Hydrothermal Depolymerization of Biorefinery Lignin-Rich Streams: Influence of Reaction Conditions and Catalytic Additives on the Organic Monomers Yields in Biocrude and Aqueous Phase

Abstract

Hydrothermal depolymerization of lignin-rich streams (LRS) from lignocellulosic ethanol was successfully carried out in a lab-scale batch reactors unit. A partial depolymerization into oligomers and monomers was achieved using subcritical water as reaction medium. The influence of temperature (300–350–370 °C) and time (5–10 minutes) was investigated to identify the optimal condition on the monomers yields in the lighter biocrude (BC1) and aqueous phase (AP) fractions, focusing on specific phenolic classes as well as carboxylic acids and alcohols. The effect of base catalyzed reactions (2–4 wt. % of KOH) was compared to the control tests as well as to acid-catalyzed reactions obtained with a biphasic medium of supercritical carbon dioxide (sCO2) and subcritical water. KOH addition resulted in enhanced overall depolymerization without showing a strong influence on the phenolic generation, whereas sCO2 demonstrated higher phenolic selectivity even though no effect was observed on the overall products mass yields. In conclusion, a comparison between two different biocrude collection procedures was carried out in order to understand how the selected chemical extraction mode influences the distribution of compounds between BC1 and AP.

Characterization of Chemically and Physically Activated Carbons from Lignocellulosic Ethanol Lignin-Rich Stream via Hydrothermal Carbonization and Slow Pyrolysis Pretreatment

“…The lignin-rich stream was produced in an industrial-scale lignocellulosic ethanol demo plant located in Northern Italy [18], where poplar was used as raw material. A different batch of the same material was converted via hydrothermal liquefaction and its characterization is reported in Dell'Orco et al [15]. The properties of the sample used in the present study are reported in the Results Section and are compared with those of a sulfur-free lignin from soda pulping [14].…”

“…Fructose can also lead to the formation of glyceraldehyde, which can consequently produce glycolic acid or pyruvaldehyde, which in turn forms acetic acid. Among the quantified compounds, lactic acid was the most abundant, reaching nearly 5 g L −1 at 270 • C, 2 h. Glycerol, lactic and acetic acid were also found in the raw feedstock [15], and derive from the bacterial contamination of the poplar fermentation process from which the lignin-rich stream was obtained.…”

“…To the author's knowledge, the reported experiences of lignin or lignin-rich biomass in HTC have been carried out on lignin from the pulp and paper industry or on high-purity model compounds [8,[11][12][13], both structurally differing from LRS from lignocellulosic ethanol. Typically, lignin from pulp and paper has a higher degree of purity, generally greater than 90% [8,14], while that recovered from lignocellulosic ethanol still contains up to 50% of carbohydrates degradation products [14,15], making the hydrothermal conversion of this latter material remarkably different. On the contrary, slow pyrolysis have been applied to hydrolytic lignin from biochemical plants as a pretreatment for further physical activation.…”

Novel Process to Convert Wet and Dry Organic Feedstocks into 2nd Generation Biofuels: A Scientific Review of the Heat-to-Fuel Project

“…Hydrothermal depolymerization of lignin-rich streams (LRS) from lignocellulosic ethanol was successfully carried out in a lab-scale batch reactors unit, varying parameters such as temperature, time and introducing KOH and supercritical carbon dioxide (sCO2) as catalysts for process optimization [13]. A partial depolymerization was achieved using subcritical water as a reaction medium.…”

Special Issue “Hydrothermal Technology in Biomass Utilization & Conversion II”

“…Dell'Orco et al [2] examined Lignin-Rich Stream (LRS) feedstock from lignocellulosic ethanol for hydrothermal liquefaction. Micro-batch reactors were used to carry out the experimental investigation, focusing the analysis mostly on temperature and residence times, ranging from 300 • C to 370 • C and 5 to 10 min, respectively.…”