I. The vacuum value of the system:
The airtight space of the rotary evaporator is composed of glass components such as evaporating flask, evaporating tube, sealing ring, condenser tube, vacuum buffer bottle, vacuum pump and vacuum pipeline. Among them, the most critical and changing factors affecting the system vacuum are: vacuum pump, sealing ring and vacuum tube.
Vacuum pump and vacuum controller:
The lower the vacuum pump limit, the lower the vacuum value of the system. When distilling, it is necessary to set a reasonable vacuum value through the vacuum controller to ensure the distillation efficiency and avoid bumping.
At present, the ultimate vacuum of the diaphragm vacuum pump is as low as 2mbar, and the ultimate vacuum of the circulating water pump is about 50mbar (0.095kpa). If the budget allows, a vacuum controller or vacuum valve is necessary, which can well control the system vacuum value required for distillation.
As the key seal for the evaporator tube and the condenser tube, wear resistance and corrosion resistance of the sealing ring are very important. The materials commonly used by sealing rings are: PTFE and rubber. Obviously, PTFE has better wear resistance and corrosion resistance. Some manufacturers add stainless steel buffer shrapnel to the sealing ring to achieve better wear resistance.
Material of Vacuum tube:
Generally, the manufacturers do not have standard vacuum tubes. But silicone tubes are naturally the first choice, because their aging efficiency is slower than rubber tubes.
II. Heating pot temperature:
The higher the heating pot temperature, the faster the distillation effect of the solvent, but considering the heat sensitivity of the target component and the safety of operation, the most commonly used temperature is 60°C. In addition, above 80°C, using silicone oil as the medium will cause cleaning problems. Generally, it is recommended to lower the vacuum value to achieve faster distillation efficiency. At present, the ultimate vacuum of good diaphragm vacuum pump on the market can reach 2mbar, and DMF can be distilled at room temperature.
III. The speed of the evaporating flask:
The faster the rotating speed of the evaporating flask, the larger the infiltration area of the inner surface of the flask and the larger the heated area, but at the same time, the thicker the liquid film, which will increase the heat transfer temperature difference. For materials with different viscosities, there is an ideal speed. And the rotation power is provided by the motor. There are brushless DC motors, AC motors and stepping motors on the market, which are uneven. The feedback of the brushless DC motors is highly praised, and it is maintenance-free for 10 years.
IV.The temperature of the cooling medium:
In order to ensure high distillation efficiency, the cooling medium is generally recommended to maintain a temperature difference of 40°C with the temperature of the heating pot so as to quickly condense the hot steam and reduce the influence of the steam on the vacuum of the system. Safety risk assessment shows that the safety risk of distillation mainly comes from the solvent and heating medium of the distillation.
1) If the heating medium is silicone oil, the ignition point is at least 25°C higher than the maximum temperature of the heating pot.
2) If the distillation solvent is flammable and explosive, explosion-proof glass components can be the first choice. After the distillation is completed, it is good if the instrument can automatically deflate, so as to avoid manual deflation too quickly and cause an explosion.
3) To optimize the laboratory environment, a secondary condensation device can be selected to maximize the recovery of the distillation solvent.