JP7738315B2 - How to control a rotary evaporator - Google Patents

Description

The present invention relates to a method for controlling a rotary evaporator.

Conventionally, vacuum concentration devices such as rotary evaporators are equipped with a vacuum controller (such as a vacuum pump) equipped with a pressure sensor to control the device. The vacuum controller controls the degree of vacuum within the device by adjusting the amount of cooling water flowing through it and the vertical position of the constant temperature water bath.

Furthermore, when concentrating a sample while controlling the degree of vacuum in a conventional rotary evaporator, gases (such as air) dissolved in the sample can suddenly foam, a phenomenon known as bumping. When this type of bumping occurs, the sample boils violently, forming droplets that flow into the collection flask along with the vapor. Therefore, care must be taken to prevent bumping as much as possible. To prevent sample bumping, a control method has been proposed, as shown in Patent Document 1, in which the vacuum is reduced at a predetermined reduction gradient depending on the type of solvent from the start of vacuum operation until a predetermined degree of vacuum is reached.

Japanese Unexamined Patent Publication No. 8-89705

However, due to the design of the device, conventional vacuum controllers have a pressure sensor located inside the vacuum controller, so they do not measure the vapor pressure immediately after the liquid in the distillation flask evaporates. Instead, they display the value after the vapor has been cooled in the cooler, i.e., a value that is slower than the actual value measured immediately after evaporation. As a result, it is not possible to accurately measure the saturated vapor pressure of the vapor in the distillation flask. Furthermore, with liquids that are prone to bumping or foaming, the boiling point detection may malfunction due to the generation of bubbles caused by bumping or foaming, raising concerns that the evaporation process may not be accurately tracked.

Furthermore, gradient control such as that described in Patent Document 1 is sometimes impractical due to the long gradient time, and customization of gradient control may be necessary depending on the sample.

The present invention aims to provide a method for controlling a rotary evaporator that measures the saturated vapor pressure temperature (boiling point under reduced pressure) of vapor generated from the evaporation section (evaporation flask) of the rotary evaporator in close proximity to the evaporation section, enabling more accurate measurement and control of the saturated vapor pressure temperature.

To achieve the above-mentioned objective, the present invention provides a method for controlling a rotary evaporator that concentrates a sample solution by rotating an evaporating flask containing a solution using a motor and vacuum-suctioning the sample solution in the evaporating flask while constantly heating the evaporating flask. The method detects the vapor temperature of the sample solution in the evaporating flask, which is heated at a constant temperature in a constant-temperature water bath, using a sensor installed in the evaporating flask. When the detected temperature detected by the sensor reaches a certain temperature higher than a set vapor temperature, which is set between the temperature of the constant-temperature water bath and the temperature of the cooling water, a solenoid valve opens and a vacuum pump performs vacuum suction, thereby lowering the vapor temperature. When the detected temperature reaches a certain temperature lower than the set vapor temperature, the solenoid valve closes and the vacuum pump stops vacuum suction, thereby raising the vapor temperature. This repeated control continues the concentration process.

Furthermore, as a pre-processing step of the repetitive control, if the detected temperature is higher than the steam set temperature, the evaporation flask is no longer immersed in the thermostatic water bath, and only vacuum suction by the vacuum pump is performed, initial boiling is initiated, and then the evaporation flask is immersed in the thermostatic water bath; if the detected temperature is lower than the steam set temperature, vacuum suction by the vacuum pump is stopped while the evaporation flask is immersed in the thermostatic water bath, the detected temperature is raised to a temperature higher than the steam set temperature, vacuum suction by the vacuum pump is resumed, and initial boiling is initiated.

The rotary evaporator control method of the present invention installs a temperature sensor near the liquid surface in the evaporating flask, allowing for more accurate measurement of the saturated vapor pressure temperature of the generated vapor and appropriate operation of the entire device. Even when using liquids that tend to bump or foam, bumping can be prevented.

FIG. 1 is a diagram showing an example of a rotary evaporator to which the method of the present invention can be applied. FIG. 1 is a diagram showing various states when ethanol is used as a sample solution and suction is performed inside a rotary evaporator device using a vacuum pump (diaphragm pump). FIG. 3 is a detailed view of a portion of FIG. 2; FIG. 10 is a diagram showing the state of the degree of vacuum and the temperature when the control method of the present invention is applied using ethanol as a sample solution.

An example of a rotary evaporator to which the method of the present invention can be applied is described below with reference to the drawings. Figure 1 shows an outline of the rotary evaporator. An evaporating flask 1 containing a sample solution is rotatably held by a drive unit 3 attached to a stand 2 that can be raised and lowered, and the evaporating flask 1 is immersed in a thermostatic water bath 4 with a built-in heater.

A condenser tube 5 is connected to this evaporating flask 1 via a drive unit 3. A cooling tube 7 is disposed inside the condenser tube 5, and at its bottom is a recovery flask 6 for recovering condensed solvent, etc., and an exhaust port 9 connected to a vacuum pump 8.

A vacuum level display monitor 10 and a solenoid valve 11 are provided between the exhaust port 9 and the vacuum pump 8. The solenoid valve 11 is controlled to open and close depending on the steam temperature, allowing the vacuum pump 8 to suction the inside of the evaporator. A vent needle valve 12 is also provided between the solenoid valve 11 and the vacuum pump 8, allowing ventilation to adjust the vacuum state as needed.

The evaporating flask 1 is also equipped with a steam temperature sensor 13 that detects the steam temperature inside the flask. The solenoid valve 11 is connected to a temperature controller 14 and a relay 15, and the degree of vacuum is controlled and the steam temperature is adjusted by opening and closing the solenoid valve 11 and activating the relay 15.

Using a rotary evaporator configured as described above, the control method of the present invention is carried out as follows.

The evaporating flask 1 containing the sample solution is rotated by a motor using a drive unit 3, and the sample solution in the evaporating flask 1 is heated at a constant temperature under vacuum using a vapor temperature-controlled vacuum controller, which is the control device of the present invention, thereby concentrating the sample solution. The control device controls the heater that heats the constant temperature water bath 4, the rotation drive motor that is the drive unit 3 that rotates the evaporating flask 1, and the solenoid valve 11 that maintains a vacuum inside the evaporating flask 1. The vapor temperature of the sample solution in the evaporating flask 1, which is heated at a constant temperature in the constant temperature water bath 4, is detected by a vapor temperature detection sensor 13 installed in the evaporating flask 1, and the control device automatically controls the vapor temperature and vacuum by opening and closing the solenoid valve 11, etc., while the sample solution concentration process continues until the sample solution is concentrated to dryness.

First, the temperature of the vapor generated when concentrating the sample solution in the evaporating flask 1 is detected by the vapor temperature detection sensor 13, as close as possible to the point where the vapor is generated (the liquid surface in the sample container). As the concentration process progresses and the amount of liquid in the evaporating flask 1 decreases, the vapor temperature begins to rise, making it possible to predict the end point of the concentration process. For example, by controlling the solenoid valve 11 to stop the concentration process at a point where the temperature has risen by any desired temperature (e.g., 5°C) above the set temperature, the sample solution can be considered to have been completely concentrated and dried.

Before describing the specific control method for completely concentrating and drying the sample solution, we will first discuss the phenomenon of bumping. Figure 2 shows various conditions, such as pressure, when a rotary evaporator is used with ethanol as the sample solution and without vacuum control, while suctioning the inside of the apparatus using a vacuum pump (diaphragm pump). Figure 3 is a detailed diagram of a portion of Figure 2. In conventional rotary evaporators, the temperatures of the constant-temperature water bath 4 and the cooling water circulator for the condenser tube 5 are set. Once the respective set temperatures are reached, the rotary evaporator is adjusted to the specified rotation speed, and the vacuum pump is activated without immersing the evaporating flask 1 in the constant-temperature water bath 4. Once the vacuum level in the evaporating flask 1 has dropped to a certain level, the evaporating flask 1 is immersed in the constant-temperature water bath 4, and the evaporation operation begins. When the sample solution in the evaporating flask 1 is ethanol and the apparatus is operated, the saturated vapor pressure in the evaporating flask, i.e., the vacuum level in the system, behaves as shown in the "Operating Pressure" column of Figure 2.

As mentioned above, when the degree of vacuum in the system is reduced, immersing the evaporating flask 1 in the thermostatic water bath 4 causes the vapor temperature in the evaporating flask 1 to rise due to the heat from the thermostatic water bath 4. Then, when the degree of vacuum (operating pressure) in the system reaches saturated vapor pressure, the thermal energy accumulated inside is suddenly released, causing evaporation and the formation of bubbles in the liquid. This condition is called bumping. In particular, if the sample solution is foaming, foaming will occur when the degree of vacuum reaches saturated vapor pressure, and bumping is likely to occur along with the foaming (the "bumping prone" region in Figure 2).

Explaining further with reference to Figure 3, as described above, the vacuum pump 8 reduces the pressure inside the device as shown in the "Operating Pressure" column. This reduction in pressure also lowers the boiling point of the sample solution (the boiling point under the operating pressure). When the reduced boiling point and the sample temperature (the vapor temperature detected by the sensor) become equal, the sample solution begins to boil. At this point, the accumulated heat energy is released, raising the vapor temperature and increasing the amount of evaporation, making unexpected bumping (boiling) more likely (near the black dot in Figure 3). When a typical vacuum pump is used, the device continues to draw air at a constant speed, increasing the vacuum inside the device and lowering the boiling point. However, the sample temperature does not decrease until the saturated vapor pressure corresponding to the sample temperature is reached. Therefore, even when the vacuum corresponding to the saturated vapor pressure of the sample is reached, there is a slight delay in boiling. As a result, the vacuum is reduced too much by the vacuum pump, and the sample solution begins to boil vigorously in an attempt to return to the saturated vapor pressure at the set temperature. However, this boiling is so intense that it swells more than evaporation 1, and the unboiled sample liquid is violently ejected into receiving flask 6, with most of the liquid in evaporation flask 1 moving. If this overheating and excessive vacuum can be avoided, the concentration process can be completed without bumping of the sample solution.

The rotary evaporator control method of the present invention involves a pretreatment process to initiate initial boiling without causing bumping, particularly in the case of samples with strong foaming and bumping tendencies, and then controls the opening and closing of the solenoid valve 11 while comparing the temperature detected by the vapor temperature detection sensor 13 (detected temperature) with the set temperature, thereby achieving stable control.

In the present invention, the required steam temperature is first set (steam set temperature). The temperature of the constant temperature water bath 4 and the cooling water temperature are then set accordingly (for example, if the temperature of the constant temperature water bath 4 is 40°C and the temperature of the cooling water is 5°C, the set temperature is 20°C).

Next, we will explain the pre-treatment process. For example, in areas where bumping is likely to occur, such as near the ● part in Figure 3, bumping and foaming can be prevented by controlling the boiling point so that it drops slowly below the temperature in air that is close to unheated.

If the detected temperature is higher than the set steam temperature, it is assumed that the sample solution is in a state where bumping is likely to occur, so immersion of the evaporating flask 1 in the constant temperature water bath 4 is discontinued and only vacuum suction by the vacuum pump 8 is performed. For samples with strong foaming or bumping tendencies, if the difference between the sample solution temperature and the set steam temperature is 1°C or more, the set steam temperature is brought closer to the sample solution temperature (0-0.5°C higher), and then, once boiling of the sample solution is confirmed (initial boiling has begun), the set steam temperature is reset to the specified temperature, and the evaporating flask 1 is immersed in the constant temperature water bath 4 to continue the concentration process.

Also, if the detected temperature is lower than the set steam temperature, the evaporation flask is temporarily immersed in the thermostatic water bath 4, the vacuum suction by the vacuum pump 8 is stopped, the liquid temperature of the sample solution is raised by 0 to 0.5°C above the set temperature, and vacuum suction by the vacuum pump 8 is resumed. After that, once boiling of the sample solution is confirmed, the evaporation flask 1 is slowly immersed in the thermostatic water bath 4 to continue the concentration process. In this way, the concentration process of the sample solution can be continued without bumping or foaming.

When using a vacuum pump 8 with a large displacement, the time it takes for the sample to reach its saturated vapor pressure can be adjusted by adjusting the vent needle valve 12 to let in a small amount of air, thereby preventing bumping during the initial boiling process.

Next, we will explain the control method used when continuing the concentration process after the initial boiling has begun as described above. When the sample begins to boil, the temperature of the sample solution (temperature at saturated vapor pressure) also drops as it boils due to the pressure reduction caused by the vacuum pump 8. When the detected temperature and the set vapor temperature become the same, stable control becomes possible. In other words, since the thermal energy that had been accumulated up to that point is being released, the degree of vacuum is dependent on the stable vapor temperature, and control can continue.

Here, we will explain in more detail the control of the vacuum pump 8 and solenoid valve 11 used to concentrate the sample solution. When the detected temperature of the vacuum pump 8 reaches a certain temperature (e.g., 0.1°C) higher than the set vapor temperature, solenoid valve 11 opens and performs vacuum suction. This increases the degree of vacuum within the rotary evaporator system, causing the sample temperature to drop. When the detected temperature reaches a certain temperature (e.g., 0.1°C) lower than the set vapor temperature, solenoid valve 11 closes and vacuum suction is stopped. This causes the degree of vacuum within the evaporating flask to deteriorate, and the sample temperature begins to rise. This process is repeated to ensure stable control.

For example, the sample solution was ethanol, the temperature of the thermostatic water bath 4 was 40°C ± 2°C, the cooling water temperature was 2-4°C, the rotation speed of the drive unit 3 was 120 rpm, the vapor temperature was set to 20°C, the constant temperature was set to 0.1°C, and evaporation was initiated after the pretreatment process. The results are shown in Figure 4, where the solenoid valve 11 was opened and closed (repeated control) as described above. At a concentration time of 25 minutes and 4 seconds, 399.05 g of ethanol sample was recovered from 400.58 g, representing a recovery rate of 99.6%. Although the constant temperature was controlled at 0.1°C, there was a response delay in the solenoid valve opening and closing, resulting in the vapor temperature being controlled between 17.8.3°C and 20.6°C. Furthermore, by controlling the opening and closing of the solenoid valve 11 for a certain period of time while this control is being performed, it is possible to perform intermittent vacuum suction inside the evaporation flask 1. This range of state changes makes it possible to avoid sudden changes in the state of the sample solution, allowing the concentration process to continue stably and preventing further bumping.

Furthermore, as evaporation progresses and the amount of concentrated residue decreases, the detection temperature rises, making repeated control as described above impossible. However, this state is not a problem as it indicates that concentration is nearing completion. In Figure 4, the process is considered complete when the temperature has risen by approximately 6°C, but if the temperature rises by, for example, 5°C from the steam set temperature, the solenoid valve 11 automatically closes to stop the concentration process, and the sample solution can be considered to have been completely concentrated and dried.

Note that although ethanol is used as the sample solution above, other solvents may also be used.

1. Evaporation flask, 2. Stand, 3. Drive unit, 4. Thermostatic water bath, 5. Condenser tube, 6. Recovery flask, 7. Cooling tube, 8. Vacuum pump, 9. Exhaust port, 10. Vacuum level display monitor, 11. Solenoid valve, 12. Vent needle valve, 13. Steam temperature sensor, 14. Temperature controller, 15. Relay

Claims (2)

A method for controlling a rotary evaporator that concentrates a sample solution by rotating an evaporating flask containing the sample solution by motor drive and vacuum-suctioning the sample solution in the evaporating flask while heating the sample solution at a constant temperature, comprising:
The vapor temperature of the sample solution in an evaporation flask, which is heated to a constant temperature in a constant temperature water bath, is detected by a sensor provided in the evaporation flask;
When the temperature detected by the sensor becomes higher by a certain temperature than the steam set temperature, which is set between the temperature of the constant temperature water bath and the temperature of the cooling water, the solenoid valve opens and the vacuum pump performs vacuum suction to lower the steam temperature.
When the detected temperature becomes lower than the steam set temperature by a certain temperature, the solenoid valve closes and the vacuum pump stops vacuum suction, thereby raising the steam temperature.
This is a method for controlling a rotary evaporator that continues the concentration process by repeating these steps. As a pre-processing step of the repetitive control,
If the detected temperature is higher than the steam set temperature, the evaporation flask is no longer immersed in the constant temperature water bath, and only vacuum suction by the vacuum pump is performed, and after initial boiling has started, the evaporation flask is immersed in the constant temperature water bath;
2. The method for controlling a rotary evaporator according to claim 1, wherein, when the detected temperature is lower than the set steam temperature, the vacuum suction by the vacuum pump is stopped while the evaporating flask is immersed in the thermostatic water bath, the detected temperature is raised to a level higher than the set steam temperature, and the vacuum suction by the vacuum pump is resumed to start initial boiling.