Pyrolysis, slow product yields

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. 

The main product yield (after slow or flash pyrolysis) is the liquid phase and Sawagushi found that this is mainly composed styrene monomers, dimers and trimers. For a residence time of 60 min, increasing the temperature from 310 to 350°C increases the monomer fraction up to 78%. Table 10.16 shows the proportions of these three components in the liquid phase as a function of the temperature. 

Differences between flash and slow pyrolysis have been pointed out, especially for PE and PP. Products yields by slow pyrolysis at high temperature (700°C) are similar to... 

In pyrolysis the wood material is heated rapidly to about 500 °C at which temperature the wood decomposes to a maximum amount of liquid product. At lower temperatures more char is formed and less liquid and gas, and at higher tenperatures the energy requirements are higher without producing noticeably more liquid. The pyrolysis process is carried out in a fluidised bed where milled material is fed into the bed and the product stream is condensed at temperatures between 30 and 60 °C. The char is usually separated before the condenser and used as fuel - along with the gas -to provide heat to the fluidised bed. The fluidised bed may be bubbling or circulating. In both cases a fast pyrolysis is obtained in contrast to slow pyrolysis which usually yields lower amounts of liquids. 

Pyrolysis entails thermal decomposition of biomass molecules in the absenee of oxygen, usually at the temperatures up to 650-800 K. To produee liquid oils, the heating process should be short [i.e., short residenee time), thus this process is usually referred to as fast pyrolysis. At high temperature, the biomass is vaporized and then condensed upon cooling to produce a liquid oil mixture which may be comprised of more than 300 compounds such as alkanes, aromatic aliphatic, sugars, alcohols, ketones, aldehydes, acids and esters. If the residence time is longer (slow pyrolysis), the product mixture is likely to produce more solid coke than liquid fuels. An advantage of fast pyrolysis is that it is economical for use on a small scale ie., 50-100 tons biomass per day). Yields of bio-oil production in excess of 70% have been... 

Due to the wide range of processing conditions (temperature and residence time) available and feedstock options (woody biomass, agricultural biomass, and diverse organic residues) that can be processed in slow pyrolysis units, the yield and properties of biochar can vary widely. This provides an opportunity to optimize the production to yield biochar with properties matching its application. In their research Ronsse et al. (2013) and Zhao et al. (2013) showed that certain biochar properties are primarily affected by processing conditions (eg, surface area, pH, carbon sequestration potential), while others are mainly feedstock-dependent (eg, content of total organic carbon. 

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. 

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-... 

Moreover, polymers 6 and 8 were pyrolyzed in bulk. These pyrolysis experiments were performed in a slow stream of nitrogen and the samples were heated to 1000°C at a rate of 10°C min", remaining at this temperature for 30 minutes Both of the ceramic products were black powders and in X-ray powder diffraction studies they showed only broad peaks of low intensity, indicating the presence of mainly amorphous material To obtain crystalline materials, the ceramic products were heated slowly to 1400°C where they were held for 5 hours. The X-ray powder diffraction showed exclusively sharp peaks, characteristic of P-SiC, respectively. The increased ceramic yield obtained by pyrolysis of the metal modified carbosilane 8, as compared with the polycarbosilane 6, can be explained by an increased concentration of carbon as impurity, which was additionally evidenced by elemental analysis. 

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