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This article seeks to be a handy document for the academy and the industry to get quickly up to speed on the current status and prospects of biomass pretreatment for biorefineries. It is divided into two biomass sources: vegetal and animal. Vegetal biomass is the material produced by plants on land or in water (algae), consuming sunlight, CO2, water, and soil nutrients. This includes residues or main products from, for example, intensive grass crops, forestry, and industrial and agricultural activities. Animal biomass is the residual biomass generated from the production of food from animals (e.g., manure and whey). This review does not mean to include every technology in the area, but it does evaluate physical pretreatments, microwave-assisted extraction, and water treatments for vegetal biomass. A general review is given for animal biomass based in physical, chemical, and biological pretreatments.

High temperature aqueous treatment of wood is the preferred technology for deconstructing lignocellulosics. Many studies have been carried out on the kinetics and mechanism of hot-water extraction. However, most were performed in batch or integral plug flow reactors, which are not optimal for measuring intrinsic dissolution kinetics of the lignocellulosic components. Therefore, we used a continuous mixed batch reactor (or Berty reactor) to determine the intrinsic dissolution kinetics of xylan, mannan, and lignin from milled hardwood (Acer rubrum) at three different temperatures (150, 160, and 170 8C) and four constant pH values: 2, 3, 4, and 5. During the initial phase of autohydrolysis (carbohydrate-free), lignin and (lignin-free) xylan dissolve starting at a high rate and then a slowly decreasing rate, respectively. This is followed by the dissolution of xylan-lignin complexes and finally cellulose xylan complexes when cellulose has been significantly hydrolysed. The kinetics and molecular weight distribution of the removed wood polymers are used to describe the topochemistry of autohydrolysis based on recent knowledge of the ultrastructure of hardwood fibres.

The effect of hot-water extraction and two types of fungal decay, brown rot and white rot, on wood crystalline cellulose structure was examined using a combination of X-ray diffraction (XRD) and 13 C solid-state nuclear magnetic resonance (NMR) spectroscopy. Although having opposite effects on the overall crystallinity of the wood, the XRD results revealed that both extraction and brown-rot decay caused a significant decrease in the 200 crystal plane spacing (d-spacing) not seen for the white-rotted samples. This effect was found to be additive, as samples that were first extracted, then decayed showed a double decrease in d-spacing compared to that caused by extraction alone. This suggested that, despite having a similarly directed effect on the spacing of the crystalline planes, the two treatment methods facilitate a decrease in d-spacing in different ways. NMR results support the conclusion of differing structural effects, suggesting that the hot-water extraction procedure was causing a co-crystallization of existing crystalline domains, while the brown rot decay was depolymerizing the cellulose chains of the crystals, possibly allowing the remaining crystalline material the freedom to relax into a more energetically favorable, tightly packed state. These findings could have important implications for those seeking to understand the effects of modification treatments or biodegradation of crystalline cellulose nanostructures in their native states.

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