Glycerol etherification with benzyl alcohol over sulfated zirconia catalysts

Article abstract of DOI:10.1016/j.apcata.2015.04.027

Glycerol (GLY) etherification with benzyl alcohol (BA) was conducted with different zirconia-based heterogeneous acid catalysts, aiming to produce mono- (ME) and dibenzyl glycerol ethers (DE). Physicochemical properties of the prepared catalysts were obtained through XRD, SEM and adsorption of ammonia. The catalytic tests were performed at different temperatures (120-140°C) and initial reactant mass ratios (GLY:BA 1:1 and 2:1). The highest BA conversions were obtained with the catalyst having the highest sulfuric acid content (2S/ZrO₂). An increase in the reaction temperature and the GLY:BA initial mass ratio led to an increase in the BA conversion. Two kinetic models (a potential and a hyperbolic approach) were proposed to describe the process performance, including not only reactants evolution with time, but also that of ME, DE and the undesired self-condensation product of BA (benzyl ether, BE). Kinetic parameters for each model were estimated by data fitting and both models were able to accurately describe the evolution of the system, in terms of reactants and product distribution as a function of time under the experimental conditions studied.

Full text of DOI:10.1016/j.apcata.2015.04.027

Accepted Manuscript
Title: Glycerol Etherification with Benzyl Alcohol over
Sulfated Zirconia Catalysts
´
´
Author: Marıa A. Jaworski Sergio Rodrıguez Vega Guillermo
´
J. Siri Monica L. Casella Arturo Romero Salvador Aurora
´
Santos Lopez
PII:
S0926-860X(15)00260-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.04.027
APCATA 15364
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
29-12-2014
14-4-2015
18-4-2015
Please cite this article as: M.A. Jaworski, S.R. Vega, G.J. Siri, M.L.
´
Casella, A.R. Salvador, A.S. Lopez, Glycerol Etherification with Benzyl
Alcohol over Sulfated Zirconia Catalysts, Applied Catalysis A, General (2015),
http://dx.doi.org/10.1016/j.apcata.2015.04.027
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Glycerol Etherification with Benzyl Alcohol over Sulfated
Zirconia Catalysts
María A. Jaworski1,2, Sergio Rodríguez Vega3, Guillermo J. Siri1,2, Mónica L. Casella1,*,
Arturo Romero Salvador3, Aurora Santos López3,
1 CINDECA, CCT La Plata-CONICET and Departamento de Química, Facultad de
Ciencias Exactas, Universidad Nacional de La Plata, calle 47 Nº 257 (1900) La Plata
(Argentina)
2 PIDCAT, Facultad de Ingeniería, Universidad Nacional de La Plata, calle 1 y 47 (1900)
La Plata (Argentina)
3 Departamento de Ingeniería Química, Facultad de Ciencias Químicas, Universidad
Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain
(*) corresponding author: casella@quimica.unlp.edu.ar
Keywords: glycerol; benzyl alcohol; etherification; sulfated zirconia catalysts; kinetic
modeling
ABSTRACT
Glycerol (GLY) etherification with benzyl alcohol (BA) was conducted with different
zirconia-based heterogeneous acid catalysts, aiming to produce mono- (ME) and dibenzyl
glycerol ethers (DE). Physicochemical properties of the prepared catalysts were obtained
through XRD, SEM and adsorption of ammonia. The catalytic tests were performed at
different temperatures (120ºC to 140ºC) and initial reactant mass ratios (GLY:BA 1:1 and
2:1). The highest BA conversions were obtained with the catalyst having the highest
sulfuric acid content (2S/ZrO2). An increase in the reaction temperature and the GLY:BA
initial mass ratio led to an increase in the BA conversion. Two kinetic models (a potential
and a hyperbolic approach) were proposed to describe the process performance, including
not only reactants evolution with time, but also that of ME, DE and the undesired self-
condensation product of BA (benzyl ether, BE). Kinetic parameters for each model were
estimated by data fitting and both models were able to accurately describe the evolution of
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the system, in terms of reactants and product distribution as a function of time under the
experimental conditions studied.
1. Introduction
Biodiesel (monoalkyl esters of long chain fatty acids) is an alternative diesel fuel derived
from the reaction of vegetable oils or lipids and a short chain alcohol [1]. The new energy
legislation implemented in Europe promotes the use of biofuels for transport purposes.
Thus, traffic fuels should contain 10% of energy content produced from renewable sources
by the end of 2020 [2]. In this context, the production of biodiesel in the European Union is
expected to grow further in the next years [3]. The catalytic process that converts raw
triglycerides into biodiesel also produces important quantities of glycerol as side product:
for every ton of biodiesel produced, around 100 kg of glycerol is formed [4].
Due to the growing biodiesel production, the price of glycerol significantly dropped,
making it one of the most promising platform chemicals of the near future. Moreover, using
glycerol as starting raw material for the synthesis of value-added chemicals is of great
industrial importance, because it is also a nontoxic, edible, sustainable and biodegradable
compound [5].
A large portfolio of reaction pathways for catalytic conversion of glycerol is available,
including selective oxidation, selective hydrogenolysis to propanediol, dehydration to
acrolein, pyrolysis and gasification, steam reforming, thermal reduction to syngas,
oligomerization/polymerization, selective transesterification, etherification to fuel-
oxygenates, conversion into glycerol carbonate and synthesis of epichlorohydrin [5,6].
Concerning the etherification reaction, the selective mono- or di-etherification of
glycerol with alcohols using acid catalysts originates chemicals with high-added value
[3,7]. Glycerol ethers have been identified as valuable replacement of fuel additives which
depends on depleting sources, price uncertainty and growing environmental concern of
petroleum feedstock. These glycerol-based fuel additives are excellent additives with large
potential for diesel and biodiesel formulation that assist to a decreasing in particles,
hydrocarbons, carbon monoxide and unregulated aldehydes emissions [1,5]. Besides, these
glycerol-based additives seem to catch the motivation and interest of many researchers
lately because this approach is a promising and economically viable alternative since not
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only makes a good use of the glycerin by-product but also increases the yield to biofuel in
the overall biodiesel production process. [3,8].
Depending on the alcohol used, the selective glycerol monoetherification also leads to
the production of high value added chemicals which have a wide range of biological
applications such as anti-inflammatory, antibacterial, antifungal, antitumor, among others.
Thus, there have been reported in the literature some examples of the glycerol etherification
with benzyl, propargyl and allyl alcohols which have resulted in the formation of the
corresponding ethers in moderate yields [9].
In order to improve the yield of the etherification of glycerol different acid catalysts
have been used. Da Silva et al. reported the etherification of glycerol with benzyl alcohol
catalyzed by different solid acid catalysts. They found that with zeolite β and Amberlyst-35
the mono-benzyl-glycerol ether was the main product formed, whereas over K-10
montmorillonite and p-toluene sulfonic acid the di-benzyl ether was formed. Another solid
acid catalyst, niobic acid, was inactive toward the reaction [7]. Other authors found that the
best catalytic results were achieved with strong acid ion exchange resins (Amberlyst type)
as catalysts, despite the temperature limitations of this kind of materials [10,11].
González et al. studied the glycerol etherification with isobutene over several types of
silicas (MCM-41, SBA-15 and HMS) modified by incorporating aluminium or by
introducing phosphorus species or sulfonic groups. They found that the incorporation of
aluminum increased the amount of Brønsted acid sites in their structure, leading to higher
catalytic activity than pure silicas, but with a low selectivity to di- and tri-tertiary butyl
ethers of glycerol (h-GTBE). The introduction of phosphoric groups, with higher acidity
strength, improved the selectivity to h-GTBE [12]. Also, sulfonic acid-functionalized
mesostructured materials have demonstrated an excellent catalytic behavior in the
transformation of glycerol into oxygenated compounds for fuel formulation [3,8,13].
In this context, the objective of this work is to study the glycerol (GLY) etherification
with benzyl alcohol (BA), using zirconia-based heterogeneous acid catalysts prepared at
our laboratory, aiming to produce mono- (ME) and di-benzyl glycerol ethers (DE). A non-
desired reaction, the self-condensation of benzyl alcohol yielding benzyl ether (BE), can be
also produced (as showed in Scheme 1). Experiments were conducted varying the operative
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conditions (temperature and GLY:BA concentration ratio) and two kinetic models were
proposed to explain the results obtained.
Scheme 1
2. Experimental
2.1. Catalyst preparation
For the preparation of ZrO2, a procedure described elsewhere was followed [14]. The
precursor salt, ZrOCl2·8H2O (Fluka), was dissolved in distilled water and aqueous
ammonia was added until the pH of the solution reached a value of 10 and the formation of
the gel was observed. The mixture was aged for 8 days at room temperature. The obtained
precipitate was washed with distilled water until free from chloride ions (determined by
AgNO3), filtered and dried at 105°C for 24 h. The hydrous zirconia was calcined at 600°C
for 2 h. The following equation represents the zirconia preparation:
ZrOCl2 .6H2O  OH  ZrO2  2Cl  H  6H2O
To prepare sulfated zirconia, a portion of hydrous zirconia was mixed with an
appropriate volume of either 1 M or 2 M H2SO4 (Merck p.a.) and stirred for 24 h. After
filtration, the sample was dried at 105ºC and calcined for 2 h at 600ºC to form 1S/ZrO2 and
2S/ZrO2, respectively.
2.2. Catalyst characterization
The textural properties of the solids (specific surface area, SBET, and pore volume) were
measured by N2 adsorption–desorption at -196°C using a Micromeritics Accusorb 2100E
apparatus. The SBET was calculated by the BET equation and the pore volume (Vp) was
estimated using the adsorption branch of the nitrogen isotherm curve at P/P0=0.98 single
point. The textural properties of the catalysts are listed in Table 1.
The structural characterization was completed by X-ray powder diffraction (XRD)
performed on a Philips PW 1050/70 diffractometer using Cu K radiation (λ= 0.154 nm).
XRD data were recorded in the range of 2 = 5°– 70° at a scanning speed of 2º min-1. The
fractions of the monoclinic and tetragonal phases of zirconia were calculated with the
following equation [15]:
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Im 111  I 111
m 




Xm 
(1)
Im 111  I 111  I 101
m  



t
where Im( 111) and Im(111) are the line intensities of the ( 111) (at 2 = 28.2º) and (111) (at
2 = 31.5º) peaks for the monoclinic phase (m-ZrO2) and It (101) is the intensity of the
(101) (at 2 = 30.2º) peak for the tetragonal phase (t-ZrO2) of zirconium oxide.
The total acidity of the prepared catalysts was studied by adsorption of ammonia using a
thermobalance (Shimadzu TGA 50). In a typical procedure, the sample was dried in a He
flow (30 mL min-1) by heating from room temperature up to 500°C at a rate of 10°C min-1
to remove adsorbed water and other volatiles. Then, the sample was cooled in a He flow to
70°C. At that temperature, the catalyst was exposed to an NH3-He mixture (5 vol%) at 60
mL min-1 flow for the adsorption of the base, until a constant weight was obtained.
SEM/EDX measurements were carried out using a FEI Quanta 200 scanning electron
microscope equipped with an energy dispersive X-ray spectroscopy facility (EDX SDD
Apollo 40).
2.3. Catalytic test
The glycerol (GLY) etherification with benzyl alcohol (BA) was performed in a glass
reactor vessel (50 mL) at atmospheric pressure, under continuous stirring and with a
temperature controller. The reaction was conducted at different temperatures ranged
between 120°C to 140°C for 6 h under continuous N2 gas flow to avoid glycerol oxidation
and to remove water formed from the reaction. GLY:BA initial mass ratios used were 1:1
and 2:1 and catalyst concentration was 25g/kg, referred to the total initial mass of reactants.
The stirring speed was selected in order to limit external mass transfer effects. In a typical
run, once the reaction temperature had been reached, the appropriate amounts of anhydrous
GLY and catalyst were added into the reactor and this time has been considered as the
starting point of the reaction. The liquid samples obtained from the etherification of GLY
were collected at specific intervals during the reaction and the reaction products were
analyzed by GC/MS in an Agilent 6890 chromatograph (Agilent Technologies, USA). The
chromatograph was equipped with an HP Innowax chromatographic column. with the
following dimensions: 60 m length × 0.32 mm i.d. and 0.25 μm film thickness. Initial oven
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temperature was 90ºC and final oven temperature was 250ºC, with two programmed
temperature ramps of 1 and 3ºC·min-1.
3. Results and Discussion
3.1. Catalyst characterization
The physicochemical properties of ZrO2, 1S/ZrO2 and 2S/ZrO2 catalysts were
examined by X-ray powder diffraction, BET surface area and TG analysis of ammonia
adsorption. The XRD patterns of the three catalysts are shown in Figure 1. The
corresponding phase composition, BET surface area, pore volume and acidity results are
presented in Table 1. As can be seen from Figure 1, the ZrO2 sample calcined at 600ºC
presents a mixture of monoclinic and tetragonal phases, with a prevalence of the
monoclinic one (see also Table 1). On the other hand, the sulfated samples exhibit
prominent lines due to tetragonal phase, indicating that the impregnated sulfate ions show a
strong influence on the phase modification of zirconia from thermodynamically more stable
monoclinic to the metastable tetragonal phase [16,17].
Figure 1
ZrO2 sample has a specific surface area of 45 m2g-1, presenting a weak acidity (see
Table 1). The inclusion of sulfate anions in 1S/ZrO2 and 2S/ZrO2 not only favors an
increment of the surface area but of the acidity of the catalysts as well, clearly indicating
that impregnated sulfate ions show a strong influence on the acidic properties of the
zirconia. Total pore volume slightly increases with the incorporation of sulfuric acid. From
results in Figure 2 showing the SEM micrographs of the ZrO2, 1S/ZrO2 and 2S/ZrO2
catalysts, it is noticed that irregular edge-shaped large particles are obtained for the three
catalysts. At the microscopic scale, the surface of the samples appears to be porous, as can
be seen in Figure 2. No significant change in the morphology has been noted after
impregnation of sulfate.
Figure 2
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3.2. Catalytic results
All the prepared catalysts were evaluated in the GLY etherification using BA as active
alcohol, at a reaction temperature of 120°C. The results indicated that ZrO2 was inactive for
this reaction in the operating condition range used, while both sulfated zirconia-based
catalysts were active. This behavior can be explained taking into account the well-known
fact that the etherification of alcohols is a reaction catalyzed by acids. In the presence of an
acidic catalyst, a hydroxyl group of an alcohol is protonated, which renders it a good
leaving group. Considering the pKa values of GLY (14.15) and BA (15.40), the lower
acidity of BA favors its protonation versus GLY. Accordingly, the protonation of BA is
produced by action of the acid catalyst, and when it loses a water molecule a carbocation is
formed, which is in turn attacked by a OH-, either of GLY or of another BA molecule. This
allows to explain the formation of BE, and also the fact that there have not been observed
neither aldehydes nor GLY dimers.
Based on these results, the influence of some experimental variables was evaluated for
both sulfated zirconia catalysts, 1S/ZrO2 and 2S/ZrO2.
3.2.1. Influence of acidity
The effect of the content of sulfuric acid in the preparation of the sulfated zirconia
catalysts was analyzed in the etherification of GLY with BA in equal initial mass ratio.
Figure 3(a) compares the evolution of the conversion of BA as a function of time (t) at
120°C for both 1S/ZrO2 and 2S/ZrO2 catalysts, while Figure 3(b) shows the same progress
when the reaction was carried out at 140°C.
BA conversion was defined according to Eq. (2), being CBAo and CBA the benzyl alcohol
concentration at zero and t times, respectively (mol/Kg).
Figure 3
The results presented in Figures 3(a) and 3(b) clearly show that a higher BA conversion
is obtained using the catalyst with the higher sulfuric acid content and that this difference in
activity is most noticeable when the temperature is increased from 120°C to 140°C. The
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greater activity of 2S/ZrO2 catalyst at the same temperature can be associated with its
higher acidity presented in Table 1. This same trend has been found by Pico et al. who
studied the glycerol etherification with tert-butyl alcohol using cationic exchange resins
with different acidity [18].
3.2.2. Influence of temperature
The effect of temperature on the catalytic activity of the system that showed the best
performance, 2S/ZrO2, was evaluated with some more detail. To do this, BA conversion
obtained at temperatures of 120, 130 and 140°C were plotted in Figure 4. As expected, the
trend towards greater activity with increased temperature was confirmed. The upper
temperature limit was set taking into account the vapor pressure of BA.
Figure 4
Global Yield (Y) and Selectivity (S) of the 2S/ZrO2 catalyst to sum of monoethers (YME,
SME), sum of diethers (YDE, SDE) and benzyl ether (YBE, SBE) has been defined as:
Being CME, CDE and CBE the monoethers, diethers and benzyl ether concentration,
respectively, expressed as mol/Kg. Obviously, from equations (2) to (5) it is deduced that:
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Global yield and selectivity obtained at reaction temperatures of 120 to 140°C with a
GLY to BA mass ratio of 1:1 are shown in Figure 5. As shown in this figure, the selectivity
to ME decreases with time and with temperature, as a result of the formation of DE through
a consecutive reaction. In turn, a slight decrease in the BE selectivity with reaction time is
noticed. Temperature has a lower effect in selectivity to BE.
Figure 5
3.2.3. Influence of reactants ratio
The effect of the initial concentration of the reactants was studied at 120°C, using two
GLY:BA initial mass ratios, 1:1 and 2:1. The results of BA conversion versus time are
plotted in Figure 6. As can be seen, a higher concentration of GLY causes an increase in
BA conversion.
Figure 6
The global yield and selectivity of ME, DE and BE at the two GLY to BA initial mass
ratios tested (1:1 and 2:1) at 120ºC can be seen in Figure 7. As can be seen in this figure,
the yield and selectivity to desired products (ME and DE) increased with higher amounts of
GLY. While the yield to BE was slightly increased (because BA conversion also did), the
selectivity to this undesirable product decreased when initial GLY:BA was increased.
Figure 7
3.3. Kinetic modeling
Two kinetic strategies, summarized in Table 2 were proposed to describe glycerol
etherification with benzyl alcohol: a potential and a hyperbolic kinetic model, where only
GLY is considered to be adsorbed in the catalyst surface. Both models were developed
according to the reaction pathway shown in Scheme 1. The water content was considered to
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be negligible because of reaction conditions, which approaches the system to irreversible.
Reaction rates for both models can be seen in Table 2, where the effect of reaction
temperature is included in the kinetic constants considered as temperature-dependent
according to the Arrhenius equation:
Table 2
Three key compounds were selected, BA, BE and ME. From the mass balance in a batch
reactor, the evolution of the concentration of this key compounds with time can be
obtained, according to equations shown in Table 3 while the concentration of GLY and DE
can be obtained from this key compounds by stoichiometry (also summarized in Table 3).
Table 3
Results obtained with 2S/ZrO2 catalyst at different temperatures (120-140ºC) and initial
mass ratios of reactants (1:1 and 2:1) were used to develop both kinetic models, the
potential and the hyperbolic approach. Kinetic parameters in Tables 2 and 3 were calculated
by experimental data fitting (concentrations of BA, BE and ME as a function of time).
Nonlinear regression (Marquadt algorithm) was coupled with a Runge−Kutta integration
step in the fitting procedure. The kinetic parameters obtained after fitting of the
experimental data are summarized in Tables 4 and 5 (for potential and hyperbolic model,
respectively) including their standard error values.
Table 4
Table 5
The sum of squares obtained with the hyperbolic model is slightly smaller than that
obtained with the potential one; however both fit the experimental values in an appropriate
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way. In Figures 4-7, experimental results are plotted as symbols while estimated values
using the potential model are plotted as lines. As can be observed, a good agreement
between experimental and predicted data is obtained, which validates the proposed kinetic
models.
Conclusions
Two solid acid catalysts were prepared modifying the zirconia with sulfuric acid at two
concentration levels: 1 and 2 M (1S/ZrO2 and 2S/ZrO2 catalysts). The addition of sulfuric
acid favored to obtain a tetragonal zirconia phase, regardless of the sulfuric content. The
2S/ZrO2 catalyst was the most acidic, according to the ammonia adsorption measured by
TGA.
GLY etherification with BA was carried out using the prepared catalysts, both of them
being active for the reaction in the range of temperatures studied. BA conversion increased
with increasing temperature from 120 to 140ºC. The higher acidity of the catalyst, the
higher activity was obtained at any temperature. The main reaction products were ME and
DE, although the self-etherification of BA to give BE was also observed. By increasing the
GLY:BA initial mass ratio, the BE selectivity decreased. On the contrary, as temperature
increases, BE selectivity also increases. Both evidences are well explained by the kinetic
model proposed and validated by data fitting.
BA self-condensation follows a second order reaction in BA with higher activation
energy than the ME and DE reactions from BA, being these reactions first order in the
benzyl alcohol concentration.
NOMENCLATURE
Cio: Concentration at zero time of specie i (mol/Kg).
Ci: Concentration at time t of specie i (mol/Kg).
Eaj: Activation energy of reaction j (kJ/mol).
Im(111): Line intensities of the ( 111) (at 2 = 28.2º) peaks for the monoclinic phase (m-
ZrO2).
Im(111): Line intensities of the (111) (at 2 = 31.5º) peaks for the monoclinic phase (m-
ZrO2).
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kj: Kinetic constant of reaction j (kg/mol·min).
k0j: Pre-exponential factor of kinetic constant kj in reaction j (kg/mol·min).
K
GLY: Equilibrium constant of glycerol adsorption (kg/mol).
rj: Rate of reaction j (mol/kg·min).
Ri: Production rate of specie i in the batch reactor (mol/kg·min).
S: Selectivity of the 2S/ZrO2 catalyst, defined in Eq. (3-5).
Sg BET: Specific surface area (m2 g-1).
T: Reaction temperature (°C).
t = Reaction time (min).
Vp: Pore Volume (cm3 g-1).
XBA: Benzyl alcohol conversion defined according to Eq. (2).
Xm: Fraction of the monoclinic phase of zirconia according to Eq. (1).
Y: Global Yield of the 2S/ZrO2 catalyst, defined in Eq. (3-5).
Abbreviations
BA: Benzyl alcohol.
BE: Benzyl ether.
DE: di-benzyl glycerol ether.
GLY: Glycerol.
ME: Mono-benzyl glycerol ether.
TE: Tri-benzyl glycerol ether.
W: Water.
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Figure Captions
Scheme 1. Reaction pathway proposed for the catalytic etherification of glycerol (GLY)
with benzyl alcohol (BA). Reaction products: glyceryl monobenzyl ethers (ME); glyceryl
dibenzyl ethers (DE); glyceryl tribenzyl ether (TE) and benzyl ether (BE) (a non-desired
product, form through the self-condensation of BA).
Figure 1. XRD patterns of calcined zirconia (ZrO2) and sulfated zirconia (1S/ZrO2 and
2S/ZrO2) catalysts. (▲) Characteristic lines due to monoclinic zirconia; () characteristic
lines due to tetragonal zirconia.
Figure 2. SEM micrographs of the studied samples: (a) ZrO2; (b) 1S/ZrO2 and (c) 2S/ZrO2.
Figure 3. Evolution of BA conversion with time employing 1S/ZrO2 and 2S/ZrO2 catalysts.
GLY:BA initial mass ratio 1:1. Catalyst concentration: 25g/kg. Reaction Temperature: (a)
120ºC and (b) 140ºC.
Figure 4. Evolution of BA conversion with time employing 2S/ZrO2 catalysts. Catalyst
concentration: 25g/kg; initial GLY:BA mass ratio 1:1. Reaction Temperature: 120ºC,
130ºC and 140ºC. Symbols: experimental data. Lines: estimated with potential kinetic
model.
Figure 5. Global yield of ME (a), DE (b) and BE (c) and selectivity to ME (d), DE (e) and
BE (f). Catalyst concentration: 25g/kg; initial GLY:BA mass ratio 1:1. Reaction
Temperature: 120ºC, 130ºC and 140ºC. Symbols: experimental data. Lines: estimated with
potential kinetic model.
Figure 6. Influence of the reactants ratio on the evolution of BA conversion with time.
GLY:BA initial mass ratio of 1:1 and 2:1. Catalyst: 2S/ZrO2 (25g/kg). Reaction
Temperature: 120ºC. Symbols: experimental data. Lines: estimated with potential kinetic
model.
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Figure 7. Influence of the reactants ratio on the global yield of ME (a), DE (b) and BE (c)
and on the selectivity to ME (d), DE (e) and BE (f). GLY:BA initial mass ratio of 1:1 and
2:1. Catalyst: 2S/ZrO2 (25g/kg). Reaction Temperature: 120ºC. Symbols: experimental
data. Lines: estimated with potential kinetic model.
15
Page 15 of 23

Table 1. Physicochemical characteristics of the studied catalysts.
Catalyst
Sg BET
(m2 g-1)
45
Pore Volume
(cm3 g-1)
0.11
Crystalline phase of
Acidityb
(mmol NH3 ads gcat-1)
0.068
a
ZrO2
ZrO2
M (90%) and T
1S/ZrO2
2S/ZrO2
89
0.08
T
T
0.125
92
0.09
0.248
a M: monoclinic phase; T: tetragonal phase
b measured by TGA
16
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Table 2. Potential kinetic model and hyperbolic kinetic model for the catalytic
etherification of glicerol with benzyl alcohol.
Reaction rate
Reaction
Stoichiometric equation
Gly  BA  ME W
BA  ME  DE W
2BA  BE W
Potential Model
Hyperbolic Model
k1 CBACGLY
r  k1 CBACGly
r 
1
2
3
1
1
1 KGLY CGLY
k2CBACME
r 
r  k2CBACME
2
2
1 KGLY CGLY
k3 CB2A
r  k3 CB2A
r 
3
3
1 KGLY CGLY
17
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Table 3. Mass balance of reactants and products in a batch reactor involved in the catalytic
GLY etherification with BA. BA, BE and ME selected as key compounds.
Compound
Concentration
t
CBA  C

r  r  2r dt
Benzyl alcohol (BA)


1
2
3

BA0
0
t
CBE

r dt
Dibenzyl ether (BE)
 
3

0
t
Monobenzyl glycerol ether
(ME)
CME

r  r dt


1
2

0
CME CBA0  CBA
CGly  CGly0  CME  CDE  CGly0


 CBE
Glycerol (GLY)
2
2
CBA0  CBA  2CBE  CME
CDE

Dibenzyl glycerol ether (DE)
2
18
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Table 4. Kinetic and statistical parameters obtained for the catalytic GLY etherification
with BA using the potential kinetic model.
Parameter
Value
Standard Error
8.5 103
5.36·102
1.33 104
1.29·104
3.29·103
1.21·102
12.8
25.9
22.7
1.31
8.01
2.96
19
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Table 5. Kinetic and statistical parameters obtained for the catalytic GLY etherification
with BA using the hyperbolic kinetic model.
Parameter
Value
Standard Error
1.26·104
9.59·102
8.80·103
1.21·104
3.86·102
2.46·103
24.3
14.8
24.1
23.4
9.42·10-1
5.97
20
Page 20 of 23

Glycerol Etherification successfully carried out over Sulfated Zirconia Catalysts
The prepared catalysts fully characterized by XRD, SEM and NH3 adsorption
Highest benzyl alcohol conversion obtained with the most acidic catalyst
Two kinetic models proposed to describe the process performance
21
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*Graphical Abstract
Sulfated zirconia surface
Page 22 of 23

The new figure (Figure 8) included in the manuscript is shown here:
Key Catalyst
80
1S/ZrO2
2S/ZrO2
60
40
a)
20
0
b)
30
20
10
0
c)
30
20
10
0
d)
30
20
10
0
0
100
200
t (min)
300
400
Figure 8. Evolution of a) BA conversion with time and global yield of b) ME, c) DE and d)
BE. GLY to BA mass ratio of 1:1. Catalyst 1S/ZrO2 and 2S/ZrO2 (25g/kg). Reaction
Temperature 140ºC. Symbols: experimental data. Lines: estimated with potential kinetic
model
Page 23 of 23