Thursday, April 21, 2016

Chemistry for Preppers: Distillation

One of the most common and useful chemical processes for preppers is distillation. Everyone has seen the water purification systems that boil the source water, cool the steam, and produce pure (distilled) water. The simple “solar still” method of collecting water uses the same principle at a much lower production rate and without an extra energy source.

How It Works
Distillation is a method of separating mixed chemicals based upon their boiling points (BP). If the difference in boiling points is more than roughly 25° C a simple still will work, but if the difference is less than 25° C you'll need to look into fractional distillation. The boiling points for various chemicals can be found in most chemistry reference books as well as the ubiquitous Material Safety Data Sheets (MSDS or SDS) that producers are required to make available for every product they handle.

For most survival situations, specific chemical composition is not going to be known and resources are going to be scarce, so a simple still will be the best choice. For production of fuel or other trade goods, a fractional still will make a more pure product but requires more time and materials. Running your product through a still more than once will usually give a more pure product; before the introduction of reverse osmosis we used “triple distilled” water as pure water for general chemistry lab work.

There are mixtures that cannot be separated by use of a still. If the boiling points are too close to each other, or if they form an azeotrope (a mixture where the BP of the mixture is higher or lower than either of the constituents), you will not be able to get complete separation from a still. Be careful if dealing with petrochemicals or explosive compounds as they may decompose (violently) when heated, long before they reach boiling point.

If you are distilling anything for consumption, use only food-safe material in the construction of your still. Galvanized metal and lead-based solder will impart toxic levels of metals into your product. Stick with glass, copper, or stainless steel if at all possible.


Bottoms: The material left over after you have distilled out what you want.

Condenser: A pipe or passage that acts as a heat exchanger to cool the vapors back into liquid phase. The common moonshiner's term for a condenser is “worm”, since they use coiled copper tubing that looks like a snake or worm. For cooling fuel-grade alcohol an old car radiator would work, but the metals present would make the distillate unsafe to drink. Running cold water over the exchanger will make it more efficient, but simply moving air past it will also work.

Distillate: The product that comes out of the still.

Fractioning Column: A vertical column rising above the pot, fitted with trays or packing. (Explanation below) Fractioning columns will often have more than one outlet, to allow the collection of parts of complex mixtures like crude oil.

Pot or Still-pot: The container that holds the raw or mixed beginning solution. It must be capable of being sealed to the condenser and withstand the heat need to boil the mixture.

Receiver: The container that catches your distillate.

Reflux: Recycling a portion of the distillate to pass it through the still again. Often used in continuous distillation processes instead of running batches through multiple times to increase the purity of the distillate.

Thump Tub: An intermediate cooling stage commonly found in moonshine stills. Vapor from the top of the pot is passed over a container of water on its way to the condenser. This allows for the removal of some of the chemicals that can impart bad flavors to drinking alcohol.

Simple Distillation
Purifying water or alcohol can be accomplished in a simple still. Here is a picture of a simple copper batch still, where the pot and condenser coil are easy to pick out. The pot is filled and placed on a heat source and the “worm” is placed in a tub of cold water (if available). There are electric and stove-top versions of this simple still on sale for purifying water, but as you can see they aren't that hard to cobble together. This one is almost a hundred years old and could probably still be used today.

Fractional Distillation
Here's a good diagram of a fractional distillation tower for separating crude oil into useful parts.

It is common practice to use the waste gas coming off the top to fuel the furnace that heats the incoming crude oil. Waste not, want not.

The trays are designed to allow the heated vapors to rise through the column, but the “caps” on the holes in the trays cause some of them to condense at the temperature present at that height. The condensed liquid helps maintain the temperature at that height and is drawn off in a continuous stream.

Fractional distillation would be useful for long-term situations as a way to recycle used motor oil or production of fuel from local supplies of crude oil (which is more common that you may believe, I've seen oil wells in Iowa and Nebraska). By using a taller tower with more trays, it would be possible to sort out the constituent parts of the gasses produced by roasting coal or wood to produce fuels and solvents such as methanol (wood alcohol) and acetone.

There is also a lot of research going on right now into the recycling of waste tires and various biological wastes into crude oil through pyrolysis. If we ever get to the Mad Max stage of survival, knowing how to produce lubricating oils and fuel could be a valuable skill.

Other Uses
This has been an extremely simple overview of distillation. There are so many uses for this method of separating compounds that it is difficult to keep things prepper-related. Distilling out essential oils for medicinal uses, concentrating the flavors of certain spices to make them easier to transport, making useful chemicals, and so many more all use the same basic mechanisms -- with special attention being paid to the details like temperature and pressures. If you need more specific information, please comment on our Facebook page and I will try to help as best I can.

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