Process optimization by response surface methodology for transesterification of renewable ethyl acetate to butyl acetate biofuel additive over borated USY zeolite

Article abstract of DOI:10.1039/c4ra14771e

Butyl acetate, a renewable biofuel additive was synthesized by transesterification of butanol with ethyl acetate via a renewable and sustainable route. Use of fermentation derived bio-butanol and bio-ethyl acetate for synthesis of butyl acetate would be a more advantageous route over conventional Fischer Esterification. For the first time, a heterogeneous zeolite catalyst such as Ultra Stable Y (USY) and its modified versions obtained by borating on parent USY were used for the synthesis of butyl acetate. Response surface methodology (RSM) was employed to optimize the process parameters for transesterification of butanol with ethyl acetate over a 4% (w/w) B-USY catalyst. The influence of three crucial process variables such as catalyst loading, molar ratio, and reaction temperature on yield of butyl acetate were addressed by Box-Behnken experimental design (BBD). 4% (w/w) B-USY was proved to be a potential catalyst with 96% yield of butyl acetate at optimum process parameters. The 4% (w/w) B-USY catalyst was found to be reusable for 6 catalytic cycles. This journal is

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DOI: 10.1039/C4RA14771E
A table of contents entry:
Response surface methodology revealed that 4% (w/w) B/USY zeolite is stable (reusable for
6 cycles) and potential catalyst with 96% yield of butyl acetate.

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Process Optimization by Response Surface Methodology for Transesterification of
DOI: 10.1039/C4RA14771E
Renewable Ethyl Acetate to Butyl Acetate Biofuel Additive over Borated USY Zeolite
Kakasaheb Y. Nandiwale, Nitish D. Galande and Vijay V. Bokade*
Catalysis and Inorganic Chemistry Division, CSIR - National Chemical Laboratory, Pune-
411008, India.
*Correspondence to:
Dr. Vijay V. Bokade,
Catalysis and Inorganic Chemistry Division,
CSIR - National Chemical Laboratory,
Pune-411008, India.
Ph; +91-20-25902458, Fax; +91-20-25902634
E-mail: vv.bokade@ncl.res.in
1

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DOI: 10.1039/C4RA14771E
Abstract
Butyl acetate, a renewable biofuel additive was synthesized by transesterification of
butanol with ethyl acetate via renewable and sustainable route. Use of fermentation derived
bio-butanol and bio-ethyl acetate for synthesis of butyl acetate would be more advantageous
route over conventional Fischer Esterification. For the first time, a heterogeneous zeolite
catalysts such as Ultra Stable Y (USY) and its modified versions obtained by borating on
parent USY were used for the synthesis of butyl acetate.
Response surface methodology (RSM) was employed to optimize the process
parameters for transesterification of butanol with ethyl acetate over 4% (w/w) B-USY
catalyst. The influence of three crucial process variables such as catalyst loading, molar ratio,
reaction temperature on yield of butyl acetate were addressed by Box–Behnken experimental
design (BBD). 4% (w/w) B-USY was proved to be potential catalyst with 96% yield of butyl
acetate at optimum process parameters. The 4% (w/w) B-USY catalyst was found to be
reusable for 6 catalytic cycles.
Keywords: Ethyl acetate; Transesterification; Boroted USY; Response surface
methodology; Butyl acetate; Biofuel additive.
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DOI: 10.1039/C4RA14771E
1 Introduction
The inevitable depletion of fossil fuel reserves and the subsequent hike in fuel price
along with the environmental concerns of conventional fuels has drawn much attention of
researchers to develop an industrially and environmentally benign process for production of
biofuels and biofuel additives from the renewable resources. Recently, butyl acetate bearing
high flash point (295 K) and very low freezing point (200 K) has been recognized as a
potential biofuel additive.1-3 Low freezing point (200 K) of butyl acetate improves the cold
flow properties of biodiesel without significantly affecting cetane number and the mixture’s
heat of combustion. Moreover, its high flash point (295 K) makes it safer to use as biodiesel
additive and it also makes superior than the ethyl acetate with flash point of 269 K and
similar other biodiesel additives.1-4
The process for production of ethyl acetate5 and butanol6,7 by renewable routes has
been widely researched. Recent advancements in bioprocess and biotechnology has
developed an environmentally benign and economically feasible fermentation process to
produce butanol and ethyl acetate.1,8,9 Hence transesterification of this fermentation derived
bioethylacetate with bio-butanol to produce bio-butyl acetate would be green process.
Transesterification of butanol with ethyl acetate can be carried out over homogeneous
catalyst, but due to the well-known disadvantages of homogeneous catalysts are reinforced by
environmental policies.1 Thus, it is technological challenge to develop ecofriendly and highly
active heterogeneous catalytic process for butyl acetate synthesis. Very limited literature is
available on transesterification of butanol with ethyl acetate over heterogeneous catalysts.1 To
the best of our knowledge, till date, only one report is available on the heterogeneously
catalyzed transesterification of butanol with ethyl acetate to synthesize butyl acetate
(renewable biofuel additive).1 Moreover, it was also recognized that there are no reports
available for the transesterification of butanol with ethyl acetate over zeolites. Hence it was
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thought of interest to investigate catalytic performance of USY and borated USY for
DOI: 10.1039/C4RA14771E
transesterification of butanol with ethyl acetate. These zeolites were used because of their
peculiar properties of temperature stability, porosity, surface area, acidity etc. as compared to
other zeolites.
In addition to the selection of catalysts, the process optimization of the
transesterification reaction is also equally important to optimize the process or operating
parameters so as to identify potential catalysts for industrial application. Response surface
methodology (RSM) is widely adapted for optimization of various process parameters in
esterification and transesterification.10-16 RSM has been effectively employed for several
processes involved in biodiesel production using enzyme or heterogeneous catalysts.10-
15Application of RSM to study the insights on influence of process parameters on butyl
acetate production by transesterification of butanol with ethyl acetate has not been reported,
so far.
This study explores new avenues on development of highly active, stable and cheap
solid acid catalyst and process optimization by RSM for the efficient production of butyl
acetate (renewable biofuel additive). For the first time, USY and borated USY are used as
heterogeneous catalysts for transesterification of butanol with ethyl acetate. This research
also involves application of design expert software obtaining most favorable (optimum)
process parameters for the transesterification reaction with aim to achieve maximum yield of
butyl acetate. The influences of three critical process parameters like catalyst loading, butanol
to ethyl acetate molar ratio and reaction temperature on yield of butyl acetate were examined
with Box-Behnken experimental design (BBD) of RSM and eventually an experimental
mathematical equation was established to predict the correlation between the process
variables. The most favorable process variables recommended by RSM were validated by
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experiments. The reusability of potential catalyst at optimum process parameters is VaiewlsAorticle Online
DOI: 10.1039/C4RA14771E
presented.
2 Results and discussion
2.1 Catalyst characterizations
The synthesized catalysts were characterized by XRD, BET and TPAD. Fig. 1 shows
powder X-ray diffraction patterns of USY, 1% (w/w) B-USY and 4% (w/w) B-USY
catalysts. The XRD patterns of parent USY and borated USY were found to be fully
crystalline without contribution of amorphous phase and also confirmed the phase purity of
synthesized catalyst samples. Osiglio and Blanco19 reported that, boric acid calcined at 593 K
presents sharp peaks at 2θ of 14.8º and 27.9º, attributing to boric oxide. These peaks were not
found in XRD patterns of borated USY catalysts. This implied that boric oxide was well
dispersed on the USY support. The BET surface area of USY was observed to be decreased
with boration due to the narrowing of pores by boron species (Table 1). The total acidities of
USY and borated USY samples are depicted as Table 1. With increase in percentage boron on
USY the acidity was found to be increased. The well dispersed boron species on surface of
USY catalyst, as evidenced by XRD, unswervingly participate to the acidity of the catalyst,
as the hydration of boron species leads to generation Brönsted acid sites.
2.2 Catalytic performance of catalysts
The catalytic performance of blank (without catalyst), USY and 1-5% borated USY
catalysts at identical set of process parameters: catalyst loading of 5%, molar ratio of butanol
to ethyl acetate of 4, reaction temperature of 373 K, reaction time of 0.5-5 h, speed of
agitation of 400 rpm and catalysts’ average particle size of 82.5 µm are represented as Fig. 2.
The blank (thermal) reaction was conducted to see the effect of catalyst. It can be seen from
Fig. 2 that, the maximum yield of butyl acetate was obtained at reaction time of 4 h. All the
set of experiments were carried out in triplicate and had 2% error as depicted by the error
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bars in the Fig. 2. The activity trend at reaction time of 4 h follows: 5% (w/w) B-USY (53%)
DOI: 10.1039/C4RA14771E
> 4% (w/w) B-USY (52%) > 3% (w/w) USY (35%) > 1% (w/w) B-USY (18%) > USY (6%).
All the borated catalysts showed higher activity than the parent USY catalyst; this can be due
to higher acidity of borated USY catalysts (Table 1). The 5% (w/w) B-USY catalyst exhibited
1% higher yield of butyl acetate than 4% (w/w) B-USY catalyst. This may attributed to the
multilayer formation boron species on USY at higher loading. Hence 4% (w/w) B-USY
catalyst exhibiting 52% butyl acetate yield was selected as a potential catalyst. All the
experiments were done in kinetically controlled regime excluding internal and external mass
transfer resistances, by using average catalyst particle size of 82.5 µm and speed of agitation
of 400 rpm.10
In present study, 4% (w/w) B-USY catalyst was found to be potential catalyst for the
synthesis of butyl acetate. Hence, RSM design with BBD is used to investigate influence of
various process parameters. The most favorable process parameter in view to maximize the
yield of butyl acetate and reusability of 4% (w/w) B-USY catalyst is presented later.
2.3 Statistical analysis of RSM and influence of process parameters
2.3.1 Development of regression model equation
In the present research work, the correlation among response (yield of butyl acetate,
Y) and three reaction variables (Table 2) were evaluated by using RSM. The outcomes of 17
set of experiments by BBD template are presented in Table S1 (Supporting Information). All
experiments were performed in triplicate at fixed reaction time of 4 h and average value of
butyl acetate yield is presented. Table S1 and Fig. 3 implied that there was no noticeable
variation among the actual and predicted response values. Based on data of Table S1 and the
second order quadratic model equation Eq. (1) the correlation among yield of butyl acetate
(response) and the three reaction variables was regressed (in terms of original factors) by:
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Y = +87 + 16.25X1 + 2.25X2 + 12.25X3 + 0.75X1X2 + 4.75X1X3 + 8.25X2X3 -D1O2I: .180.810X391/C4-RA14771E
2
2
3.87X2 – 9.87X3
(2)
Where, X1, X2 and X3 were the coded process variables for transesterification
reaction, whereas Y was response of yield of butyl acetate (Table 2). Positive sign in front of
linear term designates that, with an increasing the variable, the response (Y, yield of butyl
acetate) increases linearly (synergistic influence), in other hand negative sign indicates
antagonistic influence.10-12,17 In the Eq. (2), terms of X1, X2, X3, X1X2, X1X3 and X2X3 had
synergistic influence to the yield of butyl acetate (response) in contrary other terms had
antagonistic influence. Percentage catalyst loading (X1) has the strongest influence on the
butyl acetate yield as the coefficient of X1 (16.25) was the highest amongst all other
variables. While, butanol to ethyl acetate molar ratio (X2, 2.25) has least influence on butyl
acetate yield in comparison to catalyst loading (X1) and reaction temperature (X3). Next
greatest influencing process variable was the reaction temperature (X3), followed by
interaction effects between parameter X2X3 and X1X3. Weakest by interaction effects between
parameters X1X2 was noticed. This can be attributed to the collective influence of process
variables, similar outcomes have been noticed by other researchers.12,18
2.3.2 Analysis of variance (ANOVA)
Statistical analysis based on the analysis of variance (ANOVA) was employed for
fitting second order quadratic model. Table S2 (Supporting Information) represents all the
model terms for all responses obtained by RSM. At confidence level of 95%, the F-value of
the model of 323.96 and with very low probability value (p < 0.001) implied that the model
fitted was highly significant. This also implied that regression model used was the reliable to
predict the yield of butyl acetate. The probability values <0.05 (p < 0.05) designate
2
2
2
significant model terms.18 In present case X1, X2, X3, X1X2, X2X3, X1 , X2 and X3 are
significant model terms. The statistical significance data corresponding to individual
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parameter in Table S2 revealed that, linear term of catalyst loading (X1) and reaction
DOI: 10.1039/C4RA14771E
temperature (X3) has significant influence on the butyl acetate yield owing to the high F-
value and low p-values. The quadratic term of catalyst loading (X1), F-value 407.14 was
observed to be more important than the reaction temperature (X3), F-value 239.51 and the
molar ratio (X2), F-value 36.88. Moreover, the consequence of interaction between molar
ratio and reaction temperature (X2X3) also influenced the butyl acetate yield expressively (F-
value 232.63) as is specified by the p-value (p < 0.0001).
2.3.3 Model fitting
The regression equation (Eq. (1)) and coefficient of determination (R2) were used to
evaluate the suitability/fit of model. A high value of the coefficient of determination (R2 =
0.9976) vindicated an exceptional association among the independent process variables,
which also intended that the second order model was precise and at least 99.76% of the
variability in the data could be elucidated by the model. The predicted R2 (R2-predicted =
0.9617) was in equitable covenant with the adjusted R2 (R2-adjusted = 0.9945) and was
observed to be very adequate to specify the high implication of the model. Adequate
precision (the signal to noise ratio) > 4 is suitable. In present investigation, adequate precision
ratio of 56.76 an acceptable signal and proved the ability of model to navigate the design
space. In addition, a moderately lesser value of the coefficient of variation (CV = 1.76%)
implied that the model possessed a superior accuracy and the experiments performed were
reliable. In present model, a minimum of 3 Lack of Fit degrees of freedom (Df) and 4 Df for
‘Pure Error’ ensured a validity of ‘Lack of Fit’ test (Table S2).
These statistical tests along with statistical model fit summary, high determination
coefficient, lack of fit tests and with a consecutive model sum of squares indicated that, the
nominated model to be reasonable for predicting the response (yield of butyl acetate). This
model was further employed to obtain most favorable (optimum) process variables for
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transesterification reaction aiming to maximize the yield of butyl acetate and to make the
DOI: 10.1039/C4RA14771E
process economical and industrially benign.
2.3.4 Influence of process variables on yield of butyl acetate
In order to investigate the individual and interactive effects of process variables on the
yield of butyl acetate, three-dimensional response surface plots and two-dimensional contour
(interaction) plots were drawn (Figs. 4-6). The three-dimensional surfaces are the graphical
illustration of the regression equation (Eq. 2) and each contour curve (two dimensional)
represented the combinations of two test variables with the other one maintained at its level
of zero (central value). It has been reported that, the circular contours denotes the negligible
interaction between the corresponding variables.10-13,17,18 On the contrary, the elliptical
contours symbolize the significant interactions amongst the relevant variables. The influence
of correlation among catalyst loading and molar ratio (Fig. 4), molar ratio and reaction
temperature (Fig. 5) and catalyst loading and reaction temperature (Fig. 6) at constant
reaction time of 4 h are indicated by 3D response surface plots and 2D contour plots.
As can be seen in Fig. 4, with increase in loading of 4% (w/w) B-USY catalyst from
5-25% at constant molar ratio (6:1) and reaction temperature (373 K), the yield of butyl
acetate found to be increased from 52 to 85%. This is attributed to the increase in catalyst
loading makes avail of more catalytically active acid sites for the transesterification reaction
(Table 1). This revels that formation of butyl acetate from ethyl acetate involves a more
active acid site demanding step. The butyl acetate yield was also observed to be proportional
to catalyst amount used; revealing that the reaction proceeds through a pure heterogeneous
mechanism. Also, as specified by low p-value (< 0.0001) (Table S2), the catalyst loading is
highly significant for transesterification reaction. With increase in molar ratio (butanol : ethyl
acetate) from 2:1 to 6:1 at constant catalyst loading of 25%, reaction time of 4 h and reaction
temperature of 373 K, the yield of butyl acetate was observed to be slightly increased from 85
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to 90%. More dilution of reactants with increase in the molar ratio at limited catDaOlyI:s1t0.1a0c3t9i/vC4eRA14771E
sites would not increase the product formation markedly. This implied that the molar ratio
has low influence (p-value of 0.0018) as compared to catalyst loading (p-value of < 0.0001)
on yield of butyl acetate, indicating that higher yield of butyl acetate could be obtained with
lower molar ratio. Hence, to avoid cost associated with separation of unreacted butanol from
final product mixture and to make the process industrially benign, low molar ratio should be
preferred. However, the interaction effect between molar ratio (X2) and catalyst loading (X1)
was found to be insignificant with shape of two dimensional contour curve circular (Fig. 3)
and with high p-value (0.2896) of X1X2 interaction term (Table S2).
The influence of interaction between molar ratio and reaction temperature at constant
catalyst loading of 15% and reaction time of 4 h is shown as Fig. 5. The significant
interaction effect of molar ratio and reaction temperature was exhibited by ellipse mound
shape of two dimensional contour curves (Fig. 5) and as was also evident from low p-value
(0.0002) of X1X3 interaction term (Table S2). With elevating temperature the yield of butyl
acetate was observed to be linearly increased. This was in agreement with the Arrhenius law,
a higher temperature results in a higher rate of transesterification leading to higher yield of
butyl acetate.20 The reaction temperature was found to be highly influencing parameter on the
yield of butyl acetate and this was also evident from low p-value (< 0.0001) (Table S2).
Fig. 6 represents the influence of catalyst loading and reaction temperature on the
yield of butyl acetate in 3D response surface and 2D interaction plot at constant molar ratio
(butanol to ethyl acetate) of 4:1 and reaction time of 4 h. It is an obvious from Fig. 6 that, at
any designated value of reaction temperature from 353 to 393 K, the yield of butyl acetate
increased proportionally with catalyst loading. The influence of individual term and
interaction term of reaction temperature and catalyst loading perceived to be highly
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significant on yield of butyl acetate, which was also supported by low p-valueD(O<I: 100..1000390/C14)RA14771E
(Table 4).
From this study, catalyst loading and reaction temperature were found to be most
contributing terms while molar ratio was least significant term for the transesterification
reaction. However, the interaction between catalyst loading and molar ratio has no influence
on the response (Y, yield of butyl acetate). Hence, it is highly crucial to develop most
favorable reaction parameters for transesterification of ethyl acetate with butanol over 4%
(w/w) B/USY in view to obtain maximum yield of butyl acetate.
2.3.5 Obtaining most favorable process parameters by RSM and model validation
The most favorable process variable for transesterification of ethyl acetate with
butanol over 4% (w/w) B-USY were achieved with numerical technique (numerical
algorithm) built in the Design-Expert® Version 8.0.7.1 software. The numerical method
examines the design space by the developed model in the analysis to find factor settings that
meet the goal of maximizing the percentage yield of butyl acetate (response). The three
independent process parameters (Table 2) were fixed in the range among low (-1) and high
(+1) while the response (yield of butyl acetate) was set to maximum value.21 The most
favorable (optimum) parameters including the predicted and experimental yield of butyl
acetate are presented in Table 3. The experimental value of yield of butyl acetate showed in
table is an average of three independent experiments (Table 3). Yield of butyl acetate of 96%
is in fine agreement with the predicted value, with a moderately trivial error of 1.6%. Thus
the experimental error is fewer than ±5%, hence the projected statistical model was suitable
to predict the yield of butyl acetate by transesterification of butanol with ethyl acetate over
4% (w/w) B-USY.
2.4 Reusability of catalyst
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The reusability of 4% (w/w) B-USY catalyst was evaluated for transesterification of
DOI: 10.1039/C4RA14771E
butanol with ethyl acetate at the most favorable process parameters obtained by RSM design
(Table 3). After each catalytic run, the catalyst from product mixture was separated by
centrifugation and used for proceeding cycle without any post-treatment. The 4% (w/w) B-
USY catalyst was perceived to be firm for five catalytic cycles (fresh and four reuses) with
96% yield of butyl acetate (Fig. 7). Thereafter, for the sixth cycle marginal decrease in yield
of butyl acetate (96-94%) was observed. This implies that the 4% (w/w) B-USY catalyst is
highly active, reusable and stable and has a potential of further application.
2.5 Merits of present method
Recent findings revealed that butanol and ethyl acetate can be produced
by
economically viable fermentation process.2,8,9 Hence, heterogeneously catalyzed
transesterification of fermentation derived bio butanol with bioethylacetate would be a viable
process for production of butyl acetate, a renewable biofuel additive. The byproduct obtained
in this process, ethanol, can be once more used to produce ethyl acetate which get reused
again for transesterification.2,5 This method of production of butyl acetate from fermentation
derived reactants would be clean and green in devoid of the drawbacks associated with the
widely used Fischer and Speier esterification.22 Also, this process does not demand superior
grade (acetic acid resistant) stainless steel equipment and it is also lacking of waste water
(formed as product) removal complications and severe adulteration (linked with the usage of
homogeneous catalysts).
In this perspective, the current process of using of 4% (w/w) B-USY catalyst for
production bio-butyl acetate from fermentation source would be environmentally and
economical viable process offering additional principles of green chemistry and engineering
with prospective welfares regarding high catalytic activity (96%, yield of butyl acetate) at
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milder operating parameters, high catalyst stability (reusable for 6 catalytic cycles) (Fig. 7),
DOI: 10.1039/C4RA14771E
renewable and clean synthetic route and devoid of waste byproducts.
3 Conclusions
Transesterification of butanol with ethyl acetate to butyl acetate (biofuel additive) was
studied over modified zeolites. The outcomes achieved in current research discloses that 4%
(w/w) B-USY zeolite is highly active, stable (reusable for 6 cycles) and potential catalyst for
production of high yields (96%) of butyl acetate.
The RSM with BBD quadratic model (R2 = 0.9976) revealed that catalyst loading and
reaction temperature are the most significant parameters for transesterification while molar
ratio (butanol to ethyl acetate) is the least significant. The present method for the synthesis of
butyl acetate over 4% (w/w) B-USY catalyst is clean and sustainable, follows the principles
of green chemistry and engineering.
4 Experimental section
4.1 Materials
Ultra Stable Y (USY) zeolite having SiO2/Al2O3 molar ratio of 30 was procured from
Zeolyst, USA. Ethyl acetate (99.8%), butanol (99%) and H3BO4 were obtained from Sigma–
Aldrich (Sigma, St. Louis, USA).
4.2 Catalyst synthesis and characterization
Typically, 60.0 g of USY catalyst was taken into a 1000 ml round bottom flask and
then 600 ml of a 0.64% H3BO4 solution in water was added. The said mixture was refluxed at
363 K for 1 h under magnetic stirring. Then solvent was evaporated using rota vapor (353 K).
The material thus obtained was in white powder form and subjected for the stepwise
calcinations in presence of nitrogen at 593 K for 5 h. A calcined material was then obtained
with a 1% boron content and designated as 1% (w/w) B-USY. Similarly, other borated USY
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catalysts were prepared with boron content of 3% (w/w) B-USY and 4% (w/w) B-USY and
DOI: 10.1039/C4RA14771E
5% (w/w) B-USY.
Powder X-ray diffraction patterns of synthesized catalyst were recorded on X-ray
diffractometer (P Analytical PXRD system, Model X-Pert PRO-1712) using CuK radiation
at a scanning rate of 0.0671/s in the 2 ranging from 5 to 50o (Fig. 1).
Nitrogen isotherms (adsorption and desorption) of synthesized catalysts were obtained
at low temperature (77 K) with Beckman Coulter SA 3100 analyzer (CA, USA). The calcined
sample was degassed at 573 K for 10 h prior to measurements. The specific surface area is
calculated using Brunaer-Emmett-Teller (BET) method (Table 1).
Acidity of catalyst was measured by temperature programmed desorption of ammonia
(TPD-NH3) with Micromeritics AutoChem (2910, USA) (Table 1). These experiments were
performed in a gas-flow system equipped with thermal conductivity detector (TCD). Prior to
the measurements, the freshly calcined catalyst sample was dehydrated at 423 K in high
purity (99.995%) helium flow (50 mL min−1) for 1 h. The temperature was then reduced to
343 K and NH3 was permitted to adsorb by exposing catalyst sample to a gas stream
encompassing of 10% NH3 in helium for 1 h. The sample was then flushed with helium for
another 1 h. The NH3 desorption was performed in helium flow (50 mL min−1) by rising the
temperature up to 873 K at heating rate of 10 K min−1.
4.3 Reaction of transesterification and analysis
The USY (parent) and different percentage (1-5%) borated USY catalysts were used
for transesterification of butanol with ethyl acetate to obtain butyl acetate (renewable biofuel
additive). The butanol, ethyl acetate and catalyst were sequentially added into 50 mL two-
necked round bottom glass flask fortified with a reflux condenser, a magnetic stirrer and a
thermometer. The temperature accuracy of ±0.5 K was maintained with an electric-heated
thermostatic oil bath. The reaction is allowed to run for desired time (1-5 h) at the set
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temperature (353–393 K) and after completion of reaction the catalyst from liquid product
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mixture was removed by centrifugation.
The obtained liquid product mixture was analyzed with gas chromatography (GC)
Chemito GC-1000, capillary column, BP-1 (50 m length and 0.3 mm width) equipped with
Flame Ignition Detector (FID) within programmable temperature range of 313 K to 473 K by
using with Nitrogen as a carrier gas. The GC-MS (Agilent-5977-AMSD) was used to confirm
the reaction products.
4.4 Box–Behnken experimental design
RSM with Design-Expert® Version 8.0.7.1 (Stat- Ease, Inc., Minneapolis, USA) was
used to design the experiments for the reaction parameters used for the transesterification of
butanol with an ethyl acetate over 4% (w/w) B-USY catalyst to synthesize butyl acetate
biofuel additive. The RSM design with three process variables was performed to gain the
optimum process parameters for transesterification reaction. The three independent process
variables selected were percentage catalyst loading (X1), butanol to ethyl acetate molar ratio
(X2) and reaction temperature (X3). The variables and their coded and uncoded values are
presented in Table 2. The percentage yield of butyl acetate (Y) was selected as
response/target parameter.
The 33 Box-Behnken experimental design (BBD) involving 17 set of experimental
runs consisting of 12 factorial points and 5 center points were performed.10-12,17,18 These fully
randomized experiment formulations consist of all possible combinations of the independent
variables at all levels.
The interaction between process variables and maximization of response (Y) was
performed by second-order quadratic model.10-12
푛
푛
푛−1
푛
2
푌 = 훼0 + ∑ 훼 푋 + ∑ 훼 푋 + ∑ ∑ 훼 푋 푋
푖 푖 푖푖 푖 푖푗 푖 푗
푖=1
푖=1
푖=1
푗=2
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(1)
DOI: 10.1039/C4RA14771E
(1)
Where, Y is the percentage yield of butyl acetate (response variable). The parameters
Xi and Xj are independent process variables. The terms of o, αi, ij are the regression
,
ii
coefficient, the linear term and squared term for the process variable i and the interaction
terms among variables i and j, respectively. The n is the total number of variables (in this
case, n = 3) used to study influence on the yield of butyl acetate. Each process variable was
coded into levels -1, 0 and +1 and shown in Table 2.
The polynomial equation was used to correlate the response and experimental levels
of each factor. The central composite rotatable design was employed to obtain second-order
regression coefficients (R2). Its significance of coefficient of regression was evaluated by the
value of F-test.
The most favorable process parameters for transesterification were achieved by
investigating the three dimensional (3D) response surfaces, two dimensional (2D) contour
plots and computing the regression equation.
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References
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H. Laavi, J. P. Pokki, P. Uusi-Kyyny, A. Massimi, Y. Kim, E. Sapei, V. Alopaeus, J.
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S. H. Ali, O. Al-Rashed, F. A. Azeez, S. Q. Merchant, Bioresource. Technol., 2011, 21,
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D. A. Ruiz, U. S. Patent, 07846223, 2010.
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Manage., 2013, 65, 392-396.
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Ayub, R. C. Rodrigues, Process Biochem., 2011, 46, 2311-2316.
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277-282.
16 L. Wai, X. Li, L. Yanxun, L. Tingliang, L. Guoji, Chem. Eng. Technol., 2013, 36, 559-
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566.
17 X. X. Han, Y. F. He, C. T. Hung, L. L. Liu, S. J. Huang, S. B. Liu, Chem. Eng. Sci.,
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19 L. Osiglio, M. Blanco, Procedia Materials Science, 2012, 1, 491-498.
20 C. H. Su, Bioresource. Technol., 2013, 130, 522-528.
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22 E. Fischer, A. Speier, Chemische Berichte, 1895, 28, 3252-3258.
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Figure captions:
Powder X-ray diffraction patterns of USY, 1% (w/w) B-USY and 4% (w/w) B-USY
catalyst.
Fig. 1
Catalytic performance of synthesized catalysts for transesterification of ethyl acetate
with butanol at catalyst loading of 5%, molar ratio (butanol to ethyl acetate) of 2:1 and
reaction temperature of 373 K.
Fig. 2
Plot of actual versus predicted values of butyl acetate yield over 4% (w/w) B-USY
catalyst.
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Response surface and contour plot for synthesis of butyl acetate as a function of molar
ratio and catalyst loading at reaction time of 4 h and reaction temperature of 373 K.
Response surface and contour plot for synthesis of butyl acetate as a function of molar
ratio and reaction temperature at reaction time of 4 h and catalyst loading of 15%.
Response surface and contour plot for synthesis of butyl acetate as a function of catalyst
loading and reaction temperature at reaction time of 4 h and molar ratio (butanol to ethyl
acetate) of 4:1.
Reusability of 4% (w/w) B-USY catalyst for the synthesis of butyl acetate at most
favorable process parameters: molar ratio of 4:1, catalyst loading of 20%, reaction time
of 4 h and reaction temperature of 383 K.
Fig. 7
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4% (w/w) B-USY
1% (w/w) B-USY
USY
5
10
15
20
25
30
35
40
45
50
2(degree)
Fig. 1
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60
50
40
30
20
10
0
Blank
USY
1% (w/w) B-USY
3% (w/w) B-USY
4% (w/w) B-USY
5% (w/w) B-USY
0
1
2
3
4
5
Reaction Time (h)
Fig. 2
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Fig. 3
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Fig. 4
23

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Fig. 5
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Fig. 6
25

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100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
Number of cycle
Fig. 7
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Table 1 Physico-chemical properties of catalysts.
Catalyst
BET Surface Area (m2 g-1)
Total Acidity (µmol g-1)
USY
839
790
771
765
753
378
511
587
640
662
1% (w/w) B-USY
3% (w/w) B-USY
4% (w/w) B-USY
5% (w/w) B-USY
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Table 2 Selected variables and coded levels used in the Box-Behnken design.
Variables
Symbol
Coded levels
-1
5
0
15
4
+1
25
6
Catalyst Loading (wt. % of ethyl acetate)
Molar Ratio (butanol to ethyl acetate)
Reaction Temperature (K)
X1
X2
X3
2
353
373
393
28