CN115096929A - Continuous flow reaction calorimetry method based on flow regulation - Google Patents

Continuous flow reaction calorimetry method based on flow regulation Download PDF

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CN115096929A
CN115096929A CN202210682951.6A CN202210682951A CN115096929A CN 115096929 A CN115096929 A CN 115096929A CN 202210682951 A CN202210682951 A CN 202210682951A CN 115096929 A CN115096929 A CN 115096929A
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reaction
flow
temperature
reaction mixture
pipeline
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叶树亮
李一帆
许启跃
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China Jiliang University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/005—Investigating or analyzing materials by the use of thermal means by investigating specific heat
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
    • G01N25/48—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on solution, sorption, or a chemical reaction not involving combustion or catalytic oxidation
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    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
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    • G05D7/06—Control of flow characterised by the use of electric means

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Abstract

The invention discloses a continuous flow reaction calorimetry method based on flow regulation. According to the method, reaction pipelines are finely segmented, the specific heat capacity of a reaction mixture and the heat release of reactants in unit mass are calculated by a linear fitting mode through changing the flow conditions during experiments for many times, and then reaction enthalpy and adiabatic temperature rise in the reaction process for safety risk assessment are calculated. The method does not need to calibrate the heat transfer coefficient of the reaction pipeline, obtains the specific heat capacity and the reaction enthalpy of the reaction mixture through the analysis of experimental data under different flow conditions, can realize the calorimetric analysis of the dynamic feeding chemical reaction under the continuous flow process, and has high experimental efficiency and safe process.

Description

Continuous flow reaction calorimetry method based on flow regulation
Technical Field
The invention belongs to the field of fine chemical engineering and reaction heat measurement and calculation, and particularly relates to a continuous flow reaction calorimetric analysis method which starts from a reaction pipeline heat balance relation, is based on flow regulation and does not need calibration.
Background
The reaction heat of the chemical reaction is an important parameter in safety assessment and production processes of the modern chemical industry, and the main tool for realizing reaction heat measurement in a laboratory at present is a reaction calorimeter, but the reaction heat is provided with a traditional kettle type stirring reactor, so that calorimetric analysis can not be carried out on the chemical reaction of dynamic feeding under a continuous flow process. On the other hand, the kettle type reaction calorimeter controls the temperature of a sample in a reaction kettle by a heat-conducting medium circulating in a jacket, so that the problems of large temperature control overshoot, low control speed and the like exist, and certain safety risks exist for some chemical reactions with high reaction rate and high heat release quantity.
For the reaction heat in the continuous flow state, the traditional heat balance-based heat measurement method needs to calibrate the heat transfer coefficient of the reaction pipeline before the experiment according to the experimental conditions such as the types of reactants, the process temperature, the flow rate of the reactants and the like, and the calibrated result affects the accuracy of the final experimental result, so that the experimental efficiency is low. In addition, there are methods of performing continuous flow reaction heat by using the seebeck effect or infrared thermal imaging equipment in combination with thermoelectric materials, but both methods require complicated circuit and mechanical structure design.
By using a continuous flow chemical technology, on one hand, the reaction volume is reduced, the mass transfer and heat transfer efficiency of the reactor is improved, and the reaction risk is reduced; on the other hand, according to the innovative continuous flow reaction calorimetric analysis method, the experiment steps are saved, and the experiment efficiency is improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a calorimetric analysis method applied to a continuous flow reaction condition, which is a high-efficiency experimental analysis method without calibrating the heat transfer coefficient of a reactor or designing a complex circuit structure and simultaneously improves the safety of high-heat-release and high-speed chemical reaction. The method comprises the following specific steps:
the method comprises the following steps: measurement of specific heat capacity of reaction mixture: under the condition of fixed flow, a heater in the pipeline is opened, so that the temperature of the reaction mixture before and after flowing through the heater is changed; changing the flow conditions in the experiment for many times, and adjusting the output power of the heater to keep the temperature difference of the reaction mixture before and after flowing through the heater under each flow condition unchanged; and carrying out linear fitting through multiple groups of experimental data to obtain the specific heat capacity of the reaction mixture.
Step two: the first step is that a plurality of experiments are carried out under different flow conditions, after a reaction system is stable in each experiment, temperature data at different flow positions of reaction pipelines are collected through temperature sensors, temperature distribution in each group of experiment reaction pipelines is obtained through interpolation, and for chemical reactions with high reaction rates, the temperature sensors are arranged more densely near the inlets of the reaction pipelines;
step three: and D, finely dividing the temperature distribution of the reaction pipeline obtained in the step two into multiple sections, performing linear fitting on multiple groups of experimental data in each temperature distribution section according to the heat balance relational expression of the reaction pipeline, calculating the heat release of the reactants in unit mass, further solving the reaction enthalpy and adiabatic temperature rise of the reaction, and completing calorimetric analysis of the experiment.
Further, after the line heater is turned on in the first step, the heat balance in the line can be expressed as the following formula (1):
P＝C p ·m·ΔT+Q (1)
wherein P represents the output power of the heater (in W), and m represents the mass flow rate at that time (in kg · s) -1 ) Δ T represents the temperature difference of the reaction mixture after passing through the heater (in K), Q represents the heat exchange of the line with the isothermal environment (in W);
and then changing the flow in the experiment for many times, adjusting the output power of the heater to keep the temperature difference delta T of the reaction mixture before and after flowing through the heater under each flow condition unchanged, and fitting through multiple groups of experimental data to obtain the specific heat capacity of the reaction mixture.
Furthermore, in the third step, the reaction enthalpy of the reaction process is obtained through linear fitting of experimental data, and the heat balance existing in the reaction pipeline during the reaction is as the following formula (2):
Figure BDA0003697015940000031
in the formula Q r The exothermic heat per unit mass of the reaction mixture (in J.kg) -1 )；C p Is the specific heat capacity (unit is J.kg) of the reaction mixture -1 ·K -1 )；T A Is the temperature change of the reaction mixture (in K); q e The heat exchange of the reaction mixture per second with a thermostatic bath at a temperature difference of 1K (in J.s) -1 ·K -1 ) (ii) a m represents the mass flow rate (in kg · s) at this time -1 )；T B Is the temperature difference (in K) between the reaction mixture and the thermostatic bath;
finely segmenting the temperature distribution of the reaction pipeline, and for a plurality of groups of experimental results under different flow conditions, segmenting the temperature distribution of each reaction pipeline by T B ·m -1 And T A And fitting the data according to a form of a linear function, solving an intercept, obtaining the heat release of the mixture per unit mass, and further solving reaction enthalpy.
The invention has the beneficial effects that:
1. in terms of experimental efficiency, the heat balance relation of the reaction coil pipe is transformed when reaction occurs, the relation between measurable variables is deduced, calorimetric analysis is carried out on chemical reaction in a mode of adjusting experimental flow, the condition that the heat transfer coefficient of a reaction pipeline needs to be calibrated according to experimental conditions in each experiment of the traditional continuous flow calorimetric method is avoided, and therefore experimental efficiency is improved.
2. From the perspective of experimental safety, the specific surface area of the continuous flow reactor is larger, the heat exchange efficiency is several times to ten times that of the traditional kettle type reactor, and the excellent mass and heat transfer characteristics can effectively shorten the reaction time and improve the production efficiency; meanwhile, the continuous flow reactor has small liquid holding volume, and can obviously reduce the use of toxic or high-risk chemical reagents, thereby improving the safety of the experiment.
3. The calorimetric result obtained by the invention can be applied to the links of risk analysis, process optimization, production amplification and the like of chemical reaction under the continuous flow condition, and can also be applied to reaction kinetic analysis under the continuous flow condition.
In conclusion, the invention does not need to design a complex circuit structure, also overcomes the problem that the heat transfer coefficient needs to be calibrated in the traditional calorimetric method, improves the experimental efficiency, and simultaneously improves the safety in the experimental process by reducing the liquid holdup.
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FIG. 1 is a schematic structural diagram of a continuous flow reaction experiment platform.
Detailed Description
For a better understanding of the technical aspects of the present invention, reference is made to the following detailed description of the invention in conjunction with the accompanying drawings and specific embodiments, it being understood that the invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for purposes of providing a more thorough understanding of the present disclosure.
This example further illustrates the calorimetric method of the present invention.
As shown in fig. 1, in the experiment, a first reactant 1 enters a first preheating pipeline 3 through a first sampling pump 2; the second reactant enters the second preheating pipeline through a second sampling pump (a temperature sensor 4 is arranged at the outlet of the preheating pipeline), and the preheating pipeline is placed in a constant-temperature bath 7, so that the temperature of the two reactants is kept constant before reaction. After preheating, two reactants enter a reaction pipeline 6 through a T-shaped mixer 5, flow out of the reaction pipeline after the reaction is finished, sequentially flow through a pipeline heater 8 and a back pressure valve 9, and then are collected through a liquid tail discharge 10. In the experimental process, the functions of preheating temperature monitoring, reaction temperature monitoring, heater temperature monitoring, reaction pressure monitoring, constant-temperature bath temperature control and sample injection flow control are realized through the central control unit 11 and the upper computer 12.
On the basis of the above experimental platform, the steps of this embodiment are as follows:
the method comprises the following steps: measurement of specific Heat Capacity C of reaction mixture p : setting the flow of two sample injection pumps to be consistent, wherein the total flow is F 1 As shown in fig. 1, the experimental platform includes a pipeline heater, after the system is stabilized, the heater in the pipeline is turned on, and the temperature of the reaction mixture before and after flowing through the heater changes, and the heat balance in the pipeline can be expressed as the following formula (1):
P 1 ＝C p ·m 1 ·ΔT+Q 1 (1)
in the formula P 1 Represents the output power of the heater, m 1 Denotes the mass flow at this time,. DELTA.T denotes the temperature difference of the reaction mixture after passing through the heater, Q 1 Indicating heat exchange of the reactants in the pipeline with a constant temperature environment;
the total flow rate in the experiment was then changed to F 2 To F 5 Adjusting the output power of the heater to keep the temperature difference delta T of the reaction mixture before and after flowing through the heater unchanged; the product m of the mass flow and the temperature difference of the reaction mixture in each set of experiments i Δ T (i equals 1,2 … 5) and the output power P of the heater i (i-1, 2 … 5) is fitted as a linear function, the slope of the fit being the specific heat capacity C of the reaction mixture p 。
Step two: as shown in fig. 1, a plurality of temperature sensors are arranged in the reaction pipeline along the flow path, the first step is to perform a plurality of experiments under different flow conditions, after the reaction system is stabilized in each experiment, the temperature data at different flow paths of the reaction pipeline are collected by the temperature sensors, the temperature distribution in each group of experiment reaction pipelines is obtained in an interpolation mode, and for the chemical reaction with a faster reaction rate, the temperature sensors are arranged more densely near the inlet of the reaction pipeline.
Step three: finely dividing the temperature distribution of the reaction pipeline obtained in the second step into a plurality of sections, wherein the heat balance existing in each section is as shown in the following formula (2):
Figure BDA0003697015940000061
in the formula Q r The exotherm per unit mass of the reaction mixture; c p Is the specific heat capacity of the reaction mixture; t is A Is a change in temperature of the reaction mixture; q e Heat exchange between the reaction mixture and the constant temperature bath at a temperature difference of 1K per second; m represents the mass flow rate at this time; t is B Is the temperature difference between the reaction mixture and the constant temperature bath;
the above-described heat balance equation (2)) can be converted into the following equation (3):
Figure BDA0003697015940000062
for multiple groups of experimental results under different flow conditions, the T in each reaction pipeline temperature distribution section B ·m -1 And T A The data are fitted in the form of a linear function, and as can be seen from the above equation (3), the intercept b of the linear function can be expressed as the following equation (4):
Figure BDA0003697015940000063
where b represents the intercept of the linear function fit.
From the above equation (4), the exothermic amount per unit mass of the reaction mixture in each temperature distribution section of the reaction line can be obtained, and the exothermic amount per unit mass can be integrated to obtain the total exothermic amount per unit mass of the mixture, as shown in the following equation (5):
Figure BDA0003697015940000071
in the formula Q total Represents the heat release (J.kg) of the mixture per unit mass -1 ) (ii) a j represents each segment of the reaction line temperature profile; n represents the total number of stages of the temperature distribution of the reaction pipeline; q r,j Shows the exothermic heat of the reaction mixture per unit mass in each segment (unit is J.kg) -1 )。
The reaction enthalpy of the reaction is then (equation (6)):
Figure BDA0003697015940000072
in the formula H r Represents the reaction enthalpy (in J. mol.) of the reaction -1 ) (ii) a ρ represents the density of the reaction mixture (in kg. m) -3 )；c 0 Indicates the initial concentration of the limiting reactant (in mol. m) -3 )。
The adiabatic temperature rise of the reaction process is (equation (7)):
Figure BDA0003697015940000073
in the formula T ad Indicating the adiabatic temperature rise (in K) during the reaction.
The above description is only one embodiment of the present invention, and is not intended to limit the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, and improvement made within the principle of the present invention should be included in the scope of the present invention.

Claims (3)

1. A continuous flow reaction calorimetry method based on flow regulation is characterized by comprising the following steps:
the method comprises the following steps: under the condition of fixed flow, a heater in the pipeline is opened, so that the temperature of the reaction mixture before and after flowing through the heater is changed;
changing the flow conditions in the experiment for many times, and adjusting the output power of the heater to keep the temperature difference of the reaction mixture before and after flowing through the heater under each flow condition unchanged;
carrying out linear fitting through multiple groups of experimental data to obtain the specific heat capacity of the reaction mixture;
step two: the first step is that a plurality of experiments are carried out under different flow conditions, after a reaction system is stable in each experiment, temperature data of different flow paths of the reaction pipelines are collected through a temperature sensor, and temperature distribution in each group of experiment reaction pipelines is obtained through interpolation;
step three: and D, finely dividing the temperature distribution of the reaction pipeline obtained in the step two into multiple sections, performing linear fitting on multiple groups of experimental data in each temperature distribution section according to the heat balance relation of the reaction pipeline, calculating the heat release of reactants in unit mass, further solving the reaction enthalpy and adiabatic temperature rise of the reaction, and completing calorimetric analysis.
2. A continuous flow reaction calorimetry method based on flow regulation, according to claim 1, characterised in that:
after the pipeline heater is turned on in the first step, the thermal balance in the pipeline is represented as:
P＝C p ·m·ΔT+Q
wherein P represents the output power of the heater, m represents the mass flow at the moment, Delta T represents the temperature difference of the reaction mixture after flowing through the heater, and Q represents the heat exchange between the pipeline and the constant temperature environment;
changing the flow in the experiment for many times, adjusting the output power of the heater to keep the temperature difference delta T of the reaction mixture before and after flowing through the heater under each flow condition, fitting through multiple groups of experimental data to obtain the specific heat capacity C of the reaction mixture p 。
3. A continuous flow reaction calorimetry method based on flow regulation, according to claim 2, characterised in that:
the third step is to obtain reaction enthalpy in the reaction process specifically as follows: the heat balance present in the reaction line during the reaction is as follows:
Figure FDA0003697015930000021
in the formula Q r The exotherm per unit mass of the reaction mixture; t is A Is a change in temperature of the reaction mixture; q e The heat exchange between the reaction mixture and the constant temperature bath is carried out every second under the temperature difference of 1K; t is a unit of B Is the temperature difference between the reaction mixture and the constant temperature bath;
finely segmenting the temperature distribution of the reaction pipeline, and for a plurality of groups of experimental results under different flow conditions, segmenting the temperature distribution of each reaction pipeline by T B ·m -1 And T A Fitting the data according to a linear function form to obtain a sectionAnd obtaining the heat release of the mixture per unit mass, and further obtaining the reaction enthalpy.
CN202210682951.6A 2022-06-16 2022-06-16 Continuous flow reaction calorimetry method based on flow regulation Pending CN115096929A (en)

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