Abstract
The selective lignin conversion into bio-based organic mono-aromatics is a major general challenge due to complex structure itself/additional macromolecule modifications, caused by the cleavage of the ether chemical bonds during the lignocellulosic biomass organosolv pulping in acidified aqueous ethanol. Herein, the acido-lysis of connected benzyl phenyl (BPE), being a representative model compound with α-O-4 linkage, was investigated in methanol, EtOH and 75 vol% EtOH/water mixture solutions, progressing each time with protonating sulfuric acid. The effect of the physical solvent properties, acidity of the reaction process media and temperature on rate was determined. Experiments suggested BPE following SN1 mechanism due to the formation of a stable primary carbocation/polarity. The product species distribution in non-aqueous functional alcohols was strongly affected. The addition of H2O was advantageous, especially for alkoxylation. Yield was reduced by a factor of 3, consequently preserving reactive hydroxyl group. Quantitative experimental results indicated key performance parameters to achieve optimum. Organosolv lignins were further isolated under significantly moderate conditions. Consecutive structural differences observed supported findings, obtained when using BPE. H2O presence was again found to grant a higher measured –OH content. Mechanistic pathway analysis thus represents the first step when continuing to kinetics, structure–activity relationships or bio-refining industrial resources.
Highlights
Serious concerns about the use of fossils fuels require the development of new procedures for the production of alternative fuels from sustainable, renewable and non-food resources
An outstanding lignin isolation/depolymerisation strategy using the formaldehyde stabilization/ hydrogenolysis has been reported by Luterbacher and co-workers[10]
Gases, solvents and external calibration standards were of reagent grade and were used without further purification, : benzyl phenyl ether (98 wt%, Tokyo Chemical Industry co LTD, Tokyo, Japan, CAS number 946-80-5), phenol (99.5 wt%, Carlo Erba Reagents SAS, Val de Reuil Cedex, CAS number 108-95-2), benzyl alcohol (≥ 99.0 wt%, Fluka Chemie GmbH, Buchs, Swizerland, CAS number 100-516), 2-benzylphenol
Summary
Serious concerns about the use of fossils fuels require the development of new procedures for the production of alternative fuels from sustainable, renewable and non-food resources. An efficient lignin depolymerisation has been a major challenge for the last decade, having led to the development of new LC biomass fractionation techniques, such as the ‘lignin-first’ approach[9] or lignin isolation through the formaldehyde stabilization[10]. LC biomass fractionation using the organosolv process has been recognized as environmentally friendly, yielding ether bond-rich lignin of higher purity compared to the lignin obtained with other methods, which is essential for its valorisation into value-added chemicals[11]. The main advantage of the organosolv process is its efficient fractionation of separate streams of major biomass components (cellulose, lignin and hemicelluloses), allowing the valorisation of all components. Considering the maturity of the bioethanol production process from LC biomass using the organosolv process, the optimization of the isolated lignin quality would facilitate lignin valorisation, improving the efficiency of a complete organosolvprocess-based biorefinery. To optimize the quality of the isolated lignin in terms of the preserved ether bonds, it is essential to understand the mechanism of the ether bond cleavage and the effects of operating conditions
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