Why Recover Solvents?
Solvent recovery is a common process in petrochemical, pharmaceutical, chemical and other industries. The primary reasons for recovering organic solvents are listed below:
Solvents can be high-value substances or act as catalysts. Recovering and recycling solvents helps cut production costs.
Organic solvents are environmentally hazardous. They must be recovered and treated prior to discharge to reduce the burden on environmental protection.
Principle of Solvent Recovery Using Vacuum Pumps
Vacuum distillation is widely adopted to recover organic solvents via distillation. Certain organic solvents feature high thermal sensitivity and are unstable at elevated temperatures. The negative pressure generated by vacuum pumps enables the recovery of such organic solvents at lower temperatures.
Selection of Vacuum Pumps for Solvent Recovery
- Liquid Ring Vacuum Pumps The negative pressure generated by liquid ring vacuum pumps enables organic solvent recovery. Working principle: the liquid ring vacuum pump creates negative pressure inside the reactor. After vaporization, the organic solvent flows into a condenser, where vapor is condensed into liquid and transferred to the recovery tank connected to the condenser, thus completing the recovery of organic solvents.
- Screw Vacuum Pumps Screw vacuum pumps can also deliver negative pressure for organic solvent recovery. Working principle: the screw pump generates negative pressure for the reactor. Vaporized organic solvent flows directly into the screw vacuum pump. A condenser is fitted at the exhaust port of the screw vacuum pump. The liquefied organic solvent then flows into the solvent recovery tank to realize solvent recovery.
Advantages and Disadvantages of Liquid Ring Vacuum Pumps and Screw Vacuum Pumps for Solvent Recovery
Both liquid ring vacuum pumps and screw vacuum pumps generate negative pressure for reactors. Taking advantage of differences in boiling points of organic solvents, they recover solvents via vacuum distillation. Apart from differences in system configuration, solvent recovery systems equipped with liquid ring vacuum pumps and screw vacuum pumps feature distinct characteristics.
Disadvantages of solvent recovery using liquid ring pumps:
- Liquid ring pumps rely on a water-based liquid ring to compress and seal gas. If the recovered organic solvent reacts with water to form new corrosive substances, these substances may corrode the liquid ring pump and shorten its service life.
- During solvent recovery with liquid ring pumps, approximately 5% of the gaseous solvent may bypass the condenser and directly enter the liquid ring pump to dissolve in water. As a result, complete recovery of organic solvents cannot be achieved.
- The ultimate pressure of liquid ring vacuum pumps is affected by water temperature. At a water temperature of 15 °C, the typical ultimate vacuum reaches 33 mbar.
Solvent recovery using screw pumps enables full recovery of organic solvents. Since screw pumps operate without water as sealing liquid and feature an oil-free pump chamber, the gas will neither be absorbed nor contaminated when passing through the pump. Complete and clean organic solvents can therefore be obtained. Furthermore, the inlet ultimate pressure of screw vacuum pumps can reach approximately 10 Pa. Nevertheless, the operating temperature of screw pumps stands at around 60–70 °C.
The specific pump model or vacuum pump unit to be selected requires a detailed analysis of process gas characteristics, vacuum level at the operating point, required pumping speed and other parameters.
liquid ring vacuum pump screw vacuum pump
If you have solvent recovery requirements, please send us your working condition parameters, and we can assist you with pump selection.
