Fuente: Robert M. Rioux, Ajay Sathe & Zhifeng Chen, Universidad Estatal de Pensilvania, University Park, PA
vacío se requiere de una serie de procedimientos de laboratorio. Esto se logra más rutinariamente en el laboratorio por el uso de bombas de vacío. Además de trabajar a bajas presiones, bombas de vacío puede usarse para habilitar el cambio rápido de las atmósferas en un reactor o un frasco por evacuación y rellenar.
Operations requiring vacuum have multiple hazards associated with them. Vessel implosion can lead to flying glass and other materials, the release of chemicals to the working environment, and potentially fire due to the condensation of liquid oxygen. Vacuum operations should be set up properly and only operated after potential risks have been identified and properly mitigated.
Vacuum pumps are employed in a wide array of laboratory procedures. Common examples include filtration, drying, degassing, evaporative coating, and mass spectrometry.
Pump equipment must be maintained and operated safely to prevent equipment failures, explosions and chemical release. This video will introduce several common pump designs, discuss common precautions to be observed when setting up vacuum equipment, and demonstrate operational safety.
Let’s begin by exploring various pump designs.
In rotary-vane pumps air and other gases are drawn through an inlet by a rotor. The gases are forced via an oil-sealed exhaust, which prevents backflow, to the outlet leaving the system. Rotary vane pumps can generate vacuums of ten to the negative three Torr. These pumps are self-lubricating, but require oil changes and are vulnerable to corrosion by water vapor.
In scroll pumps air passes through an inlet between two eccentric spiral scrolls, one fixed, the other orbiting. The motion compresses the air and pushes it toward the outlet. Vacuums of ten to the negative two Torr can be achieved. Scroll pumps are “dry” mechanisms – they do not require oil or water, but the scrolls must be periodically replaced as they wear down. Scroll pumps and rotary-vane pumps are suitable for distillation, filtration, and degassing.
A water aspirator is another type of pump often found in laboratories. In this type of pump water enters through an inlet to a high-speed nozzle, and exits as a low-pressure fluid jet. The gases are drawn in through a side port and forced to the outlet. Water aspirators produce vacuums of only 10 Torr. Although they easily connect to ordinary sink faucets, they require large amounts of water. Water aspirators are frequently used for drying and extraction.
Lastly, turbomolecular pumps produce ultrahigh vacuum. Air is forced in through alternating stator and turbine blades that drive the gas molecules through the outlet connected to a roughing pump. Turbomolecular pumps can produce vacuums as low as ten to the negative ten Torr, but require another pump to first lower the pressure to 1 Torr. Turbomolecular pumps are used for electron microscopy, crystal growth, and evaporative coating.
Now that you’re familiar with the designs, let’s examine personal protection and safety measures that should be observed before operating these vacuum pumps.
If possible, operate all vacuum equipment inside a fume hood with the sash lowered. Wear safety goggles and a face shield. These provide protection against chemicals and debris in case the glassware implodes under the vacuum.
Use glassware and equipment rated for use with the expected level of vacuum. Check the glassware and tubing for cracks or other defects. Defective or inappropriate equipment can easily implode under vacuum. Wrap glassware larger than 250 mL in tape, netting, or plastic, as a further precaution against flying debris.
If the procedure is known to generate corrosive vapors, select a pump that can withstand those vapors. Ensure the pump is clean and free from corrosion. For oil pumps, check the oil level and change the oil periodically.
Ensure the pump is level and balanced. Connect the pump outlet to the fume hood exhaust. Securely place tubing inside the hood to prevent the release of chemicals. Ensure all tubing is unrestricted, and that there are no leaks, especially near the flanges.
Now that the vacuum pump is set up, let’s examine safety considerations during and after pump operation.
Connect the pump inlet to the glassware via a cold trap. A cold trap is a glass container that protects the pump by freezing volatile organics evacuated from the apparatus.
During the procedure, the cold trap is submerged in dry ice or a Dewar of liquid nitrogen. Use cryogenic protective equipment when handling these coolants.
A potential hazard is the condensation of oxygen in the cold trap to yield highly explosive liquid nitrogen. To prevent its formation, start the vacuum pump and evacuate the apparatus before submerging the cold trap in liquid nitrogen. Never allow the cold trap to contact liquid nitrogen if not under vacuum, and never open the vacuum line to air with the cold trap in place.
Check the cold trap for condensed solvents and liquid oxygen regularly. If necessary empty the cold trap to prevent solvents entering the tubing and vacuum pump. If liquid oxygen, a light blue fluid, is visible, terminate the procedure and call for assistance, but do not stop the vacuum or remove the liquid nitrogen.
Once the procedure is complete, withdraw the cold trap from the coolant and then switch off the pump. Bleed the vacuum lines slowly before disconnecting the cold trap and pump, to prevent sudden pressurization.
You’ve just watched JoVE’s introduction to lab safety for vacuum-based equipment. You should now be familiar with different types of vacuum pumps, their potential hazards, and precautions to be observed to ensure safe operation. As always, thanks for watching!
