I've been kicking around the idea of building a simple solar oven to remove the methanol from byproduct for soap making. I don't have a recovery still set up yet and I don't want to boil the methanol out into the air.

It would be based on something like this:



I'd put the byproduct into a sealed black bucket and place it in the solar oven. If I plumbed some tubing to the bucket lid and routed it through the back wall and into a receiver located in the shady area below and behind the oven, would the vapor condense inside the tubing and drip into the container? I don't care how long it would take if it actually worked. I could leave it for several days if necessary. There is virtually no temperature control in solar ovens so I understand there would be water mixed in the recovered methanol. Temperatures of 180°C have been seen inside these types of ovens with direct sun exposure so I believe it would get hot enough. If this actually works could the methanol/water mix be distilled with a proper still at a later date?

Ken

Bunk,

I've never tried it, but I've been wanting to for some time. I think it's worth trying, and you've come up with a simpler method than I was considering.

Ken, surface area is helpful for getting all of the methanol out of a batch of glycerol. At our shop we do it in an appleseed...We are circulating our gly or bio during the recovery phase to speed up recovery. If you do it in an unstirred bucket you might get some pockets of unrecovered methanol

What about some sort of small black tank with a little circ pump? I found a very small water heater at a salvage yard that could do the trick... strip the guts out of a 10 gal heater and paint it black, then build the oven around that, rig it up with a little solar pump like a mini appleseed??

A plastic bucket will not be too pretty after it reaches 180F.

The other challenge is getting it hot enough. I take our recovery all the way up to 212 F before I feel safe using the GLY for soap. Its not just getting it over the BP of methanol, but driving it all out. This takes higher temps for some reason.

Good thinking...
Farmer

Thanks Rick & Farmer.
From what I've been reading the interior temps (when empty) can get up to 180°C (356°F). The byproduct wouldn't get nearly that hot as long as it had something in it to boil off. After the boiling was finished it would probably take a very long while to climb anywhere near deep-fry temps. The sun would probably set before it even got close. I don't know exactly what to expect from it because I've never built or used one before. But, even if it doesn't archive the highest temperatures I'm hoping for, a plastic bucket still probably wouldn't last too long. Maybe I should start with mason jars and scale up from there.

Ken

I was going to try building a solar still similar to the photo you put up. I was going to dump the glycerin into a shallow tray and allow the methanol vapors to rise and condense on the glass. The glass would be angled down, and as the condensed liquid ran down the glass it would get collected and routed to a collection vessle outside of the cooker/sunhouse/still. I was going to start very small using that foam board insulation for the bottom and walls with some spare glass I have lying around. I want to paint it all black to absorb as much solar radiation as possible. I figure putting it in a shallow tray will ensure that all of the liquid heats to well above 140F. We'll see, its pretty cold in CT right now and I am not sure how much solar gain I would get.

Hi folks

You want your glyc container to be as wide as the window (window as wide as possible too, to get as many kW as you can) and as shallow as possible, or you'll just get it up to temp ... and the sun will set!

Thin and wide glyc container will speed up the response time for heating, then you can de-meth in small batches.

If you try to do a big batch, or with a cube-shaped container, you'll wait forever.

Right on Ghraham! In my post above I indicated I was going to use a tray. I had planned to build the solar box only a little bigger than the tray. I've been rummaging through the wife's cooking elements looking for a suitable baking tin/pan. Should make for a fun experiment this summer.

I experimented a bit with my first solar oven today. It's not really a solar oven as much as it's a small wedge shaped clear plastic disposable container with a black plastic base slightly larger than a delicious slice of apple pie with just the right amount of cinnamon. I set it in the sun and stuck the outdoor temperature probe from my indoor/outdoor digital thermometer inside. The interior temp hit 138°F (59°C). The outside air temp was 50°F (10°C). Not too bad considering the lack of insulation and the angle of the January sun. I think this is going to work well in the summer.

Ken

Thats great! Thanks for the update. I plan to give it a try this summer as well.

you may also want to look over on the solar side of the forum, they have a string about a beer can solar heater that gives much higher temps.
here's the link
~Harvey~

I've seen the beer can heaters before. I'm still brainstorming. The more I think about it the more my design ideas change. I'm currently thinking about using a box type solar oven to pre-heat the byproduct in a bucket metal pail and pipe it through a control valve into a vapor sealed sloped solar oven extension. It will gravity feed from the pail through the pipe onto the solar heated slide and slowly run down it like a sliding board. This should give it plenty of surface area and heat. Maybe a piece of rain gutter painted black for that part.

It would look something like this dehydrator but longer and less of an angle for slower flow. I'd have to plumb a catch container at the bottom to recover the byproduct.



Ken