玉米秸秆主要共价键含量及热解过程中自由基生成特征研究OA

As pyrolysis serves as the important technology for the comprehensive utilization of corn stalks(hereinafter referred to as"stalks"),the process follows a free radical reaction mechanism.Understanding the compositions of covalent bonds in stalks and the generation characteristics of free radicals during pyrolysis is of great significance for elucidating the underlying mechanisms of free radical reactions and their relationships with organic structures,thereby contributing to the optimization of pyrolysis processes.The contents of major covalent bonds in stalks were calculated based on elemental analysis and carbon skeleton structural parameters derived from 13C NMR characterization.9,10-dihydroanthracene was employed as a molecular probe to indirectly quantify the formation of active free radicals during pyrolysis.Additionally,the numbers and g-values of stable free radicals formed after pyrolysis were determined using electron spin resonance(ESR)spectroscopy.The results show that the contents of Cal—Cal and Car—Car in stalks are 28.47 mmol/g and 4.95 mmol/g,respectively,with Cal—O(with a content of up to 28.57 mmol/g)as the dominant C—O type.The concentration of active free radicals(cR-A)gradually increases with higher temperature and longer residence time,reaching 4.60 mmol/g to 29.44 mmol/g after 12 min of pyrolysis at 300℃to 420 ℃.During pyrolysis of stalks,weak bonds such as β-O—Cal and β-Cal—Cal are likely to be cleaved,generating active free radicals primarily consisting of aliphatic carbon radicals,oxygen radicals bonded to aromatic carbons,and aliphatic carbon radicals bonded to aromatic carbons.As the pyrolysis of stalks proceeds,the concentration of stable free radicals first increases rapidly,then decreases slowly,and finally increases slightly again.Large-sized active radicals of aromatic structures(especially·Cal—Car)are more likely to transform into stable free radicals during coupling.The g-value of newly formed stable free radicals gradually decreases with the extension of pyrolysis time,with more oxygen-containing radicals.