J. Oh et al. / Applied Catalysis A: General 455 (2013) 164–171
165
OH
Glycerol
on a Chemisorption Analyzer (BEL-CAT) with bypass mode. The
catalyst (100 mg) was activated at 400 ◦C for 1 h under He flow
(30 ml/min) and then cooled to 50 ◦C. The NH3 flow was main-
tained for 1 h, and the sample was then flushed with He for 5 min to
remove any physisorbed NH3. The desorption profile was recorded
by increasing the sample temperature from 50 ◦C to 850 ◦C at a
ramp rate of 10 ◦C/min. The NH3 concentration in the effluent
stream was monitored with a thermal conductivity detector, and
the areas under the peaks were integrated to determine the amount
of desorbed NH3 during TPD. The specific surface area and the pore
volume were determined by N2 adsorption–desorption isotherm
(Micromeritics Autochem II). The sulfur content was measured
with an elemental analyzer (EA1110, CE Instruments).
(B)
O
C
O
H2C
O
R
Glycerol
O
C
O
C
HO
R
HC
O
O
C
O
R
R
O
R
(A)
Biolubricant
OH
H2C
C
Scheme 1.
should be investigated to explore the potential for the synthesis of
biolubricants.
2.2. Reaction test
zirconia catalysts were studied as superacids in various industrial
processes such as hydrocarbon isomerization and alkylation, and
their potential for biomass conversion has been actively explored
various precursors of zirconium propoxide, zirconium hydroxide,
or zirconium oxychloride. The physical properties and catalytic
activity of sulfated zirconia showed large dependence on the type
of zirconium precursor. Long chain alcohols (≥C8) or neo-polyols as
shown in Scheme 2 were used as co-reactants. The property of the
alcohol affected the activity significantly as well. Unsaturated FFAs
formed a mixture of unsaturated ester and fully saturated esters
after the reaction with alcohols. In situ hydrogenation occurred
using alcohol as a hydrogen source. Recyclability of the sulfated
zirconia catalysts was tested. The kinematic viscosity and viscosity
index of the esters produced were compared with those of com-
mercial lubricants. Direct transesterification of soybean oil with
various alcohols and simultaneous reaction of esterification and
transesterification were also investigated.
2.2.1. Esterification of free fatty acid with alcohols
Esterification was carried out in a stainless steel autoclave
reactor equipped with 30 ml of Teflon liner and a Teflon-coated
magnetic stirring bar. A mixture of free fatty acid (6.25 mmol), alco-
hol (7.5 mmol), and catalyst (100 mg) was charged into the Teflon
liner. The mixture was heated at 140 ◦C for 4 h with stirring at
300 rpm. After the reaction, the reaction mixture was cooled to
room temperature, and the catalyst was separated from the reac-
tion mixture by centrifuging. To test the recyclability of the catalyst,
the catalyst was recovered after the reaction by washing three
times with a mixture of hexane and acetone (hexane:acetone = 1:1).
Then the catalyst was dried at 100 ◦C for 24 h. The reaction was
repeated five times.
The collected liquid product was analyzed with gas chro-
matography (Younglin, Acme 6000GC) using a DB-1 column
(30 m, 0.25 m ID) and flame ionization detector. The products
were further identified by gas chromatography-mass spectrometry
(GC–MS; Agilent 5975C). Nuclear magnetic resonance (NMR; JEOL
JNM-ECP300, 300 MHz) and Fourier-transformed infrared spec-
troscopy (FT-IR; PerkinElmer, Spectrum 100 FT-IR) were also used
to analyze the products. Kinematic viscosity and viscosity indexes
were measured using ASTM D445 and ASTM D2270 (Cannon instru-
2. Experimental
2.1. Preparation of catalysts
2.2.2. Transesterification of soybean oil with alcohols
Transesterification was carried out in a stainless steel autoclave
reactor equipped with 30 ml of Teflon liner and a Teflon-coated
magnetic stirring bar. A mixture of soybean oil, alcohol, solvent, and
catalyst was charged into the Teflon liner. The mixture was heated
at 140 ◦C for 4 h with stirring at 300 rpm. Simultaneous reaction
of transesterification and esterification was also performed for the
mixture of soybean oil and oleic acid using alcohol (1-octanol or
neopentane glycol or trimethylol propane) and solvent at 140 ◦C for
4 h with stirring at 300 rpm. After the reaction, the reaction mixture
was cooled to room temperature, and the catalyst was separated
from the reaction mixture by centrifuging.
The collected liquid product was analyzed with gas chromatog-
raphy (Younglin, Acme 6000GC) with a MXT-5 column (0.53 mm,
0.25 m ID) and a flame ionization detector. The products were
further identified by gas chromatography–mass spectrometry
(GC–MS; Agilent 5975C).
Three different types of sulfated zirconia were prepared
with different zirconium precursors. Type 1 was synthesized
from zirconium propoxide with a one-step sol–gel method [25].
Zr(OCH2CH2CH3)4 solution (5 ml, Aldrich, 70 wt% in 1-propanol)
was mixed with 6.6 ml of 1-propanol (Aldrich, 99.5%). Aqueous sul-
furic acid (0.5 M, Duksan) solution was prepared separately, and
9.7 ml of the aqueous sulfuric acid solution was added dropwise
to the solution of Zr(OCH2CH2CH3)4 in 1-propanol with vigorous
stirring for at least 6 h; a gel was formed. The gel was filtered, dried
at 100 ◦C, and calcined at 625 ◦C for 4 h. Type 2 was synthesized
from zirconium oxychloride with a modified two-step procedure.
ZrOCl2·8H2O (5 ml, Aldrich, 99.5%) was slowly added to 1 M NaOH
(Duksan, 93%) aqueous solution at room temperature with stir-
ring until the pH reached 8. The mixture was then dried at 100 ◦C
for 24 h. The Zr(OH)4 (5.2 g) that had been prepared was mixed
with 4.6 ml of 0.5 M sulfuric acid at room temperature and stirred
overnight. The gel was filtered, dried at 100 ◦C, and calcined at
625 ◦C for 4 h. Type 3 was synthesized with commercial zirconium
hydroxide. Zr(OH)4 (5.2 g, Aldrich, 97%) was mixed with 4.6 ml of
0.5 M sulfuric acid at room temperature and stirred overnight. The
gel was filtered, dried at 100 ◦C, and calcined at 625 ◦C for 4 h.
X-ray diffraction (XRD) patterns of the catalysts were
recorded on a Rigaku Miniflex diffractometer. The scanning speed
was 2◦/min and the scanning range was over 10–70◦. NH3
temperature-programmed desorption (NH3-TPD) was performed
3. Results and discussion
Biolubricants can be produced by esterification of FFA extracted
from vegetable oils (path A of Scheme 1) or direct transesterification
of vegetable oils (path B of Scheme 1). The exact evaluation of the
products of direct transesterification is often very difficult because
of many potential side products. We therefore studied esterifica-
tion of FFAs with various alcohols to synthesize well-defined ester