Effect Of Thermal Treatment With Aromatic Solvent Of Zhundong Coal On Its Structure And Distribution Of Hydrogenation Liquefaction Products

Coal hydrogenation liquefaction is an important way to clean and efficiently use low-rank coal in modern coal chemical industry.It can transform solid coal into liquid fuel with higher utilization value,which is of great significance to China's energy security.In recent years,Zhundong coal mined in the Zhundong area of Xinjiang is an ideal raw material for Coal hydrogenation liquefaction,due to its large reserves and good reactivity.However,its high sodium ion content leads to a low yield of liquefied oil,which greatly limits its application range.Therefore,this paper selects Zhundong sodium-rich coal as the Experiment research object,and systematically studies the change of physicochemical structure of Zhundong coal in the solvent thermal treatment process and its influence on the subsequent liquefied product distribution.In view of the changes in the physicochemical structure of Zhundong coal,this paper uses thermogravimetric coupled with Fourier transform infrared spectroscopy to study the effect of solvent thermal treatment on the physicochemical structure and pyrolysis performance of coal samples.The main conclusions are as follows:?1?The exchangeable sodium was loaded into the coal matrix by ion exchange treatment to study its behavior during the thermal conversion process.After ion exchange treatment,the maximum mass loss of the coal sample becomes smaller,the crosslinked structure in the coal is enhanced,and the coal matrix structure is more compact.However,the skeleton structure of Zhundong coal has not changed significantly and the relative proportion of its amorphous carbon structure and macro aromatic ring system is almost unchanged.?2?After the solvent thermal treatment,the surface of the Zhundong coal becomes rough and the specific surface area increases,but the macromolecular skeleton structure is not affected,and only some of the carboxyl groups are decomposed.After the solvent thermal treatment,most of the sodium ions are retained in the coal,but the content of it form is changed.The exchangeable sodium ion content associated with the coal organic matter decreased,while the water-soluble sodium ion content increased.?3?Due to the extraction of small molecular substances in the mobile phase,the macromolecular structure of Zhundong coal becomes loose and rearranged,resulting in more volatile substances.Because of that,weight loss and weight loss rate of the treated coals sample are higher than the raw coal.The gas components released during the pyrolysis process are mainly CO,CO₂,H₂O and CH₄.Due to the hydrogen supply of tetrahydronaphthalene,the tetrahydronaphthalene pretreated coal samples release more CH₄ and H₂O,and the amount of CO₂ released from the pretreated coal samples is significantly reduced due to the decomposition of some carboxyl groups during solvent thermal treatment.?4?As a result of the increase in specific surface area and the decrease in the exchangeable sodium ion content,the direct liquefied oil yield of the solvent thermal treated coal is significantly improved.As a good hydrogen supply solvent,tetrahydronaphthalene can pre-hydrogenate the coal matrix during the pretreatment process,resulting in significantly higher oil yield than methyl naphthalene pretreated coal samples.The extraction of short chain hydrocarbons in the mobile phase results in a decrease in the gas yield of the solvent thermal treated coal.Considering the liquefied product yield and economic benefits,the optimal solvent thermal treatment conditions for Zhundong coal are:?1?solvent:tetrahydronaphthalene or other hydrogen-rich solvent;?2?temperature:200-250?;?3?atmosphere:nitrogen.