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A mixture of US southern hardwood chips was treated with aqueous acetic and formic acid (FA) solutions in a modified Dionex ASE100 extractor. The amount and selectivity of hemicelluloses dissolution increase at higher acetic acid (AA) and FA concentrations, but cellulose remains intact in the residual wood. Even at the highest AA concentration of 100 g l-¹, the dissolved hemicellulose fragments are still oligomeric except for arabinose. The formation of lignin-like condensation products (LCPs) and decomposition of dissolved mannose, arabinose, and galactose were observed at the highest AA concentration. Sugar hydrolysis is more pronounced with the addition of FA at increasing temperature. The concentration of xylose in the FA extract is approximately the same as that of xylooligomers at 160°C. Formation of LCPs is only observed at 170°C during 10 g l-¹ FA treatment. The concentrations of dissolved wood components increase linearly with increased recycling of the FA extract. [ABSTRACT FROM AUTHOR]

The overall target of this project, called Bioforest, is to develop an economic process for the production of commodity chemicals from mixed forest biomass, consisting of logging residues of hardwoods (HW) and softwoods (SW) and also from recycled fibers. The aim is to dissolve the biomass lignin and to produce monosugars based on hemicelluloses and hydrolyzed cellulose in high yield. The hydrolyzate could subsequently be converted into chemicals by modified acetone-butanol-ethanol fermentation. Here, the total mass balances of SO2-ethanol-water fractionation of different types of biomass feedstocks, such as SW and HW biomass, and deinked pulp are presented. Chemical composition of the feedstocks, solid residues (pulps) and spent liquors of fractionation were analyzed to gain more understanding about the fractionation procedure. The analysis was focused on carbohydrates, lignin, ash, acetyl groups and sugar degradation products. It was also examined if all feedstocks could be treated simultaneously in one digester because a larger feedstock supply within an economic transport radius improves the viability of the process. The fractionation approach was successful and it can be concluded that the method presented is very versatile for future applications in lignocellulosic biorefineries. [ABSTRACT FROM AUTHOR]

In a forest based biorefinery, pulp and paper are the main products, while side-streams are utilized for value-added products. One biorefinery concept is to remove hemicelluloses from wood by extraction prior to pulping and converting them into biofuels or chemicals. This study presents a concept of a larch wood based biorefinery and focuses on the mass balance of pre-extraction. Sugar rich extracts were obtained by hot water extraction of Siberian larch ( Larix sibirica Lebed.) wood chips at different temperatures and times. At 160°C and 60-90 min the extract contains 13-16% hemicelluloses (on wood). The composition of extracts and extracted wood has been determined to have a basis for mass balances. Fermentation of the hydrolyzed extract with Bacillus coagulans MXL-9 resulted in consumption of all C6 and C5 sugars and produced lactic acid in high yield. In an earlier work, it was demonstrated that water pre-extraction of larch chips followed by polysulfide-anthraquinone (PSAQ) pulping still produced a good papermaking pulp at a yield comparable to the corresponding non-extracted kraft pulp. Accordingly, the present results show that a larch wood based biorefinery has a potential for industrial application. [ABSTRACT FROM AUTHOR]

Special oxygen delignification experiments were performed in a differentially operated continuous stirred tank reactor (CSTR). Because the dissolved oxygen and alkali concentrations in the reactor are constant, the rate of lignin removal may be determined from the dissolved lignin content in the outflow stream measured by UV absorption. The delignification kinetics were determined at different temperatures, oxygen pressures and caustic concentrations on softwood kraft pulps of different kappa numbers. The kinetics are first order in residual lignin content [hexenuronic acid (HexA) corrected], and follow a Langmuir-type behavior for adsorption of oxygen on the active aromatic lignin sites. The first order in residual lignin content implies that the active lignin sites are uniformly distributed and have the same reactivity. It is proposed that the active site is the 3 carbon of the aromatic ring, where oxygen reacts to form a hydroperoxide, with a p Ka of almost 2 units higher than that of phenolic lignin. The kinetics of phenolic delignification can be described by assuming that the reaction between adsorbed oxygen and carbon 3 of the aromatic ring is the rate determining step. Alternatively, the decomposition of the hydroperoxide anion is rate determining. Peeling delignification has been proposed as an additional delignification route by peeling of hemicelluloses which have lignin fragments covalently bound to them. It is shown that the impact of peeling delignification is relatively small and limited to the initial delignification phase. Finally, data are presented showing that radicals may provide an essential contribution to delignification by their removal of non-lignin and non-HexA oxidizable structures contributing to the kappa number. [ABSTRACT FROM AUTHOR]