Pyrolysis, flash liquid products

The main drawback with the thermochemical route for biomass utilization is the strong dependence on scale-up. To be competitive, the capacity has to be of the order of a small oil refinery (approx. 1 million tonnes per year), but there then exists the problem of the cost of transporting the biomass relatively long distances to this production capacity. Pyrolysis or related technologies ( flash or fast ) could transform biomass into liquid products that are more easily transported, and these liquid products could then be the input for a large, centralized... 

In a study by Sato et al. [62], the primaries dissolved in the melted PS or the solvent where the low mass transfer rate lead to significant secondary products. Ohtani et al. [61] avoided secondary products by employing hehum carrier. They reported monomer, dimer, and trimer of styrene. Flash pyrolysis of PS in a fluidized bed under atmospheric conditions rendered liquid products, mainly containing styrene monomer, toluene, ethyl benzene, and naphthalene [33]. 

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. 

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). 

Thus, while flash pyrolysis and flash hydropyrolysis have not advanced too far beyond the bench-scale studies, there are several potential commercial ventures that employ the pyrolysis of coal as a means of producing liquid products that are becoming more and more viable with the ever-increasing price of petroleum and the more conventional liquid fuels (Chapters 18,19, and 26). 

The occidental flash pyrolysis process originally called the Garrett process (Sass, 1974 Howard-Smith and Werner, 1976) (Figure 19.4) involves the pyrolysis of the feed coal particles at a temperature not in excess of 760°C (1400°F) in an entrained system to produce a liquid product, char, and gas. 

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... 

Fig. 10. Liquid-fuel production by flash pyrolysis usiag char recycle.

Samolada, M.C., Baldauf, W., Vasalos, I.A., Production of bio-gasoline by upgrading biomass flash pyrolysis liquids via hydrogen processing and catalytic cracking, Fuel, 1998, 77, 1667. 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical liquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of liquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quality transportation fuels, and to study liquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

The formation of gas was low. From the carbon balance, only 3% of the total carbon formed gaseous products. The hydrogen consumption was approximately 3100 scf/bbl, of which nearly 80% was consumed in liquid hydrogenation. This preliminary result demonstrated that the flash pyrolysis coal tar derived from a subbituminous coal is amenable to hydrorefining. 

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]. 

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]. 

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