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Enviromental Aspects of Activated Carbon

Activated carbon, when manufactured from a sustainable source such as coconut shell, is in many ways the ideal ‘carbon capture’ product.

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Image by Brian Patrick Tagalog
Coconut Trees
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How is Activated Carbon Environmentally friendly?

Nothing is wasted from the harvesting of coconuts. The flesh is used predominantly for food and cooking, the milk/water is used in beverages and pharmaceuticals, and the cold pressed meat is also used for cosmetics. The shells can be used to manufacture activated carbon and even the coir is used to make articles such as door mats in mostly cottage industries operated in developing countries. The shell of the coconut is regarded as a waste product or by-product of the food industry.

"Nothing is wasted from the harvesting of coconuts."

 

Most coconuts fall on the ground and, unless germinated or harvested, are wasted. In nature, these coconuts decompose naturally to carbon dioxide and water (from whence they came, via photosynthesis) and a few other, minor, volatile, organic compounds. There are some natural, inorganic compounds produced also that are representative of the elements in the Earth’s crust.  The carbon dioxide slowly emitted over a period of several months is part of the natural carbon cycle.

 

The shell of the harvested coconut is frequently used as fuel for cooking and heating in developing countries. In which case, the carbon dioxide emitted from the combustion is returned to atmosphere, again with no net gain of carbon to the environment, unlike the burning of fossil fuels, such as oil or coal.

"The shell of the harvested coconut is frequently used as fuel for cooking and heating in developing countries."

 

In contrast, the manufacture of activated carbon from the coconut shell results in a permanent sequestration of the carbon. The carbon cycle is disrupted and the carbon dioxide that would be in the atmosphere is now locked as elemental carbon which is stable on the geological timescale of some 107 years. So, even if the activated carbon is not recycled and is sent to landfill, the net ‘carbon’ contribution to the atmosphere is negative. For every ton of activated carbon produced, 3.7 tons of carbon dioxide are essentially prevented from being released to the atmosphere. (Each deodorant can, containing 120 g of activated carbon locks away the equivalent of 440 g of CO2).

"The carbon dioxide that would be in the atmosphere is now locked as elemental carbon."

Coconut shells have a high energy content, provided by nature, essentially from sunlight (photosynthesis). In the activated carbon manufacturing process, the coconut shells are firstly converted to charcoal by heating in a deficiency of oxygen. In a modern plant, the coconut shells are charred in a reactor and the volatiles released from this pyrolysis are captured and used under controlled conditions to produce thermal energy for the next phase of the process, activation. Activation requires the treatment of the char with high temperature steam which is raised from the carbonisation stage. The process is therefore self-sustaining with no net requirement for energy.

T A Ryan - 23 Nov. 2021

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