Abstract The effects of vacuum freeze drying (VFD) pretreatment on poplar (PP), switchgrass (SG), and wheat straw (WS) biochar properties were studied in a muffle at air atmosphere with varied final pyrolysis temperatures (300, 500, and 700 °C). Conventional drying (CD) was used as control. As final pyrolysis temperatures increased, biochar yields from both CD- and VFD-pretreated PP, SG, and WS decreased, and yields from VFD-pretreated biomass were lower than those from CD-pretreated biomass. As temperatures increased, the pH of CD-pretreated biochar increased, while the pH of VFD-pretreated biochar did not significantly change. Higher pyrolysis temperatures increased carbon contents in all biochar. According to Fourier-transform infrared spectroscopy (FTIR), CD and VFD pretreatment had a significant effect on biochar’s functional groups. Compared to CD pretreatment, VFD-pretreated materials and biochar have an intact porous surface structure and VFD-pretreated biochar contain more micropores, suggesting that VFD pretreatment could generate high-quality porous biochar.

中文翻译：

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真空冷冻干燥预处理对生物质和生物炭特性的影响

摘要 真空冷冻干燥 (VFD) 预处理对杨树 (PP)、柳枝稷 (SG) 和小麦秸秆 (WS) 生物炭特性的影响在马弗炉中在不同最终热解温度 (300、500 和 700 ℃）。常规干燥 (CD) 用作对照。随着最终热解温度的升高，CD 和 VFD 预处理的 PP、SG 和 WS 的生物炭产量下降，并且 VFD 预处理的生物质的产量低于 CD 预处理的生物质的产量。随着温度升高，CD预处理的生物炭的pH值增加，而VFD预处理的生物炭的pH值没有显着变化。较高的热解温度增加了所有生物炭中的碳含量。根据傅里叶变换红外光谱 (FTIR)，CD 和 VFD 预处理对生物炭的官能团有显着影响。