In order to determine which vacuum pump is most suitable for an application, it is important to understand the distillation process, the factors for distillation and the characteristics of different types of pumps. Then how to choose the vacuum pump for vacuum distillation.
How does distillation work?
Distillation, degassing, drying, filtration, membrane separation, adsorption and crystallization are all separation processes depending on the physical properties of the substances in the mixture. Distillation depends on the difference between boiling point or vapor pressure and temperature characteristics. Heating, evaporation and condensation are tools used in distillation to separate liquid components from liquid mixtures.
In order to separate liquid components with boiling point difference less than 30 ° C, it is generally recommended to use a fractionator with plate or packing. When the reflux moves up the tower, it can make the reflux repeatedly condense and re evaporate to better separate the components.
The liquid with higher volatility has lower boiling point or higher vapor pressure than the temperature curve, and is easier to evaporate. The vapor phase mixture is rich in highly volatile compounds, which can then be condensed, contained and returned for further separation and purification if necessary. The greater the difference in volatility between components and mixtures, the easier it is to separate them.
For the refining process of liquid products, the last step is often distillation. The main purposes are: to maintain the physical and chemical properties of the product; the refining yield of the product is as high as possible; taking the product as the positive fraction, to remove the low boiling part as the solvent and the high boiling part of the waste material, so as to achieve the product quality index. Liquid products usually have the heat sensitivity of thermal deterioration, so it is very important to achieve refining at a lower temperature.
Similarly, from the consideration of economy and environmental protection, the removed solvent must be recycled. The refining of liquid products is required to be carried out under high vacuum as much as possible, and the normal operating pressure is below 10Pa (one standard atmospheric pressure is 101325pa). There are two kinds of single pump: slide valve vacuum pump, liquid ring vacuum pump and roots vacuum unit.
(1) roots vacuum unit.
Its operating power is quite high. For the unit with the same air extraction capacity as claw pump, the unit power is 20kW. For the vacuum generating device in continuous operation day and night, the difference of 12.5KW means the difference of electricity charge of 90000 yuan (calculated by 300 working days and nights every year) after one year. 1 yuan / kWh).
(2) spool pump.
It must have a vacuum pump to work effectively. When the gas flows through the vacuum pump, it is inevitable that the vacuum pump oil will be entrained out. This means that the recovered solvent cannot be applied directly, or the environment can be wasted and polluted. In addition, the slide valve pump requires high operation and maintenance. In the cold season, if the switch is a little careless, it is very easy to damage.
(3) liquid ring vacuum pump.
With liquid ring vacuum pump, there is no problem in recovering solvent under normal pressure. In addition, due to its good structure, excellent processing and complete accessories, once put into use, it has low requirements, wide range of use, long service life and convenient cleaning and maintenance. When a higher vacuum is needed, it can be used as a front stage pump to form a vacuum unit conveniently.
It can be seen that the liquid ring vacuum pump is a quite reasonable option for the high vacuum refining of liquid products.