15.8 Ethanol fractionating still

Ethanol is hygroscopic, so picks up water in the extraction process, and there are limits to how concentrated a pot still can keep keep the 190 proof alcohol you paid a high price for.  Purities higher than about 120 proof are typically achieved in a compound refluxing still, which uses a column packed with raschig rings or ribbon made from either stainless steel or copper.  The raschig rings are available in both metal and ceramic.  Some colums have also been operated packed with marbles.

They way they operate is that the vapors from boiling the alcohol solution in the lower tank rise up through the column of packing, where they lose heat to the packing and re-condense into a liquid, which drips back down to the boiling pot.  

Eventually with the continual refluxing, the vapors that do make it to the top are those are the elements with the lowest boiling point, in this case the alcohol.  Those vapors are then condensed using a water chilled heat exchanger and can achieve around 95.6% purity before reaching azeotropic balance between the ethanol and the water.

Purity greater than azeotropic balance is achieved either through use of a drying agent, of vacuum distillation.

In addition to keeping your 190 proof pristine, you can also use a compound refluxing still to increase the concentration of 80 proof vodka or 150 proof Everclear in a pinch.  In point of fact, it can be used to extract the alcohol from mash or a fermented sugar wash, but check the legality of doing so at your location.

I designed our own compound refluxing still, which has a capacity under one gallon and is operated for extracting essential oils.  It could have been done with just the right height column, but I kept it under one meter by adding an Allihn condenser at the top. 

In those locations where it is legal, refluxing column sections can be added and the assembly attached to a larger still.

 I named it The Enabler, as it was intended to enable OMMP cannabis medical patients to maintain the quality of the 190 proof they are using for extraction, and for patients to produce their own 190 proof from lower grades where 190 proof is not available. I simply used the 6" X 6" tank and lid from a Lil Terp, and added a 48" X 1 1/2 stainless sanitary spool packed with stainless steel pot scrubbers from Hong's Restaurant Supply.

What is unique about the enabler, is that it can be controlled two different ways.  One is liquid control and the other is vapor control.

For Liquid Control we capture the liquid rain falling down from the Allihn condenser.   For a more refined separation, controlling water flow to the Allihn condenser at the top of the column, allows you to control what vapors make it past it, to a Liebig condenser to return it to a liquid.

Liquid Control is used for gross refinement, with water flow high in the top Allihn condenser, so nothing rises above it and everything making it that high exits the valve on the right side of the top cross, to be condensed by the Liebig condenser that follows it.

You can tell what vapors are present at the top of the column, by reading the thermocouple in the other side of the top cross and relating it to the boiling points of the different constituents and azeotropes. 

Because water steam is 0.6 the density of air and ethanol vapors are 1.6 times as dense, steam will rise and alcohol vapors will sink until their concentration falls below around 41% by volume at the top of the column.  Handy when stripping washes with a wide open valve.  You determine when you've reached Tails by watching the temperature.   

Any Ethyl Acetate or Methanol present, as well as their azeotropes come off in the Heads and are typically discarded.  Next comes the ethanol until about 41% by volume at the top of the column is reached, where the Tails follow with fusil oils and other undesirable cogens.

The big advantage to Liquid Control, is that controlling the water temperature and flow the Allihn condenser is as critical, and the flow pretty much slows to a trickle at 41%, so it is more self regulating and easier to determine when to stop

For Vapor Control we close the discharge valve on the right side of the top cross, and control both the water flow and its temperature through the top Allihn, until the lowest boiling point vapors at the very top of the column rise above it and pass through to another Liebig condenser to liquify it.

You can tell what those vapors are, by simply reading the digital thermometer in the head cross.

Vapor Control is used when finer control is required, but accomplishing that end requires closely controlling cooling water pressure, temperature, and flow.

As an alternative to that, the settings on the Allihn can be left constant and the boiler heat can be increased so that the head load on the condenser exceeds its capacity and the vapors are driven out the top and into the arms of the waiting Liebig condenser.

One of the advantages of the Enabler design, is that it can easily be converted to a Pot Still by simply removing the column and attaching the head directly to the boiler.  Here is the conceptual design: 

Enabler compound refluxing still

The column and other sanitary fittings came from Glacier Tank, and I scored a dozen of the stainless pot scrubbers from Hong’s Restaurant supply for about $6.

Stainless scrubs

I pulled the pot scrubbers a part and rammed them into the column using a wooden dowel, sandwiching them between two screened Viton sanitary gaskets to hold it all in place.

 

Packing

 

 The Enabler ready for insulating.

 


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