[Bioconversion] Fireball update #2

[AJH]

On Mon, 14 Nov 2005 19:26:22 -0500 (EST), Jeff Davis wrote:

>Driving into work, today, I was tring to remember a charcoal term. Think
>its "activated charcoal". I think that is were the charcoal get
>heated/cooked more, so that all the (for lack of better word) tar is
>removed. I wonder by stealing charcoal out of my stove if I could be
>getting activated charcoal and maybe it is too porous. Just thinking out
>loud. Later!

OK you need to distinguish the various stages of "cooking" wood to
make charcoal from activating it. Carbon ( and probably many other
substances) has the ability to adsorb chemicals onto its surface,
there is a weak bond which holds the chemical, so carbon can filter
out some compounds and lock them this way. As this filtering requires
a large surface area a number of processes are used to increase this
surface area by treating suitable carbons (animal bone charcoal being
a favourite) with other chemicals to pit the surface and thus magnify
the surface area available for adsorption to take place. This is
similar to what has evolved in our lungs, we have acres of surface
area contained in our chests. The amount of surface area is measured
by its iodine number but I'm not sure how it is done.

So all freshly made charcoal has the ability to adsorb chemicals on
its surface, activated charcoal has a much greater surface area.

Simplistically the amount of fixed carbon in a sample of charcoal is
related to the temperature at which it is cooked, charcoal made in a
simple clamp at ~300C will be <80% fixed carbon and the other 20% less
volatile tars still in the matrix, yields can be above 45%. Increase
the temperature to 900C  and fixed carbon shoots up to nearly pure
carbon plus ash but yield drops to 15%.
>
>Your friend and antipodean....

Ah there you are, it's a bit hard to track where people are posting
from with some e-mail addresses.