Effects of Mild Alkali Pretreatment and Hydrogen-Donating Solvent on Hydrothermal Liquefaction of Eucalyptus Woodchips

Abstract

Eucalyptus woodchips (EWC) were pretreated with mild aqueous NaOH solution, followed by liquefaction in a water–hydrogen donor (tetralin) mixture at a temperature from 220 to 330 °C to produce bio-oil. As a reference, pure tetralin and water were also used as liquefaction media. Compositional analysis and scanning electron microscopy (SEM) observation were performed to study the effect of the pretreatment on the EWC structural change. The influences of the temperature and tetralin content in mixed solvent on conversion and heavy oil (HO) yield were determined. The SEM image showed that pretreatment made the fiber structure loose and destroyed biomass through hemicellulose and lignin dissolution. In comparison to water or tetralin as solvent, water–tetralin mixed solvent (WTMS) shows a better effect on the conversion and HO yield in the tested temperature range. The highest conversions for liquefaction of untreated EWC were 66, 88.1, and 88.3 wt %, and the highest HO yields were 19.7, 26.4, and 43.2 wt %, with water, tetralin, and WTMS, respectively. The optimized conditions to achieve both high conversion (97.3 wt %) and HO yield (57.3 wt %) is liquefaction in WTMS at 300 °C using 1.0 wt % NaOH-pretreated EWC. Gas chromatography–mass spectrometry (GC–MS) analysis showed that phenols, ketones, aromatics, and alkenes are the main components in HOs.

Thermochemical Conversion of Plastic Waste into Fuels, Chemicals, and Value‐Added Materials: A Critical Review and Outlooks

“…[180] In addition to hydrogen donor solvents, non-hydrogen donor solvents (e. g., pyrene and fluoranthene) may also enhance the plastic waste conversion and the quality of fuel, as similar findings were found when converting biomass. [181] Alcohols such as ethanol have a lower dielectric constant than water, providing a better solubility of organic compounds at ambient and supercritical conditions. Most importantly, alcohols have lower corrosivity and also have hydrogen donation capability, preventing char formation and thus leading Figure 14.…”

Modularized production of fuels and other value‐added products from distributed, wasted, or stranded feedstocks

“…We recommend initially focusing on non‐supercritical hydrothermal liquefaction as the front‐end for processing the initial candidate feedstocks because of its omnivorism (Elliott, ; Lu, Yang, Wang, & Yang, ), ready scalability (Barreiro, Gómez, Hornung, Kruse, & Prins, ; Inoue, Okuma, Masuda, Yasumuro, & Miura, ), tolerance of wet feedstocks, and demonstrated production of a tractable bio‐oil (Elliott, ; Goudriaan & Peferoen, ) with an attractive greenhouse gas footprint (Connelly, Colosi, Clarens, & Lambert, ) (see Appendix). Examples of feedstocks that have been processed with hydrothermal liquefaction include wood (Zhixia Li et al, ), cellulose (Nan, Shende, Shannon, & Shende, ), microalgae (Barreiro et al, ; Brown, Duan, & Savage, ; Connelly et al, ; Faeth, Valdez, & Savage, ), macroalgae (Zhou, Zhang, Zhang, Fu, & Chen, ), food waste (Anouti, Haarlemmer, Déniel, & Roubaud, ), sewage sludge (Snowden‐Swan et al, ), and municipal solid waste (Chiaberge et al, ). Another process, IH 2 ® from the Gas Technology Institute (Marker et al, ), offers some of those benefits but requires high pressures (>160 bar) of hydrogen, and therefore poses a safety concern and a logistical issue (getting the product to its customers).…”

Deep Eutectic Solvents for Pretreatment, Extraction, and Catalysis of Biomass and Food Waste

“…Two feasible methods for the valorization of lignocellulosic biomass for bioenergy applications are: (1) fermentation of sugars from cellulose and hemicellulose components to biofuel [21] or (2) hydrothermal liquefaction and gasification to produce bio-oil [93,94,95] and biogas [96,97] (Figure 1 and Figure 3). In all these methods, pretreatment and solvation are critical steps, and it is important to find green solvents that can substitute the previously used hazardous solvents.…”