Composition, biomass celluloses

The higher plant cellulosic fiber is sub-divided into non-woody fibers (straw, grass, bast, trunk, stem, frond, leaf, seed and fruit) and woody fibers (pine, rubber. Acacia, teak) (Nazir, 2013). Different plant biomass possesses different composition of cellulose (g/g) such as jute (61-71.5%), flax (71%), hemp (60.2-74.4%), ramie (68.6-76.2%), kenaf (31-39%), sisal (67-78%), pineapple leaf fiber (70-82%), henequen (77.6%), cotton seed (82.7%), rice... 

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... 

Biomass is complex in composition, consisting of starch, cellulose, hemicellu-lose and lignin and small amounts of fats. In the past, typically only one of these constituents of the biomass was converted, and the rest discarded. The operations were thus highly inefficient when compared with fossil hydrocarbon refinery. 

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. 

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. 

In addition to the variations in the LHC composition that occur from species to species, each species has its extractives, which include resins and waxes. These constituents are capable of interfering with cellulose hydrolysis because of their hydrophobic nature. Tannins and other highly reactive materials are constituents of some woody species. When LHC is obtained from nonwoody (herbaceous) species, the range of interfering constituents increases greatly. Sugars, starches, dextran, carotenoids, and many isoprenoids are to be found. Operators of a cellulose hydrolysis process that uses municipal solid waste as its biomass resource may experience seasonal variations in composition and chance inclusion of crankcase oil and other products that inhibit enzymes or kill yeast. 

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... 

Flash pyrolysis in FFR is a usefnl means to remove snlphnr from coal [19, 21]. As shown by Li et al. [22], it can also be ntilized to remove heteroatom molecules from biomass. Both the yield and the composition of the resnltant gas depend on the biomass composition. The gas ontpnt is richer in hydrogen in the case of cellulose and hemicel-Inlose than in the case of lignin. Smaller biomass particle sizes and higher fast pyrolysis temperatnres also boost hydrogen content. The total of carbon monoxide and hydrogen content is reported to be 65.4% for legnme straw and 55.7% for apricot stone. 

Using cellulose as a representative feedstock composition, estimates of the enthalpy changes for some of the primary reactions that take place in biomass... 

What are unambiguous ways to study biomass composition and its relationship to pyrolysis rate and products Are traditional, operational definitions of composition such as cellulose, Klason or Kraft lignin, and extractives weight fraction useful What other composition metrics are useful especially as under-utilized or transgenic biomass species are examined ... 

The traditional pulp/paper composition metrics (e.g. specific lignin and cellulose contents) are based on chemical reaction (depolymerization) of the native biomass into fractions. Each separated fiaction is then independently pyrolysed, and the pyrolysis yields are fit to models, and the composite used to predict other woody species ... 

Using regression analysis to quantify the intrinsic cellulose, lignin, and ash fractions effects on a few products, MacKay and Roberts (1982) studied the pyrolytic behavior of 20 unmodified or native powdered Hgnocellulosic materials. Linear regression models for total mass and carbon yields of the products were developed, assuming each constituent fraction of the biomass was pyrolyzed independently. They concluded that char yield increased with substrate ca n content char yield from lignin content was found to be three times that of cellulose content. They did not study the gas nor tar composition in their experiments. In addition their particle sizes... 

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. 

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