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Sugar maple (Acer saccharum) wood chips were pretreated with aqueous sodium hydroxide, sodium borohydride, and hydrogen peroxide pretreatments, and the characterization (i.e., amount, molar masses, and molar mass distributions) of the lignin dissolved during the pretreatments was performed. Of the applied pretreatments, especially borohydride pretreatments were efficient in dissolving lignin from this feedstock, as 20% to 28% of the dissolved organics were found to consist of dissolved lignin, contributing to 3.4% to 9.0% of the initial wood lignin. Corresponding values for 2.5% and 5.0% alkaline peroxide pretreatments were from 5.9% to 9.2% dissolved lignin of the total dissolved organics and from 1.1% to 3.2% of the initial wood lignin. Additionally, determined molar masses and molar mass distributions indicated that borohydride pretreatments generally led to the formation of smaller-molar-mass lignin fragments when compared to reference pretreatments and to pretreatments conducted with alkaline peroxide process, indicating more efficient lignin degradation caused by borohydride addition. For example, Mn and Mw values of the analyzed reference effluents were 54%-62% and 66%-71% higher when compared to the corresponding borohydride effluents, respectively. [ABSTRACT FROM AUTHOR]

The objective of this work was to determine the effect of sodium methyl mercaptide (SMM) on the yield of the packaging-grade kraft pulp. Based on our experience with bleachable grade kraft pulping using SMM, only a co-addition of 4.38% SMM with white liquor was studied. The cooking temperature and H-factor were adjusted to reach the target kappa number. The experimental results showed about a 2.7% (on O.D. (oven dry) wood basis) increase in the pulp yield after the co-addition of 4.38% SMM (on O.D. wood basis). The use of 4.38% SMM allowed lowering of the severity of the following process variables: the white liquor effective alkali charge (EA, on O.D. wood basis) by 2.4%, the cooking temperature from 165 °C to 157 0C, and the H-factor from 535 to 295. For 98 kappa pulp, the increase in pulp yield was mostly due to the increased retention of xylan (1.63%, on wood basis) and lignin (1.71%). The retention of galactoglucomannan was negligible (0.26%). There was a minor loss of cellulose (0.70%). The increase in the pulp yield in the presence of SMM can be explained by two non-exclusive mechanisms: stabilization of carbohydrate-reducing end groups during impregnation, and faster delignification during the bulk cooking phase. Based on the experimental data, we presently do not know which of the two mechanisms for increasing the pulp yield is dominating. [ABSTRACT FROM AUTHOR]

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]

Sugarcane straw (SCS) lignin is extracted by SO 2 -Alcohol-Water (SAW) fractionation (155 °C, 1 h) using methanol, ethanol or isopropanol as pulping solvent (SO 2 /Alcohol/Water = 12/44/44 wt%). The SAW fractionation removes 90–95% lignin from SCS of which only 30–45% is isolated as precipitated lignin after solvent evaporation. The precipitated and pulp residual lignin (5–10%) are analyzed for their degree of sulfonation (S/C9) while precipitated lignin is further analyzed in terms of molecular weight distribution (MWD) and alkoxylation reactions. Similar S/C9 values for methanol, ethanol and isopropanol lignin show that the degree of sulfonation is independent of fractionation solvent. However, the sulfonated lignin is comparatively less soluble in the methanol-based liquor compared to the corresponding lignins in the ethanol- and isopropanol-based liquors. The mass average molecular weight, M w , is highest for isopropanol lignin (∼3800) while the numbers for methanol and ethanol lignins are comparatively smaller but nearly equal in magnitude (∼3000). Alkoxyl groups and nuclear magnetic resonance (NMR) analyses are performed to interpret the differences in lignin M w and alkoxylation reactions. Different ether and ester type linkages are identified in NMR spectra confirming lignin alkoxylation. Lignin carbohydrate complexes (LCC) are also found in NMR spectra confirming that some of the detected carbohydrates are covalently bound to lignin. [ABSTRACT FROM AUTHOR]

Wheat straw was pretreated at 150 °C for 100 min at a liquor-to-straw ratio of 6 L/kg (oven dry basis) straw using aqueous formic acid (FA) concentrations ranging from 0 to 15 g/L. The results showed excellent sugar and lignin mass balances for pretreatment, and precipitated lignin in the hydrolysate obtained at 15 g/L of FA decreased to 0.31 g/100 g straw compared to autohydrolysis (no FA) of 0.94 g/100 g straw. The average molecular weight of precipitated lignin decreased from 1970 g/mole for autohydrolysis to 710 g/mole at 15 g/L of FA. The monomeric sugar yield during pretreatment improved from 3.83 g/100 g for autohydrolysis to 23.5 g/100 g at 15 g/L FA. [ABSTRACT FROM AUTHOR]

Lignin and ash material balances of SO 2 -ethanol–water (AVAP®) fractionation of sugarcane (SC) straw were thoroughly studied at various conditions. Most of straw lignin and ash dissolve in the liquor and 40–80% of lignin is precipitated after ethanol removal as a pure (∼99%) and sulfur-lean (<2%) fraction. Most of the acid-soluble ash and its elements (Na, K, Fe, Al) as well as large portion of silica are removed from the fiber phase. Straw lignin behavior exhibited differences compared to wood lignin including high apparent content in fiber, higher degree of sulfonation of dissolved lignin, and dense char-like precipitate formation upon ethanol removal. Variation in fractionation conditions did not have significant effect on lignin properties, while post-sulfonation was capable of changing its form from char-like to colloidal precipitate. [ABSTRACT FROM AUTHOR]

The sulfur balance of SO 2 -ethanol-water (AVAP®) fractionation of sugarcane (SC) straw was investigated. Hydrogen sulfite and sulfite anions are nearly absent in the liquors, despite cations present in straw, whose effect is thus limited to neutralization of lignosulfonic acids decreasing the acidity. Higher degree of sulfonation was observed for dissolved straw lignin compared to wood lignin (0.8–0.9 vs. 0.25 S/C9). Sulfur dioxide amounts of 0.9–1.2, 4.1–4.3 and 44–49 g per o.d. kg straw were bound to pulp, precipitated lignin and lignosulfonic acid, respectively, while the rest of SO 2 was recovered by distillation from the spent fractionation suspensions. [ABSTRACT FROM AUTHOR]