Lignocelluloses physical methods

The purposes of pretreatment of lignocellulosic materials are the removal of lignin and hemicellulose, reduction of cellulose crystallinity, and increase in the porosity of the materials. Among the physical methods, mechanical treatments, such as chipping, grinding and milling are used to reduce cellulose crystallinity. The... 

Separation of biomass components is the very important initial step for the upcoming efficient utilization of biomass sources. Several physical and chemical separation methods are currently employed to overcome the recalcitrance of lignocelluloses. These methods include acid hydrolysis, alkaline hydrolysis, ammonia fiber expansion, hot water, organic solvent, and ionic liquid separation technologies. In this section of the chapter, all of the above separation methods are discussed. 

Several methods for the fractionation of hemicellulose from lignocellulose have been described in the literature. These include physical methods such as steam treatment (7-73), and chemical methods such as for exanq>le organosolv processes (d, 14, 75). In addition, microwave irradiation of lignocellulose in the presence of water has been investigated for the purpose of enzymatic saccharification and ethanol production (7d-7S) and within our project for the extraction of hemicellulose (7). 

In cellulosic ethanol production processes, a pretreatment procedure is needed to disrupt the recalcitrant structure of the lignocellulosic materials so that the cellulose can be more efficiently hydrolyzed by cellulase enzymes [2], These pretreatments include physical, biological, and chemical ways, such as uncatalyzed steam explosion, liquid hot water, dilute acid, flow-through acid pretreatment, lime, ammonium fiber/freeze explosion, and ammonium recycle percolation [3, 4], Most of these methods involve a high temperature requirement, which is usually achieved through convection- or conduction-based heating. 

For the last twenty years much work has been done in the study of the thermal stability of lignocellulosic materials by thermal analytical methods. Since these materials are complex mixtures of organic polymers, thermogravimetric (TG) analysis causes a variety of chemical and physical changes depending on the nature of the sample and its treatment prior to analysis. These problems have been reviewed recently. ... 

The pretreatment of any lignocellulosic biomass is cmcial before enzymatic hydrolysis. The objective of pretreatment is to decrease the crystallinity of cellulose which enhances the hydrolysis of cellulose by cellulases (17). Various pretreatment options are available to fractionate, solubilize, hydrolyze and separate cellulose, hemicellulose and lignin components (1,18-20). These include concentrated acid (27), dilute acid (22), SOj (25), alkali (24, 25), hydrogen peroxide (26), wet-oxidation (27), steam explosion (autohydrolysis) (28), ammonia fiber explosion (AFEX) (29), CO2 explosion (30), liquid hot water (31) and organic solvent treatments (52). In each option, the biomass is reduced in size and its physical structure is opened. Some methods of pretreatment of Lignocellulose is given in Table I. 

Physical pre-treatment processes are employed without chemical agent and microorganisms (Zheng et al, 2014). The common methods are mechanical machines, irradiation and extrusion (Karimi et al., 2013) with the objectives to open up lignocelluloses, reducing crystallinity, and increasing surface area and porosity, for more attacking availability of post-treatment (Behera etal., 2014). 

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