A review of classic Fenton's peroxidation as an advanced oxidation technique.

Lignocellulosic biomass pyrolysis mechanism: A state-of-the-art review

In recent years, growing attention has been devoted to the conversion of biomass into fuel ethanol, considered the cleanest liquid fuel alternative to fossil fuels. Significant advances have been made towards the technology of ethanol fermentation. This review provides practical examples and gives a broad overview of the current status of ethanol fermentation including biomass resources, microorganisms, and technology. Also, the promising prospects of ethanol fermentation are especially introduced. The prospects included are fermentation technology converting xylose to ethanol, cellulase enzyme utilized in the hydrolysis of lignocellulosic materials, immobilization of the microorganism in large systems, simultaneous saccharification and fermentation, and sugar conversion into ethanol.

Ethanol fermentation from biomass resources: current state and prospects.

Lignins are complex natural polymers resulting from oxidative coupling of, primarily, 4-hydroxyphenylpropanoids. An understanding of their nature is evolving as a result of detailed structural studies, recently aided by the availability of lignin-biosynthetic-pathway mutants and transgenics. The currently accepted theory is that the lignin polymer is formed by combinatorial-like phenolic coupling reactions, via radicals generated by peroxidase-H2O2, under simple chemical control where monolignols react endwise with the growing polymer. As a result, the actual structure of the lignin macromolecule is not absolutely defined or determined. The ``randomness'' of linkage generation (which is not truly statistically random but governed, as is any chemical reaction, by the supply of reactants, the matrix, etc.) and the astronomical number of possible isomers of even a simple polymer structure, suggest a low probability of two lignin macromolecules being identical. A recent challenge to the currently accepted theory of chemically controlled lignification, attempting to bring lignin into line with more organized biopolymers such as proteins, is logically inconsistent with the most basic details of lignin structure. Lignins may derive in part from monomers and conjugates other than the three primary monolignols (p-coumaryl, coniferyl, and sinapyl alcohols). The plasticity of the combinatorial polymerization reactions allows monomer substitution and significant variations in final structure which, in many cases, the plant appears to tolerate. As such, lignification is seen as a marvelously evolved process allowing plants considerable flexibility in dealing with various environmental stresses, and conferring on them a striking ability to remain viable even when humans or nature alter ``required'' lignin-biosynthetic-pathway genes/enzymes. The malleability offers significant opportunities to engineer the structures of lignins beyond the limits explored to date.

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Lignins: Natural polymers from oxidative coupling of 4-hydroxyphenyl- propanoids

The conversion of biomass by thermochemical means is very promising for the substitution of fossil materials in many energy applications. Given the complexity of biomass the main challenge in its use is to obtain products with high yield and purity. For a better understanding of biomass thermochemical conversion, many authors have studied in TG analyzer or at bed scale the individual pyrolysis of its main constituents (i.e. cellulose, hemicelluloses and lignin). Based on these studies, this original work synthesizes the main steps of conversion and the composition of the products obtained from each constituent. Pyrolysis conversion can be described as the superposition of three main pathways (char formation, depolymerization and fragmentation) and secondary reactions. Lignin, which is composed of many benzene rings, gives the highest char yield and its depolymerization leads to various phenols. The depolymerization of the polysaccharides is a source of anhydro-saccharides and furan compounds. The fragmentation of the different constituents and the secondary reactions produce CO, CO2 and small chain compounds. For temperature higher than 500 °C, the residues obtained from the different constituents present a similar structure, which evolves towards a more condensed polyaromatic form by releasing CH4, CO and H2. As the aromatic rings and their substituent composition have a critical influence on the reactivity of pyrolysis products, a particular attention has been given to their formation. Some mechanisms are proposed to explain the formation of the main products. From the results of this study it is possible to predict the reactivity and energy content of the pyrolysis products and evaluate their potential use as biofuels in renewable applications.

A review on pyrolysis of biomass constituents: Mechanisms and composition of the products obtained from the conversion of cellulose, hemicelluloses and lignin

1 Chemical Composition of Wood and Pulps: Basic Constituents and Their Distribution.- 2 Separation and Analysis of Wood Constituents with Respect to Their Morphological Location.- 3 Carbohydrates.- 4 Lignin.- 5 Extractives.- 6 Direct Characterization of Chemical Properties of Fibers.- 7 Characterization of Pulping Liquors.- 8 Analysis of Bleach Liquors.- 9 Analysis of Papermaking Process Waters and Effluents.- 10 Analysis of Inorganic Constituents.

Analytical Methods in Wood Chemistry, Pulping and Papermaking

Formation of the main degradation compound groups from wood and its components during pyrolysis

Norway spruce (Picea abies) was heated for 2–8 h in the temperature range 180–225 °C, under a steam atmosphere. The chemical analyses of the treated feedstock samples indicated that during heating (total mass loss 1.5–12.5% of the initial DS) carbohydrates (hemicelluloses and cellulose) were clearly more amenable to various degradation reactions than lignin. In addition, major water-soluble products released from the feedstock material during the treatments were classified into several compound groups and changes in the relative mass portion of these groups were monitored by GC during a separate experiment.

Thermochemical behavior of Norway spruce ( Picea abies ) at 180–225 °C

Scots pine ( Pinus sylvestris ) and silver birch ( Betula pendula ) were heated for 4-8 h in a steam atmosphere at low temperatures (200-230°). The birch feedstock decomposed slightly more extensively (6.4-10.2 and 13.5-15.2% of the initial DS at 200° and 225°, respectively) than the pine feedstock (5.7-7.0 and 11.1-15.2% at 205° and 230°, respectively). The results indicated that the differences in mass loss between these feedstocks were due to mainly the fact that carbohydrates (cellulose and hemicelluloses) were more amenable to various degradation reactions than lignin in intact wood. The degradation reactions were also monitored in both cases by determining changes in the elemental composition of the heat-treated products.

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Thermal Behavior of Scots Pine ( Pinus Sylvestris ) and Silver Birch ( Betula Pendula ) at 200-230°

A multivariate chemometric method for monitoring the mass loss of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) by IR spectroscopic determination of chemical changes occurring during the heat treatment (160 - 260 °C, 2 - 8 h) of these wood materials was developed. The method was based on the handling of FTIR data on treated and untreated wood powder samples by the partial least squares (PLS) method. In addition, unknown samples (treated and untreated pine and spruce) were classified into separate groups by the principal component analysis (PCA) method. The chemical changes occurring in the wood samples during heating were also briefly discussed.

Raimo Alén

Papers

Analytical Methods in Wood Chemistry, Pulping and Papermaking

Formation of the main degradation compound groups from wood and its components during pyrolysis

Thermochemical behavior of Norway spruce ( Picea abies ) at 180–225 °C

Thermal Behavior of Scots Pine ( Pinus Sylvestris ) and Silver Birch ( Betula Pendula ) at 200-230°

FTIR Monitoring of Chemical Changes in Softwood During Heating