Esterification of acetic acid with n-Butanol using vanadium oxides supported on γ-alumina

Article abstract of DOI:10.1016/j.crci.2012.06.004

Esterification of acetic acid with n-Butanol has been studied in a heterogeneous reaction system using two γ-alumina-supported vanadium oxide catalysts with different V loadings, which were prepared by the impregnation of a precipitated alumina. The alumina support and the supported catalysts were characterized using X-ray diffraction, N₂ adsorption, EDX analysis and NH₃-TPD techniques. The effects of the reaction time, of the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the catalyst on the catalytic properties were studied. In the presence of the supported catalyst containing 10 wt % V₂O₅ (10V-Al₂O₃ sample) the conversion reached 87.7% after 210 min of reaction at 100 °C with an n-Butanol-to-acetic acid mole ratio equal to one. The conversion as well as the total acidity measured by TPD of NH ₃ increased in the following order: Al₂O₃ < 5V-Al₂O₃ (5 wt % V₂O₅/Al ₂O₃) < 10V-Al₂O₃. In all cases the reaction was completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three reaction cycles with 10 V₂O ₅-Al₂O₃ catalyst was observed.

Full text of DOI:10.1016/j.crci.2012.06.004

C. R. Chimie 15 (2012) 793–798
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´
Full paper/Memoire
Esterification of acetic acid with n-Butanol using vanadium oxides
supported on
g
-alumina
a
b
c
a,
´
´
*
´
´
Gheorghita Mitran , Eva Mako , Akos Redey , Ioan-Cezar Marcu
a Laboratory of Chemical Technology and Catalysis, Department of Organic Chemistry, Biochemistry and Catalysis, Faculty of Chemistry, University of Bucharest, 4-
12, boulevard Regina Elisabeta, 030018 Bucharest, Romania
b Institute of Materials Engineering, Faculty of Engineering, University of Pannonia, 10, Egyetem Street, 8201 Veszpre´m, Hungary
c Department of Environmental Engineering and Chemical Technology, Faculty of Engineering, University of Pannonia, 10, Egyetem Street, 8201 Veszpre´m, Hungary
A R T I C L E I N F O
A B S T R A C T
Article history:
Esterification of acetic acid with n-Butanol has been studied in a heterogeneous reaction
Received 16 February 2012
Accepted after revision 12 June 2012
Available online 4 August 2012
system using two
g-alumina-supported vanadium oxide catalysts with different V
loadings, which were prepared by the impregnation of a precipitated alumina. The
alumina support and the supported catalysts were characterized using X-ray diffraction,
N2 adsorption, EDX analysis and NH3-TPD techniques. The effects of the reaction time, of
the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the
catalyst on the catalytic properties were studied. In the presence of the supported catalyst
containing 10 wt % V2O5 (10V-Al2O3 sample) the conversion reached 87.7% after 210 min
of reaction at 100 8C with an n-Butanol-to-acetic acid mole ratio equal to one. The
conversion as well as the total acidity measured by TPD of NH3 increased in the following
order: Al2O3 < 5V-Al2O3 (5 wt % V2O5/Al2O3) < 10V-Al2O3. In all cases the reaction was
completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three
reaction cycles with 10 V2O5–Al2O3 catalyst was observed.
Keywords:
Esterification
n-Butanol
Acetic acid
Butyl acetate
g-alumina-supported vanadium oxides
ß 2012 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
´
´
R E S U M E
´
´
´ ´ ´
´
´ ´
-alumine avec
diffe´rentes teneurs en vanadium qui ont e´te´ pre´pare´s par l’impre´gnation d’une alumine
´ ´
`
L’esterification de l’acide acetique avec le n-Butanol a ete etudiee en catalyse heterogene
´
´
en presence de deux catalyseurs d’oxyde de vanadium supportes sur
g
´
´
´
´
´
precipitee. Le support d’alumine ainsi que les catalyseurs supportes ont ete caracterises
´
par diffraction de rayons X, adsorption d’azote, analyse chimique EDX et desorption
thermique programme´e d’ammoniac. Les effets du temps de re´action, du rapport molaire
des re´actants, de la vitesse d’agitation ainsi que de la masse du catalyseur sur les proprie´te´s
´ ´ ´
´
´
´
catalytiques ont ete etudies. En presence du catalyseur supporte contenant 10 % V2O5 en
´
`
% apres
poids (echantillon 10V-Al2O3) la conversion atteinte est voisine de 87,7
210 minutes de re´action a` 100 8C et avec un rapport molaire entre n-Butanol et acide
´
´
`
´
´
´
acetique egal a un. La conversion ainsi que l’acidite totale mesuree par desorption
´
thermique programmee d’ammoniac augmentent dans l’ordre suivant : Al2O3 < 5V-Al2O3
(5 % en poids V2O5/Al2O3) < 10V-Al2O3. Dans tous les cas la re´action a e´te´ comple`tement
´
´
´
´
selective pour l’acetate de n-butyle. Neanmoins, une perte de l’activite catalytique du
`
´
´ ´
´
catalyseur 10 V2O5–Al2O3 apres trois cycles de reaction a ete observee.
ß 2012 Acade´mie des sciences. Publie´ par Elsevier Masson SAS. Tous droits re´serve´s.
* Corresponding author.
E-mail addresses: ioancezar.marcu@g.unibuc.ro, ioancezar_marcu@yahoo.com (I.-C. Marcu).
1631-0748/$ – see front matter ß 2012 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2012.06.004

794
G. Mitran et al. / C. R. Chimie 15 (2012) 793–798
1. Introduction
n-Butanol with acetic acid have been for the first time
studied and compared with those of -alumina support. The
g
The esterification reaction is an extremely slow reaction
and needs the addition of a catalyst in order to obtain high
actual yields. The most common catalysts used for an
esterification reaction are strong mineral acids such as
sulfuric and hydrochloric acids as well as sulfonic acids [1].
Their catalytic activity is high, but they have several
disadvantages, such as their corrosive nature, the existence
of side reactions and they are often hardly separated from
the reaction mixture. The use of solid acid catalysts offers
an alternative as they can be easily separated from the
liquid reaction mixture by filtration or decantation and,
thus, reused, they have high selectivity and, last but not
least, they are environmentally friendly. The solid catalysts
mostly used in esterification reactions are classical solid
acids including ion-exchange resins [2–6], zeolites [7–9]
and superacids like sulphated zirconia [10]. The commer-
cially available solid acid catalysts have recently been
comparatively studied in the esterification of acetic acid
with butanol [11].
effects of the reaction time, the molar ratio between the
reactants, the speed of agitation and the catalyst loading on
the reaction were investigated.
2. Experimental
2.1. Catalyst preparation and characterization
Al2O3 support was prepared from Al(NO3)3Á9H2O (Fluka
Analytical) by precipitation with ammonium carbonate
(Lachema) at controlled pH of 6.5. V2O5 was introduced at
two concentrations, 5% and 10% by weight, via incipient
wetness impregnation of the alumina support with
aqueous NH4VO3 (Fluka Analytical) solutions containing
appropriate amounts of vanadium. After impregnation, the
samples were dried in air at 100 8C and then calcined at
600 8C for 4 h. The 5 wt % V2O5/Al2O3 and 10 wt % V2O5/
Al2O3 samples were labelled 5V-Al2O3 and 10V-Al2O3,
respectively.
It is well known [12] that oxides of elements with
valence five or higher, such as tungsta, molybdena,
vanadia, phosphoric anhydride and niobia, present
strong to very strong Brønsted acidity which make them
good candidates as acid catalysts. Some of them have
already been studied as catalysts for esterification [13–
17] and transesterification [18–20] reactions. Thus,
Nb2O5/SiO2–Al2O3 has been studied as catalyst for the
esterification reaction of acetic acid with ethanol, n-
Butanol and iso-pentanol showing conversions of 83, 87
and 91%, respectively, and 100% selectivity for esters (8 h
reaction time) [13]. WO3/USY showed good catalytic
performances (conversion above 74% at 200 8C and
reaction time 2 h) in the esterification of oleic acid with
ethanol [14], and WO3/ZrO2 was an effective catalyst in
the esterification of the free fatty acids from dark oil to
fatty acid methyl esters with conversion of 96% at 150 8C
(2 h reaction time) [15]. It has recently been shown that
The crystalline phases were investigated by the X-ray
diffraction (XRD) method. XRD patterns were obtained
with a Philips PW 3710 type diffractometer equipped with
˚
a source (l = 1.54 A), operating at 50 kV and 40 mA.
a CuK
They were recorded over the 10–708 angular range with
0.028 (2 ) steps and an acquisition time of 1 s per point.
u
Data collection and evaluation were performed with PC-
APD 3.6 and PC-Identify 1.0 software.
Surface areas of the catalysts were measured from the
adsorption isotherms of nitrogen at –196 8C using the BET
method with a Micromeritics ASAP 2020 sorptometer.
Qualitative and quantitative electron probe microana-
lyses were performed using
a Philips XL 30 ESEM
(Environmental Scanning Electron Microscope) having
EDX (Energy Dispersive X-ray) analyzer. An accelerating
voltage of 20 kV was used. The powder samples were fixed
on a holder and sample compartment was evacuated in
order to prevent the electrical charging. Electron beams
were very finely focused. Therefore, elemental analysis of
very small area on specimen surface was done in so-called
spot mode. Simultaneously, the surface of the sample was
photographed, the micrographs obtained being presented
in Fig. S1.
The acidity of the catalysts was estimated by tempera-
ture-programmed desorption of ammonia (NH3-TPD).
About 0.1 g of the catalyst sample was dehydrated at
500 8C in dry air for 1 h and purged with N2 for 0.5 h. The
sample was then cooled down to 100 8C under the flow of
N2, and NH3 was supplied to the sample until its saturation.
For desorption of the physisorbed ammonia, a nitrogen
stream was passed over the sample, at the same
temperature, until no more NH3 was observed in the exit
flow. Finally, the chemisorbed NH3 was desorbed in a N2
flow by increasing the temperature successively up to
350 8C and 500 8C with a heating rate of 10 8C/min. The
ammonia desorbed was bubbled through a solution of
sulfuric acid. The acid in excess was titrated with a solution
of NaOH, the amount of ammonia desorbed being then
calculated. The ammonia desorbed at temperatures lower
than 350 8C accounted for the weak and medium-strength
MoO3 supported on
g-alumina is an efficient (81%
conversion at 100 8C and 2 h reaction time) and stable
solid acid catalyst for the esterification of acetic acid with
n-Butanol [16], and MoO3 supported onto a thin alumina
film has found to give 62% conversion and 100%
selectivity for ester in the esterification reaction of
acetic acid with ethanol [17]. Unsupported and silica-
supported V2O5 catalysts have been tested in the
transesterification reaction of dimethyl oxalate with
phenol, the unsupported system showing relatively good
performances (35% dimethyl oxalate conversion and
total selectivities to methyl phenyl oxalate and diphenyl
oxalate exceeding 75%) [18], but, to the best of
our knowledge, there are no studies investigating
alumina-supported V2O5 as catalysts for the esterifica-
tion reaction in general and for the esterification of acetic
acid with n-Butanol in particular. The reaction product,
butyl acetate as the most of alkyl acetates is generally
used as solvent, as component in flavoring and as
additive in perfumes [1].
In the present work, the catalytic properties of vanadium
oxides supported on
g-alumina in the esterification of

G. Mitran et al. / C. R. Chimie 15 (2012) 793–798
795
acid sites while that desorbed in the temperature range
from 350 to 500 8C, for the strong acid sites.
Characterization of the catalysts samples has been
performed before and, for some of them, after the catalytic
test.
2.2. Esterification reactions
10V-Al O
2
3
The esterification reactions of acetic acid (Chimactiv,
99.5%) with n-Butanol (Riedel-de Hae¨n, 99.5%) were
performed in a 150 mL two-neck flask equipped with a
condenser and an additional port for sample withdrawal.
The above assembly was heated using a thermostated
hotplate. The reaction was carried out at 100 8C with a
molar quantity of acetic acid of 0.09 and an n-Butanol-to-
acetic acid molar ratio varied from 1 to 3. Cyclohexane
(Riedel-de Hae¨n, 99.5%) was always added to the reaction
mixture for water removal, the cyclohexane-to-acetic acid
molar ratio being kept at 1. The amount of catalyst was
varied between 0.5 and 1.0% of the mass of mixture charge
in the reaction and the reaction time varied between 30
and 120 min. Unless specified, all experiments were
conducted at a speed of agitation of 600 rpm. All the
catalysts used in the reaction were in the powder form.
Samples from the organic layer were withdrawn at regular
intervals and analyzed with a Thermo Finnigan chromato-
graph using a DB-5 column and a flame ionization detector.
Under the employed conditions of reaction, both in the
presence and in the absence of a catalyst, butyl acetate was
the only product detected. The mass balances, calculated
after a reaction time of 120 min, were always higher than
94%.
5V-Al O
2
3
Al O
2
3
10
20
30
40
50
60
70
2-theta (degrees)
Fig. 1. X-ray diffraction patterns of the alumina support and of the
alumina-supported V2O5 catalysts.
of 5V-Al2O3 sample suggesting that vanadia is relatively
well dispersed on the alumina support in the latter case,
while crystalline V2O5 (PDF 41-1426) is evident in the case
of 10V-Al2O3 sample. This is in line with the observed
decrease in the surface area with increasing the vanadia
loading.
3. Results and discussion
The chemical compositions of the vanadium-containing
samples before and after the catalytic test, determined by
EDX analysis, are reported in Table 1. They showed that the
vanadium content is much higher than the nominal value
for both samples. This is not surprising because the EDX
analysis give, in the conditions used, the surface and
subsurface rather than bulk composition of the solids. On
the other hand, it can be observed that the vanadium
content strongly decreased after the catalytic test for both
samples, suggesting the loss of vanadium during the
catalytic reaction.
3.1. Catalysts characterization
Table 1 lists the BET surface areas of the catalysts. It can
be seen that the surface area of the alumina support was
higher then that of the supported catalysts and for the
latter, as expected, the surface area decreased with
increasing vanadia loading. This has already been observed
for alumina-supported vanadia [21] and may be due to the
blockage of pores of alumina by vanadia with increasing its
loading.
A key point to understand the catalytic behavior in the
esterification reaction is to investigate the acidity of the
catalyst. This was achieved using the NH3-TPD technique.
The total acidities of the catalysts, expressed as the total
The XRD patterns of the alumina support and of the
supported vanadia catalysts are presented in Fig. 1. Only
broad lines corresponding to
g
-alumina (PDF 10-425) were
observed in the case of
g-alumina support and in the case
Table 1
Specific surface areas and chemical compositions of the catalysts.
Catalyst
BET surface area (m2/g)
Chemical composition (wt. %) obtained by EDX
Before the catalytic test
After the catalytic testa
V
Al
O
V
Al
O
Al2O3
227
178
147
–
–
–
–
–
–
5V-Al2O3
10V-Al2O3
15.30
20.75
45.58
40.34
39.12
38.91
6.49
8.32
50.72
50.55
42.79
41.13
a
Reaction conditions: 0.7 wt % catalyst, temperature 100 8C, n-Butanol-to-acetic acid molar ratio = 3:1 and reaction time 120 min.

796
G. Mitran et al. / C. R. Chimie 15 (2012) 793–798
Table 2
Number and strength of acid sites of the catalysts.
Catalyst
Number of acid sites (mmol/g)
Weak and medium
Total number
(mmol/g)
Strong
104 (mmol/m2)
Al2O3
0.097
0.076
0.068
0.060
0.027
0.094
0.182
0.150
0.124
0.170
0.250
0.210
5.46
11.56
14.04
–
5V-Al2O3
10V-Al2O3
10V-Al2O3 useda
a
Reaction conditions: 0.7 wt % catalyst, temperature 100 8C, n-Butanol-to-acetic acid molar ratio = 3:1 and reaction time 120 min.
number of acid sites per gram of catalyst, determined by
NH3-TPD, are presented in Table 2. It can be observed that
the total acidity increased by adding vanadia to alumina
and by increasing its content following the order:
Al2O3 < 5V-Al2O3 < 10V-Al2O3. It can also be observed
that the number of weak and medium-strength acid sites
decreased while the number of strong acid sites increased
by adding vanadia to alumina and by increasing its
content. This behavior has already been observed for
alumina-supported vanadia systems [22]. Note that, at
similar transition-metal oxide loadings, the total number
of acid sites was twice lower while their strength was
higher for supported vanadia than for supported molib-
dena catalysts [16].
(conversion 38.7%) and Al2O3 (conversion 32.2%) catalysts
that have both lower acid site densities and strengths. The
catalytic performances of the V2O5/Al2O3 catalysts were
comparable with those of the MoO3/Al2O3 catalysts with
similar transition-metal loadings and measured in similar
reaction conditions [16]. With increasing the reaction time
from 120 to 210 min for 10V-Al2O3 catalyst, the conversion
of acetic acid increased from 62.6 to 87.7% without a
change in the selectivity for n-butyl acetate (Fig. 2b).
70
(a)
60
50
40
30
20
10
0
The acidity of the 10V-Al2O3 sample has also been
determined after the catalytic test (Table 2), a decrease of
the total number of the acid sites being observed. This is in
line with the loss of vanadium observed by EDX chemical
analysis.
3.2. Catalytic activity
Some factors such as reaction time, acid to alcohol mole
ratio and catalyst amount influence the conversion of
acetic acid in the esterification reaction of acetic acid with
n-Butanol. These influences are presented below.
0
30
60
90
120
150
Reaction time (min.)
3.2.1. Influence of the reaction time
The influence of the reaction time was studied in the
following reaction conditions: 8 mL of n-Butanol, 5 mL of
acetic acid (n-Butanol-to-acetic acid mole ratio 1:1) and
10 mL of cyclohexane; the catalyst represents 0.7% of the
mass of mixture charge in the reaction; the reaction
temperature was kept at 100 8C. In these conditions, the
selectivity of n-butyl acetate was, in all cases, 100%. This
means that the conversion of acetic acid can represent the
yield of n-butyl acetate. The conversion of acetic acid
measured in these reaction conditions as a function of the
reaction time over Al2O3, 5V-Al2O3 and 10V-Al2O3
catalysts as well as in the absence of a catalyst is shown
in Fig. 2a. As expected, the conversion of acetic acid was
higher in the presence of a catalyst than without a catalyst
and increased remarkably with the prolonging of the
reaction time. The activities at 120 min of reaction time are
compared in the following. As known, esterification is a
typical acid catalyzed reaction, and the acidity of the
catalyst would exert a great influence on the catalytic
activity. The highest conversion (62.6%) of acetic acid over
10V-Al2O3 catalyst may thus be due to its higher acid site
density and strength (Table 2) compared with 5V-Al2O3
100
90
80
70
60
50
40
30
20
10
0
(b)
0
50
100
150
200
250
Reaction time (min.)
Fig. 2. Conversion of acetic acid as a function of the reaction time in the
catalytic and non-catalytic esterification reaction at 120 min (a) and
240 min (b). Reaction conditions: n-Butanol-to-acetic acid molar
ratio = 1:1, reaction temperature 100 8C, 0.7 wt
catalytic reaction, –Al2O3, –5V-Al2O3, –10V-Al2O3).
% catalyst ( –non-

G. Mitran et al. / C. R. Chimie 15 (2012) 793–798
797
70
60
50
40
30
20
10
0
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
Mass fraction of the catalyst (%)
Fig. 4. Effect of catalyst concentration on the esterification of acetic acid
with n-Butanol using 5V-Al2O3 ) and 10V-Al2O3 ) as catalysts.
Reaction conditions: temperature 100 8C, n-Butanol-to-acetic acid molar
ratio = 2:1 and reaction time 60 min ( ) and 120 min ( ).
(
,
( ,
,
,
3.2.3. Influence of the catalyst loading
The effect of catalyst loading on the acetic acid
conversion was studied for the vanadia-supported cata-
lysts at 0.5, 0.7 and 1% by mass of the total reaction
mixture, n-Butanol-to-acetic acid mole ratio equal to 2:1
and reaction times of 60 and 120 min. The results are
presented in Fig. 4. In all cases, a significant increase of the
conversion of acetic acid with increasing the catalyst
loading from 0.5 to 0.7% was observed, while the
conversion tends to a plateau for catalyst loadings higher
than 0.7% suggesting that this is the optimal mass fraction
of the catalyst in the reaction medium.
Fig. 3. Effect of mole ratio on the esterification of acetic acid with n-
Butanol using 5V-Al2O3 (a) and 10V–Al2O3 (b) as catalysts. Reaction
conditions: temperature 100 8C, 0.7 wt % catalyst.
3.2.4. Influence of the speed of agitation
The influence of the speed of agitation on the
conversion of acetic acid was carried out for 10V-Al2O3
catalyst samples at three different speeds, i.e. 450, 600 and
750 rpm, to examine the influence of a possible external
mass transfer effect under the following reaction condi-
tions: n-Butanol-to-acetic acid mole ratio was 2:1, 0.7 wt %
catalyst, reaction temperature 100 8C and reaction times
60 and 120 min. The results obtained are shown in the
Fig. 5. It is clear from the figure that there was no effect of
the speed of agitation in the range 450–750 rpm on the
conversion of acetic acid. This implies that there was no
resistance to mass transfer of acid to the external surface of
the catalyst.
3.2.2. Influence of the molar ratio of reactants
The effects of different feed ratio on acetic acid
conversion over 5V-Al2O3 and 10V-Al2O3 catalysts were
studied and the results are presented in Fig. 3. By
increasing the n-Butanol-to-acetic acid mole ratio from
1:1 to 2:1 the conversion increased, as expected, for both
catalysts for all the reaction times considered. Neverthe-
less, by further increasing the mole ratio to 3:1, a decrease
in conversion was observed probably due to the leaching of
vanadia from alumina support in line with the observed
loss of vanadium (Table 1) and decrease of the number of
acid sites (Table 2) of the catalyst after the catalytic test.
This phenomenon has already been observed during the
esterification of acetic acid with n-Butanol on montmoril-
lonite-supported dodecatungstophosphoric acid catalyst
[23]. Note that the selectivity for n-butyl acetate was, in all
cases, 100% and the conversion of acetic acid reached 66.4%
in the presence of 10V-Al2O3 catalyst for an n-Butanol-to-
acetic acid mole ratio equal to 2:1 and a reaction time of
120 min.
3.2.5. Reusability of the catalyst
In order to know if the catalysts lose their catalytic
activity during the reaction, the 10V-Al2O3 catalyst was
recovered and reused as catalyst in the esterification
reactions under the following reaction conditions: n-
Butanol-to-acetic acid mole ratio was 1:1, 0.7 wt %
catalyst, reaction temperature 100 8C. After the first
catalytic test (2 h reaction time), the catalyst was filtered,
washed with distilled water several times, dried at 120 8C
in air and then used in the esterification reaction with a

798
G. Mitran et al. / C. R. Chimie 15 (2012) 793–798
Fig. 5. Effect of the speed of agitation on the conversion of acetic acid for
10V-Al2O3 catalyst at 60 min and 120 min reaction time. Reaction
conditions: n-Butanol-to-acetic acid molar ratio = 2:1, reaction
temperature 100 8C, 0.7 wt % catalyst.
Fig. 6. Reusability of the 10V-Al2O3 catalyst. Reaction conditions: n-
Butanol-to-acetic acid molar ratio = 1:1, reaction temperature 100 8C,
0.7 wt % catalyst.
Appendix A. Supplementary data
fresh reaction mixture in a second test. The procedure was
repeated in a third reaction test. The results obtained,
presented in Fig. 6, show a loss of activity of the 10V-Al2O3
catalyst with its subsequent reuse. Thus, for a reaction
time of 2 h the conversion of 62.6% in the first run
decreased to 52.0% in the second run and to 47.6% in the
third run. This decrease in catalytic activity is probably
due to the subsequent leaching of vanadia from the
alumina support into the liquid phase during the catalytic
reactions as suggested by the EDX chemical analysis of the
catalysts after the catalytic test (Table 1). Note that the
selectivity for n-butyl acetate remained 100%.
Supplementary data Fig. S1 associated with this article
can be found, in the online version, at http://dx.doi.org/
10.1016/j.crci.2012.06.004.
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4. Conclusions
The present work demonstrates that vanadium oxides
supported on
g-alumina containing well dispersed VOx
species on the alumina support act as relatively efficient
solid acid catalysts for the esterification of acetic acid with
n-Butanol. In all the esterification reactions the selectivity
for butyl acetate was 100%. The conversion increased in the
following order: uncatalytic < Al2O3 < 5V-Al2O3 < 10V-
Al2O3 in line with the total acid site density and strength
measured by NH3-TPD. There was no resistance to mass
transfer of acid to the external surface of the catalyst and
the optimal catalyst loading in the reaction medium was
around 0.7%. Although the selectivity for butyl acetate
remained 100%, the catalytic activity of the 10V-Al2O3
catalyst decreased after three successive reactions because
of the leaching of vanadia from the alumina support.
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The authors are grateful to Mr. Oravetz Dezso¨ for
technical assistance with scanning electron micrographs
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