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Topic: Pyrolysis of wood  (Read 612 times)

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Offline gatewood

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Pyrolysis of wood
« on: February 19, 2020, 04:23:15 AM »
I've been producing some charcoal through wood pyrolysis for some time now, however, I've started to become intrigued with the volatilites that are given off by the wood. Does anyone understand this process and what is generally produced by such process? Do they hold any practical use?

Offline Enthalpy

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Re: Pyrolysis of wood
« Reply #1 on: February 19, 2020, 02:48:15 PM »
Pyrolysis is long known, though not in every detail because so many reactants and products are involved. Wiki for instance should tell more.

The gaseous (and condensible) products include things of little value like water vapour and carbon dioxide, plus gases that can burn, for instance CO and methanol, plus dirty things like tar which are used because they're available.

The products of wood pyrolysis are similar to coal pyrolysis (but not the same). They are toxic too, and use to have even less value. I've heard of no present commercial use. But when gasoline was unavailable, some people ran their car from the gases.

Offline gatewood

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Re: Pyrolysis of wood
« Reply #2 on: February 21, 2020, 09:59:04 PM »
Pyrolysis is long known, though not in every detail because so many reactants and products are involved. Wiki for instance should tell more.

The gaseous (and condensible) products include things of little value like water vapour and carbon dioxide, plus gases that can burn, for instance CO and methanol, plus dirty things like tar which are used because they're available.

The products of wood pyrolysis are similar to coal pyrolysis (but not the same). They are toxic too, and use to have even less value. I've heard of no present commercial use. But when gasoline was unavailable, some people ran their car from the gases.

I heard that, you could extract useful hydrocarbons, such as benzene, xylene and toluene from the destructive distillation of wood and charcoal.

Offline billnotgatez

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Re: Pyrolysis of wood
« Reply #3 on: February 21, 2020, 10:41:36 PM »
To get an idea of your setup,
are you  treating chemistry as a hobby at home?

What kind of woods are you putting through this process?

Are you creating the charcoal like they did in the old days or do you have a more advanced setup?

Inserted below is a WIKI link to aid in the discussion.
https://en.wikipedia.org/wiki/Charcoal

Offline gatewood

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Re: Pyrolysis of wood
« Reply #4 on: February 22, 2020, 12:35:35 PM »
To get an idea of your setup,
are you  treating chemistry as a hobby at home?

More or less, yes (im well aware of the dangers of these chemicals). I'm wondering what kind of tar I'll get in the presence, as well as in the absence of oxygen (so im building a simple reactor).

What kind of woods are you putting through this process?

Chloroxylon and teak.

Are you creating the charcoal like they did in the old days or do you have a more advanced setup?

Inserted below is a WIKI link to aid in the discussion.
https://en.wikipedia.org/wiki/Charcoal

Yes basically. As stated by my post, I just recently became interested in the volatilites of wood, destructive distillation, so I'm not terribly familiar with any process yet. I only know that, if I condense the gases, I'll get some wood tar that I would need to further refine (with fractional distillation), to get these chemicals in pure form.

Preparation of benzene:

https://www.brainkart.com/article/Preparation-of-benzene_36508/

Given, that is coal tar, but its not that different.
« Last Edit: February 22, 2020, 01:45:04 PM by gatewood »

Offline rolnor

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Re: Pyrolysis of wood
« Reply #5 on: February 22, 2020, 04:38:37 PM »
I made pyrolysis of wood as an experiment as a youth. The tar is mainly used to preserve wood, or? I think before the gas was used in large scale in the same way as propane is today, it is called "lysgas" in swedish, "lightgas".

Offline billnotgatez

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Re: Pyrolysis of wood
« Reply #6 on: February 22, 2020, 06:30:07 PM »
...
Chloroxylon and teak.
...

That will make for some expensive charcoal

Offline gatewood

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Re: Pyrolysis of wood
« Reply #7 on: February 22, 2020, 10:48:43 PM »
...
Chloroxylon and teak.
...

That will make for some expensive charcoal

yeah thanks for the help... not if its made from dead, decaying plant matter
« Last Edit: February 23, 2020, 01:25:47 AM by gatewood »

Offline gatewood

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Re: Pyrolysis of wood
« Reply #8 on: February 25, 2020, 10:09:07 PM »
I got the answer I needed:

https://chemistry.stackexchange.com/questions/6954/why-does-a-wood-fire-create-benzene/7004

If anyone else is interested.


mod edit for clarity
« Last Edit: February 26, 2020, 12:30:06 AM by billnotgatez »

Offline billnotgatez

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Re: Pyrolysis of wood
« Reply #9 on: February 26, 2020, 02:05:36 AM »
From WIKI
Quote
Modern methods employ retorting technology, in which process heat is recovered from, and solely provided by, the combustion of gas released during carbonisation.[5] Yields of retorting are considerably higher than those of kilning, and may reach 35%-40%.

It appears that during the commercial process they burn the gasses produced during the charcoal process as fuel to produce the charcoal.


Offline Borek

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Re: Pyrolysis of wood
« Reply #10 on: February 26, 2020, 03:29:55 AM »
Or they make a lot of smoke.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Enthalpy

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Re: Pyrolysis of wood
« Reply #11 on: February 26, 2020, 07:13:43 PM »
I heard that you could extract useful hydrocarbons, such as benzene, xylene and toluene from the destructive distillation of wood and charcoal.

These three compounds are useful but very cheap. Extracted train-wise from petrol, with very little transformation. I can't imagine wood pyrolysis on reasonable scale competing against that. Same for methanol and more compounds.

More generally, petrol and coal too are pyrolysis products of wood and similar substances. You find similar compounds in all of them. They are the compounds that form indistinctly from very rough and uncontrolled reactions. You get aromatics because of the H/C ratio and the stability of aromatic rings. Lighter alcohols, aldehydes and ketones at the beginning, polycyclic aromatics at the end.

In this context, I doubt that a major product of wood pyrolysis has a market value not spoiled by coal and petrol products. What you might try:

Find a minor compound that is not usually extracted from coal nor petrol. Since petrol is already well pyrolysed and coal even more, you might have better chances with the early pyrolysis products. Just a gut feeling. If you obtain for instance a solvent with pleasant odour, different from turpentine, it has more value than white spirit.

Or do more than a bare pyrolysis. Add some cheap compound (natural gas, alcohol, aldehyde, amine...) and check is something more useful comes out. Again, early products should be more differentiated than late ones.

Pyrolysis makes many moderate carcinogens, so you'll have to sort out the products.

Offline gatewood

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Re: Pyrolysis of wood
« Reply #12 on: February 27, 2020, 02:07:33 PM »
From WIKI
Quote
Modern methods employ retorting technology, in which process heat is recovered from, and solely provided by, the combustion of gas released during carbonisation.[5] Yields of retorting are considerably higher than those of kilning, and may reach 35%-40%.

It appears that during the commercial process they burn the gasses produced during the charcoal process as fuel to produce the charcoal.

They do that to avoid spreading the volatilites all over the place (as Borek mentioned). Extra heat is not necessary though, I guess it might speed up the process. Interesting.

Its actually pretty easy to do (if anyone is interested), a dense cloud of wood gas will quickly ignite and further break down into CO and CO2, which avoids extra contamination of carcinogenic compounds.

Which wiki article is that?
« Last Edit: February 27, 2020, 02:26:09 PM by gatewood »

Offline gatewood

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Re: Pyrolysis of wood
« Reply #13 on: February 28, 2020, 12:32:58 PM »
I heard that you could extract useful hydrocarbons, such as benzene, xylene and toluene from the destructive distillation of wood and charcoal.

These three compounds are useful but very cheap. Extracted train-wise from petrol, with very little transformation. I can't imagine wood pyrolysis on reasonable scale competing against that. Same for methanol and more compounds.

More generally, petrol and coal too are pyrolysis products of wood and similar substances. You find similar compounds in all of them. They are the compounds that form indistinctly from very rough and uncontrolled reactions. You get aromatics because of the H/C ratio and the stability of aromatic rings. Lighter alcohols, aldehydes and ketones at the beginning, polycyclic aromatics at the end.

In this context, I doubt that a major product of wood pyrolysis has a market value not spoiled by coal and petrol products. What you might try:

Find a minor compound that is not usually extracted from coal nor petrol. Since petrol is already well pyrolysed and coal even more, you might have better chances with the early pyrolysis products. Just a gut feeling. If you obtain for instance a solvent with pleasant odour, different from turpentine, it has more value than white spirit.

Or do more than a bare pyrolysis. Add some cheap compound (natural gas, alcohol, aldehyde, amine...) and check is something more useful comes out. Again, early products should be more differentiated than late ones.

Pyrolysis makes many moderate carcinogens, so you'll have to sort out the products.

" Lighter alcohols, aldehydes and ketones at the beginning"

You know why is that exactly?

Thanks for the input, thats some pretty useful insight right there :)
« Last Edit: February 28, 2020, 02:02:48 PM by gatewood »

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