P. Sangnikul, et al.
AppliedCatalysisA,General574(2019)151–160
while the liquid product was stored in an amber bottle and kept in the
refrigerator prior to subsequent analysis.
The acidic properties of the prepared catalysts were analyzed by
temperature-programmed desorption of ammonia (NH3-TPD) using
Belcat-Basic Chemisorption analyzer. The calcined catalyst (0.05 g) was
dried using He gas at a flow rate of 50 ml/min for 30 min and then
heated from ambient temperature to 300 °C at 10 °C/min and held at
300 °C for 1 h. After cooling down to 100 °C, the treated sample ad-
sorbed NH3 in the presence of 7/3 (v/v) NH3/He fed into the system at
50 ml/min for 30 min. At this temperature, non-adsorbed NH3 was
flushed out from the system using He gas at a flow rate of 50 ml/min for
15 min. The desorption of NH3 adsorbed in the sample was performed
from 100 to 600 °C at a heating rate of 10 °C/min. The eluted NH3 was
analyzed using a thermal conductive detector (TCD) and He gas was
used as the carrier at a flow rate of 30 mL/min.
2.4. Preparation of bio-oil and HDO of the bio-oil
Typically, GUA is used as a representative compound of lignin-de-
rived bio-oil [3]. This research used cassava rhizomes as the raw ma-
terial for bio-oil production since they are an abundant renewable
product including as a waste product in Thailand and contain a high
portion of lignin (21.7 wt%) [19]. To prepare the bio-oil, the dried
cassava rhizome powder (∅ = 212–600 μm) containing 2.5 wt%
moisture, 75.7 wt% volatile matter, 10.5 wt% fixed carbon and 11.3 wt
% ash was pyrolyzed in the fluidized bed reactor with a feed rate ca-
pacity of 100 g/h, while silica sand (∅ = 212–600 μm, 150 g) was used
as the fluidizing and heat transfer material.
X-ray photoelectron spectroscopy (XPS) was performed on an Axis
Ultra DLD spectrometer (Kratos, Manchester, UK) equipped with
monochromated Al-Kα X-ray source (hν = 1486.6 eV) and fixed ana-
lyzer pass energy of 40 eV under ultrahigh vacuum conditions (UHV;
3 × 10−9 Torr). The XPS spectra were recorded using an analysis area
of 700 x 300 μm. The spectrometer also consisted of a high pressure cell
(HPC) used for reduction of the prepared catalysts, which were in the
oxide forms. Each catalyst sample was put into the HPC and sealed from
UHV chamber. It was then reduced under 1 bar H2 pressure (99.999%
purity) at 300 °C for 30 min in the HPC. After reduction, the sample was
transferred under UHV to the electron spectrometer for analysis. The
binding energy (BE) of samples was calibrated using the C1s peak at-
tributed to carbon surface impurities at 284.6 eV. For analysis, the
background was subtracted by the Shirley method and curve-fitting was
performed with the convolution of Gaussian-Lorentzian functions in the
Vision 2 Processing software.
The biomass particles were continuously fed into the reactor with
the aid of a preheated N2 gas (300–400 °C) at a flowrate of 7 L/min. The
pyrolysis temperature was kept constant at 500 °C. During pyrolysis, the
pyrolysis vapor together with char fines was filtered by a hot vapor
filtration unit using glass wool (5 g). The obtained pyrolysis vapor was
rapidly condensed in a series of condensation devices using ethanol as a
coolant and was then passed through an electrostatic precipitator to
collect most of the aerosols by condensing into a liquid at the wall and
flowing downwards into a glass bottle. The residue vapor was further
cooled by two dry-ice/acetone condensers and the non-condensable gas
stream was filtered by a cotton wool filter before leaving the unit. This
pyrolysis condition yielded 43 wt% bio-oil, 32 wt% char and 25 wt%
gas products.
The HDO of the obtained bio-oil (33 g) was also performed in the
same reactor used for the HDO of GUA without the assistance of any
solvent. This reaction was comparatively catalyzed by 15 wt% NiMo,
NiMo4Cu or NiMo4Ce based on the bio-oil content under 10 bar initial
2.6. Product characterization
The degree of GUA conversion, product distribution and composi-
tions of the liquid product generated from the HDO of GUA were cal-
culated from material balance and the peak area obtained from gas
H
2 pressure at 300 °C for 1 h. The procedure was similar to the HDO of
GUA as described above. The mixture of liquid and solid products were
dissolved in THF (50 ml) over 24 h and then separated by suction fil-
tration and dried at 120 °C in the oven. The liquid product was purified
using a rotary evaporator in order to remove THF.
chromatography-mass
spectrometry
(GC–MS;
Shimadzu-2010)
equipped with a DB-5 column (∅ = 0.25 mm; L = 30 m) using He as
the carrier gas at a flow rate of 1.65 mL/min. The initial column tem-
perature was controlled at 40 °C for 3 min before ramping to 150 °C at
10 °C/min and then held at 150 °C for 16 min. The injection and de-
tector temperatures were kept at 200 and 230 °C, respectively. Before
analyzing, the liquid product was diluted 103-fold using 2-propanol and
then 1 μL was injected into the system with a split ratio of 1:30. The
GUA conversion level and yield of each component in the liquid pro-
duct were calculated following Eqs. (3) and (4), respectively:
2.5. Catalyst characterization
The surface area, pore volume and average pore size of the prepared
catalysts (0.5 g/each) were determined from N2 physisorption eval-
uated by Micromeritics ASAP-2020 following the Brunauer-Emmett-
Teller (BET) equation for calculation of the surface area and the Barrett-
Joyner-Halenda (BJH) method on the N2 desorption stage for the eva-
luation of the average pore size.
Unreacted GUA (g)
Type and crystalline matters of each calcined catalyst were eval-
uated by X-ray diffractometry (XRD) (Bruker, D8 Advance) using CuKα
radiation (λ = 1.54°A; 40 kV; 40 mA). The 2θ range was scanned be-
tween 5 and 80° at a rate of 1°/s. The crystallite size (dp) of nickel oxide
(NiO) and molybdenum oxide (MoO3) of all samples was calculated
following the Scherrer equation [13], shown in Eq. (2);
1
Fed GUA (g)
(3)
Selectivity × Reacted GUA in liquid form (g)
Total reacted GUA (g)
(4)
where "Total reacted GUA” was the summation of the reacted GUA in
dp
liquid, solid and gas forms.
cos
(2)
For calculation of the solid product, thermogravimetric analysis
(TGA) performed by Perkin Elmer (Pyris Diamond Model) of spent
catalysts under an air atmosphere was used to determine the coke
formation deposited on the surface of the catalysts during the HDO of
GUA. The spent catalyst (15 mg) was heated from 40 to 900 °C at 10 °C/
min in the presence of air at a flow rate of 50 mL/min. The percentage
of weight loss between 200–700 °C was attributed to coke formation
[20]. However, this weight loss was only a rough estimation of the
amount of coke deposition, and potentially an underestimatation, due
to the potential oxidation of the reduced catalysts during the TGA
analysis, which could result in a marked gain in the catalyst weight.
The compositions of the liquid products, except the unreacted GUA,
where κ is the Scherrer constant (0.9), λ is the wavelength of X-ray
(1.54°A), θ is the diffraction angle and β is the half-peak width (radian)
The reduction temperature of all prepared catalysts was measured
by H2-temperature-programmed reduction (TPR) using Micromeritics
AutoChem II 2920. A 0.1 g portion of the calcined catalyst was dried
under an Ar atmosphere at a flow rate of 50 ml/min from room tem-
perature to 100 °C at a heating rate of 10 °C/min for 1 h. Then, the
reduction step was performed in the presence of a 1/9 (v/v) H2/Ar
mixed gas and heated from 100 °C to 900 °C at the same gas flow and
heating rates.
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