Composition of Biomass

Biomass contains more oxygen than fossil sources (30-50 wt.%, see Fig. 6.1). In Fig. 6.1, (biomass and fossil) sources and fuels (fuel blends) are positioned in the O/C-H/C plane. 

Along with carbon, hydrogen and oxygen, lignocellulosic biomass also contains hetero elements such as alkali and other metals. The amounts of these ashes vary over a broad range, from 30-50 wt.% in chicken litter to 1-3 wt.% in wood. Moisture is always present in lignocellulosic biomass and can be up to 80 wt.% in some cases. Detailed information on the composition of biomasses can be found in data bases, e.g., Phyllis [21] from the Dutch Energy Research Foundation (ECN). Table 6.2 lists the compositions of some typical biomasses. 

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Ash Characteristics. The elemental ash composition of biomass waste and municipal soHd waste differs dramatically from that of coal (qv). ... 

The compositions of biomass among fuel types are considerably varied, especially with respect to inorganic constituents important to the critical problems of fouling and slagging. Alkali and alkaline earth metals, in combination with other fuel elements such as silica and sulfur, and facilitated by the presence of chlorine, are responsible for many imdesirable reactions in combustion furnaces and power boilers. 

The measure of mass is important with respect to calculating mass balance. However, the elemental composition of biomass is normally ill defined. Another reason for determining biomass is the need for a reference when calculating specific rates (q ) q = r /x. An ideal measure for the biocatalysts in a bioreaction system of interest would be their activity, physiological state, morphology or other classification rather than just their mass. Unfortunately, these are even more difficult to quantify objectively and this is obviously why the biomass concentration is still of the greatest interest. 

Yields of the different pyrolysis products (i.e. char, bio-oil, and gases) are dependent on the chemical composition of biomass. Biomass with high lignin content produces more char compared to biomass with lower content [20], Furthermore, biomass with high alkali and alkali earth metal concentrations generates less bio-oil and instead more char and gases [14, 15, 21]. Prior to pyrolysis, it is beneficial to dry the biomass to less than 10 wt% moisture in order to minimize the water content in the bio-oil [14],... 

The analytical methods used to determine the composition of biomass materials are also a source of some variance in this kind of analysis. It must be determined whether variance due to sampling and measurement techniques is significant in light of variance from genetic and environmental sources. 

Table 3.2 Elemental composition of biomass burning aerosols in the Amazon basin measured during the SCAR-B experiment and comparison with long-term ground-based measurements at Alta Floresta and Cuiaba.

Intuitively, it might also be expected that the composition of biomass would vary over a broad range because there are so many different types and species. 

Biomass is composed of various components such as cellulose, hemicellulose, lignin, extractives and mineral water. The composition of biomass plays a definitive role in altering the product distribution and their properties [2-3J. As is shown in earlier publications [4-S] different biomass, on pyrolysis, give different product yield with different product properties. In order to choose a biomass for a particular process (carbonisation, liquefaction, gasification or adsorbent char) knowledge on the product distribution and properties for various biomass are essential. 

Further, it is also possible to obtain the suitability of biomass knowing only the initial composition of biomass. For this purpose various correlations developed and reported in previous publications [4-8] are employed in order to obtain the required product yield and their properties so as to enable rating of a biomass for a process. 

CHEMICAL COMPOSITION OF BIOMASS FAST PYROL YSIS UQUID... 

PHYLLIS—database on composition of biomass and waste. Energy Research Centre of the Netherlands http //www.ecn.nl/phyllis/ (accessed Nov 16, 2003). 

The isotopic composition of biomass carbon is given by Equation (5). 

The chemical composition of biomass with respect to carbon, hydrogen and oxygen can be approximated by the formula C6H9O4, that is biomass contains a little less... 

The chemical composition of biomass materials is generally discussed in terms of cell wall polysaccharides (cellulose and hemicelluloses), phenolics (lignin and polyphenols), extractives, and ash content. Wood normally contains small amounts of ash (1 percent) and various quantities of extractives... 

Before detailing the pyrolysis processes and its reactors, it is necessary to specify the origin, properties, and chemical compositions of the raw material, as well as products from biomass. Several experimental studies have reported cases on the composition of biomass. A review was quite extensive and recently studied by Vassilev et al. (2010). Naturally, the composition of the vapors and gases produced depends on the characteristics of the raw material, the pyrolysis process, and operating conditions. Therefore, knowledge of the chemical nature is the first and essential step in this process. 

VassUev SV, Baxter D, Andersen LK, VassUeva CG. (2010). An overview of the chemical composition of biomass. Fuel, 89(5), 913-933. 

Rakotoarivonina H, Herman B, Monthe N, Remond C. (2012). The hemicellulolytic enzyme arsenal of Thermobacillus xylanolyticus depends on the composition of biomass used for growth. Microb Cell Fact, 11, 159. 

Goldstein IS. Composition of biomass. In Goldstein IS, editor. Organic chemicals from biomass. Boca Raton (FL, USA) CRC Press 1981. p. 9—18.2nd printing. 

Alen R. Structure and chemical composition of biomass feedstocks. In Alen R, editor. Biorefining forest resources. Helsinki (Finland) Paper Engineers Association/Paperi ja Puu 2011.p. 17—54. 

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