Fractional Distillation Apparatus

The crude alcohol produced by the beer-stripper is transferred to the fractional distillation apparatus shown in Figures 3, 4, 5, 6 and 7. Whereas the beer stripper is an elementary piece of equipment, easy to understand and easy to use, the fractional distillation apparatus is rather more complicated. Few non-scientists have ever heard of such an animal, and have never seen or read about one. Yet a fractionating still is the one essential piece of equipment required to produce pure alcohol and is the key to the success of this whole project.

Material of construction: Glass would really be the ideal material for making small-scale stills, being inert, clean, and transparent. One can see exactly what is going on and it is aesthetically pleasing. For those fortunate few who live close to a university or research institute therefore, and have access to a glassblower, a glass apparatus is described later with a glass still-head being shown in Figure 6.

For the majority of people however, the choice will have to be metal and the only decision left then is whether it should be made of copper or stainless steel.

The advantages of using copper are that it is relatively inexpensive, it is readily available from any plumbing supply store and, most importantly, it can be worked and soldered together easily by amateurs. Furthermore, the high thermal conductivity of copper makes the cooling coil extremely effective. Commercial whisky distilleries have used copper stills for centuries so it is clearly a very acceptable metal to use.

But then there's the solder. There is no reason to believe that ordinary lead solder is not completely safe — it has been used routinely for many years in domestic plumbing. However, lead-free solder is readily available nowadays and you may wish to use it.

An alternative would be to use silver solder, frequently employed professionally for the fabrication of equipment where the joint may come into contact with chemical solutions. Silver-soldering does, however, require the use of high temperatures, so if you decide to go this route, it probably would be a good idea to assemble the parts yourself and then take the apparatus along to a professional for brazing or silver-soldering. It would only be a few minutes work and should not be expensive.

Stainless steel, of course, is a perfect material of construction for an apparatus such as a still, but it is not one which an amateur will find it easy to work with. We have taken the design to a stainless steel fabricator, however, and obtained a price, and this information will be listed later for those who prefer to use nothing but the best.

Construction: As will be seen from the sketch in Figure 3., the apparatus consists of a boiler surmounted by a 3 to 4 ft. length of 1/ inch copper tubing. At the top of the tube is the still-head where the vapours rising from the boiler are condensed and split into two streams. The major stream, consisting of 90% of the condensed liquid, flows back down the column while the remaining 10% is directed to the outside world via a small valve. Let us look at each part of the still in more detail.

The boiler: Just as we did for the beer-stripper we use a domestic hot-water heater for the boiler but in this case it can be quite a bit smaller in size. The kind used for apartments is ideal. They vary in size but are usually in the 5 to 8 US gallon range (20 to 30 litres) and are normally heated by a single element of about 1500 watts at 120 volt or 240 volt, depending on which country you live in. We want the contents of the boiler to boil so, after removing the insulation, remove or by-pass the thermostat just as you did in the case of the beer-stripper.

To the cold water inlet at the bottom of the boiler fit a ball-valve with a hose-bib attachment. To the hot water outlet at the top fit a short 3/4 inch brass nipple and the adapter necessary to install a 1/ inch union. If there is a magnesium corrosion-prevention rod in the boiler, remove it and close the opening with a 3/4 inch ball-valve. This valve is not really necessary but access to the boiler is useful for cleaning.

The packed column which will be mounted above the boiler has only a limited capacity to allow vapours to rise up through the packing against the downward flow of condensed liquid so the boil-up rate must not be too great or the column will choke. The 1500 watt heater supplied is, in fact, unnecessarily large so we need to reduce the wattage in some way. A simple and cheap solution is to substitute a 750 watt heater for the 1500 watt one supplied with the water heater. It can then be plugged straight into a socket with no need for a voltage controller.

An alternative is to introduce half-wave rectification of the electricity supply. This has the advantage that you can then heat quickly at 1500 watt, reducing to 750 watt when up to temperature. A diode is an electrical component which accomplishes this by allowing current to pass through it in one direction only. Power supplies in most countries deliver alternating power at around 50 to 60 cycles per second. The diode therefore acts like a switch that opens and closes 100 to 120 times every second. With a diode in the circuit, the heater is therefore switched on and off at this rate and, being powered for only 50% of the time, delivers only half the energy it would if left switched on all the time. A 1500 watt heater would therefore deliver only 750 watts if controlled with a diode. A discussion of diodes and how to construct a controller using one is included in Appendix IV.

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  • tewelde elias
    How to wash steel distillation apparatus choke?
    8 years ago
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    How to design a batch fractionation distillation assembly?
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