Wiped Film Still Components - Part IV - Wiper System

The wipers or wiping system is critical to the function of the still.  The material to be processed is fed into the still body where it is met by the wipers.  The wipers spread the material around the entirety of the cylinder.  The material flows down the cylinder while being constantly agitated and sheered by the wiper blades.  This allows the volatile material to easily escape the mixture.  It is a very dramatic advantage over a pot style distillation where the volatile material tries to escape from the entire volume of feed material.   Because of this, wiped film stills can be used to remove volatile materials to ppm or none detected levels, while this is not possible in systems like a rotovap or a reactor.

The wiper drive motor sits on top of the still.  The motor connects to the wiper retainer.  The wiper retainer extends down into the still body through a mechanical seal and holds the wiper blades.  Many manufactures offer Teflontm and carbon slotted wiper blades.  Other manufactures may have rollers instead of wipers.  Each has their advantages and disadvantages depending on the physical characteristics of the feed material.  The wipers are held against the inside of the cylinder either by springs or by centripetal force from the wiper blades spinning. 

Many wiper blades are slotted at an angle that forces the material down the still body and minimizes retention time in the still.  The wiper blades agitate the surface of the thin film and allow volatile materials to easily escape from the heated film.  The speed of the wipers is controlled by a variable frequency drive (VFD).