[Terrapreta] volatile matter and char

[Sean K. Barry]

Hi Gerrit,

What is the source/cause of high volatile matter in char?  Does this VM (since it is 'volatile') decrease/volatize by itself over a short time?  


According to the article "VM" content is "a measure of the susceptibility of charcoal to further decompose and form carbon when heated."


Translation, please?? 

We've asked Dr. Michael J. Antal this very question, when he was subscribed to the list.  He was vague about what VM actually is then, too.  It is measurable as the percent weight (VM%) of a charcoal sample (this is done using a "proximate analysis" test), but its chemical analysis is a mystery.  Some others have recently mentioned VM has an insecticidal effect (Dr. Reddy).  Edward Someus also says high VM% content on charcoal is a problem in soil.  People working with Eprida, Danny Day, Dr. Christoph Steiner, etc., were wondering if the VM% was a benefit as "food for microbes".

>From what I have read about pyrolysis reactions, the VM% content is be dictated primarily by maximum internal particle temperature in the char bits (this can be somewhat related to residence time in the reactor).  Low VM% is obtained at high temperatures, basically.  Higher temperatures produce a more "activated" charcoal too ("activated" charcoal has a high adsorption surface area).  Now, charring biomass on a forest floor or in the soil will not likely allow such high temperatures (~1000C) to be achieved, so one wonders how the original Terra Preta soil was made with low temp char and does not suffer from toxicity.  Perhaps any toxicity in fresh low temperature charcoal is lost over time once it is in the soil.

As you suggest, VM is "volatile", so I imagine it does dissipate somewhat off the surface of the charcoal, through reduction by oxygen from the air, or water.  This has been recognized as a "storage" problem for fresh charcoal.  Fresh charcoal can spontaneously ignite!  THis occurs when the VM reacts and creates heat).  Another question I had was,  ... What about charcoal from natural forest fires that are quenched out by rain, for instance?.  Wouldn't these be low temperature and leave toxins in the soil?  But, as has been observed, soils on which forest fires have run across do not stop plant growth.  In fact, there is a "bloom" of new growth.  So, what's up? (with this "toxicity of of high VM% on low temperature charcoal" scare).

I think this premise needs testing.  I think no none who has provided any "field results of using charcoal in soil" here yet, has known that the charcoal they used was low VM% or even what temperature the char was made at (no data on this presented).  I can make charcoal with my reactor and control the max temperature inside the reactor core.  I can do a "proximate analysis" test on any charcoal produced and make measurements of VM%.  I cannot discover any ways yet to characterize the chemical analysis of the VM in any way.  Dr. Antal got short with me when I asked him about doing this.  He told me, like in the paper, Volatile Matter is only quantifiable, not characterize-able.  (Who gets to say, "That's bunk!" to a PhD?).

It may be that the processes required to produce low VM% charcoal are more expensive than otherwise, so these producers are trying to play up the value of their product.  I think the premise needs testing.  I think most testing occurring now is NOT seeing this detriment in their plant growth results.

Carry on.

Regards,

SKB
  ----- Original Message ----- 
  From: Gerald Van Koeverden<mailto:vnkvrdn at yahoo.ca> 
  To: Terrapreta Preta<mailto:terrapreta at bioenergylists.org> 
  Sent: Thursday, December 20, 2007 7:53 PM
  Subject: [Terrapreta] volatile matter and char


  G.


  The article is at the following link:


  http://www.ctahr.hawaii.edu/DeenikJ/Downloads/Tai_Charcoal_CTAHR_Sym_2007.pdf<http://www.ctahr.hawaii.edu/DeenikJ/Downloads/Tai_Charcoal_CTAHR_Sym_2007.pdf>
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