Pyrolysis characteristics and hydrogen production process of lignite at different heating rates
Hydrogen production from coal is currently the main source of hydrogen in China.The study on the pyrolysis reactions and hydrogen production mechanisms of lignite under different temperature conditions is crucial to improving hydrogen yield,optimizing process flow,and ensuring efficient and clean utilization of lignite.Based on the research ideas of experimental test,molecular simulation and theoretical analysis,this paper studies the pyrolysis process of Xianfeng lignite by thermal analysis,infrared gas chromatography-mass spectrometry(TG-FTIR-MS)experimental test and molecular dynamics simulation(ReaxFF MD).The main pyrolysis products at different heating rates(10 ℃/min,20 ℃/min,and 30 ℃/min)are analyzed,especially the generation characteristics of hydrogen gas.In addition,the pyrolysis route of hydrogen atoms is calibrated.Finally,the molecular mechanism of hydrogen generation by lignite pyrolysis is explored from multiple perspectives.And the following research results are obtained.First,the final weight loss rates of lignite pyrolysis at different heating rates are close.The higher the heating rateis,the easier the reaction becomes.Second,at 20℃/min,the gas products of lignite pyrolysis are the most abundant,with small molecular gases such as CO2 and H2 as the main compositions.The total amount of gas precipitation shows a trend of first increasing and then decreasing with the increase of the heating rate.Third,the generation process of hydrogen gas mainly involves the shedding of hydrogen atoms from the fatty chain to generate hydrogen radicals,which combine together to form hydrogen gas.In conclusion,the precipitation process of hydrogen gas by lignite pyrolysis is divided into three stages.In the first stage,the temperature is about 350-700℃,and hydrogen gas is generated slowly,which is mainly the combination of broken methyl C-H bonds and the hydroxyl O-H bonds.In the second stage,the temperature ranges from 700℃ to 900℃,and hydrogen gas is generated rapidly,which is associated with the reaction of hydrogen bond cleavage in carboxyl functional groups,fatty hydrocarbon structures and pyrrole structures.In the third stage,the temperature is over 900℃,and a large amount of hydrogen gas is generated,which is characterized by the increase of hydrogen-free radicals in aromatic structures.
Xianfeng ligniteCoal pyrolysisHydrogen production processMolecular dynamicsHeating rateTG-FTIR-MS
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