When using a laboratory instrument, a rotating evaporator, I usually don’t know how to set it up when I use it for the first time, especially if I don’t know what to separate, what is the temperature setting of the rotary evaporator? What are the requirements? Today, I will discuss the temperature setting of the rotary evaporator.
Some people who use rotary evaporators for the first time have many problems. For example, will a solvent with a higher boiling point than water remain in the original flask, while a solvent with a lower boiling point than water will remain in the flask connected to the condenser, such as acetone? In addition, how should the water temperature be set?
In fact, when we use the rotary steamer, the common solvents can be evaporated. The temperature depends on the vacuum of your system. If the vacuum is high enough, 50 degrees can be used to steam the DMF out. Usually, 30 degrees is enough. The temperature of the water is usually the solvent can be steamed at 45 degrees. If the water is distilled, a higher temperature is required, but it should not exceed 65 degrees.
In addition, I personally think that the key to the use of rotary steaming is not the rotary steaming itself, but the water pump. When the distillation problem occurs, most of them are shut down. If the steaming is slow, the first thing to consider is the vacuum degree rather than the water bath temperature.
If the temperature of the water bath is too high, the steam may be condensed and not sucked into the pump in time. If the water rotovap pumps are used for a long time, the water inside should be replaced in time, otherwise, the vacuum will drop if the temperature is too high.
Generally, the inlet and outlet water are opened at the same time for use, or some ice cubes are added to it. The mixed solvent usually has azeotrope. If you want to separate the two solvents, the effect is very poor. The temperature setting is roughly the pressure halved and the boiling point is reduced by 15°C. The fugacity of the solvent is also related. It cannot be said that the low boiling point at room temperature must come out first.
First of all, you must understand the boiling point of the substance you want to separate. Generally, the temperature setting is 2 to 3 degrees lower than the boiling point and it can be evaporated. For example, the solvent is toluene, the general temperature is set to 80°C or higher to be distilled. Food testing is generally set For pesticide residue testing, the temperature of the water bath should not be higher than 40 degrees.
If the rotary evaporator evaporates the methanol aqueous solution, the basic temperature can be adjusted to 35-40 degrees. If the solution concentration is high, the pressure should not exceed 0.08, which is easy to spray. I don’t know if the contents of the solution will be damaged if heated. If you are afraid of damage, you can evaporate to dryness under reduced pressure at 60 degrees; if you are not afraid, you can use a rotary evaporator to remove the methanol first, and the rest Steam to dry at 80-100 degrees in a water bath. If your thing is a plant extract, just remove the methanol, and there is no problem if some water remains.
Generally, the solvent reaches 35 degrees. Using a rotary evaporator is a vacuum distillation. If the boiling point of the removed solvent is above 100 degrees, it should be set between 60 and 70 degrees. At the same time, when the temperature of the condensing medium used is low, the solvent removal speed can be accelerated. If the rotary evaporator is used to remove toluene, it can be set to about 64 degrees, and the condensing temperature of the intelligent constant temperature circulator is about 0 degrees, which can not only ensure a faster desolventizing speed but also prevent the volatilization of toluene from polluting the environment.
Rotary steaming speed is related to temperature. It cannot be said separately. The speed depends on the heating temperature of the water bath. Generally speaking, the high temperature steaming speed is fast, and the low temperature evaporation speed is slow; the higher the boiling point of the steamed solvent, the more difficult it is to steam; The higher the vacuum, the easier it is to steam out, that is, the lower the internal pressure, the easier it is to steam out. The judgment is based on the dripping speed of the vaporized solvent (approximately 2-3 drops per second) while avoiding bumping of the solution.
Specifically: Please select the temperature of the water bath according to the vacuum degree provided by the pump and the boiling point of the solvent, such as water solvent and water pump rotary steaming, usually about 60-70C, and then turn on the rotary switch to start from zero. Until the solvent drop rate reaches the target. Some pumps can provide adjustable or higher vacuum, so the water temperature should be set lower when heating starts, and the speed should be lower. That is to say, the higher the vacuum, the lower the initial water temperature.