Hydrothermal carbonization (HTC)

[Gerrit]

Just checking an old steam engineers handbook to find that steam at 400 F, which is pretty close to 200 C, has a pressure of 250 lbs./sq.in.

My high pressure sprayer (air mist) actually pumps at just over 200lb./sq.in., and it just uses pipe to conduct the spray to the nozzles...

Whatever, I was checking stovetop autoclaves on the 'net (the cheapest boiler-type thing I could find) and they seem rated at only about 160 C.

[Fukudairafarm]

Originally Posted by Gerrit

The name of the catalyst? They might have given it away. Check out the photo at the top of the article referred to above.
Gerrit

You don't have to look at the label, just click on the movie link at the bottom right of the last page of the PDF. You will be brought to the Max Planck Society homepage. Then you can watch the quicktime movie, where they say water is added, with a citric acid catalyst, then it is heated for 12 hours at 180 degrees C.
However, they don't give us the pressure. They only mention it is heated in an autoclave. I wonder if a pressure cooker would work?

[Gerrit]

Thanks for that tip to watch the video! It looks simple doesn't it? A dollop of lemonade with a dash of iron ions heated up to 180C...and presto - charcoal!

But there is a catch - the high pressure boiler required. (Go back to message #33 in this thread to see a letter I posted there from the researcher.) At 180C, the steam pressure in any boiler will build up to about 145 psi. Unfortunately, steam pressure food cookers are only rated for about 15 psi. To get the higher pressures, you need at least a stovetop autoclave.

[Gerrit]

For the do-it-yourselfer to experiment with hydrothermal carbonization, I wonder if an old hydraulic cylinder would be the ideal boiler? They are generally designed for 3,000 psi, which is way more than needed...

[mervenvs]

Hi there,

I would like to quote this for information:

The reaction was carried out in a nonstirred, 60 mL capacity Teflon-lined stainless steel autoclave, which was put in a programmable oven. In a typical procedure, 5-20 g of biomass was dispersed in 40 mL of deionized water. Ten milligrams of citric acid was added to ensure comparable acidic carbonization conditions. The autoclave was sealed and tempered at 180-250 °C (default 200 °C) for 16 h and then allowed to cool to roomtemperature. The products were filtered off, washed several times with distilled water and absolute ethanol, and finally dried in a vacuum at 60 °Cfor4h.

Warning: we seriously caution against repeating the experiments without additional safety measures using too high concentrations of too easily carbonizable material, as the reaction is exothermic

source: Titirici et al. Chem. Mater. 2007, 19, 4205

The citric acid is just used to catalyse the reaction in the beginning. Then acid is formed so the reaction is autocatalysed (this is basically a dehydration). This is just to avoid a induction time that would cost more energy that what is needed to produce the minute quantity of citric acid needed (you can press a slice of lemon to provide citric acid).

I have access to scientific litterature. Any question is welcome.

[mervenvs]

ooops, looks like this thread was a bit dead

[Getting A Life]

I have questions

With a pressure valve rated at required psi, and a reaction vessel rated above this, and a lemon tree in the yard for the odd squeeze, this would work safely?

What ratio water:biomass for vegetable byproduct (brassicas, herbs, toms, peppers, cucurbits etc)?

What temperature for creating a garden char product with resins etc intact?

I could put excess steam into a reservoir of water in a greenhouse each evening with such a system.

Or is it so dangerous one should not have such a unit in a suburb. I've seen steam boiler explosions, nasty.