Chemical and structural properties of carbonaceous products obtained by pyrolysis and hydrothermal carbonisation of corn stover

TLDR

Long‑term carbon sequestration requires detailed study of soil responses and residence times of the chars, particularly hydrochar. The study examined the main properties of corn stover chars produced by pyrolysis at 550 °C or by hydrothermal carbonisation. Chars were characterised using SEM, solid‑state ¹³C NMR, FT‑IR, Raman, XPS, and measured for elemental composition, cation exchange capacity, acid groups, BET surface area, and yield. Hydrochar showed lower ash, acidic pH (4.7), higher carbon recovery (57 %) and higher O/C and H/C ratios, whereas biochar had higher ash, alkaline pH (~10), lower carbon recovery (46 %) but more aromatic carbon; both chars are suitable soil amendments for distinct applications.

Abstract

The main properties of chars produced from corn stover, either by pyrolysis at 550°C (to produce biochar) or by hydrothermal carbonisation (to produce hydrochar), were studied. Carbonaceous materials were characterised by: SEM imaging, solid-state 13C NMR, FT-IR, Raman spectroscopy, and XPS. The following parameters were determined: elemental composition, cation exchange capacity, acid groups contents, BET, and yield. The hydrochar had a low ash content and low pH (4.7); recovery of C was high (57%), although only about half of the C was aromatic. Atomic O/C and H/C ratios in the hydrochar were higher than in the biochar. The same pattern was observed for the estimated concentration of carboxylic functional groups (0.07 compared with 0.04 mol/kg). The biochar had higher ash content than the hydrochar, and also higher pH (~10) (lime equivalence ~40 kg CaCO3/t). The C recovery (46%) was lower than in the hydrochar, although most of the C recovered was aromatic. Both chars could be used as soil amendments, for very different requirements. Soil responses and the residence times of the chars (especially the hydrochar) must be studied in detail to pursue long-term C sequestration.