High-pressure liquefaction products

The liquefaction of solid biomass followed by hydrotreating is viewed as an attractive route to the production of petroleum like liquid fuels [1], While liquefaction processes (e.g. high pressure liquefaction or fast pyrolysis) have already been demonstrated at a relatively large scale [2], the hydroprocessing step still requires development and demonstration. 

At Pacific Northwest Laboratory we have been testing the use of high-moisture biomass (marine and fresh-water biomass, post-harvest field residues and food processing wastes) in a thermochemical conversion system to produce useful fuels. Although the main focus of the work (19) has been gasification (catalytic production of methane) we have also performed a limited number of tests under high-pressure liquefaction conditions. 

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid 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 quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

Figure 1 shows the atomic H/C vs. O/C ratios for a series of fossil fuels. It is evident from the figure that coal-derived asphaltenes stand alone, with H/C atomic ratio about 60% of those derived from other fossil fuels. The asphaltenes from coal liquefaction products have experienced hydrotreatment at high pressures (2000-4000 psi) and temperatures near 450° C, yet they are much more aromatic than petroleum asphaltenes. Asphaltenes from coal have an aromaticity, /a, determined from 13C nuclear magnetic resonance, of 0.60-0.70, while petroleum values are listed as 0.40-0.55. 

It was concluded from this assessment that the most promising process for gasoline production by direct liquefaction of biomass is atmospheric flash pyrolysis. The high-pressure process may have the same future potential, but the uncertainties are much greater. 

Liquefaction processes for biomass conversion can be categorized as slurry-phase. high-pressure processing, usually with catalysts or as dry pyrolysis at low or reduced pressure. The research has concentiated on the fuel properties and has often overlooked tiie detailed chemical analysis of the biomass-derived products. Both process types produce a complex mix of oxygenated organic components. The... 

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