Pique the Geek 20091108. Distillation, not Just for Beverages

Distillation is a technique of “squeezing” out the essence of a given material (or series of thoughts to one or a few abstractions) into a concentrated product.  The term is from the Latin, distillo, from the combining term de, meaning “down” and the noun stilla, a drop.  Thus, distilled water is literally a drop of water coming down something.  Taken to the extreme, distilled water literally means “a coming down drop of water that is water”.  That does not fit with the modern usage, but is illustrative.

Aristotle, with all of his faults, noted that seawater, boilt under cool sponges, would yield fresh water when the sponges were pressed.  Distillation was known in the ancient world, but not much used except for preparing “medical” remedies, most of them toxic, in a manner that I will describe to you later, in a more modern form.

Actually, the earth is a huge still, with the water cycle reproducing exactly, but on a massive scale, what goes on in an industrial or laboratory still.  Heating, evaporation, segregation of components, and condensation are all essential parts of distillation, and our planet does it well.  Without that process, the planet would not be recognizable.

Some housekeeping before we start.  I was very tempted to do a “conservative food fest” tonight, but I decided to keep it straight.  Soon, for snark I will.  It was a pretty good idea, just not for here.

I still have not bought cigarettes since March, but I love me my Prince Albert.

Eldest Son will be married next month.  I hope to have some exclusive pictures

Finally, the pics and recipes of Christmas goodies will be here on 05 December.

First, let us think of the definition in more unbound terms.  To distill many facts into a few concepts fits, although only in concept but not in practice, what we call teaching.  I do this here all of the time, and get very good response.  I intend to continue to do so.  This is important:  I start with many facts, interpretations, ideas and concepts, and then attempt to distill them down to only a few basis truths.  That is what a scientist does.  There are others, especially in the hard right media and blogosphere, who do exactly the opposite.  They take preconceived notions and talking points, then attempt to expand them to make it appear that the “facts”, “interpretations”, “ideas”, and “concepts” agree with their preconceived “distillate”.  Actually, they are diluting their distillate, going in reverse.  They take the little bit left over, supposedly filled with the good stuff, and dilute it with nonsense.

Folks think that the beverage alcohol industry are the be all and end all for distillation.  Whilst they are somewhat old, this is not true at all.  Petroleum refining is by far the largest user of distillation (along with several other techniques) and will be so in the foreseeable future.

Let us define the process.  In modern terms, it means to heat some mixture of materials to separate them.  There are several variations.  The most common is when a mixture of volatile materials is heated, and the different ones are caught as they condense somewhere.  That somewhere will be undefined for a while so that we can keep up here.  This is called normal distillation.  In theory, the process does not change the composition of the materials being separated, but in practice, it almost always does if the temperature is much over cryogenic ones.

The other is destructive distillation, when heat is applied to materials to make them decompose into simpler compounds.  Thus when coal (or wood, or petroleum) is heated without oxygen (we will allow that most all distillation processes exclude air) are subjected to very high temperatures that cause their conponents to be released, or to change.  Change is very likely at elevated temperatures, and chemical reactions are likely.

So in the middle are the mixtures that boil around the boiling point of water.  The cryogenic distillation processes produce hardly any chemical changes, the middles ones many, and the destructive ones very, very many.  Let us look at an example of each.

Many industrial processes are dependent on having more or less pure oxygen, nitrogen, and argon, amongst other gases.  The cheapest way to make them is to liquefy air, put it in a still, and allow it to come to the boil.  Nitrogen, 78% by volume of the atmosphere, boils out first, with a boiling point of 77 Kelvins (-196 degrees C, or -320 degrees F).  This is caught and either compressed and marketed in cylinders under pressure, or reliquefied and sold as a cryogenic liquid in Dewar flasks.  Argon, boiling at 87 K, comes next, then oxygen boiling at 90K.  The heavier rare gases, except for helium, are obtained from the residue after these three gases are boiled out of the mixture.  Helium is so rare in the atmosphere that it is produces by distilling it from helium rich natural gases.

The boiling points of those three gases are really pretty close together, so the still has to be very efficient to get clean separation.  We shall discuss that a bit later.  In this process, very little chemical change is made in the liquefied air as it is distilled, in part because of the extremely low temperatures, and in part because these gases do not react with each other very readily.

Air is a rather simple mixture of very simple elements for the most part, so there is not much opportunity for chemical reaction.  Now let us consider making charcoal, which involved the destructive distillation of wood.  Wood in a very complex mixture of long chain carbon compounds (the cellulose part), and a proteinaceous lignin part that serves to bind the cellulose together into a coherent mass.  The cellulose is only carbon, hydrogen, and oxygen, but the lignin contains lots of nitrogen, some phosphorous and sulfur, and other elements as well.  There are also the metals, potassium being important.

When wood is distilled destructively, historically in heaps covered by earth, but now in steel retorts so that the vapors can be collected, it transforms from what we know as wood to charcoal as the hydrogen and oxygen (along with the other elements except for the metals) are driven out as water mostly.  By the way, charcoal briquettes are made from pulverized charcoal glued together with clay and other binders.  Real charcoal, and Royal Oak markets a product that is real charcoal, is just the charred wood.  In any event, because of the high temperatures, the hydrogen, oxygen, and other elements begin to react.  The volatile fraction of wood distillation consists, after water, of methanol (that is why it is called wood alcohol), acetic acid (vinegar), and many complex substances that are termed tar.  This tar contains thousands of compounds, most all of them formed during the high temperature treatment of the wood in the absence of oxygen.  Most would have just burnt up otherwise, but keeping air out makes a difference.

The tar can be redistilled to isolate the important components of it, and in the past they were important wood preservatives before more modern materials were developed.  The take home lesson is that hardly any of these compounds were present in the wood before it was distilled, but formed during the process.

The middle ground is lower temperature (at the boiling point of water) distillation.  We shall discuss that in a bit, but first some really geeky information should be presented.

Still basics

All stills have some container to hold the substance to be heated.  For the planet, these are the oceans.  For the moonshiner, it is the boiler.  There is also a heat source, and for the planet it is the sun, for those distilling liquid air just ambient air, and for the chemist, a heating mantle.  Finally, there must be a conduit between the boiler and receiver.  For liquid air, it is just a metal pipe, since the components have to be either compressed or reliquified.  For other uses, that conduit is usually cooled by some means to that a liquid product can be isolated.

There are two basic types of stills.  Simple stills (aka pot stills) use a boiler and a direct connection to a condenser tube, cooled with a heat exchange medium, usually water, and deliver the condensed product to some sort of receiver.  For chemists, this is often a Claissen condenser, and for moonshiners it is the worm tube.  Pot stills are not very efficient, but they are great for separating salt from water, since the boiling points are hundreds of degrees apart.  The other type is called a reflux still, and it uses an intermediate column to fractionate the various components.  All liquid air stills are reflux stills because the boiling points are so close for the components, as mentioned earlier.

This difference is because of the reflux column, which essentially redistills the components of the boiler over and over again.  It is usually a fairly large diameter, insulated vertical column that is carefully temperature controlled.  Each level of the column is at a defined temperature, and only materials that are just vapors ready to condense can exist there.  Lower boiling ones go to the top, and lower ones do not go up that far.  These are much more efficient that a pot still, because several distillations at once are done.  Most reflux columns are packed with an inert material to allow the vapors to condense, then be bombarded by more hot vapor.  The hot vapor knocks the lighter fractions upwards, and the loss of energy from that transaction allows the heavier ones to drop down to the hotter section.

Just two more, related, geeky things, and then we shall discuss practical things, and I will even give a design for a simple still that you can make yourself.

The first concept is what is called a theoretical plate, and that is, in simple terms, the separation of two substances by simple boiling point difference.  Thus, any still has at least one theoretical plate by the simple act of boiling.  Pot stills have one plate, because they condense everything that reaches the worm tube.  For reflux stills, with an efficient column, that column performs one or more additional distillations, as explained before.  This brings the concept of the height equivalent to a theoretical plate (HETP), which defines the efficiency of the column.  In petroleum refining, the columns are hundreds of feet high, and the HETP may be around 10, meaning that every foot of column is like distilling the products ten times.  The higher the HETP, the better the separation.

Now back to real stuff.  When folks make bourbon whiskey, pot stills are normally used.  The wash, the fermented liquid to be distilled, is distilled with one plate in a pot still, and, assuming around 10% alcohol in the wash, about 55% comes out of the end, for a while.  There are the high shots and the low shots, but this is beyond the scope of this essay.  Normally, bourbon is distilled at least twice in a pot still to get the alcohol content high enough and the bad stuff content low enough to go to aging in wood.  This is a time and energy inefficient process.

For grain neutral spirits (vodka, gin, and especially pure grain alcohol are neutral spirits with some or no flavoring ingredients added later) a reflux still is used, so that “pure” alcohol with little of no scented products can be tapped off continuously.  The feedstock can be whatever the cheapest source of alcohol happens to be, so it might be sugar, potatoes, beets, or corn.  Often these vary by region, and sometimes by season.  Neutral spirits are just that:  the only flavor is the alcohol, with no additional materials in them.  They are used as is or flavored with other things after this step.  For example, gin is made by redistilling neutral spirits with juniper berries and other spices after it is made.

It is not possible to make 100% alcohol by distillation, no matter how good your column might happen to be.  In theory, a perfectly efficient column can resolve two different boiling point liquids, as long as they are zeotropic.  This means that they do not have molecular interactions that make their behavior complex.  Liquid air is zeotropic, and so is helium mixed with natural gas.  However, alcohol and water form an azeotropic mixture, and it boils at a lower temperature than either water or alcohol itself.  The azeotrope is around 96% alcohol, and without using other techniques, it is not possible to produce 100% alcohol from water solutions.

If you like to make perfumes or other scents from native flowers, the instructions often say, “Now distill this until you get so much product”.  Without a still, that is difficult.  Here is how to make one for those purposes (it does not have the capacity to get anyone drunk, and it is federal offense to distill alcohol without a license, so do not try it and do not think that I am advocating distilling alcohol).  You need a large stockpan, a lid that when fitted on it is concave, a bowl that is preferably thick stoneware, and a rack to keep the bowl out of hot water.

Put whatever flowers or herbs that you want the essence of in the stockpot along with some water.  Put the stoneware bowl on some sort of support that whilst it is the middle of the stockpot, it is elevated above the water.  This is very important.  Bring the water to the boil, and add an ice cube to the bowl.  Invert the lid of the stockpot over the pot, and fill it with ice and cold water.  Watch it like a hawk, so that the piece of ice in the bowl does not melt and allow the scent to heat up and escape.  You can distill a few milliliters of very fragrant flower or herb extracts with it.  This works well with rose petals and with orange peel.  You can not make enough this way to make alcohol practical, since your fuel and ice requirements are high, but it is a nice way to make spice distillates and perfumes from flowers.

Well, you have done it again.  You have no excuse.  You have wasted a perfectly good batch of photons reading this distillation of many concepts.  Since this has been sort of a sad week, with the folks at the military base, I will not present a joke tonight.  I will say that I always learn much more that I could possibly hope to teach from your comments, corrections, questions, and other topics.  Remember, I never look things up during comment time, and I value your input.

Warmest regards,

Doc

Crossposted at Dailykos.com