Page 250 - Biosystems Engineering

228 Cha pte r Se v e n

is 1,6-anhydro-β-D-glucopyranose (levoglucosan) accounting gener-
ally for around 2 mass% of bio-oils. Other sugars found are cellobio-
san, 1,6-anhydroglucofuranosem, and fructose. Anhydrosugars with
molecular weights of around 500 g/mol account for up to 10 mass%
of the whole oil (Garcia-Pérez et al. 2007a, 2008).
Families E and F account for up to 35 mass% of crude bio-oils and
mainly consist of oligomers with molecular masses between 600 and
10,000 g/mol. These families are the result of pyrolysis reactions lead-
ing to the formation of dimers and trimers and of aging reactions
(Garcia-Pérez et al. 2007, 2008). Family E is formed by lignin-derived
oligomers commonly found in water-insoluble CH Cl soluble frac-
2 2
tions. Although the exact composition of the compounds forming
peak F is not well known, some authors have attributed this peak to
cellulose- and hemicellulose-derived oligomers (Garcia-Pérez et al.
2007, 2008).
Table 7.3 compares the chemical composition of crude bio-oils and
crude petroleum oils in terms of the percentage of compounds with
equivalent boiling points. Bio-oil composition in terms of volatility
compares very well with the composition of crude petroleum oils.
Although crude bio-oils contain oxygenated hydrocarbons from the
thermal degradation of cellulose, hemicellulose, and lignin abundant in
earthy biomasses, petroleum is composed of hydrocarbons with a very
low-oxygen content. These hydrocarbons are generated from the pre-
served remains of prehistoric zooplankton and algae that have been
settled to the sea bottom in large quantities under anoxic conditions.
Zooplankton and algae are very rich in triglycerides and proteins.

Physicochemical Properties of Bio-Oil
Some of the most common physicochemical properties of bio-oils are
presented in Table 7.4. The water content of bio-oils varies between 5
and 30 mass%. This water results from pyrolysis reactions (pyrolytic
water) and from biomass moisture. Water contents over 30 percent
results in the formation of two separate phases (an aqueous phase
and an oily phase). Bio-oil density is approximately 1.2 times higher
than that of distilled water. It decreases almost linearly with the tem-

Petroleum Crude Bio-Oil
Boiling Point (°C) Fraction Mass% Fraction Mass%
30–250 Naphtha 15–30 Family A, B, C 20–65
200–300 Kerosene 4–12 Family D 5–35
300+ Gas oil and 35–65 Family E and F 10–35
residual oil

TABLE 7.3 Comparison between the Composition of Crude Bio-Oils and
Petroleum