A Sustainable Approach on Spruce Bark Waste Valorization through Hydrothermal Conversion

Abstract

In the context of sustainable use of resources, hydrothermal conversion of biomass has received increased consideration. As well, the hydrochar (the solid C-rich phase that occurs after the process) has caused great interest. In this work, spruce bark (Picea abies) wastes were considered as feedstock and the influence of hydrothermal process parameters (temperature, reaction time, and biomass to water ratio) on the conversion degree has been studied. Using the response surface methodology and MiniTab software, the process parameters were set up and showed that temperature was the significant factor influencing the conversion, while residence time and the solid-to-liquid ratio had a low influence. Furthermore, the chemical (proximate and ultimate analysis), structural (Fourier-transform infrared spectroscopy, scanning electron microscopy) and thermal properties (thermogravimetric analysis) of feedstock and hydrochar were analyzed. Hydrochar obtained at 280 °C, 1 h processing time, and 1/5 solid-to-liquid ratio presented a hydrophobic character, numerous functional groups, a lower O and H content, and an improved C matter, as well as a good thermal stability. Alongside the structural features, these characteristics endorsed this waste-based product for applications other than those already known as a heat source.

Microwave-Assisted Extraction of Condensed Tannins from Branches of Prunus spinosa L.: Response Surface Modeling and Optimization

“…The proximate analysis (Table 2), consisting of the determination of moisture (%), total ash, and the insoluble-in-HCl-100 g/L [38], soluble substances (extractable) (%) in different extraction solvents: ethanol 30, 50, 70% v/v, distilled water, methanol, solution density (g/mL), pH, and residue (%), was carried out according to the methods described in Section 2.1 and in the laboratory analytical procedures for standard biomass analysis (NREL) [39]. The extractables (soluble substances) determined in different solvents provides valuable data in establishing the conditions for extracting the bioactive compounds.…”