Reactivity of cellulose during hydrothermal carbonization of lignocellulosic biomass

Abstract

Hydrothermal carbonization of pure cellulose and birchwood samples was carried out at temperatures between 160 and 280 °C, 0.5 h residence time and biomass-to-water ratio of 20 wt% dry basis, to investigate HTC reactivity of cellulose naturally occurring lignocellulosic biomass. Pure cellulose samples remained unaltered at temperatures up to 220 °C, but significantly decomposed at 230 °C producing a thermal recalcitrant aromatic, high energy-dense material, showing lignin-like behavior. Fourier Transform Infrared spectroscopy (FTIR) showed dehydration and aromatization reactions occurring at temperatures equal or higher than 230 °C for pure cellulose samples while similar increase in aromatization for birchwood hydrochars was evident only at temperatures equal or higher than 260 °C. Acid hydrolysis, Thermogravimetric analysis (TGA) and FTIR suggest that a higher thermal resistance of natural occurring cellulose in birchwood (when compared to pure cellulose sample) could be related to a 'protecting shield' offered by interlinked lignin in the plant matrix.

Process Water Recirculation during Hydrothermal Carbonization of Waste Biomass: Current Knowledge and Challenges

“…Proximate and elemental compositions of hydrochars, obtained from HTC steps with deionized water and recirculated PW as a solvent, are reported in Table 2. After recirculation steps, as it can be observed, the hydrogen (H) and nitrogen (N) contents remained almost unchanged, as commonly observed during HTC of lignocellulosic waste biomass [59]. Differently, carbon (C) and fixed carbon (FC) contents increased while oxygen (O) and volatile matter (VM) contents decreased [46,66,67,73].…”

“…Hydrolytic reactions lead to various monosaccharides units such as hexoses and pentoses [58]. In a similar way, cellulose is hydrolyzed at higher temperatures (200-230 • C) [59] to form other sugars (e.g., glucose). Soluble lignin is hydrolyzed into phenolic compounds while not soluble lignin (most of the lignin), together with un-hydrolyzed cellulose and hemicelluloses, form the hydrochar matrix through a solid-solid conversion mechanism [60].…”

Challenges and opportunities of hydrothermal carbonisation in the UK; case study in Chirnside

“…This being said experiments by Volpe determined that pure cellulose remained unaltered at temperatures up to 220 C, yet signicantly decomposed at 230 C to produce recalcitrant aromatic and high energy-dense material. 36 3.2.1 Hydrolysis. Hydrolytic reactions occur on the surface of solid biomass, where water reacts with biomacromolecules by breaking both ester and ether bonds to produce a wide range of products.…”

Hydrothermal Carbonization as a Strategy for Sewage Sludge Management: Influence of Process Withdrawal Point on Hydrochar Properties

“…HTC proceeds via a series of mechanisms, including hydrolysis, dehydration, decarboxylation, decarbonylation, and demethanation. HTC is performed in 80-95 vol% water [17][18][19][20], making it an ideal processing pathway for wet biomasses [21,22] such as sewage sludge. As well recognized in the literature, HTC not only leads to reduced volume and energy densification of the solid residue, considerably improving its dewaterability [23,24], but also significantly increases its solid fuel properties while stabilizing and disinfecting the sludge [25,26].…”