Composition, biomass hemicelluloses

Cellulose is found in nature in combination with various other substances, the nature and composition of which depend on the source and previous history of the sample. In most plants, there are three major components cellulose, hemicelluloses, and lignin. Efficient utilization of all three components would greatly help the economics of any scheme to obtain fuel from biomass. Hemicelluloses, lignocellulose and lignin remaining after enzymatic degradation of the cellulose in wood would require chemical or thermal treatment - as distinct from biochemical - to produce a liquid fuel. 

Another approach to produce chemicals via degraded molecules is the fast pyrolysis of biomass at high temperatures in the absence of oxygen. This gives gas, tar and up to 80 wt.% of a so-called bio-oil liquid phase, which is a mixture of hundreds molecules. Some of compounds produced by pyrolysis have been identified as fragments of the basic components of biomass, viz. lignin, cellulose and hemicellulose. The bio-oil composition depends upon the nature of starting... 

The basic structure of all wood and woody biomass consists of cellnlose, hemicelluloses, lignin and extractives. Their relative composition is shown in Table 2.4. Softwoods and hardwoods differ greatly in wood stmctnie and composition. Hardwoods contain a greater fraction of vessels and parenchyma cells. Hardwoods have a higher proportion of cellulose, hemicelluloses and extractives than softwoods, but softwoods have a higher proportion of lignin. Hardwoods ate denser than softwoods. 

Complex pyrolysis chemistry takes place in the conversion system of any conventional solid-fuel combustion system. The pyrolytic properties of biomass are controlled by the chemical composition of its major components, namely cellulose, hemicellulose, and lignin. Pyrolysis of these biopolymers proceeds through a series of complex, concurrent and consecutive reactions and provides a variety of products which can be divided into char, volatile (non-condensible) organic compounds (VOC), condensible organic compounds (tar), and permanent gases (water vapour, nitrogen oxides, carbon dioxide). The pyrolysis products should finally be completely oxidised in the combustion system (Figure 14). Emission problems arise as a consequence of bad control over the combustion system. 

However, the research of the conversion of the biomass containing cellulose, such as com stalk, into biohydrogen is lacking. In general, it is hard to convert directly raw crop stalk wastes into biohydrogen gas by microbe anaerobic fermentation because of their complex chemical composition, e.g., cellulose, hemicellulose, lignin, protein, fat. 

Bio-oil from rapid pyrolysis is usually a dark brown, free-flowing liquid having a distinctive smoky odor. It has significantly different physical and chemical properties compared to the liquid from slow pyrolysis processes, which is more like a tar. Bio-oils are multicomponent mixtures comprised of different size molecules derived primarily from depolymerization and fragmentation reactions of the three key biomass building blocks cellulose, hemicellulose, and lignin. Therefore, the elemental composition of biooil resembles that of biomass rather than that of petroleum oils. Basic properties of biooils are shown in Table 33.7. More detail on fuel-related characteristics is provided in the literature.571... 

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. 

In wood pyrolysis, it is known that several parameters influence the yield of pyrolytic oil and its composition. Among these parameters, wood composition, heating rate, pressure, moisture content, presence of catalyst, particle size and combined effects of these variables are known to be important. The thermal degradation of wood starts with free water evaporation. This endothermic process takes place at 120 to 150 C, followed by several exothermic reactions at 200 to 250°C, 280 to 320 C, and around 400 C, corresponding to the thermal degradation of hemicelluloses, cellulose, and lignin respectively. In addition to the extractives, the biomass pyrolytic liquid product represents a proportional combination of pyrolysates from cellulose, hemicelluloses. 

Cellulosic fiber reinforced polymeric composites find applications in many fields ranging from the construction industry to the automotive industry. The reinforcing efficiency of natural fiber is related to the namre of cellulose and its crystallinity. The main components of natural fibers are cellulose (a-cellulose), hemicelluloses, lignin, pectins, and waxes. For example, biopolymers or synthetic polymers reinforced with natural or biofibers (termed biocomposites) are a viable alternative to glass fiber composites. The term biocomposite is now being applied to a staggering range of materials derived wholly or in part from renewable biomass resources [23]. 

No discrete groupings or clusters were observed among the clones when plotted in a 3D graph (Fig. 2). Several multivariate analyses were performed, but all proved to be inconclusive and are not presented here. Most of the willow clones analyzed have similar biomass composition however, there are several clones that have distinctively more or less cellulose, hemicellulose, or lignin (Fig. 2). This could be very important in future selection of willow varieties optimized for a particular application. 

The other analytical methods involving biomass composition that are currently in development (FT-IR, NIR, and pyMBMS) are able to resolve and quantify individual sugar composition. This is not possible with HR-TGA however, in conjunction with H nuclear magnetic resonance (NMR), sugar residues can be identified, and their abundance can be determined. Carbohydrate compositional profiles of lignocellulosic biomass can be accurately quantified based on the 600 MHz H-NMR spectram of unpurified acid hydrolyzates wherein the hemicellulose and cellulose ftactions of biomass have been reduced to a mixmre of sugars in acidic solution [23]. 

Within the GC detectable range, we identified the different composition of the liquid products from the various origins by using a GC-MS analysis. The liquid products from Kraft pine lignin contain mainly guaiacol and methyl dehydroabietate. The liquid products from oat hull, hardwood, and switchgrass contain acetic acid, 1-hydroxy-2-propanone, and/ or furfural, which are the products of hemicellulose and cellulose. This further confirms that these three materials contain hemicellulose and cellulose. The liquid products have only two to three component differences from one biomass species to another. But the composition distributions are quite different among species (Table 4). So the composition of liquid products depends on the type of raw materials. 

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 examining biomass conversion approaches in detail, we first briefly review the chemical composition of plant biomass. The main biomass compraients [16, 17] are cellulose [18-20], hemicellulose [21], starch, sugars, lignin [22], oils, fats, and waxes [23, 24], proteins [25, 26], and various extractives. Those most relevant to the biorefinery are shown in Fig. 3. 

Bamboo, belonging to the grass family Poaceae, is an abundant renewable natural resource capable of producing maximum biomass per unit area and time as compared to counterpart timber species (Tewari 1995). The chemical composition of D. strictus has been studied, which was found to contain Cross and Bevan cellulose 68.0% and lignin 32.20% (Singh et al. 1991). Its hemicellulose (18.8%) has also been shown to consist of xylose 78.0%, arabinose 9.4%, and uronic acid 12.8% (Tewari 1995). 

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