Catalysis Science & Technology
Paper
AV is also particularly abundant in the peat infused whisky
from Islay and Orkney in Scotland. Essentially, AV has been
(model 4848, 160 mL) equipped with an automatic temper-
ature control system and a mechanical stirring device.
About 1 g of lignin was dissolved in 30 mL of alkaline solu-
1
5
16
reported in the synthesis of AS and V, and it has anti-
1
7
−1
inflammatory capabilities.
tion (80 g L of NaOH) by sonication. After full dissolu-
CWAO of phenolic compounds and lignin is mostly pre-
ferred due to its mild conditions, good selectivity and short
reaction time with the application of molecular oxygen as an
tion, the resultant mixture was diluted with alkaline solu-
tion until a final volume of 70 mL was reached in a reactor
in the presence of a catalyst (20% w/w on lignin). The reac-
tion mixture was kept under agitation at 400 rpm. The
reaction zone was temperature and pressure controlled. The
reaction time started to count when the required tempera-
ture set point (170 °C) was reached, and about 1.5 bars of
oxygen was introduced to the reactor. The total pressure in
the reactor was kept at 8.5 bars. (This was made of two
5
oxidant owing to its modest price, abundance and environ-
1
8
mental friendliness. Various catalysts, such as the homoge-
neous copper salts, have been used in catalytic oxidation
1
9
reactions and wood delignification. During the lignin oxida-
tion, CuIJII) is reduced to CuIJI),which is oxidized back to CuIJII)
2
0
species in the presence of molecular oxygen.
Very little information on the acetoderivative transforma-
tion into valuable aromatic aldehydes is available in the liter-
ature. Because of this, the current study has shown great
interest in the investigation of their fate during CWAO with
the goal of recovering value-added aldehydes. Therefore, good
understanding and appropriate control of acetoderivatives'
behaviour during the oxidation process will not only get rid
of them along the waste stream, but also enlighten us about
the mechanism of lignin degradation into aromatic alde-
hydes as well as diversify biorefinery raw materials.
parts – the vapour (H O) pressure built up in the system,
2
which is about 7.0 bars, and additional 1.5 bars of oxygen
partial pressure filled in). This partial pressure was basi-
cally kept constant by the continuous supply of O2 during
the reaction process. In all the experiments, pH remained
above 13 after the reaction time. When AV was used as
the starting material, similar treatments (vol. = 70 mL, T =
170 °C) were also followed, but with 0.05 g of the material
each time.
The aim of this work is to explore acetoderivative and
bamboo lignin oxidative degradation in alkaline solution uti-
lizing copper sulphate pentahydrate as a catalyst, so that a
feasible process could be developed for future applications.
GC-MS analysis
Prior to the GC-MS analysis, the liquid in the reactor was
collected in a beaker, then acidified to pH 1–2 with dilute
HCl to enhance precipitation of non-oxidized lignin, and
the organic compounds were allowed to recover in the
organic phase. The solid and liquid products were separated
with a vacuum filter using a Millipore membrane (0.45 μm
pore size). The liquid portion was extracted with an equal
quantity of ethyl acetate (50 mL × 3) forming two phases
which were separated in a separatory funnel. The ethyl ace-
tate solution obtained was dried over anhydrous sodium sul-
fate, filtered and evaporated at 45 °C in a vacuum rotary
evaporator.
Experimental
Materials
Vanillin (99%), syringaldehyde (98%), acetovanillone (98%),
ethyl vanillin (98%), and copper sulphate pentahydrate (99%)
were all purchased from Aladdin Industrial Corporation.
Acetosyringone (98%) was supplied by Shanghai Macklin Bio-
chemical Co. Ltd. Hydrochloric acid (37%), sodium hydroxide
(96%) and ethyl acetate (99.5%) were supplied by the local Lu
Yin Co. Bamboo lignin was purchased from Geyi Energy Co.
Ltd., which is an alkaline lignin (i.e. it was extracted with
alkaline solution from the steam-treated bamboo, and the
obtained black liquid was concentrated, and finally the red-
dish lignin powder was obtained by spray drying of the con-
centrated black liquid). Before use, the lignin was pretreated
by dissolving it in demineralized water, then filtered to
remove the solid particles, precipitated with dilute HCl,
washed several times until pH > 5.0, and finally dried for 24
h at 55 °C in an oven. Pure acetovanillone and acetosyring-
one were used as model compounds to study their fate dur-
ing the oxidation process. The oxygen and helium gases were
supplied from Linde Gas Co. Ltd., Xiamen.
The ethyl acetate extract was redissolved in the same sol-
vent; about 1.5 mL was obtained to be injected into the GC-
MS for identification and quantitative analysis. The identifi-
cation and quantification of the isolated reaction products
were carried out using a GC-MS (QP 2010 SE, Shimadzu,
Japan) equipped with an Rtx-5MS (30 m × 0.25 mm × 0.25
μm) capillary column. The volume of the sample injected was
1 μL with a split ratio of 10 : 1, and the flow rate of helium
−
1
employed as carrier gas was 2 mL min . The injection pres-
sure and temperature were 120.5 kPa and 270 °C, respec-
tively. The capillary column was heated from 55 °C, held for
−
1
2 min, to 210 °C at a heating rate of 7 °C min . The tempera-
ture of the ion source was 200 °C, the interface temperature
was 275 °C, the solvent delay was 2.0 min, and the mass scan
range was from 35 to 500 m/z. The identification of detected
compounds was carried out using the NIST database. Ethyl
vanillin (98%) was added to the organic phase as an internal
standard for GC-MS quantitative analysis (RRF – relative
response factor method).
Methods
Procedures for alkaline oxidative reaction
The lignin and acetoderivative oxidative batch experiment
was carried out in a stainless steel autoclave made by Parr
This journal is © The Royal Society of Chemistry 2015
Catal. Sci. Technol., 2015, 5, 3746–3753 | 3747