Abstract Hydrochars of cotton stalk (CS) at the hydrothermal temperature of 180−280 °C and the retention time of 0−120 min were used for the purpose of developing fuel pellets. Subsequently, the physical properties and combustion characteristics of the hydrochar pellets were evaluated to assess the solid biofuel production potential. Then, the hydrochar samples were analyzed by FTIR, TGA, XRD, and SEM, aiming to investigate the evolution mechanism of the chemical compositions (hemicellulose, cellulose, and lignin) with the increasing hydrothermal temperatures and their effects on the compressive strength of the hydrochar pellets. The results indicated that the hydrochar pellets exhibited higher fixed carbon contents, elevated heating values, enhanced physical properties, and more stable combustion characteristics than the raw biomass pellets. Moreover, the skeleton structure of the crystalline cellulose was the critical factor affecting the compressive strength of the hydrochar pellets. In parallel, lignin was observed to be beneficial for fabricating solid bridges and also exhibited a substantial influence on the bonding performance. However, the crystalline cellulose completely decomposed into amorphous carbon, and the high carbonization degree of the lignin caused it to lose its bonding capacity, which led to a sharp decrease in the compressive strength of the hydrochar pellets pretreated at 280 °C to 2.9 MPa, lower than the CS pellets (4.2 MPa). Finally, the pictorial depiction of the chemical components’ structural characteristics exhibited in the hydrothermal carbonization process was displayed along with their influences on the hydrochar densification process.

中文翻译：

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Hydrochar 颗粒的抗压强度与化学成分之间的相关性：演化和致密化机制

摘要 以水热温度 180~280 °C、停留时间 0~120 min 的棉秆 (CS) 水炭为研究对象，用于开发燃料芯块。随后，评估了氢化碳颗粒的物理特性和燃烧特性，以评估固体生物燃料的生产潜力。然后，通过FTIR、TGA、XRD和SEM对水炭样品进行分析，旨在研究化学成分（半纤维素、纤维素和木质素）随水热温度升高的演变机制及其对水炭抗压强度的影响。颗粒。结果表明，与生物质颗粒相比，氢化炭颗粒表现出更高的固定碳含量、更高的热值、增强的物理性能和更稳定的燃烧特性。此外，结晶纤维素的骨架结构是影响水炭颗粒抗压强度的关键因素。同时，观察到木质素有利于制造实心桥，并且对粘合性能也有显着影响。然而，结晶纤维素完全分解为无定形碳，木质素的高碳化程度使其失去结合能力，导致280℃预处理的水焦颗粒的抗压强度急剧下降至2.9 MPa，低于 CS 颗粒 (4.2 MPa)。最后，展示了水热碳化过程中化学成分结构特征的图形描述以及它们对水热碳化过程的影响。结晶纤维素的骨架结构是影响水炭颗粒抗压强度的关键因素。同时，观察到木质素有利于制造实心桥，并且对粘合性能也有显着影响。然而，结晶纤维素完全分解为无定形碳，木质素的高碳化程度使其失去结合能力，导致280℃预处理的水焦颗粒的抗压强度急剧下降至2.9 MPa，低于 CS 颗粒 (4.2 MPa)。最后，展示了水热碳化过程中化学成分结构特征的图形描述以及它们对水热碳化过程的影响。结晶纤维素的骨架结构是影响水炭颗粒抗压强度的关键因素。同时，观察到木质素有利于制造实心桥，并且对粘合性能也有显着影响。然而，结晶纤维素完全分解为无定形碳，木质素的高碳化程度使其失去结合能力，导致280℃预处理的水焦颗粒的抗压强度急剧下降至2.9 MPa，低于 CS 颗粒 (4.2 MPa)。最后，展示了水热碳化过程中化学成分结构特征的图形描述以及它们对水热碳化过程的影响。