A SINGLE STEP PROCESS FOR THE PREPARATION OF BUTYL ACETATE

Abstract

The present invention discloses a single step, environmentally and economical viable process for the preparation of butyl acetate from ethyl acetate and n-butanol with high yield using boron loaded zeolite catalyst.

Claims

1. A single step transesterification process for the preparation of butyl acetate comprising heating a reaction mixture of n-butanol, ethyl acetate and boron loaded zeolite (B-USY) catalyst for the period in the range of 1 to 10 hr, wherein that yield of butyl acetate is 50-96%.

2. The process as claimed in claim 1, wherein ethyl acetate to butanol molar ratio range is 1:1 to 1:6.

3. The process as claimed in claim 1, wherein catalyst loading is in the range of 5-30%.

4. The process as claimed in claim 1, wherein catalyst loading is in the range of 20-30%.

5. The process as claimed in claim 1, wherein the boron loading in said catalyst is in the range of 1-7%.

6. The process as claimed in claim 1, wherein the boron loading in said catalyst is 4%.

7. The process as claimed in claim 1, wherein said reaction is carried out at temperature in the range of 80-120° C.

8. The process as claimed in claim 1, wherein said process is carried out in batch or continuous mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1: Powder X-ray diffraction patterns of USY, 1% (w/w) B-USY and 4% (w/w) B-USY catalyst

[0029] FIG. 2: SEM of the catalyst prepared for the synthesis of butyl acetate.

[0030] FIG. 3: 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 100 ° C.

[0031] FIG. 4: 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 100° C.

[0032] FIG. 5: 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%.

[0033] FIG. 6: 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.

[0034] FIG. 7: 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 110 C.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Present invention provides a single step, environment friendly, environmentally and economical viable process for the preparation of butyl acetate, offering additional principles of green chemistry and engineering with prospective welfares regarding high catalytic activity (96%, yield of butyl acetate) at milder operating parameters, high catalyst stability and clean synthetic route and devoid of waste byproducts using boron loaded zeolite catalyst.

[0036] The present invention provides a single step process for the conversion of ethyl acetate to butyl acetate catalyzed by boron loaded zeolite catalyst, characterized in that boron loading is in the range of 1-7% and yield of butyl acetate is >50%.

[0037] The present invention provide a single step trans esterification process for the preparation of butyl acetate comprises of heating the reaction mixture of n-butanol, ethyl acetate and boron loaded zeolite (B-USY) catalyst for the period of 1-10 hr, characterized in the yield of butyl acetate is 96%.

[0038] The ratio of ethyl acetate: butanol is in the range of 1:1 to 1:6.

[0039] Boron loading in said catalyst is in the range of 1-7% preferably 4%.

[0040] The process may be batch or continuous and is carried out at temperature in the range of 80-120° C.

[0041] The catalyst loading for said process is in the range of 5-30% preferably 20-30%.

[0042] The present invention provides a new heterogeneous catalyst comprising boric acid (H.sub.3BO.sub.3) supported on dealuminated HY (USY) for transesterification of ethyl acetate with n-butanol.

[0043] The catalyst is prepared by refluxing zeolite with a solution of boric acid solution in water, evaporating the water to obtain a white powder and calcining the powder in air at 500-600° C. for 1-10 hours.

[0044] The powder X-ray diffraction patterns of synthesized catalyst is recorded on X-ray diffractometer (P Analytical PXRD system, Model X-Pert PRO-1712) using CuKoc radiation at a scanning rate of 0.0671/s in the 2θ ranging from 5 to 50° (FIG. 1).

[0045] The nitrogen isotherms (adsorption and desorption) of synthesized catalysts are obtained at low temperature (77 K) with Beckman Coulter SA 3100 analyzer (CA, USA). The calcined sample is degassed at 573 K for 10 h prior to measurements. The specific surface area is calculated using Brunaer-Emmett-Teller (BET) method (Table 1).

[0046] The acidity of catalyst is measured by temperature programmed desorption of ammonia (TPD-NH.sub.3) with Micromeritics AutoChem (2910, USA) (Table 1). These experiments are performed in a gas-flow system equipped with thermal conductivity detector (TCD). Prior to the measurements, the freshly calcined catalyst sample is dehydrated at 150° C. in high purity (99.995%) helium flow (50 mL min.sup.−1) for 1 h. The temperature is then reduced to 70° C. and NH.sub.3 is permitted to adsorb by exposing catalyst sample to a gas stream encompassing of 10% NH.sub.3 in helium for 1 h. The sample is then flushed with helium for another 1 h. The NH.sub.3 desorption is performed in helium flow (50 mL min.sup.-1) by rising the temperature up to 500° C. at heating rate of 10 K min.sup.−1.

[0047] 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 are 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 is found that, the circular contours denotes the negligible interaction between the corresponding variables. 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.

[0048] From FIG. 4 it is clear that, 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 is also observed to be proportional to catalyst amount used; revealing that the reaction proceeds through a pure heterogeneous mechanism.

[0049] 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 100 C, the yield of butyl acetate is observed to be slightly increased from 85 to 90%. More dilution of reactants with increase in the molar ratio at limited catalyst active sites does 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 may 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 is preferred.

[0050] 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 is exhibited by ellipse mound shape of two dimensional contour curves (FIG. 5) and it is also evident from low p-value (0.0002) of X.sub.1X.sub.3 interaction term. With elevating temperature the yield of butyl acetate is observed to be linearly increased. This is in agreement with the Arrhenius law, a higher temperature results in a higher rate of transesterification leading to higher yield of butyl acetate. The reaction temperature is found to be highly influencing parameter on the yield of butyl acetate and this is also evident from low p-value (<0.0001).

[0051] 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 80 to 120 C, 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 significant on yield of butyl acetate, which is also supported by low p-value.

[0052] From this study, catalyst loading and reaction temperature are found to be most contributing terms while molar ratio is 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.

[0053] The most favorable process variable for transesterification of ethyl acetate with butanol over 4% (w/w) B-USY are 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) are fixed in the range among low (−1) and high (+1) while the response (yield of butyl acetate) is set to maximum value. The most favorable (optimum) parameters including the predicted and experimental yield of butyl acetate are presented in Table 4.

[0054] The experimental value of yield of butyl acetate showed in table is an average of three independent experiments (Table 4). 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 is suitable to predict the yield of butyl acetate by transesterification of butanol with ethyl acetate over 4% (w/w) B-USY.

[0055] The reusability of 4% (w/w) B-USY catalyst is evaluated for transesterification of butanol with ethyl acetate at the most favorable process parameters obtained by RSM design (Table 4). After each catalytic run, the catalyst from product mixture is separated by centrifugation and used for proceeding cycle without any post-treatment. The 4% (w/w) B-USY catalyst is 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%) is observed. This implies that the 4% (w/w) B-USY catalyst is highly active, reusable and stable and has a potential of further application.

EXAMPLES

[0056] The following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.

[0057] Ultra Stable Y (USY) zeolite having SiO.sub.2/Al.sub.2O.sub.3 molar ratio of 30 was procured from Zeolyst, USA. Ethyl acetate (99.8%), butanol (99%) and H.sub.3BO.sub.4 were obtained from Sigma-Aldrich (Sigma, St. Louis, USA).

Example 1

Catalyst Synthesis and Characterization

[0058] Typically, 60.0 g of USY catalyst was taken into a 1000 ml round bottom flask and then 600 ml of a 0.64% H.sub.3BO.sub.4 solution in water was added. The said mixture was refluxed at 90 C for 1 h under magnetic stiffing. Then solvent was evaporated using rotavapor (80 C). The material thus obtained was in white powder form and subjected for the stepwise calcinations in presence of nitrogen at 320 C for 5 h. A calcined material was then obtained with 1% boron content and designated as 1% (w/w) B-USY. Similarly, other borated USY catalysts were prepared with boron content of 3% (w/w) B-USY and 4% (w/w) B-USY and 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 20 ranging from 5 to 50° (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 300 C 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-NH.sub.3) 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 150° C. in high purity (99.995%) helium flow (50 mL min.sup.−1) for 1 h. The temperature was then reduced to 70° C. and NH.sub.3 was permitted to adsorb by exposing catalyst sample to a gas stream encompassing of 10% NH.sub.3 in helium for 1 h. The sample was then flushed with helium for another 1 h. The NH.sub.3 desorption was performed in helium flow (50 mL min.sup.−1) by rising the temperature up to 600° C. at heating rate of 10 K min.sup.−1.

TABLE-US-00001 TABLE 1 Physico-chemical properties of catalys Catalyst BET Surface Area (m.sup.2 g.sup.−1) Total Acidity (μmol g.sup.−1) USY 839 378 1% (w/w) B-USY 790 511 3% (w/w) B-USY 771 587 4% (w/w) B-USY 765 640 5% (w/w) B-USY 753 662

[0059] A. Dealuminated HY (USY) catalyst treated with 2.57% H.sub.3BO.sub.3 ie (4% B/USY)

[0060] 60.0 g of dealuminated HY (USY-720) catalyst was taken into a 1000 ml ound bottom flask and then 600 ml of a 2.57% H.sub.3BO.sub.3 solution in water was added. The said mixture was refluxed at 90° C. for 1 hour under magnetic stiffing. Then solvent was evaporated using rota vapour (80° C.). The material thus obtained was in white powder form and then subjected to stepwise calcination in presence of air at 550° C. for 5 h. The calcined material was then obtained with a boron content of 4%.

[0061] The same procedure for synthesis was exercised for other boronated USY samples, 2% B/USY and 5% B/USY.

Example 2

Reaction of Transesterification and Analysis

[0062] 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 temperature (80-120° C.) and after completion of reaction the catalyst from liquid product 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 40° C. to 200° C. by using with Nitrogen as a carrier gas. The GC-MS (Agilent-5977-AMSD) was used to confirm the reaction products.

Example 3

[0063] i. Catalyst characterizations

[0064] 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 Blanco reported that, boric acid calcined at 320 C presents sharp peaks at 20 of 14.8° and 27.9°, 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 Bronsted acid sites.

[0065] ii. Catalytic Performance of Catalysts

[0066] 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 100° C., 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 bars in the FIG. 2. The activity trend at reaction time of 4 h follows: 5% (w/w) B-USY (53%)>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. 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.

[0067] iii. Statistical Analysis of RSM and Influence of Process Parameters

[0068] a. Development of Regression Model Equation

[0069] 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. All experiments were performed in triplicate at fixed reaction time of 4 h and average value of butyl acetate yield is presented. FIG. 3 implied that there was no noticeable variation among the actual and predicted response values.

TABLE-US-00002 TABLE 2 Selected variables and coded levels used in the Box-Behnken design. Coded levels Variables Symbol −1 0 +1 Catalyst Loading (wt. X.sub.1 5 15 25 % of ethyl acetate) Molar Ratio (butanol X.sub.2 2 4 6 to ethyl acetate) Reaction X.sub.3 353 373 393 Temperature (K)

[0070] b. Analysis of Variance (ANOVA)

[0071] Statistical analysis based on the analysis of variance (ANOVA) was employed for fitting second order quadratic model. 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 significant model terms. In present case X.sub.1, X.sub.2, X.sub.3, X.sub.1X.sub.2, X.sub.2X.sub.3, X.sub.1.sup.2, X.sub.2.sup.2 and X.sub.3.sup.2 are significant model terms. The statistical significance data corresponding to individual parameter in Table 3 revealed that, linear term of catalyst loading (X.sub.1) and reaction temperature (X.sub.3) has significant influence on the butyl acetate yield owing to the high F-value and low p-values. The quadratic term of catalyst loading (X.sub.1), F-value 407.14 was observed to be more important than the reaction temperature (X.sub.3), F-value 239.51 and the molar ratio (X.sub.2), F-value 36.88. Moreover, the consequence of interaction between molar ratio and reaction temperature (X.sub.2X.sub.3) also influenced the butyl acetate yield expressively (F-value 232.63) as is specified by the p-value (p<0.0001).

TABLE-US-00003 TABLE 3 ANOVA for response surface quadratic model. p-value Source Sum of squares Df Mean square F-value Prob > F Model 4998.24 9 555.36 323.96 <0.0001 X.sub.1 2112.5 1 2112.5 1232.29 <0.0001 X.sub.2 40.5 1 40.5 23.63 0.0018 X.sub.3 1200.5 1 1200.5 700.29 <0.0001 X.sub.1X.sub.2 2.25 1 2.25 1.31 0.2896 X.sub.1X.sub.3 90.25 1 90.25 52.65 0.0002 X.sub.2X.sub.3 272.25 1 272.25 158.81 <0.0001 X.sub.1.sup.2 697.96 1 697.96 407.14 <0.0001 X.sub.2.sup.2 63.22 1 63.22 36.88 0.0005 X.sub.3.sup.2 410.59 1 410.59 239.51 <0.0001 Residual 12.0 7 1.71 — — Lack of Fit 12.0 3 4.0 — — Pure Error 0 4 0 — — Cor Total 5010.24 16 — — — R.sup.2 = 0.9976; R.sup.2-adjusted = 0.9945; R.sup.2-predicted = 0.9617; CV = 1.76%

[0072] c. Model fitting

[0073] The regression equation (Eq. (1)) and coefficient of determination (R.sup.2) were used to evaluate the suitability/fit of model. A high value of the coefficient of determination (R.sup.2=0.9976) indicated 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 R.sup.2 (R.sup.2-predicted =0.9617) was in equitable covenant with the adjusted R.sup.2 (R.sup.2-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. 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 transesterification reaction aiming to maximize the yield of butyl acetate and to make the process economical and industrially benign.

[0074] d. Influence of Process Variables on Yield of Butyl Acetate

[0075] 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 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. 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.

[0076] 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 (100 C), 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 4), 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 100 C, the yield of butyl acetate was observed to be slightly increased from 85 to 90%. More dilution of reactants with increase in the molar ratio at limited catalyst active 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 (X.sub.2) and catalyst loading (X.sub.1) was found to be insignificant with shape of two dimensional contour curve circular (FIG. 3) and with high p-value (0.2896) of X.sub.1X.sub.2 interaction term.

TABLE-US-00004 TABLE 4 Most favorable process parameters for trans-esterification of ethyl acetate with butanol over 4% (w/w) B-USY for reaction time 4 h and validation model adequacy Molar Catalyst ratio loading, butanol to X.sub.1 ethyl Reaction Process (wt. acetate), temperature, Yield of Parameters %) X.sub.2 X.sub.3 (K) Butyl acetate, Y (%) Predicted 19.7 4.3 383.3 97.6 Experimental 20 4 383 96

[0077] 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 X.sub.1X.sub.3 interaction term. 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. 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).

[0078] 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 80-120 C, 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 significant on yield of butyl acetate, which was also supported by low p-value (<0.0001).

[0079] 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.

[0080] e. Obtaining most Favorable Process Parameters by RSM and Model Validation

[0081] 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. The most favorable (optimum) parameters including the predicted and experimental yield of butyl acetate are presented in Table 4. The experimental value of yield of butyl acetate showed in table is an average of three independent experiments (Table 4). 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.

[0082] iv. Reusability of Catalyst

[0083] The reusability of 4% (w/w) B-USY catalyst was evaluated for transesterification of butanol with ethyl acetate at the most favorable process parameters obtained by RSM design. 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.

[0084] v. Box—Behnken Experimental Design

[0085] 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 (X.sub.1), butanol to ethyl acetate molar ratio (X.sub.2) and reaction temperature (X.sub.3). 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.

[0086] The 3.sup.3 Box-Behnken experimental design (BBD) involving 17 set of experimental runs consisting of 12 factorial points and 5 center points were performed. These fully randomized experiment formulations consist of all possible combinations of the independent variables at all levels.

[0087] The interaction between process variables and maximization of response (Y) was performed by second-order quadratic model.

[00001]$Y={\alpha }_0+\underset{i=1}{\overset{n}{.Math.}}.Math..Math.{\alpha }_i.Math.X_i+\underset{i=1}{\overset{n}{.Math.}}.Math..Math.{\alpha }_{\mathrm{ii}}.Math.X_i^2+\underset{i=1}{\overset{n-1}{.Math.}}.Math..Math.\underset{j=2}{\overset{n}{.Math.}}.Math..Math.{\alpha }_{\mathrm{ij}}.Math.X_i.Math.X_j$

[0088] Where, Y is the percentage yield of butyl acetate (response variable).The parameters X.sub.i and X.sub.j are independent process variables. The terms of α.sub.o, α.sub.i, α.sub.ii, a.sub.ij are the regression 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.

[0089] 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 (R.sup.2). 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.

Example 4

[0090] Catalyst Characterization

[0091] A. Physico-chemical properties of USY catalyst

TABLE-US-00005 Properties USY Molar ratio SiO.sub.2/Al.sub.2O.sub.3 32 % Crystallinity >95% Phase HY Pore Opening 6.1 Å Particle Size 0.6-0.7 μm BET Surface Area 839 m.sup.2/g Appearance White powder Odor Odorless Ph Not Applicable Solubility in Water Negligible

Advantages of the Invention

[0092] Batch and continuous modes possible [0093] Water is not wasted as by product [0094] Conversion rate is high [0095] Recyclable catalyst