Rotary Evaporator

Overview

A rotary evaporator removes a solvent from a sample gently, by boiling it off under reduced pressure at a temperature low enough to leave heat-sensitive compounds intact. It is standard equipment in synthetic chemistry and natural-product labs, where the last step of a workup is almost always "rotovap it down" to recover a dissolved product as a residue or oil. Two tricks make it work: the flask spins to spread the liquid into a thin, fast-evaporating film, and the system runs under vacuum so the solvent boils far below its normal point. Rotating ethanol off at 40 °C under vacuum, for instance, would otherwise need close to 80 °C at atmospheric pressure.

The instrument is a marriage of a small machine and a glass distillation train: a motor, a heated bath, and a lift on the mechanical side, feeding a borosilicate flask-condenser-receiver set on the glass side.

How it works

The sample sits in the Evaporating Flask, clipped to the Rotation Drive. A brushless motor spins the flask at a set speed through a reduction gear; centrifugal force films the liquid up the flask wall so a large surface is always presented to evaporate. The lower part of the flask dips into the Heating Bath, a stainless pan of water or silicone oil warmed by a tubular element. An NTC probe holds the bath at setpoint, and a thermal fuse cuts power if it ever runs dry.

Vacuum is the other half. The Vacuum System connects an external pump and lets the operator pull the pressure down while a gauge reads it; the lower the pressure, the lower the boiling point, so evaporation stays gentle. Solvent vapor leaves the flask through the Glassware Set train, up the vapor duct, into the chilled coil condenser, where it recondenses and drips into the receiving flask. The rotating joint is sealed against the static condenser by a PTFE Vapor Seal, the one component that has to both spin and hold vacuum.

At the end of a run the Motorized Lift raises the whole head on a ball screw to pull the flask clear of the hot bath, and the Control Board coordinates speed, bath temperature, and the lift while the operator works from the Display & Keypad.