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Old 02-26-2006, 09:42 AM   #1 (permalink)
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Activated carbon

Some interesting info on what keeps outsiders from smelling our babies.

There are two main methods of producing activated carbon: Chemical activation and Steam activation.

Chemical activation is generally used for the production of activated carbon from sawdust,
wood or peat and uses chemicals for activation.

Chemical activation involves mixing an inorganic chemical compound with the carbonaceous raw material
and the most widely used activating agents are phosphoric acid and zinc chloride.

Use of Zinc Chloride poses the danger of zinc traces in the end-product.
The fall in imports of Chinese activated carbon into the UK has been attributed to their continuous use of zinc chloride in the Chinese production process.

Steam activation is generally used for coal-based, coconut shell and grain
based activated carbons and uses gases, vapours, or a mixture of both.

Most activated carbon operations which have come on stream in the last twenty years have been based on coal,
mostly bituminous coal but also lignite and anthracite.

Coal is by far the most widely-used raw material in the industrialised countries,
as many companies are related to coal processing and steel industries.

In industrialised countries, capacity expansions are either underway or under consideration by American Norit,
Calgon Carbon, Chemviron and Atochem North America.

Examples where local suppliers and cost factors have led to the use of raw materials other than coal are
Norit's use of sawdust in the UK and Westvaco's use of wood in the USA.

Norit obtain wood raw materials as waste-products from the saw mill-milling industry located between Glasgow and Edinburgh.
Wood used by Westvaco is a waste-product from the company?s own paperboard operations.

In developing countries coconut shells are by far the most widely used raw material.

However, investment in activated carbon plants in developing countries have been slow,
due to high investment costs in plant and machinery and high licensing costs of proprietary production processes.
Individual manufacturers restrict the use of their proprietary production process,
stopping the transfer of technology of activated carbon manufacturing to developing countries to make good use
of valuable waste-product like refuse grain and coconut shells.

Coconut shells have a high volatile content and give a lower yield of activated carbon than grain and coal,
but their abundant supply as a waste-product from the coconut oil and desiccated coconut industry proves to be relative
competitive than grain and coal-based activated carbon producers who have to pay for their grain and coal feedstock.

The fixed carbon content of various raw materials used for the production of activated carbon is as follows:

Material Approximate carbon content (%)
Soft wood 35
Hard wood 40
Coconut shell 35
Grain and agro products 40
Lignite 60
Bituminous coal 75
Anthracite 90

The conceptual framework offered by the technology supplier is based on processing an existing feedstock,
which has resulted from an already operating processing line.

For example, the discarded shells from coconut, walnut or similar product operations are processed to produce a high quality activated carbon.
The technology for producing activated carbon is straightforward,
the refuse feedstock is processed with a thermal desorption process with a final product of activated carbon.
The thermal desorption process is a separation process that removes unwanted materials under varying heat applications.

This technique is low-cost and meets all environmental standards,
where others need expensive solutions to achieve the same results.
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