Selection of rotary evaporator and method of setting vacuum and temperature

The rotary evaporator is a common equipment used in the laboratory. It is composed of a heat bath rotating motor evaporator condenser pipe and other parts. Through electronic control, the vaporator rotates at a constant speed under the most suitable rotation. The vaporator rotates and is heated at a constant temperature in the heating bath at the same time, making the material in the vaporator evenly heated. In rotating, the material adheres to the wall of the evaporator and increases the evaporation area. The vacuum pump is used to make the evaporation flask in the negative pressure state. The evaporation temperature decreases under the negative pressure of the solution in the flask and the evaporation rate is accelerated. The cooling medium is adopted in the spiral pipe of the high efficiency cooler to liquefy the separated steam and realize separation.

The core technology of rotary evaporator

The principal requirements for rotary evaporator are corrosion resistance and high vacuum. Therefore, the core technology of rotary evaporator is that the moving parts can withstand the corrosion of various solvents and the sealing in the state of motion. Special ceramic bearing PTFE Fluororubber and borosilicate 3.3 glass seal are adopted, which can resist corrosion of various solvents (except strong alkali and other few kinds), and has durable and reliable air tightness. Non-metal design, especially suitable for the extraction of materials that need to avoid metal ion pollution.

Optional rotary evaporator

l  The first step is to select the specification of the rotary evaporator

The specification of the rotary evaporator is distinguished by the volume of the evaporator. The size of the required evaporator depends on the quantity of the evaporated material. Generally speaking, 2L, 3L and 5L rotary evaporator are suitable for small amount test in laboratory. 5L, 10L and 20L are suitable for the pilot test; 20L and 50L are suitable for pilot test and production.

l  The second step considers the evaporation rate of the rotary evaporator

For the rotavator of the same specification, the factors affecting the evaporation rate of the rotavator are mainly the following four.

1.         Heating bath temperature

The higher the temperature of the heating bath, the more intense the evaporation. But the material thermal resistance, the restriction of the use of safe and energy consumption, is the most commonly used temperature 60 ℃. Heating bath temperature minus the evaporation bottle Δ T₁ and evaporation heat, heat transfer temperature difference is the material temperature. The heat tolerance of materials mainly refers to the allowable temperature of bioactive materials without denaturation, and the safety of use mainly refers to the fact that there is no risk of scald in the process of replacing evaporation bottles. The temperature of heating bath is moderate, the rate of evaporation of water is low and the energy efficiency is high.

2.         Vacuum degree in rotary evaporator: the recommended vacuum degree is 95 ~ 98kPa(absolute pressure 2 ~ 5kPa).

3.         Temperature of condenser cooling medium: Material temperature Δ T₂ minus the condenser heat transfer temperature difference and condensate supercooling degree, That is the average temperature of the cooling medium required by the condenser.

The relation between material temperature and vacuum degree conforms to the relation between material saturation temperature and saturated pressure. The temperature of the cooling medium depends on the type of material when the temperature and vacuum of the heating bath are determined.

4.         Vaporator speed: The higher the rotational speed of the evaporator, the larger the infiltration area and the larger the heating area. But at the same time, the thickness of the liquid film is also thicker, increasing the heat transfer temperature difference. For materials with different viscosity, there is optimal speed.

Since temperature of heating bath, vacuum degree and temperature of cooling medium are related parameters, Related to the type of material and the recovery rate of condensate.

l  The third step select supporting equipment

Ancillary equipment means vacuum equipment and cold source equipment.

Vacuum pumps recommend the use of solvent - resistant vacuum pump or diaphragm vacuum pump. The vacuum controller is optional to achieve a more efficient and controllable distillation process.

The cold source equipment is selected according to the temperature and evaporation of the cooling medium.

Typical use process (distillation process)

1)         Check whether the power supply is connected correctly and the cooling medium pipe is connected correctly before starting.

2)         Turn on the power supply of cold source equipment, vacuum equipment, heating bath and rotary evaporator.

3)         Start the cold source equipment so that the cooling medium passes through the condenser and check whether the cooling medium pipe is leaking. Start the vacuum equipment and check the vacuum connection pipe for leakage.

4)         Set the temperature of the cold source equipment and set the vacuum degree (if equipped with vacuum controller); Set the temperature of the heating bath and wait for the heating medium to reach its working temperature.

5)         The distilled solution is added to the evaporator to ensure that the volume of the solution added does not exceed 2/3 of that of the evaporator. Put the evaporator bottle on the rotary evaporator. Set the rotation speed and start the distillation.

6)         After cooling medium temperature, vacuum degree and heating bath temperature reach the preset value for a period of time, The distillation conditions can be optimized again according to the properties of the solvent, the rate of distillation and the recovery rate of condensation.

7)         When the distillation is completed, stop rotating, lift the bottle out of the heating liquid level of the bath pot, and turn off the power of the bath pot. Enter air or inert gas for pressure relief according to process requirements, close the vacuum pump and cold source equipment, remove the evaporation bottle and collection bottle for further treatment.

8)         Clean rotavator, stand by.