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

Motivated by the production of compounds of good industrial value, pyrolysis of fir wood catalyzed by alkaline compounds (NaOH, KOH, Na2CO3, K2CO3, KC2H3O2, and NaCl) has been investigated. Catalysts have been impregnated in wood (preliminarily extracted with water) by means of aqueous solutions resulting in concentrations of the K or Na ion in wood of about 0.37-0.41%. Pyrolysis experiments have been done with a fixed-bed reactor preheated at 800 K. The decomposition process is anticipated at lower temperatures with conversion times from 2.5 (NaOH) to 1.7 (NaCl) times shorter. Formation of char, carbon dioxide, and water is favored with total yields between 70 and 61 % versus 48% of extracted wood (dry sample mass basis). The yields of carbon monoxide are increased approximately from 4% to 6% while the yields of organic compounds are lowered to 19-29% (versus 43%) with the disappearance of sugar compounds and a strong diminution in other typical products of uncatalyzed wood pyrolysis but hydroxypropanone. However, sodium and potassium hydroxides increase the yields of some minor carbohydrate compounds (1-hydroxy-2butanone, 2-methyl-2-cyclopentenone, 3-ethyl-2-hydroxy-2-cyclopentenone, and 3-methyl-2-cyclopentenone) by factors of 4-6 (yields of about 0.8-0.12%). The yields of total phenols are also increased. In particular, NaOH is slightly more effective for the production of guaiacol, cresols, and 4-ethylguaicol (factors of increase between 3 and 4 with yields of 0.3-1.2%), whereas KOH is slightly better for the production of phenol, cis-isoeugenol and transisoeugenol (factor of increase of 2-6 with yields between 0.7 and 0.2%). Finally, the production of furfuryl alcohol can be augmented up to factors of about 15 by potassium hydroxide or carbonate (yields up to 0.6%).