A method for studying the reaction kinetics of functional groups in coal supercritical water gasification

Abstract

The present application relates to a kind of functional group reaction kinetics research methods in coal supercritical water gasification, comprising: configuration water coal slurry and carry out coal supercritical water gasification experiment, obtain the infrared spectrogram of solid product at different temperatures;Extract the area of each functional group, and the evolution of each functional group is divided into several reaction stages;Set up multiple reaction temperature points and multiple reaction residence time, carry out systematization gasification experiment;The coal sample before and after reaction is carried out fourier infrared spectrum test, extracts the integral area of characteristic absorption peak and calculates conversion rate;Using candidate kinetic model, the conversion rate is fitted to obtain reaction rate constant, according to the fitting degree of reaction rate constant and reaction temperature and empirical method determine target kinetic model, solve the core kinetic parameters of each functional group, and the kinetic analysis of each functional group is compared.The method constructs the hierarchical kinetics research system of full-temperature zone adaptation, realizes microcosmic fine kinetics analysis.

Description

Technical Field

[0001] This invention belongs to the field of chemical reaction kinetics technology, specifically relating to a method for studying the reaction kinetics of functional groups in supercritical water gasification of coal. Background Technology

[0002] Coal is a pillar energy source in my country's energy structure, and achieving low-carbon, clean, and efficient utilization of coal is the core key to my country's energy transformation and the realization of its dual-carbon goals. Supercritical water gasification hydrogen production technology, leveraging the unique physicochemical properties of supercritical water—low viscosity, high diffusivity, strong solubility, and strong reactivity—can achieve tar-free, pollution-free, and low-emission hydrogen-rich conversion of coal under medium-temperature and high-pressure conditions. Compared to traditional high-temperature coal gasification and pyrolysis technologies, it has significant advantages such as milder reaction conditions, higher product purity, easier CO2 enrichment and capture, and environmental friendliness, making it a promising new clean coal conversion technology for industrial application.

[0003] The essence of supercritical water gasification of coal is a microscopic chemical reaction process involving the cracking, ring-opening, and reconstruction of various functional groups within the coal. The reaction rate, activation energy, and reaction order of these functional groups directly determine the overall gasification efficiency and reaction characteristics of the coal. Reaction kinetics is the core theoretical foundation for revealing the microscopic mechanism of gasification, optimizing process parameters, and guiding reactor design and industrial scale-up. Therefore, accurately defining the supercritical water gasification reaction kinetic model for each core functional group of coal has significant theoretical and engineering value for the clean conversion and utilization of coal and the practical engineering implementation of related technologies.

[0004] Currently, kinetic studies on supercritical water gasification of coal both domestically and internationally generally employ the macroscopic lumped parameter method. This method treats coal as a single, holistic reaction system, ignoring the differentiated reaction characteristics of its various microstructures, such as aliphatic, aromatic, and oxygen-containing functional groups. It obtains a single kinetic model and reaction parameters by measuring macroscopic parameters such as the amount of gaseous products generated and the weight loss of solid coal samples. However, traditional lumped parameter models oversimplify the coal reaction process, completely ignoring the differences in structural stability and cracking patterns of different functional groups within the coal. This fails to elucidate the reaction essence of supercritical water gasification of coal at the microscopic molecular level, resulting in an insufficiently clear mechanistic explanation.

[0005] Meanwhile, existing kinetic studies on coal functional groups are limited to low-temperature inert pyrolysis scenarios below 500℃, relying on thermogravimetric analysis (TGA) data for macroscopic fitting. These studies fail to adapt to the unique reaction environment of supercritical water, do not cover the entire supercritical water gasification temperature range of 400-800℃, and cannot distinguish the kinetic differences between low-temperature pyrolysis, medium-temperature main gasification, and high-temperature side reaction stages. Furthermore, they lack refined kinetic studies at different temperature ranges and for different types of functional groups, failing to accurately quantify the reaction progress of functional groups at different temperatures and residence times. This results in low prediction accuracy for coal gasification behavior, making it difficult to meet the needs of process optimization and precise reactor design. Additionally, current technologies cannot quantify the activation and synergistic effect of supercritical water on coal functional group pyrolysis, nor can they accurately identify the rate-controlling steps of functional groups at each gasification stage, hindering targeted guidance for supercritical water gasification process optimization.

[0006] Therefore, existing research on the kinetics of supercritical water gasification in coal suffers from several drawbacks, including reliance on macroscopic lumped parameter models, neglect of microscopic reaction differences among functional groups in coal, weak adaptability to operating conditions across the entire temperature range, fuzzy mechanistic analysis, low prediction accuracy, and an inability to clearly define the reaction rate control steps and the activation mechanism of supercritical water. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies, this invention provides a method for studying the reaction kinetics of functional groups in supercritical coal water gasification. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a method for studying the reaction kinetics of functional groups in supercritical water gasification of coal, including: Step 1: Select the target coal type, grind and sieve the target coal type to prepare coal-water slurry, carry out supercritical water gasification experiment of coal, and obtain infrared spectra of solid products at different temperatures after the reaction is completed. Step 2: Extract the area of ​​each functional group based on the infrared spectrum, and divide the evolution of each functional group into several reaction stages according to the change of the area of ​​each functional group with temperature. Step 3: Set multiple reaction temperature points according to the reaction stages of each functional group, and set multiple reaction residence times for each reaction temperature point. Conduct a full-coverage systematic gasification experiment to obtain coal samples after reaction under various working conditions. Step 4: Perform Fourier transform infrared spectroscopy on the coal samples before and after the reaction under each working condition, extract the integral area of ​​the characteristic absorption peaks of each functional group, and calculate the conversion rate of each functional group at each reaction stage under each working condition. Step 5: The conversion rate of each functional group is fitted using a candidate kinetic model to obtain the reaction rate constant. The target kinetic model of each functional group is determined based on the fit between the reaction rate constant and the reaction temperature and empirical methods. The core kinetic parameters of each functional group at each reaction stage are solved based on the fitted line, and the kinetics of each functional group are compared and analyzed.

[0008] In one embodiment of the present invention, the conditions for carrying out the supercritical water gasification experiment of coal in step 1 include: a temperature range of 400-800℃, a temperature interval of 20℃, and a reaction time of 10 min.

[0009] In one embodiment of the present invention, step 2 includes: Step 2.1: Use fitting software to perform peak fitting processing on the infrared spectrum to obtain each characteristic absorption peak of the fitted infrared spectrum and its corresponding functional group. At the same time, obtain the integral area of ​​each functional group and calculate the normalized area based on the integral area. The normalized area is the ratio of the absorption peak area of ​​each functional group at different temperatures to the peak area of ​​the corresponding functional group in the raw coal. Step 2.2: Analyze the law of the integral area size changing with temperature, and perform first derivative analysis on the normalized area-temperature curve of each functional group. Use the local extreme point of the derivative curve as the boundary temperature of the reaction stage, and divide the evolution of each functional group into several reaction stages.

[0010] In one embodiment of the present invention, the functional groups include aliphatic CH, aromatic C=C, carbonyl C=O, ether CO, and hydroxyl -OH; The characteristic absorption peak of the hydroxyl group (-OH) is located in the range of 3100-3750 cm⁻¹. -1 The characteristic absorption peak of the aliphatic CH is located at 2750-3000 cm⁻¹. -1 The characteristic absorption peak of the carbonyl C=O group is located in the 1650-1800 cm⁻¹ range. -1 The characteristic absorption peak of the aromatic C=C group is located at 1490-1600 cm⁻¹. -1 The characteristic absorption peak of the CO bond in the ether bond is located in the range of 1000-1315 cm⁻¹. -1 ; The aliphatic CH includes CH in aliphatic -CH3, CH in aliphatic -CH2, and CH in aliphatic -CH, corresponding to 2851 cm⁻¹. -1 2867 cm -1 2895 cm -1 2920 cm -1 and 2950 cm -1 Five sub-peaks; The aromatic C=C includes C=C in polycyclic aromatic compounds, C=C in bicyclic aromatic compounds, and C=C in monocyclic aromatic compounds, corresponding to 1490 cm⁻¹. -1 1570 cm -1 and 1600 cm -1 Three sub-peaks; The carbonyl C=O group includes C=O in quinone groups, C=O in ketone groups, C=O in carboxyl groups, and C=O in ester groups, corresponding to 1655 cm⁻¹. -1 1678 cm -1 1705 cm -1 and 1730 cm -1 Four sub-peaks; The ether bond CO corresponds to 1079 cm⁻¹ -1 1144 cm -1 1166 cm -1 1214 cm -1 and 1272 cm -1 Five sub-peaks; The hydroxyl group -OH corresponds to 3280 cm. -1 3400 cm -1 and 3530 cm -1 Three sub-peaks.

[0011] In one embodiment of the present invention, for red willow forest bituminous coal, the aliphatic CH group is divided into three reaction stages: 400-460℃, 460-600℃, and 600-800℃; the aromatic C=C group is divided into three reaction stages: 400-500℃, 500-680℃, and 680-800℃; the carbonyl C=O group is divided into two reaction stages: 400-540℃ and 540-800℃; the ether bond CO group is divided into three reaction stages: 400-500℃, 500-620℃, and 620-800℃; and the hydroxyl group -OH group is divided into three reaction stages: 400-440℃, 440-620℃, and 620-800℃.

[0012] In one embodiment of the present invention, in step 3, for Hongliulin bituminous coal, the reaction temperature points include 400℃, 420℃, 460℃, 560℃, 600℃, 660℃, 700℃, 740℃ and 800℃; The reaction residence times include 30 s, 60 s, 120 s, 240 s, 480 s and 900 s.

[0013] In one embodiment of the present invention, in step 4, the formula for calculating the conversion rate is:

[0014] in, This represents the integral area of ​​the functional groups in raw coal. Let be the integral area of ​​the functional group at time t.

[0015] In one embodiment of the present invention, step 5 includes: Step 5.1: Establish a candidate kinetic model library; the candidate kinetic model library includes chemical reaction models, two-phase interface reaction models, and diffusion reaction models; the chemical reaction models include first-order reaction models, second-order reaction models, third-order reaction models, and n-order reaction models; the two-phase interface reaction models include one-dimensional reaction models, two-dimensional reaction models, and three-dimensional reaction models; the diffusion reaction models include one-dimensional diffusion models, two-dimensional diffusion models, and three-dimensional diffusion models. Step 5.2: For each reaction temperature point, substitute the conversion rate at each reaction residence time into the integral form of each candidate kinetic model. In the middle, draw the integral form residence time of the reaction The curve was obtained and linearly fitted, and the slope of the fitted line was taken as the reaction rate constant at the stated reaction temperature. ; Step 5.3, according to the logarithmic form of the Arrhenius formula ,draw For 1 / R T The curve was linearly fitted, and the slope and intercept of the fitted line were -E and -E, respectively. The core kinetic parameters were calculated as follows: activation energy E and pre-exponential factor A. Step 5.4: Using the degree of fit of the fitted straight line, the model closest to 1 is taken as the target dynamic model for each functional group; when the difference in the degree of fit is less than a preset value, the target dynamic model is determined by an empirical method. Step 5.5: Based on the core kinetic parameters, conduct a comparative analysis of the kinetics of each functional group to clarify the rate control steps for each stage of supercritical water vaporization across the entire temperature range.

[0016] In one embodiment of the present invention, for red willow forest bituminous coal, Aliphatic CH both conform to the third-order reaction model in the first reaction stage at 400-460℃ and the second reaction stage at 460-600℃. Aromatic C=C reactions conform to a second-order reaction model in the first reaction stage at 400-500℃ and the second reaction stage at 500-680℃, and conform to a fourth-order reaction model in the third reaction stage at 680-800℃. The carbonyl C=O group follows a third-order reaction model in the first stage of the reaction at 400-540℃. The first stage of the reaction of CO with ether bond at 400-500℃ conforms to the fourth-order reaction model. The second reaction stage of the hydroxyl group -OH at 440-620℃ conforms to a fourth-order reaction model. The activation energies of the five functional groups range from 38.45 to 134.80 kJ·mol⁻¹ -1 The activation energies of the aliphatic CH and the aromatic C=C increase with increasing temperature in both the first and second reaction stages, while the activation energy of the aromatic C=C decreases slightly with increasing temperature in the second and third reaction stages. Simultaneously, the reactions of the five functional groups in each stage are affected by concentration.

[0017] In one embodiment of the present invention, it further includes: Step 6: The experimental values ​​of functional groups from supercritical water vaporization experiments at different temperatures are compared with the predicted values ​​of the target kinetic model to verify the reliability of the target kinetic model.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention abandons the traditional macroscopic lumped parameter research mode and takes the functional groups of coal as independent research units. By extracting the integral area of ​​characteristic absorption peaks, calculating conversion rate and reaction rate constant, and fitting the reaction rate constant with the reaction temperature, it realizes the kinetic study of functional groups in supercritical water gasification of coal. It systematically elucidates the microscopic reaction mechanism of supercritical water gasification of coal from the molecular structure level, and solves the technical problems of vague mechanism explanation and inability to distinguish the reaction differences of microstructure of different functional groups in the existing technology. 2. This invention addresses the kinetic differences in the low-temperature pyrolysis, medium-temperature main gasification, and high-temperature side reaction stages by constructing a graded kinetic research system adaptable to the entire temperature range. Based on the change of the integral area of ​​each functional group with temperature, the evolution of each functional group is divided into several reaction stages. Multiple reaction temperature points and multiple reaction residence times are set for different reaction stages to carry out a comprehensive and systematic gasification experiment. This overcomes the shortcomings of traditional single models that cannot adapt to complex reactions in a wide temperature range. It can accurately cover the entire working condition of supercritical water gasification at 400-800℃, greatly improving the adaptability of working conditions and solving the technical problem of weak adaptability of existing technologies across the entire temperature range. 3. This invention uses a candidate kinetic model to fit the conversion rate of each functional group to obtain the reaction rate constant, and determines the target kinetic model based on the fit between the reaction rate constant and the reaction temperature and empirical methods. Then, it solves the core kinetic parameters of each functional group at each reaction stage. The research is highly accurate and can accurately predict the reaction progress of each functional group and the overall gasification characteristics of coal at different temperatures and residence times. It has strong reliability and practicality. 4. By systematically comparing and analyzing the core kinetic parameters of each functional group in each reaction stage, this invention can clarify the rate control steps of each stage in the full temperature range of supercritical water gasification, accurately quantify the energy reduction and activation mechanism of supercritical water on the cracking of coal functional groups, and reveal the core principle of high efficiency and energy saving of supercritical water gasification from a kinetic perspective. 5. The refined kinetic parameter system and reaction law formed by this invention can be directly used for numerical simulation of supercritical water gasification, optimization of process parameters, reactor structure design and prediction of operating conditions, providing core theoretical support for basic research, pilot-scale amplification and industrialization of coal supercritical water gasification technology, and has high industrial application value. Attached Figure Description

[0019] Figure 1 A schematic flowchart illustrating the method for studying the reaction kinetics of functional groups in supercritical water gasification of coal provided in this embodiment of the invention; Figure 2 FTIR spectra of the residues after gasification of Hongliulin bituminous coal in supercritical water at different temperatures; Figure 3 The raw coal from Hongliulin is 2800-3000 cm³. -1 Schematic diagram of the fitted curve; Figures 4a-4b The integral area and normalized area of ​​aliphatic functional groups in Hongliulin bituminous coal vary with temperature. Figure 5 The FTIR spectra of the solid products of Hongliulin bituminous coal at 400℃ and 420℃ under different reaction times are shown. Figure 6 It is a comparison between the fitted curves and the actual integral areas of the aliphatic CH reaction model in the first and second stages. Figure 7 The reaction models and activation energies of the five functional groups at each stage are provided; Figure 8 This is a comparison of the predicted and experimental values ​​of the reaction kinetics models of various functional groups in Hongliulin bituminous coal gasified by supercritical water at different temperatures. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0021] Example 1 This invention aims to address the technical problems of existing research on the kinetics of supercritical water gasification in coal, which relies on macroscopic lumped parameter models, neglects the differences in microscopic reactions of functional groups in coal, has weak adaptability to operating conditions across the entire temperature range, suffers from fuzzy mechanistic analysis, low prediction accuracy, and cannot clearly define the reaction rate control steps and the activation mechanism of supercritical water. By constructing a refined kinetic research system segmented by temperature range and functional group, this invention accurately obtains the kinetic parameters of supercritical water gasification for the main functional groups in coal, reveals the reaction evolution laws of each functional group, clarifies the rate control steps of the gasification process, and quantifies the energy reduction and efficiency enhancement mechanism of supercritical water. This provides precise theoretical support for the mechanistic analysis, process parameter optimization, reactor design, and industrial scale-up of supercritical water gasification in coal.

[0022] Please see Figure 1 , Figure 1 This is a flowchart illustrating the method for studying the reaction kinetics of functional groups in supercritical water gasification of coal provided in this invention. The method selects five core functional groups—aliphatic CH, aromatic C=C, carbonyl C=O, ether CO, and hydroxyl -OH—as independent research units. It utilizes Fourier transform infrared spectroscopy to detect the relative content of functional groups and combines gradient experiments with kinetic fitting analysis to achieve refined kinetic research. Specifically, it includes: Step 1: Select the target coal type, grind and sieve the target coal type to prepare coal-water slurry, carry out supercritical water gasification experiment of coal, and obtain infrared spectra of solid products at different temperatures after the reaction is completed.

[0023] Specifically, the target coal type can be selected from Hongliulin bituminous coal, Ningxia anthracite, or Zhundong coal. The following steps in this embodiment all take Hongliulin bituminous coal as the research object.

[0024] Specifically, Hongliulin bituminous coal was ground and sieved to obtain coal powder with a particle size of less than 100 μm. The coal powder and deionized water were then mixed to prepare a coal-water slurry with a mass concentration of 5 wt%. A quartz tube reactor was used to conduct supercritical water gasification experiments on coal over a wide temperature range of 400-800℃. The temperature inside the supercritical water gasification reactor was maintained above 375℃ and the pressure above 22.06 MPa to ensure that the entire process was in a supercritical reaction state. The reaction time was set to 10 min. After the reaction, Fourier transform infrared spectroscopy (FTIR) was used to characterize the solid products, obtaining infrared spectra of the solid products at different temperatures. Please refer to [link to relevant documentation]. Figure 2 , Figure 2This image shows the FTIR spectra of the residue from supercritical water gasification of Hongliulin bituminous coal at different temperatures. The spectra visually reflect the changes in functional groups with temperature. Specifically, the absorption peak intensity of -OH changes very little at lower temperatures, then decreases with increasing temperature. The absorption peak intensity of aliphatic CH groups gradually decreases with increasing temperature. The absorption peak intensity of C=O is difficult to observe from the image due to overlap with the absorption peak of aromatic C=C and its relatively small peak height. The peak intensity of aromatic C=C shows little change in the lower temperature range, but decreases with increasing temperature in the medium to high temperature range. The peak intensity of CO shows a trend of first decreasing and then increasing with increasing temperature.

[0025] Step 2: Extract the area of ​​each functional group based on the infrared spectrum, and divide the evolution of each functional group into several reaction stages according to the change of the area of ​​each functional group with temperature.

[0026] Step 2 includes: Step 2.1: Use fitting software to perform peak fitting on the infrared spectrum to obtain the characteristic absorption peaks and their corresponding functional groups of the fitted infrared spectrum.

[0027] Specifically, without integrating the FTIR spectrum, the evolution of functional groups can be qualitatively analyzed. However, when performing quantitative analysis of functional groups in solid products, due to the overlap between peaks, it is necessary to deconvolve the FTIR spectrum, that is, to perform peak fitting on the spectrum to obtain the actual peak area of ​​each functional group, i.e., the integrated area.

[0028] Specifically, the segmented regions of the FTIR spectrum include: 3000-3750 cm⁻¹. -1 (Stretching vibration of hydroxyl groups), 2800-3000 cm -1 (Stretching vibrations of aliphatic functional groups, including CH in methyl, methylene, and methine groups), 1500-1850 cm⁻¹ -1 (Stretching vibrations of C=O in the carboxyl group and C=C in the aromatic ring) and 930-1500 cm -1 (CO stretching vibration and bending vibrations of aliphatic functional groups methyl and methine CH). The fitting software used was Peakfit v4.12, with a maximum of 500 iterations and R0. 2 >0.99, the fitting method is Gauss+Lorentz Area, with variable width and shape. Baseline correction is required for each fitting region before fitting. The number and position of sub-peaks for each segment during fitting are generally shown in Table 1. Due to the complexity of coal chemical structure, the number of sub-peaks for each functional group in the infrared spectrum can be increased or decreased according to actual conditions. Aliphatic absorption peaks (2800-3000 cm⁻¹) in the infrared spectrum of Hongliulin raw coal.-1 Peak fitting processing diagram as shown in the figure Figure 3 As shown, Peak 1 and Peak 4 are the stretching vibration peaks of CH in the methylene group, Peak 2 and Peak 5 are the stretching vibration peaks of CH in the methyl group, and Peak 3 is the stretching vibration peak of CH in the methine group. It is worth noting that the peaks with relatively high abundance were selected when analyzing the infrared spectrum; therefore, the bending vibrations of aliphatic CH were not considered for the time being.

[0029] Table 1. Peak positions and their meanings in the fitted infrared spectra

[0030] Step 2.2: Analyze the law of change of the integral area with temperature, and perform first derivative analysis on the normalized area-temperature curve of each functional group. Use the local extreme point of the derivative curve as the boundary temperature of the reaction stage, and divide the evolution of each functional group into several reaction stages.

[0031] Specifically, semi-quantitative analysis of functional groups was performed based on the peak areas of each functional group obtained after fitting. The integral area of ​​a functional group is related to its content; therefore, the evolution of functional groups with temperature can be quantitatively analyzed using the integral area and normalized area of ​​the functional group absorption peaks. The following is a study on the temperature variation of the integral areas of aliphatic CH, aromatic C=C, C=O, CO, and -OH groups.

[0032] 1) Reaction rules of aliphatic groups.

[0033] Aliphatic substances in coal generally consist of low-molecular-weight hydrocarbons formed by non-covalent bonds such as hydrogen bonds or van der Waals forces, and aliphatic side chains attached to aromatic rings. The low-molecular-weight hydrocarbons are mainly n-alkanes, while the aliphatic side chains primarily contain alkanes, substituted alkanes, and hydrogenated aromatic rings. During coal gasification, aliphatic groups readily break and transform into alkane gases. Aliphatic CH bonds are mainly found in methyl (-CH3), methylene (-CH2), and methine (-CH) groups. In infrared spectra, by fitting the CH peak, the CH group in the methyl group (2867 cm⁻¹) can be obtained. -1 2950 cm -1 ), CH in the methylene group (2851 cm) -1 2920 cm -1 ) and CH in methine (2895 cm) -1 The integral area of ​​these functional groups is obtained by further solving for the normalized area of ​​these functional groups.

[0034] Please see Figures 4a-4b , Figures 4a-4bThe integral area and normalized area of ​​aliphatic functional groups in Hongliulin bituminous coal vary with temperature. Figure 4a For the integral area, Figure 4b The normalized area is defined as follows: the integral area of ​​total aliphatic CH is the sum of the integral areas of CH in -CH3, -CH2, and -CH, and the normalized area of ​​total aliphatic CH is the ratio of the integral area of ​​total aliphatic CH in the solid product to the integral area of ​​total aliphatic CH in the raw coal.

[0035] As shown in Figure 4, for Hongliulin bituminous coal, the order of the content of the three aliphatic groups in the temperature range of 400-600℃ is -CH2>-CH3>-CH, while in the temperature range of 600-800℃, the order of the aliphatic group content is -CH2>-CH3=-CH. The integral area of ​​CH in -CH3 and -CH2 changes significantly, indicating that the cracking and gasification of Hongliulin bituminous coal mainly occurs in the 400-600℃ range, and that -CH3 in Hongliulin bituminous coal is almost completely gasified at 600℃. Combining the changes in total CH and the integral and normalized areas of each peak with temperature, it can be seen that the reactions of the aliphatic functional groups in Hongliulin bituminous coal are all staged. The changes in total aliphatic CH4 in Hongliulin bituminous coal can be divided into three stages: 400-460℃, 460-600℃, and 600-800℃. The cracking and gasification of its aliphatic functional groups mainly occur in the first and second stages, with the cracking and gasification in the first stage being significantly more intense than in the second. Within the 640-800℃ range, the normalized area of ​​CH4 in -CH2 and -CH3 does not change significantly, indicating that the more easily fractured -CH2 and -CH3 groups have already been completely gasified in the first two stages.

[0036] 2) Reaction rules of aromatic groups.

[0037] The most abundant carbon structure in coal is the aromatic structure. Aromatic structures are generally found in condensed aromatic hydrocarbons and aromatic hydrocarbons, with condensed aromatic hydrocarbons exhibiting greater stability than aromatic hydrocarbons. The functional groups corresponding to aromatic structures in coal include aromatic CH (3000-3100 cm⁻¹). -1 ) and aromatic C=C (1490-1600 cm) -1 After deconvolution, the aromatic CH absorption peaks of the three types of coal were almost undetectable. Therefore, this embodiment only studies the reaction rules of aromatic C=C. Because condensed aromatic hydrocarbons have extremely high molecular stability, and the principle of infrared spectroscopy is that molecules in the sample absorb the energy of infrared light and undergo energy level transitions to produce an absorption spectrum, the C=C absorption peak of condensed aromatic hydrocarbons is extremely indistinct in the infrared spectrum. Therefore, the C=C detected in the infrared spectrum is basically the C=C functional group in aromatic hydrocarbons. The aromatic C=C absorption peak contains three sub-peaks, located at 1490 cm⁻¹. -11570 cm -1 and 1600 cm -1 These three peaks are generated by the C=C stretching vibrations in polycyclic, bicyclic, and monocyclic aromatic structures, respectively. It is worth noting that polycyclic aromatic structures refer to aromatic structures containing three or slightly more rings.

[0038] Furthermore, the integral areas and normalized areas of the total aromatic C=C groups and their three peaks in Hongliulin bituminous coal were obtained. The integral area of ​​the total aromatic C=C groups is the sum of the integral areas of C=C groups in polycyclic, bicyclic, and monocyclic aromatic structures. The variation of the integral and normalized areas of each functional group with temperature was analyzed. The analysis showed that at medium and low temperatures, the relative content of C=C bonds in monocyclic and bicyclic aromatic structures in Hongliulin bituminous coal is higher than that in polycyclic aromatic structures. At higher temperatures, the relative content of C=C bonds in monocyclic, bicyclic, and polycyclic aromatic structures in Hongliulin bituminous coal is similar.

[0039] The evolution of aromatic C=C in Hongliulin bituminous coal with temperature can be divided into three stages: 400-500℃, 500-680℃, and 680-800℃. In the first stage, due to the low temperature, a large number of polycyclic aromatic compounds in the coal cannot undergo ring-opening. Simultaneously, a small number of relatively unstable monocyclic and bicyclic aromatic structures are released from the coal as phenolic substances through hydrolysis, resulting in a small change in the normalized area of ​​total aromatic C=C. In the second stage, a large number of monocyclic, bicyclic, and polycyclic aromatic structures undergo cracking and gasification, causing a sharp decrease in the change in the normalized area of ​​total aromatic C=C. In the third stage, aromatic structures undergo condensation polymerization, forming structurally stable polycyclic aromatic hydrocarbons, causing the normalized area of ​​total aromatic C=C to decrease at a relatively slow rate. The reactions in the second stage are more intense than those in the first and third stages. In addition, it should be noted that since FTIR spectrometers have difficulty detecting C=C groups in fused-ring aromatic structures, although the integral area and normalized area of ​​total aromatic C=C in the third stage are very small, they do not necessarily indicate that the content of aromatic structures in the solid product is very low.

[0040] The changes in the normalized area of ​​the three aromatic sub-peaks with temperature indicate that the evolution of C=C in monocyclic, bicyclic, and polycyclic aromatic structures is staged. The evolution of C=C in monocyclic and bicyclic aromatic structures follows a similar pattern to that of the total aromatic C=C in Hongliulin bituminous coal, both exhibiting three stages: 400-500℃, 500-680℃, and 680-800℃. The reaction stages for C=C in polycyclic aromatic structures are 400-500℃, 500-700℃, and 700-800℃. The cracking and gasification occurring in the second stage of monocyclic, bicyclic, and polycyclic aromatic structures are more intense than the cracking in the first stage and the condensation in the third stage.

[0041] 3) Reaction rules of carbonyl groups.

[0042] The C=O groups in coal mainly exist in quinone, ketone, carboxyl, and ester groups, with the quinone group being the most stable and the carboxyl group the least stable. The breaking and gasification of the C=O group are the main sources of CO2. The four sub-peaks shown in Table 1 were used to fit the C=O peaks. During the fitting process, it was found that no ketone C=O sub-peaks existed in the FTIR spectrum of Hongliulin bituminous coal. The integral areas of each C=O sub-peak are shown in Table 2.

[0043] Table 2. Integral areas of each C=O sub-peak in Hongliulin bituminous coal

[0044] Further analysis of the temperature-dependent changes in the integral and normalized areas of carbonyl C=O groups in Hongliulin bituminous coal reveals two distinct phases: 400-540℃ and 540-800℃. In the first phase, the integral and normalized areas of total C=O decrease sharply, indicating the extensive decomposition and gasification of quinone, ester, and carboxyl groups containing C=O. The order of C=O group content in the solid products is quinone > carboxyl > ester. Furthermore, the normalized area shows that the decomposition rates of ester and carboxyl groups in Hongliulin bituminous coal are similar but greater than those of quinone groups, with ester and carboxyl groups completely gasified at 460℃ and 520℃, respectively. In the second phase, the integral and normalized areas of total C=O show no significant change. This is because the easily decomposed ester and carboxyl groups are largely gasified in the first phase, leaving only a small amount of relatively stable quinone groups that slowly decompose and gasify in this phase.

[0045] 4) Reaction rules of ether bonds.

[0046] CO in coal is usually found in phenols and ethers, at 1000-1300 cm⁻¹ in FTIR spectra. -1 The CO corresponding to the absorption region generally refers to ether bonds, which are the main cross-linking structures in coal that connect aromatic compounds. Ether bonds mainly consist of aliphatic ether bonds (C). al -O and aromatic ether bonds C ar -O, where aliphatic ether bonds are less abundant in coal than aromatic ether bonds, and aliphatic ether bonds are more prone to decomposition during the reaction. Furthermore, the CO group is relatively more stable than the C=O group.

[0047] Further analysis of the normalized area of ​​ether-bonded CO in Hongliulin bituminous coal with temperature reveals the following reaction stages: 400-500℃, 500-620℃, and 620-800℃. In the first stage, the normalized area of ​​CO decreases sharply with increasing temperature, indicating that a large number of CO bonds decompose. In the second stage, the normalized area of ​​CO shows no significant change, indicating that the more easily decomposed CO groups were almost entirely gasified in the previous stage, leaving only structurally stable CO that did not undergo significant reaction in this stage. In the third stage, the normalized area of ​​CO gradually increases with increasing temperature, which is due to the reaction between the active carbon structure in the coal and H2O molecules to form a cross-linked structure containing CO.

[0048] 5) The reaction rules of hydroxyl groups.

[0049] The -OH groups in coal generally exist as hydrogen bonds, alcoholic hydroxyl groups, phenolic hydroxyl groups, and bound water. Hydrogen bonds are intermolecular forces, and the broad absorption peak of the -OH stretching vibration in the infrared spectrum is primarily due to hydrogen bonds. This peak is located in the 3100-3600 cm⁻¹ infrared spectrum. -1 The absorption region generally represents alcohol hydroxyl groups and phenolic hydroxyl groups. Since sub-bituminous coal, bituminous coal, and anthracite have low alcohol hydroxyl content, this wavenumber range generally refers to phenolic hydroxyl groups.

[0050] Further analysis of the normalized area of ​​-OH in Hongliulin bituminous coal with temperature reveals three reaction stages: 400-440℃, 440-620℃, and 620-800℃. In the first stage, the normalized area of ​​-OH changes little with increasing temperature. This is because hydrolysis is the primary reaction at this stage, forming phenolic hydroxyl groups on aromatic rings, while small amounts of phenolic substances with single aromatic rings, such as phenol and p-methylphenol, are released from the coal. In the second stage, the normalized area of ​​-OH gradually decreases with increasing temperature. This is because structurally unstable phenolic substances in the coal detach from and are released from the aromatic structure. Due to the high solubility and diffusivity of supercritical water, these phenolic substances dissolve rapidly in the supercritical water, leading to a significant reduction in the -OH content. In the third stage, the normalized area of ​​-OH decreases slowly with increasing temperature. This can be attributed to the gradual cracking of -OH groups connected to heterocyclic and aromatic rings in the coal due to the breaking of heterocycles and the condensation of aromatic structures.

[0051] In summary, the evolution of functional groups in Hongliulin bituminous coal with temperature can be divided into 2-3 stages: aliphatic CH groups are divided into three reaction stages: 400-460℃, 460-600℃, and 600-800℃; aromatic C=C groups are divided into three reaction stages: 400-500℃, 500-680℃, and 680-800℃; carbonyl C=O groups are divided into two reaction stages: 400-540℃ and 540-800℃; etheric CO groups are divided into three reaction stages: 400-500℃, 500-620℃, and 620-800℃; and hydroxyl -OH groups are divided into three reaction stages: 400-440℃, 440-620℃, and 620-800℃.

[0052] Step 3: Set multiple reaction temperature points according to the reaction stages of each functional group, and set multiple reaction residence times for each reaction temperature point. Conduct a full-coverage systematic gasification experiment to obtain coal samples after reaction under various working conditions.

[0053] Specifically, a full-coverage systematic gasification experiment was conducted in a quartz tube reactor using red willow forest bituminous coal at a concentration of 5 wt%. Based on the reaction stage division in step 2, three temperature gradients were set: 400℃, 420℃, and 460℃ in the low-temperature stage (approximately 400-500℃); 560℃, 600℃, and 660℃ in the medium-temperature stage (approximately 500-680℃); and 700℃, 740℃, and 800℃ in the high-temperature stage (approximately 680-800℃). Six residence times were set for each temperature point: 30 s, 60 s, 120 s, 240 s, 480 s, and 900 s. Coal samples were obtained after the reaction under various operating conditions.

[0054] Step 4: Perform Fourier transform infrared spectroscopy (FTIR) tests on coal samples before and after the reaction under each working condition, extract the integral area of ​​the characteristic absorption peaks of each functional group, and calculate the conversion rate of each functional group at each reaction stage under each working condition.

[0055] Specifically, FTIR tests were performed on the solid products of Hongliulin bituminous coal at different reaction times (30 s, 60 s, 120 s, 240 s, 480 s, and 900 s) at 400℃, 420℃, 460℃, 560℃, 600℃, 660℃, 700℃, 740℃, and 800℃. Figure 5 As shown, Figure 5 The images show the FTIR spectra of the solid products of Hongliulin bituminous coal at 400℃ and 420℃ for different reaction times. For details on the method of extracting the integral area of ​​the characteristic absorption peaks of each functional group from the FTIR spectra, please refer to step 2; it will not be repeated here.

[0056] To analyze the functional group kinetics of coal, the integral area of ​​the functional group spectrum is used to represent the mass of the reactants and the conversion rate. Defined as:

[0057] in, This represents the integral area of ​​the functional groups in raw coal. Let be the integral area of ​​the functional group at time t.

[0058] Step 5: The conversion rate of each functional group is fitted using a candidate kinetic model to obtain the reaction rate constant. The target kinetic model of each functional group is determined based on the fit between the reaction rate constant and the reaction temperature and empirical methods. The core kinetic parameters of each functional group at each reaction stage are solved based on the fitted line, and the kinetics of each functional group are compared and analyzed.

[0059] Step 5 includes: Step 5.1: Establish a candidate dynamic model library.

[0060] Specifically, the candidate kinetic model library includes chemical reaction models, two-phase interface reaction models, and diffusion reaction models; chemical reaction models include first-order reaction models, second-order reaction models, third-order reaction models, and n-order reaction models; phase interface reaction models include one-dimensional reaction models, two-dimensional reaction models, and three-dimensional reaction models; and diffusion reaction models include one-dimensional diffusion models, two-dimensional diffusion models, and three-dimensional diffusion models.

[0061] Kinetic mechanism functions of each reaction model and its integral form The expression depends on the transformation mechanism and its mathematical model. This typically represents a controlled stage of the reaction: such as chemical reactions, random nucleation and nucleus growth, interfacial reactions, or diffusion reactions. Commonly used coal reaction kinetic mechanism functions... and its integral form As shown in Table 3.

[0062] Table 3 Commonly Used Solid-State Reaction Kinetic Mechanism Functions

[0063] Step 5.2: For each reaction temperature point, substitute the conversion rate at each reaction residence time into the integral form of each candidate kinetic model. In the middle, draw the integral form residence time of the reaction The curve was plotted and linearly fitted, and the slope of the fitted line was taken as the reaction rate constant at the reaction temperature. .

[0064] Specifically, for each reaction temperature point, the conversion rate at each reaction residence time is substituted into the integral form of each candidate kinetic model in Table 3. In the middle, draw the integral form residence time of the reaction The curve is obtained by performing a first-order linear fit on the curve, and the slope of the resulting straight line is the reaction rate constant at the reaction temperature. .

[0065] Step 5.3, according to the logarithmic form of the Arrhenius formula ,draw For 1 / R T The curve was linearly fitted, and the slope and intercept of the fitted line were -E and -E, respectively. The core dynamic parameters were calculated as follows: activation energy E and pre-exponential factor A.

[0066] Specifically, the Arrhenius formula is expressed as follows: ,in, The reaction temperature. The value of is the ideal gas constant, which is 8.314 J·K. -1 ·mol -1 .

[0067] Taking the logarithm of both sides of the Arrhenius formula, we get: .

[0068] draw For 1 / R T The curve was subjected to first-order linear fitting, and the slope and intercept of the fitted line were -E and -E, respectively. Thus, the core dynamic parameters are calculated: activation energy E and pre-exponential factor A.

[0069] Step 5.4: Using the degree of fit of the fitted straight line, the model closest to 1 is selected as the target dynamic model for each functional group; when the difference in the degree of fit is less than a preset value, the target dynamic model is determined by empirical methods.

[0070] Specifically, the choice of reaction kinetic model depends on the various models used. Received For 1 / R T The goodness of fit of the fitted line (R) 2The model whose goodness of fit is closest to 1 is selected as the kinetic model. When the difference in goodness of fit is less than a preset value, some empirical methods are used to judge, such as chemical reactions occurring more easily at lower temperatures and diffusion reactions occurring more easily at higher temperatures. When the goodness of fit of chemical reaction models of different orders or phase interface reactions or diffusion reactions of different dimensions is extremely small, the simplest model is selected as the kinetic model.

[0071] The kinetic analysis of aliphatic CH, aromatic C=C, C=O, CO and -OH groups at each reaction stage in this embodiment is as follows.

[0072] 1) Kinetic analysis of aliphatic groups.

[0073] Aliphatic CH groups in coal mainly undergo breakage and gasification during supercritical water gasification, generating small molecule gases such as CH4. Aliphatic CH groups show little change in the third stage (600-800℃). This example presents a kinetic analysis of the first and second stage reactions of aliphatic groups.

[0074] The reaction rate constants of aliphatic CH at 400℃, 420℃, 460℃, 560℃ and 600℃ are shown in Table 4, and the calculated activation energy and pre-exponential factor are shown in Table 5.

[0075] Table 4. Reaction rate constants of the aliphatic CH at various temperatures obtained from the fitting reaction models.

[0076] Table 5. Reaction models and related parameters of CH at each reaction stage.

[0077] As can be seen from Tables 4 and 5, the reactions in both the first and second stages conform to the third-order reaction model, indicating that the concentration of aliphatic CH in Hongliulin bituminous coal has a significant impact on the reaction rates of aliphatic group cracking and gasification in both stages; and the goodness of fit between the reaction model and the reaction rate constant R 2 All values ​​are greater than 0.93. The activation energy of the aliphatic CH reaction increases rapidly with increasing temperature. In the first stage, the aliphatic CH reaction follows a third-order reaction model, with an activation energy of 38.45 kJ·mol⁻¹. -1 This indicates that supercritical water-coal gasification can significantly reduce the activation energy of aliphatic CH4 reactions. In the second stage, due to the relatively stable methyl and methylene structures attached to the benzene ring, the cracking of aliphatic CH4 requires higher energy, resulting in an activation energy greater than that in the first stage, at 85.07 kJ·mol⁻¹. -1It undergoes fracture and vaporization in a third-order reaction mode. Furthermore, the reaction rate constant of the third-order reaction model corresponding to the aliphatic CH in the first stage is smaller than that corresponding to the third-order reaction model in the second stage, indicating that the reaction rate of cracking and vaporization of aliphatic CH in the first stage is lower than that in the second stage.

[0078] Figure 6 This figure compares the fitted curves and actual integrated areas of aliphatic CH4 in the first and second stage reaction models. It is clear from the figure that the integrated areas of aliphatic CH4 under different actual operating conditions are basically located on the fitted curves, indicating a good agreement between the two.

[0079] 2) Kinetic analysis of aromatic groups.

[0080] In this embodiment, kinetic analysis was performed on all three reaction stages of the aromatic group.

[0081] The reaction rate constants of the aromatic C=C reaction models at various temperatures are shown in Table 6. Based on these reaction rate constants and empirical methods, the optimal reaction kinetic model for aromatic C=C was derived, and its relevant parameters are shown in Table 7. The goodness of fit in Table 7 is greater than 0.98, and the experimental values ​​and the fitted curves agree well, indicating that the reaction models for the three stages of aromatic C=C are all reasonable.

[0082] Table 6. Reaction rate constants of aromatic C=C at various temperatures obtained from the fitted reaction models.

[0083] Table 7. Reaction models and relevant parameters of aromatic C=C at each reaction stage.

[0084] In Tables 6 and 7, the reaction rate constants of aromatic C=C in the three stages increase with increasing temperature. The activation energy increases with increasing temperature in the first and second stages, but decreases slightly in the third stage. This indicates that the energy barrier to overcome for the cracking and vaporization of aromatic structures is highest in the second stage, while the condensation of aromatic structures is more likely to occur than their cracking and vaporization. The reactions of aromatic C=C in the first and second stages conform to a second-order reaction model, while the reaction in the third stage conforms to a fourth-order reaction model. This suggests that the concentration has a relatively small impact on the reaction rates of aromatic structure cracking and vaporization in the first two stages, but a significant impact on the reaction rates of aromatic structure condensation and vaporization in the third stage.

[0085] In the first stage, when the temperature increased from 400℃ to 460℃, the reaction rate constant of the aromatic C=C group increased from 4.28 × 10⁻⁶. -4 s -1 Increased to 8.19×10 -4 s-1 The activation energy is 45.22 kJ·mol⁻¹. -1 This is because the temperature is low at this stage, resulting in a very low rate of aromatic structure decomposition. In the second stage, the activation energy for the decomposition and vaporization of aromatic C=C is 134.80 kJ·mol⁻¹. -1 This is an increase of 89.58 kJ·mol compared to the first stage. -1 This is due to the extensive cleavage of monocyclic, bicyclic, and polycyclic aromatic structures during this reaction stage, releasing large amounts of monocyclic phenolic compounds into supercritical water. In the third stage, the activation energy for aromatic ring condensation is 123.69 kJ·mol⁻¹. -1 The activation energy of the third stage is similar to that of the second stage. In this stage, the main processes are the condensation and gasification of aromatic rings and the cracking of heterocyclic rings. When the reaction temperature increases from 700℃ to 800℃, the reaction rate constant increases from 0.32 to 1.31, which is much greater than the reaction rate constants of the first and second stages, indicating that the intensity of the reaction in the third stage is much greater than that of the first and second stages. The fused-ring aromatic structures produced in this stage are difficult to gasify due to their stable structure. Since the fused-ring aromatic structures in this stage are mainly formed by the condensation of monocyclic, bicyclic, and polycyclic aromatic structures that did not completely crack in the second stage, the formation of fused-ring aromatic structures can be suppressed by enhancing the ring-opening and cracking of aromatic structures in the second stage or by adding substances that can inhibit the condensation of aromatic structures in the third stage. This provides a research direction for further studies on enhancing coal gasification in supercritical water.

[0086] 3) Kinetic analysis of carbonyl groups.

[0087] According to the analysis in step 3, C=O in Hongliulin bituminous coal is basically gasified in the first stage, and there is no significant change in the second stage (540-800℃). Therefore, the reaction kinetics of C=O in the first stage are studied.

[0088] The reaction rate constants of the kinetic models for C=O at various temperature points in the first stage are shown in Table 8. Based on the reaction rate constants of each reaction model and empirical methods, the third-order reaction model showed the best fit to the experimental data. This indicates that the concentration of C=O in the Hongliulin bituminous coal has a significant impact on the reaction rate of C=O decomposition and gasification in this stage. The relevant kinetic parameters of this reaction model are shown in Table 9. The goodness of fit of the third-order model in Table 9 is greater than 0.99, and the model fitting curve basically matches the experimental values, indicating that the model is relatively reasonable.

[0089] Table 8. Reaction rate constants of the fitted C=O reaction model at various temperatures.

[0090] Table 9. Reaction model and relevant parameters of C=O in the first stage.

[0091] In Table 8, as the temperature increases from 400℃ to 460℃, the reaction rate constant corresponding to the third-order reaction model increases from 3.66 × 10⁻⁶. -3 s -1 It rapidly increased to 7.79 × 10 -3 s -1 As can be seen from Table 9, the activation energy of C=O in the first stage reaction is 51.04 kJ·mol⁻¹. -1 This indicates that C=O is easily broken during supercritical water vaporization. Simultaneously, the more easily vaporized ester and carboxyl groups are completely vaporized at this stage, leaving only a very small amount of less vaporizable quinone groups. Based on the stability of different quinone compounds, it can be inferred that the remaining quinone groups are all directly attached to the aromatic ring, such as p-benzoquinone, ortho-benzoquinone, and far-benzoquinone, whose structures are very stable, making C=O difficult to decompose.

[0092] 4) Kinetic analysis of ether bonds.

[0093] This section focuses on the kinetics of the first stage of CO decomposition, where the decomposition is relatively obvious.

[0094] Table 10 shows the reaction rate constants of CO at various reaction temperatures corresponding to each model, obtained through fitting. Table 11 shows the optimal reaction model for CO in the first stage, along with its kinetic parameters, obtained through empirical methods and the reaction rate constants of each reaction model. In Table 11, the CO reaction in the first stage conforms to a fourth-order reaction model, indicating that the CO concentration in Hongliulin bituminous coal has a significant impact on the reaction rate of CO decomposition and gasification. The model's goodness of fit is 0.99, and the model fitting curve matches the experimental values ​​well, indicating that the kinetic model is reliable.

[0095] Table 10. Reaction rate constants of CO at various temperatures obtained from the fitted reaction models.

[0096] Table 11 Reaction models and related parameters of CO at each reaction stage

[0097] By comparing the model fitting curves and experimental values ​​of the CO integral area under different residence times in supercritical water gasification of Hongliulin bituminous coal at different temperatures in the first stage, it can be seen that the rate of decrease of the CO integral area gradually increases with increasing temperature, indicating that the decomposition and gasification rate of CO is directly proportional to temperature in this stage. Furthermore, the CO integral area decreases rapidly in the 0-480 s range at various temperatures, while the rate of decrease slows down in the 480-900 s range. This indicates that in this stage, aliphatic ethers and more easily broken aromatic ethers decompose in large quantities within the 0-480 s range, releasing small molecule gases such as CO2 and CO. When the residence time exceeds 480 s, the decomposition rate of ether bonds slows down and gradually reaches an equilibrium state.

[0098] In Table 10, as the reaction temperature increases from 400℃ to 460℃, the reaction rate constant corresponding to the fourth-order reaction model increases from 9.05 × 10⁻⁶. -4 s -1 Increased to 3.19 × 10 -3 s -1 This demonstrates, in concrete numerical terms, that the reaction rate in the first stage increases rapidly with increasing temperature. Table 11 shows that the activation energy for the CO reaction in the first stage is 85.64 kJ·mol⁻¹. -1 This indicates that the activation energy of the CO reaction is significantly reduced when Hongliulin bituminous coal is gasified in supercritical water.

[0099] 5) Kinetic analysis of hydroxyl groups.

[0100] Since the changes in -OH are very small in the first and third stages, this embodiment performs a kinetic analysis on the reaction of -OH in the second stage.

[0101] Table 12 shows the reaction rate constants of the -OH reaction model at various temperatures in the second stage. Combining empirical methods and the goodness of fit obtained from fitting the reaction rate constants, it can be concluded that the -OH reaction in the second stage conforms to a fourth-order reaction model. This indicates that the concentration of -OH in Hongliulin bituminous coal has a significant impact on the cracking reaction rate of -OH. The relevant kinetic model parameters are shown in Table 13. The goodness of fit between the fourth-order reaction model and the reaction rate in Table 13 is 0.998, and the actual integral area under each condition matches well with the calculated values ​​on the model fitting curve, indicating that the fourth-order model for the second stage is reasonable.

[0102] Table 12. Reaction rate constants of -OH obtained from the fitted reaction model at various temperatures.

[0103] Table 13 Reaction model and related parameters of -OH in the second stage

[0104] By comparing the model fitting curve and the actual integrated area of ​​-OH in the second stage, it can be seen that the integrated area of ​​-OH at each temperature point gradually decreases with increasing temperature and residence time, while the reaction rate gradually increases with increasing temperature. In the range of 0-480 s, the integrated area of ​​-OH decreases rapidly, while the rate of decrease is relatively slow in the range of 480-900 s. This indicates that the removal of -OH from coal mainly occurs before 480 s, and when the residence time exceeds 480 s, the reaction rate of -OH cracking slows down and gradually reaches equilibrium.

[0105] As shown in Table 12, when the reaction temperature increases from 460℃ to 600℃, the reaction rate constant corresponding to the fourth-order reaction model increases from 1.34 × 10⁻⁶. -3 s -1 Increased to 4.68×10 -3 s -1 In Table 13, the activation energy of -OH in the second stage is 47.05 kJ·mol⁻¹. -1 This indicates that the breakage of -OH groups is more likely to occur during supercritical water gasification than during pyrolysis. The reduction of -OH groups during coal pyrolysis is related to the breakage of aliphatic groups, specifically the detachment of -OH groups from the aromatic structure and their combination with hydrogen in the aliphatic group to form water. During supercritical water gasification, the breakage of -OH groups themselves is less frequent, with the majority of the -OH groups being released from the coal as phenols such as phenol and p-methylphenol. Therefore, it can be inferred that the content of -OH groups undergoing breakage during coal pyrolysis is higher than that during supercritical water gasification, resulting in a significantly lower activation energy for the -OH reaction in the 440-620℃ range during supercritical water gasification compared to the corresponding temperature range during coal pyrolysis. Furthermore, the high solubility, fluidity, diffusivity, and permeability of supercritical water greatly promote the removal of phenols from the coal structure and their dissolution in supercritical water, effectively reducing the condensation polymerization of phenols with the aromatic structures in the coal at high temperatures.

[0106] Step 5.5: Based on the kinetic comparative analysis of each functional group using core kinetic parameters, the rate control steps for each stage of supercritical water vaporization across the entire temperature range are clarified.

[0107] Please see Figure 7 , Figure 7 The figure shows the reaction models and activation energies for the five functional groups at each stage. As can be seen from the figure, the activation energies for the five functional groups range from 38.45 to 134.80 kJ·mol⁻¹. -1 The activation energies of aliphatic CH and aromatic C=C in the first and second stages increased with increasing temperature, while the activation energy of aromatic C=C in the second and third stages decreased slightly with increasing temperature. Furthermore, the reactions of all five functional groups in each stage were controlled by chemical reactions, indicating that the reactions of all five functional groups in each stage were affected by concentration.

[0108] In the low-temperature stage, the main reactions involve the vigorous decomposition of CO and C=O, as well as the extensive cleavage of aliphatic CH4, with a small amount of aromatic C=C undergoing cleavage as well. The reactions of aliphatic CH4, aromatic C=C, C=O, and CO in the low-temperature stage conform to third-, second-, third-, and fourth-order reaction models, respectively, indicating that the cleavage reaction of aromatic C=C is least affected by concentration, the decomposition and vaporization of aliphatic CH4 and C=O are less affected by concentration, and the decomposition and vaporization of CO are most affected by concentration. The activation energy of CO in the first stage (400-500℃) is 85.64 kJ·mol. -1 The activation energy is the highest among all activation energies in the low-temperature stage, followed by the activation energy of C=O in the 400-540℃ stage (51.04 kJ·mol⁻¹). -1 The activation energies of C=C in the 400-500℃ range (45.22 kJ·mol⁻¹) -1 The smallest activation energy is that of aliphatic CH in the 400-460℃ range (34.05 kJ·mol⁻¹). -1 Based on the activation energy, it can be seen that the energy barrier that needs to be overcome for CO decomposition is the highest at low temperatures.

[0109] In the mesophilic stage, the main reactions are the cleavage of aromatic C=C and the breaking of -OH and aliphatic CH. The reactions of aliphatic CH, aromatic C=C, and -OH in this stage conform to third, second, and fourth order reaction models, respectively, indicating that in the mesophilic stage, the cleavage of aromatic C=C is least affected by concentration, followed by the breaking of aromatic CH, while the breaking of -OH is most affected by concentration. The activation energy of aromatic C=C is the highest in the 500-680℃ range (134.80 kJ·mol⁻¹). -1 Secondly, the activation energy of aliphatic CH in the 460-600℃ range (85.07 kJ·mol⁻¹) -1 The smallest activation energy is that of -OH in the 440-620℃ range (47.05 kJ·mol⁻¹). -1 This indicates that the cleavage of -OH is the easiest to occur, followed by the cleavage of aliphatic CH, and the most difficult to occur is the cleavage of aromatic C=C.

[0110] In the high-temperature stage, the main processes are the condensation polymerization of aromatic structures and the formation of aromatic ether bonds. The reaction of aromatic C=C in the 680-800℃ stage conforms to a fourth-order reaction model, indicating that the condensation polymerization of aromatic structures is greatly affected by concentration. The activation energy of aromatic C=C in this stage is 123.69 kJ·mol⁻¹. -1 The activation energy is slightly less than that of the aromatic C=C in the second stage, indicating that the ease with which the aromatic structure undergoes condensation in the third stage is similar to that of the cleavage in the second stage.

[0111] Step 6: Compare the experimental values ​​of functional groups from supercritical water vaporization experiments at different temperatures with the predicted values ​​from the target kinetic model to verify the reliability of the target kinetic model.

[0112] Specifically, the reaction kinetic model of the functional group needs to agree well with the experimental data and be able to predict the gasification effect of the functional group under other operating conditions. In order to verify the kinetic model corresponding to each functional group in the reaction stage discussed in step 5, this step compares the experimental values ​​and kinetic model predictions of functional groups in supercritical water gasification of Hongliulin bituminous coal at reaction temperatures of 440℃, 580℃, 720℃ and 780℃ within a wider range of reaction stages within the functional group reaction stage.

[0113] Please see Figure 8 , Figure 8 This figure compares the predicted and experimental values ​​of the functional group reaction kinetics models for supercritical water gasification of Hongliulin bituminous coal at different temperatures. The experimental values ​​at 440℃ validate the kinetic models for aliphatic CH, aromatic C=C, C=O, and CO in the first stage; the experimental values ​​at 580℃ validate the kinetic models for aliphatic CH, aromatic C=C, and -OH in the second stage; and the experimental values ​​at 720℃ and 780℃ validate the kinetic model for aromatic C=C in the third stage. Figure 8 It is evident that the kinetic models of each functional group at each stage are in high agreement with the experimental values, demonstrating the reliability of the kinetic models.

[0114] The method in this embodiment clarifies the rate control mechanism and quantifies the supercritical water enhancement mechanism by constructing a graded dynamics research system that is adaptable to the entire temperature range. It achieves microscopic and refined dynamic analysis, breaks through the limitations of traditional mechanisms, has high research accuracy, strong reliability and practicality, and high engineering application value, which can support the industrialization of the technology.

[0115] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for studying the reaction kinetics of functional groups in supercritical water gasification of coal, characterized in that, include: Step 1: Select the target coal type, grind and sieve the target coal type to prepare coal-water slurry, carry out supercritical water gasification experiment of coal, and obtain infrared spectra of solid products at different temperatures after the reaction is completed. Step 2: Extract the area of ​​each functional group based on the infrared spectrum, and divide the evolution of each functional group into several reaction stages according to the change of the area of ​​each functional group with temperature. Step 3: Set multiple reaction temperature points according to the reaction stages of each functional group, and set multiple reaction residence times for each reaction temperature point. Conduct a full-coverage systematic gasification experiment to obtain coal samples after reaction under various working conditions. Step 4: Perform Fourier transform infrared spectroscopy on the coal samples before and after the reaction under each working condition, extract the integral area of ​​the characteristic absorption peaks of each functional group, and calculate the conversion rate of each functional group at each reaction stage under each working condition. Step 5: The conversion rate of each functional group is fitted using a candidate kinetic model to obtain the reaction rate constant. The target kinetic model of each functional group is determined based on the fit between the reaction rate constant and the reaction temperature and empirical methods. The core kinetic parameters of each functional group at each reaction stage are solved based on the fitted line, and the kinetics of each functional group are compared and analyzed.

2. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 1, characterized in that, The conditions for conducting the supercritical water gasification experiment of coal in step 1 include: a temperature range of 400-800℃, a temperature interval of 20℃, and a reaction time of 10 min.

3. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 1, characterized in that, Step 2 includes: Step 2.1: Use fitting software to perform peak fitting processing on the infrared spectrum to obtain each characteristic absorption peak of the fitted infrared spectrum and its corresponding functional group. At the same time, obtain the integral area of ​​each functional group and calculate the normalized area based on the integral area. The normalized area is the ratio of the absorption peak area of ​​each functional group at different temperatures to the peak area of ​​the corresponding functional group in the raw coal. Step 2.2: Analyze the law of the integral area size changing with temperature, and perform first derivative analysis on the normalized area-temperature curve of each functional group. Use the local extreme point of the derivative curve as the boundary temperature of the reaction stage, and divide the evolution of each functional group into several reaction stages.

4. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 3, characterized in that, The functional groups include aliphatic CH, aromatic C=C, carbonyl C=O, ether CO, and hydroxyl -OH; The characteristic absorption peak of the hydroxyl group (-OH) is located in the range of 3100-3750 cm⁻¹. -1 The characteristic absorption peak of the aliphatic CH is located at 2750-3000 cm⁻¹. -1 The characteristic absorption peak of the carbonyl C=O group is located in the 1650-1800 cm⁻¹ range. -1 The characteristic absorption peak of the aromatic C=C group is located at 1490-1600 cm⁻¹. -1 The characteristic absorption peak of the CO bond in the ether bond is located in the range of 1000-1315 cm⁻¹. -1 ; The aliphatic CH includes CH in aliphatic -CH3, CH in aliphatic -CH2, and CH in aliphatic -CH, corresponding to 2851 cm⁻¹. -1 2867 cm -1 2895 cm -1 2920 cm -1 and 2950 cm -1 Five sub-peaks; The aromatic C=C includes C=C in polycyclic aromatic compounds, C=C in bicyclic aromatic compounds, and C=C in monocyclic aromatic compounds, corresponding to 1490 cm⁻¹. -1 1570 cm -1 and 1600 cm -1 Three sub-peaks; The carbonyl C=O group includes C=O in quinone groups, C=O in ketone groups, C=O in carboxyl groups, and C=O in ester groups, corresponding to 1655 cm⁻¹. -1 1678 cm -1 1705 cm -1 and 1730 cm -1 Four sub-peaks; The ether bond CO corresponds to 1079 cm⁻¹ -1 1144 cm -1 1166 cm -1 1214 cm -1 and 1272 cm -1 Five sub-peaks; The hydroxyl group -OH corresponds to 3280 cm. -1 3400 cm -1 and 3530 cm -1 Three sub-peaks.

5. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 3, characterized in that, For Hongliulin bituminous coal, the reaction of aliphatic CH groups is divided into three stages: 400-460℃, 460-600℃, and 600-800℃; the reaction of aromatic C=C groups is divided into three stages: 400-500℃, 500-680℃, and 680-800℃; the reaction of carbonyl C=O groups is divided into two stages: 400-540℃ and 540-800℃; the reaction of etheric CO groups is divided into three stages: 400-500℃, 500-620℃, and 620-800℃; and the reaction of hydroxyl-OH groups is divided into three stages: 400-440℃, 440-620℃, and 620-800℃.

6. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 1, characterized in that, In step 3, for Hongliulin bituminous coal, the reaction temperature points include 400℃, 420℃, 460℃, 560℃, 600℃, 660℃, 700℃, 740℃ and 800℃; The reaction residence times include 30 s, 60 s, 120 s, 240 s, 480 s and 900 s.

7. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 1, characterized in that, In step 4, the formula for calculating the conversion rate is: in, This represents the integral area of ​​the functional groups in raw coal. Let be the integral area of ​​the functional group at time t.

8. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 1, characterized in that, Step 5 includes: Step 5.1: Establish a candidate kinetic model library; the candidate kinetic model library includes chemical reaction models, two-phase interface reaction models, and diffusion reaction models; the chemical reaction models include first-order reaction models, second-order reaction models, third-order reaction models, and n-order reaction models; the two-phase interface reaction models include one-dimensional reaction models, two-dimensional reaction models, and three-dimensional reaction models; the diffusion reaction models include one-dimensional diffusion models, two-dimensional diffusion models, and three-dimensional diffusion models. Step 5.2: For each reaction temperature point, substitute the conversion rate at each reaction residence time into the integral form of each candidate kinetic model. In the middle, draw the integral form residence time of the reaction The curve was obtained and linearly fitted, and the slope of the fitted line was taken as the reaction rate constant at the stated reaction temperature. ; Step 5.3, according to the logarithmic form of the Arrhenius formula ,draw For 1 / R T The curve was linearly fitted, and the slope and intercept of the fitted line were -E and -E, respectively. The core kinetic parameters were calculated as follows: activation energy E and pre-exponential factor A. Step 5.4: Using the degree of fit of the fitted straight line, the model closest to 1 is taken as the target dynamic model for each functional group; when the difference in the degree of fit is less than a preset value, the target dynamic model is determined by an empirical method. Step 5.5: Based on the core kinetic parameters, conduct a comparative analysis of the kinetics of each functional group to clarify the rate control steps for each stage of supercritical water vaporization across the entire temperature range.

9. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 8, characterized in that, For Hongliulin bituminous coal Aliphatic CH both conform to the third-order reaction model in the first reaction stage at 400-460℃ and the second reaction stage at 460-600℃. Aromatic C=C reactions conform to a second-order reaction model in the first reaction stage at 400-500℃ and the second reaction stage at 500-680℃, and conform to a fourth-order reaction model in the third reaction stage at 680-800℃. The carbonyl C=O group follows a third-order reaction model in the first stage of the reaction at 400-540℃. The first stage of the reaction of CO with ether bond at 400-500℃ conforms to the fourth-order reaction model. The second reaction stage of the hydroxyl group -OH at 440-620℃ conforms to a fourth-order reaction model. The activation energies of the five functional groups range from 38.45 to 134.80 kJ·mol⁻¹ -1 The activation energies of the aliphatic CH and the aromatic C=C increase with increasing temperature in both the first and second reaction stages, while the activation energy of the aromatic C=C decreases slightly with increasing temperature in the second and third reaction stages. Simultaneously, the reactions of the five functional groups in each stage are affected by concentration.

10. The method for studying the reaction kinetics of functional groups in supercritical water gasification of coal according to claim 1, characterized in that, Also includes: Step 6: The experimental values ​​of functional groups from supercritical water vaporization experiments at different temperatures are compared with the predicted values ​​of the target kinetic model to verify the reliability of the target kinetic model.

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