Indian Journal of Chemical Technology
Vol 3, September 1996, pp. 253-255
A comparison of catalytic activity of zeolites with some Lewis acids
in esterification reaction
N Nagaraju· & P Mehboob
Department of Chemistry, St Joseph's College, P.O. Centre, 46, Langford Road, Bangalore, 560 027, India
Received 24 July 1995; accepted 13 February 1996
In this paper, an attempt has been made to compare the catalytic activity of zeolites of the types
NaX, NaY and NaZSM-S and their protonated forms with some conventional Lewis acids such as
anhydrous ZnCI2, AlCl3 and H2S04 in the esterification reaction between isoamyl alcohol and acetic
acid in liquid phase. The product has been analysed by chemical methods and confirmed· by FTIR
and IH NMR spectral studies. The percentage of ester in the reaction product has been estimated
using gas chromatographic technique. It is observed that zeolites are more active than the conventional Lewis acids in catalysing this reaction and among the zeolites HZSM-5 resulted in 100% yield
of the ester in the product extract. Selectivityfor eSterformation has also been found to be 100%.
Esters are valuable. starting materials in the synthesis of complex organic molecules1 and widely
used as industrial solvents for paints. Industrially
esters are synthesised by direct esterification with
sulphuric acid as the catalyst. However, this synthetic method has several drawbacks2, i.e., (i) sulphuric acid can cause several side reactions and
decreases the Yield of ester and (ii) corrosion of
the equipment used is so severe by strong acid
that etched parts have to be replaced frequently
resulting in the rise of operation cost considerably.
There has· been a considerable amount of interest in using solid acids such as metal oxides3• zoolites4 and clays5 as catalysts in many industrially
important acid catalysed reactions. These materials possess several advantages over conventional
Lewis acids6, for instance (a) less or no corrosion,
(b) no waste or disposal problems, (c) setting up
of continuous process in fixed bed reactions easily
and (d) high thermal stability.
Catalytic activity of the solid acids in most of
the industrially important reactions has been investigated in vapour phase usin~ fixed bed reaCtors. Only a few papers have appeared on the use
of solid acids in liquid phase reactions 7 - 9• In the
present investigation, an attempt has been made
to find out the catalytic activity of zeolites in esterification reaction between acetic acid and isoamyl alcohol in liquid phase and compare their activity with the conventional Lewis acids.
•Author to whom corres~
should be addressed.
Experimental Procedure
Reagents and catalysts-Synthetic grade isoamyl
alcohol, glacial acetic acid and laboratory grade
aIlhydrous ZnCI2, AlCl3 and conc. H2S04 were
used in this investigation. The catalysts aIlhydrous
ZnCI2, AlCl3 and conc. H2S04 were used as such.
Zeolite samples of type NaX, NaY and NaZSM-5
(Si/ Al ratio = 1, 3 and 75 respectively) were supplied by IPCL, Baroda. Sodium forms of the zeolites were converted into their H-form using
NH4N03 (15 cm3 of 10% solution per gram of
the zeolite) following standard procedures. These
H-form of the zeolites are designated' as HX, HY
andHZSM-5.
Catalytic activity studies-Catalytic activity of
the solid catalysts in the esterificationI'eaction between isoamyl alcohol and acetic acid in liquid
phase was studied both at room and refluxing
temperatures. A mixture of the alcohol and the
acid (25 cm3 in 1:1 molar ratio) was miXed with 2
g of the catalyst. The zeolites were activated at
500°C for 6 h before using them in the reaction.
The reaction mixture was refluxed for 20 h over a
mantle using water cooled condensor. After the
Specified time reaction mixture was cooled and
the· product formed was separated as per the
procedure described elsewhere10.
Analysis of the products-The product extracts
from various reactions carried out with different
catalysts were analysed and the presence of ester
was confirmed. IR and 1H-NMRspectra of a 'few
product samples (sample nps. 1, 2, 5, 9, as given
in Table 1) and an authentic sample of isoamyla- .
rl
254
INDIAN 1. CHEM. TECHNOL.,
cetate obtained from a local industry, were recorded. Gas chromatographic analysis of all the
products and authentic samples of isoamyl alcohol, acetic acid and ester were carried out using
Netal Chromatograph (with a TCD and 2 m stainless steel column packed with DC-20() as the stationary phase) at a column temperature of 200°C
using hydrogen as the carrier gas.
Results and Discussion
Gas chromatographic analysis clearly indicated that
the zeolites showed 100% selectivity towards formation of the ester. The percentage of ester (as calculated from GC analysis) present in the product
extract obtained from each of the reactions is given in Table 1. The effect of refluxing time and the
amount of catalyst in the reaction in presence of
HY is given in Table 2. IR spectra of some of the
product samples (1, 2, 5, 9) mentioned in Table 1
are given in Fig. 1. Assignment of various absorption peaks! I in IR and IH NMR spectra indicate
that the product is isoamyl acetate. It can be inferred from results (Table 1) that both Lewis acids and the zeolites catalyse esterification reaction
and the catalytic activity of the zeolites used is
comparable with that of concentrated sulphuric
Table I-Catalytic
activity of different Lewis acids and zeolites in esterif\cation reaction .
Weight of the catalyst = 2g,Refluxingtime = 20h,
Reaction mixture = 1:1 isoamyl alcohol and glacial acetic acid
(1:1 molar).
NaX
HY
NaZSM-579.00
HZSM-5
NaY
HX
79.80
76.80
75.12
82.22
100.00
%
of
78.87
75.62
ester
in the
66.36
AICI] Catalyst
ZnCI2
Sample number H2SO4
prod uct extract
SEJYfEMBER 1996
acid. HZSM-5 being catalytically most active,
showed 100% ester in the reaction product. NaX
and NaY were found to have same activity as
their protonated forms (HX and HY) under similar reaction conditions. When HY catalyst was employed, it was found that the yield of ester decreased
with increase in retluxing time and decrease in the
amount of catalyst (Table 2).
Zeolites are known for their catalytic activity in
a number of acid catalysed organic "reactions4.
The strength and the distribution of the acid sites
depend on the type of zeolitel2.This property of
zeolites is clearly revealed in this investigation as
different zeolites showed catalytic activity to different extents and it is not only the amount but
also the strength of the acid sites associated with
the zeolites that plays an important role in catalysing a particular reaction13·14. This property is observed in the present investigation in the case of
NaX and NaY zeolites which showed almost
same catalytic activity in terms of the per.centage
of the ester formed, as their protonated forms,
though the latter forms are known to have higher
total acidity than their sodium forms. This is
probably because the number and strength of acid
sites responsible for catalytic activity remain almost the same in both sodium and protonated
forms.
Decrease in percentage of ester in the product
extract when amount of the catalyst was decreased from 2 g to 1 g may be due to the decrease in the number of acid sites available for the
reaction.
The availability
of
the catalytic
sites with appropriate acid strength in zeolites accounts for their higher catalytic activity on being
compared with conventional Lewis acids.
Conclusion
In general, zeolites showed better catalytic aca
b
Table 2-Effect
of reaction conditions on esterification activity of HY catalyst
Reaction mixture-isoamyl alcohol and glacial acetic acid (I: I
molar)
hAmount
ester
93.48
79.80
20
32 %ofthe
47.90
Refluxing
time
Catalyst
I
3
S
e
""
E
••
c:
+
d
13
•..
•....
4000 35003-000-
2500 2000 l500 1000 500
Wavp numbprs ,em-I
Fig. I-IR spectra of the product extracts obtained in the
presence of (a) cone. H2S04, (b) HX, (c) ZnClz, (d) HZSM-5
catalysts, and (e) authentic sample isoamyl acetate
I
"
I
NAGARAJU
& MEHBOOB: CATALYTIC ACTIVITY OF ZEOLITES
tivity in the esterification reaction between isoamyl alcohol and acetic acid than the conventional
Lewis acids such as anhydrous ZnCI2, AlCl) and
cone. H2S04, The selectivity towards ester formation is 100%. Thus zeolites may be tailored to get
active catalytic sites with appropriate acid
strength to increase the percentage of ester in the
reaction.
Acknowledgements
The authors acknowledge the assistance provided by Ms Joyce D'Souza and Ms Bina V in
conducting some of the experiments. One of the
authors (NN) is indebted to Dr A B Halgeri,
IPCL, Baroda for his suggestions and constant encouragement.
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