Extraneous Materials

A large number of compounds are available in lignocelluloses, known as extra­neous materials, which can be extracted by means of polar and nonpolar solvents. The composition and content of these materials vary among lignocelluloses spe­cies. Based on their solubility in water, extraneous materials are divided into two categories: extractives or nonextractives (Fan et al. 1982). The most important parts of extractive components are resins (fats, fatty acids, resin acids, and phy­tosterols), terpenes (isoprene alcohols and ketones), and phenols (residue and byproducts of lignin biosynthesis) (Fan et al. 1982; Fengel and Wegener 1984).

The inorganic components such as alkali earth carbonates, oxalates, starches, pectins, and proteins make the nonextractives part of extraneous materials. In some types of grasses and straws, there is also a significant level of nonextractive silica crystals (Fan et al. 1982). Particularly, rice straw is covered by a layer of silica, which results in a different behavior in the pretreatments compared with other similar biomass, e. g., wheat straw (Binod et al. 2010).

Usually, the extraneous parts are not considered to play much of a role in lowering cellulosic biomass biological conversions, and fewer attempts have been made in this direction. Although it might be intriguing, it would be difficult to see the effect of these components, since they are in large numbers and mostly present in low amounts.

3.3

Подпись: Fig. 3.3 Pretreatment of lignocelluloses for different proposes

Pretreatment

The main purpose of lignocellulosic materials pretreatment is to improve their biological conversion in the subsequent bioprocessing (Figs. 3.3 and 3.4). This process is known as a key for economically feasible production of different chemicals, e. g., ethanol, butanol, lactic acid, and biogas, as well as animal feed (Cameron et al. 1990, 1991; Shah et al. 1991; Castro et al. 1993; Deschamps et al. 1996; Wang et al. 2004; Yang and Wyman 2008; Taherzadeh and Karimi 2008; Aad et al. 2010; Teghammar et al. 2010).

Подпись: Wood chips Pretreated wood chips Fig. 3.4 The effects of pretreatment on biomass [Unpublished data (Shafiei et al. 2012)]

Highly compact and Disrupted and more accessible structure

protected structure with less crystalline cellulose

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