CO formation from glucose and cellulose as treated in ionic liquids.

The formation of carbon monoxide (CO) from glucose and cellulose by the treatment with various ionic liquids was studied. Ionic liquids with an imidazolium structure as cation and the chloride or acetate as anion were used. Additionally, 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) was employed as an additive. CO was generated from glucose with a maximum yield of 0.57 mol% after 90 min of treatment at 120 °C in the reaction system in which DBU was added to the ionic liquid. Pyrolysis above 600 °C has been commonly employed for the gasification of lignocellullosics to produce useful gases such as CO. However, this study has revealed that gasification of lignocellullosics to produce CO can occur at significantly lower temperature, specifically at 120 °C.

Vanillin Production Pathways in Alkaline Nitrobenzene Oxidation of Guaiacylglycerol-ß-guaiacyl Ether.

Alkaline nitrobenzene oxidation (AN oxidation) is a significant method for chemical analysis of lignin. Despite its importance in lignin chemistry, the detailed chemical reactions involved in AN oxidation are not yet fully understood. Surprisingly, there is almost no experimentally supported information available regarding the reaction pathways in the AN oxidation of guaiacyl glycerol-ß-guaiacyl ether (GG), a common model compound in lignin chemistry. This study reports the results of our investigation into the formation pathway of vanillin (4-hydroxy-3-methoxybenzaldehyde) in the AN oxidation of GG. Our series of experiments proposed a vanillin formation pathway involving an enol ether with a C2 side chain, 2-methoxy-4-[2-(2-methoxyphenoxy)-ethenyl]-phenol C2EE, as an intermediate, in which C2EE is produced by the non-oxidative degradation of GG by alkali. Another enol ether with a C3 side-chain, Z-4-[3-hydroxy-2-(2-methoxyphenoxy)-1-propen-1-yl]-2-methoxyphenol (C3EE), and the condensation products formed under alkaline conditions were found to be insignificant as vanillin sources. On the other hand, the comparison of the vanillin yields from GG and isolated C2EE (80.7 and 86.5 mol %, respectively) in their AN oxidation to the C2EE yield from GG in the absence of nitrobenzene (69.9 mol %) also suggested that the vanillin formation from GG involved unknown pathways in which C2EE is not an intermediate.

Fire and termite resistance of wood treated with PF6-based ionic liquids.

Six PF6-based ionic liquids (ILs) were investigated to evaluate their potential as chemicals for enhancing fire and termite resistance of wood. The ILs used in this study included 1-methyl-1-propylpyrrolidinium hexafluorophosphate ([MPPL]PF6), 1-methyl-1-propylpiperidinium hexafluorophosphate ([MPPR]PF6), 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM]PF6), tetrabutylphosphonium hexafluorophosphate ([TBP]PF6), trihexyltetradecylphosphonium hexafluorophosphate ([THP]PF6), and 1-butylpyridinium hexafluorophosphate ([BPYR]PF6). All of the IL-treated wood samples did not undergo any morphological changes, and exhibited enhanced fire- and termite resistance compared with untreated wood. The fire resistance properties of all of the prepared IL-treated wood specimens were comparable. However, the [EMIM]PF6- and [THP]PF6-treated wood showed slightly inferior termite resistance among the tested IL-treated woods. Overall, [TBP]PF6 was the most promising candidate among the evaluated PF6-based ILs because it is stable in wood without leaching after water penetration.

Production of 5-hydroxymethylfurfural from Japanese cedar (Cryptomeria japonica) in an ionic liquid, 1-methylimidazolium hydrogen sulfate.

Production of 5-hydroxymethylfurfural (5-HMF) from Japanese cedar (Cryptomeria japonica) using an ionic liquid, 1-methylimidazolium hydrogen sulfate ([MIM]HSO4), was investigated. 5-HMF can be produced from C. japonica at temperatures above 120 °C. The maximum yield of 5-HMF was about 9 wt% after 15 min of treatment at 160 °C. However, 5-HMF produced in this process tended to decompose as the treatment continued. To avoid decomposition and to provide a means of recovering 5-HMF from [MIM]HSO4, three reaction systems based on [MIM]HSO4 were investigated: biphasic [MIM]HSO4/organic solvent system, [MIM]HSO4 with vacuum distillation, and [MIM]HSO4 with vacuum steam distillation. The [MIM]HSO4 reaction system combined with vacuum steam distillation was most effective. The maximum yield of 5-HMF was 17.5 wt% after treatment for 45 min at 160 °C. The combination of [MIM]HSO4 treatment with vacuum steam distillation is suitable for 5-HMF production because it is a one-pot process without the need for catalysts or pretreatment.

Selective production of bio-based aromatics by aerobic oxidation of native soft wood lignin in tetrabutylammonium hydroxide.

Aerobic oxidation of native soft wood lignin in an aqueous solution of Bu4NOH facilitates efficient production of vanillin (4-hydroxy-3-methoxybenzaldehyde), which is one of the platform chemicals in industry. Oxidation of Japanese cedar (Cryptomeria japonica) wood flour at 120 °C for 4 h under O2 in Bu4NOH-based aqueous solutions produced vanillin in 23.2 wt% yield based on the Klason lignin content of the starting material. This yield was comparable to that in alkaline nitrobenzene oxidation of the same material (27.2%), which indicated that our aerobic oxidation exploited the full potential of the wood flour for vanillin production. Further mechanical investigation with lignin model compounds suggested that the vanillin formation occurred mainly through following successive reactions: alkaline-catalyzed degradation of ß-ether linkages in middle units of lignin polymer to form a glycerol end group, oxidation of the glycerol end group by O2 to a HCα[double bond, length as m-dash]O moiety, and release of vanillin from the HCα[double bond, length as m-dash]O end. One of the reasons for the high performance of Bu4NOH for the vanillin production was explained by the general understanding in organic chemistry that Bu4OH is a stronger base than simple alkali, e.g. NaOH. The other more fundamental mechanical aspect was that Bu4N+ suppressed disproportionation of the vanillin precursor (the CαHO end group) probably due to strong interaction between the cation and the HCα[double bond, length as m-dash]O end group.

Effect of ionic liquid treatment on the ultrastructural and topochemical features of compression wood in Japanese cedar (Cryptomeria japonica).

The morphological and topochemical changes in wood tissues in compression wood of Japanese cedar (Cryptomeria japonica) upon treated with two types of ionic liquids, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]) and 1-ethylpyridinium bromide ([EtPy][Br]) were investigated. Compression wood tracheids were swollen by both ionic liquids but their swelling behaviors were different in the types of ionic liquids used. Under the polarized light, we confirmed that crystalline cellulose in compression wood is amorphized by [C2mim][Cl] treatment whereas it changes slightly by [EtPy][Br] treatment. Raman microscopic analyses revealed that [C2mim][Cl] can preferentially liquefy polysaccharides in compression wood whereas [EtPy][Br] liquefy lignin. In addition, the interaction of compression wood with ionic liquids is different for the morphological regions. These results will assist in the use of ionic liquid treatment of woody biomass to produce valuable chemicals, bio-fuels, bio-based composites and other products.

Microscopic characterization of tension wood cell walls of Japanese beech (Fagus crenata) treated with ionic liquids.

Tension wood that is an abnormal part formed in angiosperms has been barely used for wood industry. In this study, to utilize the tension wood effectively by means of liquefaction using ionic liquid, we performed morphological and topochemical determination of the changes in tension wood of Japanese beech (Fagus crenata) during ionic liquid treatment at the cellular level using light microscopy, scanning electron microscopy and confocal Raman microscopy. Ionic liquid treatment induced cell wall swelling in tension wood. Changes in the tissue morphology treated with ionic liquids were different between normal wood and tension wood, moreover the types of ionic liquids. The ionic liquid 1-ethyl-3-methylimidazolium chloride liquefied gelatinous layers rapidly, whereas 1-ethylpyridinium bromide liquefied slowly but delignified selectively. These novel insights into the deconstruction behavior of tension wood cell walls during ionic liquid treatment provide better understanding of the liquefaction mechanism. The obtained knowledge will contribute to development of an effective chemical processing of tension wood using ionic liquids and lead to efficient use of wood resources.

Anatomical and Topochemical Aspects of Japanese beech (Fagus crenata) Cell Walls After Treatment with the Ionic Liquid, 1-Ethylpyridinium Bromide.

Changes in the ultrastructure and chemical components, and their distribution in Japanese beech (Fagus crenata), during the ionic liquid 1-ethylpyridinium bromide ([EtPy][Br]) treatment were examined at the cellular level by light microscopy, scanning electron microscopy, and confocal Raman microscopy. Each of the tissues, including wood fibers, vessels and parenchyma cells treated with [EtPy][Br] showed specific morphological characteristics. Furthermore, lignin can be preferentially liquefied and eluted in [EtPy][Br] from the cell walls when compared to polysaccharides. However, the delignification was heterogeneous on the cell walls as lignin maintained a relatively high-concentration at the compound middle lamella, cell corners, inner surface of the secondary wall, and pits after [EtPy][Br] treatment.

Topochemical and morphological characterization of wood cell wall treated with the ionic liquid, 1-ethylpyridinium bromide.

MAIN CONCLUSION : [EtPy][Br] is more reactive toward lignin than toward the PSs in wood cell walls, and [EtPy][Br] treatment results in inhomogenous changes to the cell wall's ultrastructural and chemical components. The effects of the ionic liquid 1-ethylpyridinium bromide ([EtPy][Br]), which prefers to react with lignin rather than cellulose on the wood cell walls of Japanese cedar (Cryptomeria japonica), were investigated from a morphology and topochemistry point of view. The [EtPy][Br] treatment induced cell wall swelling, the elimination of warts, and the formation of countless pores in the tracheids. However, many of the pit membranes and the cellulose crystalline structure remained unchanged. Raman microscopic analyses revealed that chemical changes in the cell walls were different for different layers and that the lignin in the compound middle lamella and the cell corner resists interaction with [EtPy][Br]. Additionally, the interaction of [EtPy][Br] with the wood cell wall is different to that of other types of ionic liquid.

Bioethanol from cellulose with supercritical water treatment followed by enzymatic hydrolysis.

The water-soluble portion and precipitates obtained by supercritical (SC) water treatment of microcrystalline cellulose (Avicel) were enzymatically hydrolyzed. Glucose could be produced easily from both substrates, compared with the Avicel. Therefore, SC water treatment was found to be effective for enhancing the productivity of glucose from cellulose by the enzymatic hydrolysis. It is also found that alkaline treatment or wood charcoal treatment reduced inhibitory effects by various decomposed compounds of cellulose on the enzymatic hydrolysis to achieve higher glucose yields. Furthermore, glucose obtained by SC water treatment followed by the enzymatic hydrolysis of cellulose could be converted to ethanol by fermentation without any inhibition.

Fermentability of water-soluble portion to ethanol obtained by supercritical water treatment of lignocellulosics.

The water-soluble (WS) portion obtained by supercritical water treatment of lignocellulosics was studied for its fermentability to ethanol. A fermentation test of the WS portion showed it was not fermented to ethanol. Therefore, a wood charcoal treatment was applied to the WS portion to remove furan and phenolic compounds, which are thought to be the inhibitors to sugar fermentability. It was found that treatment with wood charcoal can be effective at removing these inhibitors and improving the fermentability of the WS portion without reducing the levels of fermentable sugars.

Effect of wood ash treatment on improving the fermentability of wood hydrolysate.

Softwood hydrolysates were overlimed with wood ash to improve the fermentability of hydrolysates. It could be demonstrated in fermentation tests that wood ash treatment increases fermentability compared to the hydrolysates untreated and treated with alkaline compounds such as Ca(OH)(2), NaOH, and KOH, which are commonly used for overliming. The enhanced fermentability of the hydrolysate treated with wood ash is due to the reduction of the inhibitors of the fermentation such as furan and phenolic compounds and to nutrient effects of some inorganic components from the wood ash on the fermentation.