconut shell in the kiln will carbonize first, resulting in a glowing orange color emanating from the bottom coals. From the initial application of heat to this glowing orange stage often takes around 12 hours.

Pacification

Once this has happened, air flow is cut off to the bottom layer of the drum and the coals start to cool—this stage is called the “pacification phase.”   This is important because if the charcoal is allowed to burn for too long, it will turn to ash. The shells need to be caught at the appropriate time in the carbonization process—not before and not after.

After the carbonization process, one is left with coconut charcoal, also known as coconut carbon. The next step is activating the coconut carbon in order for it to be effective as a filter.

Steam Activation

The primary purpose of activation is to increase the pore size of the carbon so that it can catch more particulates and contaminants. Coconut carbon can be activated by soaking with chemicals like phosphoric acid, but there is also a steam method for activation.

In the steam method, an inert gas is brought to a temperature of about 800-1100 degrees Celsius in a rotary kiln, creating steam which dehydrates the charcoal and reduces the level of VOCs in it. This temperature is ideal—much higher and the charcoal starts to burn, leaving the manufacturer with less of the finished product. Much lower temperatures and the process takes far too long.

Dual Rotary Kilns

While the coconut carbon is steaming, its pores are enlarged until they are the perfect size to catch the small molecules in water. Once the pores have reached the correct size, you are left with activated coconut carbon. Finally, the activated carbon is crushed, graded and sorted into different mesh sizes.