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Using a Berty-type CSTR reactor, Ji (2007. Kinetics and mechanism of oxygen delignification, Ph.D. thesis. The University of Maine) obtained oxygen delignification kinetics first order in lignin when neglecting the higher initial delignification phase. In the present study the same Berty/CSTR reactor with an improved temperature control was used to determine the oxygen delignification kinetics of Southern Pine kraft pulp, with the kinetics now corrected for lignin removed by oxygen-free alkaline leaching. This removes the initial high delignification rate peak so that the kinetics over the entire lignin range can be modelled as first order in "reactive" lignin, which is lignin corrected for a small amount of unreactive lignin. It suggests that softwood pulp oxygen delignification consists of two contributions; phenolic delignification and alkaline leaching. The initial alkaline leaching phase is mathematically described by semi-infinite alkaline diffusion of dissolved lignin trapped in the cell wall after pulp washing. For phenolic delignification, the reaction orders in alkali concentration and oxygen of the power law delignification equation are 0.3 and 0.44 respectively, while the activation energy is 63 kJ/mol. Taking into account the unreactive HexA, the small amount of unreactive lignin, and the lignin removed by alkaline leaching, the kappa number is well predicted by the new delignification kinetics. [ABSTRACT FROM AUTHOR]

The objective of this work was to determine the effect of sodium methyl mercaptide (SMM) as an additive on the minimization of carbohydrate peeling reactions in Rock/Hard Maple (Acer saccharum) chips during kraft pulping. Two methods were evaluated for SMM addition to the pulping process: 1) pre-treatment before pulping and 2) co-addition with white liquor. The experimental results showed about 2.5% (on wood basis) increase in the kraft pulp yield after pre-treatment with 4.38% SMM (on wood basis) or the co-addition of the same amount of SMM with white liquor. The use of 4.38% SMM allowed a decrease in the white liquor effective alkali charge of 3% (on wood basis) to produce the target 14–15 kappa pulp. The 4.38% SMM charge was determined to be the optimum for both pre-treatment and co-addition. The increase in kraft pulp yield was mostly due to increased retention of cellulose (about 0.8% on wood) and xylan (about 1.8% on wood). The retention of glucomannan was insignificant in all cases. Based on the increase in intrinsic viscosity, it is concluded that the increased cellulose yield with SMM addition is caused by both reduced primary peeling and faster delignification rate (less alkaline hydrolysis followed by secondary peeling). The increased xylan retention is due to the lower effective alkali concentration during kraft pulping with SMM addition. [ABSTRACT FROM AUTHOR]

High solvent recovery and monomeric sugar yield are essential for a viable biochemical conversion technology. The SO2-ethanol-water (SEW) or AVAP® process has great potential to produce easily fermentable pulp fibers and sugars dissolved in the spent liquor stream. The SEW fractionation process is evaluated for delignification, xylan removal and potential reactions between ethanol and sugarcane straw (SCS) carbohydrates. α-ethyl-xyloside (aEX) and β-ethyl-xyloside (bEX) formed by reaction of ethanol with xylose are quantified. The fractionation experiments are carried out at 135°C, 145°C, and 155°C for 20-120 min at fixed liquor composition (SO2/EtOH/H2O = 12:44:44, w/w) and liquor to feedstock ratio (4 l kg-1). The results are interpreted in terms of combined severity factor (CSF). Maximum ethyl xylosides (EX, or sum of aEX and bEX) and monomeric xylose concentrations are observed at CSF of 2.4 ± 0.1. The maximum amount of EX in spent liquor accounts for nearly 1.4% of EtOH (feedstock basis). The implications for downstream recovery of EtOH and sugars from the spent liquor are discussed. [ABSTRACT FROM AUTHOR]

In the present study the advantages of multistage oxygen delignification was explored in comparison with a single-stage process at the same level of total caustic charge. A pine kraft pulp with kappa number of 65 (Kn65) was bleached with the focus on the effect of NaOH-charge distribution on Kn, pulp yield, and selectivity of oxygen delignification. The effect of initial chelation with ethylenediaminetetraacetic acid (EDTA) and interstage pulp treatment with peroxymonosulfuric acid (Px) were also investigated. It is shown that the chelated pulp with high Kn may be delignified in three stages to Kn15, but at an unacceptable reduction in pulp viscosity and yield. In contrast, interstage treatment of the chelated pulp with Px at a total charge of 2% active oxygen (based on pulp) in combination with three stages of oxygen delignification enables Kn reduction to about 15 at acceptable viscosity and total yield advantage of about 0.5% (based on wood) compared to an oxygen-delignified kraft pulp with Kn24 derived from the same pine wood chips. [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]

SO2-ethanol-water (SEW) pulping is a promising fractionation process for lignocellulosics to produce pulp and value-added chemicals as a contribution to the concept of forest biorefinery. The presence of SO2 leads to dissolution of hemicelluloses in high yield mostly as monomeric sugars, while lignin becomes soluble through sulfonation. After lignin removal, the dissolved sugars may be used as feedstock for fermentation to ethanol or butanol. SEW pulping may be considered a hybrid between solvent pulping (organosolv pulping by solvolysis) and acid sulfite pulping. Absence of an inorganic base leads to simplification of the recovery cycle. Furthermore, alcohol increases the impregnation rate of dissolved SO2 into wood, so that a separate impregnation phase is not necessary. Also, the presence of SO2 allows cooking of softwoods, while ethanol pulping is limited to hardwoods. Thus, SEW pulping may be applied to a wide variety of lignocellulosics at lower temperatures and similar cooking times than those used in kraft pulping. In the present study, SEW pulping experiments were performed on spruce chips at cooking temperatures of 135–165°C with a 12% SO2 solution at a liquor-to-wood ratio of 6:1 l kg-1. The effect of cooking temperature and time on kappa number, yield, and intrinsic viscosity of the pulp was determined. Based on these results, the kinetics of delignification, hemicelluloses removal, and cellulose hydrolytic destruction were established. [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]

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 objective of this study is to develop a process for conditioning spent liquor produced by SO2-ethanol-water (SEW) fractionation of spruce wood chips for fermentation to butanol, ethanol and acetone/isopropanol, i.e., by means of the so called acetone-butanol-ethanol (ABE) process using Clostridia bacteria. This study serves as part of an overall project aiming at the development of economic processes for producing chemicals and biofuels from mixed forest biomass via SEW fractionation and ABE fermentation technologies. [ABSTRACT FROM AUTHOR]