Wiped Film Still Components - Part VI - Condenser

So far in this series, we have followed our feed material on its journey through the feed system, onto the wall of the still body, wiped into a thin film and finally heated to form vapors.  These vapors are now collected and returned to liquid phase by the condenser.  The volatile vapors are separated from the non-volatile components of the feed, resulting in the desired purification.

A condenser is a heat exchanger that is held at a temperature below the boiling temperature of the distillate.  That way, once the distillate vaporizes from the still wall, the condenser will turn the vapors to liquid.  That liquid is then collected as the distillate stream.

 Wiped film stills have two common configurations.  The difference between the two is the location of the condensers.  In the short path or molecular still configuration (MS), the condenser is placed inside the still, it comes up into the still from underneath the body, and the condenser runs inside the wiper retainer.  This condenser has two outlets.  One outlet is for distillate collected on the condenser and the other is for residue (the material that did not vaporize off of the still wall). 

The other configuration is to place the condenser outside of the still body.  This configuration is called a Wiped Film Evaporator (WFE).  The vapors rise out of the still and go to the condenser, which is placed between the still and the vacuum source.  As the vapor travel towards the vacuum pull, they interact with the condenser, and form a liquid, dropping out of the vapor phase.  The bottom of the still body has a cone installed, which is where the residue is collected in this configuration.  The WFE configuration requires more heat to distill the same amount of material as the MS because the vapors have to be forced up and out of the still to the external condenser. 

The main reason for choosing the WFE configuration is when there is a high volume of material to remove, and the internal condenser does not have enough surface area or condensing power to condense it.  An external condenser can be sized as needed, while an internal condenser is limited by the space available inside the still. 

Picture 1 is a Short Path unit or MS still.   Picture 2 is a Wiped Film Evaporator (WFE) with the external condenser.

Pictures are courtesy of