Spinning Band Distillation

Dean Stark
Uncommon Stills

“Spinning band” is a distillation process that uses a column with internally moving packing to perform a separation of components, even those with very close boiling points. Spinning band provides a very high degree of separation within a small footprint. This technique is a type of rectification and is best used to create high-purity ethanol.

When you read about all those distilled spirits competitions with a Vodka category called “most neutral character”, this is the device you use to win it!

The spinning band column, showing the impeller (20), reflux condenser (16), boiler (10), distillate takeoff (28), and column jacket (26)

In our craft, we rectify spirits using columns with a high number of vapor-liquid interfaces, known as theoretical plates of separation. These columns include packed columns, bubble cap and tray columns, and Oldershaw type columns. The more packing or trays we have, the more plates are created. The difference with spinning band is that the column packing is moving or spinning, rather than stationary. By adjusting the spin rate, the number of theoretical plates is varied. The packing material is a screen shaped into an impeller. This blade runs the vertical length of the column and is made of an inert metal, such as platinum (like ours).

A closer view of the platinum impeller at left and right. Notice how the blade is in two sections, one above and one below the takeoff controls. The small blue point in the globe is a drip tip to aim the condensate takeoff tube to the receiver.

The blade is magnetically coupled to a stirrer at the top of the column. The blade width is in very close tolerance to the column wall. The blade itself is a mesh material and provides around 2-4 theoretical plates. Once it is spinning, it can provide 20 or more theoretical plates.

Our setup in glass and under vacuum. The receiver is the round bottom at right. The addition funnel at left is to add more stripping run material.

The column wall is typically heated with an electrical coil along its length to ensure a uniform temperature from top to bottom. Temperature is a variable to very carefully control, sometimes within a tenth of a degree!

Metal heating coil running along the column length. Temperature is controlled with a Variac.

The entire column sits on top of a boiling flask. A reflux condenser and reflux control sit at the top of the column, above the blade.

The takeoff controls. The knob at left opens a valve to permit the condensate to take off, flowing to the right. The knob at the right opens a drain to the receiver.

We use a Precision closed loop chiller with glycol, and insulated the reflux condenser as shown. We can operate as low as -8’C with our setup.

The reflux condenser at the top of the spinning band column, in insulation. The reflux takeoff controls are the two knobs below the insulation in white.

As wash vapors rise from the boiler, they meet the spinning platinum impeller. Vapors continue to rise through the column, and once they reach the reflux condenser, they are condensed to the liquid phase. The impeller forces the liquid to the the blade edge and downward, in close contact to the heated column wall, returning some of it to return to the vapor phase. The vapor is trying to rise all the while the liquid is being returned downward faster than it can fall by gravity. These intimate exchanges are occurring very quickly over the spinning blade, providing multiple equilibrium (vapor-liquid) stages.

Magnetic coupling and spinning the impeller.

Running this still under vacuum creates one more variable to control, but the small size of this unit makes that fairly easy. When you distill your stripping run distillate with a spinning band column under vacuum, you will break the ethanol-water azeotrope a little! The pressure swings a bit in the top of the column, and coupling this to the high separation efficiency makes this possible. We have measured as high as 98.1% ABV in some runs from this device.

Here are the downsides!

  1. They are very hard to find surplus. We see about one a year pop up on Ebay. Sometimes, the platinum impeller is gone for precious metals recovery.
  2. They are small. Our whole setup is based on a 1 Liter boiler. The output is for a boutique, very high end product, not a mass-produced product.
  3. They are ridiculously expensive new.

If you find one intact surplus, $500USD or less is a great deal.

Happy spinning! – Dean

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