Pyrolysis, slow

PhenoHc and furfuryl alcohol resins have a high char strength and penetrate into the fibrous core of the fiber stmcture. The phenoHc resins are low viscosity resoles some have been neutralized and have the salt removed. An autoclave is used to apply the vacuum and pressure required for good impregnation and sufficient heat for a resin cure, eg, at 180°C. The slow pyrolysis of the part foUows temperatures of 730—1000°C are recommended for the best properties. On occasion, temperatures up to 1260°C are used and constant weight is possible even up to 2760°C (93). 

Slow pyrolysis, also called carbonization, is characterized by a high charcoal yield and is not considered for hydrogen production processes. The slow pyrolysis of wood (24 h typical residence time) was a common industrial technology to produce charcoal, acetic acid, methanol, and ethanol from wood until the early 1900s. 

Slow Pyrolysis, Therombalance Rapid Pyrolysis, Free Fall Reactor ... 

Scheme 48). The very slow pyrolysis of the (4-methylphenyl)amine derivative (1223, R = Me) at 540°C and 10 5 torr resulted in IR absorption at 2079 cm-1, indicating the presence of methyleneketene (1224, R = Me). Under less carefully controlled pyrolysis conditions at higher pressure, the 2079 cm-1 absorption was accompanied by an absorption at 2123 cm 1, pointing to the presence of imidoylketene (1225, R = Me). Above 600°C, both intermediates disappeared and quinoline (1226, R = Me) was the only product. 

Poly(a-phenylethyl isocyanide), however, yields complex products distinguishable from monomer upon thermal degradation at 20 mm Hg (13). At 300° C a viscous condensate is produced which is free of isocyanide absorption in its infrared spectrum and appears very similar to the recently synthesized oligo-isocyanides, a,co-dihydrotri(a-phenylethyl isocyanide) and a,co-dihydrohexa(a-phenylethyl isocyanide) (15). Pyrolysis at 500° C produces an intense broad infrared absorption band in the range about 3300 cm-1, which is the range of associated N il bonds. Pyrolysates obtained at 700° C reveal nitrile absorption at 2270 cm"1, that becomes more intense in pyrolysates produced at temperatures up to 1300° C. A slow pyrolysis at 200-300° C is indicated for the study of primary structural changes in poly(a-phenylethyl isocyanide). Pyrolysates of poly(<7-... 

Considering the volatiles that evolve from hot pressing and heat-treating operations, it is concluded that the major chemical changes occurring in this stage are pyrolytic. Methanol, acetic acid, furfural, and ligneous tars are the common volatiles produced by the slow pyrolysis of wood practiced in destructive-distillation processes. The temperatures used in the board conversion operations approach pyrolysis temperatures of wood and the evidence indicates that pyrolysis is indeed active in board conversion. 

Pyrolysis of biomass is divided into slow pyrolysis, which is well known to produce charcoal, for example, fast pyrolysis, which produces a high yield of liquid biofuels and other chemicals (Bridgwater, 2000) and flash pyrolysis. Slow pyrolysis (or carbonisation) requires low temperatures and very long residence time. In the carbonisation process the amount of char is maximised. 

Polak and Molenaar described a method for the determination of acetylcholine from brain tissue by pyrolysis-gas chromatography-mass spectrometry [200]. The deuterium-labeled acetyl-choline is pyrolytically demethylated with sodium benzenethiolate, followed by quantitative GC-MS analysis. In this method, care must be taken so that the samples do not contain appreciable amounts of choline since exchange of deuterium-labeled groups between acetylcholine and choline during pyrolysis may yield erroneous results. The same authors have also reported a method for the determination of acetylcholine by slow pyrolysis combined with mass fragment analysis on a packed capillary column [201]. 

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... 

For many centuries, wood slow-pyrolysis liquids were a major source of chemicals such... 

Pyrolysis. All of the Texas lignite pyrolysis data reported in the literature have been based on slow pyrolysis rates (e.g., 3-10 C/min). Goodman et al. (20) performed an early study (1958> on the effect of final carbonization temperature on the yields from several lignites, one of which was a Wilcox lignite. More recently Edgar et al. (21) reported a series of atmospheric pressure studies to evaluate the effects of other carbonization parameters (heating rate, particle size) on carbonization yield and decomposition rate. 

The following section reviews the literature data summarizing the behaviour during carbonization of five individual polymers, i.e. polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). Eor each polymer, results will first be presented for flash pyrolysis then for slow pyrolysis by the isothermal and dynamic methods. 

In slow pyrolysis, temperatures are generally lower than for flash pyrolysis, but residence time is longer. Meanwhile, there are two different methods. One method is the isothermal-static method where the charge is directly heated at a given temperature and maintained during a certain time while in the dynamic method (TGA) the charge is progressively heated. 

Table 10.5 PE slow pyrolysis decomposition mass balance...

In slow pyrolysis by the dynamic method, the temperature domain is generally large and in this case, the main parameter is the heating rate. Table 10.6 indicates the temperature interval for the decomposition of the PE defined between the temperatures Ts and T95. These two temperatures are defined respectively as the temperature at which the conversion starts T5 at 5% conversion) and Tg (close to the end of conversion, at 95%). The maximum rate of conversion occurs between T5 and Tgs, at Tmax-... 

Table 10.6 PE slow pyrolysis (dynamic method) characteristic parameters...

The initial temperature for the decomposition of LDPE is lower than that of HDPE [17], Eor the two types of PE, total degradation occurs at 490°C. The gas phase composition in slow pyrolysis is presented in Table 10.7. 

In slow pyrolysis, the gas phase contains less methane and ethylene and more ethane and propane than hy flash pyrolysis (see Tables 10.4 and 10.7). The product yields obtained in the literature by different authors for the PE for slow pyrolysis (Pinto, Madorsky, Bockhom, Tsuji and Williams) and fast pyrolysis (Kaminsky, Williams, Scott and Conesa) are respectively presented in Eigures 10.2 and 10.3. 

During the slow pyrolysis of polyethylene, for a temperature increase from 400 to 700° C, the yield in liquid phase remains higher than 80% with a very small increase in the yield of gas phase (less than 20%). On the other hand, in flash pyrolysis of polyethylene, an increase of temperature from 550 to 700°C leads to a decrease of the yield in the liquid phase to less than 40% with an increase in the yield of the gas phase up to 60%. 

In slow pyrolysis, the experiments are conducted at constant temperature and the mass balance is presented in Table 10.10. 

By slow pyrolysis, the dynamic method is more appropriate to estimate the decomposition interval for the polypropylene decomposition. Table 10.11 indicates the temperature interval for the decomposition of the PP defined between the temperatures and... 

At higher temperature (700°C), in slow pyrolysis, the gas phase contains less methane and more propane, propene and butene than by flash pyrolysis (see Tables 10.9 and 10.12). 

The conversion yield x of polystyrene by slow pyrolysis after a residence time of 60 min is presented at different temperatures in Table 10.14. 

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