Synthesis of carboxylic acid esters in the presence of micro- and mesoporous aluminosilicates

Article abstract of DOI:10.1134/S1070427214060184

The catalytic properties of zeolites HY, HBeta, and HZSM-12 and of mesoporous amorphous aluminosilicate in liquid-phase esterification of aliphatic (monobasic C₁-C₁₈, dibasic C₆, C₁₀) and aromatic (benzoic, trimellitic, phthalic) carboxylic acids with butanol were studied. Zeolite HBeta appeared to be the most active catalyst. Procedures were developed for preparing esters in the presence of zeolitic catalyst HBeta, ensuring 100% selectivity of ester formation at 90-98% conversion of the acid.

Full text of DOI:10.1134/S1070427214060184

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 6, pp. 773−779. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © N.G. Grigor’eva, A.M. Suleimanova, M.R. Agliullin, B.I. Kutepov, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 6,
pp. 767−774.
INORGANIC SYNTHESIS AND INDUSTRIAL
INORGANIC CHEMISTRY
Synthesis of Carboxylic Acid Esters in the Presence
of Micro- and Mesoporous Aluminosilicates
N. G. Grigor’eva, A. M. Suleimanova, M. R. Agliullin, and B. I. Kutepov
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences, pr. Oktyabrya 141, Ufa, 450075 Russia
e-mail: ngg-ink@mail.ru
Received February 18, 2014
Abstract—The catalytic properties of zeolites НY, НBeta, and НZSM-12 and of mesoporous amorphous
aluminosilicate in liquid-phase esterification of aliphatic (monobasic С1–С18, dibasic С6, С10) and aromatic
(benzoic, trimellitic, phthalic) carboxylic acids with butanol were studied. Zeolite HBeta appeared to be the most
active catalyst. Procedures were developed for preparing esters in the presence of zeolitic catalyst НBeta, ensuring
100% selectivity of ester formation at 90–98% conversion of the acid.
DOI: 10.1134/S1070427214060184
Carboxylic acid esters are one of the most demanded
classes of organic compounds. The fields of their applica-
tion are very diverse: solvents, fruit essences, aromatiz-
ers, preservatives, components of lubricating oils and
hydraulic fluids, biodiesel, etc. [1–4]. In the total volume
of production of polymer plasticizers, the share of esters
is about 85%, and the total volume of their production
exceeded 5 million tons annually [5].
The use of synthetic microporous aluminosilicates
(zeolites) and mesoporous metallosilicates as catalysts
of ester synthesis has been reported recently [6–12].
The majority of studies dealing with esterification in the
presence of zeolitic catalysts concern synthesis of acetic
or phthalic acid esters. Preparation of esters of other
mono- and dicarboxylic acids in the presence of zeolites
has been studied insufficiently.
This study was aimed at developing efficient proce-
dures for preparing butyl esters of various aliphatic and
aromatic carboxylic acids, based on using microporous
crystalline aluminosilicates (zeolites НY, НBeta, НZSM-
12) and mesoporous amorphous aluminosilicates.
The majority of industrial procedures for ester syn-
thesis consist in direct esterification of carboxylic acids
with alcohols at elevated temperature (100–200°С) in the
presence of various catalysts. Traditional acid catalysts
for esterification are sulfuric, hydrochloric, phosphoric,
benzenesulfonic, and p-toluenesulfonic acids. To remove
them from the crude ester after the synthesis, it is neces-
sary to perform neutralization with a base agent and a
series of washings with water, which gives rise to a large
amount of liquid wastes and to the product loss. The
drawbacks of using mineral acids are possible tarring of
organic compounds and formation of by-products as a
result of alcohol dehydration. Furthermore, with sulfuric
acid as catalyst, unsaturated compounds arising from side
reactions undergo sulfonation, and sulfonic acid esters
are formed.
EXPERIMENTAL
Zeolites of structural types FAU (Y), BEA(Beta), and
MTW (ZSM-12) in the H form, and also mesoporous
aluminosilicate (MAS) were studied as catalysts.
The starting zeolite NaY (molar ratio SiO
2/Al2O3
М = 4.9) was prepared by the procedure described in
[13]. The NaY decationization (replacement of Na+ cat-
ions by Н+) was performed from an NН4NО3 solution
in three steps with intermediate calcination at 540°С
for 4 h. The Na+/Н+ exchange in zeolite НY was 95%.
Progress in the development of modern esterification
technologies is associated with the replacement of mineral
and organic acids by heterogeneous catalysts.
Zeolites NH4–Beta (M = 18) and NH4–ZSM-12
(M = 34), synthesized at the Angarsk Plant of Catalysts
773

774
GRIGOR’EVA et al.
Table 1. Physicochemical properties of zeolitic catalystsa
Acid properties
Equilibrium adsorption
capacity for indicated
vapor,b cm3 g–1
concentration of acid sites,
Catalyst
Structure
β, % SiO2/Al2O3
Tmax, °C
μmol g–1
water
0.29
benzene
0.33
I
II
cI
cII
c
HY
12-rings;
7.4×7.4 Å
100
4.9
18
300
420
410
520
930
НВeta
12-membered; 100
5.6 × 5.6 Å
6.6 × 7.2 Å
0.26
0.15
0.32
0.16
280
450
450
530
410
340
260
870
670
НZSM-12 12- membered; 100
34
300
5.6 × 6.0 Å
a (cI, cII, c) Concentrations of weak (I) and strong (II) acid sites and their total concentration; (β) degree of crystallinity.
b At T = 20°C, p/ps = 0.8.
and Organic Synthesis, were converted to the H form by
heat treatment in air at 540°С for 3 h.
НZSM-12 (Тmax = 450°С for both). In zeolite НY, the
acid sites are weaker (Тmax = 420°С), which is consistent
with published data [16, 17].
The catalysts were characterized by X-ray diffraction
(XRD) analysis, low-temperature nitrogen adsorption,
and temperature-programmed ammonia desorption (TPD
NH3).
Sample of mesoporous aluminosilicate was syn-
thesized by the sol–gel procedure involving stirring of
oligomeric orthosilicic acid esters [ethyl silicate 40, TU
(Technical Specification) 2435-427-05763441–2004]
with an aqueous-alcoholic solution of Al(NO3)·9H2O
(Merck, 99 wt %) at 20–25°С for 25–30 min, fol-
lowed by heating to 60°C with stirring. To ensure more
complete hydrolysis of the compounds, we used the
H2O/SiO2 molar ratio of 10 [18]. The resulting gel was
treated with an aqueous-alcoholic solution of ammonia
at the SiO2/NH4OH molar ratio of 5, dried for 8 h in air
at 150°С, and then calcined for 5 h in a muffle furnace
at 650°С. The calcined aluminosilicate was ground to
the particle size smaller than 100 μm. The pore structure
of MAS is characterized by the presence of mesopores
with broad size distribution (in the interval 2–5 nm). The
BET specific surface area of the mesoporous alumino-
silicate is 607 m2 g–1, and the specific mesopore volume
is 1.05 cm3 g–1. The SiO2/Al2O3 molar ratio is 20. The
total concentration of acid sites, measured by TPD NH3,
is 550 μmol g–1, and the concentration of strong (II) acid
sites is 250 μmol g–1.
The physicochemical properties of the zeolites studied
are given in Table 1.
The zeolitic catalysts differ in the structure of the
crystal lattice [14], molar ratio of the Si and Al atoms,
and acid properties [15]. Zeolites НYand НBeta are char-
acterized by the widest cavities (Y) and channels (Beta)
permeating aluminum–silicon–oxygen frameworks, and
in zeolite НZSM-12 the channel size is smaller (Table 1).
According to the X-ray diffraction patterns, the degree
of crystallinity of the initial zeolite samples is close to
100%.Adsorption characteristics confirm the high degree
of crystallinity (Table 1).
In the acidity spectra of zeolitic catalysts, measured
by TPD NH3, there are two peaks characterizing weak
acid sites with the temperature maximum Тmax in the
interval 100–350°С and strong acid sites with Тmax
>
350°С (Table 1). The concentration of strong acid sites,
which are the most important for chemical transforma-
tions, decreases in the order НY > НBeta > НZSM-12.
Comparison of the strength of acid sites (evaluated by
the shift of the maximum of the high-temperature peak,
Aliphatic and aromatic carboxylic acids (monocar-
boxylic: acetic, propionic, butyric, valeric, caproic,
enanthic, caprylic, pelargonic, capric, palmitic, stearic,
benzoic; dicarboxylic: adipic, azelaic, sebacic; phthalic
anhydride; trimellitic acid) were purchased from Acros.
Т
max, in the thermal desorption patterns) shows that the
strongest acid sites are present in zeolites НBeta and
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SYNTHESIS OF CARBOXYLIC ACID ESTERS
775
Table 2. Esterification of butyric (run nos. 1–5) and azelaic (run no. 6) acids with n-butanol on zeolitic catalyst НBeta (20%
catalyst, 3 h)
Selectivity, %
Run no. Т, °С
Acid : alcohol molar ratio
Time, h Conversion, %
ester
by-products
1a
2a
3a
4a
5
90
117
117
117
117
117
1 : 2
1 : 2
1 : 4
1 : 6
1 : 2
1 : 6
3
3
3
3
3
5
64
75
86
95
95
91
92
82
8
18
21
37
–
79
63
100
100
6
–
a Run nos. 1–4 were performed with simultaneous loading of the acid and alcohol.
n-Butanol was of analytically pure grade [GOST (State
Standard) 6006–78].
spectra were recorded with a Vertex 70v Fourier IR spec-
trometer from KBr pellets. High-resolution mass spectra
were taken with a Fisons device using a chromatograph
equipped with a DB 560 capillary quartz column (50 m).
Esterification of carboxylic acids with n-butanol was
performed in a four-necked flask equipped with a ther-
mometer, a stirrer, a reflux condenser, and a Dean–Stark
trap. The flask was charged with the acid, catalyst, and
toluene (for azeotropic removal of water released in the
reaction) and heated to the required temperature with
continuous stirring, after which n-butanol was gradually
added. Samples were taken for analysis at definite time
intervals. After the experiment, the reaction mixture was
cooled, the catalyst was filtered off, and the filtrate was
analyzed by gas–liquid chromatography. The esters were
isolated from the reaction mixture at reduced pressure.
RESULTS AND DISCUSSION
For the development of selective heterogeneous-
catalytic procedures for preparing esters, we studied
the reaction of aliphatic monocarboxylic acids С2–С18
with n-butanol at 60–117°С in the presence of various
zeolytic catalysts and mesoporous aluminosilicate, taken
in amounts of 10–30%.
When the acid and alcohol were loaded into the reac-
tor simultaneously, the reaction mixture contained, along
with n-butyl esters of the corresponding monocarboxylic
acids, also ethers and esters of isomeric butyl alcohols and
butene dimers and trimers. Their yield increases with an
increase in temperature and in alcohol excess (Table 2,
run nos. 1–4).
The acid conversion was calculated from the results
of determining the acid number of the reaction mixture
[(mg KОН) g–1].
Quantitative analysis of the reaction mixture was per-
formed by gas–liquid chromatography on a GC-2014 gas
chromatograph (Shimadzu) equipped with a flame ioniza-
tion detector. Device characteristics: packed column 2 m
long, 3 mm inside diameter; stationary phase SE-30, 5%
on Сhromaton N-AW-HMDS, fraction 0.20–0.25 mm.
Analysis conditions: 50–280°С, programmable heating
at a rate of 8 deg min–1; vaporizer temperature 300°С;
carrier gas helium.
The by-products are formed by isomerization, de-
hydration, and esterification of butanol, and also by
oligomerization of alcohol dehydration products, butenes
(Scheme 1).
The results obtained are close to those given in [19],
where transformations of butanol on zeolitic catalyst are
reported to occur even at 40°С.
The products were identified by gas chromatogra-
1
phy–mass spectrometry (GC–MS), by IR and H and
The kinetic relationships of esterification of acetic
acid with propanol and butanol on zeolitic catalysts are
described most accurately by the Eley–Rideal model [20]
in accordance with which acetic acid molecules, which
are more polar than alcohol molecules, are adsorbed on
acid sites of the catalyst with the formation of protonated
13C NMR spectroscopy, and by elemental analysis. The
spectral characteristics obtained are consistent with
1
published data. The H and 13С NMR spectra were re-
corded on a Bruker Avance-400 spectrometer operating
at 400.13 MHz for 1H and at 100.62 MHz for 13С. The IR
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014

776
GRIGOR’EVA et al.
K, %
catalytic systems that we tested are less active in this
reaction. Increased activity of zeolite НBeta is due both
to the presence of strong acid sites in high concentration
and to specific features of the crystal structure of this
catalyst, formed by wide channels intersecting in three
planes, which ensures good accessibility of active sites
to the reacting molecules.
We believe that lower activity of zeolite НYand alumi-
nosilicate МАС is due to lower strength of the acid sites
compared to zeolite НBeta. Low conversion of caproic
acid on zeolite НZSM-12 is caused by diffusion hindrance
to transport of the reactants to the active sites, because
this zeolite is characterized by the narrowest pores among
the catalysts tested.
No catalyst
MAS
Fig. 1. Influence of the catalyst structure on the acid conversion
K in reaction of caproic acid with n-butanol. Reaction condi-
tions: 117°С, 20% catalyst, acid : alcohol molar ratio 1 : 2, 3 h.
intermediates. These intermediates react with alcohol
molecules occurring in the bulk of the reaction mixture to
form alkyl acetate. An increase in the alcohol concentra-
tion gives rise to the competing adsorption effect, leading
to a decrease in the reaction rate.
The acid conversion increases as the temperature is
increased from 60 to 117°С, the catalyst concentration is
increased from 10 to 30%, the acid : alcohol molar ratio
is increased from 1 : 1 to 1 : 6, and the reaction time is
increased to 3 h (Fig. 2).
We assumed on the basis of these data [20] that the
esterification rate can be increased and the rate of undesir-
able side processes can be decreased by adding the alco-
hol to the reaction mixture gradually, in small portions.
Indeed, fractional addition of alcohol allows preparation
of butyl esters of both mono- and dicarboxylic acids with
up to 100% selectivity (Table 2, run nos. 5, 6).
In the reaction of butyric acid with butanol, the highest
conversion of the acid (95–99%) was reached at 117°С
with 20–30 wt % zeolite НBeta at the acid : alcohol molar
ratio from 1 : 2 to 1 : 6 (Fig. 2).
Data on esterification of various monocarboxylic
acids with butanol on zeolite НBeta show (Fig. 3)
that the conversion of acids in the series from acetic
to caproic acid is 95–98%. As the hydrocarbon chain
length in the acid molecule is increased further, the
acid conversion gradually decreases: to 73–85% for
С7–С10 acids, 54% for palmitic (С16) acid, and 44%
for stearic (С18) acid. These results can be attributed to
two trends. First, with an increase in the hydrocarbon
chain length the capability for carbocation formation
decreases owing to weakening of the positive inductive
effect of the alkyl chain; second, for longer molecules
the diffusion hindrance to their transport in channels of
zeolitic catalysts increases.
The relationships between the structure of the catalysts
and their catalytic activity in synthesis of monocarboxylic
acid esters were studied with esterification of caproic acid
with butanol as example (Fig. 1).
It should be noted that esterification of aliphatic car-
boxylic acids can also occur without catalyst, but the acid
conversion in this case is low. For example, in thermal
esterification, the conversion of caproic acid is 38%,
whereas in the catalytic reaction it increases to 60–95%
(Fig. 1). The selectivity of butyl hexanoate formation on
all the catalysts, as already noted, is 100%.
The catalytic properties of micro- and mesoporous
aluminosilicates in synthesis of aliphatic dicarboxylic
Zeolite HBeta is the most active in the synthesis of
butyl hexanoate among the catalysts tested. The other
Scheme 1.
n
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SYNTHESIS OF CARBOXYLIC ACID ESTERS
777
(b)
(a)
K, %
ccat, wt %
T, °C
(d)
(c)
K, %
τ, h
1 : 1
1 : 2
1 : 4
1 : 6
Acid : alcohol
Fig. 2. Influence of (a) temperature Т, (b) amount of zeolite HBeta сcat, (c) acid : alcohol molar ratio, and (d) reaction time τ on butyric
acid conversion K.
3330–2500 cm–1, characterizing stretching vibrations
of the free and hydrogen-bonded hydroxy group of the
monoester, respectively.
acid esters were studied with esterification of the most
practically important acids, adipic (С6), azelaic (С9), and
sebacic (С10), with butanol as example.
Under the conditions of our experiments, the
reaction yielded the corresponding dibutyl esters with
100% selectivity. Monobutyl esters were not detected,
which was confirmed by the GC–MS data and by the
absence of IR absorption bands of at 3550–3500 and
As in esterification of monocarboxylic acids, zeolite
HBeta is the most active in the synthesis of dibutyl esters
of dicarboxylic acids (in particular, of dibutyl sebacate)
(Fig. 4). The catalyst activity decreases in the order
НBeta > МАС > НZSM-12 > НY.
K, %
Fig. 3. Conversion K of monocarboxylic acids in reaction with n-butanol on zeolite НBeta. Reaction conditions: acid : alcohol molar
ratio 1 : 2, 117°С, 15% catalyst, 3 h. Acid: (1) acetic, (2) propionic, (3) butyric, (4) valeric, (5) caproic, (6) enanthic, (7) caprylic, (8) pel-
argonic, (9) capric, (10) palmitic, and (11) stearic.
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778
GRIGOR’EVA et al.
K, %
Table 3. Influence of reaction conditions on adipic acid
conversion in reaction with n-butanol on zeolitic catalyst
НBeta (5 h)
Catalyst amount,
%
Acid : alcohol
molar ratio
Conver-
sion, %
Т, °С
20
20
20
10
30
20
20
20
50
1 : 4
1 : 4
1 : 4
1 : 4
1 : 4
1 : 2
1 : 3
1 : 6
38
81
97
33
97
88
90
117
117
117
117
117
117
MAS
Fig. 4. Esterification of sebacic acid with n-butanol on micro-
and mesoporous catalylsts. Reaction conditions: 30% catalyst,
120°С, acid : alcohol molar ratio 1 : 4, 5 h. (K) conversion.
92
97
Unfortunately, we failed to synthesize tributyl melli-
tate with high selectivity. Even at the acid : alcohol molar
ratio increased to 1 : 9, the reaction products contained
di- and tributyl trimellitates.
Table 4. Esterification of aromatic acids with n-butanol on
catalysts НBeta and MAS (30% catalyst, 117°С, 5 h)
Selectivity, %
Acid :
alcohol Conver-
molar sion, %
ratio
Catalyst
Acid
mono-
ester
CONCLUSIONS
diester triester
(1) Catalytic properties of synthetic microporous and
mesoporous aluminosilicates in liquid-phase esterification
of various carboxylic acids (aliphatic monobasic С1–С18
and dibasic С6, С10; aromatic: benzoic and trimellitic
acids, phthalic anhydride) with butanol were studied. The
ester yield depends on the structure of the acid, acidity
of the catalyst, and also, in the case of zeolites, on the
accessibility of catalytically active sites.
НBeta Benzoic
1 : 4
1 : 4
95
83
100
–
–
–
–
Phthalic
100
Trimellitic 1 : 6
80
45
40
–
100
–
25
–
75
–
MAS Benzoic
Phthalic
1 : 4
1 : 4
100
–
(2) The most effective esterification catalyst is zeolite
НBeta. It allows synthesis of esters of aliphatic mono-
and dicarboxylic acids in 95–99% yield and of aromatic
acid esters in 80–95% yield. Zeolitic catalysts of other
structural types (НY, НZSM-12) and mesoporous alumi-
nosilicate showed lower activity in esterification.
A study of the influence of reaction parameters
(temperature, catalyst amount, reactant molar ratio,
time) on the adipic acid conversion showed that 90–95%
conversion of the acid was reached in the presence of
20–30% zeolite НBeta at 110–117°С in 5 h at the acid :
alcohol molar ratio from 1 : 4 to 1 : 6 (Table 3).
(3) As demonstrated by the example of aliphatic
carboxylic acids, the acid conversion increases with an
increase in the reaction temperature (50–117°С) and time,
in the catalyst amount (10–30%), and in the catalyst :
alcohol molar ratio. In the series of aliphatic monocar-
boxylic acids, the acid conversion tends to decrease with
an increase in its alkyl chain length, and in the series of
aromatic acids it tends to decrease with an increase in the
number of –СООН groups.
Butyl esters of aromatic carboxylic acids (benzoic,
phthalic, trimellitic) were synthesized using zeolite НBeta
and aluminosilicate MAS (Table 4).
Similarly to esterification of aliphatic carboxylic acids,
the reaction of butanol with aromatic acids is the most
active in the presence of zeolite НBeta. The conversion
of benzoic acid and phthalic anhydride on mesoporous
aluminosilicate MAS is considerably lower, 40–45%.
Butyl benzoate and dibutyl phthalate were obtained on
both catalysts (НBeta, MAS) with the selectivity close
to 100%.
(4) Procedures were developed for preparing butyl es-
ters of carboxylic acids in the presence of zeolitic catalyst
НBeta with up to 100% selectivity of ester formation.
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SYNTHESIS OF CARBOXYLIC ACID ESTERS
779
pp. 35–39.
ACKNOWLEDGMENTS
9. Bedard, J., Chiang, H., and Bhan, A., J. Catal., 2012,
The study was supported by the Russian Foundation
for Basic Research (project no. 14-03-97021, New Ap-
proach in Syntheses of Catalysts for Petrochemical Pro-
cesses, Based on Zeolites with Hierarchic Pore Structure).
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pp. 136–143.
11. Gokulakrishnan, N., Pandurangan, A., and Sinha, P.K.,
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