2
V.S. Chandane et al. / C. R. Chimie xxx (2017) 1e9
drawbacks of this production process are high corrosive-
ness to the equipment, non-reusability of acid catalysts,
extra purification steps and environmental troubles [11,12];
as a result, a huge quantity of environmental acidic waste is
produced [2]. Heterogeneous solid catalysts are developed
for the sustainable production of esters. These solid het-
erogeneous catalysts provide significant stability and ac-
tivity, easy separation from the reaction mixture,
reusability and do not cause any corrosion problem to the
equipment [13]. In this context, solid acid catalysts such as
zeolites, sulfated zirconia and acidified silica have been
and the optimal reaction conditions corresponding to
maximum conversion of acetic acid and % yield of ester
were determined using response surface methodology
with the BoxeBehnken Design (BBD).
2. Experimental section
2.1. Chemicals and materials
FACs were collected from Vipra Ferro Alloy Pvt. Ltd.
(Nagpur, Maharashtra, India), which contains approxi-
mately 70% (SiO2 þ Al O þ Fe O ). Before its use, it was
2
ꢀ
used. The esterification reactions catalyzed by SO
Al eSiO catalyst [14], zinc oxide [15], cobalt oxide [16]
4
/
2
3
2 3
2
O
3
2
sieved to a size of <100 mm. Acetic acid (purity >99%) was
and sulfated zirconia [17,18] are reported in recent years.
In addition, supported ionic liquids [19,20], supported
montmorillonite K10 [21,22], supported palladium [23],
sulfated Si-doped zirconia [24] and sulfonated carbon
purchased from Merck, and n-octanol (purity >99%) was
obtained from Loba Chemie Pvt. Ltd. (Mumbai, India).
Ammonium sulfate (purity >99.5%) was procured from
Fisher scientific, India. Methanol (purity >99%) and Karl
Fischer reagent were procured from Rankem Chem. Ltd.
(Mumbai, India). n-Hexane (GC grade, purity >99%) was
procured from SigmaeAldrich. All of the chemicals used in
this study were of analytical reagent grade. Deionized,
double distilled water was used in the experiments.
[25,26] have been used as an efficient and active hetero-
geneous catalyst for the various esterification reactions.
Cenospheres are referred as fly ash cenospheres (FACs),
mainly composed of the high amount of silica and alumina
2 3 2
with few traces of Fe O and TiO . It can be used as a
catalyst or catalytic support for the esterification reaction
because of its high silica content, which is associated with a
significant amount of surface acidity. FAC is a very low-cost
and abundantly available waste material. Most of the ele-
ments including alumina and Fe present in FACs are
leached out during the acid treatment. As a result, the silica
content of FACs is increased, which subsequently enhances
the surface acidity [27]. Moreover, FACs possess unique
properties like light weight, constant spherical structure
and good mechanical, chemical and thermal stability. In
addition, the high silica content facilitates in catalysis of
various chemical reactions and also provides support to
different catalytic species on the surface [28]. Owing to
these highly significant characteristics, FACs are believed to
be a significant material for the synthesis of a heteroge-
neous catalyst. Earlier, the authors reported an efficient
solid acid catalyst by using fly ash as a catalytic support for
transesterification reactions [3,29]. However, to the au-
thor's knowledge, no information is available in the open
literature describing the application of the FAC-supported
heterogeneous catalyst for the esterification reaction to
synthesize flavor esters. In view of above, an attempt is
made to develop a suitable, efficient and cost effective FAC-
based catalyst for the esterification reaction. The ester
synthesized in the present esterification reaction is n-octyl
acetate, which has an odor reminiscent of oranges and
grapefruits. This ester is widely applied as an artificial fla-
vor and also as a solvent in many chemical industries.
In the present work, for the first time the FAC-supported
heterogeneous acid catalyst was prepared by impregnating
it with ammonium sulfate. The catalyst was synthesized by
a low-cost method using a cost-effective precursor, and it is
used in the synthesis of high-value product viz., ester. The
prepared catalyst was characterized and its catalytic per-
formance was investigated in the esterification of n-octanol
and acetic acid. With the aim of optimizing the conversion
of acetic acid and % yield of ester, the effects on various
process parameters, namely, catalyst loading, molar ratio of
alcohol/acid and reaction temperature were investigated,
2
.2. Synthesis of solid acid catalyst
The FAC-supported solid acid catalyst was synthesized
by the method of wet impregnation. The required amounts
of the aqueous stock solution of ammonium sulfate were
laden onto different quantities of FACs with a constant
manual stirring. Particularly, 15.4 mL of an aqueous stock
solution of ammonium sulfate was added gradually to 15 g
of FACs with constant stirring. The mixture was stirred
properly to fill up the pores of FACs. Then, it was kept for
drying in hot air oven at 80 C for about 2 h. The dried
material was then calcined in a muffle furnace at 400 C for
4
ꢁ
ꢁ
h. Finally, the calcined material was stored in a dry stor-
age bottle before using it for the esterification reaction.
2.3. Catalyst characterization
Powder X-ray diffraction (XRD; PANalytical 3 kW X'pert
Powder) was performed for the identification of crystalline
nature and crystalline size of the FAC-supported solid acid
catalyst. XRD was performed using Cu
Ka radiation
(
l
¼ 1.5406 Å) with a generator setting of 30 mA and 40 kV.
ꢁ
The XRD patterns were recorded in the 2q range of 10e100
with a scanning speed of 0.1 s . The crystalline size was
determined by the DebyeeScherrer equation:
ꢁ
ꢀ1
B ¼ 0:9
l
=
b
cos
q
(1)
where B represents the crystalline size,
l
is the X-ray
wavelength (1.54 Å for Cu K ),
peak (measured as full width at half-maximum intensity)
and represents the peak position.
Fourier transform infrared (FTIR equipped with atten-
uated total reflection) (Thermo Scientific iD5) spectro-
scopic measurements were carried out for the
identification of surface functional groups of the FAC-sup-
ported solid acid catalyst. The FTIR spectra were recorded in
a b is the broadening of the
q
ꢀ
1
the range of 400e4000 cm
.
Please cite this article in press as: V.S. Chandane, et al., Efficient cenosphere supported catalyst for the esterification of n-octanol