Control method for rotary evaporators

Abstract

To provide a control method of a vapor temperature of a rotary evaporator that can measure and control a saturated vapor pressure temperature more accurately.SOLUTION: A vapor temperature of a sample solution in an evaporation flask 1 being heated in a constant temperature water tank 4 is detected with a sensor 13 provided in the evaporation flask 1. A concentration process is continued by repeat control by which a step in which when the detected temperature is higher by a given temperature than a set vapor temperature set between a temperature of the constant temperature water tank 4 and a temperature of cooling water, an electromagnetic valve 11 opens, so that vacuum aspiration by a vacuum pump 8 is performed to decrease the vapor temperature and a step in which when the detected temperature becomes lower by the given temperature than the set vapor temperature, the electromagnetic valve 11 closes, so that the vacuum aspiration by the vacuum pump 8 is stopped to increase the vapor temperature are repeatedly performed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a rotary evaporator. [Background technology]

[0002] Conventionally, a vacuum concentration apparatus such as a rotary evaporator is provided with a vacuum controller (such as a vacuum pump) equipped with a pressure sensor to control the apparatus. The vacuum controller controls the degree of vacuum within the apparatus by adjusting the flow rate of cooling water and the vertical position of the constant temperature water bath.

[0003] Furthermore, when concentrating a sample while controlling the degree of vacuum in a conventional rotary evaporator, a phenomenon known as bumping may occur, in which gas (e.g., air) dissolved in the sample suddenly foams. When this bumping occurs, the sample boils violently, forming droplets that flow into the recovery flask along with the vapor. Therefore, care must be taken to prevent bumping as much as possible. To prevent this, a control method has been proposed, as shown in Patent Document 1, in which the degree of vacuum is reduced at a predetermined decompression gradient depending on the type of solvent from the start of decompression operation until a predetermined degree of vacuum is reached. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-89705 Summary of the Invention [Problem to be solved by the invention]

[0005] However, due to the design of conventional vacuum controllers, the pressure sensor is located inside the controller, so it does not measure the vapor pressure immediately after evaporation of the liquid in the distillation flask. Instead, it displays the value after the vapor has been cooled in a cooler, i.e., a value slower than the actual value 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, for 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.

[0006] Furthermore, the gradient control described in Patent Document 1 is sometimes impractical due to the long gradient time, and customization of the gradient control may be required depending on the sample.

[0007] Therefore, an object of the present invention is to provide a method for controlling a rotary evaporator that can measure the saturated vapor pressure temperature (boiling point under reduced pressure) of vapor generated from the evaporation section (evaporation flask) of a rotary evaporator in the immediate vicinity of the evaporation section, thereby enabling more accurate measurement and control of the saturated vapor pressure temperature. [Means for solving the problem]

[0008] In order to achieve the above object, 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 comprises the steps of: detecting 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 provided in the evaporating flask; when the detected temperature detected by the sensor reaches a certain temperature higher than a set vapor temperature that is set between the temperature of the constant-temperature water bath and the temperature of the cooling water, opening a solenoid valve and performing vacuum suction with a vacuum pump to lower the vapor temperature; and when the detected temperature reaches a certain temperature lower than the set vapor temperature, closing the solenoid valve and stopping the vacuum suction with the vacuum pump to raise the vapor temperature; and repeating these steps to continue the concentration process.

[0009] Furthermore, as a pre-processing step of the repetitive control, if the detected temperature is higher than the steam set temperature, the immersion of the evaporating flask in the constant temperature water bath is stopped, and only vacuum suction by the vacuum pump is performed, initial boiling is started, and then the evaporating flask is immersed in the constant temperature water bath; if the detected temperature is lower than the steam set temperature, vacuum suction by the vacuum pump is stopped while the evaporating flask is immersed in the constant temperature water bath, the detected temperature is made higher than the steam set temperature, vacuum suction by the vacuum pump is resumed, and initial boiling is started. [Effects of the Invention]

[0010] According to the method for controlling a rotary evaporator of the present invention, a temperature sensor is provided near the liquid surface in the evaporation flask, which allows for more accurate measurement of the saturated vapor pressure temperature of the generated vapor, thereby enabling the entire apparatus to be operated appropriately. Even when using liquids that tend to bump or foam, bumping can be prevented. [Brief explanation of the drawings]

[0011] [Figure 1]FIG. 1 is a diagram showing an example of a rotary evaporator to which the method of the present invention can be applied. [Figure 2] 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). [Figure 3] FIG. 3 is a detailed view of a portion of FIG. 2. [Figure 4] 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. DETAILED DESCRIPTION OF THE INVENTION

[0012] An example of a rotary evaporator to which the method of the present invention can be applied will be described below with reference to the drawings. Figure 1 shows an outline of the rotary evaporator, in which 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.

[0013] A condenser tube 5 is connected to this evaporating flask 1 via a drive unit 3, and a cooling tube 7 is disposed inside the condenser tube 5, and at the bottom of the condenser tube 5, a recovery flask 6 for recovering the condensed solvent and the like, and an exhaust port 9 connected to a vacuum pump 8 are provided.

[0014] A vacuum level display monitor 10 and a solenoid valve 11 are provided between the exhaust port 9 and the vacuum pump 8, and the solenoid valve 11 is controlled to open and close depending on the steam temperature, so that the inside of the evaporator is evacuated by the vacuum pump 8. A vent needle valve 12 is provided between the solenoid valve 11 and the vacuum pump 8, so that ventilation can be performed to adjust the vacuum state as necessary.

[0015] A vapor temperature detection sensor 13 for detecting the vapor temperature inside the evaporating flask 1 is provided inside the flask. A solenoid valve 11 is connected to a temperature controller 14 and a relay 15, and the degree of vacuum is controlled and the vapor temperature is adjusted by opening and closing the solenoid valve 11 and activating the relay 15.

[0016] Using the rotary evaporator configured as above, the control method of the present invention is carried out as follows.

[0017] 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 vacuum controller with vapor temperature control, which is the control device of the present invention, thereby concentrating the sample solution.The control device controls a heater that heats the constant temperature water bath 4, a rotation drive motor that is the drive unit 3 that rotates the evaporating flask 1, and an electromagnetic valve 11 that maintains a vacuum inside the evaporating flask 1, and the vapor temperature of the sample solution in the evaporating flask 1 that is heated at a constant temperature in the constant temperature water bath 4 is detected by a vapor temperature detection sensor 13 provided in the evaporating flask 1, and the vapor temperature and degree of vacuum are automatically controlled by the control device by opening and closing the electromagnetic valve 11, etc., while the concentration process of the sample solution is continued until the sample solution is concentrated and dried.

[0018] In this process, 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 operation of the concentration process at a point where the temperature has risen by an arbitrary temperature (for example, 5°C) from the set temperature, the sample solution can be considered to have been completely concentrated to dryness.

[0019] Before describing the specific control method for completely concentrating and drying a sample solution, we 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. Conventional rotary evaporators typically involve setting the temperatures of the constant-temperature water bath 4 and the cooling water circulator for the condenser tube 5. Once the respective set temperatures are reached, the rotary evaporator is adjusted to a predetermined 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, exhibits the behavior shown in the "operating pressure" column of Figure 2.

[0020] As mentioned above, when the degree of vacuum in the system is reduced, the evaporation flask 1 is immersed in the thermostatic water bath 4, and the vapor temperature in the evaporation flask 1 rises due to the heat from the thermostatic water bath 4. When the degree of vacuum (operating pressure) in the system subsequently reaches the saturated vapor pressure, the thermal energy accumulated inside is suddenly released, causing evaporation and bubbles to form 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 the saturated vapor pressure, and bumping is likely to occur along with the foaming (the "area prone to bumping" in Figure 2).

[0021] Referring further to Figure 3, as described above, the pressure inside the device is reduced by vacuum suction using the vacuum pump 8, 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 dots in Figure 3). When a typical vacuum pump is used, the vacuum continues at a constant rate, increasing the vacuum inside the device and lowering the boiling point. However, the sample temperature does not drop until the saturated vapor pressure corresponding to the sample temperature is reached. Therefore, even when the vacuum level corresponding to the saturated vapor pressure of the sample is reached, there is a slight delay in boiling. As a result, the vacuum level 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 some of the sample liquid, including the unboiled sample liquid, is violently ejected into receiving flask 6, causing most of the liquid in evaporation flask 1 to move. If this overheating and excessive vacuum state can be avoided, the concentration process can be completed without bumping of the sample solution.

[0022] The method of controlling a rotary evaporator in the present invention involves carrying out a pretreatment step to initiate initial boiling without causing bumping, particularly in the case of samples that are highly foaming and prone to bumping, and then controlling the opening and closing of solenoid valve 11 while comparing the temperature detected by vapor temperature detection sensor 13 (detected temperature) with the set temperature, thereby achieving stable control.

[0023] In the present invention, first, the required steam temperature is set (steam set temperature), and the temperature of the constant temperature water bath 4 and the temperature of the cooling water are set accordingly (for example, when 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).

[0024] Next, we will explain the pre-treatment process. For example, in areas where bumping is likely to occur, such as the area around the ● in Figure 3, bumping and foaming can be prevented by controlling the temperature in air that is close to unheated so that the boiling point drops slowly below the temperature in this state.

[0025] If the detected temperature is higher than the set steam temperature, it is understood that the sample solution is in a state where bumping is likely to occur, so stop immersing the evaporation flask 1 in the constant temperature water bath 4 and only perform vacuum suction with the vacuum pump 8. In the case of a sample that is highly foaming and prone to bumping, if the difference between the sample solution temperature and the set steam temperature is 1°C or more, bring the set steam temperature closer to the sample solution temperature (raise it by 0 to 0.5°C), and then, once boiling of the sample solution is confirmed (initial boiling has begun), reset the set steam temperature to the specified temperature, immerse the evaporation flask 1 in the constant temperature water bath 4, and continue the concentration process.

[0026] Furthermore, if the detected temperature is lower than the set vapor 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.

[0027] When using a vacuum pump 8 with a large displacement, the time required 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 at the start of initial boiling.

[0028] Next, we will explain the control method used when continuing the concentration process after the initial boiling has started as described above. When the sample starts boiling, the temperature of the sample solution (temperature at saturated vapor pressure) also drops as the pressure is reduced 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 accumulated up to that point is being released, the degree of vacuum is dependent on the stable vapor temperature, and control can be continued.

[0029] Here, the control of the vacuum pump 8 and solenoid valve 11 for the sample solution concentration process will be explained in more detail. When the detected temperature of the vacuum pump 8 reaches a certain temperature (e.g., 0.1°C) higher than the set vapor temperature, the 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, the solenoid valve 11 closes and the vacuum suction stops. 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.

[0030] For example, the sample solution was ethanol. The temperature of the constant-temperature water bath 4 was set to 40°C ± 2°C, the cooling water temperature to 2-4°C, the rotation speed of the drive unit 3 to 120 rpm, the vapor temperature set to 20°C, and the constant temperature set to 0.1°C. The pretreatment process was then started, and the solenoid valve 11 was opened and closed (repeated control) as described above. Figure 4 shows the results. At a concentration time of 25 minutes and 4 seconds, 399.05 g of ethanol was recovered from a 400.58 g sample, representing a recovery rate of 99.6%. Although the constant temperature was controlled at 0.1°C, a response delay occurred in the solenoid valve opening and closing, resulting in the vapor temperature being controlled between 17.83°C and 20.6°C. Furthermore, by controlling the opening and closing of the solenoid valve 11 for a set period of time during this control, vacuum suction inside the evaporation flask 1 could be intermittently performed. This range of state changes prevented abrupt changes in the sample solution, allowing the concentration process to continue stably and preventing further bumping.

[0031] Furthermore, as evaporation progresses and the amount of concentrated residue decreases, the detection temperature rises, making repeated control like that described above impossible, but this state is not a problem because it indicates that concentration is nearing completion. In Figure 4, the process is considered complete when the temperature rises by about 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.

[0032] Although ethanol is used as the sample solution, other solvents may also be used. [Explanation of symbols]

[0033] 1···Evaporation flask, 2···Stand, 3···Drive unit, 4···Constant temperature 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···Ventilation needle valve, 13···Steam temperature detection sensor, 14···Temperature controller, 15···Relay

Claims

1. 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.

2. 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.

Images