Correlations between the physicochemical properties of hydrochar and specific components of waste lettuce: Influence of moisture, carbohydrates, proteins and lipids.

This study aims to figure out the influence of moisture content and chemical constitution, i.e. carbohydrates, proteins and lipids, of waste lettuce on the physicochemical structure of hydrochar produced via hydrothermal carbonization. The experimental results showed that homogenized carbon material can be obtained by hydrothermal treatment, regardless of the moisture content of feedstock. During the hydrothermal carbonization process of waste lettuce, carbohydrates were the most active reactants contributing to hydrochar formation. Meanwhile, Maillard reaction between proteins and carbohydrates occurred, which promoted the aromatization of the organic intermediates and increased the relative content of nitrogenous heterocyclic functional groups on the surface of hydrochar from 10.7 to 18.7%. Different from these two constitution, lipids did not participate in the carbonization reaction, the main hydrolyzates of lipids were adsorbed to the surface of hydrochar, leading to an increase in the mass of solid products.

Correlations between hydrochar properties and chemical constitution of orange peel waste during hydrothermal carbonization.

For efficient hydrothermal treatment of biomass, this study aims to figure out the correlations between complex chemical constitution of orange peel (OraPeel) as typical bio-waste and the physicochemical structure of its derived hydrochar, which could be utilized to adjust hydrochar properties for specific applications (e.g., adsorbent, fuel) by regulating respective proportions of each component in bio-waste. Cellulose, hemicellulose and lignin were used as the control variables of feedstocks composition in this work. After hydrothermal process, lignin added feedstock produced more hydrochar, which contained rougher surface with nearly doubled BET areas and more benzene rings. Hemicellulose-aided hydrochar possessed higher density of carbonaceous microspheres and richer hydroxyl. This char was simultaneously covered by more esters or lactones with more aromatic oxygen-containing groups inside. Similar to hemicellulose, cellulose improved the formation of diverse oxygenous groups but reduced the size of microspheres on hydrochar.