Gasification cellulose

TABLE 9.1 Enthalpies of Selected, Stoichiometric, Cellulose Gasification Reactions"... 

Gasification assisted with partial oxidation is effective for cellulose gasification and a carbon gasification efficiency of 68% was obtained for nickel catalyst at a reaction temperature as low as 400 C and reaction time as short as 5 minutes. 

Figure 1 illustrates the critical role played by step 2 in cellulose gasification. By increasing the temperature achieved by the gas phase volatile matter from 500°C to 750°C, the carbon conversion efficiency nc is increased from qc = 0.1 to nc = 0.76. 

Because about 20% of the carbon initially in the cellulose is carried by the char product of step 1, the data presented in Figure 1 indicates that for gas phase temperatures above 750°C and residence times of 2 sec or more, permanent gases and char are essentially the only products of cellulose gasification. Less than 4% of the feedstock carbon is carried by the condensible fraction of the reactor effluent. 

Another option to extend the ligno-cellulosic feedstock base is the development of BTL through biomass gasification and subsequent Fischer-Tropsch synthesis. Although BTL is fully compatible with diesel fuel, ligno-cellulosic BTL has not yet been commercialised. 

Lignocellulose biomass is a mixture of phenolic lignin and carbohydrates -cellulose and hemi-cellulose. It grows abundantly on earth and is largely available as agricultural and forestry residues. Lignocellulose can be converted via four major routes pyrolysis, gasification, hydrolysis and fermentation. 

Catalysts for low-temperature gasification include combinations of stable metals, such as rathenium or nickel bimetallics and stable supports, such as certain titania, zirconia, or carbon. Without catalyst the gasification is limited (Krase et al., 2000). Sodium carbonate is effective in increasing the gasification efficiency of cellulose (Minowa et al., 1997). Likewise, homogeneous, alkali catalysts have been employed for high-temperature supercritical water gasification. 

Over the past two decades, considerable interest has been directed toward the conversion of cellulosic biomass (such materials as wood wastes, bagasse, and straw) into useful products, notably fuels. Several procedures, including fermentation, gasification, liquefaction, and pyrolysis, have been commercially applied to carbohydrates with various degrees of success. In order to use the polysaccharides present in lignocel-lulosic materials as a substrate in fermentation processes, pretreatments are necessary, such as with steam (under slightly acid conditions) or... 

In the area of waste utilization, Fred s program on the heat content, gasification, and carbonization of forest fuel is now recognized as a major step in our understanding of forest fires. The acid-catalyzed pyrolysis of cellulosic waste to afford l,6-anhydro-3,4-dideoxy-)3-D-g/ycero-hex-3-enopyranos-2-ulose ( levoglucosenone ) pointed the way to another method of chemical conversion of cellulosic wastes similar to cat-cracking in the petrochemical industry. 

Table 2.2. Energy change for idealised cellulose thermal conversion reactions. (Source T. Reed (1981)., Biomass Gasification, reproduced with permission. Copyright 1981, Noyes Data Corporation.)...

Under idealized conditions, the primary products of biomass gasification by pyrolysis, partial oxidation, or reforming are essentially the same The carbon oxides and hydrogen are formed. Methane and light hydrocarbon gases are also formed under certain conditions. Using cellulose as a representative feedstock, examples of some stoichiometries are illustrated by these equations ... 

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