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A rotary evaporator is a piece of equipment commonly used in chemistry laboratories to reduce the volume of solvents,e.g.,in separating and purifying the products of synthetic reactions.It improves evaporation efficiency by rotating the flask so that the solvent is uniformly distributed while being heated and evaporated under vacuum.It is mainly used for rapid evaporation of solvents by means of rotary heating under reduced pressure at lower temperatures,so as to separate and purify substances.The control of vacuum degree is one of the key factors in the operation of rotary evaporator,which directly affects the speed of solvent evaporation and the purification effect of substances.
1.Selection of vacuum pumps
Vacuum pump is the main equipment for generating vacuum degree,and the selection of suitable vacuum pump is crucial for the control of vacuum degree.Commonly used vacuum pumps are oil-sealed mechanical pumps,oil-free dry mechanical pumps and water ring vacuum pumps.Oil-sealed mechanical pumps have large pumping rate,but may produce oil vapor pollution;oil-free dry mechanical pumps have no oil vapor pollution,but smaller pumping rate;water ring vacuum pumps are suitable for occasions where a large amount of water vapor exists.According to the experimental needs and budget,choose the appropriate vacuum pump.
2.Use of vacuum gauges
Vacuum gauges are used to show the vacuum level of the system and are usually of two types:pointer type and digital type.Pointer type vacuum gauges are intuitive and easy to read,but have lower accuracy;digital vacuum gauges have high accuracy,but are more expensive.During the experiment,the reading of the vacuum gauge should be observed regularly to ensure that the vacuum level is within the appropriate range.
3.Vacuum degree adjustment
The adjustment of vacuum degree is mainly realized by adjusting the pumping rate of the vacuum pump and the opening of the inlet valve.At the beginning of the experiment,you can gradually increase the pumping rate of the vacuum pump,so that the vacuum degree is gradually increased;when the vacuum degree reaches a predetermined value,adjust the inlet valve appropriately,so that the vacuum degree remains stable.In the experimental process,according to the evaporation rate of the solvent and the temperature of the material,adjust the vacuum degree at the right time.
4.Prevent solvent boiling
In the process of rotary evaporation,to avoid the occurrence of solvent boiling.When the vacuum is too high,the boiling point of the solvent is lowered,easy to burst boiling.In order to prevent the explosion of boiling,you can start heating before opening the air inlet valve,so that the air pressure in the system is slightly higher than atmospheric pressure,and then gradually increase the vacuum.In addition,you can also add anti-boiling stone or use a rotary evaporator with a cooling device to prevent boiling.
5.Handling after the end of the experiment
At the end of the experiment,gradually reduce the pumping rate of the vacuum pump and then turn off the vacuum pump.Before shutting down the vacuum pump,close the air inlet valve so that impurities in the air do not enter the system.Finally,the change of vacuum level during the experiment should be recorded so that the experimental results can be analyzed and summarized.
Control of the vacuum of the rotary evaporator needs to be adjusted according to the specific requirements of the experiment and the characteristics of the solvent,and the operator should operate reasonably according to the experimental program and equipment instructions to ensure the safety and accuracy of the experiment.At the same time,the operation process should strictly comply with laboratory safety regulations,wear appropriate personal protective equipment.
The vacuum of the rotary evaporator can be effectively controlled by choosing a suitable vacuum pump,using a vacuum gauge,reasonably adjusting the vacuum level,preventing solvent from bursting and boiling,and correctly handling the system at the end of the experiment,thus improving the experimental effect.
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