Char typical

Recycl Blacks. The pyrolysis of carbon black containing rubber goods has been promoted as a solution to the accumulation of waste tires. In the processes in question, tires are pyrolyzed in the absence of oxygen, usually in indirect fired rotary kiln-type units. The mbber and extender oils are cracked to hydrocarbons which are collected and sold as fuels or petrochemical feedstocks. The gaseous pyrolysis products are burned as fuel for the process. Steel tire cord is removed magnetically and the remainder of the residue is milled into a pyrolysis black. This contains the carbon black, silica, and other metal oxides from the rubber and some newly created char. Typically these materials have 8-10% ash, and contain... 

Cane sugar.—Melts, darkens, then chars, and finally burns, with a marked odour of burnt sugar. Typical of the changes given by mono- and di-saccharides. 

Heatshield thickness and weight requirements are determined using a thermal prediction model based on measured thermophysical properties. The models typically include transient heat conduction, surface ablation, and charring in a heatshield having multiple sublayers such as bond, insulation, and substmcture. These models can then be employed for any specific heating environment to determine material thickness requirements and to identify the lightest heatshield materials. 

Formation of Airborne Emissions. Airborne emissions are formed from combustion of waste fuels as a function of certain physical and chemical reactions and mechanisms. In grate-fired systems, particulate emissions result from particles being swept through the furnace and boiler in the gaseous combustion products, and from incomplete oxidation of the soHd particles, with consequent char carryover. If pile burning is used, eg, the mass bum units employed for unprocessed MSW, typically only 20—25% of the unbumed soHds and inerts exit the combustion system as flyash. If spreader-stoker technologies are employed, between 75 and 90% of the unbumed soHds and inerts may exit the combustion system in the form of flyash. 

Silicone foam thus formed has an open ceU stmcture and is a relatively poor insulating material. Cell size can be controlled by the selection of fillers, which serve as bubble nucleating sites. The addition of quartz as a filler gready improves the flame retardancy of the foam char yields of >65% can be achieved. Because of its excellent dammabiUty characteristics, siUcone foam is used in building and constmction fire-stop systems and as pipe insulation in power plants. Typical physical properties of siUcone foam are Hsted in Table 10. 

Wood in its untreated form has good resistance or endurance to fire penetration when used in thick sections for walls, doors, floors, ceilings, beams, and roofs. This endurance is due to low thermal conductivity, which reduces the rate at which heat is transmitted to the interior. Typically, when the fire temperature at the surface of softwood is 870—980°C, the inner char 2one temperature is - 290° C, and 6 mm further inward, the temperature is 180°C or less. The penetration rate of this char line is mm/min, depending on the species, moisture content, and density (45,46). Owing to this slow... 

Process development of the use of hydrogen as a radical quenching agent for the primary pyrolysis was conducted (37). This process was carried out in a fluidized-bed reactor at pressures from 3.7 to 6.9 MPa (540—1000 psi), and a temperature of 566°C. The pyrolysis reactor was designed to minimize vapor residence time in order to prevent cracking of coal volatiles, thus maximizing yield of tars. Average residence times for gas and soHds were quoted as 25 seconds and 5—10 rninutes. A typical yield stmcture for hydropyrolysis of a subbiturninous coal at 6.9 MPa (1000 psi) total pressure was char 38.4, oil... 

Typical pyrolysis yields and oil qualities for two bituminous coals, Utah A and lUinois No. 6, are presented in Table 27-15. The major problem with any pyrolysis process is the high yield of char. 

Some of the typical conditions of polycondensations used for aliphatic and aromatic monomers are not suitable for furan derivatives, e.g., the melt polycondensation of 2,5-furan dicarboxylic acid chloride with 2,5-b/s(hydroxymethyl) furan at about 80 °C only yields a black insoluble product5. The hydrochloric acid liberated in the reaction is clearly responsible for the charring of the furanic diol which like its simpler homologue furfuryl alcohol, resinifies rapidly in acidic media (see below). 

These polymers are self-extinguishing in air with LOI between 24 and 65 (see Table 8). Their thermal stabilities (300-400 °C) are typical of organic polymers, but the char yields are higher ( -30%), and a low heat release capacity is observed [582]. 

The term charring refers to the complete degradation of a polymer after which there is no longer any polymeric character to observe. Charring results from chain scission reactions that are left unchecked and is the typical process by which thermosets degrade. The resulting material is typically black and brittle. 

Gibov et al. (9) showed that combustion vapors and air could penetrate through a typical char layer. Capillarity served to bring molten polymer to the surface where it could pyrolyze and burn. One answer to this problem is obviously to create a closed cell foam. Gibov et al. showed that the incorporation of boric acid and ammonium phosphate helped minimize penetrability of the char (Fig. 1). 

Reaction of HCofPfOPh), with PMMA. A 1.0g sample of PMMA and 1.0g of the cobalt compound were combined as above. After pyrolysis at 375°C for two hours the tube is noted to contain char extending over the length of the tube with a small amount of liquid present. The gases were found to contain CO, C02, hydrocarbon (probably methane), and 0.1 Og methyl methacrylate. Upon addition of acetone, 1.0g of soluble material and 0.19g of insoluble may be recovered. The infrared spectrum of the insoluble fraction is typical of char. 

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