Low-pressure upgrading

Renaud, M. Grandmaison, J.L. Roy, C. Kaliaguine, S. "Low pressure upgrading vacuum pyrolysis oils from wood." In This Volume. 

Low-Pressure Upgrading of Vacuum-Pyrolysis Oils from Wood... 

Renaud M, Giandmaison JL, Roy C, Ktiliaguine S. 1988. Low pressure upgrading of vacuum-pyrolysis oils from wood. In Soltes EJ, Milne TA (editors). Pyrolysis Oils from Biomass. American Chemictil Society Symposium Series 376. American Chemictil Society. 

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. 

These redox processes are usually appHcable for small sulfur capacities. The sulfur is typically produced as a slurry, and can be upgraded to cake or molten sulfur. At low pressures, the redox processes can replace the amine Claus and tail gas cleanup processes with a single step, yet obtain sulfur recoveries of 99%. At higher pressures, the redox processes experience sulfur plugging and foaming problems. 

Some reactants in atmospheric-pressure reactors must be highly diluted with inert gases to prevent vapor-phase precipitation, while generally no dilution is necessary at low pressure. However, atmospheric pressure reactors are simpler and cheaper. They can operate faster, on a continuous basis and, with recent design improvements, the quality of the deposits has been upgraded considerably and satisfactory deposits of many materials, such as oxides, are obtained. 

The Exxon process for diesel oil production with sulfur levels between 200-500 ppm was introduced in 1989. The process is particularly interesting for feeds containing cracked stocks. The low pressure results in an efficient use of hydrogen in diesel upgrading. Since its introduction 9 units have been licensed outside the Exxon group. Various catalysts are approved for this process. RT 601 is the most active one. 

Laboratory (4) and Process Development Unit (5,6) studies originally conducted at the Universite de Sherbrooke, and now conducted jointly with the private industry at Universite Laval, province of Quebec, have led to the conclusion that thermal decomposition under reduced pressure is an attractive approach for the conversion of biomass into chemicals and fuels products. The process uses a multiple-hearth furnace for wood pyrolysis. This approach is characterized by a low pressure and a short residence time of the vapor products in the rciactor. When compared with conventional, atmospheric pressure carbonization, vacuum pyrolysis has the potential to significantly enhance the yields of organic liquid products with respect to solid and gaseous products. The pyrolysis oils (biooils) obtained from this process can be deoxygenated into transportation fuels upon further upgrading (7). Specialty as well as commodity (Pakdel, H. Roy, C. Biomass, in press) chemicals can also be extracted from the pyrolysis oil product. 

Air preheating is a elassic example of upgrading low-valued heat This is done by providing heat to raise the combustion air temperature from ambient temperature using waste heat. Air preheat can be accomplished via low-pressure steam or flue gas. lypically, air preheat can increase fired heater efficiency up to 5%, which is more significant than reducing 2%. 

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