Pyrolysis products celluloses

Several compounds were also found to have a seasonal distribution. Kubatova et al. (2002) found that concentrations of lignin and cellulose pyrolysis products from wood burning were higher in aerosol samples collected during low-temperature conditions. On the other hand, concentrations of dicarboxylic acids and related products that are believed to be the oxidation products of hydrocarbons and fatty acids were highest in summer aerosols. PAHs, which are susceptible to atmospheric oxidation, were also more prevalent in winter than in summer. These results suggest that atmospheric oxidation of VOCs into secondary OAs and related oxidative degradation products are key factors in any OA mass closure, source identification, and source apportionment study. However, additional work is much desirable to assess the extent and seasonal variation of these processes. 

Besides the water elimination from the position 2,3 of the glucose unit as indicated above, other elimination positions such as 1,2 or 3,4 or 3,6 are possible. Because the side group elimination does not affect the DP value of the polymer, this reaction must be followed by the cleavage of the polymeric bonds to generate smaller molecules. These small molecules are the ones identified in cellulose pyrolysis products by techniques such as Py-GC/MS. 

The yield of hydroxyacetaldehyde can be significant in cellulose pyrolysis depending on pyrolysis conditions and was reported to vary from 7% to 19%. Mono and disaccharides with an attached C2 cleavage fragment [such as 1-(2-hydroxyethenyl)-a-glucopyranoside] were also identified in cellulose pyrolysis products. 

The Whatman No. 1 paper (as received) contained 4.1 vol Z moisture and 0.074 wt Z ash. All results reported here are on a moisture- ash-free basis unless other wise specified. Table II summarizes some analytical results of cellulose and condensed-phase cellulose pyrolysis products. A comparison of the results In Table II for cellulose and cellulose tars Indicates that the elemental composition of these two materials Is very similar. (The heating... 

Table 15.6 Cellulose Pyrolysis Products at Different Temperatures...

However, with the one-dimensional VBS there is an intrinsic problem compounds with similar volatility can be very different chemically. For example, two compounds with a (sub-cooled liquid) saturation concentration near 10 pg m are tricosane (C23H4g) and levoglucosan (CeHioOs). Each are important in the atmosphere - tricosane is a constituent of lubricating oil [9] while levoglucosan is an important tracer for wood burning because it is a cellulose pyrolysis product... 

Interesting work continues on the cellulose pyrolysis product levoglucosenone (35)3 C- -branched-chain derivatives having been produced by Michael addition reactions. Direct adducts such as (36) were obtained but, in addition, a 2 1 product (37) was... 

Acetic anhydtide is a mature commodity chemical ia the United States and its growth rate in the 1970s and 1980s was negative until 1988 when foreign demand neatly doubled the exports of 1986. This increase in exports was almost certainly attributable to the decline in the value of the U.S. doUar. Over four-fifths of all anhydtide production is utilized in cellulose acetate [9004-35-7] manufacture (see Cellulose esters). Many anhydtide plants are integrated with cellulose acetate production and thus employ the acetic acid pyrolysis route. About 1.25 kg acetic acid is pyrolyzed to produce 1.0 kg anhydtide. 

Although the pyrolysis of some classes of polysaccharide materials has been studied quite extensively in the food, petrol and tobacco industry, very little has been published specifically on polysaccharide binders (arabic gum, tragacanth gum, fruit tree gum, honey and starch). The pyrolysis of glucane based polymers, especially cellulose, has been studied in detail [6,55], highlighting how anhydrosugars and furan derivatives are the main pyrolysis products, together with one-, two- and three-carbon aldehydes and acids. 

J. Piskorz, P. Majerski, D. Radlein, A. Vladars-Usas, and D. S. Scott, Flash pyrolysis of cellulose for production of anhydro-oligomers, J. Anal. Appl. Pyrol., 56 (2000) 145-166. 

In order to fireproof wood and cotton products and to thermally convert biomass into chemicals, researchers must understand cellulose pyrolysis. Extensive research has been conducted in this area and several reviews are available (1-7). 

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. 

Conversion of polymers and biomass to chemical intermediates and monomers by using subcritical and supercritical water as the reaction solvent is probable. Reactions of cellulose in supercritical water are rapid (< 50 ms) and proceed to 100% conversion with no char formation. This shows a remarkable increase in hydrolysis products and lower pyrolysis products when compared with reactions in subcritical water. There is a jump in the reaction rate of cellulose at the critical temperature of water. If the methods used for cellulose are applied to synthetic polymers, such as PET, nylon or others, high liquid yields can be achieved although the reactions require about 10 min for complete conversion. The reason is the heterogeneous nature of the reaction system (Arai, 1998). 

Dihydro-2-hydroxymethyl-4//-pyran and/or its tautomeric forms are among the pyrolysis products of cellulose.298... 

F. Shafizadeh, R. H. Furneaux, T. T. Stevenson, and T. G. Cochran, l,5-Anhydro-4-deoxy-D-g7ycero-hex-l-en-3-ulose and other pyrolysis products of cellulose, Carbohydr. Res., 67 (1978) 433-447. 

The residence time is calculated based on the fluidizing gas velocity, assuming that the "free volume" (i.e. the volume of the expanded bed minus the volume of the sand) is fully utilized. At the temperature, total reactor gas flow rates, and sand bed volumes used, the residence time was about 0.5-1.0 sec. A typical operation began by washing the sand in 10% HNO3 and distilled water to remove impurities, such as iron, which may act as catalysts, and then calcined at 850° C for at least 12 hours to remove any sulfides and carbonates. The coal feed is then begun and pyrolysis products then exit the pyrolyser to a set of two cold traps fitted with cellulosic thimble filters maintained at 0° C. The outlet gas temperature after the first trap is 30-34° C. Much of the light char formed is entrained in the exit gas and carried into these traps, with most of it in the first trap. 

The addition of a Lewis acid, i.e., ZnC significantly decreases the production of tar and enhances the production of char due to the enhanced dehydration reactions. At higher temperatures the glycosyl units and the random condensation products are further degraded to a variety of volatile products, as shown in Table V (9). Comparison of this table with the high temperature pyrolysis products listed for cellulose in Table III shows that the products of both fractions are basically similar. The significant increase in the yields of 2-furaldehyde, water and char and decrease in the yield of tar by the addition of ZnCl verifies the enhanced dehydration and is similar to observed effects in cellulose pyrolysis. 

The list of pyrolysis products of cottonwood shown in Table VII (llj reflects the summation of the pyrolysis products of its three major components. The higher yields of acetone, propenal, methanol, acetic acid, CO, water and char from cottonwood, as compared to those obtained from cellulose and xylan, are likely attributed to lignin pyrolysis. Other results are similar to those obtained from the pyrolysis of cell-wall polysaccharides. This further verifies that there is no significant interaction among the three major components during the thermal degradation of wood. 

TABLE I. ANALYSIS OF THE PYROLYSIS PRODUCTS OF CELLULOSE AT 300° UNDER NITROGEN... 

TABLE III. PYROLYSIS PRODUCTS OF CELLULOSE AND TREATED CELLULOSE AT 600°... 

One important thermal degradation mechanism of cellulose fibres (cotton, rayon, linen, etc.) is the formation of the small depolymerisation product levoglucosan (Fig. 8.7). Levoglucosan and its volatile pyrolysis products are extremely flammable materials and are the main contributors to cellulose combustion. Compounds that are able to hinder levoglucosan formation are expected to function as flame retardants for cellulose. The crosslinking and the single type of esterification of... 

Fig. 10 shows the thermograms of cellulose in atmospheres of helium and of oxygen, obtained by Tang and Neill. In the helium atmosphere, there is an endothermic dip in the differential thermal analysis curve and a sharp loss of weight in the thermogravimetric analysis curve beginning at about 300°, which denote the pyrolytic reactions. In the oxygen atmosphere, instead of the endothermic dip, there is an exotherm due to oxidation of the pyrolysis products. 

The former variables affect the deposition of heat in the solid fuel and its transient temperature-profile, as well as the diffusion of the volatile pyrolysis products and their distribution and mixing with the surrounding atmosphere. The latter factors influence the nature and sequence of the primary and secondary reactions involved, the composition of the flammable volatiles, and, ultimately, the kinetics of the combustion. Consequently, basic study of the combustion of cellulosic materials or fire research has been channeled in these two directions. 

Coating theories.—These attribute the action to a coating of the fibers by the melted or foamed retardant, or both, restricting the escape of volatile pyrolysis products of the cellulosic material and the access of atmospheric oxygen to the reaction zone. 

Strong energy source, decompose to form pyrolysis products, which also burn in the gas phase with flaming combustion. The residual char bums at a lower rate by surface oxidation or glowing combustion. The cellulosics are converted mainly to combustible and noncombustible volatiles, including water and CO2, while the lignins contribute mainly to the char fraction. 

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