Effect Of Extracts In Coal On The Structure And Pyrolysis Behaviours Of Coal

China is rich in coal resources but is relatively short of oil and natural gas with a higher Degree of Dependence on Foreign and need to import for a long time.China's energy resource structure of“rich coal,poor oil and less gas”,determines that coal has long dominated China's energy consumption as the major energy resource.The proportion of coal in China's primary energy consumption was about 70%.Xinjiang is located in the border area with vast territory and abundant coal resources in China.The total amount of resources predicted is about 22,000 million tons,accounting for about 40%of the country.The coal is rich in aromatic hydrocarbon structure,especially condensed multi-ring and heterocyclic ring,which is beneficial to the preparation of high-value chemicals.The clean and efficient utilization of coal can promote local economic development and guarantee national energy security.In the process of coal conversion,pyrolysis is a key step.It's necessary to further understand the pyrolysis process of coal that can promote the development of technologies of liquid fuels and chemicals made from coal.Based on the two-phase model of coal,the main line“Network Structure Model of Coal–Structure and Pyrolysis Behavior of Residue and Swollen Coal–Composition and Characteristics of Products”was investigated.The Naomaohu lignite,Yili sub-bituminous coal and Hutubi non-caking coal in Xinjiang area were selected and pretreated with 20%CH₃COOH for 48h,and then extracted with pyridine and swollen with its solvent vapor,respectively.The structural characterization and pyrolysis experiments of residue and swollen coal were carried out.By analyzing the changes of structure and pyrolysis behavior,the effect of extracts in coal on the structure and pyrolysis behavior of coal were investigated,and the results are as follows:?1?The raw coals were pretreated by 20%CH3COOH to exchange and reduce the metal cations in coal,e.g.Ca²⁺,Mg²⁺,Na⁺,K⁺,that destroy the ionic bond in coal,and improve the pore structure of the coal to a certain extent and increases the average pore diameter of the coal.As the organic acid,the pretreatment could remove the carbonate minerals in the coal,where limited change the covalent bond in coal,and promote the pyrolytic reaction of coal.?2?As a solvent,pyridine is a good extraction solvent of coal and can obtain a higher extraction yield.Meanwhile,pyridine is a good acceptor of hydrogen bond,and could destroy the hydrogen bond and the cross-linking structure of coal during the swelling process.The smaller the particle size of the coal particles and lower the extraction yield,the higher the content of aliphatic and oxygen-containing groups in the extract,the more soluble small molecule compounds.After the extraction treatment,the average pore size of coal was increased to some extents,and the porosity of coal was improved,where the effects of swelling are opposite.?3?The results of the pyrolysis experiment indicated that the tar yield of swollen coals increased,where the tar yield of residue reduced obviously and that of gas yield increased obviously.The removal of the extract not only reduces the yield of the pyrolysis tar of the coal,but also greatly reduces the proportion of the micropore structure of the char,owing to the extraction process reduces the microporous structures of residue.At the same time,the new microporous structures produced by the decomposition and polycondensation of the extracts were reduced during the pyrolysis process.The extracts are an important part of coal and can be easily depolymerized,which has important influence on coal pyrolysis process.The effects of extracts in situ?swollen coal?and missing?residue?states on the structure and pyrolysis behaviours of coal are compared and analyzed by selective fracture of non-covalent bonds?e.g.,hydrogen bonds and hydrogen bonds?in coal.The above study shows that the pretreatment effectively destroys the ionic bond in coal with low-concentration organic weak acid,and the swelling process destroys the cross-linking structure of coal,increases the pore diameter of coal,and reduces the polycondensation reaction.When the extracts were extracted,the extraction process also loosed the macromolecular network structure of coal,formed macroscopic porosity,which is conducive to the diffusion of volatile components.The extracts have an important effect on the tar produced from pyrolysis of coal,which is an important source of the formation.The liquid-phase products?colloids?from extracts can stabilize the free radical fragments and reduce the secondary reaction.The cracking of extracts increases the proportion of the micropore structure of the char.