Molecular Mass Distribution of Lignin from the Alkaline Pulping of Hardwood,Softwood, and Wheat Straw

Abstract

The behavior of lignin during kraft (hardwood, softwood, and wheat straw) and soda-AQ (wheat straw) pulping was studied, mainly in terms of delignification degree and molecular mass distribution (MMD). In the initial delignification phase (at 140°C for 15–60 min), a prominent part of the dissolved softwood kraft lignin (18–25 g/L, MM mostly > 3,000 Da) was found in the liquid phase of chip cavities, rather than in the external bulk black liquor (5–7 g/L, MM mostly < 3,000 Da). The maximum weight average MM values ( _w) of the soluble lignin under conventional cooking conditions were detected for the kraft softwood (4,100 Da), and kraft birch (3,400 Da) when the degree of delignification was 65–75%, corresponding to a residual lignin content of 5–10%. The maximum _w of the dissolved wheat straw kraft (5,050 Da) and soda-AQ (5,900 Da) lignins was clearly higher than that of wood-based kraft lignins (2,950–4, 100 Da).     

Fabrication of cation exchange membrane from polyvinyl alcohol using lignin sulfonic acid: Applications in diffusion dialysis process for alkali recovery

We report polyvinyl alcohol (PVA)-based hybrid membranes composed of salt of lignin sulfonic acid (LSA) and tetraethyl orthosilicate. The concentration of LSA with respect to PVA varied from 10% to 40%. The hybrid membranes showed water uptake (W_U) in the range of 122–210%, ion exchange capacities in the range of 0.32–0.75 mmol g^?1, dialysis coefficient (U_OH) from 0.0068 to 0.0119 m h^?1, and selectivity (S) from 15 to 26. The hybrid membranes also showed thermal and mechanical stability.     

Acidic pretreatment of wheat straw in decanol for the production of surfactant, lignin and glucose

Wheat straw is an abundant residue of agriculture which is increasingly being considered as feedstock for the production of fuels, energy and chemicals. The acidic decanol-based pre-treatment of wheat straw has been investigated in this work. Wheat straw hemicellulose has been efficiently converted during a single step operation into decyl pentoside surfactants and the remaining material has been preserved keeping all its promises as potential feedstock for fuels or value added platform chemicals such as hydroxymethylfurfural (HMF). The enzymatic digestibility of the cellulose contained in the straw residue has been evaluated and the lignin prepared from the material characterized. Wheat-based surfactants thus obtained have exhibited superior surface properties compared to fossil-based polyethoxylates decyl alcohol or alkyl oligoglucosides, some of which are largely used surfactants. In view of the growing importance of renewable resource-based molecules in the chemical industry, this approach may open a new avenue for the conversion of wheat straw into various chemicals.     

Homology modeling of a heme protein, lignin peroxidase, from the crystal structure of cytochrome c peroxidase

A 3-dimensional model of lignin peroxidase (LiP) was constructedbased on its sequence homology with other peroxidases, particularlycytochrome c peroxidase, the only protein with a known crystalstructure in the peroxidase family. The construction of initialconformations of insertions and deletions was assisted by secondarystructure predictions, amphipathic helix predictions, and considerationof the specific protein environment. A succession of moleculardynamics simulations of these regions with surrounding residuesas constraints were carried out to relax the bond lengths andangles. Full protein molecular dynamics simulations with explicitconsideration of bound waters were performed to relax the geometryand to identify dynamically flexible regions of the successivemodels for further refinement. Among the important functionallyrelevant structural features predicted are: (i) four disulfidebonds are predicted to be formed between Cys3 and Cys15, Cys14and Cys285, Cys34 and Cys120 and Cys249 and Cys317; (ii) a glycosyla-tionsite, Asn257, was located on the surface; (iii) Glu40 was predictedto form a salt bridge with Arg43 on the distal side of the hemeand was considered as a possible origin for the pH dependenceof compound I formation; and (iv) two candidate substrate bindingsites with a cluster of surface aromatic residues and flexiblebackbones were found in the refined model, consistent with thenature of known substrates of LiP. Based on these predictedstructural features of the model, further theoretical and experimentalstudies are proposed to continue to elucidate the structureand function of LiP.     

Elucidation of the interaction among cellulose,xylan, and lignin in steam gasification of woody biomass

The reaction mechanism for gas and tar evolution in the steam gasification of cellulose, lignin, xylan, and real biomass (pulverized eucalyptus) was investigated with a continuous cross‐flow moving bed type differential reactor, in which tar and gases can be fractionated according to reaction time. In the steam gasification of real biomass, the evolution rates of water‐soluble tar (derived from cellulose and hemicelluloses) and water‐insoluble tar (derived from lignin) decrease with increasing reaction time. It was found that the evolution of water‐soluble tar occurs earlier than in the gasification of pure cellulose, indicating an interaction of the three components. The predicted yield of water‐insoluble tar is substantially less than that of real biomass. This implies that the evolution of tar from the lignin component of biomass is enhanced, compared with pure lignin gasification, by other components. The gas evolution rate from real biomass is similar to that predicted by the superposition of cellulose, lignin, and xylan. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Enzymatic acidolysis in hexane to produce n−3 or n−6 FA-enriched structured lipids from coconut oil: Optimization of reactions by response surface methodology

Response surface methodology is a statistical design that helps one to determine optimal conditions for an enzyme-catalyzed reaction by performing a minimal number of experiments. This methodology was adapted for modifying coconut oil TAG by using lipase-catalyzed acidolysis in hexane to incorporate n−3 or n−6 PUFA. FFA obtained after hydrolysis of cod liver oil and safflower oil were used as acyl donors. Immobilized lipase, Lipozyme IM60, from Rhizomucor miehei was used for catalyzing the reaction. The reaction conditions—substrate molar ratio, incubation time, and temperature—were optimized. The experimental data were fitted to a response function based on the central composite rotatable design. The optimal conditions generated from models indicated that maximal incorporation of n−3 PUFA occurred at a 1∶4 molar ratio of TAG/FFA when incubation was carried out for 34 h at 54°C. Similarly, maximal incorporation of n−6 FA was predicted at a 1∶3 molar ratio of TAG/FFA when incubated for 48.5 h at 39°C. Experiments conducted at optimized conditions predicted by the equation obtained from response surface methodology yielded structured lipids with 13.65 and 45.5% of n−3 and n−6 FA, respectively. These values agreed well with that predicted by the model. The reactions were also scaled up to 100 g levels in batch reactors with the incorporation level of n−3 and n−6 fatty acids agreeing closely with that observed when the reactions were carried out at lab scale (100 mg). These studies indicated that response surface methodology is a useful tool in predicting the conditions for incorporating desired levels of specific FA during the synthesis of structured lipids.     

The Effect of 7 H -Dibenzo[ c,g ]carbazole and Benzo[ a ]pyrene Mixture on DNA Adduct Formation in Strain A/J Mouse Model: Preliminary Report

Complex mixtures consist of homocyclic and heterocyclic polycyclic aromatic compounds (PACs) represented by benzo[ a ]pyrene (B a P) and 7 H -dibenzo[ c,g ]carbazole (DBC), respectively. To exert their biological effects, PACs are metabolized into reactive intermediates, which can form DNA adducts. In this preliminary report, male A/J mice were given a single intraperitoneal injection. Groups of three animals were treated with DBC (2 or 10 mg/kg) or B a P (10 or 100 mg/kg). Mixtures of DBC:B a P were given at doses of 2:10, 2:100, 10:10, or 10:100 mg/kg. DNA adduct levels in lungs collected three days posttreatment were determined by the 32 P-postlabeling method. The results indicate that, in the lungs, exposure to mixtures containing more B a P than DBC resulted in the absence of adduct 3 (DBC) and significantly higher total adduct levels. This suggests that B a P is being preferentially metabolized, resulting in less DBC adduction.     

Changes in the hydrogenative ring-opening mechanism of cyclohexene oxide over Cu/SiO2 resulting from the addition of cyclohexene, a major product

The ring-opening mechanism influencing effect of a major product in the cyclohexene oxide–D₂ system was investigated over a Cu/SiO₂ catalyst. This product is cyclohexene, thus, the hydrogenative ring opening of a 1:1 cyclohexene oxide–cyclohexene mixture was studied in the presence of D₂ at 403 K in a closed circulation reactor. It was found that the mechanism of single C–O scission was not affected, but that of the double C–O scission was changed. Simultaneous bond cleavage was the major route of ring opening in the additive-free system and it became consecutive on cyclohexene addition. Added cyclohexene was hydrogenated with a very low rate, but it transformed the surface of the catalyst and, thus, facilitated the change in the mechanism. An explanation concerning the seemingly anomalous lack of deuterium in a product (cyclohexane) not seen in the additive-free system is also suggested. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synbiotic Food Consumption Reduces Levels of Triacylglycerols and VLDL,but not Cholesterol,LDL, or HDL in Plasma from Pregnant Women

To our knowledge, no reports are available indicating the effects of synbiotic food consumption on blood lipid profiles and biomarkers of oxidative stress among pregnant women. This study was conducted to evaluate the effects of daily consumption of a synbiotic food on blood lipid profiles and biomarkers of oxidative stress in pregnant women. This randomized, double-blind, controlled clinical trial was performed among 52 primigravida pregnant women, aged 18 to 35-year-old at their third trimester. After a 2-week run-in period, subjects were randomly assigned to consume either a synbiotic (n = 26) or control food (n = 26) for 9 weeks. The synbiotic food consisted of a probiotic viable and heat-resistant Lactobacillus sporogenes (1 × 10⁷ CFU) and 0.04 g inulin (HPX)/g as the prebiotic. Patients were asked to consume the synbiotic and control foods two times a day. Biochemical measurements including blood lipid profiles, plasma total antioxidant capacity (TAC) and total glutathione (GSH) were conducted before and after 9 weeks of intervention. Consumption of a synbiotic food for 9 weeks resulted in a significant reduction in serum TAG (P = 0.04), VLDL (P = 0.04) and a significant rise in plasma GSH levels (P = 0.004) compared to the control food. No significant effects of the synbiotic food consumption on serum TC, LDL, HDL and plasma TAC levels (P > 0.05) were observed. Trial registry code: http://www.irct.ir. IRCT201212105623N3.