Method for evaluating adsorption performance of porous carbonization layer of asphalt thermal decomposition process on flue gas

Abstract

The present application provides a kind of asphalt thermal decomposition process porous carbonization layer smoke adsorption performance evaluation method, belong to asphalt flame retardant material research and development technical field, solve the problem that it is difficult to evaluate the micro adsorption of porous carbonization layer formed by intumescent flame retardant at high temperature to asphalt smoke by experimental method at present.The present application carries out analysis to the element type, functional group structure and chemical valence of porous carbonization layer by experiment, constructs the molecular model of porous carbonization layer, analyzes the common smoke component generated by asphalt and flame retardant asphalt by experiment, establishes the molecular model of asphalt smoke, and based on adsorption kinetics theory, draw the adsorption isotherm of porous carbonization layer model to asphalt smoke model at different temperatures, and the interaction energy index is combined to evaluate the adsorption of porous carbonization layer model to asphalt smoke model, provide a new evaluation method for evaluating the adsorption of porous carbonization layer to asphalt smoke, provide a theoretical basis for studying environmental protection and efficient intumescent flame retardant.

Description

Technical Field

[0001] This invention relates to a method for evaluating the adsorption performance of porous carbonized layers on flue gas during the thermal decomposition of asphalt, belonging to the field of asphalt flame retardant material research and development technology. Background Technology

[0002] In the early stages of highway tunnel construction, cement pavement was generally used for tunnel road surfaces. In recent years, with increasing demands for driving safety and comfort, asphalt pavement has gradually replaced cement pavement as the mainstream tunnel paving method due to its better anti-skid properties, lower noise levels, and shorter construction period. However, because tunnels are semi-enclosed tubular spaces, the surface temperature at the fire source can quickly reach over 700°C, far exceeding the initial pyrolysis and combustion temperature of asphalt. Burning asphalt at high temperatures releases large amounts of CO2 and H2O, along with numerous complex toxic, flammable, explosive, and corrosive volatile organic compounds, which not only promote the spread of fire but also significantly hinder disaster relief efforts. Therefore, the fire safety of asphalt materials has received widespread attention from scholars both domestically and internationally. To suppress the pyrolysis and combustion of tunnel asphalt, provide longer escape time for people fleeing the fire scene, and facilitate rapid fire suppression by rescue personnel, effective flame-retardant measures are needed.

[0003] Currently, research on flame retardant technology for asphalt materials mainly references polymer flame retardant technology theory. This involves adding organic or inorganic flame retardants to increase the limiting oxygen index of asphalt with minimal impact on its basic properties, thus changing it from a flammable to a flame-retardant grade. Currently, the most mature flame retardant technology on the market is intumescent flame retardant. Its flame retardant mechanism involves forming a porous char layer on the material surface at high temperatures, hindering heat transfer and smoke release, isolating oxygen, and achieving condensed-phase flame retardancy. Its composition generally consists of a charring agent, an intumescent agent, and a dehydrating agent. Furthermore, the porous char layer can maintain a certain molecular structure at high temperatures. Numerous experiments have shown that the release of volatile organic compounds from asphalt combustion is significantly reduced after adding intumescent flame retardants. However, the mechanism by which intumescent flame retardants inhibit the release of smoke during asphalt combustion remains unclear.

[0004] Studies have shown that the types and release amounts of volatile organic compounds (VOCs) from asphalt vary under different working conditions and at different stages of thermal decomposition under the same working condition. Currently, the mechanism by which intumescent flame retardants suppress the release of asphalt fumes at high temperatures remains unclear. However, the adsorption mechanism of the porous carbonized layer formed by intumescent flame retardants at the microscale on asphalt fumes can be studied using molecular dynamics simulations. The basic principle of molecular dynamics simulation is based on Newton's second law, assuming the existence of a certain number of interacting particles in the system, and giving each particle a corresponding force field and charge. At the start of the simulation, the initial velocity and position of each particle are randomly assigned according to the temperature and pressure to be achieved. Then, the interaction force between particles is calculated using the energy expression of the particles, and the acceleration is calculated using Newton's second law. The initial velocity and position of the next particle are then calculated, and this process is repeated to obtain the particle's trajectory and various properties.

[0005] Adsorption refers to the process by which atoms or molecules of one substance adhere to the surface of another substance. It is caused by the difference in forces acting on free molecules at the interface and molecules within the solid phase. For a gas-solid interface, the imbalance of forces on the solid surface molecules generates a residual force field, which in turn causes adsorption of gas molecules. However, the adsorbed gas molecules remain in motion and can overcome the surface stress of the solid, leading to desorption, until a dynamic equilibrium is reached between adsorption and desorption. A common method for describing adsorption phenomena is to plot adsorption isotherms and determine their type; that is, to study the relationship between the amount of adsorption and relative pressure at a given temperature. For the adsorption of asphalt fumes by the porous carbonized layer formed by intumescent flame retardants at high temperatures, conventional testing instruments are insufficient to determine the adsorption isotherm of the porous carbonized layer on asphalt fumes under fire conditions, as well as other indicators characterizing the adsorption performance of the porous carbonized layer on asphalt fumes.

[0006] In summary, although numerous experimental studies have shown that adding intumescent flame retardants can effectively reduce the amount of smoke released from asphalt under fire conditions, the inhibition mechanism of intumescent flame retardants on asphalt smoke release at high temperatures is unclear. The adsorption mechanism of the porous carbonized layer formed by the intumescent flame retardant on asphalt smoke is even more ambiguous, and existing experimental instruments cannot measure the microscopic adsorption effect of the porous carbonized layer formed by the intumescent flame retardant on asphalt smoke at high temperatures. Therefore, this invention uses molecular dynamics simulation to study the adsorption effect of the porous carbonized layer formed by the intumescent flame retardant on asphalt smoke at high temperatures. This provides a new evaluation method and indicators for assessing the microscopic adsorption effect of the porous carbonized layer on asphalt smoke, and provides a theoretical basis for the development of environmentally friendly and efficient intumescent flame retardants for asphalt. Summary of the Invention

[0007] (1) Technical issues

[0008] The purpose of this invention is to provide a method for evaluating the adsorption performance of porous carbonized layers on flue gas during the thermal decomposition of asphalt. This method uses molecular dynamics simulation technology to study the adsorption effect of porous carbonized layers formed by intumescent flame retardants at high temperatures on asphalt flue gas. This solves the problem that it is currently difficult to evaluate the adsorption effect of porous carbonized layers formed by intumescent flame retardants on asphalt flue gas through experimental methods, and there is no evaluation method or index for the microscopic adsorption effect of porous carbonized layers formed by intumescent flame retardants on asphalt flue gas. This method more accurately characterizes the adsorption performance of porous carbonized layers on asphalt flue gas.

[0009] (2) Technical solution

[0010] Given the current difficulty in evaluating the microscopic adsorption effect of the porous carbonized layer formed by intumescent flame retardants on asphalt fumes at high temperatures through experimental methods, and the lack of evaluation methods and indicators for the adsorption effect of the porous carbonized layer formed by intumescent flame retardants on asphalt fumes, this invention provides a method for evaluating the adsorption performance of the porous carbonized layer on fumes during the thermal decomposition of asphalt. First, thermogravimetric analysis is performed on the intumescent flame retardant to determine the temperature range within which the intumescent flame retardant forms and maintains a stable porous carbonized layer. Then, the elemental composition, functional group structure, and chemical valence state of the porous carbonized layer are analyzed experimentally to construct a molecular model of the porous carbonized layer. Secondly, intumescent flame retardant asphalt was prepared. Pyrolysis-gas chromatography-mass spectrometry (GC-MS) experiments were conducted on asphalt and flame retardant asphalt. Common flue gas components from the pyrolysis process of both asphalt and flame retardant asphalt were selected to construct a molecular model of asphalt flue gas. Then, the molecular model of the porous carbonized layer and the molecular model of asphalt flue gas were combined to construct an interface model of asphalt flue gas / porous carbonized layer. Molecular dynamics simulations and potential energy calculations were performed on the interface model at different temperatures. Adsorption and desorption isotherms of the porous carbonized layer for asphalt flue gas were plotted at different temperatures. The interaction energy was used as an indicator to evaluate the microscopic adsorption effect of the porous carbonized layer on asphalt flue gas.

[0011] (3) Beneficial effects

[0012] For a long time, in studies on the inhibitory effect of intumescent flame retardants on asphalt fume release, researchers have mostly compared the detection data of asphalt and the fumes generated by the pyrolysis of asphalt retarded by intumescent flame retardants through experiments. They have not given detailed consideration to the adsorption effect of the porous carbonized layer formed by the combustion of the intumescent flame retardant on the asphalt fume, nor have they developed evaluation methods and indicators for the adsorption effect of the porous carbonized layer on asphalt fume. This has resulted in a simple development process for intumescent flame retardants but difficulty in optimizing their formulation. Furthermore, since the adsorption of asphalt fume by the porous carbonized layer occurs at high temperatures, conventional gas adsorption performance tests are often conducted at low temperatures, making it difficult to study the microscopic adsorption effect of the porous carbonized layer on asphalt fume through normal gas adsorption performance tests. This invention uses molecular dynamics simulation to simulate the adsorption process of asphalt fumes by the porous carbonized layer produced by the combustion of intumescent flame retardants. It comprehensively evaluates the microscopic adsorption effect of the porous carbonized layer on asphalt fumes at different temperatures using interaction energy, adsorption isotherm, and desorption isotherm as indicators. This provides a new evaluation method and indicators for studying the adsorption effect of porous carbonized layers on asphalt fumes, and provides a theoretical basis for the development of more efficient and environmentally friendly intumescent flame retardants. Detailed Implementation

[0013] This invention provides a method for evaluating the flue gas adsorption performance of a porous carbonized layer during the asphalt thermal decomposition process. The specific implementation steps are as follows:

[0014] (1) Thermogravimetric analysis was performed on the intumescent flame retardant to determine the temperature range in which the intumescent flame retardant can form and maintain a stable porous carbonized layer. Elemental analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were performed on the porous carbonized layer within the temperature range to analyze the elemental types, functional group structures and chemical valence states of the porous carbonized layer. A molecular model of the porous carbonized layer was constructed in molecular dynamics software.

[0015] (2) Intumescent flame retardant asphalt was prepared by melt blending method. The asphalt and flame retardant asphalt were subjected to thermal pyrolysis-gas chromatography-mass spectrometry. The total ion chromatogram obtained from the experiment was compared with the standard spectrum of NIST / EPA / NIH Mass Spectrometry Library 8 (NIST08) to select the volatile organic compounds common to asphalt and flame retardant asphalt and construct the molecular model of asphalt smoke.

[0016] (3) Perform geometric optimization and annealing on the porous carbonized layer molecular model and the asphalt fume molecular model respectively, and construct an interface model composed of the porous carbonized layer molecular model and the asphalt fume molecular model, so that the distance between the asphalt fume molecular model and the porous carbonized layer molecular model is greater than the van der Waals force cutoff radius set in the simulation.

[0017] (4) Perform molecular dynamics simulation on the interface model constructed in step (3) at different temperatures, draw the adsorption isotherms and desorption isotherms of the porous carbonized layer molecular model on the asphalt flue gas molecular model at different temperatures, and determine the type of adsorption isotherm and desorption isotherm according to the classification of adsorption isotherms summarized by the International Union of Pure and Applied Chemistry (IUPAC) to evaluate the microscopic adsorption effect of the porous carbonized layer on the asphalt flue gas.

[0018] (5) Perform potential energy calculations on the interface model system constructed in step (3) at different temperatures, calculate the interaction energy between the porous carbonized layer molecular model and the asphalt smoke molecular model. The magnitude of the interaction energy represents the strength of the adsorption effect of the porous carbonized layer on the asphalt smoke. Thus, the microscopic adsorption effect of the porous carbonized layer on the asphalt smoke is comprehensively evaluated by combining the interaction energy index.

Claims

1. A method for evaluating the flue gas adsorption performance of a porous carbonized layer during the asphalt thermal decomposition process, characterized in that... The specific steps of this method are as follows: (1) Thermogravimetric analysis was performed on the intumescent flame retardant to determine the temperature range in which the intumescent flame retardant can form and maintain a stable porous carbonized layer. Elemental analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were performed on the porous carbonized layer within the temperature range to analyze the elemental types, functional group structures and chemical valence states of the porous carbonized layer. A molecular model of the porous carbonized layer was constructed in molecular dynamics software. (2) Intumescent flame retardant asphalt was prepared by melt blending method. Thermal pyrolysis-gas chromatography-mass spectrometry was performed on asphalt and flame retardant asphalt. The total ion chromatogram obtained from the experiment was compared with the standard spectrum of NIST / EPA / NIH mass spectrometry library 8th edition. Volatile organic compounds common to asphalt and flame retardant asphalt were selected to construct asphalt smoke molecular model. (3) Perform geometric optimization and annealing on the porous carbonized layer molecular model and the asphalt fume molecular model respectively, and construct an interface model composed of the porous carbonized layer molecular model and the asphalt fume molecular model, so that the distance between the asphalt fume molecular model and the porous carbonized layer molecular model is greater than the van der Waals force cutoff radius set in the simulation. (4) Perform molecular dynamics simulation on the interface model constructed in step (3) at different temperatures, draw the adsorption isotherms and desorption isotherms of the porous carbonized layer molecular model on the asphalt flue gas molecular model at different temperatures, determine the type of adsorption isotherm and desorption isotherm according to the classification of adsorption isotherms summarized by the International Union of Pure and Applied Chemistry, and evaluate the micro-adsorption effect of the porous carbonized layer on the asphalt flue gas. (5) Perform potential energy calculations on the interface model system constructed in step (3) at different temperatures, calculate the interaction energy between the porous carbonized layer molecular model and the asphalt smoke molecular model. The magnitude of the interaction energy represents the strength of the adsorption effect of the porous carbonized layer on the asphalt smoke. Thus, the microscopic adsorption effect of the porous carbonized layer on the asphalt smoke is comprehensively evaluated by combining the interaction energy index.