Lignin char

This investigation was extended to wood and lignin chars prepared at 400 °C to determine the effect of preexisting aromatic nuclei of lignin in the charring reactions. The permanganate oxidation analysis indicated that these chars, like cellulose chars, have considerably condensed or cross-linked aromatic structures, even at 400 C. The NMR data also showed that the chars from similar cellulose, wood. 

Lignin char prepared by carbonizing equal parts of lignin and sodium hydroxide. Char washed before activation. 

The rate of heat penetration through the char layer is in proportion to the thermal properties and porosity of the char (43,44) since the mode of heat transfer to the unreacted lignin/char interface is by ordinary conduction through the char rather than by electron bombardment. Thus the apparent rate of devolatilization as measured by weight loss kinetics is slower (k > 1-10 min ) than one might predict from electron pseudotemperatures in the gas plasma. After an initial period, these apparent devolatilization rates are consistent with rates for conduction in porous char (44,49). 

Characterization in liquid wastes from eucalyptus wood and kraft lignin charring by flame-ionization gas-chromatography and gas-chromatography/ mass-spectrometry [2868],... 

Identification in liquid wastes from eucalyptus wood and kraft lignin charring [2868]. 

It has been shown that aromatic aldehydes including vanillin, syfingaldehyde, coniferaldehyde, siaapaldehyde, and ethyl lignin come from charred wood, the length of matufing directly affects the amount of aldehydes formed, the lower proof spirits have more aldehydes than higher proof spirits do, and the used and new uncharred barrels produce about one-third of the aromatic aldehydes found ia new charred barrels (Table 3) (8). 

The conditions used for char preparation in the present chemisorption studies (i.e., progressive slow charring of wood) are intended to be relevant to "real life" smoldering combustion situations. Most previous studies of chemisorption have used chars from cellulose (i.e., avoiding hemicellulose and lignin... 

Pyrolysis has a long history in the upgrading of biomass. The dry distillation of hardwood was applied in the early 1990s to produce organic intermediates (methanol and acetic acid), charcoal and fuel gas [3]. Today s processes can be tuned to form char, oil and/or gas, all depending on the temperature and reaction time, from 300 °C and hours, to 400-500 °C and seconds-minutes, to >700 °C and a fraction of a second [3, 19, 23, 24], The process is typically carried out under inert atmosphere. We illustrate the basic chemistry of pyrolysis by focusing on the conversion of the carbohydrate components (Fig. 2.4). The reaction of the lignin will not be covered here but should obviously be considered in a real process. Interested readers could consult the literature, e.g., [25]. Pyrolysis is discussed in more details elsewhere in this book [26],... 

The products of low temperature pyrolysis are char and low molecular components, see pathway 1 in Figure 53. At moderate temperature levels, the formation of a variety of lignin monomers (see Figure 49) occurs via pathway 2. And at high temperatures (> 500°C), fragmentation reactions take place, forming CO, H2, and reactive vapours. [67]... 

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. 

On carbonization, this lignin gives yields of about 60% of its dry weight of char, plus tars, acetic acid and methanol. 

Charring is known to preserve aspects of the physical structure of wood, seeds, and fruit (42). Srinivasan and Jakes (43) have shown that in charring some aspects of the physical shape of Indian hemp fiber are retained. In the carbonization of wood, Ercin et al (44) report the loss of cellulose, hemicellulose and lignin infrared absorbance bands in the range of 1300-1000 cm-1 and the appearance of two new bands at 1250 cm 1 attributed to the asymmetric C-O-C and at 1450 cm-1 attributed to aliphatic C-H bending. 

Charred back willow displays the distinctive peaks of its oxalate inclusions but the lignins that were observed in the uncharred material are no longer present (Figure 9). Charred red cedar produced similar results with outstanding oxalate bands observed. 

In some cases new information may be revealed as a result of charring. The infrared spectrum of charred common milkweed (Figure 10) displays oxalates that are not as apparent in the uncharred sample. In some cases of charred fibers, the spectrum can be said to be cellulosic, but further distinction of the organic structure based on lignins cannot be made. 

In examining charred dyed milkweed (Figure 23), the oxalates can be seen as before but the features of the dye are not readily apparent. Similarly in examining the infrared spectrum of Seip 36 (Figure 12), no oxalates or lignins can be seen although the overall shape is similar to that of a charred cellulosic. Some iron oxide is noted but no 617 cm-1 peak as was noted in fibers dyed with bedstraw. Much more work will need to be done on comparative dye materials, and the effective colorant add-on and the means to identify those colorants. 

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. 

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