Thursday, January 20, 2011

Getting at the gasoline, part one

Distillation is a chemical process that separates a substance into it's constituent chemical components.

Generally, there are two methods of doing this, depending upon the nature of the substance being broken down: "destructive distillation" and "fractional distillation".

Destructive distillation is done when solids need to be deconstructed for their individual contents. For example, if you heat wood in a closed container without oxygen present, then you can collect the methane gas that is given off. The wood is forever changed, though, and becomes charcoal.

Most of us are more familiar with the other process, called "fractional distillation" which is used mainly to separate liquids. Fractional distillation is possible because various liquids boil at different temperatures.

A person who makes whiskey back in the woods is using the chemical principle of fractional distillation. He is after only one chemical - ethanol - so he doesn't need to have apparatus that is too precise with regards to temperature, as long as his fire is just hot enough to boil off the alcohol in his mixture.

Usually fractional distillation is more precise than that, and great attention is paid to the various boiling temperatures of the components that make up the substance being distilled. Perhaps the most common example is the fractional distillation (refining) of crude oil.

We will take a closer look at the process of fractional distillation next time.


  1. Cannabis biomass? Hemp does have many uses.

  2. Speaking as a man who has driven a wood-fired tractor, I'd just like to point out that in wood-gasification by pyrolysis, the resultant fuel gas is about twenty% carbon-monoxide, 20% hydrogen , less than 5% methane, and the rest is nitrogen.

    Methane's not really a big part of it at all.

    Being a bit obsessive about combustion and flames and heat, I've had a bit of an interest in making heat out of various forms of biomass for some time. There are freely available plans on the internet to make simple wood-gas fired camping stoves. You put wood in, and with no smoke at all, get a little stove that burns with blue jets of flame.
    All made out of old cans!

  3. @Jeff King - It IS intriguing! Thanks for stopping by.

    @A. - I don't think anyone noticed that except you and me. :)

    @Soubriquet - Your knowledge of stuff never ceases to amaze me. I am SO interested in those kinds of things. I must study up more. So much to learn, so little time...

  4. My problem too. So many things i'd like to learn, so little time.
    And i really want to go time travelling, but preferably without dying from some gnat-bite or other.

    Combustion though. One of the cool things about making pottery is that it gives you an excuse to play with fire. And to find the best way of getting 25 feet of flame and 1% ash out of a tiny sliver of wood.
    Oh. And burning old crankcase oil at 2300 degrees F.
    It's all good clean fun. Cement boils, melts, makes a mottled green glass at that temperature.



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