Analysis of Factors Affecting the Distillation Efficiency of Rotary Evaporator

Rotating evaporator is mainly composed of: motor, distillation flask, heating pot, condenser, and other parts of the laboratory equipment. For the same solvent, the more efficient the distillation, the more samples can be distilled. So what are the factors that affect the distillation efficiency of the rotary evaporator?

1. The vacuum value of the system

The rotary evaporator’s enclosed space consists of glass components, including evaporator bottles, evaporator tubes, seal rings, condenser tubes, vacuum buffer bottles, vacuum pumps, and vacuum pipes. Among them, the vacuum pump, seal ring, and vacuum tube are the three most critical and variable factors affecting the system vacuum.

diaphragm vacuum pump

Vacuum pump
For the diaphragm vacuum pump and vacuum controller for rotary evaporator, the lower the vacuum pump limit, the lower the vacuum value of the system. During distillation, a reasonable vacuum value must be set by a vacuum controller to ensure distillation efficiency and avoid collisions. Currently, the ultimate vacuum of diaphragm vacuum pumps is as low as 2mbar, while the ultimate vacuum of circulating pumps is about 50mbar (0.095kpa). It’s necessary to get a vacuum controller or vacuum valve to control the system vacuum required for distillation if there is enough budget for it.

Sealing ring
The sealing ring is a key seal of the evaporator tube and condenser tube, and its wear resistance and corrosion resistance are crucial. The PTFE and rubber sealing rings are frequently used.  For wear resistance and corrosion resistance, PTFE has better performance. Also, stainless steel buffer shrapnel is added to the seal ring by some manufactures, for better wear resistance.

Vacuum tube
Generally, manufacturers do not have standards for vacuum tubes. If bought by yourself, the silicone tubes are better than rubber tunes with slower aging efficiency.

2. Heating pot temperature

The higher the heating pot temperature, the faster the solvent distillation effect, but considering the heat sensitivity of the target component and the safety of operation, the commonly used temperature is 50°C. In addition, above 80°C, changing to silicone oil as the medium will cause cleaning problems. In general, lowering the vacuum value to achieve faster distillation efficiency is recommended.

3. Rotation speed of evaporating flask

The speed depends on the speed of the rotor and the radius of rotation of the particles. When clarifying the evaporation conditions, it is often expressed by the relative evaporation force field. In practice, the data of the evaporation force field refers to its uniform value. It refers to the evaporation force field experienced by the particles at the midpoint of the evaporation solution.
The faster the rotating speed of the evaporating flask, the larger the infiltration area on the inner surface of the flask and the larger the heated area; but at the same time, the thicker the liquid film thickness increases the heat transfer temperature difference. The motors supply the rotation power required. There are DC brushless motors, AC motors, and stepping motors on the market, and they are uneven. The feedback of the DC brushless motors is better.

4. The temperature of the cooling medium

In order to ensure a good distillation efficiency, it is generally recommended that the cooling medium maintain a temperature difference of 40°C with the temperature of the heating pot, in order to condense the hot steam fast and make the influence of the steam on the vacuum of the system lower.

5. Maintenance

At present, the rotary evaporator is generally suitable for various tests. After the experiment is completed with the rotary evaporator, some dirt from the condenser tube, collection bottle, and evaporating bottle will be easily left. These dust and dirt will not only affect the performance of the rotary evaporator and shorten the service life and more seriously will directly affect the experimental results. The rotary evaporator will be more or less dusty during use or storage, so the maintenance should be dust-proof and dirt-proof. Regular dust-removal and cleaning is an important part of the maintenance and maintenance of the instrument.

How to clean this dirt and dust?

1. A small amount of continuous drainage device can be used to control the concentration ratio of the condenser of the rotary evaporator within a certain range so that the precipitation of scale can be effectively prevented, which saves a lot of cleaning of the rotary evaporator in the later stage force;
2. Make the surface evaporation temperature of the rotary evaporator below 40 degrees, and also use a large amount of water, so that the surface of the condenser tube is always covered with a water film, and there is no drypoint;
3. When the rotary evaporator is produced, the pre-film anti-fouling treatment can be done, that is, the pre-film is used to form a protective film on its surface, which can effectively prevent the adhesion of dirt crystals on the surface.