Influences of the Chemical State of Alkaline Compounds and the Nature of Alkali Metal on Wood Pyrolysis

The pyrolysis of a packed bed of fir wood particles, after impregnation with KOH, is investigated. For a heating temperature of 800 K, maximum variations in the pyrolysis characteristics are observed for KOH concentrations in wood below 1%. Decomposition temperatures become lower (35-70 K), and conversion times are rapidly more than halved. Also, the char, water, and gas yields increase (factors of 1.4, 1.6, and 1.7, respectively) at the expense of liquid-phase organic products. Levoglucosan presents a very steep decay, whereas the diminution in hydroxyacetaldehyde and acid acetic is much slower, and a wide zone of approximately constant values appears for hydroxypropanone. However, small quantities of KOH in wood (about 0.2-0.6%) are apt to increase the yields of furfuryl alcohol up to a factor 15 and some carbohydrates (3-ethyl-2-hydroxy- 2-cyclopentenone, 3-methyl-2-cyclopentenone, 1-hydroxy-2-butanone) and phenols (phenol, cresols, hydroquinone, guaiacol, isoeugenol-trans, isoeugenol-cis, 4-acetonguaiacol, 4-ethylguaiacol) up to factors of 2-6. Higher KOH concentrations cause a further increase in the yields of char and CO2 associated with a decay to very small yields of all of the organic compounds. Finally, increasing the heating temperature from 600 to 900 K (KOH concentration in wood of about 0.6%) essentially favors devolatilization and cracking of vapor-phase organic products with conversion times roughly reduced by a factor of 6.