Characterization of lignin-derived products from various lignocellulosics as treated by semi-flow hot-compressed water

To elucidate the decomposition behaviors of lignin from different taxonomic groups, five different lignocellulosics were treated with hot-compressed water (230 °C/10 MPa/15 min) to fractionate lignins into water-soluble portions, precipitates, and insoluble residues. The lignin-derived products in each fraction were characterized and compared. The delignification of monocotyledons [nipa palm (Nypa fruticans) frond, rice (Oryza sativa) straw, and corn (Zea mays) cob] was more extensive than that achieved for Japanese cedar (Cryptomeria japonica, gymnosperm) and Japanese beech (Fagus crenata, dicotyledon angiosperm). The water-soluble portions contained lignin monomers like coniferyl alcohol and phenolic acids, while the precipitates contained higher molecular weight lignin with high content of ether-type linkages. Lignin in the insoluble residues was rich in condensed-type structures. In all five lignocellulosics, ether-type linkages were preferentially cleaved, while condensed-type lignin showed resistance to hot-compressed water. In the monocotyledons, lignin–carbohydrate complexes were cleaved and gave lignins that had higher molecular weights than those eluted from the woods. These differences would facilitate the delignification in monocotyledons. Such information provides useful information for efficient utilization of various lignocellulosics.     

Two-step hydrolysis of Japanese beech as treated by semi-flow hot-compressed water

A two-step hydrolysis of Japanese beech (Fagus crenata) was conducted by semi-flow treatment with hot-compressed water. The first treatment stage was conducted at 230°C/10 MPa for 15 min and the second at 270°C/10 MPa for 15 min. Hemicellulose and lignin were found to be hydrolyzed in the first stage, while crystalline cellulose was hydrolyzed in the second stage. The treatment solubilized 95.6% of the Japanese beech wood flour into water with 4.4% remaining as water-insoluble residue, which was composed mainly of lignin. Hydrolysis products from the first stage were xylose and xylo-oligosaccharides, glucuronic acid and acetic acid from O-acetyl-4-O-methylglucuronoxylan, and hydrolyzed monomeric guaiacyl and syringyl units and their dimeric condensed-type units from lignin. Products from the second hydrolysis stage were glucose and cello-oligosaccharides from cellulose. The dehydrated products levoglucosan, 5-hydroxymethylfurfural (5-HMF), and furfural, as well as fragmented products glycolaldehyde, methylglyoxal, and erythrose, were recovered in the first stage from hemicellulose, and to a greater extent in the second stage from cellulose. Furthermore, organic acids such as glycolic, formic, acetic, and lactic acids were recovered in both stages. Based on these lines of evidence, decomposition pathways of O-acetyl-4-O-methylglucuronoxylan and cellulose are independently proposed.     

Two-step hydrolysis of Japanese cedar as treated by semi-flow hot-compressed water

Two-step hydrolysis of Japanese cedar (Cryptomeria japonica) was studied as treated by semi-flow hot-compressed water at 230°C/10 MPa for 15 min and 280°C/10 MPa for 30 min as the first and second stages, respectively. At the first stage, hemicelluloses and para-crystalline cellulose, whose crystalline structure is somewhat disordered, were found to be selectively hydrolyzed, as well as lignin decomposition, whereas crystalline cellulose occurred at the second stage. In all, 87.76% of Japanese cedar could be liquefied by hot-compressed water and was primarily recovered as various hydrolyzed products, dehydrated, fragmented, and isomerized compounds as well as organic acids in the water-soluble portion. The remainder, 12.24%, could not be hydrolyzed and remained as the water-insoluble residue composed entirely of lignin. Based on the distribution of various products from hemicelluloses in Japanese cedar, their decomposition pathways were proposed as independent.     

MALDI-TOF/MS analyses of decomposition behavior of beech xylan as treated by semi-flow hot-compressed water

Japanese beech (Fagus crenata) was treated with semi-flow hot-compressed water at various temperatures of 150–230 °C under 10 MPa. The obtained various products were then analyzed with matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/MS). In a temperature range of 150 °C up to 210 °C, however, no hydrolyzed products were found, and at 210 °C/10 MPa, O-acetyl-4-O-methylglucuronoxylo-oligosaccharides (X _n Ac _m MG _i ) and O-acetyl-xylo-oligosaccharides (X _n Ac _m ) were obtained, indicating the first cleavage of native xylan β-1,4-glycosidic linkages followed by a cleavage of α-1,2-glycosidic linkage in 4-O-methylglucuronic acid (MG) residue at mainly 220–230 °C under 10 MPa. At subsequent stage of 230 °C/10 MPa, X _n Ac _m were predominantly recovered. As the treatment was prolonged at 230 °C, X _n Ac _m were reduced, but remained to some extent, indicating that the acetyl group which is hydrolyzed to be acetic acid is more resistant than MG residue. In such a stage of treatment, cellulose started to hydrolyze to cello-oligosaccharides. These lines of evidence can clearly indicate the hydrolysis pathway of native O-acetyl-4-O-methylglucuronoxylan as treated by hot-compressed water. Thus, xylo-oligosaccharides recovered in a very early stage of the semi-flow hot-compressed water treatment preserve native O-acetyl-4-O-methylglucuronoxylan.     

Characterization of lignin-derived products from Japanese beech wood as treated by two-step semi-flow hot-compressed water

Japanese beech (Fagus crenata) wood was treated by two-step semi-flow hot-compressed water (the first stage: 230 °C/10 MPa/15 min, the second stage: 270 °C/10 MPa/15 min), and produced lignin-derived products in the hot-compressed water-soluble portions at the first and second stages, and the final residue of the second stage was characterized with alkaline nitrobenzene oxidation method and gel permeation chromatographic analysis. As a result, the lignin-derived products at the first stage, where hemicellulose was also decomposed, consisted of lignin-based monomers and dimers and oligomers/polymers in the water-soluble portion. A large part of the oligomers/polymers was, however, recovered as the precipitate during 12 h setting after hot-compressed water treatment. By the analysis of nitrobenzene oxidation products, there were relatively higher contents of ether-type lignin in the precipitate at the first stage than in original beech wood. Since the ether linkages of lignin are more preferentially cleaved by this hot-compressed water, lignin-based polymeric fractions were flowed out from the porous cell walls from which hemicellulose was removed. On the other hand, at the second stage condensed-type lignin remained in the precipitate and residue. Based on these results, decomposition behavior of lignin in Japanese beech wood as treated by the two-step semi-flow hot-compressed water was discussed regarding the topochemistry of lignin structure.     

Process integration of ethanol production from Japanese beech as treated with hot-compressed water followed by enzymatic treatment

Ethanol was produced from the hydrolysate collected as a water-soluble (WS) portion and a residue after hot-compressed water (HCW) treatment of Japanese beech with and without fractionation. Simultaneous saccharification with β-xylosidase and isomerization with xylose isomerase followed by fermentation with Saccharomyces cerevisiae were applied to the WS portion; simultaneous saccharification with cellulase and fermentation with S. cerevisiae was applied to the residue. Integration of the processes for the WS portion and the residue was investigated to improve the conversion efficiency throughout the whole process. The ethanol yield in the integrated process without fractionation was comparable with that for the process with fractionation. Ethanol yields were improved for both of the processes by modifying the operation pattern in which cellulase was added prior to fermentation of the residue.     

Fractionation and characterization of oil palm (Elaeis guineensis) as treated by supercritical water

In order to investigate the potential for efficient utilization of oil palm (Elaeis guineensis), supercritical water treatment (at 380°C and 100 MPa for 8 s) was applied to fractionate extractives-free samples into water-soluble portion and water-insoluble portion. The water-insoluble portion was further fractionated into methanol-soluble portion and methanol-insoluble residue. Samples were prepared from various parts of oil palm, i.e., trunks, fronds, mesocarp fibers, shells, empty fruit bunches, and kernel cake. These fractionated products were then characterized analytically. The water-soluble and methanol-soluble portions were determined to be mainly composed of carbohydrate-derived products and lignin-derived products, respectively. The methanol-insoluble residue was mainly composed of lignin (more than 84 wt%) and the phenolic hydroxyl contents determined by the aminolysis method was higher than for untreated oil palm samples. In addition, an alkaline nitrobenzene oxidation analysis indicated that the methanol-insoluble residue contained fewer oxidation products than untreated samples did. These findings imply that the water-soluble portion could be utilized for organic acid production, whereas the methanol-soluble portion and the insoluble residue could be used for the production of phenolic chemicals.     

Characterization of the lignin-derived products from wood as treated in supercritical water

Sugi (Cryptomeria japonica D. Don) and buna (Fugus crenata Blume) woods were treated with supercritical water (>374°C, >22.1 MPa) and fractionated into a water-soluble portion and a water-insoluble residue. The latter was washed with methanol to be fractionated further into a methanol-soluble portion and a methanol-insoluble residue. Whereas the carbohydrate-derived products were in the water-soluble portion, most of the lignin-derived products were found in the methanol-soluble portion and methanol-insoluble residue. The lignin-derived products in the methanol-soluble portion were shown to have more phenolic hydroxyl groups than lignin in original wood. The alkaline nitrobenzene oxidation analyses, however, exhibited much less oxidation product in the methanol-soluble portion and methanol-insoluble residue. These lines of evidence suggest that the ether linkages of lignin are preferentially cleaved during supercritical water treatment. To simulate the reaction of lignin, a study with lignin model compounds was performed;-O-4-type lignin model compounds were found to be cleaved, whereas biphenyl-type compounds were highly stable during supercritical water treatment. These results clearly indicated that the lignin-derived products, mainly consisting of condensed-type linkages of lignin due to the preferential degradation of the ether linkages of lignin, occurred during supercritical water treatment.This study was presented in part at the 45th lignin symposium, Ehime, Japan, October, 2000; and the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1988     

TGA modeling of the thermal decomposition of CCA treated lumber waste

 To guide the development of thermal decomposition methods for disposal of CCA treated wood, reactions during the thermal decomposition of CCA treated wood were modeled using thermogravimetric analysis (TGA), with special focus placed on arsenic volatilization. Simple inorganic compounds, such as As₂O₅, CuO, and Cr₂O₃, were used to model the thermal behavior of the inorganics in CCA treated wood. In air and nitrogen, arsenic (V) oxide began to volatilize at 600 °C during temperature ramps at 5 °C/min. During a 5 °C/min ramp in a hydrogen mix, arsenic (V) oxide began decomposition at 425 °C. Arsenic volatile loss from CCA treated wood can depend strongly on the gases produced by wood thermal decomposition. In the presence of As₂O₅, chromium (III) oxide and copper (II) oxide formed arsenates in air and nitrogen. Chromium arsenates began decomposition as low as 790 °C. This suggested that chromium arsenates in CCA treated wood formed during original preservative fixation may decompose as low as 790 °C. Copper arsenates were stable up to 900 °C in air, but showed only a limited range of stability in nitrogen. Depending on process conditions, the formation of copper arsenates may limit arsenic loss during thermal decomposition of CCA treated wood up to 900 °C. The thermal decomposition of inorganic oxides was influenced by interactions with wood and wood decomposition products. In a dry YP sawdust/As₂O₅ mix, arsenic (V) oxide volatilized at 370 °C during inert pyrolysis at 5 °C/min and at 320 °C during smoldering combustion at 5 °C/min. Thermal dwells of a dry YP/As₂O₅ mix showed no arsenic loss at 250 °C, but significant loss occurred during higher temperature dwells. During inert pyrolysis at 5 °C/min, the formation of complexes and hydrates were shown to prevent arsenic loss up to 400 °C. Received 14 July 1999     

Study of crystalline behavior of heat-treated wood cellulose during treatments in water

The crystalline behavior of heat-treated wood cellulose treated at 85% relative humidity (RH), in water, or boiled in water after heat treatment was investigated. The normal increased crystallinity was significantly depressed for samples that were oven-dried and then treated in 85% RH or in water. In the case of boiling-water treatment, a more pronounced increased in crystallinity was initially observed, which then decreased gradually. The crystallinity decreased more than untreated wood for samples that were heat treated for long periods and was slightly higher than the decreased crystallinity from the beginning of the above two treatments. On the other hand, no significant change in crystallinity was observed for samples of increased crystallinity or decreased crystallinity that were treated under high-moisture conditions, for all three treatments. The results show that the crystalline state of wood cellulose heat treated under oven dry or high-moisture conditions behave differently if treated in water after heat treatment. Results suggested that the mechanism of crystallization might be different for samples that are subjected to heat treatment under oven-dry and high-moisture conditions.     

The sorption of water vapour by chemically modified softwood: analysis using various sorption models

The sorption data for Corsican pine wood chemically modified with a homologous series of linear chain carboxylic acid anhydrides was analysed using various models, namely, BET, Dent, Le and Ly, Hailwood and Horrobin, Nelson, and Henderson. Hailwood and Horrobin resulted in the more appropriate model to represent the equilibrium data of chemically modified wood. In the present study, the parameter representing the molecular weight of the dry cell wall in the Hailwood and Horrobin isotherm was perfectly correlated with the weight percentage gain of anhydride. A linear relation was proposed between these two parameters in order to fit all experimental isotherms (the results showed an r²=0.993).     

Carbon and nitrogen dynamics in early stages of forest litter decomposition as affected by nitrogen addition

The effects of nitrogen(N) availability and tree species on the dynamics of carbon and nitrogen at early stage of decomposition of forest litter were studied in a 13-week laboratory incubation experiment.Fresh litter samples including needle litter(Pinus koraiensis) and two types of broadleaf litters(Quercus mongolica and Tilia amurensis) were collected from a broadleaf-korean pine mixed forest in the northern slope of Changbai Mountain(China).Different doses of N(equal to 0, 30 and 50 kg·ha-1yr-1, respecti...     

Litter decomposition and the degradation of recalcitrant components in Pinus massoniana plantations with various canopy densities

To understand the decomposition characteristics of Pinus massoniana foliar litter and the degradation of its refractory compounds in plantations under five canopy densities,a litter bag experiment over a decomposition time of 392 days was carried out.The results show that canopy density significantly affected decomposition rates of litter and degradation rate of lignin and cellulose.Litter decomposition rates decreased significantly with decreasing canopy density.Both lignin and cellulose degradation rates were lower with canopy densities of 0.62 and 0.74 as compared with the three other densities.Lignin and cellulose losses were more rapid in the first 118 days.Soil fauna had significant impacts on litter decomposition and the degradation of refractory compounds.Canopy density had significant effects on factors such as soil properties and soil fauna community structure,which could be conducive to the decomposition of litter and the degradation of litter recalcitrant components.Canopy density between 0.6 and 0.7 might be a favorable management practice promoting litter decomposition and beneficial for the sustainable development of P.massoniana plantations.     

Dynamic water vapour sorption properties of wood treated with glutaraldehyde

The dynamic water vapour sorption properties of Scots pine (Pinus sylvestris L.) wood samples were studied to investigate the modifying effects of glutaraldehyde. Pine sapwood was treated with solutions of glutaraldehyde and a catalyst (magnesium chloride) to obtain weight per cent gains of 0.5, 8.6, 15.5, and 21.0%, respectively. The sorption behaviour of untreated and treated wood was measured using a Dynamic Vapour Sorption apparatus. The results showed considerable reduction in equilibrium moisture content of wood and the corresponding equilibrium time at each target relative humidity (RH) due to glutaraldehyde treatment. The moisture adsorption and desorption rates of modified and unmodified wood were generally faster in the low RH range (up to approximate 20%) than in the high range. Modification primarily reduced the adsorption and desorption rates over the high RH range of 20–95%. Glutaraldehyde modification resulted in a reduction in sorption hysteresis due to the loss of elasticity of cell walls.     

Impact of water storage on mechanical properties of spruce as detected by ultrasonics

Summary The impact of a five months water storage together with a bacterial treatment, on the mechanical properties of spruce is analysed by ultrasonic waves. The Bacillus subtilis is used to improve the permeability of spruce sapwood. The attack of bacteria on the torus of aspirated pits is expected to lead to a better transport of preservative liquids. The elastic constants were calculated through ultrasonic velocities which were measured at different types of specimens. The results were compared with the constant E_L as determined by a static bending test. The calculated loss of strength seems to be negligible but variations in the elastic properties of anatomical plaines consisting radial axes, can be well predicted.     

Organic matter decomposition in an acidic forest soil in Denmark as measured by the cotton strip assay

Decomposition of organic matter in forest soils controls mineralization of nutrients. The decomposition is to a large extent controlled by climatic and soil conditions. Four different soil treatments of water and nutrients were applied to a Norway spruce (Picea abies) stand in Denmark, and the relative changes in decomposition rate were quantified by the cotton strip assay. Additions of water and nutrients to the soil increased the decomposition of the cotton strips significantly, especially in the deeper soil layers. Reduced water addition during the summer, thereby creating ‘summer drought’, caused no changes in the decomposition compared to an untreated control situation, but the spatial variability in the decomposition within the treatment plot was strongly increased. The decomposition of the cotton strips decreased linearly with the soil depth (1st order).     

Allomorphs of native crystalline cellulose I evaluated by two equatoriald-spacings

The aim of this study was to develop a facile method for categorizing native celluloses as the algal-bacterial type or the cotton-ramie type and for estimating the I_α/I_β (triclinic/monoclinic) ratio of the cellulose samples. We investigated various native celluloses by X-ray diffractometry; and discriminant analysis was carried out using two equatoriald-spacings: 0.59–0.62 nm (d ₁) and 0.52–0.55 nm (d ₂). All of the samples were classified into the two groups without error. The function used to discriminate between the two groups is represented as:Z=1693d₁ — 902d ₂ — 549, whereZ>0 indicates the algal-bacterial (I_α-rich) type andZ<0 indicates the cotton-ramie (I_β-dominant) type. Another X-ray diffraction study of hydrothermally treatedCladophora cellulose revealed the relation between thed-spacings (d ₁,d ₂) and the I_α/I_β ratio. A calibrating equation by which the I_α/I_β ratio was estimated from the two parameters,d ₁ andd ₂, was then prepared. In the case of relatively highly crystalline native celluloses, it was found that the I_α/I_β ratio is easily determined by applying the two parameters in the equation.     

On the mechanical behaviour of water soaked wood at various states of stress

Summary The paper is concerned with an experimental investigation of the swelling strains and mechanical strains of water soaked wood under one- and two-dimensional stress states at changing moisture content. The aim of this paper is to develop an experimental basis for setting up the physical relations between strains, stresses and moisture content in wood.