The Amphora Society is proud to announce the availability of pure copper structured packing material for the small-scale distiller.  This is the same material that we use in our ultra-efficient PDA-1 distilling equipment.  If you already have built a column-type distilling apparatus, don't be left behind by the march of progress – you, too can now have the many advantages of the pure copper structured packing.

So what exactly is "Structured" packing?

Now packing, in order to be effective, has to be able to pass vapor through all regions with equal ease, while allowing room for liquid reflux to be held on the strands and to trickle downwards evenly as separation proceeds.  It is not enough that the packing be distributed randomly, for anyone who has tossed a penny and noted the results of that random exercise will know that you very rarely get a consistent run of "heads - tails - heads - tails, etc" (the math wizards among you will know that such an even distribution is not random!).  Instead, it is usually the case that you get a run of heads or of tails in the middle of a run.  Overall, you may end up counting as many heads as you do tails, but they are not necessarily distributed evenly.  In the case of packing, such a "random" distribution is just not good enough.

This is what one of our recent customers had to say about it, having used Raschig rings up till now:

I have to let you know that your copper mesh arrived sooner then expected and I immediately replaced the rings with it.  I had a sugar wash ready, and I still can't believe how much the quality has improved from my stainless still.  The end product runs sweet and crystal clear, no off odor or taste, and I doubt if I will need to polish with carbon.  What a delight!

Thank you,
Scott

Why do you need good packing?

In distillation, we depend on the fact that different substances have different volatilities.  In purifying water, we take advantage of this fact as salts dissolved in the water have almost negligible volatility and do not come off in the steam , but get left behind in the boiler.

However, if we boil a mixture of two or more liquids , then it is an entirely different matter.  It would be nice if the most volatile liquid boiled off first because, on its own, it has the lowest boiling point, followed by all the rest in neat order of their individual boiling points.  The argument for this is persuasive, as it is true that the boiling points of liquids decreases as their volatility increases, and it seems 'obvious' that the most volatile substances will boil off first as we raise the temperature.

 Unfortunately, it's not as simple as that.  If we mix two liquids together, one with a boiling point of A⁰C and the other at a higher temperature B⁰C, then the mix will not start to boil at A⁰ C, boil off the first liquid, and then suddenly rise to boil at B⁰C when only the second liquid is left.  Instead, the mixture boils at some intermediate temperature depending on how much of each liquid is in the mix.

What we do find, however, is that the vapor given off when the mixture boils is richer in the most volatile substance than it was in the mixture it came from, and when we condense that vapor we get a liquid that has this new composition.  Boil that liquid, and the concentration of that most volatile substance increases still further ... and so on.  The end result, after repeated condensations and reboilings, is that we finally manage to separate the two liquids.

You could do this with an ordinary pot still, but it would be both tedious and wasteful, as some of the liquid you are trying to separate out would be left behind with each reboiling.  Fortunately, the whole process can be automated by simply passing the vapor through a column packed with material that offers a large surface area onto which the vapor can condense to a liquid, and then be held in place while it is re-evaporated.  The less volatile liquid tends to accumulate on these surfaces as the more volatile liquid is preferentially removed at each stage, and eventually trickles down back to the boiler as the increasingly volatile vapors rise to the top of the column. 

Many different materials have been used to provide these surfaces onto which condensed vapor settles, and it is fairly obvious that the best ones are those that offer a very large surface area compared with the volume they occupy.  However, large surface area alone is not the answer, as the material chosen has to offer a free pathway for vapor to rise through the packing.  Sand has an enormous surface area for a given volume, but would be useless as it would be impossible for vapor to pass through it.  The selected material therefore has to be chosen carefully, and to this end we did some calculations and published them in The Compleat Distiller.