Pyrolytic char

The observed enhancement in oxygen index could be attributed to phase segregation in these block copolymers, which leads to domination of siloxane on the polymer surface. Siloxanes have solid-phase activity rather than vapor-phase activity and reduce flammability through increased formation of pyrolytic char. 

The pyrolytic gasification of biomass has been interpreted to involve the decomposition of carbohydrates by depolymerization and dehydration followed by steam-carbon and steam-carbon fragment reactions. So the chemistries of coal and biomass gasification are quite similar in terms of the steam-carbon chemistry and are essentially identical after a certain point is reached in the gasification process. Note, however, that biomass is much more reactive than most coals. Biomass contains more volatile matter than coal, and the pyrolytic chars from biomass are more reactive than pyrolytic coal chars. 

Pyrolytic char yields of the Odeillo experiments were quite low ranging between one and four percent. Gas yields were also... 

At still higher temperatures (> 700 0, pyrolytic char reacts with steam to produce hydrogen, carbon monoxide and carbon dioxide. Rates of gasification of biomass-derived chars are known to be higher than coal-derived chars (2) however, much higher temperatures are required to achieve char gasification than were initially required for the pyrolysis reactions. Catalysis of char gasification has been reported (11.12) with limited success. 

Kutrieb Corporation (Chetek, Wisconsin) operates a pyrolator process for converting tires into oil, pyrolytic filler, gas, and steel. Nu-Tech (Bensenvike, Illinois) employs the Pyro-Matic resource recovery system for tire pyrolysis, which consists of a shredding operation, storage hopper, char-coUection chambers, furnace box with a 61-cm reactor chamber, material-feed conveyor, control-feed inlet, and oil collection system. It is rated to produce 272.5 L oil and 363 kg carbon black from 907 kg of shredded tires. TecSon Corporation (Janesville, Wisconsin) has a Pyro-Mass recovery system that pyroly2es chopped tire particles into char, oil, and gas. The system can process up to 1000 kg/h and produce 1.25 MW/h (16). 

Other techniques include oxidative, steam atmosphere (33), and molten salt (34) pyrolyses. In a partial-air atmosphere, mbber pyrolysis is an exothermic reaction. The reaction rate and ratio of pyrolytic filler to ok products are controlled by the oxygen flow rate. Pyrolysis in a steam atmosphere gives a cleaner char with a greater surface area than char pyroly2ed in an inert atmosphere however, the physical properties of the cured compounded mbber are inferior. Because of the greater surface area, this pyrolytic filler could be used as activated carbon, but production costs are prohibitive. Molten salt baths produce pyroly2ed char and ok products from tine chips. The product characteristics and quantities depend on the salt used. Recovery of char from the molten salt is difficult. 

Pyrolysis Of the many alternative chemical conversion processes that have been investigated, pyrolysis has received the most attention. Pyrolysis has been tested in countless pilot plants, and many full-scale demonstration systems have been operated. Few attained any longterm commercial use. Major issues were lack of market for the unstable and acidic pyrolytic oils and the char. 

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

Processes which generate heat in organic materials are reviewed. At ordinary temperatures, respiration of living cells and particularly the metabolism of microorganisms may cause self-heating, while at elevated temperatures pyrolysis, abiotic oxidation, and adsorption of various gases by charred materials drive temperatures up whenever the released heat is unable to dissipate out of the material. The crucial rate of pyrolytic heat release depends on exothermicity and rates of the pyrolysis process. 

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. 

Pyrolysis produces three principal products - pyrolytic gas, oil, and char. Char is a fine particulate composed of carbon black, ash, and other inorganic materials, such as zinc oxide, carbonates, and silicates. Other by-products of pyrolysis may include steel (from steel-belted radial tires), rayon, cotton, or nylon fibers from tire cords, depending on the type of tire used. 

Contrary to H2S, the amount of S02 evolution remains constant with coal maturation. The peak temperature of S02 rises from about 350 C for the peat sample to about 650 C for the anthracite sample. This temperature increase with coal maturation could be due to a loss of inflammable volatile matter which accelerates the char oxidation, and a relative enrichment of the char in condensed aromatic nuclei more resistant to pyrolytic breakdown, as seen by PTP and Py-GC, but also to a reduction of the size of micropores during coalification which hampers oxygen penetration into the solid matrix. 

By way of an early example, the effect of calcium carbonate, ATH, and MH fillers on smoke production from styrene butadiene (SBR) foams has been reported.47 It was evident that all the fillers reduced soot formation relative to unfilled foam with the hydrated fillers being more effective than the calcium carbonate, which was considered to act merely as matrix diluent. ATH and MH were found to give enhanced char formation with the promotion of solid-state cross-linking as opposed to pyrolytic degradation. An afterglow effect, occurring after the extinction of the flame, was noted with MH and attributed to the slow combustion of carbon residues. 

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