Dissertations in Forestry and Natural Sciences

Thermal processing of wood
and Miettinen et al. (2015). Fagernäs et al. (2012a) analyzed slow
pyrolysis products from birch and found that the aqueous
phases were composed mainly of acetic acid (60% of the
compounds), methanol (9%), hydroxypropanol (5–6%), furfural
(3–4%), and acetone (2–5%). The compositions of tars were
similar to the aqueous phases, but they consisted also of lignin
monomers phenols, guaiacol, and syringols. The amount of
polycyclic aromatic hydrocarbons (PAHs) in tars ranged from
0.1 wt% to 0.4 wt%. PAHs have harmful effects on human health
and the environment, and therefore, Fagernäs et al. (2012b)
conducted a further study of the PAHs present in pyrolysis
products. PAHs are mostly concentrated in the heavy tars which
collect at to the bottom of the retort, but low PAH contents are
also found in the tar-free aqueous phases as well as in the noncondensable
gases. Miettinen et al. (2015) showed that the slow
pyrolysis oil from unbarked pine was composed mainly of
various wood extractives and lignin degradation products
whereas the aqueous phase contained saturated fatty acids,
degradation products of lignin, anhydrosugars, and other
oxygen-rich compounds.
Tars and liquids derived from the thermal processing of
wood have been stated to possess a huge potential in a vast
number of applications (Fagernäs et al. 2015). So far, hundreds
of chemicals have been identified from tars and liquids, and
new ways to separate valuable chemicals and chemical families
from these fractions are being developed (Brown and Brown
2014). Their potential applications include their use as biocides,
repellents, pesticides, material coating and medicines. However,
the presence of PAHs may limit the widespread applications of
tars (Fagernäs et al. 2012a).
Examples of chemicals with a high commercial potential are
levoglucosan, furfural, glycolaldehydes, and phenolic
compounds, such as guaiacol and catechol (Abou-Zaid and
Scott 2012). Furfural, glycolaldehydes, guaiacol, and catechol
can be utilized in resin production whereas levoglucosan can be
used as a pesticide and in the production of antibiotics and
polymers. Other rather valuable compounds identified in wood
Dissertations in Forestry and Natural Sciences No 222 69