Efficient Method of Lignin Isolation Using Microwave-Assisted Acidolysis and Characterization of the Residual Lignin

Abstract

Microwave heating is characterized by high efficiency and selectivity in biomass treatment. Due to the high thermal stability and low polarity of lignin, isolation of lignin by high-temperature microwave treatment is a promising subject for investigation. In this paper, microwave treatment is applied to polysaccharide liquefaction and lignin isolation from softwood at 160−210°C for 10 min with dilute sulfuric acid. Mass balance/element analysis/FTIR/TG/solid-state 13 C NMR/Py-GC/MS are applied to investigate the processed residues (residual lignin). At 190°C processing temperature, the residual lignin is a material rich in aromatics. High lignin purity (93 wt %) and yield (82 wt %) could be achieved by a simple protocol, which usually takes days or even weeks using conventional milled wood lignin protocols. The Py-GC/MS is applied to check the structure of lignin by a newly developed approach. The liquid phase after isolation is analyzed by GC-MS and liquid carbon NMR. Most chemicals in processed liquid are from cellulose and hemicellulose, suggesting that lignin is preserved well in the residue. By comparison, we found that microwave isolation causes less lignin degradation than conventional acidolysis under equivalent conditions. It is concluded that microwave treatment is potentially a promising tool for isolation of polysaccharide-free lignin with high efficiency.

Production of fermentable species by microwave-assisted hydrothermal treatment of biomass carbohydrates: reactivity and fermentability assessments

“…Several processes have been addressed for biomass pyrolysis, 9,[17][18][19][20][21][22][23][24] hydrothermal depolymerisation, 17,18,22,[25][26][27][28][29][30] fractionation and solvolysis. 18,[31][32][33][34][35][36][37][38] Microwave heating is based on the high frequency rotation of polar molecules, which produces a quicker and higher heating of the species with high polarity. [17][18][19][25][26][27]33,39 As lignin has a lower polarity than cellulose and hemicellulose, it is less active during microwave heating.…”

“…This allows the solubilisation of the carbohydrate content of the biomass without significantly solubilising the lignin fraction. 35,40 This minimises the presence of ligninderived inhibitors in the hydrolysate. However, it must also be borne in mind that the intensive hydrogen bonds within the cellulose structure together with its high crystallinity hinder the depolymerisation of cellulose 41,42 during microwave heating, which also decreases the reactivity of this carbohydrate in comparison to hemicellulose or alginic acid.…”

Agricultural and Forest Residues towards Renewable Chemicals and Materials Using Microwave Liquefaction

“…Biomass Type. Since Krzan et al first applied microwave energy to liquefaction [19,20], a variety of biomass types including sweetgum sawdust [8]; agricultural residues including bagasse, corn stover, rice straw, wheat straw, cotton stalk, and corncobs [24][25][26]; organosolv lignin of olive tree prunings [27]; Sargassum polycystum C. Agardh [28]; microalgae [29]; Ulva prolifera [30]; wheat straw alkali lignin International Journal of Polymer Science [31]; sugar beet pulp [32]; peony oil palm empty fruit bunch fiber [16]; oil palm empty fruit bunch cellulose [33]; poplar; Chinese fir; bamboo; hemp xyloid stem [22]; mixed softwood pellets [34]; banana pseudostem [35]; coconut fiber [36]; and grapefruit [37] have been studied as raw materials for microwave-assisted liquefaction for the production of renewable chemical platforms and/or biobased materials. The chemical composition (cellulose, hemicellulose, lignin, and ash) and microstructure of the lignocellulose feedstocks greatly differed with each other, which may influence their liquefaction behaviors under microwave heating.…”

A Review of Microwave Assisted Liquefaction of Ligninin Hydrogen Donor Solvents: Effect of Solvents and Catalysts

“…Solvents and catalysts played important roles during the microwave assisted liquefaction of lignin [28][29][30][31]. Polar solvents, which were proper microwave receptors, were previously regarded to be effective during the lignin depolymerization, coupled with suitable catalysts and microwave heating [31][32][33]. Zhang et al reported that lignin structure had a great effect on the lignin degradation with CrCl 3 and Pd/C as catalysts in methanol [28].…”