Pyrolysis, flash liquid yields

With respect to partial conversion by flash pyrolysis, the principal consideration in a choice between otherwise equivalent coals is the fact that liquid yields tend to increase with rank up to high volatile bituminous coals and thereafter to fall off sharply. 

A report on the continuous flash pyrolysis of biomass at atmospheric pressure to produce liquids indicates that pyrolysis temperatures must be optimized to maximize liquid yields (36). It has been found that a sharp maximum in the liquid yields vs temperature curves exist and that the yields drop off sharply on both sides of this maximum. Pure cellulose has been found to have an optimum temperature for liquids at 500°C, while the wheat straw and wood species tested have optimum temperatures at 600°C and 500°C, respectively. Organic liquid yields were of the order of 65 wt % of the dry biomass fed, but contained relatively large quantities of oiganic acids. 

The maximum gas yield reaches 65% at 650°C whereas the carbon deposit increases up to 20-30%. These results show that the liquid yield decreases more rapidly than by flash pyrolysis. By a two-stage pyrolitic gasification process (450 and 800°C), it is possible to improve the quality of the gaseous products and the gas yield. In these conditions, the gas yield reaches 74% [22]. 

An oil of low flash point in the range 14-18°C, and of 41-43 MJ Kg gross calorific value has been obtained in batch pyrolysis [36] of automobile tyre waste. In a pilot plant with semi-continuous feeding [37] the liquid yield of tyre waste decreased seriously with increasing temperature, and it was always lower in an atmosphere containing oxygen that in nitrogen. 

It is interesting to compare flash vacuum pyrolysis of LDPE and PS in a free-fall reactor. Temperature rise causes the solid residues to fall and the liquid and gas yields to increase. The LDPE figures exceed the corresponding PS values in the case of the solid residue and gas yield by about 50 and 10% respectively. In contrast, the liquid yield of LDPE is about one-fifth of PS. These findings are in harmony with the activation energies 270-331 kJ/mol for LDPE and 126-151 kJ/mol for PS [34]. 

Several studies have been published describing results from the flash pyrolysis of biomass. Most of these studies were carried out at higher temperatures and were intended to promote biomass gas production. However, the work of Roy and Chornet [4] reported high liquid yields from biomass pyrolysis under vacuum conditions. More recently, Roy et al. [5] have described a vacuum pyrolysis system for the production of liquids from biomass, based on a multiple hearth type of reactor. Knight et al. [6] have developed an upward flow entrained pyrolyzer for the production of liquids from the thermal pyrolysis of biomass. 

Flash pyrolysis in methane, toluene, or methanol atmosphere was proposed but failed to increase the yield of liquid products (Calkins and Bonifaz, 1984 Doolan and Makie, 1985 Hayashi et al., 1996). It is evident that contact at molecular level between hydrogen donor solvents and the coal is essential for increasing the BTX liquid yields (Morgan and Jenkins, 1986 Graff and Brandes, 1987 Kahn, 1989b Kahn et al., 1989 Miura et al., 1991 Miura, 2000). 

The optimum yield of liquid product is obtained in the coal-to-liquids process at approximately 1075 F. A typical product distribution for coal-to-liquida processing using this coal is 56% char, 35% tar, 7% gas, and 2% water. The residence time for this process is also kept as short as possible which maximizes the yield and prevents further cracking of the liquid product. The effect of flash pyrolysis on the liquid yield is shown by the fact that the tar and light oil yield for this coal from... 

The ORC flash pyrolysis process has been used with minor modifications to process municipal and industrial solid wastes. The emphasis is on liquid yield. More preparation of the feed is involved than for coal gasificaltion or coal liquefaction. A process schematic is shown in Figure 3. In addition to grinding and drying, an air classification process and screening are used... 

The parent azocine (91) was isolated at —190 °C from flash vacuum pyrolysis of diazabas-ketene (90) (71JA3817). The compound, which must be handled in KOH-coated glassware, decomposes at -50 °C to colored tarry material. Characterization was by mass spectrum (m/e 107), NMR spectrum (see 91) and conversion with potassium in liquid ammonia to a dianion, which on quenching and hydrogenation gave azocane in low yield. 

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. 

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%. 

A significant liquid phase is observed during the flash pyrolysis of polystyrene with styrene as the main component [8]. Except for one experiment by Kaminsky [11] the yield in styrene formed during the flash pyrolysis of PS (between 520 and 710°C) is near 75%. The major other products are aromatic compounds (oligomeric styrenes) [11]. 

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. 

The optimum pyrolysis temperature is 395°C to give a recovery ratio of 0.97 (i.e. 1000 kg polystyrene will yield 970 L liquid monomer) and 5 to 10% char residue. Fuel made from polystyrene feedstock will be high in aromatic character and have an energy content of 50 MJ/kg and a pour point of —67°C. However the flash point is only 26°C and the cetane rating only 12.6. The fuel needs to be blended with polyolefin-derived diesel or regular diesel in order to upgrade the flash point and cetane rating to within specification. 

Karaduman [80] investigated the effects of temperature on the yields in flash pyrolysis of PE. The gas yield continued to increase with temperature. The yield of liquid products and the total conversion rate also kept increasing up to a certain temperature, but after this point, began to fall slowly due to partial decomposition of the expected products. The yield of solid residue decreased with the increase of temperature. 

In a similar process, thermolysis of 8 in the liquid state gave 9, while flash-vacuum pyrolysis gave a low yield of l,2,3-tris(trifluoromethyl)cyclopropcnc (10). ... 

Aliphatic or aromatic aldehydes react with (ethoxycarbonyliodomethyl)triphenyl-phosphorane (183) in the presence of potassium carbonate in a two-phase liquid-solid system to give acetylenic esters 184 . Pyrolysis of a-halophosphoranes 185 (X = Cl or Br R = Ar or t-Bu) results in 1-haloalkynes 186. Vacuum pyrolysis of the betaine 188, formed from the phenoxymethylenephosphorane 187, yields the acetylenic ether 189 Flash-vacuum pyrolysis of the phosphorane 190 at 750°C gives triphenylphosphine oxide and phenylacetylene with elimination of the ethoxycarbonyl groups... 

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