Coal classification method based on biodegradability of organic matter in coal

Abstract

This invention relates to the field of coal biogasification technology, specifically to a method for classifying coal types based on the biodegradability of organic matter in coal. The method includes: collecting coal samples to be classified, extracting soluble organic matter and separating aromatic hydrocarbon components; quantitatively analyzing the content of six compounds (naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, biphenyl, and methylbiphenyl) and the total aromatic hydrocarbon content using gas chromatography-mass spectrometry; and calculating the biodegradation index f. bio = (Sum of contents of six types of compounds / Total aromatic hydrocarbon content) × 100%; f bio Compared with a preset threshold, coal samples are classified into recalcitrant, moderately degradable, or readily degradable types. This invention establishes a quantitative classification standard based on the relative content of major organic matter (aromatic hydrocarbons) in coal, which can effectively characterize the initial microbial degradation potential of coal samples and provide a scientific basis for screening feedstocks for coal biogasification.

Description

Technical Field

[0001] This invention relates to the field of coal biogasification technology, specifically to a method for classifying coal types based on the biodegradability of organic matter in coal. Background Technology

[0002] Coal biogasification is a technology that utilizes microbial metabolism to convert organic matter in coal into methane, and it is one of the important pathways to achieve clean coal utilization. Current research generally suggests that low-rank coal, due to its lower degree of coalification and rich aliphatic structures, has high biogasification potential. However, some scholars have proposed the opposite view, arguing that high-rank coal, dominated by aromatic structures, has a more significant biogasification efficiency, leading to a lack of consensus on the correlation between coal rank and biogasification potential. In recent years, research on the biodegradation patterns of different components in coal has made new progress. Studies have found that the degradation degree of aromatic hydrocarbons in coal under microbial action can reach PM5-7 levels, significantly higher than the PM4-5 levels of saturated hydrocarbons. This phenomenon clearly contradicts the classic understanding in traditional petroleum geology that "saturated hydrocarbons are preferentially degraded," revealing the unique characteristics of the degradation mechanism of organic matter in coal. Further research indicates that aromatic hydrocarbon components in the soluble organic matter of coal are important substrates for microbial degradation, and their relative proportion is one of the key factors affecting the final methane production. The biodegradability of aromatic hydrocarbons is mainly controlled by the number of aromatic rings and the number and type of alkyl substituents: low-ring-number (2-3 ring) parent compounds and low-substituted derivatives degrade faster, while high-ring-number or highly substituted compounds are difficult for microorganisms to utilize, resulting in a significant decrease in degradation efficiency. However, current screening and potential evaluation of coal biogasification feedstocks still lack a systematic indicator system centered on the biodegradability of aromatic hydrocarbons. Existing evaluation methods mostly focus on the macroscopic composition or total organic matter content of coal, and have not yet established an evaluation method that can effectively characterize the relationship between the structural characteristics of aromatic hydrocarbons and their microbial availability, making it difficult to accurately predict the true biogasification potential of coal samples.

[0003] Currently, the classification and evaluation of coal samples mainly employ the following methods: (I) Coal classification method based on coal rank Coal rank (degree of coalification) is currently the most widely used basis for coal classification. Internationally, the American Society for Testing and Materials (ASTM) standard D388 classifies coal into four major categories and thirteen subcategories based on rank: lignite, sub-bituminous coal, high-volatile bituminous coal, medium-volatile bituminous coal, low-volatile bituminous coal, semi-anthracite, and anthracite. The core characterization indicator for coal rank is vitrinite reflectance (VDR). R o ) or maximum reflectance of vitrinite ( R o,maxThe vitrinite reflectance index is obtained by measuring the light reflection intensity of a polished surface of coal under oil immersion conditions using a reflected light microscope system. ASTM D2798 specifies the detailed method for determining vitrinite reflectance, requiring measurements at least 100 points for a single sample and 150 points for mixed coals. my country's coal classification system also uses vitrinite reflectance as a coal rank parameter, supplemented by parameters such as higher calorific value, dry ash-free volatile matter, and caking index for comprehensive classification.

[0004] In coal biogasification research, researchers generally use coal rank as a reference for feedstock selection. Numerous studies have shown that low-rank coal has a higher potential for biogas production than high-rank coal; biomethane production using long-flame coal as a substrate increased by 10.82%, 38.88%, and 73.49% compared to lignite, gas coal, and coking coal, respectively; and the higher the coal rank, the lower the total biogas production. However, some literature reports that anthracite (high-rank coal) has a higher biogasification potential than lignite (low-rank coal). Therefore, the limitations of evaluating biogasification potential based on coal rank classification are quite obvious: First, vitrinite reflectance reflects the overall maturity of coal and is related to the degree of aromatic ring condensation during coalification, but it cannot distinguish the differences in biodegradability of different organic components in coal at the molecular structure level; second, coal samples of the same rank may have drastically different organic matter compositions and biogasification potentials due to differences in sedimentary environment, parent material, and other factors; third, there is no unified understanding of the relationship between coal rank and biogasification potential (whether it is positive or negative), indicating that coal rank alone cannot accurately characterize the actual bioavailability of aromatic hydrocarbon components in coal. Therefore, the coal rank classification method is difficult to directly and quantitatively characterize the initial microbial degradation potential of coal samples.

[0005] (ii) Evaluation methods based on total aromatic hydrocarbon content or total soluble organic matter content Another common approach is to determine the total extraction rate of chloroform pitch "A" or the total content of aromatic compounds in coal to evaluate its biogasification potential. Studies have shown that the extraction rate of chloroform pitch "A" reflects, to some extent, the total amount of organic matter in coal that can be utilized by microorganisms. The chloroform pitch "A" extraction rate of Longkou lignite is between 1.8% and 7.5%, and it is considered a good source rock; the chloroform pitch "A" content of Jurassic oil-rich coal in northern Shaanxi is also relatively high. In addition, some researchers use infrared spectroscopy or nuclear magnetic resonance technology to determine the ratio of aromatic carbon to total carbon in coal (i.e., apparent aromaticity) as a structural parameter for evaluating the structural characteristics of coal.

[0006] However, the limitations of this method are also prominent: the total aromatic hydrocarbon content or total soluble organic matter content only reflects the "quantity" of extractable organic matter and cannot distinguish between "easily biodegradable" and "difficult-to-biodegrade" components. The aromatic hydrocarbon components of coal constitute an extremely complex mixture system, containing various compounds ranging from monocyclic to polycyclic and from unsubstituted to highly substituted. Among these, compounds with low ring numbers and low substitution rates degrade faster, while compounds with high ring numbers or high substitution are difficult for microorganisms to utilize. Therefore, even if two coal samples have similar total aromatic hydrocarbon contents, the relative proportions of their easily degradable components may differ significantly, leading to vastly different actual biogasification effects. Simply relying on the total content index cannot provide accurate guidance for screening feedstocks for coal biogasification.

[0007] (III) Evaluation methods based on specific polycyclic aromatic hydrocarbon monomer concentrations or biomarker parameters In recent years, some researchers have attempted to use gas chromatography-mass spectrometry (GC-MS) to analyze specific biomarker compounds in coal to evaluate the degree of coal biodegradation. For example, the degree of biodegradation is determined by analyzing the distribution characteristics and degradation sequences (n-alkanes > steranes > hopanes) of saturated hydrocarbons; or by using parameters such as the methylphenanthrene index to determine the maturity of organic matter; and other studies utilize the distribution characteristics of naphthalene, phenanthrene, and biphenyl series of aromatic compounds to indicate biodegradation. In biogasification process research, GC-MS has been used to analyze the changes in organic matter composition during biogas production from coal of different ranks.

[0008] However, these methods mainly suffer from the following problems: First, existing studies mostly focus on single or a few compound indicators. The variability of a single compound is large and significantly affected by the original sedimentary environment and coalification, which is insufficient to reflect the biodegradability characteristics of the overall aromatic hydrocarbon composition. Second, existing biomarker parameters are mostly qualitative or semi-quantitative indicators, lacking systematic quantitative classification standards. Third, these methods are mainly used to assess the degree of biodegradation that coal has undergone (i.e., "historical degradation record"), rather than predicting the "initial degradation potential" of coal under artificial biogasification conditions. The former focuses on processes that have already occurred in geological history, while the latter focuses on the content of effective components that can currently serve as microbial substrates. The two are fundamentally different in their evaluation objectives and application directions. Fourth, existing methods have not yet established a coal sample type classification system based on biodegradability, and cannot provide intuitive raw material classification guidance for engineering applications.

[0009] In summary, existing methods for classifying and evaluating coal samples have significant shortcomings in characterizing the initial degradation potential of microorganisms: coal rank classification methods focus on the degree of coalification rather than bioavailability; total aromatic hydrocarbon content is difficult to distinguish between easily degradable and difficult-to-degrade components; and specific compound indicators exhibit high variability and lack systematic quantitative standards. Summary of the Invention

[0010] To address the shortcomings of the existing technologies, the purpose of this invention is to provide a coal classification method based on the biodegradability of organic matter in coal, thereby solving the problem that existing coal sample classification methods cannot directly characterize the initial degradation potential of microorganisms.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for classifying coal types based on the biodegradability of organic matter in coal includes the following steps: Coal samples to be classified were collected, soluble organic matter was extracted from the coal samples, and aromatic hydrocarbon components were separated.

[0012] The contents of six compounds—naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, biphenyl, and methylbiphenyl—in aromatic hydrocarbon components were quantitatively analyzed using gas chromatography-mass spectrometry, and the total aromatic hydrocarbon content was determined.

[0013] The above six classes of compounds all have bicyclic structures and a small number of substituents, representing typical components in coal that are easily biodegraded. Quantitative analysis was performed using the external standard method. Deuterated dibenzothiophene was the preferred external standard for aromatic hydrocarbon analysis. The linear correlation coefficient R of the standard curve was [value missing]. 2 ≥0.9999.

[0014] Based on the calculation of the biodegradation index f bio Formula: f bio =(C s / C total )×100%.

[0015] In the formula, C s This represents the sum of the contents of six compounds: naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, biphenyl, and methylbiphenyl, expressed in μg / g; C total The total aromatic hydrocarbon content is expressed in μg / g.

[0016] The biodegradation index f bio The coal samples are compared with preset thresholds, and the coal samples are classified into recalcitrant, moderately degradable, or easily degradable types based on the comparison results.

[0017] In a preferred embodiment of the present invention, soluble organic matter in the coal sample is extracted using Soxhlet extraction to extract dichloromethane extract, with dichloromethane as the extraction solvent and an extraction time of 72-120 h; aromatic hydrocarbon components are separated using liquid-liquid phase separation, with alumina and silica gel as the stationary phases, and a volume ratio of Valumina:Vsilica gel = 2:3; the eluent is a mixture of petroleum ether and dichloromethane, with a volume ratio of Vpetroleum ether:Vdichloromethane = 1:2.

[0018] In a preferred embodiment of the present invention, the gas chromatography-mass spectrometry analysis employs the external standard method for quantification, and the external standard for aromatic hydrocarbon analysis is deuterated dibenzothiophene.

[0019] In a preferred embodiment of the present invention, the preset threshold is determined by K-means clustering analysis, specifically including: collecting biodegradation index data of multiple known coal samples, performing K-means clustering after Z-score standardization, setting the number of clusters k=3, obtaining three cluster centers, and using the average value of adjacent cluster centers as the segmentation threshold.

[0020] In a preferred embodiment of the present invention, the preset threshold is determined by K-means clustering analysis. The specific steps are as follows: Biodegradation index data of multiple known coal samples are collected (it is recommended that the number of samples be no less than 50, covering different coal ranks); the data are standardized using Z-scores; K-means clustering iterative optimization is performed with a cluster size of k=3 to obtain three cluster centers; the arithmetic mean of adjacent cluster centers is used as the segmentation threshold. In a preferred embodiment, based on 69 sample data covering low-rank, medium-rank, and high-rank coals, the preset thresholds are: a first threshold of 3.5%, a second threshold of 8.9%; the coal sample classification standard is: when f bio When the content is <3.5%, it is classified as recalcitrant; when 3.5% ≤ f bio When the content is ≤8.9%, it is classified as moderately degradable; when f bio When the content is greater than 8.9%, it is classified as easily degradable.

[0021] In a preferred embodiment of the present invention, when the coal sample is recalcitrant, it indicates that the readily biodegradable aromatic hydrocarbon components are significantly lost and the initial degradation potential of microorganisms is low; when it is moderately degradable, it indicates that the readily degradable components are moderately preserved, possessing both degradation initiation potential and recalcitrant structure retention; when it is readily degradable, it indicates that the readily degradable components are intact and have strong biodegradability.

[0022] The following recommendations are made for the application of the above three types of coal samples in coal biogasification: easily degradable coal samples are suitable as preferred raw materials for direct biogasification; moderately degradable coal samples can have their gasification efficiency improved through pretreatment or microbial acclimatization; and difficult-to-degrade coal samples need to undergo physical or chemical pretreatment to increase the proportion of easily degradable components.

[0023] The application of the method described in this invention in the screening of raw materials for coal biogasification.

[0024] The application of the method in the screening of feedstocks for coal biogasification includes the following steps: Obtain coal samples to be screened and determine their biodegradability index f using the method described in any one of claims 1-5. bio The coal sample type was determined based on the classification criteria.

[0025] When the coal sample is easily degradable, it is directly selected as the preferred raw material for biogasification.

[0026] When the coal sample is of moderate degradation type, it is selected as a candidate raw material and pretreated or acclimated to microorganisms before biogasification to improve gasification efficiency.

[0027] When the coal sample is non-degradable, it should not be used as a feedstock for direct gasification, or it should be subjected to physical or chemical pretreatment to increase the proportion of easily degradable components before evaluation.

[0028] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention proposes and quantifies the innovative index of "relative content of easily biodegradable aromatic hydrocarbons in coal". From the complex aromatic hydrocarbon composition of coal, this invention specifically identifies six specific compounds: naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, biphenyl, and methylbiphenyl. These compounds all have bicyclic structures and few substituents, and are typical components that are most easily and preferentially degraded by microorganisms in coal. This avoids the problems of large variability and insufficient representativeness of single compounds in the prior art.

[0029] 2. This invention innovatively constructs a biodegradation index f. bio The ratio formula = (sum of contents of six easily degradable compounds / total aromatic hydrocarbon content) × 100% effectively eliminates the interference of differences in total aromatic hydrocarbon content among different coal samples, directly reflects the relative enrichment of the "easily degradable part" in the overall aromatic hydrocarbons, and overcomes the defect of existing technologies where the total content index cannot distinguish between easy and difficult degradation.

[0030] 3. This invention uses the K-means clustering algorithm to perform unsupervised learning on a large number of actual coal samples, and scientifically determines two quantitative thresholds of 3.5% and 8.9%, clearly classifying coal samples into three categories: difficult-to-degrade, moderately degradable, and easily degradable. This upgrades the originally vague qualitative judgment to a quantitative classification standard with clear data support, providing an intuitive basis for raw material screening for engineering applications.

[0031] 4. The coal sample types classified by the method of this invention are highly positively correlated with the actual methane production of biogasification. The cumulative methane production of easily degradable coal samples can reach more than 6 times that of difficult-to-degrade coal samples, which fully demonstrates the reliable guiding value of the method of this invention for the screening of coal biogasification feedstocks. Attached Figure Description

[0032] Figure 1 This is a flowchart of the coal classification method based on biodegradability according to the present invention.

[0033] Figure 2 The results are statistical findings for coal samples classified based on the biodegradation index. Detailed Implementation

[0034] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0036] Example 1 This embodiment provides a method for classifying coal types based on biodegradability, and the specific steps are as follows ( Figure 1 ): (1) Sample collection: Collect coal samples to be tested and record their origin, coal-forming age and petrographic characteristics. This example uses bituminous coal samples from a coal mine as an example.

[0037] (2) Extraction of soluble organic matter: The coal sample was crushed to pass through a 200-mesh sieve. 20g of coal sample was placed in a Soxhlet extractor and extracted with dichloromethane as solvent for 72h. The extract was concentrated by rotary evaporation and then transferred to a weighing bottle that had been weighed to constant weight. The extract was dried at 40℃ to constant weight and the weight of the dichloromethane extract (i.e., soluble organic matter) was measured. Each sample was repeated three times and the average value was taken.

[0038] (3) Separation of aromatic hydrocarbons: The dichloromethane extract (i.e., soluble organic matter) was dissolved in petroleum ether and filtered to remove asphaltenes. The chromatography column was packed with alumina and silica gel (volume ratio 2:3). Saturated hydrocarbons were eluted sequentially with 30 mL of petroleum ether, aromatic components were eluted with a mixture of 20 mL of petroleum ether and dichloromethane (volume ratio 1:2), and non-hydrocarbon components were eluted with 10 mL of dichloromethane. The aromatic eluent was collected, dried to constant weight, and then weighed.

[0039] (4) Chromatographic-mass spectrometry analysis: The separated aromatic hydrocarbon components were dissolved in chromatographic-grade dichloromethane, and deuterated dibenzothiophene internal standard was added. A full scan and selected ion monitoring were performed using gas chromatography-mass spectrometry. The chromatographic column was an HP5MS (30m × 0.25mm × 0.25μm). The temperature program was: initial temperature 60℃, held for 2 min, increased to 150℃ at 3℃ / min, and then increased to 300℃ at 5℃ / min, held for 15 min. Qualitative analysis was performed based on the retention time of the standard and characteristic ions. Quantitative analysis was performed using the external standard method to calculate the contents of six compounds: naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, biphenyl, and methylbiphenyl. The total aromatic hydrocarbon content was also calculated.

[0040] (5) Calculate the biodegradation index: according to formula (1) f bio =( C s / C total The coal sample in this embodiment is calculated by multiplying the product by 100%. f bio It is 6.72%.

[0041] (6) Classification: f bio =6.72% Compared with the preset thresholds of 3.5% and 8.9%, 3.5%≤6.72%≤8.9%, so the coal sample is classified as medium degradation type.

[0042] Example 2: Cluster Analysis with Determined Thresholds To determine the classification threshold, 69 coal samples covering different coal-forming epochs (Carboniferous, Permian, Jurassic, and Cretaceous) and different coal ranks (low, medium, and high rank) were collected. The biodegradation index of each coal sample was determined according to the method in Example 1. The obtained data ranged from 0.01% to 17.25%, with a mean of 3.12% and a standard deviation of 3.74%.

[0043] Z-score normalization was performed on 69 biodegradation index data: x' i =(x i μ) / σ. K-means clustering was performed with k=3, initial cluster centers were randomly selected, the maximum number of iterations was 100, and the convergence criterion was that the change in the sum of squares within each cluster was less than 0.001. After clustering, the standardized values ​​of the three cluster centers were obtained. The original percentages after destandardization were: cluster 1 center 0.76%, cluster 2 center 6.22%, and cluster 3 center 11.53%. The average value of adjacent cluster centers was calculated to obtain threshold 1 as (0.76+6.22) / 2=3.49% and threshold 2 as (6.22+11.53) / 2=8.875%. After rounding and fine-tuning, the final thresholds were determined to be 3.5% and 8.9%.

[0044] The 69 coal samples were divided according to the above thresholds. Figure 2 The results are shown in Table 1. This classification result is consistent with the coal rank evolution pattern, verifying the rationality of the threshold.

[0045] Table 1. Results of coal sample classification based on biodegradability Non-degradable 45 65.22 0.75 0.89 moderately degradable 18 26.09 6.22 1.69 biodegradable 6 8.70 11.55 1.78 Example 3: Application of the method in the screening of feedstocks for coal biogasification In a selected coal biogasification project, three coal samples were divided using the method of this invention. The three coal samples had similar basic properties (R o, max All had ash content of 0.77-0.83% and ash yield of 911%, but their biodegradability indices were 0.01%, 5.17%, and 9.48%, respectively. According to the method of this invention, S42 is a recalcitrant type, S66 is a moderately degradable type, and S25 is an easily degradable type. Figure 2 ).

[0046] Subsequent 30-day coal biogasification experiments were conducted using methanogenic bacteria. The results showed that the most readily degradable coal sample S25 had the highest cumulative methanogenesis, at 12.8 mL / g coal; the moderately degradable coal sample S66 was second, at 8.2 mL / g coal; and the least degradable coal sample S42 had the lowest, at only 2.1 mL / g coal. These results demonstrate that the coal sample types classified by the method of this invention have a good correlation with their actual biogasification potential, providing a reliable basis for the selection of feedstocks for coal biogasification processes.

[0047] Results Analysis Figure 1 This is a flowchart of the coal classification method based on biodegradability of the present invention. Based on the above six steps, a coal classification result diagram based on the biodegradability index of 69 coal samples is obtained. Figure 2 It can be seen that when f bio When the content is <3.5%, it is classified as recalcitrant; when 3.5% ≤ f bio When the content is ≤8.9%, it is classified as moderately degradable; when f bio When the content is >8.9%, it is classified as easily degradable. Among them, there are 45 recalcitrant coal samples, accounting for 65.22% of the total samples. bio The mean value was 0.75% ± 0.89%, mainly distributed in low-rank and high-rank coals. This type of sample accounted for the highest proportion, reflecting the characteristics of most coal samples having a low proportion of easily degradable components and limited initial microbial degradation potential under natural conditions. This is because low-cyclic and low-substituted aromatic hydrocarbons in low-rank coals are easily lost due to high volatility and early diagenesis, while high-rank coals are affected by thermal evolution leading to structural condensation, both significantly increasing the difficulty of initiating degradation. There were 18 moderately degradable coal samples, accounting for 26.09% of the total samples. bio The mean value was 6.22% ± 1.69%, mainly medium-rank coal, with a moderate total amount of readily degradable components, averaging 1.31 μg / g. This type of coal sample is in a transitional stage of coal rank evolution, with moderate preservation of readily degradable components, exhibiting both good potential for initiating microbial degradation and some retention of recalcitrant aromatic structures. There were 6 readily degradable coal samples, accounting for 8.70% of the total samples. bio The mean value was 11.55% ± 1.78%, which was also concentrated in medium-rank coal. The total amount of easily degradable components was the highest, with an average of 2.86 ug / g, indicating that the low-cyclic and low-substituted aromatic hydrocarbons of this type of coal sample were relatively well preserved and had the strongest biodegradability.

[0048] Overall, the distribution of the three types of coal samples showed a significant imbalance, with recalcitrant coals dominating and readily degradable coals being scarce. This distribution pattern is closely related to the evolution of coal rank; readily biodegradable low-cyclic aromatic hydrocarbons are mainly enriched in medium-rank coals, while they are largely lost in low-rank and high-rank coals due to early diagenetic volatilization and thermal evolution condensation, respectively. This classification not only validates the rationality of the threshold setting but also provides a basis for differentiated samples for subsequent synergistic degradation experiments.

[0049] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0050] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for classifying coal types based on the biodegradability of organic matter in coal, characterized in that, Includes the following steps: Coal samples to be classified were collected, soluble organic matter was extracted from the coal samples, and aromatic hydrocarbon components were separated. The contents of six compounds, namely naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, biphenyl and methylbiphenyl, in aromatic hydrocarbon components were quantitatively analyzed by gas chromatography-mass spectrometry, and the total aromatic hydrocarbon content was determined. Based on the calculation of the biodegradation index f bio Formula: f bio =(C s / C total )×100%; In the formula, C s This represents the sum of the contents of six compounds: naphthalene, methylnaphthalene, ethylnaphthalene, dimethylnaphthalene, biphenyl, and methylbiphenyl, expressed in μg / g; C total The total aromatic hydrocarbon content is expressed in μg / g. The biodegradation index f bio The coal samples are compared with preset thresholds, and the coal samples are classified into recalcitrant, moderately degradable, or easily degradable types based on the comparison results.

2. The coal classification method based on the biodegradability of organic matter in coal according to claim 1, characterized in that, Soluble organic matter in coal samples was extracted using Soxhlet extraction to extract dichloromethane extract. The extraction solvent was dichloromethane, and the extraction time was 72-120 h.

3. The coal classification method based on the biodegradability of organic matter in coal according to claim 1, characterized in that, Gas chromatography-mass spectrometry analysis was performed using the external standard method for quantification. The external standard for aromatic hydrocarbon analysis was deuterated dibenzothiophene.

4. The coal classification method based on the biodegradability of organic matter in coal according to claim 1, characterized in that, The preset threshold was determined by K-means clustering analysis, which specifically included: collecting biodegradation index data of multiple known coal samples, performing K-means clustering after Z-score standardization, setting the number of clusters k=3, obtaining three cluster centers, and using the average value of adjacent cluster centers as the segmentation threshold; The preset thresholds are: a first threshold of 3.5% and a second threshold of 8.9%; the coal sample classification standard is: when f bio When the content is <3.5%, it is classified as recalcitrant; when 3.5% ≤ f bio When the content is ≤8.9%, it is classified as moderately degradable; when f bio When the content is greater than 8.9%, it is classified as easily degradable.

5. The coal classification method based on the biodegradability of organic matter in coal according to claim 1, characterized in that, When the coal sample is classified as recalcitrant, it indicates that the readily biodegradable aromatic hydrocarbon components are significantly lost and the initial degradation potential of microorganisms is low; when it is classified as moderately degradable, it indicates that the readily degradable components are moderately preserved, possessing both degradation initiation potential and recalcitrant structure retention; when it is classified as readily degradable, it indicates that the readily degradable components are intact and the biodegradability is strong.

6. The application of the method according to any one of claims 1-5 in the screening of feedstock for coal biogasification.

7. The application of the method according to claim 6 in the screening of feedstock for coal biogasification, characterized in that, Includes the following steps: Obtain coal samples to be screened and determine their biodegradability index f using the method described in any one of claims 1-5. bio And determine the coal sample type according to the classification criteria; When the coal sample is easily degradable, it is directly selected as the preferred feedstock for biogasification. When the coal sample is of moderate degradability, it is selected as a candidate raw material and pretreated or acclimated to microorganisms before biogasification to improve gasification efficiency. When the coal sample is non-degradable, it should not be used as a feedstock for direct gasification, or it should be subjected to physical or chemical pretreatment to increase the proportion of easily degradable components before evaluation.

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