Biljana Bujanovic

Evaluation of different sulfur-free delignification methods for hot-water extracted hardwood.

Abstract Hot-water extraction (HWE) of hardwoods may be performed as a part of sequential disintegration of hardwoods in a biorefinery system. In this study, different sulfur-free delignification methods were investigated for their respective effectiveness in lignin removal from unextracted (SM) and hot-water-extracted sugar maple (SMHWE). Peracetic acid and tetrahydrofurfural alcohol were investigated as attractive delignification agents, which may be produced on site (biorefinery products). Oxygen was used in combination with the organic solvents acetone and ethanol, designed sugar fermentation products from hydrolyzed hot-water extracts. The delignification degree and delignification selectivity were compared for SM and SMHWE. SMHWE consistently showed a higher degree of delignification. Also, a higher selectivity was observed in delignification of SMHWE with all investigated agents except peracetic acid. Oxygen delignification in an acetone:water mixture was the most selective in delignification of SMHWE. The delignification results obtained using the acetone-water-oxygen system for sugar maple were confirmed using Eucalyptus (unextracted, Eu, and hot-water-extracted, EuHWE). These results indicate that the structural and chemical changes occurring during HWE of hardwoods provide for a more efficient subsequent delignification with a wide range of delignification agents.

Polyoxometalates in Oxidative Delignification of Chemical Pulps: Effect on Lignin

Chemical pulps are produced by chemical delignification of lignocelluloses such as wood or annual non-woody plants. After pulping (e.g., kraft pulping), the remaining lignin is removed by bleaching to produce a high quality, bright paper. The goal of bleaching is to remove lignin from the pulp without a negative effect on the cellulose; for this reason, delignification should be performed in a highly selective manner. New environmentally-friendly alternatives to conventional chlorine-based bleaching technologies (e.g., oxygen, ozone, or peroxide bleaching) have been suggested or implemented. In an attempt to find inorganic agents that mimic the action of highly selective lignin-degrading enzymes and that can be applicable in industrial conditions, the researchers have focused on polyoxometalates (POMs), used either as regenerable redox reagents (in anaerobic conditions) or as catalysts (in aerobic conditions) of oxidative delignification. The aim of this paper is to review the basic concepts of POM delignification in these two processes.

Polyoxometalate Delignification of Birch Kraft Pulp and Effect on Residual Lignin

Abstract To advance the understanding of delignification with polyoxometalates (POMs) that have been explored for use in bleaching of chemical pulps, the transformation of lignin during anaerobic treatment of birch kraft pulp with an equilibrated POM mixture composed of Na5(+2)[SiV1(-0.1)MoW10(+0.1)O40] was investigated. The conversion factor between the Klason lignin and the kappa number corrected for the hexenuronic acid (HexA) contribution gradually increased, indicating loss of lignin oxidizability. Comparative analysis of residual lignins isolated from pulps of decreasing kappa number showed that lignin undergoes changes that include a sharp reduction in the content of PhOH groups, a gradual demethylation, and a high increase in carbonyl groups. The results indicated that the POM treatment of kraft pulps leads to the loss of aromaticity, most likely caused by the conversion of aromatic rings to quinone moieties. The 2D NMR studies revealed the disappearance of the correlations assigned to stilbene structures formed during kraft pulping, and the weakening of those assigned to the native lignin bonds. The GPC studies showed a gradual lignin depolymerization.

Lignin modification in the initial phase of softwood kraft pulp delignification with polyoxometalates (POMs)

Abstract Commercial softwood kraft pulp with kappa number 30.5 (KP30.5) was delignified with polyoxometalates (POM, Na5(+2)[SiV1(-0.1)MoW10(+0.1)O40]), and POM-treated kraft pulp of kappa number 23.6 was obtained (KPPOM,23.6). Residual lignin from pulps was isolated by mild acid hydrolysis and characterized by analytical and spectral methods to gain insight into lignin reactions taking place during the initial delignification phase. Lignin from POM-delignified pulp was isolated in lower yield. Comparative analysis of residual lignins (RL-KP30.5, RL-KPPOM,23.6) showed that POM leads to products enriched in carbonyl/carboxyl groups and carbohydrates. POM lignins have a lower molecular mass and a lower content of phenolic hydroxyl and methoxyl groups. Based on these results and FTIR spectra, we suggest that aromatic ring cleavage and quinone formation occur during POM delignification. The degree of lignin-cellulose association increases after POM delignification. Lignin-cellulose association was found to be partially unstable under mild alkaline conditions, as residual lignin isolated after alkaline extraction of KPPOM,23.6 pulp (RL-KPPOM/NaOH) exhibited lower glucose content, higher Klason lignin content, and less extraneous material.

CHAPTER 7:Niche Position and Opportunities for Woody Biomass Conversion

For centuries, humans used plant biomass as food and heat, but use of biomass for fuel and chemicals was largely displaced by fossil sources after the commercial utilization of coal, and more recently petroleum and natural gas. Fossil sources have certain advantages over biomass in terms of energy density, shipping, and storage. However, fossil fuel combustion by a rapidly expanding world population over the past century has led to sharp increases in atmospheric CO2, and may very well be linked to human-induced climate change. Moreover, petroleum is an unsustainable energy source; even the most conservative projections indicate crude oil reserves will be depleted by the year 2100 (1). Rebuilding the potential of biomass as a renewable source of materials and cleaner energy is imperative to the sustainability of human civilization. Commercial deployment of lignocellulosic-based biorefinery technology, making full use of all available forest materials, woody biomass crops, perennial grasses, and agricultural residues, is the niche opportunity pathway in woody biomass conversion for ABS Process™ Biorefinery Technology, incorporating Hot Water Extraction™ cooking to contribute toward sustainable world development. A critical factor in defining the success of this process may be integration of lignin products into the product portfolio.