The PAHs In The Raw Coal Extracts And Their Pyrolysis Properties

Some PAHs have been formed during the coal ultilization. Researchers at home and abroad have payed much attention on the PAHs'formation, transportation and control due to its potential harm to the human-being and the environment. This study put the key on the 16 PAHs extracted from the raw coals in order to know the mechanism of PAHs'formation.15 different rank coals from lignite to anthracite were collected and extracted by the Gerhardt Soxtherm maro 414 with the dichloromethane. Then the quality and quantity of the 16 PAHs in the extraction were analyzed by the GC-MS. From the analysis results, the relationships of the carbon content, the volatile yields, the O/C, the H/C and the PAHs were gotten. Then the extracts were pyrolyzed at different temperature and the yields were analyzed by the GC-MS, and the variation trends of the PAHs were concluded.1. Looked into the Gerhardt Soxtherm macro 414 Soxhlet parameters to ensure that the PAHs can be extracted fully from the raw coals by the CH2Cl2. The rapid Soxhlet extraction have the characters of higher efficiency, less time, higher recovery efficiency of the solvent compared to the traditional Soxhlet extraction. The results of the Soxhlet extraction present that the extraction efficiency of CH2Cl2 decrease as the coalification of the coal increase, and the extraction efficiency of CH2Cl2 not be accordant with the PAHs percentage in the extracts, which is decided by the coal rank.2. The amount of the PAHs in extracts from the raw coals increase as the carbon content increase,the peak point at the carbon content being 80.41% then decrease and vary steadily as the carbon content higher than 86.46%; The amount of the PAHs in the middle rank coal are higher than that in lower and higher coals.3. The tendancy of the relationship between volatile yield and the PAHs amount is contrary to that the relationship between carbon content and the PAHs amount. The PAHs amount vary obviously at the volatile yields about 35%, and achieve to the peak point at the volatile yields being 37.19%; The amount of the PAHs in the lower and high coals are relatively small compared to the middle rank coal; The relationship between H/C ratio and the amount of the PAHs don't obey a principle. The amount of the PAHs came to the maximum at the O/C ratio being 0.1.4. Except for the coals the carbon content varying from 86.46%-89.47, the volatile yields being 9.84%-22.31%, the amount of the low-ring PAHs are higher than high-ring PAHs in the coals. The amount of the different-ring PAHs in the coals doesn't obey a principle as the H/C ratio increasing. The O/C ratio could regard parameters to evaluate the high-ring PAHs in the extracts for their obeying a trend. But it couldn't work for the three-ring PAHs. 5. The extracts are pyrolyzed at the different temperature, and main conclusions are as the followings: The amount of the PAHs achieve to the maximum at 300℃. The free PAHs in the raw coals release at 200℃. And the tendancy of the relative amount is similar to the that of the PAHs amount in the raw coals; The high-ring PAHs in the extracts can be decomposed into low-ring PAHs; The amount of the PAHs achieve to another peak point at the temperature in the area of 1000℃-1400℃;There are no high-ring PAHs formed during the pyrolysis, On the whole, the high-ring PAHs in the raw coals are higher than the low-ring ones but them may be cracked into low ring PAHs during extracts pyrolysis and the high-ring PAHs may be from the decoposition of macromoleclar structure during coal pyrolysis.