Comparison of structural characteristics and combustibility analysis about hydrochar and pyrochar

Abstract

The structure characteristics and combustibility of pyrochar and hydrochar were compared using scanning electron microscopy, nitrogen adsorption, Fourier transform infrared spectrum, Raman spectrum and thermogravimetry. The random pore model was applied to analyze the combustion process of chars. With the temperature increasing, analysis of physical structure revealed that the pore structure of hydrochar was more developed than that of pyrochar. Meanwhile, the hydrothermal process had an advantage over pyrolysis in terms of removing oxygen-containing functional groups and improving the coal rank, mainly attributed to the existence of subcritical water. In addition, the high determination coefficient of random pore model indicated that the model could accurately obtain the kinetic parameters. The activation energies calculated of hydrochars were higher than that of pyrochars, indicating that carbon in hydrochar had a more structural stability. The pyrochar obtained after 220 °C was less combustible than hydrochar due to its severe pore collapse during the combustion process.

Machine learning and computational chemistry to improve biochar fertilizers: a review

“…The experiments were conducted at 216 °C, with retention times ranging from 2 to 4 h, using sewage sludge with 80% moisture content as the feedstock. The results showed that regardless of the retention time, the weight-based yield of pyro-char was 19% higher than that of hydrochar, which aligns with the findings of Huang et al (2022a;. The findings from Arauzo et al (2020) and Huang et al (2022a; indicate that pyro-char undergoes more significant modifications, as evidenced by pyro-char's higher fixed carbon content compared to hydrochar produced under the same temperature conditions.…”

“…The results showed that regardless of the retention time, the weight-based yield of pyro-char was 19% higher than that of hydrochar, which aligns with the findings of Huang et al (2022a;. The findings from Arauzo et al (2020) and Huang et al (2022a; indicate that pyro-char undergoes more significant modifications, as evidenced by pyro-char's higher fixed carbon content compared to hydrochar produced under the same temperature conditions. Additionally, the higher heating value of pyro-char surpasses that of hydrochar due to the formation of 5-hydroxymethylfurfural from cellulose and hemicellulose in the liquid phase of the biomass, along with the presence of an aromatic outer-layer structure (Arauzo et al 2020).…”

“…Moreover, Huang et al (2022a; observed that pyrochar generally possesses larger pore diameters than hydrochar. The pore diameter for pyro-char ranged from 8.96 to 20.43 nm, while for hydrochar, it was recorded as 8.36-15.66 nm.…”

“…Metal modification is also a standard post-treatment method, and biochar doped with metal nanoparticles typically exhibits higher phosphorus removal rates than unmodified biochar. Iron-modified biochar materials significantly affect phosphorus adsorption (Huang et al 2022a;. There are two standard methods for modifying loaded metal elements.…”