Tech Team · Kintek Solution

The boiling point of ethanol in a rotary evaporator is not a fixed value but depends on the vacuum level applied. Under standard atmospheric pressure (760 mmHg), ethanol boils at 78.37°C. However, in a rotary evaporator, the boiling point decreases as the vacuum level increases. For ethanol extraction, the recommended vapor temperature is typically maintained between 15-20°C, which requires adjusting the vacuum level and water bath temperature accordingly. The water bath temperature is usually set about 20°C higher than the desired vapor temperature to ensure efficient evaporation. Factors such as rotation speed, condenser efficiency, and system tightness also play a role in achieving the desired boiling point and evaporation rate.

Key Points Explained:

1. Boiling Point of Ethanol Under Vacuum:

   • Under standard atmospheric pressure (760 mmHg), ethanol boils at 78.37°C.
   • In a rotary evaporator, the boiling point decreases as the vacuum level increases due to reduced pressure.
   • The boiling point can be significantly lower than 78.37°C, depending on the vacuum applied.

2. Recommended Vapor Temperature for Ethanol:

   • The recommended vapor temperature for ethanol in rotary evaporation is between 15-20°C.
   • This temperature range ensures efficient recovery of ethanol while minimizing solvent loss.

3. Water Bath Temperature:

   • The water bath temperature is typically set about 20°C higher than the desired vapor temperature.
   • For ethanol, if the target vapor temperature is 15-20°C, the water bath should be set to approximately 35-40°C.

4. Factors Influencing Evaporation:

   • Vacuum Level: A higher vacuum lowers the boiling point, allowing ethanol to evaporate at lower temperatures.
   • Rotation Speed: Faster rotation increases the surface area of the liquid, enhancing evaporation.
   • Condenser Efficiency: Efficient condensation ensures that the evaporated ethanol is effectively recovered.
   • System Tightness: A well-sealed system maintains the desired vacuum level, which is crucial for controlling the boiling point.

5. Key Components Affecting Vacuum:

   • Vacuum Pump: The power and efficiency of the vacuum pump determine the achievable vacuum level.
   • Sealing Rings and Tubes: Materials like PTFE offer better wear and corrosion resistance, ensuring a tight seal.
   • System Pressure Resistance: The system must balance the vacuum level with the equipment's pressure resistance to avoid damage.

6. Practical Considerations for Ethanol Extraction:

   • Heat Sensitivity: Ethanol is relatively heat-sensitive, so precise control of the water bath temperature and vacuum level is essential to prevent degradation.
   • Evaporation Rate: The rate of evaporation can be optimized by adjusting the rotation speed, vacuum level, and water bath temperature.
   • Condenser Temperature: The condenser should be kept at a low temperature to ensure efficient recovery of the evaporated ethanol.

By understanding and controlling these factors, you can effectively determine and manage the boiling point of ethanol in a rotary evaporator, ensuring efficient and safe extraction.

Summary Table:

Factor	Details
Boiling Point (760 mmHg)	78.37°C
Recommended Vapor Temp	15-20°C
Water Bath Temp	20°C higher than vapor temp (e.g., 35-40°C for 15-20°C vapor temp)
Key Influencing Factors	Vacuum level, rotation speed, condenser efficiency, system tightness
Heat Sensitivity	Ethanol is heat-sensitive; precise control of temperature and vacuum is key

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