Preparation of low calorie structured lipids catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene(TBD)-functionalized mesoporous SBA-15 silica in a heterogeneous manner

Article abstract of DOI:10.1021/jf405434a

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD, a strong bicyclic guanidine base) functionalized SBA-15 material has been found to be an efficient solid catalyst for the interesterification between tributyrin and methyl stearate in a solvent-free system for the production of low-calorie structured lipid (LCSL). The solid base catalyst was characterized by using small-angle X-ray scattering, Fourier transform infrared spectra, thermo gravimetric analysis, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption, and elemental analysis techniques. The obtained LCSL was analyzed by reverse-phase high-performance liquid chromatography for triacylglycerol composition. The influence of various reaction parameters, such as the substrate ratio, reaction temperature, and reaction time, on the interesterification reaction was investigated systematically. More than 90% LCSL was obtained at 80°C within 1 h when the methyl stearate/tributyrin molar ratio of 2:1 was employed. The obtained solid catalyst could be recovered easily and reused for several recycles with a negligible loss of activity. By using the solid base catalyst, an eco-friendly more benign process for the interesterification reaction in a heterogeneous manner was developed.

Full text of DOI:10.1021/jf405434a

Article
pubs.acs.org/JAFC
Preparation of Low Calorie Structured Lipids Catalyzed by 1,5,7-
Triazabicyclo[4.4.0]dec-5-ene(TBD)-functionalized Mesoporous SBA-
15 Silica in a Heterogeneous Manner
Wenlei Xie* and Cong Qi
School of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou 450052, P. R. China
ABSTRACT: 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD, a strong bicyclic guanidine base) functionalized SBA-15 material has
been found to be an efficient solid catalyst for the interesterification between tributyrin and methyl stearate in a solvent-free
system for the production of low-calorie structured lipid (LCSL). The solid base catalyst was characterized by using small-angle
X-ray scattering, Fourier transform infrared spectra, thermo gravimetric analysis, scanning electron microscopy, transmission
electron microscopy, nitrogen adsorption−desorption, and elemental analysis techniques. The obtained LCSL was analyzed by
reverse-phase high-performance liquid chromatography for triacylglycerol composition. The influence of various reaction
parameters, such as the substrate ratio, reaction temperature, and reaction time, on the interesterification reaction was
investigated systematically. More than 90% LCSL was obtained at 80 °C within 1 h when the methyl stearate/tributyrin molar
ratio of 2:1 was employed. The obtained solid catalyst could be recovered easily and reused for several recycles with a negligible
loss of activity. By using the solid base catalyst, an eco-friendly more benign process for the interesterification reaction in a
heterogeneous manner was developed.
KEYWORDS: heterogeneous catalyst, interesterification, structured lipid, SBA-15
Industrially, the interesterification process is carried out by
homogeneous base catalysts to improve the physicochemical
properties of oils and produce distributed fatty acid residues
among TAG molecules.10 Sodium hydroxide and sodium
alkoxide are the most preferred choice of catalysts for the
CIE processes.10−12 Although these homogeneous bases are
highly efficient and of low cost, they can cause the problem of
tedious purification of the product, and the undesired
wastewater is inevitably generated. For this reason, the
heterogenization of active catalysts is always an appealing
option for practical application from both commercial and
environmental point of view. More recently, the development
of heterogeneous catalysts has attracted increasing attention
because of the easy recovering, possible recycling of the catalyst
and simple operation procedures.13 Up to now, a variety of
different heterogeneous base catalysts have been investigated,
including supported alkali or alkaline earth metals, basic
zeolites, hydrotalcites, zeolites, and ion-exchange resins.13−16
Supported organic bases, such as guanidines immobilized on
polymers or encapsulated in zeolite cages, have been used as
solid catalysts for biodiesel production from vegetable oils.17,18
However, to our knowledge, the heterogeneous base catalysts
have rarely been reported to be employed for the CIE reaction
so far,19 despite their proven catalytic efficiency in a variety of
other organic reactions.16,17 Therefore, from both environ-
mental and economical point of views, it is of interest to
develop environmentally friendly and high efficient catalysts for
the interesterification reaction.
INTRODUCTION
■
Most native vegetable oils have limited applications in their
original forms. The interesterification of vegetable oils can be
used to obtain fats with desired functional and nutritional
properties, by altering the original specific triacylglycerol
(TAG) composition of the blend components, which can
widen their commercial use.1,2 Low-calorie structured lipid
(LCSL) is a family of structured lipid that provides the desired
physical and nutritional characteristic of fats, but with
approximately half of the calorie of typical edible oil. Generally,
the LCSL is composed of two types of TAGs; one contains two
short-chain and one long-chain acyl residues (here designated
as SSL), and another contains two long-chain and one short-
chain acyl residues (here designated as SLL). Due to the lower
caloric content of short-chain acyl residues, the LCSL contains
lower caloric contents than the naturally occurring TAGs and
accordingly is intended for use in coatings, baking chips, baked
products, or as cocoa butter substitutes. The most common
process used for the production of LCSL is through the
interesterification reaction, which is carried out in the presence
of a catalyst.2−5
In general, the interesterification can be conducted chemi-
cally or enzymatically. Enzymatic interesterification (EIE)
processes are advantageous owing to their selectivity, milder
reaction condition and ease of product recovery.6−8 However,
the application of EIE reactions is limited by the high cost
associated with the lipase used. Chemical interesterification
(CIE) is a cheaper process that is tried-and-true on an
industrial scale, as it has been around for a long time and
relevant industrial procedure and equipment are readily
available.8,9 Hence, in a practical application point of view,
CIE reaction seems to be the most attractive method in the
edible oil industry.
Received: December 4, 2013
Revised: March 29, 2014
Accepted: March 30, 2014
Published: March 31, 2014
© 2014 American Chemical Society
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other materials used were of either analytical or chromatographical
grades.
Mesoporous molecular sieves have attracted significant
attention especially in their application in catalysis. Among
the mesoporous silica materials, SBA-15 silica is emerged as a
promising catalyst support in heterogeneous catalysis owing to
its well-ordered structure, nanosized channel, large surface area,
and sufficient silanol group for surface modification.20 The
immobilization of organic base groups on the surface of the
mesoporous material by grafting or co-condensation can be
recognized as a promising approach to create efficient solid
base catalysts with improved catalytic properties as compared
to conventional homogeneous catalysts.20−22 This approach
can allow the catalyst to be separated easily from the reaction
mixture with no wastewater originating from the catalyst
neutralization step.
Catalyst Preparation. Mesoporous silica SBA-15 was prepared
according to a hydrothermal approach using Pluronic P123 triblock
copolymer as a template under acidic conditions.20 In a typical
synthesis, 10 g of Pluronic copolymer P123 was first dissolved in 75
mL of double distilled water and 300 mL of 2 mol/L HCl solution at
room temperature, and then stirred at 313 K until a homogeneous
solution was obtained. Thereafter, 21 g of tetraethylorthosilicate
(TEOS) was added under stirring to the P123 solution, and the
stirring was continued for 24 h at 40 °C. Subsequently, the solution
was taken in a Teflon-lined autoclave and heated at 100 °C for 48 h.
After cooling to room temperature, the solid product was filtered, then
washed thoroughly with deionized water, and finally dried in air at
room temperature. The SBA-15 powder was obtained by calcining the
material in air at 550 °C for 6 h to remove the template. The
mesoporous SBA-15 silica was used as a support material for
preparation of the solid catalyst.
The organic base TBD can be allowed to immobilize onto the
surface of SBA-15 silica through the condensation reactions of TBD-
organosilane with the surface silanol group. Initially, the TBD-
organosilane was prepared by the reaction of 1,3-glycidyloxypropyl-
trimethoxysilane with TBD base. Typically, 0.6 g of TBD was added to
a solution of 1,3-glycidyloxypropyl-trimethoxysilane (4 mL) in dry
DMF (10 mL), and after this the resulting mixture was continued to
stir for 48 h at room temperature under nitrogen atmosphere.
Thereafter, the solution was poured into a flask containing dry toluene
(15 mL) and SBA-15 (1.2 g, previously heated at 350 °C for 10 h),
after which the mixture was refluxed for 48 h under nitrogen
atmosphere. The solid base catalyst thus obtained was filtered under
vacuum, washed carefully with toluene and methanol, and extracted
with a Soxhlet apparatus for 24 h using a 1/1 diethyl ether/methylene
chloride mixture. Finally the solid catalyst was dried at 60 °C for 12 h
under vacuum prior to use.
Catalyst Characterization. Small-angle X-ray scattering (SAXS)
measurements were performed on a Bruker AXS Nanostar instrument
with the Cu Kα radiation using an acceleration voltage of 40 kV and a
current of 30 mA. Fourier transform infrared spectroscopy (FT-IR)
was recorded for functional group detection in the 400−4000 cm−1
range on a Shimadzu IR-Prestige-21 spectrometer using the usual KBr
pellet method.
Thermogravimetric measurements (TG-DTA) were conducted on a
TA Instrument TG 2050 thermogravimetric analyzer with a heating
speed of 20 °C/min under air atmosphere with a flow rate of 100 mL/
min. Scanning electron microscope (SEM) measurements were carried
out with a field-emission microscope (JEOL, JSM-6390LV) using an
accelerating voltage of 15 kV. Transmission electronic microscopy
(TEM) images were taken using a JSM-6390LV transmission
electronic microscopy at an accelerating voltage of 200 kV.
The elemental analysis for carbon, hydrogen and nitrogen contents
of the samples to measure the TBD loading in the solid catalyst were
carried out on a Carlo-Erba 1106 elemental analyzer.
TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene) is a strong bicyclic
guanidine base (pKb = 25) widely utilized as a homogeneous
base catalyst for various chemical reactions.23 Mesoporous silica
materials could be organically functionalized through grafting
reactions in which the organic base is anchored onto the surface
of the pores with the preservation of a pore host structure.
Kalita et al. covalently grafted TBD onto MCM-41 nano-
particles and proved that the TBD-functionalized MCM-41
material is efficient for Michael-addition reactions under
solvent-free conditions.24 However, this kind of heterogeneous
base catalysts is seldom used for the CIE reaction.19 Due to the
increased interest and demand for practical application, the
environmentally friendly benign and easy-separable solid base
catalysts are highly desirable. In the present contribution, for
the purpose of providing a highly efficient and green procedure
for the interesterification reaction, the guanidine base TBD was
covalently bound onto the surface of the mesoporous SBA-15
silica to form the heterogeneous catalyst SBA-15-pr-TBD.
Thereafter, this hybrid organic−inorganic material was tested
for the interesterification of tributyrin and methyl stearate in
solvent-free system for the production of LCSL. For this
purpose, the TBD base was previously linked to 1,3-
glycidyloxypropyl-trimethoxysilane by nucleophilic addition to
the epoxide moiety. The resulting TBD-organosilane com-
pound was then anchored to the mesoporous SBA-15 silica by
reaction of the trimethoxysilyl group with the surface silanol.
The as-prepared solid base catalyst was characterized by using
small-angle X-ray scattering (SAXS), Fourier transform infrared
(FT-IR) spectra, thermo gravimetric analysis (TG-DTA),
scanning electron microscopy (SEM), transmission electron
microscopy (TEM), nitrogen adsorption−desorption and
elemental analysis techniques. By using this solid base catalyst,
the LCSL was produced in a solvent-free system by
interesterification of tributyrin and methyl stearate in a batch
reactor. The TAG compositions of the interesterified products
were determined by high-performance liquid chromatography
(HPLC). Moreover, the interesterification parameters, includ-
ing the molar ratio of substrate, reaction temperature, reaction
time, and reusability of the solid catalyst were investigated
systematically in the present investigation.
The textural properties of the solid catalysts were measured by
nitrogen adsorption−desorption isotherm method at liquid nitrogen
temperature (−196 °C) using a Quantachrome NOVA 1000e
instrument. The specific surface area was calculated by using the
Brunauer−Emmett−Teller (BET) method. The total pore volume and
the pore size distribution were assessed according to the Barrett−
Joyner−Halenda (BJH) method based on the adsorption isotherm.
Interesterification Procedures. A certain amount of tributyrin
and methyl stearate mixture was charged into a 50 mL round-bottom
flask. After raw materials were melted absolutely and dried under
reduced pressure at 80 °C, the CIE reaction was carried out in solvent-
free system by the addition of 1.5 wt % of TBD-functionalized SBA-15
silica as a catalyst. The interesterification of tributyrin with methyl
stearate was allowed to proceed under reduced pressure at 80 °C in a
water bath with magnetic stirring (∼750 rpm). After completion of the
reaction, the interesterified product was filtered, and then employed
for subsequent analysis.
MATERIALS AND METHODS
■
Materials. Tributyrin (≥98%) and methyl stearate (≥98%) were
obtained from Sinopharm Chemical Reagent Corporation (Sanghai,
China). Pluronic copolymer P123 (EO20PO70EO20, average molecular
weight was 5800), 1,3-glycidyloxypropyl-trimethoxysilane (≥99.8%),
1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD, ≥98%) and tetraethylor-
thosilicate (TEOS, ≥98%) were purchased from Sigma-Aldrich. All the
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Analyses of TAG Composition. Reversed-phase high-perform-
ance liquid chromatography (HPLC) was used to determine the TAG
composition of the interesterified product. A commercially packed
Genesis C18 HPLC column (15 cm length × 4.6 mm) was used to
separate the TAGs. The protocol employed for the mobile phase
involved linear elution gradients for a dichloromethane/acetonitrile
(HPLC grade) system from 35% acetonitrile increasing to 55%
dichloromethane in 45 min. The mobile phase flow rate was 1.2 mL/
min. The column temperature was held at 40 °C. The TAG species
were detected by an Alltech 500eVaporative light scattering detector.
Individual peaks were identified tentatively according to Han et al.5
HPLC analysis was run in duplicate for each sample of the
interesterified product.
peak for (110) and (200) reflection was detected mostly likely
owing to the decrease in the scattering contrast between the
SBA-15 support walls and the filled pores with the organic
moieties, which showed that the organic component was
embedded into the channel of the support.24−26 Moreover, the
(100) peak of the functionalized SBA-15 silica was shown to
shift to higher 2-theta value, revealing the reduction of pore size
because of the incorporation of organic components into the
pore channel of the support.27 By drawing on the results, the
ordered meso-structure of the siliceous SBA-15 is preserved
after the incorporation of organic groups.
Figure 2 represents the FT-IR spectra of SBA-15 silica and
SBA-15-pr-TBD sample. In the case of nonfunctionalized SBA-
RESULTS AND DISCUSSION
■
Catalyst Characterization. Surface functionalization has
been employed to prepare TBD-functionalized mesoporous
SBA-15 material. The TBD base can be covalently tethered
onto the framework surface of the mesoporous SBA-15 silica
due to the presence of silanol groups, which can form strong
chemical bonds with TBD-containing organosilane precur-
sors.22 In the present study, the solid base catalyst was prepared
by two steps. The TBD base was first reacted with 3-
trimethoxysilylpropoxymethyloxirane in anhydrous DMF to
afford a TBD-containing organosilane by nucleophilic addition
of TBD to the epoxide moiety. Then, in the second step, the
resulting solution was allowed to react with the SBA-15 silica
forming the solid base catalyst. The obtained solid catalyst was
identified by FT-IR spectroscopy, SAXS, TG-DTA analysis,
nitrogen adsorption−desorption, and elemental analysis
techniques.
Figure 1 shows the SAXS patterns of SBA-15 silica and
functionalized SBA-15 silica. The SAXS pattern of siliceous
Figure 2. Fourier transform infrared spectra for samples. (a) SBA-15
and (b) SBA-15-pr-TBD.
15 silica, there was a broad IR absorption band centered at
3460 cm−1 mostly ascribed to the stretching vibration of
framework hydroxyl groups and adsorbed water molecules, and
the peak located at 1635 cm−1 was principally attributable to
the bending mode of adsorbed water present in the SBA-15
material.25 Moreover, a weak band in the mid-infrared region at
950 cm−1 for the SBA-15 support could be mainly responsible
for Si−OH groups in SBA-15 silica.27 Besides, three character-
istic absorption bands around 1080 cm−1, 780 cm−1, and 470
cm−1 were the typical vibration modes of mesoporous
framework Si−O−Si attributed to the condensed silica net in
the samples.27,28 By comparing the IR spectrum of the TBD-
functionalized SBA-15 material, the IR characteristic peaks of
surface hydroxyl groups at 3460 and 950 cm−1 were observed to
decrease significantly in intensity after the organofunctionaliza-
tion, thereby suggesting that the surface hydroxyl groups
reacted with the anchored functional groups to form the
functionalized SBA-15 material. In comparison with the SBA-15
support, new IR absorption bands at 2942 and 2876 cm−1 due
to the CH2 asymmetric and symmetric vibration respectively
were appeared for the SBA-15-pr-TBD sample.24,25 Addition-
ally, the characteristic peaks at 1587 and 675 cm−1 for the TBD-
functionalized SBA-15 material could be ascribed to the CN
stretching vibration and N−H bending vibration of TBD,18,24
and these IR peaks were not found in the IR spectrum of the
nonfunctionalized SBA-15 silica. On the basis of the results, the
TBD has been successfully anchored on the surface of the SBA-
15 material.
Figure 1. Small angle X-ray photoelectron spectroscopy patterns for
samples: (a) SBA-15 and (b) SBA-15-pr-TBD.
SBA-15 exhibited an intense peak at 0.91° corresponding to the
(100) reflection, and two low-intensity peaks at 1.56° and 1.76°
that could be indexed as (110) and (200) reflections.19,25 The
(100) reflection was characteristic for p6mn symmetry,
evidencing the formation of a well formed uniform hexagonal
lattice.24 For the functionalized SBA-15 material, the (100)
peak was also observed in the SAXS pattern, however the (110)
and (200) peaks were not clearly registered as evident from
Figure 1. This observation suggested that the long-range
ordering of the mesoporous structure remained unaltered even
after incorporation of TBD into the SBA-15 silica. No obvious
The thermal behavior of SBA-15-pr-TBD is illustrated in
Figure 3. As indicated in this figure, the small amount of mass
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Figure 5. The TEM images confirmed the presence of a
honeycomb-like hexagonal array through the material for SBA-
15 silica and TBD-functionalized SBA-15 silica.25 The slight
change in TEM image was observed after the functionalization
of SBA-15 silica, thus implying that the incorporation of TBD
into the SBA-15 silica does not destroy the mesopore structure
of SBA-15 silica. This result is in good agreement with the
other characterization technique results.
The C, H and N elemental analysis results for the solid base
catalyst are summarized in Table 1. According to the results,
the loading amount of TBD on the SBA-15 silica was calculated
to be 2.35 mmol/g, which is in line with the result obtained
from TG-DTA measurements.
The nitrogen adsorption−desorption isotherms of SBA-15
silica and SBA-15-pr-TBD catalyst are presented in Figure 6.
For the two samples, the adsorption isotherm could be classed
as type IV isotherm with H1-type hysteresis loop according to
IUPAC classification, which was the typical behaviors of highly
ordered mesoporous molecular sieves with narrow pore size
distributions.25,27 Moreover, the adsorption branch of isotherm
displayed a sharp inflection at a relative pressure of about 0.65.
This is characteristic of capillary condensation with uniform
pore dimensions and high-ordering of the material. This
phenomenon suggested that after the functionalization with the
organic base the SBA-15 material could still maintain its
mesoporous structure.
The textural properties of the samples are listed in Table 2.
BET surface area and pore-size distribution were calculated
using nitrogen adsorption at −196 °C. For pure SBA-15 silica,
the mean pore size calculated from the N2 adsorption−
desorption isotherm was 6.65 nm, and the measured surface
area and pore volume were determined to be 807 m2/g and
1.25 cm3/g, respectively, which are in accordance with the value
reported in the literature.19,24 As indicated in Table 2, for the
SBA-15-pr-TBD catalyst, a surface area of 312 m2/g and a pore
volume of 0.43 cm3/g were determined, and the pore size
distribution was narrow with a mean pore diameter of 4.45 nm.
Obviously, the SBA-15-pr-TBD catalyst showed some loss of
surface area and a pronounced reduction in pore volume and
pore diameter after the organofunctionalization, implying that
the organic base was incorporated into the SBA-15 support.
The decrease of these parameters upon the functionalization of
SBA-15 silica could be expected since the partial filling of
functionalized TBD base inside the mesopores would increase
the average wall thickness, thus decreasing the pore diameter
and BET surface area. Although such a change in the textural
Figure 3. Thermo gravimetric curves of SBA-15-pr-TBD catalyst.
loss (about 8.7%) below 200 °C could be apparently originated
from the removal of physically adsorbed water. Meanwhile, an
endothermic event between 0 and 200 °C was also observed in
the DTA curve. With further increasing the temperature, as
shown in Figure 3, a significant mass loss in the temperature
range of 200−750 °C (about 54.2%) and a strong endothermic
event at about 500 °C were appeared. This main mass loss
could be principally ascribed to the thermal decomposition of
the organic moieties in the solid base catalyst. On the basis of
the mass loss (200−750 °C), the amount of functional groups
bound on the SBA-15 material could be estimated to be 2.23
mmol/g. Beyond a temperature of 750 °C, almost no obvious
mass loss in the TG curve could be observed, revealing that the
tethered organic moiety was decomposed totally at this
temperature.
SEM techniques can be employed to study the morphology
feature of the SBA-15-pr-TBD catalyst. The typical SEM
micrograph of SBA-15-pr-TBD sample is shown in Figure 4. As
can be seen, the SBA-15 silica displayed curved faceted and
smooth rods based on elongated wheat-like macrostructures in
SEM images.19,24 The TBD-functionalized SBA-15 silica
exhibited a similar wheat-like morphology to the non-
functionalized SBA-15 silica. No significant variation in the
surface morphology occurred after the modification of SBA-15
silica except that the domains were more densely packed.
The morphology property of the solid base catalyst was also
characterized by TEM techniques. The TEM images of SBA-15
silica and TBD-functionalized SBA-15 silica are shown in
Figure 4. Scanning electron microscopy images of samples: (a) SBA-15 and (b) SBA-15-pr-TBD.
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Figure 5. Transmission electron microscopy images of samples: (a) SBA-15 in top view; (b) SBA-15 in side view; (c) SBA-15-pr-TBD in top view;
(d) SBA-15-pr-TBD in side view.
that contains three long-chain acyl residues), suggesting that
the interesterification proceeded smoothly by using the solid
base catalyst. As indicated in Figure 7, the content of SLL was
increased obviously with the reaction time in the first 1 h, and
the increase became very slow beyond 1 h. However, upon
prolonging the reaction time to 5 h, the content of SSL was
gradually decreased and then remained almost constant beyond
the reaction duration of 5 h. As observed, the LCSL content
was shown to increase with increasing the reaction time from
0.5 to 1 h, and no remarkable alteration was found between 1
and 3 h. However, there was a decrease trend in the LCSL
content beyond 3 h. In light of the results, it can be concluded
that the suitable reaction time required for obtaining a good
LCSL yield is 1 h.
Reaction temperature is another variable that can affect the
interesterification reaction. The effect of reaction temperature
on the interesterification reaction was investigated, and the
results are illustrated in Figure 9. In absence of any solvent, the
reaction temperature needs to be above the melting point of
methyl stearate (38 °C), so that the interesterification reaction
can be conducted by using the solid catalyst. As seen in Figure
8, when the reaction temperature was increased from 50 to 80
°C, the SLL content also increased from 33.7 to 47.3%.
However, with subsequent increase in reaction temperature, the
SLL content was dropped slightly. Besides, the SSL content was
shown to decrease as the reaction temperature was increased
from 50 to 80 °C, but no further variation in SSL content was
observed beyond 80 °C. Moreover, the LCSL content of the
interesterified product was gradually increased to 91.5% with
Table 1. Results for C, H, and N Elemental Analysis
sample
SBA-15
C (wt %)
H (wt %)
N (wt %)
a
a
a
NF
NF
NF
SBA-15-pr-NR3OH
16.92
2.85
1.76
a
NF stands for not found.
properties, the functionalized SBA-15 silica still remained the
typical mesoporous structure after the organofunctionalization
reaction.
Influence of Interesterification Parameters. In the
present study, the interesterification can substantially alter the
TAG profiles of the starting oil blend, and the LCSL is
produced by the interesterification of tributyrin and methyl
stearate. The interesterified product was characterized by the
combination of short-chain and long-chain acyl residues into a
triacylglycerol structure. As shown in Figure 7, two new types
of TAGs (SSL and SLL) were produced, representing the
incorporation of stearoyl groups into the new type of TAGs. By
varying the fatty acid composition and the ratio of SSL/SLL,
the properties of the LCSL product can be improved
accordingly.
As expected, there was no catalytic activity for the
interesterification reaction to be observed for the SBA-15
support. However, after incorporation of TBD into the support,
the SBA-15-pr-TBD catalyst displayed comparable activities
toward the reaction. Figure 8 shows the TAG compositions on
the solid base catalyst as a function of reaction time. At a
reaction time of 0.5 h, the interesterified product contained
46.5% of SSL, 37.8% of SLL, and 3.4% of LLL (triacylglycerol
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Figure 8. Evolution of the triacylglycerol distribution with reaction
time during the interesterification reaction. Reaction conditions:
methyl stearate/tributyrin molar ratio 2:1, reaction temperature 80 °C.
SSL, triacylglycerol that contains two short-chain and one long-chain
acyl residues; SLL, triacylglycerol that two long-chain and one short-
chain acyl residues; LLL, triacylglycerol that contains three long-chain
acyl residues; LCSL, low-calorie structured lipid.
Figure 6. Nitrogen adsorption/desorption isotherms and pore size
distribution profiles of samples: (a) SBA-15 and (b) SBA-15-pr-TBD.
Table 2. Textual Characteristics of SBA-15 and SBA-15-pr-
NR3OH Catalyst
a
b
c
sample
SBA-15
SBA-15-pr-NR3OH
SBET (m2/g)
Vp (cm3/g)
DBJH (nm)
807
1.25
0.43
6.65
4.45
312
a
b
c
BET surface area. Pore volume. Average pore diameter from BJH
desorption.
Figure 9. Evolution of the triacylglycerol distribution with reaction
temperature during the interesterification reaction. Reaction con-
ditions: methyl stearate/tributyrin molar ratio 2:1, reaction time 1 h.
SSL, triacylglycerol that contains two short-chain and one long-chain
acyl residues; SLL, triacylglycerol that two long-chain and one short-
chain acyl residues; LLL, triacylglycerol that contains three long-chain
acyl residues; LCSL, low-calorie structured lipid.
increasing the reaction temperature to 80 °C, and thereafter
was diminished slightly at a temperature of 90 °C. Accordingly,
in the present investigation, the proper temperature for the
interesterification reaction is 80 °C.
The interesterification reaction is generally employed to
produce structured lipids that have the improved functionality
by rearranging the fatty acids on the glycerol backbone. For
different mixtures of substrates, the interesterification was
carried out by using the solid catalyst at a temperature of 80 °C.
As shown in Figure 10, for all the experimental trials involving a
variety of molar ratios of methyl stearate to tributyrin, the rapid
depletion of tributyrin species occurred affording new SSL and
SLL of TAGs simultaneously. With increasing methyl stearate/
tributyrin molar ratio to 2:1, the content of SLL triacylglycerol
in the interesterified product increased, while the SSL content
Figure 7. High performance liquid chromatography for the
triacylglycerol compositions of the interesterified product. SSS,
Tributyrin; SSL, triacylglycerol that contains two short-chain and
one long-chain acyl residues; SLL, triacylglycerol that two long-chain
and one short-chain acyl residues; LLL, triacylglycerol that contains
three long-chain acyl residues.
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Figure 11. Low-calorie structured lipid content of the interesterified
product over several catalyst cycles. Reaction conditions: methyl
stearate/tributyrin molar ratio 2:1, reaction temperature 80 °C,
reaction time 1 h. LCSL, low-calorie structured lipid.
Figure 10. Evolution of the triacylglycerol distribution with tributyrin/
methyl stearate ratio during the interesterification reaction. Reaction
conditions: reaction temperature 80 °C, reaction time 1 h. SSL,
triacylglycerol that contains two short-chain and one long-chain acyl
residues; SLL, triacylglycerol that two long-chain and one short-chain
acyl residues; LLL, triacylglycerol that contains three long-chain acyl
residues; LCSL, low-calorie structured lipid.
structure remained almost unchanged, which was favorable for
improving the contact between the catalytically active
component and reactants. Further, the solid catalyst is
applicable to the interesterification reaction as a stable and
highly active catalyst. Over this catalyst, the LCSL, composed of
stearic acid and butyric acid, was successfully prepared in a
heterogeneous manner. In the previous work, Han et al.
reported that the interesterification of tributyrin and methyl
stearate was conducted using a commercially immobilized
lipase, Lipozyme RM IM.5 Compared to the immobilized
lipase, the SBA-15-pr-TBD catalyst shows higher activities for
the interesterification reaction owing to the shorter reaction
time employed and lower catalyst loading.
diminished. In this case, with higher methyl stearate/tributyrin
molar ratio than 2:1, the SLL content was declined slightly and
the SSL content remained nearly constant. In all of these trials,
the LLL triacylglycerol was observed to increase on increasing
the methyl stearate/tributyrin molar ratio. From Figure 9, it was
observed that the content of LCSL was initially ascended from
84.7 to 91.5% with the increase in methyl stearate/tributyrin
molar ratio from 0.5:1 to 2:1. However, beyond the molar ratio
of 2:1, the lower content of LCSL was observed. Given the
present results, the appropriate molar ratio of methyl stearate to
tributyrin is found to be 2:1, with the LCSL content of 91.5%.
Reusability of the Catalyst. The reusability is an
important aspect to evaluate the feasibility of a heterogeneous
catalyst for its application in industrial processes, which makes
it economic and preferable over homogeneous one. In order to
study the catalyst reusability, consecutive reaction runs were
carried out using the SBA-15-pr-TBD catalyst. At the end of the
interesterification, the catalyst was recovered by filtration,
washed with cyclohexane and ethanol, and dried at 120 °C
overnight in a vacuum oven. The recovered catalyst was used
for the next cycle, and this process was repeated for several
times under the optimized reaction conditions as described
above. The experimental results are illustrated in Figure 11. It
was indicated that the LCSL yield was almost kept stable
without significant loss of its catalytic activity (91.5% in the first
cycle versus 85.8% in the fifth cycle) for up to five times of use,
thus indicating the good stability of the catalyst. However, the
catalytic activity was obviously decreased as the catalyst was
used more than five times, mostly owing to the accumulation of
impurities on the catalyst surface.
AUTHOR INFORMATION
Corresponding Author
*E-mail: xwenlei@163.com. Phone: +86 371 67756302. Fax:
+86 371 67756718.
■
Funding
This work was financially supported by research grants from the
National Natural Science Foundation of China (Project No.
21276066), the Plan for Scientific Innovation Talent of Henan
Province (144200510006) and the Program for Innovative
Research Team in Universities of Henan Province in China
(2012IRTSTHN009).
Notes
The authors declare no competing financial interest
ABBREVIATIONS USED
■
BET, Brunauer−Emmett−Teller; BJH, Barrett−Joyner−Halen-
da; CIE, chemical interesterification; DMF, N,N-dimethylfor-
mamide; EIE, enzymatic interesterification; FT-IR, Fourier
transform infrared; HPLC, high-performance liquid chroma-
tography; LCSL, low-calorie structured lipid; LLL, triacylgly-
cerol that contains three long-chain acyl residues; SAXS, small-
angle X-ray scattering; SEM, scanning electron microscopy;
SSL, triacylglycerol that contains two short-chain and one long-
chain acyl residues; SLL, triacylglycerol that two long-chain and
one short-chain acyl residues; TAG, triacylglycerol; TBD, 1,5,7-
triazabicyclo[4.4.0]dec-5-ene; TEM, transmission electron
In light of the aforementioned results, a heterogeneous
catalyst, SBA-15-pr-TBD, was prepared by reactions of TBD-
organosilane with the mesoporous SBA-15 material. By using
this solid base catalyst, the interesterification between tributyrin
and methyl stearate in a solvent-free system was performed for
the production of LCSL. All the characterization results
indicated the successful anchoring of organic base TBD on
the framework channel of mesoporous SBA-15 materials. After
the functionalization of SBA-15 silica, the ordered mesoporous
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with the catalytic activity. Appl. Catal. A: Gen. 2011, 400, 176−184.
microscopy; TEOS, tetraethylorthosilicate; TG-DTA, thermo
gravimetric analysis; TLC, thin-layer chromatography
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