Combustion characteristic analysis and reaction kinetics research method for plastic waste and application of combustion characteristic analysis and reaction kinetics research method

Abstract

The invention relates to the field of high polymer materials, and discloses a combustion characteristic analysis and reaction kinetics research method of plastic waste and application thereof, and the dynamic change process of thermal decomposition of two single-component plastics of PS and PVC at different heating rates is systematically researched by adopting a thermogravimetric and tubular furnace combined technology through TG / DTG and DSC curves. By judging the comprehensive combustion characteristic index of the sample and the activation energy and pre-exponential factors of each component in the decomposition stage of the plastic, the energy change of the plastic sample at different calcination temperatures is comprehensively researched, and a foundation is laid for optimizing the thermal conversion process of the plastic.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and particularly to a method for analyzing the combustion characteristics and reaction kinetics of plastic waste and its application research. Background Art

[0002] The global production and consumption of plastic products have brought huge economic value and convenience. However, the widespread use of plastic products has led to a large accumulation of non-degradable plastic waste. Therefore, the recycling of such a large amount of plastic waste has become a crucial global environmental challenge. Among various types of plastic waste, polystyrene (PS) and polyvinyl chloride (PVC) are considered to be the main components. It should be noted that the disposal of medical supplies such as masks, gloves, and protective clothing generated by medical facilities has significantly increased the amount of plastic waste. The average calorific value of municipal plastic waste is about 39.87 MJ / kg, which is approximately 80%-90% of the energy content of diesel (i.e., 45.30 MJ / kg). Therefore, waste plastics are a potential energy resource. How to utilize the heat generated during the combustion of plastics has become a promising issue.

[0003] Currently, researchers often study individual or a few representative components of plastic waste due to its wide production range, diverse types, and complex structures. However, there is a lack of comprehensive research on deeply exploring its complex reaction mechanism through kinetic and thermodynamic analyses and the actual degradation process of waste plastics (especially mixtures of different types of plastics). For researchers, it is crucial to deeply investigate the health and environmental risks involved in the waste generated in daily life. Summary of the Invention

[0004] The present invention provides a method for analyzing the combustion characteristics and reaction kinetics of plastic waste and its application to solve existing problems. This method examines the combustion behavior, kinetics, and process of a typical plastic waste model derived from real municipal solid waste. Comprehensive analysis of these diverse waste materials is carried out to study the dynamic behavior of the components polystyrene (PS) and polyvinyl chloride (PVC) during combustion and solidification. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) techniques are used to determine the thermal degradation and solidification characteristics of different plastics. In the kinetic analysis of the thermal degradation activation energy, three model-free methods, namely Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Starink (STA), are adopted. In addition, combined with the Coats-Redfern (CR) method and the Malek model, the reaction mechanism is elucidated through precise fitting. The solidification process of plastics involves complex chemical and thermal reactions. By comprehensively understanding these reactions and determining accurate kinetic models, this method further explores the activation energy and reaction path during the solidification process, revealing the dynamic evolution mechanism of plastic samples during combustion.

[0005] To solve the above technical problems, according to one aspect of the present invention, more specifically, it is a method for analyzing the combustion characteristics and reaction kinetics of plastic waste and its application technology. The combustion processes of two plastics, polystyrene (PS) and polyvinyl chloride (PVC), are analyzed, and the comprehensive combustion characteristic indexes at each stage of the combustion process are judged; the activation energies of each component are determined by three model-free methods, and the mechanism functions at each stage of plastic combustion are determined by the improved CR method; the solidification kinetics of PS and PVC are studied through DSC curves; the morphology of the residual carbon after plastic combustion at different temperatures is observed by scanning electron microscopy (SEM).

[0006] Composition of the base polymer: polystyrene (PS), polyvinyl chloride (PVC);

[0007] Research method for the combustion process: thermogravimetric analyzer (TG-DSC);

[0008] Research methods for combustion kinetics: KAS (Kissinger-Akahira-Sunose), FWO (Flynn-Wall-Ozawa), STA (Starink), CR (Coats-Redfern) combined with Malek, Sestak-Berggren non-isothermal solidification kinetics;

[0009] Furthermore, the basic polymer raw materials, polystyrene (PS) and polyvinyl chloride (PVC), are sourced from laboratory petri dishes (PS) and disposable medical masks (PVC). Before the experiment, the plastic samples were crushed and dried in an oven at 105 °C for 24 hours for later use.

[0010] Furthermore, the ignition index (T i ), burnout index (T f ), and maximum combustion rate (dw / dt) max of the samples were obtained from the thermogravimetric curves, and then the comprehensive combustion characteristic indices (C, S) of the samples were calculated to evaluate the combustion performance of the samples at different heating rates. Among them,

[0011]

[0012]

[0013] D i 、D f 、C, and S can help us comprehensively understand the behavior of materials during combustion and predict their safety, controllability, and environmental impact in extreme environments such as fires.

[0014] Furthermore, in the study of thermochemical reaction kinetics, the conversion rate: α = (m0 - m t ) / (m0 - m f ), is used to quantify the progress of chemical reactions. The reaction rate constant generally follows the Arrhenius equation: K(T) = Aexp(-E / RT), which determines the reaction rate and is affected by temperature. Here, m0 represents the initial mass of the sample, m t represents the mass of the sample at time t, and m f represents the final mass of the sample. The symbols E, A, R, and T represent the apparent activation energy (kJ / mol), pre-exponential factor, universal gas constant (8.314 J / mol / K), and absolute temperature (K), respectively.

[0015] Furthermore, in non-isothermal kinetics studies, a constant heating rate is usually adopted, i.e., the heating rate (β = dT / dt) is kept constant. In this way, the kinetic equation can be transformed as follows: dα / dt = (A / β)exp(-E / RT)f(α). Here, f(α) is usually independent of temperature and is a function of the conversion degree (in the range of 0 to 1.0).

[0016] Furthermore, the activation energy was obtained by three model-free methods, KAS, FWO, and STA. KAS: ln(β / T 2) = ln[AR / EG(α)] - E / RT, FWO: ln(β) = ln[0.0048AE / RG(α)] - 1.052E / RT, STA: ln(β / T 1.8 ) = ln[AR / EG(α)] - 1.0037E / RT. The slope of the straight line is the apparent activation energy at this conversion rate. The average value at each conversion rate is defined as the global activation energy E1.

[0017] Furthermore, it is assumed that the kinetic mechanism occurs at the interface between reactants and products in the solid-phase reaction, and the mechanism is determined separately for the key steps controlling the reaction rate. For example, the nucleation mechanism describes the formation of a new product phase at specific reaction sites (nucleation sites) within the polymer lattice. The corresponding integral expression can be expressed as: f(α) and G(α) are the differential form and integral form of the solid pyrolysis mechanism equation respectively. When α = 0.5, y(α) = (T / T0.5)×(dα / dt) / (dα / dt) 0.5 = f(α)×G(α) / f(0.5)×g (0.5) .

[0018] Furthermore, the CR combined with the Malek method is used to judge the mechanism function of each stage of sample combustion. Among them, the CR equation can be written as: Ln[G(α) / T 2 = -E / RT + Ln[AR / βE(1 - 2RT / E)]; the degradation temperature range and activation energy of plastics can be approximated as a constant. Substitute the reaction mechanism function G(α) obtained by the Malek method into the CR equation. Further, by plotting the relationship between Ln[G(α) / T 2 and 1 / T, the activation energy can be obtained. The average activation energy at each conversion rate is defined as E2. The CR equation can be interpreted as a linear equation.

[0019] Table 1. Reaction mechanism functions of combustion kinetics

[0020]

[0021]

[0022] Furthermore, the assumption that the solid-phase reaction rate is proportional to the heat flux has been widely accepted and is expressed by the following formula: The total enthalpy (h) of the curing reaction was calculated by integrating the heat flow curve obtained through non-isothermal differential scanning calorimetry (DSC) tests. The heat flow represents the enthalpy value up to time t during the curing process.

[0023] Further, the Sestak-Berggren non-isothermal curing kinetics and the Kamal-Sourour isothermal curing kinetics are used to judge the curing kinetics of the PS and PVC plastics before reaching the ignition temperature. Among them, the Sestak-Berggren non-isothermal curing kinetics equation can be written as:

[0024] dα / dt = Ae K(T) α m (1 - α) n , where m and n represent the reaction orders.

[0025] A method for analyzing the combustion characteristics and reaction kinetics of plastic waste and its application specifically include:

[0026] Step 1: Before the experiment, the PS and PVC plastic particles are dried in an air oven at 105°C for 6 hours. Subsequently, vertical planetary ball milling is performed at a speed of 500 revolutions per minute for 24 hours. After milling, these mixtures are dried in an air oven at 105°C for another 24 hours.

[0027] Step 2: TG-DSC experiments are carried out using a thermogravimetric instrument. Each thermogravimetric analysis uses approximately 10 mg of powder sample loaded into an alumina crucible for combustion analysis. The experiment is carried out in a high-purity air atmosphere with a constant purge gas flow rate of 50 mL / min. In addition, a nitrogen purge gas with a flow rate of 20 mL / min is also used as a protective gas. Before the experiment, the machine is preheated for two hours to reach a stable state.

[0028] Step 3: Subsequently, after the system reaches equilibrium, a 10-minute nitrogen purge gas is introduced. The experimental temperature is gradually increased from room temperature to the specified temperature at heating rates of β1 K / min, β2 K / min, β3 K / min, and β4 K / min, respectively.

[0029] Step 4: For the non-isothermal curing kinetics study, four fixed heating rates of β1 K / min, β2 K / min, β3 K / min, and β4 K / min are adopted. The curing kinetic parameters of the sample before ignition are obtained by combining the heat flow curves at three heating rates with the curing kinetic model.

[0030] Step 5: Each group of experiments is repeated more than three times to reduce the influence of external factors and ensure the reproducibility of the experimental results.

[0031] For the method for analyzing the combustion characteristics and reaction kinetics of plastic waste and its application provided by the present invention, compared with the prior art, the effects achieved by this method are:

[0032] 1. The combustion processes of polystyrene (PS) and polyvinyl chloride (PVC) were analyzed, and the comprehensive combustion characteristic indexes at each stage of the combustion process were judged.

[0033] 2. The activation energies of each component were determined by three model-free methods, and the mechanism functions at each stage of plastic combustion were determined by the improved CR method.

[0034] 3. The curing kinetics of PS and PVC were studied by DSC curves.

[0035] 4. The theoretical basis for optimizing the thermal conversion process of plastic materials in the present invention can improve the combustion efficiency of plastic waste, reduce environmental pollution, and is particularly suitable for the incineration treatment and energy recovery of plastic waste.

[0036] 5. The combustion characteristic analysis method of the present invention can more accurately evaluate the combustion behavior of plastic waste under different conditions, optimize the combustion process, and reduce energy waste and pollutant emissions.

[0037] 6. By applying the curing reaction kinetics model, the present invention can improve the thermal conversion efficiency of plastic waste and further promote the industrial application of the plastic incineration process.

[0038] 7. The present invention provides a combustion characteristic analysis method of plastic waste based on thermogravimetric analysis, which can significantly improve the incineration efficiency of plastic waste and provide theoretical support for related industries.

[0039] Figure 1 This is the structural schematic diagram of the present invention.

[0040] Figure 2 This is the TG / DTG curve of PS of the present invention under non-isothermal conditions.

[0041] Figure 3 This is the TG / DTG curve of PVC of the present invention under non-isothermal conditions.

[0042] Figure 4 This is the graph of solving the activation energy of PS by three model-free fittings of the present invention.

[0043] Figure 5 This is the graph of solving the activation energy of PVC by three model-free fittings of the present invention.

[0044] Figure 6 This is the graph of solving the mechanism functions of PS and PVC by fitting the CR combined with the Melek model of the present invention.

[0045] Figure 7 This is the graph of solving the curing kinetic parameters of PS by fitting the SB isothermal curing kinetics model of the present invention.

[0046] Figure 8 This is the curve graph for solving the curing kinetic parameters of PVC by fitting with the SB isothermal curing kinetic model in the present invention. Specific embodiments

[0047] To make the technical solution of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments.

[0048] Example 1

[0049] To make the technical solution of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments.

[0050] As Figure 1-8 shown, as a preferred embodiment of the present invention, the PS and PVC plastic samples used in this study are commercial polystyrene and polyvinyl chloride, and the mass of each of the two samples at each heating rate is 10 mg. The thermogravimetric analyzer (TGA) was tested at four different heating rates (β1 K / min, β2 K / min, β3 K / min, and β4 K / min). To eliminate the influence of environmental factors, each group of experiments was repeated three times and the average value was taken to ensure that the curves obtained from the experiments are true and reliable.

[0051] The PS and PVC plastic samples were subjected to thermogravimetric analysis at different heating rates, and the mass changes during the combustion process were recorded. The thermogravimetric curves were used as the main data input, and the relationship between the mass loss and temperature change at each heating rate was plotted respectively. As Figure 2-3 shown.

[0052] The combustion characteristic indices at each heating rate were obtained from the thermogravimetric curves, comprehensively considering the maximum mass loss rate, the combustion start temperature, and the maximum mass loss temperature. These characteristic quantities were used to further analyze the combustion behavior of PS and PVC plastics and quantify their combustion processes.

[0053] Table 2. Judgment of the comprehensive combustion characteristic indices of PS and PVC plastics under non-isothermal conditions

[0054]

[0055]

[0056] The activation energy of PS and PVC plastics was solved using the model-free method. At different conversion rates α (0.1, 0.2, 0.3... 0.9) under non-isothermal conditions, according to the thermogravimetric curves at different heating rates, the activation energy at different heating rates was obtained using three model-free methods: KAS, FWO, and STA. For the KAS equation, Ln[β(1, 2, 3, 4) / T 2Plot the relationship between [] and 1 / T. According to the fitting straight-line graph, find the slopes ai (i = 1, 2, 3...9) of the nine groups of fitting straight lines. The slope of the straight line is -E / R. Take the average value of the activation energies of the nine groups as the global activation energy obtained by KAS; for the FWO equation, plot the relationship between Ln[β(1, 2, 3, 4)] and 1.052 / T. According to the fitting straight-line graph, find the slopes bi (i = 1, 2, 3...9) of the nine groups of fitting straight lines. The slope of the straight line is -E / R. Take the average value of the activation energies of the nine groups as the global activation energy obtained by FWO; for the STA equation, plot the relationship between Ln[β(1, 2, 3, 4) / T 1.8 and 1.0037 / T. According to the fitting straight-line graph, find the slopes ci (i = 1, 2, 3...9) of the nine groups of fitting straight lines. The slope of the straight line is -E / R. Take the average value of the activation energies of the nine groups as the global activation energy obtained by STA; Take the average value of the activation energies obtained by the three model-free methods. The results show that the average activation energies at the four heating rates are X kJ / mol and Y kJ / mol. As Figure 4-5 shown.

[0057] According to the CR model, further deduce the pyrolysis reaction mechanism functions of PS and PVC plastics. At different conversion rates α (0.1, 0.2, 0.3……0.9), fit the thermogravimetric data with the Malek model to obtain the mechanism function G(α). This mechanism function characterizes the relationship between mass loss and reaction progress during combustion. Substitute the mechanism function into the CR equation, and plot the relationship between Ln[G(α) / T 2 and 1 / T. The slope of the straight line is -E / R. The activation energy corresponding to each conversion rate can be obtained through the slope of each curve. Take the average value of the activation energies at each conversion rate to obtain the global activation energies A kJ / mol and B kJ / mol. As Figure 6 shown.

[0058] Combined with the curing kinetics model, consider the influence of factors such as temperature and time on the curing process of PS and PVC plastics. At different conversion rates α (0.1, 0.2, 0.3……0.9), through the relationship between dα / dt and dα of plastic waste under non-isothermal conditions DSC curves at different heating rates, use the least squares method to fit the experimental data to obtain the kinetic parameters of the curing reaction, including the reaction order, pre-exponential factor, and activation energy, etc. The analysis shows that PS and PVC plastics have specific reaction rate constants and activation energies during the curing process, which characterize their curing performance. As Figure 7-8 shown.

[0059] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention shall be subject to the appended claims.

Claims

1. A method for analyzing the combustion characteristics and studying the reaction kinetics of plastic waste, characterized in that It includes the following steps: S1. Use thermogravimetry-differential scanning calorimetry (TG-DSC) technology to conduct thermal analysis on polystyrene (PS) and polyvinyl chloride (PVC) plastic samples, and obtain TG / DTG and DSC curves at different heating rates; S2. Calculate the ignition index (Ti), burnout index (Tf), and maximum combustion rate (dw / dt)max of the samples through the thermogravimetric curve, and calculate the comprehensive combustion characteristic indices (C, S) based on the formulas C = (dw / dt)max / T2 and S = (dw / dt)max×(dw / dt)mean / (T2×Tf); S3. Use three model-free methods, namely KAS, FWO, and STA, to calculate the activation energy of the plastic pyrolysis process, and determine the pyrolysis mechanism function by combining the improved Coats-Redfern (CR) method with the Malek model; S4. Analyze the curing kinetics of the plastic through the DSC curve, and use the Sestak-Berggren non-isothermal curing kinetics model to calculate the curing reaction parameters.

2. The method for analyzing the combustion characteristics and reaction kinetics of plastic waste according to claim 1, wherein: The plastic samples are selected from laboratory bacterial culture dishes (PS) and disposable medical masks (PVC), and are broken and dried at 105 °C for 24 hours before the experiment.

3. The method for analyzing the combustion characteristics and reaction kinetics of plastic waste according to claim 1, characterized in that: The thermogravimetric analysis is carried out in an air atmosphere, the gas flow rate is 50 mL / min, and 20 mL / min of nitrogen is used as the protective gas, and the heating rates are set to β1, β2, β3, and β4 K / min.

4. The method for analyzing the combustion characteristics and studying the reaction kinetics of plastic waste according to claim 1, characterized in that: The activation energy calculation methods include: KAS method: ln(β / T 2 ) = ln[AR / EG(α)] - E / RT FWO method: ln(β) = ln[0.0048AE / RG(α)] - 1.052E / RT STA method: ln(β / T 1.8 ) = ln[AR / EG(α)] - 1.0037E / RT Calculate the activation energy through the slope of linear fitting, and take the average value of the three methods as the final activation energy.

5. The method for analyzing the combustion characteristics and reaction kinetics of plastic waste according to claim 1, wherein: The method for determining the pyrolysis mechanism function is: determine the mechanism function G(α) through the Malek model, and substitute it into the CR equation Ln[G(α) / T2] = -E / RT + ln[AR / βE(1 - 2RT / E)] for linear fitting to calculate the activation energy.

6. The method for analyzing the combustion characteristics and studying the reaction kinetics of plastic waste according to claim 1, characterized in that: The curing kinetics analysis uses the Sestak-Berggren equation: dα / dt = Ae K(T) α m (1 - α) n , and the reaction orders m, n, and activation energy are determined by fitting the DSC curve data.

7. The method for analyzing the combustion characteristics and studying the reaction kinetics of plastic waste according to claim 1, wherein: The method also includes observing the morphological characteristics of the residual carbon after plastic combustion at different temperatures through a scanning electron microscope (SEM).

8. Application of the method for analyzing combustion characteristics and studying reaction kinetics of plastic waste as described in any one of claims 1-7 in optimizing the thermal conversion process of plastic waste, characterized in that, It is used to improve the combustion efficiency of plastic waste and reduce environmental pollution.

9. Application of the method for analyzing combustion characteristics and studying reaction kinetics of plastic waste as described in any one of claims 1-7 in optimizing the thermal conversion process of plastic waste, characterized in that, It is used for the heat treatment process optimization of disposable medical masks and protective supplies.

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