Biofuels produced from various lignocellulosic materials, such as wood, agricultural, or forest residues, have the potential to be a valuable substitute for, or complement to, gasoline. Many physicochemical structural and compositional factors hinder the hydrolysis of cellulose present in biomass to sugars and other organic compounds that can later be converted to fuels. The goal of pretreatment is to make the cellulose accessible to hydrolysis for conversion to fuels. Various pretreatment techniques change the physical and chemical structure of the lignocellulosic biomass and improve hydrolysis rates. During the past few years a large number of pretreatment methods have been developed, including alkali treatment, ammonia explosion, and others. Many methods have been shown to result in high sugar yields, above 90% of the theoretical yield for lignocellulosic biomasses such as woods, grasses, corn, and so on. In this review, we discuss the various pretreatment process methods and the recent literature that...

http://ucce.ucdavis.edu/files/datastore/234-1388.pdf

Methods for Pretreatment of Lignocellulosic Biomass for Efficient Hydrolysis and Biofuel Production

Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.

Fungal laccases - occurrence and properties.

4th Generation District Heating (4GDH) Integrating smart thermal grids into future sustainable energy systems

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

http://umu.diva-portal.org/smash/get/diva2:882304/FULLTEXT01

Pretreatment of lignocellulose: Formation of inhibitory by-products and strategies for minimizing their effects

The economic dependency on fossil fuels and the resulting effects on climate and environment have put tremendous focus on utilizing fermentable sugars from lignocellulose, the largest known renewable carbohydrate source. The fermentable sugars in lignocellulose are derived from cellulose and hemicelluloses but these are not readily accessible to enzymatic hydrolysis and require a pretreatment, which causes an extensive modifi cation of the lignocellulosic structure. A number of pretreatment technologies are under development and being tested in pilot scale. Hydrolysis of lignocellulose carbohydrates into fermentable sugars requires a number of different cellulases and hemicellulases. The hydrolysis of cellulose is a sequential breakdown of the linear glucose chains, whereas hemicellulases must be capable of hydrolysing branched chains containing different sugars and functional groups. The technology for pretreatment and hydrolysis has been developed to an extent that is close to a commercially viable level. It has become possible to process lignocellulose at high substrate levels and the enzyme performance has been improved. Also the cost of enzymes has been reduced. Still a number of technical and scientifi c issues within pretreatment and hydrolysis remain to be solved. However, signifi cant improvements in yield and cost reductions are expected, thus making large-scale fermentation of lignocellulosic substrates possible. © 2007 Society of Chemical Industry and John Wiley & Sons, Ltd

Enzymatic conversion of lignocellulose into fermentable sugars: challenges and

The economic dependency on fossil fuels and the resulting effects on climate and environment have put tremendous focus on utilizing fermentable sugars from lignocellulose, the largest known renewable carbohydrate source. The fermentable sugars in lignocellulose are derived from cellulose and hemicelluloses but these are not readily accessible to enzymatic hydrolysis and require a pretreatment, which causes an extensive modification of the lignocellulosic structure. A number of pretreatment technologies are under development and being tested in pilot scale. Hydrolysis of lignocellulose carbohydrates into fermentable sugars requires a number of different cellulases and hemicellulases. The hydrolysis of cellulose is a sequential breakdown of the linear glucose chains, whereas hemicellulases must be capable of hydrolysing branched chains containing different sugars and functional groups. The technology for pretreatment and hydrolysis has been developed to an extent that is close to a commercially viable level. It has become possible to process lignocellulose at high substrate levels and the enzyme performance has been improved. Also the cost of enzymes has been reduced. Still a number of technical and scientific issues within pretreatment and hydrolysis remain to be solved. However, significant improvements in yield and cost reductions are expected, thus making large-scale fermentation of lignocellulosic substrates possible. © 2007 Society of Chemical Industry and John Wiley & Sons, Ltd

Enzymatic conversion of lignocellulose into fermentable sugars: challenges and opportunities.

Working at high solids (substrate) concentrations is advantageous in enzymatic conversion of lignocellulosic biomass as it increases product concentrations and plant productivity while lowering energy and water input. However, for a number of lignocellulosic substrates it has been shown that at increasing substrate concentration, the corresponding yield decreases in a fashion which can not be explained by current models and knowledge of enzyme-substrate interactions. This decrease in yield is undesirable as it offsets the advantages of working at high solids levels. The cause of the 'solids effect' has so far remained unknown. The decreasing conversion at increasing solids concentrations was found to be a generic or intrinsic effect, describing a linear correlation from 5 to 30% initial total solids content (w/w). Insufficient mixing has previously been shown not to be involved in the effect. Hydrolysis experiments with filter paper showed that neither lignin content nor hemicellulose-derived inhibitors appear to be responsible for the decrease in yields. Product inhibition by glucose and in particular cellobiose (and ethanol in simultaneous saccharification and fermentation) at the increased concentrations at high solids loading plays a role but could not completely account for the decreasing conversion. Adsorption of cellulases was found to decrease at increasing solids concentrations. There was a strong correlation between the decreasing adsorption and conversion, indicating that the inhibition of cellulase adsorption to cellulose is causing the decrease in yield. Inhibition of enzyme adsorption by hydrolysis products appear to be the main cause of the decreasing yields at increasing substrate concentrations in the enzymatic decomposition of cellulosic biomass. In order to facilitate high conversions at high solids concentrations, understanding of the mechanisms involved in high-solids product inhibition and adsorption inhibition must be improved.

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Yield-determining factors in high-solids enzymatic hydrolysis of lignocellulose

To improve process economics of the lignocellulose to ethanol process a reactor system for enzymatic liquefaction and saccharification at high-solids concentrations was developed. The technology is based on free fall mixing employing a horizontally placed drum with a horizontal rotating shaft mounted with paddlers for mixing. Enzymatic liquefaction and saccharification of pretreated wheat straw was tested with up to 40% (w/w) initial DM. In less than 10 h, the structure of the material was changed from intact straw particles (length 1-5 cm) into a paste/liquid that could be pumped. Tests revealed no significant effect of mixing speed in the range 3.3-11.5 rpm on the glucose conversion after 24 h and ethanol yield after subsequent fermentation for 48 h. Low-power inputs for mixing are therefore possible. Liquefaction and saccharification for 96 h using an enzyme loading of 7 FPU/g.DM and 40% DM resulted in a glucose concentration of 86 g/kg. Experiments conducted at 2%-40% (w/w) initial DM revealed that cellulose and hemicellulose conversion decreased almost linearly with increasing DM. Performing the experiments as simultaneous saccharification and fermentation also revealed a decrease in ethanol yield at increasing initial DM. Saccharomyces cerevisiae was capable of fermenting hydrolysates up to 40% DM. The highest ethanol concentration, 48 g/kg, was obtained using 35% (w/w) DM. Liquefaction of biomass with this reactor system unlocks the possibility of 10% (w/w) ethanol in the fermentation broth in future lignocellulose to ethanol plants.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/bit.21115

Liquefaction of Lignocellulose at High-Solids Concentrations

Background
Pretreatment is an essential step in the enzymatic hydrolysis of biomass and subsequent production of bioethanol. Recent results indicate that only a mild pretreatment is necessary in an industrial, economically feasible system. The Integrated Biomass Utilisation System hydrothermal pretreatment process has previously been shown to be effective in preparing wheat straw for these processes without the application of additional chemicals. In the current work, the effect of the pretreatment on the straw cell-wall matrix and its components are characterised microscopically (atomic force microscopy and scanning electron microscopy) and spectroscopically (attenuated total reflectance Fourier transform infrared spectroscopy) in order to understand this increase in digestibility.

/pdf/cell-wall-structural-changes-in-wheat-straw-pretreated-for-36loedrquw.pdf

Claus Felby

Papers

Enzymatic conversion of lignocellulose into fermentable sugars: challenges and

Enzymatic conversion of lignocellulose into fermentable sugars: challenges and opportunities.

Yield-determining factors in high-solids enzymatic hydrolysis of lignocellulose

Liquefaction of Lignocellulose at High-Solids Concentrations

Cell-wall structural changes in wheat straw pretreated for bioethanol production.