Yunnan Provincial Key Laboratory of Soil Carbon Sequestration and Pollution Control, Faculty of Environmental Science & Engineering, Kunming University of Science & Technology, Kunming 650500, China.
Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China.
Environ Sci Technol. 2020 Oct 20;54(20):13274-13281. doi: 10.1021/acs.est.0c03363. Epub 2020 Oct 2.
Persistent free radicals (PFRs) may cause negative impacts to human health and the environment because of the induced reactive oxygen species. We expect that PFRs could be generated in the condensable volatiles formed during lignocellulose biomass pyrolysis. Elucidating the structural origin and the formation mechanism of PFRs is important for an in-depth understanding of air pollutants from the pyrolysis or combustion of lignocellulose biomass. This work selected rice straw and pine sawdust to represent agricultural and forest biomass residues. The pyrolysis mechanism, volatile components, and PFR generation were discussed based on the analysis of thermogravimetry-Fourier transform infrared spectroscopy-mass spectrometry (MS), pyrolysis-gas chromatography/MS, and electron spin resonance (ESR). Levoglucosan, furans, and 2-methoxyphenols were the main pyrolytic compounds for cellulose (CL), hemicellulose (HC), and lignin (LG), respectively. Obvious ESR signals were detected in the condensable volatiles of LG, while no ESR signals were detected for those of CL and HC. Higher ESR signals were detected in lignocellulose with a higher content of LG. Therefore, LG was the main structural basis to generate PFRs in lignocellulose condensable volatiles, mostly attributed to the methoxyphenol components. This study provides useful information regarding the generation mechanisms of and the structures related to PFRs, which is essential to understand the risks of lignocellulose pyrolytic volatiles.
持久性自由基（PFRs）可能会因诱导的活性氧物种对人类健康和环境造成负面影响。我们预计，在木质纤维素生物质热解过程中形成的可冷凝挥发物中会产生 PFRs。阐明 PFRs 的结构起源和形成机制对于深入了解木质纤维素生物质热解或燃烧产生的空气污染物非常重要。本工作选择稻草和松木屑来代表农业和林业生物质残余物。通过热重-傅里叶变换红外光谱-质谱（MS）、热解-气相色谱/MS 和电子自旋共振（ESR）分析，讨论了热解机制、挥发物成分和 PFR 的生成。左旋葡聚糖、呋喃和 2-甲氧基苯酚分别是纤维素（CL）、半纤维素（HC）和木质素（LG）的主要热解化合物。在 LG 的可冷凝挥发物中检测到明显的 ESR 信号，而在 CL 和 HC 的可冷凝挥发物中未检测到 ESR 信号。木质纤维素中 LG 含量越高，ESR 信号越强。因此，LG 是木质纤维素可冷凝挥发物中产生 PFRs 的主要结构基础，主要归因于甲氧基苯酚成分。本研究提供了有关 PFRs 生成机制和结构的有用信息，对于理解木质纤维素热解挥发物的风险至关重要。
