Method for measuring saturated vapor pressure of solid matter
Technical Field
The invention relates to a method for measuring the saturated vapor pressure of a solid substance.
Background
Saturated vapor pressure is an important parameter for evaluating the volatility and stability of chemicals. The invention relates to a test method for evaluating the saturated vapor pressure of a chemical substance through vacuum stability, which is a relatively deep research on the saturated vapor pressure of a liquid substance at home and abroad, and a liquid saturated vapor pressure test method is also rare, but the research on the saturated vapor pressure of a solid has a lot of blanks, and the measurement of the saturated vapor pressure of the solid is basically based on other test methods, and no test method specially used for testing the saturated vapor pressure of the solid is provided.
The invention achieves the relevant requirements of a saturated vapor pressure measuring method-a static method in the aspect of saturated vapor pressure measurement. At present, according to the conditions of literature retrieval and market investigation, no related institution designs a similar test method for saturated vapor pressure according to a vacuum stability measurement method in China, and the method has important guiding significance for measuring the saturated vapor pressure of the solid chemical substance.
Disclosure of Invention
The invention aims to solve the technical problem of low test accuracy in the prior art, provides a novel method for measuring the saturated vapor pressure of a solid substance, and has the advantage of high test accuracy.
In order to solve the problems, the technical scheme adopted by the invention is as follows: a method for measuring the saturated vapor pressure of a solid substance adopts a solid substance saturated vapor pressure testing device to test the saturated vapor pressure of the solid substance, the device comprises a low-temperature module, a high-temperature module, a testing pipe and a pressure sensor, a testing pipe seat hole is arranged on the low-temperature module and the high-temperature module, the pressure sensor is inserted on the testing pipe during testing, then the testing pipe is communicated with the pressure sensor and inserted in the testing pipe seat hole, the low-temperature module, the high-temperature module and the pressure sensor are all connected with testing software, the software controls the temperature of the low-temperature module and the high-temperature module, and simultaneously monitors the pressure of the pressure sensor in; the step of carrying out the solid matter saturated vapor pressure test comprises the following steps:
(1) preparation before experiment
Preparing a test sample and a reference substance, starting a test instrument, a computer and test software, adding liquid silicone oil into the test tube seat holes of the low-temperature module and the high-temperature module, setting the temperature of the low-temperature module to be-10 ℃ or lower, setting the temperature of the high-temperature module to be a target measurement temperature, and keeping the temperature constant for at least 10 minutes when the temperature reaches the set temperature;
(2) vacuum treatment
Inserting a pressure sensor into the test tube A, aligning a suction inlet of the pressure sensor with a vacuum pump tube inlet hole of a vacuumizing part of the test tube, placing the test tube and the pressure sensor into a seat hole of the test tube, and simultaneously carrying out the same treatment on the test tube B; connecting a vacuum pump, respectively vacuumizing the test tubes A and B, rotating the pressure sensor to disconnect the connection between a suction inlet of the pressure sensor and a vacuum tube connection hole of a vacuumizing part of the test tube, and closing the vacuum pump;
(3) air tightness detection
Opening the air tightness detection on the software, carrying out air tightness detection on the test tube A and the test tube B, and starting the test if the air tightness is good (the pressure change is less than 0.02 kPa/min);
(4) testing
Adding a test sample (4mL) into a test tube A, adding a reference substance (4mL) into a test tube B, stabilizing for 10min, repeating the vacuumizing and air tightness detection process, if the air tightness is good, taking the test tube A and the test tube B together with respective pressure sensors out of a low-temperature module, inserting the test tube A and the test tube B into a high-temperature module, ensuring that the air tightness of the test tube is good in the conversion process, opening a test program of test software, keeping the temperature for 60 min, recording pressure data (recorded once per minute) of the pressure sensors of the test tube A for 0-60 min by control software, and recording pressure P when the pressure sensors of the test tube B and the test tube B are 60 min by the control software0;
(5) Calculation of results
The control software performs data fitting on the pressure data of the pressure sensor of the test tube A for 0-60 minutes to obtain a pressure and time change curve:
(a is more than 0, b is more than 0, P is the pressure (Pa) in the test tube A, t is the test time (min)), and Pmax is P (∞) K;
the final measured saturated vapor pressure: Pmax-P0=K-P0。
In the above technical solution, preferably, the test sample is added into the test tube a, the reference material is added into the test tube B, and a layer of solid silicone grease is coated inside the test tube orifice and outside the lower end of the pressure sensor, so that the silicone oil cannot block the suction hole on the pressure sensor.
In the above technical solution, preferably, in the step (3), the airtightness detection on the software is turned on, and the airtightness detection is performed on the test tube a and the test tube B; if the pressure increase rate is more than 0.02kPa/min, the air tightness is not good, and the silicone oil needs to be coated again, and the vacuum pumping is carried out again until the pressure increase rate is less than 0.02 kPa/min.
In the above technical solution, preferably, the low temperature module: the temperature control range is-20 ℃ to 30 ℃.
In the above technical solution, preferably, the high temperature module is a saturated vapor pressure test module, the temperature control range is 30 ℃ to 150 ℃, the saturated vapor pressure of the test sample is at the set temperature, and other structures are consistent with those of the low temperature module.
Among the above-mentioned technical scheme, preferably, the test tube seat hole sets up on low temperature module and high temperature module, respectively two, during the experiment, need add silicon oil to the test tube seat hole, makes the test tube be heated evenly.
Among the above-mentioned technical scheme, preferably, test pipe A, test pipe B are the glass material, and test pipe A is the same with B's volume, and test pipe upper portion has the evacuation part, has vacuum pump pipe access hole on the evacuation part, vacuum pump pipe access hole and the inside intercommunication of test pipe.
In the above technical solution, preferably, the pressure sensor is made of stainless steel, is cone-shaped, is inserted above the test tube, has a hollow interior, has a suction hole at a lower side portion, and can be aligned with a vacuum pump pipe connection hole of a vacuum pumping part on the test tube when inserted on the test tube.
In the above technical solution, preferably, the solid substance saturated vapor pressure testing device is provided with testing software, and the testing software has functions required to 1) accurately control the temperatures of the low temperature module and the high temperature module; 2) the air tightness of the test system can be effectively detected; 3) the numerical value of the pressure in the test tube can be recorded in real time; 4) the measured data can be simply processed.
In the above technical solution, preferably, the reference substance is aluminum oxide.
Compared with the traditional test method, the test method provided by the invention is provided with the comparison device, thereby avoiding the influence of the environment and operators on the measurement of the vapor pressure and improving the measurement accuracy. The invention is provided with the low-temperature module, can measure the saturated vapor pressure at low temperature, and can be used as an environment for detecting air tightness.
Drawings
FIG. 1: a test method device diagram;
FIG. 2: test method apparatus diagram-test tube component diagram;
FIG. 3: test method apparatus diagram-pressure sensor component diagram;
FIG. 4: test method device diagram-schematic diagram of connection of test tube and pressure sensor;
FIG. 5: test method setup figure-pressure sensor cone;
FIG. 6: test method apparatus figure-test tube evacuation part;
in fig. 1: 1, a refrigerator, 2, a test tube seat hole, 3, a test tube, 4, a liquid storage tank, 5, a pressure sensor, 6, a data line and 7, a heater;
in fig. 2: 1 an evacuation tube connector component;
in fig. 3: 2 suction hole position indication; 3 a suction hole;
in fig. 5: 1 silicone grease, 2 suction holes, 3 suction hole indications;
in fig. 6: 1 vacuum pump pipe access hole.
The present invention will be further illustrated by the following examples, but is not limited to these examples.
Detailed Description
[ example 1 ]
A method for measuring the saturated vapor pressure of a solid substance utilizes the characteristic that the saturated vapor pressure of the solid substance is small under the low-temperature condition, carries out vacuum-pumping treatment on a test system under the low-temperature condition, pumps the system to absolute vacuum or approximate absolute vacuum, then places the test system at the test temperature for full volatilization, deduces the influence of residual gas of the system through setting a contrast test, and thus measures the saturated vapor pressure of a sample at the test temperature.
The invention relates to a set of corresponding testing device which is used in cooperation with a testing method. As shown in figure 1, the testing device consists of a low-temperature module, a high-temperature module, a testing pipe and a pressure sensor, and the functions and the connections of the specific components are as follows: the test tube seat hole is formed in the low-temperature module and the high-temperature module, during testing, the pressure sensor is inserted into the test tube, then the test tube is communicated with the pressure sensor and is inserted into the test tube seat hole, the low-temperature module, the high-temperature module and the pressure sensor are connected with test software, the software controls the temperature of the low-temperature module and the temperature of the high-temperature module, and meanwhile the pressure of the pressure sensor is monitored in real time.
1. A low-temperature module: the temperature control range is-20 ℃ to 30 ℃, and the device has two functions: 1) the characteristic that the saturated vapor pressure of a solid substance is small under the low-temperature condition is utilized, and the test system is vacuumized under the low-temperature condition; 2) and can measure the saturated vapor pressure within the range of-20 ℃ to 30 ℃.
2. A high-temperature module: the high-temperature module is a saturated vapor pressure testing module, the temperature control range is 30-150 ℃, the saturated vapor pressure of a test sample at a set temperature is consistent with that of the low-temperature module in other structures
3. Testing the tube seat hole: the test tube seat holes are arranged on the low-temperature module and the high-temperature module, and are respectively two, and during test, a proper amount of silicone oil needs to be added into the test tube seat holes to ensure that the test tubes are uniformly heated;
4. testing tubes: the test tubes are made of glass and are respectively numbered A and B, the appearance of the test tubes is basically consistent with that of a common test tube, and the inner volumes of the two test tubes are required to be the same and need to be calibrated. The upper part of the test tube is provided with a vacuumizing part, the vacuumizing part is provided with a vacuum pump tube connection hole, and the vacuum pump tube connection hole is communicated with the interior of the test tube;
5. a pressure sensor: the pressure sensors are made of stainless steel materials, are respectively numbered 1 and 2, are in a cone shape, are inserted above the test tube, are hollow inside, are provided with suction holes on the lower side part, and can align to the vacuum pump pipe connection holes of the vacuumizing part on the test tube when being inserted on the test tube;
the invention needs to design a set of corresponding test software which has the functions required by the test software, and 1) the temperature of the low-temperature module and the high-temperature module can be accurately controlled; 2) the air tightness of the test system can be effectively detected; 3) the numerical value of the pressure in the test tube can be recorded in real time; 4) the measured data can be simply processed.
The reference substance related by the invention is aluminum oxide, and the analytical purity is high.
In using the present invention, where it is desired to test in a fume hood having an air flow rate of 0.5 m/s or less, the exhaust system should be adapted to absorb toxic fumes and then tested according to the following steps:
(1) preparation before experiment
Preparing a test sample, placing a reference substance in a designated place, starting a test instrument, a computer and test software, adding a proper amount of liquid silicone oil into the test tube seat holes of the low-temperature module and the high-temperature module, setting the temperature of the low-temperature module to be-10 ℃ or lower, setting the temperature of the high-temperature module to be target measurement temperature, and keeping the temperature for at least 10 minutes after the temperature reaches the set temperature.
(2) Vacuumizing treatment:
4.0mL of the sample was added to test tube A using a graduated cylinder and a funnel, and 4.0mL of the reference material, alumina, was added to test tube B. Coating a thin layer of solid silicone grease on the inside of the test pipe orifice and the outside of the lower end of the pressure sensor, wherein the silicone grease can not block a suction hole on the pressure sensor, inserting the pressure sensor A into the test pipe A, aligning a suction inlet of the pressure sensor with a vacuum pump pipe connection hole of a vacuum pumping part of the test pipe, discharging the test pipe and the pressure sensor together into a test pipe seat hole, and simultaneously carrying out the same treatment on the test pipe B. The temperature is kept constant for 30 minutes. And connecting a vacuum pump, respectively vacuumizing the test tubes A and B until the minimum value is pumped, wherein the pressure is not reduced any more, rotating the pressure sensor by 90 degrees at the moment, connecting and disconnecting the suction inlet of the pressure sensor and the vacuum tube connection hole of the vacuum pumping part of the test tube, and closing the vacuum pump.
(3) Air tightness detection
And opening the air tightness detection on software, detecting the change of the internal pressure of the two test tubes within 1 minute, wherein the pressure increase rate is less than 0.02kPa/min to indicate that the air tightness is good, and meeting the requirement, if the pressure increase rate is more than 0.02kPa/min, indicating that the air tightness is not good, coating silicon oil again, and vacuumizing again until the pressure increase rate is less than 0.02 kPa/min.
(4) Testing
Adding 4.0mL of sample into a test tube A by using a measuring cylinder and a funnel, adding 4.0mL of reference substance aluminum oxide into a test tube B, stabilizing for 10min, repeating the processes of vacuumizing and air tightness detection, taking the test tubes A and B and a pressure sensor out of a low-temperature module and inserting the test tubes A and B and the pressure sensor into a high-temperature module if the air tightness is good, ensuring the good air tightness of the test tubes in the conversion process, opening a test program of test software, keeping the temperature for 60 min, recording pressure data (once per minute) of the pressure sensor of the test tube A for 0-60 min by control software, and recording the pressure P when the pressure sensor of the test tube B is 60 min0。
(5) Calculation of results
The control software performs data fitting on the pressure data of the pressure sensor of the test tube A for 0-60 minutes to obtain a pressure and time change curve:
(a is more than 0, b is more than 0, P is the pressure (Pa) in the test tube A, t is the test time (min)), and Pmax is P (∞) K;
the final measured saturated vapor pressure: Pmax-P0=K-P0. [ example 2 ]
The method was used to determine the saturated vapor pressure of p-dichlorobenzene according to the conditions and procedures described in example 1, and the specific procedure was as follows:
1. preparation before experiment
Starting the test instrument, setting the temperature of the low-temperature module to-10 ℃ and the temperature of the high-temperature module to 55 ℃. Measuring 4mL of p-dichlorobenzene and 4mL of reference substance aluminum trioxide respectively by using a measuring cylinder;
2. vacuumizing, and detecting the air tightness completely;
3. respectively adding the sample and the reference substance into a test tube A and a test tube B, stabilizing for 10min, vacuumizing, detecting the air tightness completely, taking the test tubes A and B and the pressure sensor out of the low-temperature module, inserting the test tubes A and B into the high-temperature module, keeping the temperature for 60 min, and calculating the result through software.
4. As a result: the saturated vapor pressure of p-dichlorobenzene at 55 ℃ was 1.29 kPa. (reference value 1.33kPa (55 ℃ C.)).
[ example 3 ]
The method was used to determine the saturated vapor pressure of naphthalene according to the conditions and procedures described in example 1, with the following specific procedures: 1. preparation before experiment
The test instrument was started, and the low temperature module was set to-10 ℃ and the high temperature module was set to 102.5 ℃. Measuring 4mL of naphthalene and 4mL of reference substance aluminum trioxide respectively by using a measuring cylinder;
2. vacuumizing, and detecting the air tightness completely;
3. respectively adding the sample and the reference substance into a test tube A and a test tube B, stabilizing for 10min, vacuumizing, detecting the air tightness completely, taking the test tubes A and B and the pressure sensor out of the low-temperature module, inserting the test tubes A and B into the high-temperature module, keeping the temperature for 60 min, and calculating the result through software.
4. As a result: the saturated vapor pressure of naphthalene at 102.5 ℃ was 2.61 kPa. (reference value 2.67kPa (102.5 ℃ C.)).
According to the comparison between the two groups of actual measurement result data and the reference data, the deviation between the measured result and the reference data of the experimental device is within 5 percent, and the requirement on data accuracy is met.