Device and method for efficiently and environment-friendly measuring vapor pressure of liquid chemicals

Abstract

The invention discloses an efficient and environment-friendly device and method for measuring vapor pressure of liquid chemicals in the technical field of chemistry, and the device comprises a thermogravimetric analyzer, a nitrogen cylinder is arranged corresponding to the thermogravimetric analyzer, an outlet of the nitrogen cylinder is connected with a gas inlet of the thermogravimetric analyzer through a gas inlet pipeline, a pressure reducing valve is arranged on the gas inlet pipeline, and a gas outlet of the nitrogen cylinder is connected with a gas outlet of the thermogravimetric analyzer. An exhaust port of the thermogravimetric analyzer is connected with the condenser through an exhaust pipeline, a first constant-temperature water bath is arranged corresponding to a furnace body of the thermogravimetric analyzer, and a balance of the thermogravimetric analyzer is connected with the computer. According to the invention, the vapor pressure of the liquid chemical can be measured efficiently and environmentally, the measurement automation degree is high, the sample consumption is low, and the measurement accuracy is high.

Description

Technical Field

[0001] The present invention belongs to the field of chemical technology, and particularly relates to a device and method for efficiently and environmentally friendly determining the vapor pressure of liquid chemicals. Background Art

[0002] At present, the pesticide and chemical testing guidelines have relevant recommended methods for vapor pressure testing in different ranges. Commonly used measurement methods include the static method, dynamic method, saturated gas flow method, thermogravimetric method, etc.

[0003] Problems existing in the prior art: The static method is mostly used in high-pressure and atmospheric-pressure occasions, but it is also used in the range of 0.1 - 3.0 kPa (the lower limit of the method measurement) (Ma Peisheng, 2003). Affected by factors such as the sealing performance of the instrument, temperature stability, sensitivity of the pressure sensor, gas dissolution / adsorption, etc., the static method has a large error when measuring the vapor pressure in the range of 0.1 - 3.0 kPa, and it is difficult to guarantee the reproducibility of the results. Moreover, the static method test requires manual degassing, constant temperature, pressure regulation, etc., and the degree of automation is low. The dynamic method is mostly used in occasions below atmospheric pressure. Similar to the static method, it requires manual degassing, constant temperature, pressure regulation, etc., and the degree of automation is low. The saturated gas flow method is generally used to measure complex mixtures. Its advantage is high precision, but the operation is complex, the saturation process is slow, and the test period is long. The thermogravimetric method is a commonly used method in modern vapor pressure measurement methods. This method avoids the need to spend time and effort building a complex test system device, and has the advantages of less sample consumption, short test time, simple operation, high degree of automation, etc. There are many methods for measuring vapor pressure, but for specific pesticides / chemicals, not all methods can measure accurate data. Therefore, the selection of the measurement method is crucial.

[0004] According to market research and existing domestic and foreign studies, there are currently two commonly used test methods for the vapor pressure of pesticides / chemicals, namely the static method and thermogravimetric analysis. In recent years, with the emergence of automated torque and vacuum microbalances, the thermogravimetric method for measuring vapor pressure has been widely used. The variation law and corresponding relationship of the vapor pressure measured by the thermogravimetric method with temperature can be solved using the Clausius-Clapeyron equation and the Antoine formula. John W Goodrum et al. used the thermogravimetric method to quickly and accurately measure the boiling points and vapor pressures of medium-chain and long-chain saturated triglycerides, providing important data for the development of the composition model of biodiesel fuel extenders; Walter Gückel et al. developed a method for the volatility of active ingredients used in plant protection by studying the relationship between vapor pressure, temperature, and evaporation rate. Goel A et al. determined the volatility of organochlorine and organophosphorus pesticides (chlorothalonil, chlorpyrifos-methyl, diazinon, fipronil) through the vapor pressure-temperature relationship and the calculation of evaporation enthalpy, which contributed to the development of pesticide risk assessment and improved the effectiveness of mitigation and remediation efforts.

[0005] At present, we should explore the appropriate operating conditions of these modern instruments for specific samples. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a device for efficiently and environmentally friendly determining the vapor pressure of liquid chemicals, which can achieve efficient and environmentally friendly determination of the vapor pressure of liquid chemicals, with high automation degree of measurement, less sample consumption, and high measurement accuracy.

[0007] The objective of the present invention is achieved as follows: A device for efficiently and environmentally friendly determining the vapor pressure of liquid chemicals includes a thermogravimetric analyzer. A nitrogen cylinder is correspondingly arranged relative to the thermogravimetric analyzer. The outlet of the nitrogen cylinder is connected to the inlet of the thermogravimetric analyzer through an intake pipeline. A pressure reducing valve is arranged on the intake pipeline. The exhaust port of the thermogravimetric analyzer is connected to a condenser through an exhaust pipeline. A constant temperature water bath box I is correspondingly arranged relative to the furnace body of the thermogravimetric analyzer. The balance of the thermogravimetric analyzer is connected to a computer.

[0008] As a further improvement of the present invention, the condenser includes a condensation bottle. The exhaust pipeline is connected to the side of the condensation bottle. The cross-sectional area of the condensation bottle in the horizontal direction increases from top to bottom. A vertical condensation pipe is connected to the upper end of the condensation bottle. The condensation pipe includes an inner pipe body and an outer pipe body. The lower end of the inner pipe body is communicated with the inside of the condensation bottle. The upper end of the inner pipe body is open. An annular sandwich space is left between the inner pipe body and the outer pipe body. An upper inlet pipe and a lower outlet pipe are respectively arranged on the outer periphery of the condensation pipe. Both the upper inlet pipe and the lower outlet pipe are communicated with the sandwich space. A constant temperature water bath box II is correspondingly arranged relative to the condensation pipe. The water outlet pipe and the water return pipe of the constant temperature water bath box II are respectively connected to the upper inlet pipe and the lower outlet pipe. The upper and lower ends of the annular sandwich space are closed. The volatilized gas substances enter the inner pipe body. The constant temperature water bath box II passes cold water into the sandwich space, and the gas substances are cooled and liquefied and enter the condensation bottle.

[0009] As a further improvement of the present invention, a liftable bracket for placing an alumina crucible is arranged inside the thermogravimetric analyzer. The liftable bracket is connected to the balance. The furnace body is correspondingly arranged relative to the alumina crucible. The liftable bracket is arranged on the balance, and the balance can weigh the weight of the alumina crucible.

[0010] The present invention is carried out by using a thermogravimetric analyzer. The furnace body is preheated through a constant temperature water bath. The furnace body can heat the liquid test substance or reference substance on the alumina crucible. The nitrogen cylinder passes nitrogen into the thermogravimetric analyzer. The volatilized gas substances enter the condenser. The constant temperature water bath box II passes cold water into the sandwich space, so that the gas substances entering the inner pipe body are cooled and liquefied and enter the condensation bottle to complete the collection.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: Under atmospheric pressure, a constant temperature program with different gradients is set, and a slow inert gas is purged over the test substance or reference substance at a constant flow rate. A thermogravimetric analyzer is used to measure the mass loss of the test substance or reference substance within a certain constant temperature time, and the weight loss of the test substance or reference substance between two adjacent temperature points is obtained. The exposure area is the surface area of the alumina crucible, and the exposure time of the test substance or reference substance at each detection temperature point is obtained to get the evaporation rate of the test substance or reference substance; the above process can be automatically carried out by the thermogravimetric analyzer after setting the program, without the need for on-site supervision by personnel, and only data processing is required at the end, which can effectively liberate human resources; at the same time, this method takes into account life, health and safety as well as ecological environment safety, and an absorption device for the purge gas is added. By passing the purge gas into the condensation device, the vaporized test substance is re-condensed and refluxed into the waste liquid collector to prevent it from being discharged into the environment.

[0012] The second object of the present invention is to provide a method for measuring the vapor pressure of liquid chemicals by an efficient and environmentally friendly device, which can efficiently and environmentally measure the vapor pressure of liquid chemicals by a thermogravimetric analyzer.

[0013] The object of the present invention is achieved as follows: A method for measuring the vapor pressure of liquid chemicals by an efficient and environmentally friendly device, comprising the following steps:

[0014] (1) Prepare the reference substance and the test substance, turn on the power of the computer and the thermogravimetric analyzer, turn on the power of the first constant temperature water bath, set the temperature of the first constant temperature water bath to 20 °C, so that the furnace body of the thermogravimetric analyzer is in a temperature environment of 20 °C, and keep it at a constant temperature for 1-2 h after reaching the set temperature.

[0015] (2) First, open the test software of the thermogravimetric analyzer, then open the valve of the nitrogen cylinder, and adjust the pressure of the pressure reducing valve on the inlet pipeline of the nitrogen cylinder to 0.04-0.06 MPa.

[0016] (3) The nitrogen cylinder serves as a protective gas source and a purge gas source. The thermogravimetric analyzer is in a standby state, and nitrogen is passed into the inlet of the thermogravimetric analyzer at a flow rate of 20 mL / min through the test software of the thermogravimetric analyzer.

[0017] (4) Measure the weight of the empty alumina crucible by a balance and perform calibration of the reference weight of the alumina crucible; (5) Load the reference substance into the alumina crucible. The thermogravimetric analyzer is in a working state, and nitrogen is passed into the inlet of the thermogravimetric analyzer at a flow rate of 50 mL / min. The reference substance is benzoic acid, and a stepped temperature increase is adopted. The furnace body of the thermogravimetric analyzer is first heated at a heating rate of 15 K / min at a constant speed to the first preheating temperature point, kept at a constant temperature for 30 min, and then heated at a heating rate of 5 K / min at a constant speed to the remaining detection temperature points one by one. At each detection temperature point one, it is kept at a constant temperature for 15 min.

[0018] (6) After measuring the reference material with the thermogravimetric analyzer and returning it to the standby state, take out the alumina crucible and the remaining reference material, then take a new alumina crucible and install it on the liftable bracket, and load the test material into the new alumina crucible, so that the thermogravimetric analyzer returns to the working state. Adopt stepwise heating. First, heat the furnace body of the thermogravimetric analyzer at a heating rate of 15 K / min uniformly to the preheating temperature point two, keep it at a constant temperature for 30 min, and then heat it uniformly to the remaining detection temperature points two at a heating rate of 5 K / min in sequence. Keep it at a constant temperature for 30 min at each detection temperature point two.

[0019] As a further improvement of the present invention, after reaching the set temperature, keep it at a constant temperature for 1 h, and the reference material is benzoic acid.

[0020] As a further improvement of the present invention, it further includes step (7) consisting of the following sub-steps:

[0021] S1. According to the thermogravimetric analyzer, calculate the evaporation rate V of the reference material at each detection temperature point one T , calculation formula: V T : The evaporation rate of the reference material at each detection temperature point one, unit: g·cm -2 ·h -1 ; Δm: The weight loss of the reference material at each detection temperature point one, unit: g; F: The exposure area, and the exposure area is the surface area of the alumina crucible 0.4072 cm 2 ; d: The exposure time of the reference material at each detection temperature point one, unit: h;

[0022] S2. According to the log P of the reference material T calculation formula: Calculate the log P of the reference material at each detection temperature point one T , P T is the vapor pressure of the reference material at the detection temperature point one, T = t + 273.15;

[0023] This equation is derived from the Antoine equation in the NIST Chemistry WebBook SRD 69 and is only applicable to temperature points in the range of 369.0 - 522.4 K (95.85 - 249.25 °C);

[0024] S3. According to the formula log P T = C + D × log V T and the log P of the reference material at each detection temperature point one T and V T , perform a linear regression on the log P T and log V T of the reference material to obtain the linear regression coefficients C and D of the formula;

[0025] S4. Calculate the evaporation rate V of the test substance at each detection temperature point II according to the thermogravimetric analyzer. T The calculation formula is: V T : The evaporation rate of the test substance at each detection temperature point II, with the unit of g·cm -2 ·h -1 ; Δm: The weight loss of the test substance at each detection temperature point II, with the unit of g; F: The exposure area, and the exposure area is the surface area of the alumina crucible, which is 0.4072 cm 2 ; d: The exposure time of the test substance at each detection temperature point II, with the unit of h;

[0026] S5. According to the formula: log P T = C + D×log V T , calculate the log P of the test substance at each detection temperature point II T ; P T is the vapor pressure of the test substance at the detection temperature point II, T = t + 273.15; the unit of T is K, and the unit of t is °C.

[0027] S6. According to the formula: log P T = A + B×1 / T, perform a linear regression on the log P T and 1 / T of the test substance at each detection temperature point II to obtain the linear regression coefficients A and B of the formula;

[0028] S7. Through the linear relationship between log P T and 1 / T obtained in step S6, calculate the vapor pressure P T of the test substance at the corresponding temperature. Through the formula of the reference substance: log P T = C + D×log V T , calculate the logP of the test substance at each detection temperature point II T , and finally obtain the formula of the test substance: log P T = A + B×1 / T.

[0029] As a further improvement of the present invention, the preheating temperature point I of the reference substance is 96 °C, and there are six detection temperature points I, which are 99 °C, 102 °C, 105 °C, 108 °C, 111 °C, and 114 °C in sequence.

[0030] As a further improvement of the present invention, the test substance is aniline, the preheating temperature point II of the test substance is 50 °C, and there are five detection temperature points II, which are 53 °C, 56 °C, 59 °C, 62 °C, and 65 °C in sequence.

[0031] As a further improvement of the present invention, the test substance is n-octanol, the second preheating temperature point of the test substance is 50 °C, and there are six second detection temperature points, which are 59 °C, 62 °C, 65 °C, 68 °C, 71 °C, and 74 °C in sequence.

[0032] The present invention uses a thermogravimetric analyzer to measure the vapor pressure of liquid chemicals. The furnace body is a heating body and operates under a set temperature program. The inside of the furnace can pass through purge gas and protective gas. Through the balance chamber, a high-precision balance is connected under the liftable bracket carrying the reference substance or the test substance to monitor the real-time weight change of the test substance, and the data is transmitted to the computer. Through the loss mass of the test substance, the weight change rate can be further obtained. The saturated vapor pressure of a liquid substance refers to the vapor pressure that appears above the liquid when a pure liquid and its corresponding gas are in equilibrium at a specific temperature; within a certain temperature range, the logarithm of the vapor pressure of a pure substance is linearly related to the reciprocal of the temperature under dynamic equilibrium conditions and follows the Clapeyron - Clausius equation. The present invention uses the formula of the reference substance: log P T = C + D×log V T to calculate log P of the test substance at each second detection temperature point T , and finally obtains the formula of the test substance: log P T = A + B×1 / T. According to this formula, the vapor pressure P of the test substance at 20 °C, 25 °C or other lower temperatures is calculated T . Compared with the prior art, the beneficial effects of the present invention are as follows: Compared with other methods, the technical solution of the present invention has the advantages of short test time, high accuracy, small dosage, simple operation, high automation, environmental protection, etc. for measuring liquid pesticides and chemicals, and breaks through the limitation that the thermogravimetric method can only measure extremely low pressures. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a device diagram for measuring the vapor pressure of liquid chemicals of the present invention.

[0034] Figure 2 is a schematic structural diagram of a condenser.

[0035] Figure 3 is a schematic structural diagram of the furnace body and alumina crucible of the thermogravimetric analyzer.

[0036] Figure 4 is the linear relationship between logP T and logV T of benzoic acid.

[0037] Among them, 1 is a thermogravimetric analyzer, 101 is a furnace body, 102 is a balance, 103 is a liftable support, 104 is an alumina crucible, 2 is a nitrogen gas cylinder, 3 is an intake pipeline, 4 is a pressure reducing valve, 5 is an exhaust pipeline, 6 is a constant temperature water bath tank I, 7 is a computer, 8 is a condenser, 801 is a condensation bottle, 802 is a condenser tube, 802a is an inner tube body, 802b is an outer tube body, 802c is an interlayer space, 803 is an upper inlet pipe, 804 is a lower outlet pipe, 9 is a constant temperature water bath tank II, 10 is a water outlet pipe, and 11 is a water return pipe. Detailed implementation mode

[0038] Example 1

[0039] Such as Figures 1-4 , it is a device for efficiently and environmentally friendly measuring the vapor pressure of liquid chemicals, including a thermogravimetric analyzer 1. A nitrogen gas cylinder 2 is correspondingly arranged opposite to the thermogravimetric analyzer 1. The outlet of the nitrogen gas cylinder 2 is connected to the inlet of the thermogravimetric analyzer 1 through an intake pipeline 3. A pressure reducing valve 4 is arranged on the intake pipeline 3. The exhaust port of the thermogravimetric analyzer 1 is connected to the condenser 8 through an exhaust pipeline 5. A constant temperature water bath tank I 6 is correspondingly arranged opposite to the furnace body 101 of the thermogravimetric analyzer 1. The balance 102 of the thermogravimetric analyzer 1 is connected to the computer 7.

[0040] The condenser 8 includes a condensation bottle 801. The exhaust pipeline 5 is connected to the side of the condensation bottle 801. The cross-sectional area of the condensation bottle 801 in the horizontal direction increases from top to bottom. The upper end of the condensation bottle 801 is connected with a vertical condenser tube 802. The condenser tube 802 includes an inner tube body 802a and an outer tube body 802b. The lower end of the inner tube body 802a is connected to the inside of the condensation bottle 801. The upper end of the inner tube body 802a is open. An annular interlayer space 802c is left between the inner tube body 802a and the outer tube body 802b. An upper inlet pipe 803 and a lower outlet pipe 804 are respectively arranged on the outer periphery of the condenser tube 802. Both the upper inlet pipe 803 and the lower outlet pipe 804 are communicated with the interlayer space 802c. A constant temperature water bath tank II 9 is correspondingly arranged opposite to the condenser tube 802. The water outlet pipe 10 and the water return pipe 11 of the constant temperature water bath tank II 9 are respectively connected to the upper inlet pipe 803 and the lower outlet pipe 804. The upper and lower ends of the annular interlayer space 802c are closed. The volatilized gaseous substances enter the inner tube body 802a. The constant temperature water bath tank II 9 passes cold water into the interlayer space 802c, and the gaseous substances are liquefied when encountering cold and enter the condensation bottle 801.

[0041] Inside the thermogravimetric analyzer 1, there is a liftable support 103 for placing the alumina crucible 104. The liftable support 103 is connected to the balance 102, and the furnace body 101 is correspondingly arranged opposite to the alumina crucible 104.

[0042] A measuring method for a device for efficiently and environmentally friendly measuring the vapor pressure of liquid chemicals includes the following steps:

[0043] (1) Prepare the reference substance and the test substance. Turn on the power of the computer 7 and the thermogravimetric analyzer 1, and turn on the power of the constant temperature water bath 6. Set the temperature of the constant temperature water bath 6 to 20 °C so that the furnace body 101 of the thermogravimetric analyzer 1 is in a temperature environment of 20 °C. After reaching the set temperature, keep it constant for 1 h. The reference substance is benzoic acid;

[0044] (2) First, open the test software of the thermogravimetric analyzer 1, then open the valve of the nitrogen cylinder 2, and adjust the pressure of the pressure reducing valve 4 on the intake pipe 3 of the nitrogen cylinder 2 to 0.04 - 0.06 MPa;

[0045] (3) The nitrogen cylinder 2 serves as a protective gas source and a purging gas source. The thermogravimetric analyzer 1 is in a standby state. Control the nitrogen to be passed into the intake port of the thermogravimetric analyzer 1 at a flow rate of 20 mL / min through the test software of the thermogravimetric analyzer 1;

[0046] (4) Measure the weight of the empty alumina crucible 104 with the balance 102 and perform the reference weight correction of the alumina crucible 104;

[0047] (5) Load the reference substance into the alumina crucible 104. The thermogravimetric analyzer 1 is in a working state. Pass nitrogen into the intake port of the thermogravimetric analyzer 1 at a flow rate of 50 mL / min. The reference substance is benzoic acid. Adopt a stepped temperature increase. First, the furnace body 101 of the thermogravimetric analyzer 1 is heated at a heating rate of 15 K / min at a constant speed to the first preheating temperature point, keep it constant for 30 min, and then heat at a heating rate of 5 K / min at a constant speed to the remaining detection temperature points one by one. Keep it constant for 15 min at each detection temperature point one;

[0048] (6) After measuring the reference substance, the thermogravimetric analyzer 1 returns to the standby state. Take out the alumina crucible 104 and the remaining reference substance, and then take a new alumina crucible 104 and install it on the liftable bracket 103. Load the test substance into the new alumina crucible 104 to make the thermogravimetric analyzer 1 return to the working state. Adopt a stepped temperature increase. First, the furnace body 101 of the thermogravimetric analyzer 1 is heated at a heating rate of 15 K / min at a constant speed to the second preheating temperature point, keep it constant for 30 min, and then heat at a heating rate of 5 K / min at a constant speed to the remaining detection temperature points two by one. Keep it constant for 30 min at each detection temperature point two.

[0049] (7) S1. According to the thermogravimetric analyzer 1, calculate the evaporation rate V of the reference substance at each detection temperature point one T , calculation formula: V T : The evaporation rate of the reference substance at each detection temperature point one, unit: g·cm -2 ·h -1; Δm: The weight loss of the reference substance at each detection temperature point 1, in g; F: The exposure area, and the exposure area is the surface area of the alumina crucible 104, 0.4072 cm 2 ; d: The exposure time of the reference substance at each detection temperature point 1, in h;

[0050] S2. According to the log P of the reference substance T Calculation formula: Calculate the log P of the reference substance at each detection temperature point 1 T , P T is the vapor pressure of the reference substance at detection temperature point 1, T = t + 273.15;

[0051] This equation is derived from the Antoine equation on the NIST Chemistry WebBook SRD 69 and is only applicable to temperature points in the range of 369.0 - 522.4 K (95.85 - 249.25 °C);

[0052] S3. According to the formula log P T = C + D × log V T and the log P of the reference substance at each detection temperature point 1 T and V T , perform a linear regression on the log P T and log V T of the reference substance to obtain the linear regression coefficients C and D of the formula;

[0053] S4. According to the thermogravimetric analyzer 1, calculate the evaporation rate V of the test substance at each detection temperature point 2 T , calculation formula: V T : The evaporation rate of the test substance at each detection temperature point 2, in g·cm -2 ·h -1 ; Δm: The weight loss of the test substance at each detection temperature point 2, in g; F: The exposure area, and the exposure area is the surface area of the alumina crucible 104, 0.4072 cm 2 ; d: The exposure time of the test substance at each detection temperature point 2, in h;

[0054] S5. According to the formula: log P T = C + D × log V T , calculate the log P of the test substance at each detection temperature point 2 T ; P T is the vapor pressure of the test substance at detection temperature point 2, T = t + 273.15; The unit of T is K, and the unit of t is °C.

[0055] S6. According to the formula: log P T= A + B × 1 / T, for the log P of the test substance at each detection temperature point 2 T and 1 / T are linearly regressed to obtain the linear regression coefficients A and B of the formula;

[0056] S7. The log P obtained through step S6 T and the linear relationship of 1 / T are used to calculate the vapor pressure P of the test substance at the corresponding temperature T . Through the formula of the reference substance: log P T = C + D × log V T , calculate the log P of the test substance at each detection temperature point 2 T , and finally obtain the formula of the test substance: log P T = A + B × 1 / T.

[0057] The preheating temperature point 1 of the reference substance is 96 °C, and there are six detection temperature points 1, which are 99 °C, 102 °C, 105 °C, 108 °C, 111 °C, and 114 °C in sequence.

[0058] The test substance is aniline, the preheating temperature point 2 of the test substance is 50 °C, and there are five detection temperature points 2, which are 53 °C, 56 °C, 59 °C, 62 °C, and 65 °C in sequence.

[0059] This example measures the vapor pressure of aniline:

[0060] Zero the instrument with the empty standard alumina crucible 104. Put the benzoic acid and aniline samples into the alumina crucible 104 respectively, place them in the measurement cavity of the thermogravimetric analyzer 1, use nitrogen as the carrier gas, adjust the nitrogen flow rate to 50 mL / min, and set the control program:

[0061] Benzoic acid (reference substance), heat it to 96 °C at a heating rate of 15 K / min and keep it constant for 30 min, and then heat it to 99 °C, 102 °C, 105 °C, 108 °C, 111 °C, and 114 °C at a heating rate of 5 K / min respectively and keep it constant for 15 min. Obtain the linear relationship between logP T and logV T , and the measurement results are shown in Table 1.

[0062] The linear relationship between logP of benzoic acid T and logV T is as Figure 4 .

[0063] Table 1 Linear relationship measurement results of benzoic acid logP T and logV T

[0064] ​

[0065] Aniline (the test substance) was heated to 50 °C at a heating rate of 15 K / min and held at a constant temperature for 30 min. Then, it was heated to 53 °C, 56 °C, 59 °C, 62 °C, and 65 °C at a heating rate of 5 K / min, respectively, and held at a constant temperature for 30 min each. The logP was obtained. T The linear relationship between logP and 1 / T was determined, and the results are shown in Table 2.

[0066] Table 2 Linear relationship determination results of aniline logP T and 1 / T

[0067]

[0068] Result: Through the logP T and 1 / T linear regression equation, the vapor pressure of aniline at 20 °C was extrapolated to be 39.7 Pa, which is close to the literature value (40 Pa), and the relative deviation is 0.8%. The results are reliable.

[0069] In this invention, a thermogravimetric analyzer 1 was used to measure the vapor pressure of liquid chemicals. The furnace body 101 is the heating element and operates under a set temperature program. The inside of the furnace can pass through purge gas and protective gas. Through the balance 102 chamber, the high-precision balance 102 is connected below the liftable bracket 103 that bears the reference substance or the test substance to monitor the real-time weight change of the test substance, and the data is transmitted to the computer 7. Through the loss mass of the test substance, the weight change rate can be further obtained. The saturated vapor pressure of a liquid substance refers to the vapor pressure that appears above the liquid when the pure liquid and its corresponding gas are in equilibrium at a specific temperature; within a certain temperature range, the logarithm of the vapor pressure of a pure substance is linearly related to the reciprocal of the temperature under dynamic equilibrium conditions and follows the Clapeyron - Clausius equation. In this invention, through the formula of the reference substance: log P T = C + D × log V T , the log P of the test substance at each detection temperature point was calculated T , and finally the formula of the test substance was obtained: log P T = A + B × 1 / T. According to this formula, the vapor pressure P of the test substance at 20 °C, 25 °C or other lower temperatures was calculated T . This invention has the advantages of short test time, high accuracy, small dosage, simple operation, high automation, environmental protection, etc. for measuring liquid pesticides and chemicals, and breaks through the limitation that thermogravimetry can only measure extremely low pressures.

[0070] Example 2

[0071] The difference from Example 1 is that the test substance is n-octanol, the preheating temperature point of the test substance is 50 °C, and there are six detection temperature points, which are 59 °C, 62 °C, 65 °C, 68 °C, 71 °C, and 74 °C in sequence.

[0072] In this embodiment, the vapor pressure of n-octanol was measured.

[0073] Benzoic acid (reference substance) was heated to 96 °C at a heating rate of 15 K / min and kept at a constant temperature for 30 min, and then heated to 99 °C, 102 °C, 105 °C, 108 °C, 111 °C, and 114 °C at a heating rate of 5 K / min, respectively, and kept at a constant temperature for 15 min each. The linear relationship between logP T and logV T was obtained, and the measurement results are shown in Table 1.

[0074] n-Octanol (test substance) was heated to 50 °C at a heating rate of 15 K / min and kept at a constant temperature for 30 min, and then heated to 59 °C, 62 °C, 65 °C, 68 °C, 71 °C, and 74 °C at a heating rate of 5 K / min, respectively, and kept at a constant temperature for 30 min each. The linear relationship between logP T and 1 / T was obtained, and the measurement results are shown in Table 3.

[0075] Table 3 Linear relationship between logP of n-octanol T and measurement results of l / T

[0076]

[0077] Result: Through the linear regression equation of logP T and 1 / T, the extrapolated vapor pressure of n-octanol at 25 °C was 9.91 Pa, which was close to the literature value (10 Pa), and the relative deviation was 0.9%, and the result was reliable.

[0078] The present invention is not limited to the above embodiments. Based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and deformations to some technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. An efficient and environmentally friendly device for measuring the vapor pressure of liquid chemicals, comprising a thermogravimetric analyzer, characterized in that: A nitrogen bottle is arranged corresponding to the thermogravimetric analyzer, the outlet of the nitrogen bottle is connected to the air inlet of the thermogravimetric analyzer via an air inlet pipe, a pressure reducing valve is arranged on the air inlet pipe, the exhaust port of the thermogravimetric analyzer is connected to the condenser via an exhaust pipe, a constant temperature water bath is arranged corresponding to the furnace body of the thermogravimetric analyzer, and the balance of the thermogravimetric analyzer is connected to a computer.

2. The highly efficient and environmentally friendly device for measuring the vapor pressure of liquid chemicals according to claim 1, characterized in that: The condenser includes a condensation bottle, the exhaust pipe is connected to the side of the condensation bottle, the cross-sectional area of ​​the condensation bottle in the horizontal direction is arranged to increase from top to bottom, the upper end of the condensation bottle is connected to a vertical condensation tube, the condensation tube includes an inner tube body and an outer tube body, the lower end of the inner tube body is connected to the inside of the condensation bottle, the upper end of the inner tube body is open, and an annular interlayer space is left between the inner tube body and the outer tube body, the outer periphery of the condensation tube is respectively provided with an upper inlet pipe and a lower outlet pipe, the upper inlet pipe and the lower outlet pipe are both connected to the interlayer space, and a constant temperature water bath box 2 is arranged corresponding to the condensation tube, and the outlet pipe and return pipe of the constant temperature water bath box 2 are respectively connected to the upper inlet pipe and the lower outlet pipe.

3. The highly efficient and environmentally friendly device for measuring the vapor pressure of liquid chemicals according to claim 1 or 2, characterized in that: The thermogravimetric analyzer is provided with a liftable support for placing an alumina crucible, the liftable support is connected to a balance, and the furnace body is arranged corresponding to the alumina crucible.

4. A method for measuring the vapor pressure of liquid chemicals according to any one of claims 1 to 3, characterized in that: The steps include: (1) Prepare the reference material and the test material, turn on the power of the computer and the thermogravimetric analyzer, turn on the power of the thermostatic water bath, set the temperature of the thermostatic water bath to 20°C, and keep the furnace of the thermogravimetric analyzer at a temperature of 20°C. After reaching the set temperature, keep the temperature constant for 1-2 hours. (2) First open the test software of the thermogravimetric analyzer, then open the valve of the nitrogen bottle, and adjust the pressure of the pressure reducing valve on the air inlet pipe of the nitrogen bottle to 0.04-0.06MPa; (3) The nitrogen bottle is used as the protective gas source and the purge gas source. The thermogravimetric analyzer is in standby mode. The test software of the thermogravimetric analyzer controls the flow rate of 20 mL / min of nitrogen to the air inlet of the thermogravimetric analyzer. (4) Measuring the weight of an empty alumina crucible using a balance to calibrate the reference weight of the alumina crucible; (5) The reference material is placed in an alumina crucible, the thermogravimetric analyzer is in working state, nitrogen is passed to the air inlet of the thermogravimetric analyzer at a flow rate of 50 mL / min, the reference material is benzoic acid, and a step-by-step heating method is adopted. The temperature is first uniformly increased to the preheating temperature point 1 at a heating rate of 15 K / min through the furnace of the thermogravimetric analyzer, and the temperature is kept constant for 30 minutes, and then the temperature is uniformly increased to the remaining detection temperature points 1 at a heating rate of 5 K / min in sequence, and the temperature is kept constant at each detection temperature point 1 for 15 minutes; (6) After measuring the reference material, the thermogravimetric analyzer returns to the standby state, takes out the alumina crucible and the remaining reference material, and then takes a new alumina crucible and installs it on the liftable bracket. The test material is placed in the new alumina crucible, so that the thermogravimetric analyzer returns to the working state. A step-by-step heating method is adopted. The temperature is first uniformly increased to the preheating temperature point 2 at a heating rate of 15K / min through the furnace of the thermogravimetric analyzer, and the temperature is kept constant for 30 minutes. Then, the temperature is uniformly increased to the remaining detection temperature points 2 at a heating rate of 5K / min in turn, and the temperature is kept constant at each detection temperature point 2 for 30 minutes.

5. The method for measuring the vapor pressure of liquid chemicals according to claim 4, characterized in that: After reaching the set temperature, the temperature was maintained constant for 1 hour, and the reference substance was benzoic acid.

6. The method for measuring the vapor pressure of liquid chemicals according to claim 4 or 5, characterized in that: It also includes step (7) consisting of the following sub-steps: S1. Calculate the evaporation rate V of the reference material at each detection temperature point according to the thermogravimetric analyzer. T , calculation formula: V T : The evaporation rate of the reference substance at each detection temperature point, in g·cm -2 ·h -1 ; Δm: weight loss of the reference material at each test temperature point, in g; F: exposed area, the exposed area is the surface area of ​​the alumina crucible 0.4072cm 2 ; d: exposure time of the reference material at each test temperature point, in h; S2, based on the log P of the reference T Calculation formula: Calculate the log P of the reference material at each test temperature point T , P T is the vapor pressure of the reference substance at the detection temperature point 1, T = t + 273.15; S3, according to the formula log P T =C+D×log V T log P of the reference substance at each test temperature T and V T , log P of the reference substance T and log V T Perform linear regression to obtain the linear regression coefficients C and D of the formula; S4. Calculate the evaporation rate V of the test substance at each detection temperature point according to the thermogravimetric analyzer. T , calculation formula: V T : Evaporation rate of the test substance at each test temperature point, in g·cm -2 ·h -1 ; Δm: weight loss of the test object at each test temperature point, in g; F: exposed area, the exposed area is the surface area of ​​the alumina crucible 0.4072cm 2 ; d: exposure time of the test object at each test temperature point, in h; S5. According to the formula: log P T =C+D×log V T Calculate the log P of the test object at each test temperature point T ;P T is the vapor pressure of the test object at the second detection temperature point, T = t + 273.15; S6. According to the formula: log P T =A+B×1 / T, log P of the test object at each test temperature point T Perform linear regression with 1 / T to obtain the linear regression coefficients A and B of the formula; S7, log P obtained by step S6 T The linear relationship between the vapor pressure P of the test substance at the corresponding temperature is calculated based on the linear relationship between the vapor pressure P and 1 / T. T .

7. The method for measuring the vapor pressure of liquid chemicals according to claim 6, characterized in that: The preheating temperature point one of the reference object is 96°C, and there are six detection temperature points one, which are 99°C, 102°C, 105°C, 108°C, 111°C, and 114°C respectively.

8. The method for measuring the vapor pressure of liquid chemicals according to claim 7, characterized in that: The test object is aniline, and the preheating temperature point 2 of the test object is 50°C. There are five detection temperature points 2, which are 53°C, 56°C, 59°C, 62°C, and 65°C respectively.

9. The method for measuring the vapor pressure of liquid chemicals according to claim 7, characterized in that: The test object is n-octanol, and the preheating temperature point two of the test object is 50°C. There are six detection temperature points two, which are 59°C, 62°C, 65°C, 68°C, 71°C, and 74°C respectively.

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