TWI839025B - Boiling point state detection method - Google Patents

Abstract

The present invention is a boiling point detection method, which continuously evacuates a sealed container containing a liquid to be tested, so that the pressure value in the sealed container gradually decreases and continuously detects the pressure value change in the sealed container. A processor is used to determine whether the measured pressure value meets a boiling point occurrence condition. When the pressure values meet the boiling point occurrence condition, it can be determined that the liquid to be tested is close to boiling. The present invention does not require the use of a temperature sensor. For a liquid to be tested with an unknown composition, it can automatically determine whether it has reached the boiling point state, avoiding the inconsistent results that may be caused by human judgment and saving personnel observation time.

Description

Boiling point state detection method

The present invention is a method for detecting boiling point state, particularly a method for automatically determining boiling point based on pressure changes.

The boiling point of a liquid changes with pressure rather than being a fixed value. For example, water has a boiling point of 100°C under 1 atmosphere (760 mmHg), and as the pressure drops below 760 mmHg, the boiling point will also drop below 100°C. By taking advantage of this characteristic of the boiling point changing with pressure, when operators want to perform concentration, drying, distillation, and other operations on the liquid in the container, they can use a vacuum pump to extract the air in the container to reduce the pressure inside the container, so that the boiling point of the liquid can be reached by heating it to a relatively low temperature.

The current method of determining boiling point is still through manual observation. During the liquid heating process, the operator must continue to closely monitor the state of the liquid and judge whether the boiling point has been reached based on his or her own experience. However, this method of using manual judgment has the following disadvantages:

1. Operators need to spend time continuously observing the state changes of the liquid to be tested, which results in low operating efficiency.

2. Different operators make their own judgments based on their experience and professional abilities, and the judgment results are difficult to be consistent, resulting in low reproducibility of the judgment results.

3. When the operator is controlling the pressure and temperature changes, if the pressure inside the container drops too quickly or the temperature rises too quickly, it may cause the liquid to boil suddenly, resulting in danger, loss of the liquid to be tested, etc.

In view of the above-mentioned shortcomings of the existing method of manually judging the boiling point, the main purpose of the present invention is to provide a boiling point state detection method, which automatically determines whether the liquid to be tested is approaching the boiling state by detecting the pressure change trend inside the container.

To achieve the above-mentioned purpose, the boiling point state detection method of the present invention mainly includes the following steps: continuously evacuating a sealed container containing the liquid to be tested so that the pressure value in the sealed container gradually decreases; continuously detecting the pressure in the sealed container with a pressure sensor to generate a pressure value representing the pressure inside the sealed container; receiving these pressure values with a processor, and the processor determines whether these pressure values meet a boiling point occurrence condition; when these pressure values meet the boiling point occurrence condition, the processor determines that the liquid to be tested is approaching a boiling state.

When the liquid to be tested is maintained at a fixed temperature, the present invention can judge whether the liquid to be tested is close to the boiling point state according to the pressure value change inside the sealed container. When the continuously measured pressure value meets the set boiling point occurrence conditions, it can automatically judge that the liquid is close to boiling. The operator does not need to spend time continuously observing the state of the liquid to be tested, and can also avoid inconsistent judgments caused by human factors.

10: Rotary evaporator

11: Water bath

12: Flask

20: Vacuum pump

30: Control host

31: Pressure sensor

32: Processor

Figure 1: Schematic diagram of an evaporation concentration system using the boiling point state detection method of the present invention.

Figure 2: Block diagram of an evaporation-concentration system.

Figure 3: Flow chart of the boiling point state detection method of the present invention.

Figure 4: The curve of the present invention measuring the pressure change when methanol is maintained at 30°C.

Figure 5: The curve diagram of the present invention measuring the pressure change when ethanol is maintained at 30°C.

Referring to FIG. 1 and FIG. 2, the boiling point state detection method of the present invention can be applied to the system in the figure, which is only used as an example, and includes: a rotary evaporator 10, a vacuum pump 20 and a control host 30, wherein the rotary evaporator 10 has a water bath 11, which is used to heat the liquid to be tested in a flask 12 in water insulation. The water bath 11 can be set to a required temperature by the user, and the temperature of the liquid to be tested is increased through water insulation heating and maintained at a constant temperature. The vacuum pump 20 is connected to the rotary evaporator 10 through a high-pressure hose, and is used to reduce the pressure inside the flask 12 to reduce the boiling point temperature of the liquid. The control host 30 is located between the vacuum pump 20 and the rotary evaporator 10. A pressure sensor 31 detects the pressure value inside the flask 12. A processor 32 automatically determines whether the liquid has reached the boiling point state according to the change of the pressure value P. After reaching the boiling point state, in order to avoid boiling or sudden boiling caused by the continuous decrease of the boiling point, in one embodiment, the boiling point pressure is set to be maintained. There are many ways to maintain the boiling point pressure. The control host 30 can adjust the speed of the motor of the vacuum pump 20 to change the suction force inside the flask 12, or the solenoid valve of the control host 30 can be switched on and off to achieve the result of maintaining the boiling point pressure inside the flask 12. In another embodiment, the pressure sensor 31 and the processor 32 can be disposed in the vacuum pump 20.

The flow chart shown in FIG3 is one embodiment of the flow chart of the method of the present invention, which mainly includes the following steps:

S30: The sealed container containing the liquid to be tested is vacuumed to gradually reduce the pressure value of the sealed container. In this embodiment, the sealed container refers to the flask 12 as shown in FIG. 1, and the liquid to be tested can be an unknown liquid. The vacuum pump 20 is used to vacuum the inside of the flask 12.

S31: Detect the pressure value Pn in the sealed container. The pressure sensor 31 continuously detects the pressure value of the internal space of the flask 12 at a fixed interval (for example, every second). As the vacuum pump 20 continues to extract the air inside the flask 12, the pressure value Pn will gradually decrease, where "n" refers to the nth detection, and Pn refers to the pressure value obtained by the nth detection.

S32: Convert each pressure value Pn into a pressure value Pn in digital format. If the pressure value Pn measured by the pressure sensor 31 is an analog signal, the analog pressure value Pn can be converted into a digital pressure value first; conversely, if the pressure sensor 31 provides a digital output value, there is no need to perform analog/digital conversion.

S33: Pre-process each pressure value Pn, and the pre-processing may include signal processing operations such as filtering and amplification. The processor 32 may use a digital filter to filter the pressure value Pn to eliminate noise and improve the accuracy of subsequent judgment.

S34: Determine whether the pressure values Pn meet a boiling point occurrence condition. If so, the liquid to be tested is determined to be close to the boiling point state.

In step S34, a first feasible implementation example is to calculate the difference ΔP=| _Pn - _Pn-1 | between two adjacent pressure values. When the difference ΔP is less than a first preset value _Pth (ΔP< _Pth ), it is determined that the liquid to be tested meets the boiling point occurrence condition, wherein _Pn represents the pressure value measured this time, and Pn _-1 represents the pressure value measured last time. When the liquid to be tested begins to boil, it will change from liquid phase to gas phase, and the generated vapor pressure will slightly compensate for the pressure extracted by the vacuum pump 20. Therefore, the pressure value change measured inside the flask 12 will decrease at this time point when boiling begins. When it is lower than the first preset value _Pth , the processor 32 determines that the liquid to be tested has reached the boiling point.

In step S34, a second feasible implementation example is to calculate the difference ΔP=| _Pn - _Pn-1 | between two adjacent pressure values. When the difference ΔP of several consecutive values is less than the first preset value, it is determined that the liquid to be tested meets the boiling point occurrence condition.

In step S34, a third feasible embodiment is to calculate the reduction ratio of the pressure value, and the calculation formula is as follows:

Wherein, _Pn represents the pressure value measured this time, Pn _-1 represents the pressure value measured last time, and _Cn represents the pressure value drop ratio this time. When the pressure value drop ratio _Cn is less than a second preset value, the processor 32 determines that the boiling point condition is met and the liquid to be tested is close to boiling.

In step S34, a fourth feasible implementation example is to calculate the difference between two adjacent pressure drop ratios. When the difference between the current pressure drop ratio _Cn and the previous pressure drop ratio Cn _-1 is greater than a third preset value _CTH , the processor 32 determines that the boiling point occurrence condition is met, that is, | _Cn-1 - _Cn |> _CTH .

Please refer to the pressure change curve shown in FIG4. The values of each point on the curve are the pressure values (mbar) measured at that time point. Methanol solvent is contained in the flask 12 of FIG1 and is heated in a water bath 11 to maintain the temperature of methanol at about 30°C. According to the Antoine Equation, the saturated vapor pressure of methanol at 30°C is about 218 (mbar). When the pressure sensor 31 measures the pressure change inside the flask 12, it can be observed that the pressure drops rapidly in the time section from 0 to 16 seconds, but the pressure drop suddenly decreases at about 16 seconds, and the corresponding pressure value is about 219 (mbar). According to step S34 of the present invention, the processor 32 determines that the change in the pressure value has met the boiling point occurrence condition, so it will be determined that methanol has begun to enter a micro-boiling state at about the 16th second, and the pressure value at this time will be maintained after the 16th second to avoid sudden boiling.

For example, according to the first embodiment of step S34, the processor 32 calculates the difference △P between two adjacent pressure values, and the first preset value is set to 10 (mbar). The difference △P in the 0-16 second section is greater than the first preset value, but the difference △P between the 16th and 17th seconds is 225-219=6 (mbar) less than the first preset value, so the processor 32 can determine that methanol has begun to enter the boiling point state around the 16th second. The first preset value can be formulated according to application requirements or experimental sensitivity. If the sensitivity requirement is high, a larger first preset value can be set, otherwise a smaller first preset value can be set if the sensitivity requirement is low.

According to the third embodiment of step S34, the pressure value drop ratios _Cn calculated before the 15th second are all greater than 6%, and the pressure value drop ratio calculated at the 16th second is 5.2%. If the second default value is set to 5.5%, the processor 32 can also determine that the liquid to be tested is close to boiling at the 16th second.

According to the fourth embodiment of step S34, the difference between the pressure drop ratio _C16 calculated at the 16th second and the pressure drop ratio _C15 calculated at the 15th second is approximately |5.2%-9.1%|=3.9%, which is greater than the third preset value _CTH =2%, and boiling point can also be determined to have occurred.

Please refer to FIG. 5 again. The ethanol solvent is measured under the same experimental conditions. According to the Antoine Equation, the saturated vapor pressure of ethanol at 30°C is about 104 (mbar). According to the pressure sensor 31 measuring the pressure change inside the flask 12, it can be observed that there is an obvious downward trend in the time section of 0 to 25 seconds, but at about the 25th second, the pressure drop suddenly decreases, and the corresponding pressure value is about 101 (mbar). According to step S34 of the present invention, the processor 32 determines that the change in the pressure value has met the boiling point occurrence condition, so it will be determined that ethanol has begun to enter a micro-boiling state at about the 25th second, and maintain the pressure value at this time after the 25th second to avoid sudden boiling.

For example, according to the first embodiment of step S34, the processor 32 calculates the difference △P between two adjacent pressure values, and the first default value is set to 6 (mbar). The difference △P in the 0-25 second section is greater than the first default value, but the difference △P=3 (mbar) between the 25th and 26th seconds is less than the first default value. Therefore, the processor 32 can determine that ethanol has begun to enter the boiling point state around the 25th second.

When the processor 32 determines that the liquid to be tested has reached the boiling point, the processor 32 can determine the next subsequent control method according to the application requirements, such as setting the pressure to maintain the boiling point to avoid sudden boiling and causing sample loss. This subsequent control method is not a feature of the present invention, so it will not be described in detail.

The present invention can judge whether the liquid to be tested is close to boiling only based on the change of pressure value without measuring the temperature of the liquid. This method can be widely used in equipment such as concentrators, vacuum dryers, vacuum distillation, etc. Even for liquids with unknown components, the time when the liquid changes from liquid phase to gas phase can be known by observing the change rate of pressure value. It can not only prevent sudden boiling accidents and avoid inconsistent judgment results caused by different operators, thereby improving the reproducibility of measurement results, but also save time for manual observation.

Claims (9)

A boiling point state detection method is used to determine whether a liquid to be tested has reached a boiling point. The boiling point state detection method includes: continuously evacuating a sealed container containing the liquid to be tested so that the pressure value in the sealed container gradually decreases; continuously detecting the pressure in the sealed container with a pressure sensor to generate a pressure value representing the pressure inside the sealed container; receiving the pressure values with a processor, and the processor determines whether the pressure values meet a boiling point occurrence condition; when the pressure values meet the boiling point occurrence condition, the processor determines that the liquid to be tested has reached a boiling point state. As described in claim 1, in the step of the processor determining whether the pressure values meet the boiling point occurrence condition, the processor calculates the difference between two adjacent pressure values, and when the difference is less than a first preset value, it is determined that the liquid to be tested meets the boiling point occurrence condition. As described in claim 1, in the step of the processor determining whether the pressure values meet the boiling point occurrence condition, the processor calculates the difference between two adjacent pressure values. When the difference for a number of consecutive values is less than a first preset value, it is determined that the liquid to be tested meets the boiling point occurrence condition. The method for detecting a boiling point state as described in claim 1, wherein, in the step of the processor determining whether the pressure values meet the boiling point occurrence condition, the processor calculates the pressure value drop ratio according to the following formula:

Wherein, _Pn represents the pressure value measured this time, Pn _-1 represents the pressure value measured last time, and _Cn represents the pressure value drop ratio this time; when the pressure value drop ratio _Cn is greater than a second preset value, the processor determines that the liquid to be tested has met the boiling point occurrence condition. The method for detecting a boiling point state as described in claim 1, wherein, in the step of the processor determining whether the pressure values meet the boiling point occurrence condition, the processor calculates the pressure value drop ratio according to the following formula:

Wherein, _Pn represents the pressure value measured this time, Pn _-1 represents the pressure value measured last time, and _Cn represents the pressure value drop ratio of this time; when |Cn _-1 - _Cn |> _CTH , the processor determines that the liquid to be tested has met the boiling point occurrence condition, wherein Cn _-1 is the pressure value drop ratio of the last time, and _CTH is a third preset value. A boiling point state detection method as described in any one of claim items 1 to 5, wherein the multiple pressure values generated by the pressure sensor are converted into pressure values in digital format and pre-processed, and then the processor determines whether the boiling point occurrence condition is met. The boiling point state detection method as described in claim 6, wherein the pre-processing operation includes a filtering operation. The boiling point state detection method as described in claim 7, wherein the liquid to be tested in the sealed container is maintained at a fixed temperature. The boiling point state detection method as described in claim 8, wherein, in the step of continuously evacuating the sealed container, the vacuum is continuously drawn at a preset fixed evacuation rate.