Method for measuring evaporation enthalpy by using reaction calorimeter

Abstract

The invention relates to calorimetry of a reaction calorimeter, in particular to a method for measuring evaporation enthalpy by using the reaction calorimeter. The materials are distilled out of the kettle in a reduced pressure distillation mode, collected and weighed, and the evaporation enthalpy of the materials is rapidly measured. According to the method, the speed of measuring the evaporation enthalpy of the material can be effectively increased, and measurement can be directly carried out after reaction calorimetry research. Data obtained through the method can provide underlying basic data for process design, engineering amplification and the like, and a foundation is laid for achieving process safety and improving quality and efficiency.

Description

Technical Field

[0001] The invention relates to reaction calorimetry, in particular to a method for measuring vaporization enthalpy using a reaction calorimeter. Background Art

[0002] Heat cannot generally be measured directly, so a calorimeter measures heat indirectly by measuring temperature. Some calorimeters can directly measure the rate of heat release or thermal power.

[0003] 1 Classification of calorimeters 1.1 Calorimeters can be categorized based on sample size: microcalorimeters (milligram scale), macrocalorimeters (gram scale), and laboratory-scale calorimeters (hundred grams to kilogram scale). This classification is particularly useful when limited amounts of material are available or when studying hazardous reactions. In particular, small sample sizes are crucial for ensuring safety during the experiment. Of course, larger sample sizes are more practical, as the results can better simulate production processes.

[0004] 1.2 Calorimeters can be designed with a single calorimetric cell or with two identical cells, the latter also known as a differential calorimeter. Dual-cell technology eliminates interference (such as that caused by heat dissipation to the environment) by measuring the difference in heat release between two completely symmetrical calorimetric cells (sample cells).

[0005] 1.3 Calorimeters are categorized by thermal sensitivity, ranging from a few mW / kg to 10-20 W / kg. Highly sensitive instruments allow direct testing at the target temperature. Assessing thermal risks during storage requires highly sensitive instruments. Instruments with lower sensitivity must perform measurements at higher temperatures, as these can accelerate reactions and produce measurable heat release rates. The results must be extrapolated to the lower temperatures of interest, so low-sensitivity instruments are primarily used for screening.

[0006] A reaction calorimeter is a calorimeter used to measure the heat release and heat release rate of a chemical reaction. Reaction calorimeters include fully automatic reaction calorimeters, microcalorimeters, pressure calorimeters, differential calorimeters, and adiabatic calorimeters. The calorimeter used in this article is a fully automatic reaction calorimeter, such as the RC1 reaction calorimeter from METTLER TOLEDO (Switzerland), the SIMULAR reaction calorimeter from HEL (UK), and the FlexyPAT-HFC reaction calorimeter from SYSTEM TECHNIK AG (Switzerland). These reaction calorimeters use the heat flow method for calorimetry. According to the aforementioned classification criteria, they are classified as large-scale calorimeters, consisting of a single calorimetric unit with a measurement sensitivity greater than 0.2 W / kg, and employ an isothermal mode for calorimetry.

[0007] The enthalpy of vaporization refers to the heat absorbed when a unit mass of liquid is converted into gas while the temperature remains unchanged. This heat is also equal to the heat released when a unit mass of gaseous substance is converted into liquid at this temperature and a certain pressure (such as 1 atmosphere).

[0008] The enthalpy of vaporization of a material is an indispensable parameter for studying its properties and a crucial heat parameter for studying chemical reactions. Classic methods for determining enthalpy of vaporization are the vapor pressure method and the mixing method, which generally require complex glassware and equipment. The vapor pressure method is not suitable for samples that react readily with mercury. The mixing method indirectly measures the enthalpy of vaporization by measuring the heat released when the substance's vapor condenses into a liquid phase.

[0009] If a reaction calorimeter can be used to measure the vaporization enthalpy of a substance, it will reduce the workload of scientific workers, reduce unnecessary errors in their work, speed up their progress, and improve the accuracy of reaction calorimetry. Summary of the Invention

[0010] The present invention aims to provide a method for measuring vaporization enthalpy using a reaction calorimeter.

[0011] To achieve the above purpose, the present invention adopts the following technical solutions: First, the boiling point of the material to be tested is measured using a boiling point meter. T b , determine the temperature and pressure for measuring the evaporation enthalpy, as well as the temperature of the coolant; second, add the material to be measured into the calorimetric kettle to ensure the minimum volume requirement for calorimetry, use insulation materials such as insulation cotton to insulate the kettle cover and collection pipeline of the reaction calorimeter, and ensure that the reaction calorimeter is well sealed; third, use the calibration program provided by the reaction calorimeter to calibrate the heat, use a vacuum distillation collection device to connect the kettle cover to vacuum the distilled material and collect it in the collection bottle, stop vacuuming after collecting enough distilled material, weigh the collected material, and obtain the material vaporization mass m ; Fourth, use the calibration program of the reaction calorimeter to calibrate the heat again to complete the calorimetric experiment, and process the calorimetric data to obtain the evaporation heat Q v , and thus obtain the enthalpy of vaporization H v = Q v / m .

[0012] The boiling point of the material to be measured in step 1 is particularly important for determining the temperature for measuring the vaporization enthalpy. It is necessary to ensure that the material will not reflux in the kettle under normal pressure and measurement temperature, thereby affecting the accuracy of the calorimetric measurement of the reaction calorimeter.

[0013] The instrument used in step 1 to determine the boiling point of the material is a general atmospheric boiling point tester.

[0014] The boiling point of the step 1 material is T b , determine the temperature for measuring the enthalpy of vaporization T = T b -20.0, pressure control is -80~ -70kPaG, set coolant temperature T c ≤ T -50.0℃.

[0015] The minimum material volume of the calorimetric kettle in step 2 is 250 mL for a glass kettle and 300 mL for a metal kettle, ensuring that the reaction calorimeter can be calibrated normally after 50 mL of material is evaporated.

[0016] The second step uses insulation materials such as insulation cotton to insulate the reaction calorimeter kettle cover and collection pipeline to prevent steam from encountering the pipeline and flowing back into the kettle. At the same time, it is necessary to ensure that the pipe connecting the distillation collection device to the kettle cover is short enough and the bending angle is greater than 90° to ensure that the material steamed from the kettle will not return to the kettle and affect the accuracy of the measurement. The distillation collection device is installed properly.

[0017] After installing the distillation collection device in step 3, ensure that the stirring blade speed can make the material contact the kettle wall evenly, immerse the temperature sensor and calibration heater probe into the material, ensure that the curve does not jitter, select the isothermal calorimetry mode, and heat the material temperature to the measurement temperature. T Perform vacuum distillation until a stable liquid flows out of the receiving end, stop vacuuming, use the calibration program of the reaction calorimeter to calibrate the heat, and weigh the collection bottle. m 1.

[0018] After the calibration procedure in step 3 is completed, the distillation collection device is used to vacuum the material in the kettle to evaporate, and the condensed material flows into the collection bottle in the collection device. After about 50 mL of material is collected, the vacuum collection is stopped, and all the material in the pipeline is transferred to the collection bottle. The total weight of the collection bottle and the material is weighed. m 2. Get the steamed mass of the material m = m 2- m 1.

[0019] The distillation collection device in step 3 is a conventional laboratory vacuum distillation device.

[0020] After the calibration procedure in step 4 is completed, the calorimetric data is obtained and the evaporation heat is obtained by calculation. Q v (Q v =Q flow +Q accumulation=UA×ΔT+M r ×C pr ×dT r / dt), and thus the enthalpy of vaporization is obtained H v = Q v / m .

[0021] The advantages of the present invention are as follows: the present invention proposes a specific measurement method for measuring vaporization enthalpy using a reaction calorimeter. The method of the present invention can directly and quickly measure the vaporization enthalpy of a material using existing instruments and equipment, thereby expanding the application scope of the reaction calorimeter, increasing the methods for obtaining the vaporization enthalpy of a material, reducing the workload of scientific workers, reducing unnecessary errors generated in the work, accelerating the progress of workers, and improving the accuracy of reaction calorimetry. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are further described below with reference to examples. It should be noted that the specific embodiments described here are only for illustrating and explaining the present invention, and are not intended to limit the present invention.

[0023] Taking the following water as an example, the evaporation enthalpy of water is measured using a reaction calorimeter, specifically: 1. Test the boiling point of water Weigh 5.0g of water into a test tube and place the test tube in a flammable liquid boiling point tester. The liquid level of the methanol sample to be tested is below the thermal oil in the bottle. Place a PT100 test tube in the test tube to measure the real-time temperature. The lower end of the PT100 is 0.5-1.0cm above the liquid in the tube. Turn on the boiling point meter switch and rotate the knob to adjust the heating rate to slowly increase the temperature until the sample to be tested in the test tube boils. Record the test data during the experiment and take the average of the two tests as the final test result. The boiling point of water at normal pressure is 100.0℃.

[0024] 2. Determine the temperature for measuring the evaporation enthalpy T = 100.0-20.0 = 80.0℃, control the pressure to -80~ -70kPaG, and set the coolant temperature to 25.0℃.

[0025] 3 Select a 500mL glass kettle for measurement, weigh 250.0g of water and add it into the reactor, adjust the stirring paddle speed to 250rpm, cover the kettle cover, connecting pipe and kettle neck with insulation cotton for insulation, connect the distillation collection device, set the coolant temperature to 25.0℃, control the temperature in the kettle to 80.0℃ in isothermal mode, turn on the vacuum pump, set the pressure to -75 kPaG, and perform reduced pressure distillation. When water droplets flow out steadily, stop vacuuming, run the calibration program, and weigh the collection bottle to 90.2g.

[0026] 4 After the calibration procedure is completed, turn on the vacuum pump again, set the pressure to -75 kPaG, and perform reduced pressure distillation to collect. When about 50 mL is collected, stop vacuuming and weigh the collection bottle to find that it weighs 134.5 g. The actual amount distilled out is 44.5 g.

[0027] 5. After the curve stabilizes, run the calibration program again to perform post-calorimetric calibration and process the data to obtain the evaporation heat. Q v =101.0kJ, thus obtaining the enthalpy of vaporization of water H v = Q v / m =101.0 / 44.5 / 1000=2269.7kJ / kg. After inquiry, the evaporation enthalpy of water at 80.0 is 2310.7 kJ / kg, with a relative deviation of -1.8%. The accuracy is high and can meet the calculation requirements.

Claims

1. A method for measuring vaporization enthalpy using a reaction calorimeter, characterized in that The enthalpy of vaporization of a material can be obtained using a reaction calorimeter.

2. The method for measuring vaporization enthalpy using a reaction calorimeter according to claim 1, characterized in that The reaction calorimeters include: the reaction calorimeter RC1 of METTLER TOLEDO of Switzerland, the reaction calorimeter SIMULAR of HEL of Britain, and the reaction calorimeter FlexyPAT-HFC of SYSTEM TECHNIK AG of Switzerland, all of which use the heat flow method to measure heat.

3. The method for measuring vaporization enthalpy using a reaction calorimeter according to claim 2, wherein The calorimetric principle of the measurement method is to reduce the pressure to cause the material to vaporize below the boiling point, use a reaction calorimeter to measure the heat of the vaporization process, and simultaneously condense and collect the vaporized material to obtain the mass of the vaporized material, thereby obtaining the vaporization enthalpy of the material at that temperature. This method is faster, more convenient and more accurate than previous devices.