The quality of a vacuum pump depends on its mechanical structure and the quality of the oil. It must be protected when using a vacuum pump. If the volatile organic solvent is distilled, the organic solvent will increase the vapor pressure by the oil absorption, which will reduce the evacuation efficiency. If it is acidic, it will corrode the oil pump. If it is water vapor, it will make the oil into milk. The turbid fluid evacuated the vacuum pump.
Therefore, when using a vacuum pump, the following points must be observed:
Between the distillation system and the vacuum pump, an absorption device must be installed.
Before distillation, the organic solvent vapor must be completely pumped out of the system.
If it is possible to pump air with a water pump, use a water pump as much as possible. For example, if the distillation material contains volatile substances, use a water pump to depressurize it, then use a pump.
The decompression system must be kept air-tight, all rubber plugs should be properly sized and vented, and rubber hoses should be used for vacuum hoses. Ground glass coated with vacuum grease.
Depending on the scope of use and pumping efficiency, vacuum pumps can be divided into three categories:
(1) General pumps, pressure can reach 1.333 ~ 100kPa (10 ~ 760mmHg) as "coarse" vacuum.
(2) The oil pump, pressure up to 0.133~133.3Pa (0.001~1mmHg) is the "second highest" vacuum.
(3) Diffusion pump, the pressure can reach 0.133Pa or less, (10-3mmHg) as "high" vacuum.
For lower pressures, use an oil pump that can pump 133.3 Pa (1 mmHg) or less.
In the organic chemistry laboratory, there are two kinds of vacuum pumps: a water pump and a vacuum pump. If a low pressure is not required, a water pump is available. If the water pump has a good structure and a high water pressure, the pumping efficiency can reach 1067 to 3333 Pa (8 ~25mmHg). The minimum pressure that a pump can draw is theoretically equivalent to the water vapor pressure at that time. For example, when the water temperature is 25° C., 20° C., and 10° C., the pressure of water vapor is 3192, 2394, and 1197 Pa (8-25 mmHg), respectively. When using a water pump to pump air, install a safety bottle in front of the pump to reduce the water pressure and draw back the water. Before stopping the pumping, you should first vent the air and then turn off the water pump.
More vacuum pump information is available at China Vacuum Pump Trading Network (/).
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