Investigation on parameters optimization to produce hydrochar without carbohydrate carbon

Owing to its superior energy-saving function and strong potential to be applied as a soil amendment and fertilizer, hydrochar has gained wide attention in recent years. However, hydrochar contains greater amounts of labile fractions than traditional biochar and may exacerbate the short-term greenhouse effect. To lower the risk of greenhouse gas release due to labile fractions, optimize parameters must be determined to produce hydrochar without carbohydrate carbon. In addition, the effects of varying feedstocks and process conditions on hydrochar structure as well as its dissolved organic matter (DOM) must be investigated. Spartina alterniflora and pig manure were used to produce two hydrochars (HSAs and HPMs) and their corresponding DOM samples (DSAs and DPMs) at various production temperatures (T_p) and reaction times (t_r). The carbohydrate vanishing points (CVPs) were 265 °C-1 h, 250 °C-2 h, and 245 °C-4 h for the HSAs and 260 °C-1 h, 250 °C-2 h, and 250 °C-4 h for the HPMs. With the isolation of DOM, 1.09-4.33% organic carbon of the hydrochar was released. The aromaticity of DSAs decreased with increasing T_p and t_r. The molecular weights of the DSAs and DPMs decreased with increasing T_p and t_r. This study uncovered hydrochar's molecular structure as well as the content and properties of its labile fractions. Results can be used to help design specific hydrochars for potential applications, based on the trend of the molecular change under the condition of the studied parameters optimization to produce hydrochar in this study.