This article introduces the use of rotary evaporators in organic solvent experiments. To ensure experimental safety, data accuracy, and equipment lifespan, detailed operating procedures are provided below for reference only.
I. Pre-Experiment Preparation and Inspection
1. Equipment Connection and Layout
· Place the equipment on a stable, well-ventilated workbench or in a fume hood. Operating in a fume hood is recommended, especially when handling toxic or volatile organic solvents (a solvent recovery device can be added).
· Ensure the rotary evaporator, coolant circulation pump, and vacuum pump are securely positioned, and that the connecting pipes (vacuum tubing, coolant tubing) are not excessively bent or stretched.
• Ensure sufficient operating space for observation and emergency response.
2. Cooling Circulation System Inspection
• Confirm the cooling medium level in the cooling tank is normal. Ethylene glycol aqueous solution is typically used; the temperature must be set below zero; water is prohibited as a cryogenic coolant.
• Set the cooling temperature. For most organic solvents (such as dichloromethane, ethyl acetate, ethanol, etc.), it is usually set between -10℃ and -20℃. Too low a temperature may cause the coolant to become viscous, affecting circulation; too high a temperature will reduce condensation efficiency.
• Turn on the cooling circulation system for pre-cooling. Ensure the condenser is at a low temperature before starting rotation and heating.
3. Vacuum Pump Inspection
• Circulating Water Pump: Check the water quality in the tank. If contaminated (turbid, with an odor), immediately replace with purified or deionized water. Tap water is not recommended to prevent scale buildup and corrosion.
• Corrosion-resistant Diaphragm Vacuum Pump: Check the pump oil level and color (if it is an oil-containing type), and confirm the upstream waste liquid collection bottle is empty.
• Connect the vacuum tubing and ensure all interfaces are properly sealed.
4. Rotary Evaporator Inspection
• Sealing Check: With the system unloaded, close all valves and start the vacuum pump to create a vacuum. Observe whether the vacuum gauge or the main unit's vacuum reading remains stable at a low value (e.g., <10 mbar). If the vacuum level continues to rise, it indicates a system leak, and all sealing rings need to be checked (especially the interface between the rotary evaporator flask and the condenser flask, and the main shaft seal).
• Sealing Ring Lubrication: Before installing the glassware, lightly apply a small amount of vacuum grease to the ground glass joint seals to ensure a tight seal and facilitate disassembly. Avoid contaminating the sample.
• Cleanliness: Ensure the rotary flask, receiving flask, and condenser are clean, dry, and free of residue from the previous experiment.
II. Experimental Procedure
1. Adding and Installation:
• Pour the sample solution to be concentrated into the rotary flask, ensuring the volume does not exceed half the flask's capacity to prevent bumping or liquid being drawn into the condenser.
• Securely install the rotary flask onto the main shaft and secure it with clamps.
1. Install the receiving flask (evaporation flask).
· (Critical) Ensure all valves are closed.
2. Start Cooling and Rotation:
· Step 1: Reconfirm the cooling circulation system is running and the temperature has reached the set value.
· Step 2: Start the rotation function. Begin at a low speed (e.g., 30-50 rpm) and gradually adjust to the appropriate speed (usually 80-150 rpm). Smooth rotation helps form a uniform liquid film, improving evaporation efficiency and data reproducibility.
3. Apply Vacuum:
· Step 3: Slowly and gradually open the vacuum valve connected to the vacuum pump on the rotary evaporator.
· (Critical) Observe the liquid inside the rotating flask to prevent violent boiling or bumping due to sudden decompression. If bumping occurs, temporarily close the vacuum valve and slowly reopen it after it stabilizes.
· Adjust the system vacuum to the required value. Different solvents have corresponding optimal evaporation vacuum levels. A controllable vacuum type can be selected, and a reasonable vacuum range can be set to prevent bumping.
4. Start Heating:
• Step Four: After the vacuum and rotation have stabilized, finally start the heating bath.
• Heat the water bath (or oil bath) to the set temperature. The water bath temperature should be set 20-30°C higher than the solvent's boiling point under system pressure. Do not set it too high to avoid product decomposition or violent boiling.
5. Monitoring the Experiment:
• Closely observe the entire evaporation process: whether the rotation is smooth, whether the solvent condenses smoothly in the condenser (forming continuous droplets), whether the liquid level in the receiving flask increases normally, and whether the vacuum level is stable.
• Adjust the rotation speed, vacuum level, and heating temperature appropriately to obtain the best evaporation efficiency. (It is recommended to use a controlled rotary evaporator for easy vacuum control.)
6. End of Experiment and Shutdown:
• The sequence must be the reverse of the start-up sequence:
• Step One: Cool the heating bath to room temperature or remove the rotating flask.
• Step Two: Slowly open the vent valve/vent valve to allow the system to gradually return to atmospheric pressure. This step is extremely important! Rapid venting can cause:
· Recovered solvent in the receiving flask may be backflushed into the rotary evaporation system by the gas flow.
· Potential damage to precision pressure sensors.
· Sample splashing.
· Step 3: Turn off the rotary function.
· Step 4: Turn off the vacuum pump.
· Step 5: After the system has fully returned to atmospheric pressure, carefully remove the rotary flask and receiving flask.
· Step 6: Turn off the cooling circulation device.
III. Equipment Maintenance
1. Regularly maintain the sealing rings: Regularly inspect and clean the spindle seals and all ground joint seals. Replace immediately if aging or cracking is found. Use an appropriate amount of vacuum silicone grease.
2. Keep the system clean:
· If solvent vapor accidentally enters the condenser, clean it immediately.
· If water is used in the water bath, drain and dry it after the experiment to prevent scale and corrosion. Silicone oil is recommended as a long-term heating medium.
3. Use the vacuum pump correctly:
· Circulating water pump: Change the water regularly with clean water. Drain the water if the system will not be used for an extended period. Prevent corrosion and microbial growth.
· Diaphragm vacuum pump: Regularly check the pump oil (if applicable) and replace it on time. For corrosive solvents, a cold trap and buffer bottle must be installed before the pump to prevent solvent vapor from entering the pump body. After the experiment, empty the pump to drain any remaining liquid.
4. Gentle operation: Operate valves and knobs gently to avoid damaging precision components.
5. Freeze protection: For cooling circulation devices, when the ambient temperature may be below 0°C, antifreeze coolant must be used to prevent internal piping from freezing and cracking.
6. After the experiment, the rotating flask and vent valve can be removed to prevent them from sticking together after prolonged disuse.
