Conventional pyrolysis of beech wood has been carried out for heating temperatures in the range 600−900 K, reproducing conditions of interest in countercurrent fixed-bed gasification. The yields of liquids (water and tars) increase with the heating temperature from about 40 to 55% of dry wood mass, confirming results previously obtained with a laboratory-scale gasifier. Apart from qualitative identification of ∼90 species, GC/MS techniques have been applied to quantify 40−43% of tars (40 species, with major contributions from acetic acid, hydroxypropanone, hydroxyacetaldehyde, levoglucosan, formic acid, syringol, and 2-furaldehyde). Decomposition of holocellulose leads to the formation of furan derivatives and carbohydrates, with a temperature-dominated selectivity toward hydroxyacetaldehyde against levoglucosan. Syringols and guaiacols, originating from primary degradation of lignin, present a maximum for heating temperatures of about 750−800 K whereas, owing to secondary degradation, phenols continuously increase. A comparison is also provided with fast pyrolysis liquids obtained from four commercial plants.

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Weight loss curves of thin layers (150 μm) of beech wood powder, measured for heating rates of 1000 K/min and final temperatures in the range 573−708 K, show final char yields of 37−11%. The process is kinetically controlled and, for the most part, isothermal. A one-step global reaction, with E = 141.2 ± 15.8 kJ/mol and ln A = 22.2 ± 2.9 s-1, is a degradation mechanism capable of capturing the main features of the process. The thermogravimetric curves also allow the formation rate constants to be estimated for char and total volatiles (activation energies of 111.7 ± 14.3 and 148.6 ± 17.4 kJ/mol, respectively) and, once integrated byproduct distribution, those for liquids and gases (activation energies of 148 ± 17.2 and 152.7 ± 18.2 kJ/mol, respectively). A comparison is provided with pyrolysis mechanisms available in the literature.

Motivated by the production of compounds of good industrial value, pyrolysis of fir wood catalyzed by alkaline compounds (NaOH, KOH, Na 2 CO 3 , K 2 CO 3 , KC 2 H 3 O 2 , 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%).

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