LDH-catalyzed esterification of lauric acid with glycerol in solvent-free system

Article abstract of DOI:10.1016/j.apcata.2014.01.040

Direct esterification of waste oil materials (high FFA contents) and glycerol can be an important way to improve the energy goals and afford alternative sources to emulsifier production for food and cosmetics industry. This work reports an experimental study of free-solvent esterification of lauric acid with glycerol using a LDH (layered double hydroxide, Mg-Al-CO₃) as catalyst. The experiments were performed in a mechanically stirred reactor evaluating the effect of temperature (100-180 C), lauric acid to glycerol molar ratio (1:1-3:1) and catalyst content (2-8 wt%). The results showed that relative high glycerol conversions (99%) can be obtained for the lauric acid esterification with glycerol leading to monolaurine and dilaurine. Results show that free-solvent LDH-catalyzed lauric acid esterification with glycerol might be a potential alternative route to conventional methods, as high contents of reaction products and selectivity was achieved. Furthermore, the results show that the LDH catalyst used was able to drive the reaction to the equilibrium in a relative short time - up to two hours.

Full text of DOI:10.1016/j.apcata.2014.01.040

Applied Catalysis A: General 475 (2014) 242–248
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
LDH-catalyzed esterification of lauric acid with glycerol
in solvent-free system
Fabiane Hamerski, Marcos L. Corazza∗
Department of Chemical Engineering, Federal University of Paraná (UFPR), PO Box 19011, CEP 81531-990, Curitiba, PR, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Direct esterification of waste oil materials (high FFA contents) and glycerol can be an important way to
improve the energy goals and afford alternative sources to emulsifier production for food and cosmetics
industry. This work reports an experimental study of free-solvent esterification of lauric acid with glyc-
erol using a LDH (layered double hydroxide, Mg–Al–CO3) as catalyst. The experiments were performed
in a mechanically stirred reactor evaluating the effect of temperature (100–180 ◦C), lauric acid to glycerol
molar ratio (1:1–3:1) and catalyst content (2–8 wt%). The results showed that relative high glycerol con-
versions (99%) can be obtained for the lauric acid esterification with glycerol leading to monolaurine and
dilaurine. Results show that free-solvent LDH-catalyzed lauric acid esterification with glycerol might be a
potential alternative route to conventional methods, as high contents of reaction products and selectivity
was achieved. Furthermore, the results show that the LDH catalyst used was able to drive the reaction to
the equilibrium in a relative short time – up to two hours.
Received 28 September 2013
Received in revised form 8 January 2014
Accepted 17 January 2014
Available online 27 January 2014
Keywords:
Fatty acid esterification
Heterogeneous catalyst
Acylglycerols
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Corma et al. highlighted calcined hydrotalcites as a potential
catalyst material, respectively, in the transesterification of rape-
Mono (MAGs) and diacylglycerols (DAGs) are amphiphilic
molecules used as emulsifier for foods, pharmaceutical and cos-
metic industries, lubricants for plastics and paint and additives
for perfumes [1–3]. DAGs are a group of compounds that have
been highlighted in the nutraceutical products and controlled-
release medicinal tablets [4,5]. On the other hand the DAG has
been attracted attention as fat that can prevent the obesity and
arteriosclerosis [6,7]. These compounds, conventionally, have been
prepared by the esterification of glycerol with fatty acids or by
transesterification of fatty acid triglyceride by glycerol. The process
of manufacture is conducted at high temperatures (220–250 ◦C)
employing strong inorganic alkaline catalysts such as sodium
hydroxide or strong acid such as sulfuric acid. The product has sev-
eral drawbacks for the products (low yield, dark color and burnt
test) and environmental aspects (corrosiveness, hazards of waste
catalysts) [8–10].
seed oil with glycerol and in the glycerolysis of fatty methyl
esters for monoacylglycerols synthesis due the basic charac-
teristic of these compounds [20,21]. Hydrotalcite is a layered
double hydroxide (LDH), represented by the general formula:
[M1−x2+Mx3+(OH)2]x+Xx/mm−·nH2O, where M2+ is a divalent metal
ion such as Mg2+, Ni2+, Cu2+ or Zn2+, M3+ is a trivalent metal ion such
as Al3+, Cr3+, Fe3+ or Ga3+ and Xm− is an a−nion inorganic and organic
anions charged such as CO32−, Cl−, NO3 [22,23]. The substitution
of divalent by trivalent metal ions leads the net positive charges
that need to be compensated by an equal negative charge of the
interlayer solvated anions [24]. LDHs of (Mg–Al–CO3) complex are
layered materials with ion-exchange ability having excellent bio-
compatibility and without toxicity [25,26], are applied in drugs and
as encapsulating functional biomolecules [27] and did not show
cytotoxic effect in vivo testing to animals [28]. Because of these,
the LDH of hydrotalcite type (MgAl–CO32−) could be an interesting
material for application in catalysis to obtain products that will be
applied in foods.
In this context, this work is aimed to report the experimental
data for a LDH-catalyzed synthesis of mono and diacylglycerol by
esterification of lauric acid with glycerol. In this study was syn-
thesized the LDH using the complex (Mg–Al–CO3). The variables
temperature, lauric acid to glycerol molar ratio and catalyst con-
tent were evaluated in the glycerol conversion and selectivity of
mono, di and trilaurine formation. In addition, to compare the
catalytic effect with non-catalyzed (without catalyst in the system)
The development of alternative catalysts is necessary to solve
or to minimize the contrary effects of the esterification reaction to
DAG and MAG production. A large number of studies have been
published in this area using different raw, enzymatic and chemical
catalyst [8–19].
∗
Corresponding author. Tel.: +55 41 3361 3587.
E-mail address: corazza@ufpr.br (M.L. Corazza).
0926-860X/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2014.01.040

F. Hamerski, M.L. Corazza / Applied Catalysis A: General 475 (2014) 242–248
243
Table 1
in the esterification reaction, experiments without catalyst were
conducted.
Experimental conditions of the complete factorial design (23) and kinetics.
Treatment codification
T (◦C)
CAT (%)
MR (LA:GL)
01
100
180
100
180
100
180
100
180
140
140
140
140
140
160
160
160
180
180
2
2
8
8
2
2
8
8
5
5
5
2
0
2
0
2
0
2
3:1
3:1
3:1
3:1
1:1
1:1
1:1
1:1
2:1
2:1
2:1
3:1
2:1
2:1
3:1
3:1
3:1
2:1
2. Experimental
02b
03
2.1. Synthesis of LDH
04
05
06
07
The LDH of MgAl–CO3 complex was synthesized by precipita-
tion methods at constant pH. One aqueous solution, denominated
solution A, containing aluminum and magnesium, respectively,
1 mol L−1 and 3 mol L−1, was prepared dissolving Mg(NO3)2·6H2O
(Vetec) and Al(NO3)3·9H2O (Synth) in deionized water. This solu-
tion was added drop by drop (1–1.5 mL min−1) in the solution
B having sodium carbonate (1.2 mol L−1) dissolved in deionized
water. The pH of precipitation was maintained constant (10.0) by
parallel addition of NaOH solution (2 mol L−1) and was monitored
by a pH meter (Micronal – B474). The suspension was homog-
enized with a mechanical stirrer (Quimis – Q250 M) at 250 rpm.
After ended the addition of solution A the precipitates were then
hydrothermally treated in the mother liquor at 80 ◦C during 24 h,
like described Prinetto and co-workers [29]. After that, the solu-
tion was filtered with a qualitative filter, washed with 500 mL of
deionized water and dried at 80 ◦C by 48 h.
08
09a,b
10a
11a
12
13b
14
15b
16b
17b
18
a
Central point.
Kinetics conditions.
b
(Sigma – M1765); dilaurine (Sigma – D9758) and trilaurine (Sigma
– T4891) were used as standards reference.
The mono (PML), di (PDL) and triacylglycerol (PTL) content (wt%)
were used to estimate the glycerol conversion (XGL) in the reactions
using Eq. (1). Where the stoichiometric balance of the esterification
reaction it was considered, in which one mol of glycerol is required
to produce one mol of each compound: mono, di and triglyceride. In
the same approach the selectivity was expressed by the ratio of the
glycerol consumed to form each compound and the total glycerol
consumed in the reaction, as given in Eqs. (2)–(4).
2.2. Characterization of LDH
X-ray diffraction (XRD) – Data of LDH were collected by
X-ray powder diffractometer Panalytical using Cu K␣ radiation
◦
˚
(ꢀ = 1.5406 A, 40 kV and 30 mA), in the position 2ꢁ, range 3–70 and
step size 0.02.
Specific surface area (BET) and pore size distribution – Sur-
face area was determined using the Brunauer–Emmet–Teller (BET)
method [30]. The N2 adsorption and desorption isotherms were
measured at −163 ◦C, in a NOVA-1200 Quatachrome instrument.
Fourier transform infrared (FTIR) – The spectra of LDH was
obtained at room temperature in the range of wavenumber
4000–400 cm−1, at a resolution of 4 cm−1 and 32 number of scans
on a BIO-RAD, Excalibur Series (FTS 3500 GX) spectrophotometer.
The sample was prepared in pallet by mixing powdered material
with KBr (Vetec) – spectroscopic grade (the blank) using a 1:10
ratio.
Thermogravimetric (TG) and differential scanning calorimetric
(DSC) analyses – were carried out with a Nestzsch instrument (STA
449 F3 Jupiter), using a heating rate of 10 ◦C min−1, in the range
20–1000 ◦C, alumina crucibles and nitrogen atmosphere.
Laser granulometry – The particle size distribution of LDH was
evaluated in a granulometer CILAS – Model 1064.
ꢀꢁ
ꢂ
ꢅ
ꢃ
ꢄ
MWGL
PML
PDL
PTL
MWTL
ꢈ
ꢈ
ꢈ
XGL(%) =
×
+
+
× 100 (1)
PGL
MWML
MWDL
o
ꢆ
P
ML
ML
MW
SelectivityML(%) =
SelectivityDL(%) =
SelectivityTL(%) =
× 100
× 100
× 100
(2)
ꢇ
P
P
P
TL
ML
DL
DL
+
+
+
+
MW
MW
MW
ML
TL
ꢆ
ꢆ
P
DL
DL
MW
(3)
(4)
ꢇ
ꢇ
P
P
P
ML
DL
DL
TL
MW
MW
MW
ML
TL
P
MW
TL
TL
P
P
P
ML
ML
DL
DL
TL
MW
+
+
MW
MW
TL
where PML− percentage of ML, PDL− percentage of DL, PTL− per-
centage of TL, PGL – percentage of glycerol at the beginning of
o
Scanning electron microscopy (SEM) – Morphology of LDH
surface was verified by image obtained in a scanning electronic
microscope JEOL JSM-6360.
reaction, MWGL – molecular weight of glycerol, MWML− molec-
ular weight of monolaurine, MWDL−molecular weight of dilaurine,
MWTL− molecular weight of trilaurine.
2.3. Products analyses
2.4. Reaction procedure
The compounds monoacylglycerol (monolaurine; ML), diacyl-
glycerol (dilaurine; DL), and triacylglycerol (trilaurine; TL) were
analyzed by high performance liquid chromatography in an Agi-
lent 1200-series chromatograph with diode array detector (DAD),
Kinetex C18 column (150 mm × 4.6 mm, 5 ␮m), 50 ␮L of injection
volume, isocratic elution of mobile phase, constituted by solvent
of HPLC grade (v v−1): 45% acetonitrile (J.T. Baker): 23% methanol
(J.T. Baker): 30% isopropanol (Panreac) and 2% of sulfuric acid
The esterification reactions were performed in a stainless steel
Parr® batch reactor (50 mL, model 4848HP). The substrates used in
LDH-catalyzed esterification were lauric acid (Sigma–Aldrich, 99%
purity), and glycerol (Carlo Erba, 99.5% purity). All reactions were
carried out with stirring rate adjusted to 500 rpm. Firstly, a factorial
experimental design (23) with a central point in triplicate, showed
in the Table 1 (experiment 01–11) was used to evaluate the effects
of variables lauric acid to glycerol molar ratio (MR), temperature
(◦C) and catalyst percentage (% CAT) in the esterification reaction
of glycerol with lauric acid using LDH as catalyst. The experimen-
tal design was obtained by association between levels (−1 and +1)
(0.05 mol L−1) in aqueous solution with initial flow 0.6 mL min−1
,
that was increased, in the 5 min of run, to 1 mL min−1, standing
by more 5 min, when the run was stopped. The external calibra-
tion method was used to quantitative analysis and monolaurine

244
F. Hamerski, M.L. Corazza / Applied Catalysis A: General 475 (2014) 242–248
70
(003)
700
600
500
400
300
200
100
0
60
50
40
30
(006)
(009)
(015)
(110)
60
(113)
20
10
0
(018)
10
20
30
40
θ
50
70
Angle 2
4000
3500
3000
2500
2000
1500
1000
500
Fig. 1. XRD spectra of catalyst material of complex Mg–Al–CO3.
Wavenumber (cm-1)
Fig. 2. FTIR spectra of LDH synthetized.
of the variables and a central point, defined by intermediate condi-
tions of each variable. The central point was performed in triplicate
to evaluate the repeatability of experiments). After the assays of the
experimental design have been conducted and the products ana-
lyzed, some additional experiments were performed (treatments
12–19) in more restricted conditions. Variables that had significant
influence in the preliminary reactions were then used aiming to
compare the glycerol conversion and selectivity in conditions not
evaluated in the experimental design. Moreover, the kinetics data
of this reaction were performed using the catalyst (LDH-catalyzed
– CK) and the non-catalyzed kinetic was also evaluated (that refers
one to kinetic without catalyst, just by effect of temperature – TK)
to investigate the effect of catalyst on this reaction. The reaction
time of all experiments showed in Table 1 was 120 min.
The reaction time to kinetics computation was counted from the
time that the desired temperature was reached inside the reactor
(about 5 min). Same procedure of temperature rising was repeated
for all experiments. The vessel volume occupied was always around
2/3 of the reactor volume. For each isotherm, the glycerol con-
version was measured and related as the initial conversion for all
experimental conditions studied in this work.
with those reported in the literature for LDH that have structure
like hydrotalcite with carbonate anions in the interlayer [38–40].
The FTIR spectra for the solid material is showed in Fig. 2,
that exhibit an intense and broadband adsorptions between 4000
and 2700 cm−1 due to the deformational vibrations of physically
adsorbed water, vibrations of structural OH− groups, characteris-
tic vibrations of OH. . .OH and/or CO3 OH− in hydrotalcite [41].
2
Moreover, in according with Parida and Das [42], this broad-
band may represent characteristics stretching vibration of the
Mg2+ OH− bond in Mg, Al-hydroxycarbonate. The little shoulder
visualized at 3100 cm−1 is assigned to hydroxyl interactions with
carbonate ions in the interlayer space [43,44] and it is related to
hydrogen bonding of H2O to CO32− ions in the same region [33,35].
The absorption of anion interlayer (CO3−2) was identified around
1380 cm−1 and broadband in the region below 600 cm−1 is due to
Al–OH or Mg–OH stretching [31,45].
The particle size distribution of the synthesized LDH is showed
in Fig. 3 and it indicating that was obtained a material with regular
size and with a small granulometry, probably due to the well-
controlled conditions used in the synthesis procedure (pH, flux
and stirring constant). The maximum size of the particles were
50 ␮m, however, almost 90% were smaller than 30 ␮m, 50% of par-
ticles presented size smaller than 13 ␮m and the average of the
The software Statistica 7.0 was used in the statistical data anal-
ysis to evaluate the effects of variables: temperature, percentage of
catalyst and lauric acid to glycerol molar ratio in this study.
3. Results and discussion
3.1. Characterization of catalyst
The Fig. 1 shows the XRD spectra of catalyst material identified
like the structure of hydrotalcite (JCPDS 22-700), indicating well
defined (00l) reflections as a typical layered material with more
intense and sharper reflections at low values angle (11◦, 23◦, 35◦),
planes (0 0 3), (0 0 6), (0 0 9) and broad asymmetric reflections at
higher values angle in the position of the 2ꢁ. These reflections with
relative high intensities combined with broad line shapes indicate
that the hydrotalcite has a relative high crystallinity but very small
crystallites [31]. The sharp peak (2ꢁ = 11◦) is ascribed to the diffrac-
˚
tion by planes (0 0 3), referred as the basal spacing (d003 = 7.8 A)
is in accordance with others studies [22,32,33]. Lattice parameter
˚
a = 3.0 A corresponds to the average closest metal-metal distance
˚
within a layer. The parameter c = 23.6 A is a function of the aver-
age charge of the metal cations, the nature of interlayer anion and
the water content. These parameters of cell were obtained like
described by Pérez-Ramirez et al. [34,35] and Zhao et al. [36], are
typical of an LDH of the Mg–Al–CO3 type [37] and are in agreement
Fig. 3. Profile of particle size distribution of LDH synthetized.

F. Hamerski, M.L. Corazza / Applied Catalysis A: General 475 (2014) 242–248
245
Fig. 5. TG and DSC profile of LDH in the 20–1000 ◦C range.
Fig. 4. Surface micrograph of LDH particles produced in this work.
to the studies of Prinetto and co-workers [29], this phenomenon is
due to the oxidation reactions of the organic compounds, coming
from the precursors of LDH, and occurred simultaneously to the
usual dehydroxylation of the layers. And it is evidenced by the loss
of mass in the TG curves, which hidden in part the endothermic
event, characteristic in the DSC curves of this material.
particles diameters was 15.19 ␮m. Moreover, the LDH presented
106.0 m2 g−1 of surface area, 0.29 cm3 g−1 of total porosity and pore
˚
size of 110 A, characterized as a mesopores material in according
to the classifications of International Union of Pure and Applied
Chemistry (IUPAC) [46]. The low values of particles size of meso-
porous LDH synthesized are in agree with the narrow pore size and
greater surface area obtained suggesting facility to the LDH to inter-
act with the reagents in the catalyst reactions. Aramendía et al. [47]
synthesized LDH by coprecipitation at 60 ◦C and obtained a mate-
rial with similar porosity (0.23 cm3 g−1), however the surface area
was lower (50.0 m2 g−1). While Wang and co-workers [48] obtained
about 110 m2 g−1 of area to LDH synthesized at similar conditions.
It is important to emphasize that some differences in procedure of
LDH synthesis can influence in the characteristics of final material.
Fig. 4 shows the image of the surface of LDH, obtained by MEV,
in which composed particles can be viewed by a lot of small pores
in all surface of this material that can contribute to obtain a large
surface area. The formation of this characteristic porous is favored
by the structure random lamellar of the hydrated hydroxycar-
bonates composed by divalent metal cation (Mg2+) and trivalent
metal cation (Al3+). Wang and co-workers [48] obtained a simi-
lar structure in the LDH of Mg–Al–CO3, synthesized at pH 10, and
they described that hydrotalcite morphology as “rosette” particles.
These researchers, based on the studies of Chang et al. [49], You et al.
[50] and Li et al. [51], have suggested that the formation of this
rosette hydrotalcite might be related to its isoelectric point (IEP)
which is around 10. In this condition, although the formation of
the primary particles is fast, the growth is slow because the surface
of the initially formed primary particles is electrically neutral (pH
IEP). Consequently, with the hydrothermal treatment in the syn-
thesis of LDH, the growth of hydrotalcite is favored on the surface
of low charge density, where growth of the primary nanoparticles
into nano-sheets results in the “rosette” morphology.
3.2. Esterification reaction
From the esterification reaction of lauric acid with glycerol
produces a mixture of monolaurine (ML), dilaurine (DL) and trilau-
rine (TL). In Fig. 6, are showed the results of glycerol conversion and
the selectivity of ML, DL and TL of reactions conducted according
to the conditions of experimental design explained in the Table 1.
These results indicated that the glycerol conversion was favored
with the increase of temperature and molar ratio of lauric acid to
glycerol; however the percentage of catalyst was not significant.
This can be verified in the analysis of variance (ANOVA) of estima-
tive factors effect, in which, the p values were significant (p < 0.05)
to the variables temperature (p = 0.00008), molar ratio (lauric acid
to glycerol) (p = 0.0003) and interaction between them (p = 0.003).
It can be seen that the temperature presented a major effect on
glycerol conversion. At higher temperature the conversion reached
The termogravimetric (TG) analysis of LDH showed in Fig. 5 indi-
cates, in the first stage of TG curve, the loss of 15% of mass in the
temperature up to 250 ◦C. This endothermic process, visualized by
DSC curve, occurs due to the removal of interlayer and adsorbed
water. In the temperature range comprehended between 250 and
500 ◦C it can be observed that the decomposition of hydroxyl, from
the brucite-like layer, and carbonate anions from the interlayer,
viewed by second mass loss (25%). The dehydroxylation results in
the collapse of hydrotalcite structure corresponding to his metal
oxides, MgO, Al2O3, and MgAl2O4 [33]. The similar events of mass
losses were obtained in the studies presented in the literature
[32,34,36,52,53]. In the same range of temperature (250–500 ◦C),
in the DSC curve, one exothermic event was evidenced. According
Fig. 6. Conversion of glycerol and acylglycerols selectivity at 120 min of reaction.
Dotted bars are glycerol (GL) conversion; gray bars with vertical lines are mono-
laurine (ML) selectivity; bars with diagonal lines are dilaurine (DL) selectivity and
black bars are trilaurine (TL) selectivity.

246
F. Hamerski, M.L. Corazza / Applied Catalysis A: General 475 (2014) 242–248
99% of glycerol conversion (180 ◦C) and it can be observed that
at lower temperature (100 ◦C) the maximum conversion, in all of
reactions conducted at this temperature, was about 25%. Concern-
ing the temperature effect observed from these results (Fig. 6) it
can be seen that this esterification reaction has an endothermic
character. Moreover, it can be also observed that the monolau-
rine selectivity was higher at lower temperatures, practically, in
the reactions at 100 ◦C the total glycerol conversion corresponds
to monolaurine formation. And as the temperature is increased the
selectivity of monolaurine decreases with a concomitant increasing
of dilaurine and trilaurine selectivity. This behavior can be viewed
comparing all different values of temperature studied including
the additional temperature in the experimental design (160 ◦C).
The results obtained at 160 ◦C are in agreement with the results
obtained from the experimental design and also with the exper-
iments without catalyst, performed at different temperatures. At
lower temperature the reactants miscibility is possibly disfavored
diminishing the surface contact area between components in the
reaction medium, which affects negatively the reactivity of the
system. In the reactions with catalyst, the LDH synthesized were
homogeneously dissolved or dispersed in the mixtures, due to its
solubility into acid medium, and this effect can be more accentu-
ated at higher temperatures. Then, the higher solubility catalyst,
associated with activation energy increasing, at high temperature,
are favoring the contact of reagents and catalyst activity and con-
sequently displacement of this reaction into the products can be
observed.
The lauric acid to glycerol molar ratio (LA:GL) presented the
same tendency effects of temperature in terms of the glycerol con-
version and selectivity, moreover, in the association of high molar
ratio evaluated (3:1) and highest temperature here used (180 ◦C)
the maximum glycerol conversion obtained was (99%), indepen-
dently to the catalyst amount used.
In a general way, the catalyst amount evaluated in this work
(2–8%) showed not significant effect in the reaction. According to
Machado and co-workers [54] this behavior is possibly caused by
diffusional restriction, because the reaction mixture turned highly
viscous when the percentage of catalyst is increased. Furthermore,
it is important to mention that no carbonaceous material or coke
deposits were observed at the end of the all reactions.
In Fig. 7 the kinetics values of LDH-catalyzed lauric acid esteri-
fication with glycerol at different conditions are presented. Aiming
the comparison between experiments performed with and without
catalyst, some kinetic were performed at same temperature and
molar ratio, and its kinetics results are presented in Fig. 8. Consid-
ering the LDH-catalyzed reactions (Fig. 7a–c) it can be observed that
for all conditions at 180 ◦C the reaction reached almost the total of
glycerol conversion. It can be observed from results presented in
Fig. 7 that the glycerol conversion and the monolaurine selectivity
are favored when the temperature is increased. It is observed for all
kinetic points at high temperatures. In addition, the monolaurine
is the predominant product formed and its selectivity decreases
with parallel increase of dilaurine and trilaurine production follow-
ing the reaction time. It is showing that the monolaurine, dilaurine
and trilaurine synthesis are consecutive reactions for the catalytic
reaction.
Another important observation is on the effect of catalyst in
the reaction. It can be observed that the thermal reaction, blank
conditions (Fig. 8a–c), presented considerable values of glycerol
conversion when compared with catalytic reaction. However, their
values are always lower for all kinetics. At first 30 min of reaction,
were obtained about 15%, 40% and 55% of glycerol conversion in the
kinetics performed at 140 ◦C, 160 ◦C and 180 ◦C, respectively, while
in the presence of LDH catalyst (Fig. 7a–c), the values of glycerol
conversion enhanced 30%, 70% and 90%, respectively. After 60 min
of reaction the glycerol conversion at 180 ◦C was saturated, i.e.,
100
a)
b)
c)
80
60
40
20
0
0
20 40 60 80 100 120 140 160 180 200 220 240
Time (min)
100
80
60
40
20
0
0
20 40 60 80 100 120 140 160 180 200 220 240
Time (min)
100
80
60
40
20
0
0
20
40
60
80
100 120 140 160 180 200 220 240
Time (min)
Fig. 7. Molar conversion of glycerol and selectivity of LDH-catalyzed lauric acid
esterification with glycerol. Conditions of reactions [temperature (◦C) – CAT (%) –
MR (LA:GL) (lauric acid to glycerol molar ratio] (a) [140-5-2:1]; (b) [160-2-3:1];
(c) [180-2-3:1]. Squares – glycerol conversion; triangles – monolaurine selectivity;
circles – dilaurine selectivity; rhombus – trilaurine selectivity.
reached values closer that 100%. Also, still considering the LDH-
catalyzed reaction, at 160 ◦C, the glycerol conversion was slower
and it enhanced the total glycerol conversion after 120 min. On the
other hand, the total glycerol conversion at 140 ◦C was not observed
considering the end of reaction time used in this work (240 min).
Considering the non-catalyzed reaction (without the catalyst
presence) kinetics the maximum time of reaction was 120 min and

F. Hamerski, M.L. Corazza / Applied Catalysis A: General 475 (2014) 242–248
247
100
80
60
40
20
0
Comparing the similar high glycerol conversions kinetics, one
at 160 ◦C, MR (3:1) during 120 min and another at 180 ◦C, MR
(3:1) during 60 min, both reactions which 2% of catalyst, it can be
considered that second condition is more interesting. Besides the
advantage of short reaction time, the dilaurine selectivity is higher
(30%) than in the first conditions (11%). The formation of diacylglyc-
erol, in this study dilaurine, is preferred because it presents some
potential benefits for human consumption of these compounds to
reduce postprandial serum triacylglycerol levels and thus is bene-
ficial in the obesity prevention and management [55,56].
a)
4. Conclusions
This study reports for the first time a study of LDH-catalyzed
esterification of lauric acid with glycerol in solvent-free system.
And the catalyzed kinetics results were compared to non-catalytic
results (reactions conducted without catalyst). The synthesized
material was a typical LDH, hydrotalcite type, with 15.19 ␮m of par-
ticle size diameter, high surface area (106.0 m2 g−1) characterized
as a mesopore material. It was observed that the catalyst presented
a good catalytic activity in the reaction of lauric acid esterification
with glycerol to obtaining mono, di and trilaurine.
The temperature and the lauric acid to glycerol molar ratio
presented a significant effect in the LDH-catalyzed esterification
reaction. However, the catalyst amount used in this work did
not show significant effect. The glycerol conversion was increased
with the increase in the temperature and lauric acid to glycerol
molar ratio. At the minimum temperature evaluated (100 ◦C) were
obtained, considering a reaction time of 120 min, 25% of glycerol
conversion while at maximum temperature (180 ◦C) 99% of con-
version was reached.
0
20
40
60
80
100
120
Time (min)
100
80
60
40
20
b)
The kinetics reactions conducted with LDH and higher temper-
atures showed high glycerol conversion in short reaction time. The
monolaurine was the major product synthesized in all reaction
conditions and at long reaction time the monolaurine selectivity
decreased with according to the increase in the dilaurine and tri-
laurine selectivity.
0
100
80
60
40
20
0
0
20
40
60
80
100
120
Time (min)
c)
The reaction conducted during 60 min, at 180 ◦C, lauric acid to
glycerol molar ratio (3:1) and 2% of catalyst leads to the almost total
glycerol conversion (reaching 99% of glycerol conversion) and the
highest value of dilaurine selectivity (30%) in the shorter reaction
time.
The results obtained in this work using LDH of type Mg–Al–CO3
as esterification catalyst suggest that this material would have a
potential application to obtain mono and dilaurine by esterification
of lauric acid with glycerol in a short reaction time. Further exper-
iments comprising detailed investigations of LDH-catalyzed fatty
acid from some waste sources or commercial oils are underway by
our working group.
0
20
40
60
80
100
120
Acknowledgments
Time (min)
The authors thank CNPq, Fundac¸ ão Araucária, and CAPES (Brazil-
ian Agencies) for the financial support and scholarship.
Fig. 8. Molar conversion of glycerol and selectivity of non-catalyzed (without cata-
lyst) kinetics. Conditions of reactions [temperature (◦C) – MR (LA:GL) (lauric acid to
glycerol molar ratio] (a) [140-0-2:1]; (b) [160-0-3:1]; (c) [180-0-3:1]. Squares – glyc-
erol conversion; triangles – monolaurine selectivity; circles – dilaurine selectivity;
rhombus – trilaurine selectivity.
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