The distillation efficiency is a key performance of lab rotovap. It determines both the experiment efficiency and the product quality. One obvious truth is that the higher the distillation efficiency, the more samples can be distilled for the same solvent. So what are the factors affecting the distillation efficiency of rotary evaporator?
Temperature of the Cooling Medium
In order to ensure the best distillation efficiency, the cooling medium is generally recommended to maintain a temperature difference of about 40 ° C with the temperature of the heating pot in order to quickly condense the hot steam, thereby reducing the impact of steam on the system vacuum.
Temperature of the Heating Pot
The higher the temperature of the laboratory rotary evaporator, the faster the distillation of the solvent. Considering the safety of the operation and the heat sensitivity of the target component, the most common temperature is 60 ° C or 80 ° C or more, but the silicone oil medium is difficult to clean. In general, we recommend that customers achieve faster distillation efficiency by lowering the vacuum value.
The Vacuum Value of the System
The closed space components of a laboratory rotary evaporator are as follows: an evaporation flask, an evaporation tube, a sealing ring, a condensate tube, a vacuum buffer flask, a vacuum pump and a vacuum pipeline, among which the most critical factors affecting the vacuum of the system are the vacuum pump, the sealing ring and the vacuum tube.
Generally, the lower the vacuum pump limit, the lower the vacuum value of the system.Therefore, reasonable vacuum value should be set by the vacuum controller to ensure the distillation efficiency and avoid boiling.The ultimate vacuum of the circulating water pump is about 0.095 kPa, and the ultimate vacuum of the diaphragm vacuum pump is as low as 2 mbar. However, if the budget allows, it is better to install a vacuum controller or vacuum valve, which can control the system vacuum value required for distillation.
As a key seal for the evaporation tube and the condensate tube, the sealing ring is the key to its wear resistance and corrosion resistance. Usually, a sealing ring is made of PTFE and rubbers. But comparing PTFE with rubbers, the former’s wear resistance and corrosion resistance will be better than the latter.
Silicone tube is naturally the first choice for vacuum tubes because its aging efficiency is slower than that of ordinary rubber tubes.
Speed of the Evaporator
The rotation speed of the evaporation bottle of the laboratory rotary evaporator is faster, and the larger the area of the inner surface of the bottle is, the larger the heat-receiving area is; but the thicker the liquid film is, the larger the heat transfer temperature difference is. There is optimum speed for materials of different viscosities and the rotational power is provided by the motor.
System Size and Power
The rate of distillation in a given system is primarily limited by the ability of the condenser to condense solvent vapor (which is rarely limited by the heater).If you let too much steam into the condenser, it will overload and not work effectively, which will result in valuable volatile loss.To avoid saturation, you should monitor the system pressure so that the 2/3 condenser is always covered by condensate. If liquid begins to form at the top 1/3 of the coil, there is a risk that the incoming steam will be drawn into the vacuum pump and lost forever.In practice, we often let condensed water approach 3/4 of the condenser.Another indicator is the “condensation line”, which is usually located above the area of the coil where the actual liquid is seen. This is easily seen in water distillation but is difficult to see in alcohol distillation.
How to Select Vacuum Pump for Rotary Evaporator?
The water-circulating pumps are recommended, which can bear all sorts of solvent corrosion and can vacuumize to -0.095MPa (to satisfy using requirements). According to the solvent volume, we can offer various vacuum pump types.