# Analysis of the Organic Chemical Fractions of Three Coal Extracts
## 1 Introduction  
Coal is generally formed by the long-term deposition of plant remains by physico-chemical biology and other long-term actions; the composition inside the coal is complex, and most coals have a high content of organic matter [1, 2]. Because some of the aromatic hydrocarbons contain a certain degree of toxicity, the human body and the environment suffer greater harm [3, 4], which has become a major problem in the clean utilization of coal. China is a large coal-producing country, mainly concentrated in Shaanxi, Shanxi, and other northwestern regions, and coal is an indispensable resource for us [5]. Therefore, the clean and efficient use of coal requires the removal of toxic or hazardous substances from the coal. To achieve this goal, the principle of similar solubility [6, 7], with the help of various types of substances in coal in different solvents with different solubilities, will be utilized for the extraction of coal resources for \"purification\" treatment [8]. Solvent extraction has been the most commonly used method to dissolve organic substances in coal over the years [9, 10]. [PERSON]. [11] used NMP solvent to extract Indian coking coal after ultrasonic or microwave pre-treatment and used EDA as a co-solvent. The final extraction results showed that the clean coal yield reached the highest, compared with the extraction effect of the untreated coal, which increased by 4%. [PERSON] [12] showed that DME had the shortest extraction time, the lowest energy consumption and the highest extraction rate (16.2%) by Soxllet extraction of direct coal liquefaction residue at room temperature. The extracts obtained by liquefying DME and acetone were characterizedby high carbon, low sulfur, low oxygen, and low ash (<0.1%), which finally showed that liquefied DME has the advantages of low energy consumption, short extraction time, high extraction rate, and high extractant properties, and it is a highly efficient and economical solvent for extracting DCLR. [PERSON] [13] extracted bituminous coal by using a solvent mixture of CS\({}_{2}\) and acetone, with a final extraction rate of about 12%. The extracted material is mainly alkanes, aromatic hydrocarbons, olefins, and some heteroatomic compounds, of which the aromatic hydrocarbons have the highest content, accounting for 76% of the total extract, and most of them are aromatic hydrocarbons with two and seven rings. When the number of times of extraction is increased, the extracted substances' molecular weight increases. Researchers usually use gas chromatography-mass spectrometry (GC-MS) technology to detect the composition of extracts after the extraction of coal. GC is a separation technology that can separate substances according to the differences in their boiling points, but it provides little information about the detection of substances and cannot be used to detect unknown compounds alone. MS, in contrast, happens to be an excellent detector; MS converts substances to charged ions through an ionization source, and MS sends substances to a detector through the ionization source. The detector, which detects and identifies the substances according to the difference in their mass-to-charge ratios, finally obtains the mass spectra of each compound by comparing them with a database and then determines the type and content of the substances according to their mass spectra. Therefore, GC-MS is one of the most commonly used methods for the detection of unknown compounds [14; 15; 16]. [PERSON] [17] carried out Soxhlet extraction, ultrasound-assisted extraction, and microwave-assisted extraction of Daxing coal with carbon tetrachloride. The extracted fractions were analyzed by gas chromatography-mass spectrometry (GC-MS), and the GC-MS analysis showed the following: (1) The SE method extracted the least amount of substances from the coal; on the other hand, most of the extracted compounds were chlorinated, which can be explained by the free radical mechanism. (2) MAE extracted 75 organic compounds, of which 53 were oxygenated substances.