ABSTRACT
Lignocellulosic Biomass Looking at the physicochemical differences between the main constituents of lignocellulosic biomass (extractives, inorganics, hemicellulose, cellulose, and lignin), it seems logical to explore the potential of a sequential multistep or staged fractionation approach to effectively unravel the complex biomass structure into its main fractions. Although few examples show the potential of a step-wise approach to unravel the major constituents within the complex lignocellulosic biomass (see Section 9.2.3), neglecting constituents such as inorganic matter (ash minerals) and extractives may lead to suboptimal fractionation results due to various and unknown interferences between inorganics, organic extractives, and the major fractions hemicellulose, cellulose, and lignin. To improve the biorefinery of lignocellulosic biomass, a governing principle could be that each fraction (including inorganics and extractives) is targeted according to its specific physicochemical characteristics, starting with the least severe treatment conditions. This option offers some clear advantages compared to direct transformation of the whole biomass. Firstly, it enables the valorization of all important biomass constituents, including the
nonstructural fractions. Secondly, it offers the possibility to obtain the main biomass fractions (hemi)cellulose and lignin in superior quality because of the effective removal of the other (interfering) compounds and the prevention of undesired side reactions such as the formation of “pseudolignin.” The following sequence can be envisioned: 1. (Soluble) ash removal by washing with cold acidified water 2. Removal of extractives at elevated temperature with water and organic solvents 3. Hemicellulose auto-or catalytic hydrolysis 4. Lignin and cellulose separation by organosolv delignification
In an integrated biorefinery the sequence above could be seen as the solvent-based primary biorefinery in which lignocellulosic biomass is pretreated and fractionated into products that are further processed in a secondary biorefinery. This secondary biorefinery uses dedicated technologies for each of the fractions from the primary biorefinery, as visualized in Fig. 9.1. Basically, each step results in a product that can either be fractionated further or processed via a different route such as pyrolysis, gasification, chemical conversion, or biotechnological ways (e.g., anaerobic digestion and fermentation).
