Chemical activations lignocellulosic materials

Physical activation has traditionally included a controlled gasification of the carbonaceous material that has previously been carbonized, although occasionally the activation of the precursor can be done directly. Many different carbonaceous precursors have been employed for physical activation lignocellulosic materials, coals, woods, and materials of polymeric origin. The samples are typically treated to 800-1100°C with an oxidant gas, mainly CO2 or steam, so that carbon atoms are removed selectively. Although this process obviously involves a chemical reaction (and is not merely a physical process), it is known as physical activation. 

Based on the materials highlighted by the authors of this book, it is clear that scientists throughout the world have worked diligently to improve the properties, performance, and utility of wood and other lignocellulosic materials. High-level chemical modification research activities have been developed and continuing. 

Lignocellulosic research today is poised on the threshold of a new era of research breakthroughs. It has enabled the use of a wide variety of lignocellulosic materials, low-quality wood species and sawdust, and low-value lignin products. Lignocellulosic and cellulosic research efforts are under way to produce novel products for construction, transportation, plastics, fiber, packaging, and medical applications. Some of the major activities in chemical modifications of wood, cellulose, and lignins are the main features of this book. 

Rodriguez-Reinoso F, Molina-Sabio M (1992) Activated carbons from lignocellulosic materials by chemical and/or physical activation an overview. Carbon 30(7) 1111-1118... 

The carbonization of lignocellulosic materials with metal chlorides (the basis of chemical activation). 

Frank Derbyshire and coworkers at the University of Kentucky [7,41] who carried out an extensive study of the H3PO4 activation of different raw materials, proposed an activation mechanism for the activation of lignocellulosic materials, the only materials which display interesting adsorption characteristics with this chemical reagent. Wood or lignocellulosic materials (hard fruit stones and shells) are composed of cellulose (42-50%), hemiceUulose (19-25%) and lignin (16-25%). Wood is often compared to a composite material, where most of the cellulose forms microfibrils with a crystallite structure, whereas hemicellulose and lignin fonn the matrix, an amorphous paste that surrounds the microfibrils. 

Hon DNS (1996b) Chemical modification of lignocellulosic material. Marcel Dekker, New York Inada A, Nakanishi T, Tokuda H, Sharma OP (1997) Antitumor activities of lantadenes on mouse skin tumors and mouse hepatic tumras. Planta Med 63 476-478 Jayakumar R, Mahadevappa M, Joshi S, Prasad TG (1989) Dormancy studies in Cassia sericea seeds. Seed Res 17(2) 118-121... 

The chemical activation of carbons is a complex solid-liquid reaction. The reaction takes place when the solid (carbon) reacts, at about 500°C, with a liquid (hydroxide), producing mainly H2, alkaline metal, and carbonate, if the heat treatment temperature is lower than 750°C. This reaction is a redox process in which carbon is oxidized to carbonate and hydroxide is rednced to alkali metal and hydrogen. This set of reaction products and the type of reactions taking place are not necessarily the same for all carbonaceous materials thus, for example, lignocellulosic... 

Chemical activation of lignocellulosic materials is mainly directed toward the preparation of powdered activated carbons (Studies of Caturla etal, 1991 Molina-Sabio etal., 1995, 2003 Almansa et al., 2004). As such, with the precursor being finely divided, the homogeneity of the mixture with the reagent is ensured. However, if the objective is to prepare granular activated carbon the impregnation step has to be carried out with special care to ensure an intimate contact between the precursor and the reagent. 

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