2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
Table I
Hydrolysates pH value
Temperature [°C] Time [min] pH
160 30 4.14
160 60 3.46
160 120 3.29
160 240 3.18
180 30 3.61
180 60 3.18
180 120 3.03
180 240 3.09
200 30 3.17
200 60 2.95
200 120 2.92
200 240 2.97
Table II
Yield of monosaccharides in hydrolysates
Temperature [°C] Time [min] Monosaccharides [g dm–3 ]
160 30 1.56
160 60 2.84
160 120 4.46
160 240 9.12
180 30 2.46
180 60 14.40
180 120 7.96
180 240 3.15
200 30 3.05
200 60 4.71
200 120 2.23
200 240 1.92
At the temperature 160 °C the monosaccharides amount
in the hydrolysates increased during the total time range
(Table II). At the higher temperatures the maximum yield of
monosaccharides was determined during 60 min of the hydrolysis.
It is in accordance with 2-furaldehyde amount increase
in the hydrolysate (Table IV). The highest concentration
of monosaccharides was observed at the temperature 180 °C
and the time of the hydrolysis 60 min.
The similar trend we can see at the determination of total
saccharides amount (Table III) determined after the hydrolysis
by 3 % sulfuric acid. At the biggest yields of the saccharides
(180 °C, 60 min) approximately one half of the saccharides
amount is present in the form of monosaccharides and second
half in the form of oligosaccharides and polysaccharides.
In the hydrolysates there are various volatile compounds.
Their amounts increase in dependence on the temperature and
the time of treatment in most cases (Table IV).
Methanol, arising mainly by the methoxyl group cleavage,
is extreme toxic. In some cases it is necessary to remove
it before the next treatment of the hydrolysate. In hardwoods
there are 3–5 % of acetyl groups (CH 3 CO-), they give rise
s384
Table III
Yield of total saccharides in hydrolysates
Temperature Time Total saccharides
[°C] [min] [g dm –3 ]
160 30 2.43
160 60 3.35
160 120 15.06
160 240 14.06
180 30 3.83
180 60 30.48
180 120 12.36
180 240 3.29
200 30 14.97
200 60 6.40
200 120 3.57
200 240 1.23
Table IV
Yield of volatile compounds in hydrolysates
Temp- Acetic Propionic 2-Furerature
Time Methanol acid acid aldehyde
[min] [g dm
[°C]
–3 ]
[g dm –3 ] [g dm –3 ] [g dm –3 ]
160 30 0.11 0.28 0.10 0.02
160 60 0.31 1.35 0.53 0.14
160 120 0.63 4.46 1.17 0.63
160 240 0.54 5.77 0.94 1.64
180 30 0.18 0.67 0.18 0.05
180 60 0.47 5.35 0.92 0.89
180 120 0.82 7.73 0.74 7.24
180 240 0.84 7.52 0.65 9.23
200 30 0.29 3.41 0.61 0.46
200 60 0.40 7.72 0.59 6.43
200 120 0.97 10.03 0.66 8.17
200 240 1.13 2.95 0.82 5.12
acetic acid at the hydrolysis. The acetic acid amount increases
mainly at the first 120 min of the hydrolysis, then their
increase is retarded. It corresponds with the results of birch
wood hydrolysis, where the increase of acetic acid amount
was slowed or decreased in the hydrolysis at the temperature
200 °C 15,16 .
2-Furaldehyde arises by pentose dehydratation and it
can be isolated as a valuable product under certain conditions.
The temperature of 180 °C causes the heavy increase
of 2-furaldehyde, its concentration increases due to the condensation
reactions at the temperature 200 °C.
Conclusions
From the experimental results obtained at the hydrolysis
of alder wood can be concluded that at the mild conditions
of hydrolysis the acetic acid and 2-furaldehyde concentration
increases due to the saccharides deacetylation and dehydration,
respectively. The amount of 2-furaldehyde decrease is