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[HCG34-02] Dissolution of a woody biomass (Albizia falcataria) with an ionic liquid, 1-H-3-methyl imidazolium chloride ([HMIM]Cl)
Keywords:ionic liquid, biorefinery, falcata
Trees will play important roles in space agriculture as suppliers of oxygen, wooden materials and woody biomass1). Woody biomass contains cellulose, hemicellulose and lignin and wide variety of useful chemicals. Effective utilization of the woody biomass will bring benefit in the closed ecosystem. To produce various useful materials from woody biomass, kraft pulp method, acid hydrolysis, and enzymatic saccharification have been studied. However, these method require severe conditions such as high temperatures and high pressures.
An ionic liquid is a salt that a melting point below about 100°C and has unique characteristics such as excellent solubility, low volatility, incombustibility and low viscosity2). Recently, it has been reported that some ionic liquids can dissolve cellulose and lignocellulose, and the solvent can be utilized as green solvent to produce cellulose films, acetyl cellulose and carboxymethyl cellulose. In this experiment, dissolution behavior of a woody biomass (Albizia falcataria) to a low cost ionic liquid (1-H-3-methyl imidazolium chloride) are investigated.
[Materials and methods]
Wood chips (Albizia falcataria) were provided by Nankai Plywood Co., Ltd. They were ground using a willy meal, and 40-80 mesh were used for experiments. To synthesize 1-H-3-methyl imidazolium chloride ([HMIM]Cl), 1-methyl imidazole and hydrochloric acid were mixed in ice box and stirred for 24 hours, the resulting liquid was washed with ether and evaporated in vavuo. Synthesized [HMIM]Cl was identified by NMR. Wood meals (0.5 g) and [HMIM]Cl (15 g) were added into a flask and refluxed at 90 to 120°C for 1 to 24 hours. The mixture were filtrated, wash with 150 mL of 1,3-dimethyl-2-imidazolidinone and water, and dried at 105°C to calculated insoluble residues. The lignin content in the insoluble residue were determined as Klason lignin. FT-IR spectra of the insoluble residue were recorded. Used [HMIM]Cl was recovered to add ethanol, filtrated and evaporated in vavuo.
[Results and discussion]
In the wood meal treated with [HMIM]Cl at 90°C, the content of insoluble residue decreased in 1 hour, then the content did not changed with increasing reaction time. FT-IR spectrum of insoluble residue at 90°C for 1 hour showed disappearance of a peak at 1740 cm-1 derived from C=O of acetyl group in hemicellulose. In the wood meal treated with [HMIM]Cl at 120°C, the content of insoluble residue decreased with increasing reaction time, and the lignin content in the residue increased with increasing reaction time. FT-IR spectrum of insoluble residue at 120°C for 24 hour showed disappearance of the peak in hemicellulose, and a peak at 1429 cm-1 derived from bending vibration of CH2 in cellulose. Peaks at 1600 cm-1 and 1460 cm-1 derived from aromatic rings in lignin were clearly found in the spectrum. From these results, lignin was concentrated in the insoluble residue by dissolution with [HMIM]Cl.
Recycled [HMIM]Cl after cellulose dissolution had almost the same dissolution rate compared with unused [HMIM]Cl, however, recycled [HMIM]Cl after wood meal dissolution showed low dissolution rate compared with the unused ionic liquid. Low-molecular lignin degradation products could not completely precipitate in used [HMIM]Cl by addition of ethanol.
1) Yamashita, M., Ishikawa, Y., Nagatomo, M., Oshima, T., Wada, H., Space Agriculture Task Force. Space agriculture for manned space exploration on mars. J Space Tech Sci, 21(2), 1-10, 2005
2) Miyafuji, H. Application of ionic liquids for effective use of woody biomass. J Wood Sci, 61, 343-350 (2015)