The Boerhaave Cone
Dr. Herman Boerhaave was born at Voorhout in 1668 and earned his doctorate at Leyden in 1690, teaching theoretical medicine, then practical medicine, then chemistry. He is the scientist who is credited with assigning the word “alcohol” for the spirits of wine! While an esteemed teacher, his contributions to distillation design are limited. There is one mention, however, that caught our interest: his “conical condenser in the form of a sugar-loaf”. We present, the Boerhaave Cone!
This design appears to be an air cooled condenser, in a shape resembling a tall Rosenhut. The difference is that the Rosenhut would collect condensate from the interior walls, whereas the vapor must condense and fall down the exterior side arm in the Boerhaave design. A tall modern-day Boerhaave, over 36″ tall and based on the above sketch, was constructed by Q-Glass:
In our modern-day design of this condenser, we used a 24/40 ground joint to connect to a boiler, and a 14/22 ground at the top of the cone for sampling and temperature monitoring. The cone is actually a reflux, and the skinny side arm is where condensation occurs. The receiver is a 28/15 ball joint.
Because this is an air-cooled device, the side-arm must be well-separated from the hot cone under reflux. Glass stand-offs accomplish this well.
It took us many tries to get this deceitfully simple device to work. We originally started with a 22L boiler, which overwhelmed the cone and side-arm with hot vapor. We reduced the boiler size to 3000mL which greatly helped. The wash is brought SLOWLY to a GENTLE boil. Hot vapors will being to enter the cone, and the cone will eventually come to thermal equilibrium. All the while, a thin film of condensate is observed flowing down the cone, back to the boiler, thus creating reflux.
A very handy way to monitor cone temperature is through the use of stick-on liquid crystal thermometers!
CAREFUL temperature control is needed to warm the cone to 70-75’C up to the point, but not beyond it. This operation is very similar to the Barchusen Twist. You do not want to bring the hot vapors past the point of the cone, but you need to get it as close as possible by throttling the boiler. The secret of this device is also the ROOM! Since this is an air cooled device, move the room temperature a few degrees helps to achieve that optimal heating zone.
A distillation run using the Boerhaave is a SLOW and PATIENT one. It is a drop-wise process, at around 20mL/hour of distillate. You will be rewarded with distillate that is >90% ABV however! We did our research run with a 7% ABV grape wash, with acceptable results.
