Enhancement in Conversion and Selectivity of Trivalerin Using

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Enhancement in Conversion and Selectivity of Trivalerin using Reactive Distillation Kamalpreet Kaur, Ravinder Kumar Wanchoo, and Amrit Pal Toor Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b02098 • Publication Date (Web): 08 Sep 2017 Downloaded from http://pubs.acs.org on September 12, 2017

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Industrial & Engineering Chemistry Research

Enhancement in Conversion and Selectivity of Trivalerin using Reactive Distillation Kamalpreet Kaur†, Ravinder Kumar Wanchoo†, Amrit Pal Toor†,‡,* †

Dr. S.S.B. University Institute of Chemical Engineering and Technology, Panjab University, Chandigarh, 160014, India ‡

Energy Research Centre, Panjab University, Chandigarh, 160014, India

Abstract: The feasibility and potential of reactive distillation was studied to evaluate the enhancement in trivalerin selectivity in the esterification of valeric acid with glycerol using noctane as an entrainer over sulfated iron oxide catalyst. Effect of process parameters such as entrainer loading, reaction temperature and reaction time was evaluated. Results have indicated that the selectivity towards trivalerin can be enhanced up to 95.07%, in comparison to batch process (74.80%) using stoichiometric molar ratio which describes the novelty of this work. Kinetic models such as Pseudohomogeneous, Eley Rideal and Langmuir-Hinshelwood model were used to study the kinetics of the reaction. Eley Rideal model supported the proposed mechanism with higher reliability and accuracy, resulting in the activation energy of 23.77 kJ/mol, which is plausibly less as compared to batch process (27.37 kJ/mol). KEYWORDS: Esterification, Glycerol, Sulfated iron oxide, Reactive distillation, Entrainer, Trivalerin 1. Introduction Glycerol is a well identified byproduct from transesterification reaction involved in biodiesel production. Nowadays, several important organic processes utilize glycerol as feedstock to produce value added products.1-3 Production of industrial and pharmaceutical imperative esters through esterification of glycerol is one of the organic reactions that are worth executing.4-5 Glyceryl esters are used as diesel additives, solvents in oil, coating, paint, and emulsifier, industrial and pharmaceutical intermediates.6-13 Glyceryl esters can be produced through two pathways: i) direct esterification in batch reactor and ii) reactive distillation. Batch esterification involves the reaction to proceed under reflux conditions in the presence of active catalyst. Whereas, reactive distillation allocates to work under anhydrous 1 ACS Paragon Plus Environment


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conditions, i.e. removal of water along with reaction is taken into account to shift the reaction towards forward ester formation. In general, reactive distillation couples chemical reaction along with product separation in one unit.14-16 This overcomes the need to use excess of one of the reactants in the case of batch reaction that increases the overall economics of process. In addition to many advantages, there are still shortcomings related to batch reaction process such as use of high molar ratios and catalyst loadings, less selective products, high reaction temperatures and long reaction hours. Conversion is also limited by both chemical equilibrium and reaction rate.1718

Reactive distillation rewards in achieving high selective desired product using low molar ratio

and catalyst loading in short reaction time, therefore, enhanced performance. Due to the high latent heat of water, the proper choice of entrainer should be made carefully. The need of active catalyst for esterification reaction is still appraised to accomplish the system successfully.19-20 From recent years, a large number of catalysts have been synthesized and evaluated for their catalytic activity in glycerol esterification with acetic acid such as ion exchange resins and zeolites i.e. Amberlyst 15, Amberlyst 35, HZSM-5, HUSY, heteropolyacids i.e. H3PW12O40 , silver exchanged tungstophosphoric acid, dodecatungstophosphoric acid immobilized into a silica matrix and Mesoporous Organo-silica Functionalized with Sulfonic Acid Groups, graphene oxide, carbon based acid catalysts, heteropoly acids, K-10 montmorillonite, niobic acid, niobium supported SBA-15, sulfated alumina etc.11, 21-27 Low chain esterification catalyzed systems are uncomplicated to be investigated owing to its effortlessness, short reaction time, easy availability and less probability of side product formation. However, inference on higher glycerol esterification systems is still limited due to its complexity and hence, difficult to conclude.13 Consequently, attempt has been made to broaden improved perceptive for higher heterogeneous acid catalyzed esterification systems, a set of experiments were performed for glycerol esterification with valeric acid using reactive distillation over sulfated iron oxide. In distinction to extensive review, barely research work has been done in this area, which still needs to be explored for superior findings. Detailed optimization of process parameters affecting the esterification of glycerol with valeric acid is described in our earlier work. The entire work was based on the perception to study the esterification of glycerol with valeric acid in batch reactions using Response Surface Methodology (RSM).13 However, the detailed parametric studies on reactive distillation for the production of trivalerin have not been studied. 2 ACS Paragon Plus Environment

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2. EXPERIMENTAL SECTION 2.1. Materials Valeric acid (with purity > 99%); glycerol (with purity >99%), and n-octane (purity >99.5%), were procured from Merck. Sulfated iron oxide was used as catalyst and synthesized as procedure mentioned in our previous work.13, 28-29 2.2. Apparatus and Reaction Procedure All the esterification reactions were conducted in 500 mL three necked flat bottom glass flask placed on magnetic stirrer to ensure proper mixing of reactants. Thermometer and sampling port were attuned in the two necks of reactor. Figure 1 shows the scheme of batch reactive distillation, which consists of reactive column (height= 340 mm, width= 22 mm) connected with reflux condenser for circulating chilled water to condense the vapor mixture of both organic and aqueous phases. It is further equipped with decanter of the capacity of 500 mL (height = 0.5 m, width = 12 mm), used to separate aqueous layer from organic layer. Level should be maintained to ensure the refluxing back of organic layer to reaction mixture by collecting the aqueous layer consequently. Reaction temperature was maintained within accuracy of ±0.2 °C. Valeric acid, n-octane and sulfated iron oxide catalyst were preheated to desired temperature in the reactor. Glycerol was heated separately in glass vessel and charged to reactor when attained the desired reaction temperature to reactor. The mixture was immediately stirred on and the time was considered as zero reaction time. The reaction samples were collected after particular time interval and analyzed for acid conversion through acid base titration and gas chromatography. Experiments in range of reaction temperature (388.15- 453.15K) and entrainer loading (0.0040.024 m3/m3 of reaction mixture) were studied. All the reactions were carried out at the optimum catalyst loading of 13.0 kg/m3 and stirring speed of 500 RPM keeping the molar ratio constant at 1:3 (Glycerol: Valeric acid) as reported in our earlier research work till the equilibrium was attained.13 2.3. Analysis The reaction progress was monitored by acid conversion through potentiometric titration with 0.18 N NaOH and phenolphthalein indicator. Gas chromatography with mass spectrometry was used to quantify ester product (Trace 1300 GC, TSQ 8000, Triple Quadrupole MS HP (Thermofisher scientific, USA) (GC(MS)_SCION45P) using capillary column). Helium flow rate was set at 0.7 mL/min. Small aliquot of 1 μL from collected sample was diluted in 10 mL acetone. Oven 3 ACS Paragon Plus Environment


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temperature of gas chromatography was maintained at 60°C for 3 min and then was increased to 120°C and maintained for next 3 min. For next 7 min, oven temperature was further increased to 200°C. Thereafter, the oven temperature was next increased to 250°C and maintained for next 2 min to restart the column.

Figure 1. Experimental set up for Semi Batch Reactive distillation process 3. RESULTS AND DISCUSSION Esterification of glycerol with valeric acid is a combination of the successive reactions forming mono, di, and trivalerin as product esters as shown in following reactions 1-3: Glycerol+ Valeric acid ↔ Monovalerin + Water

(1)

Monovalerin +Valeric acid ↔ Divalerin + Water

(2)

Divalerin + Valeric acid ↔ Trivalerin + Water

(3)

3.1. Product Distribution Curve As the esterification reaction of valeric acid with glycerol proceeds, mono, di and trivalerin are formed as products along with n-amyl isovalerate as a side product as shown in our previous work for batch reactions.13 The product distribution was investigated for the reactions conducted using reactive distillation process at the reaction temperature of 453.15 K, catalyst loading of 13.0 kg/m3, stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid). At the initial phase of reaction i.e. after 5 min, maximum quantity of monvalerin and divalerin were formed along with 4 ACS Paragon Plus Environment

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traces of trivalerin. With the increase in reaction time up to 0.5 h, a decrease in the selectivity of monovalerin, divalerin and n-amyl isovalerate was observed along with an increase in the selectivity of trivalerin. This increase in trivalerin formation was due to the transformation of mono and divalerin to trivalerin along with increasing fractional conversion. This has resulted in decrease in mono and divalerin amount, which has correspondingly increased trivalerin selectivity. At the reaction time of 1 h, maximum of mono and divalerin has converted to trivalerin. After the time of 3 h, no significant variation in product distribution was observed as shown in Figure 2. MV

DV

TV

AV

120 100

% Selectivity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80 60 40 20 0 0

1

2

3

4

5

Time (h)

Figure 2. Effect of reaction time on selectivity of products at reaction temperature of 453.15 K, catalyst loading of 13.0 kg/m3, stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid) and entrainer loading of 0.02 m3/m3 of reaction mixture 3.2. Effect of Entrainer and its Loading on Fractional Conversion and Selectivity of Products During esterification, water is formed as a by-product. Entrainer in reactive distillation process is used to eliminate water obtained throughout the reaction, thus altering the equilibrium towards forward direction. Reactant conversion can be augmented to contribute in high product yield by employing pertinent entrainer. Based on this relevance, research work recommending the use of appropriate entrainer is accessible in literature to enhance the reactive distillation system efficiency. For the rationale of comparison, the effectiveness of semi-batch reactive distillation (SBRD) was explored by executing reactions both with and without the use of entrainer. The

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reactions were carried out at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3, RPM of 500 at the molar ratio of 1:3 (Glycerol: Valeric acid). In absence of entrainer, there was single phase i.e. no generous separation between organic and aqueous phase was accomplished. To attain the organic and aqueous phase, n-octane was used as the entrainer. This removal of water led to the increase in conversion of the valeric acid. This is due to the formation of an azeotrope with water at the temperature of 362.15 K, hence resulted in the separation of water at lower temperatures as compared to reaction temperatures. The difference between azeotrope and reaction temperature dictates the efficacy of separation of water from Valeric acid. The moderately large difference between azeotrope (water-octane) i.e. 362.15 K and reaction temperature (378.15-453.15 K) formulate it appropriate as entrainer in this esterification system. n-octane effectively separated aqueous layer from the organic layer, thus, removing water from the reaction system. This removal of water has increased conversion by around 23% as that obtained in a batch process at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3 and a stirring speed of 500 RPM using a molar ratio of 1:3 (Glycerol: Valeric acid) after the reaction time of 3 h as shown in Figure 3 (a). In addition, the equilibrium was achieved after the time period of 3 h in SBRD, which is reasonably prompt as compared to batch process i.e. 6 h in our previous study.13 0.8 0.7

Fractional conversion

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0.6 0.5 0.4

Batch

0.3

SBRD

0.2 0.1 0 0

1

2

3 4 Time (h)

5

6

7

Figure 3(a). Comparison of fractional conversion for batch and reactive distillation process at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3 and a stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid)


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Further, the effect of entrainer loading on fractional conversion was investigated in the range from 0.004 to 0.024 m3/m3 of reaction mixture. The reactions were performed at the catalyst loading of 13.0 kg/m3 and a stirring speed of 500 RPM keeping the molar ratio constant at 1:3 (Glycerol: Valeric acid). Figure 3 (b) shows the effect of entrainer loading on fractional conversion of valeric acid at the reaction temperature of 415.65 K. It was observed that the increase in entrainer loading has substantially enhanced the fractional conversion. The major enhancement was observed at the preliminary phase of the reaction and equilibrium has been achieved after the time of 3 h. Entrainer loading of 0.004 m3/m3 of reaction mixture has resulted in the fractional conversion of 0.635 after the reaction time of 3 h and increases up to 0.697 with an increase in entrainer loading up to 0.02 m3/m3 of reaction mixture. Beyond this, no considerable variation was observed as shown in figure 3(b). Hence, entrainer loading of 0.02 m3/m3 of reaction mixture was chosen to be optimum.

10 0.68 8

0.65 0.62

6

0.59

4

0.56 2

0.53 0.5

Acid amount collected in mL

Observed Fractional Conversion Actual Fractional Conversion

Fractional Conversion

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0 4 12 16 20 24 Entrainer Loading ( x103 m3/m3 of the reaction mixture)

Figure 3(b). Effect of entrainer loading (m3/m3 of reaction mixture) on fractional conversion at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3, the molar ratio of 1:3 (Glycerol: Valeric acid) and a stirring speed of 500 RPM after the time of 3 h The overall conversion also takes into consideration the acid lost in the aqueous layer from the decanter. The acid amount was estimated by acid-base titration of the sample of aqueous layer with 0.2 N NaOH. This elimination of acid through aqueous layer directly affects the actual conversion. Hence, the effect of entrainer loading on the acid amount in aqueous layer is an important parameter to be investigated. Figure 3 (b) also shows the acid amount in an aqueous layer along with fractional conversion with varied entrainer loading at the temperature of 415.65 7 ACS Paragon Plus Environment


K after the reaction time of 3 h. At the entrainer loading of 0.004 m3/m3 of reaction mixture, the acid amount in aqueous layer was found to be 3.16 x 10-3 m3/m3, which reduced to 2.0 x 10-4 m3/m3 with the increase in entrainer loading up to 0.02 m3/m3 of reaction mixture and the further increase has not contributed in any means. This may be due to more –COOH groups taking part in a reaction, hence, leading to more products. Because of the substantial acid amount present in aqueous layer, the distinction between actual and observed fractional conversion was observed. Furthermore, at the entrainer loading of 0.02 m3/m3 of reaction mixture, difference between actual and observed conversion was found to be very less as shown in Figure 3 (b). The effect of variation in entrainer loading from 0.004 to 0.02 m3/m3 of reaction mixture on product distribution was also investigated. Main products formed in batch esterification reaction were mono, di and trivalerin along with side product n-amyl isovalerate in large quantity.13 Figure 3 (c) represents the percentage selectivity of products along with the obtained acid conversion at varied entrainer loading. With an increase in entrainer loading from 0.012 to 0.02 m3/m3 of reaction mixture, due to increase in fractional conversion, trivalerin formation was also increased. However, formation of n-amyl isovalerate has decreased. No considerable amount of mono and divalerin was obtained after the reaction time of 3 h in the reaction. Further increase in entrainer loading has not favored both fractional conversion and trivalerin formation. Hence, increase in entrainer loading up to 0.02 m3/m3 of reaction mixture has favored the fractional conversion as well as the trivalerin formation, thus, was optimum at 0.02 m3/m3 of reaction mixture. 100 90 80 70 60 50 40 30 20 10 0

AV

TV

% Conversion 70 65 60 55 50 45

12 16 20 24 3 3 3 Entrainer loading ( x10 m /m of the reaction mixture)


% Conversion

% Selectivity

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Figure 3 (c). Effect of entrainer loading on acid conversion and percentage selectivity of products after the reaction time of 3 h at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3, molar ratio of 1:3 (Glycerol: Valeric acid) and stirring speed of 500 RPM 3.3. Effect of Reaction Temperature on Fractional Conversion and Selectivity of Products The effect of reaction temperature on both fractional conversion and percentage selectivity of ester products was examined. The catalyst loading taken was 13.0 kg/m3, stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid). The increase in temperature has favored the fractional conversion and achieved to maximum at the highest temperature of 453.15 K. At the temperature of 403.15 K, the fractional conversion was observed to be 0.636. With increase in temperature to 415.65, 427.15, 439.65 and 453.15 K, the fractional conversion was achieved to be 0.693, 0.722, 0.74 and 0.774 respectively after the time of 3 h as shown in Figure 4. It was observed that maximum fractional conversion of 0.774 was obtained at the highest reaction temperature of 453.15 K. The reason behind increased conversion may be the increased movement and collisions between reactant molecules with increase in temperature, resulting in increased product selectivity. The effect of reaction temperature on the selectivity of products was also explored. Figure 4 shows the percentage selectivity of products along with the acid conversion at different reaction temperatures. At the low temperature of 403.15 K, selectivity towards trivalerin was 85.90%. With increase in temperature, trivalerin formation was favored along with decrease in n-amyl isovalerate was observed. Maximum of 95.07% selectivity towards trivalerin was achieved at the highest reaction temperature of 453.15 K.



AV

TV

% Conversion

100 90 80 70 60 50 40 30 20 10 0

90 80 70 60 50 40 30

% Conversion

% Selectivity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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20 10 0 403.15

415.65 427.15 439.65 Temperature (K)

453.15

Figure 4. Effect of reaction temperature on acid conversion and percentage selectivity of products at catalyst loading of 13.0 kg/m3, stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid) after the time of 3 h and entrainer loading of 0.02 m3/m3 of reaction mixture. 3.5. Kinetic Study Over heterogeneous catalysts, the general expression used for all the models are written in terms of activity in conduit to explain the non-ideal behavior of reaction mixture is as follows: −𝑟𝐴 = (1+𝐾

𝑎 𝑎 𝑘𝑓 𝑤𝑐𝑎𝑡 (𝑎𝐴 𝑎𝐵 − 𝐸 𝑊 ) 𝐾𝑒

(1)

𝐴 𝑎𝐴 +𝐾𝐵 𝑎𝐵 +𝐾𝐸 𝑎𝐸 +𝐾𝑊 𝑎𝑊 )𝑛

Where, rA is rate of reaction in terms of concentration of A component in kmol/L.h, aA, aB, aE and aW represents the activity of acid, alcohol, ester and water respectively, wcat is catalyst loading in kg/m3, kf is rate constant in kmol/kg.h, Ke is equilibrium reaction rate constant and KA, KB, KE and KW are adsorption constants for acid, alcohol, ester and water respectively, n is 0, 1 and 2 for PH, ER and LHHW model30-32. Rewriting equation 1 in the terms of fractional conversion, equation 2 is obtained: 2

dXA dt

𝑋 𝑋 𝑘𝑓 𝑤𝑐𝑎𝑡 𝑎𝐴𝑜 ((1−𝑋𝐴 )(𝑀− 𝐴 )− 𝐴 )

=

Where 𝐾𝑒 = (1−𝑋

3 3𝐾𝑒 𝑎𝐴𝑜 𝑋𝐴 𝑋𝐴 (1+𝐾𝐴 𝑎𝐴𝑜 (1−𝑋𝐴 )+𝐾𝐵 𝑎𝐴𝑜 (𝑀− )+𝐾𝐸 +𝐾𝑊 𝑎𝐴𝑜 𝑋𝐴 )𝑛 3 3

𝑋𝑒2 , 𝐴𝑒 )(3𝑀−𝑋𝐴𝑒 )

𝐶

(2)

M is molar ratio of alcohol to acid; M= 𝐶𝐵𝑜, XA is the fractional 𝐴𝑜 10 ACS Paragon Plus Environment

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conversion of acid and XAe is the conversion at equilibrium. PH, ER and LHHW models were fitted to the experimental data obtained for this esterification system by the least squares method where the objective function was consisted of the sum of the square of relative errors of the valeric acid, glycerol, trivalerin and water concentrations. Concentrations were measured in terms of fractional conversion in all the experiments. To represent the non-ideality of system, concentrations were then provided in terms of activities using UNIFAC method12 by calculating the group and interaction parameters as provided in Table 1.1 to 1.3 along with the values of r and q values. Table 1.1. Group Parameters for valeric acid and glycerol esterification system K

Rk

Qk

vk(1)

vk(2)

vk(3)

vk(4)

CH3

1

0.901

0.848

1

0

3

0

CH2

2

0.674

0.540

3

2

11

0

H2 O

3

0.920

1.400

0

0

0

1

COOH

4

1.301

1.224

1

1

0

0

COO

5

1.380

1.200

0

0

3

0

OH

6

1.000

1.200

0

3

0

0

CH

7

0.446

0.228

0

1

1

0

Table 1.2. Interaction Parameters for valeric acid and glycerol esterification system

CH3

CH3

CH2

CH

CH2CH2OH

H2 O

COOH

COO

0

0

0

737.5

1318

663.5

387.1



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CH2

0

0

0

737.5

1318

663.5

387.1

CH

0

0

0

737.5

1318

663.5

387.1

CH2CH2OH

-87.93

-87.93

-87.93

0

285.4

77.61

76.2

H2 O

580.6

580.6

580.6

-148.5

0

225.4

10.72

COOH

315.3

315.3

315.3

-17.59

-292

0

256.3

COO

114.8

114.8

114.8

109.9

1135

660.2

0

Table 1.3. UNIFAC values for r and q of reaction components Component

r

q

Valeric acid

4.225

4.692

Glycerol

3.551

4.152

Trivalerin

14.708

12.312

Water

0.920

1.400

This method was employed using a Microsoft Excel 2007 spreadsheet and the parameter estimation was done using the Solver tool. The rate parameters were estimated by calculating rate of reaction ‘r’ from the experimental data. Then the sum of the squares of the difference between the measured (rexp) and the calculated reaction rate rcal was minimized. The sum of (rexp –rcal)2 for all obtained data points was estimated up to ‘ith’ run. For the N number of experiments, the function to be minimized is given by minimum of the sum of squares as follows: 𝑟𝑒𝑥𝑝 −𝑟𝑐𝑎𝑙 2

𝜎 2 = ∑𝑁 𝑖=1 (

𝑁

)

(3)

Where 𝜎 2 is the minimum sum of squares, rexp is the experimental rate of reaction, rcal is the calculated rate of reaction and N are the number of performed experiments.


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Using Arrhenius equation, the values of forward rate constants obtained for different temperatures were plotted with inverse of temperature to estimate the activation energy required for the esterification reaction of valeric acid with glycerol as shown in Figure 5. 1.4 PH

1.2

ER

LHHW

1

kf (mol/ g.h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.8 0.6 0.4 0.2 0 0.0021

0.0022

0.0023 0.0024 -1 1/T (K )

0.0025

0.0026

Figure 5. Plot of kf versus 1/T for different models Batch and reactive distillation processes were compared for rate constants obtained at different temperatures. The values for corresponding temperatures are reported in Table 2. It can be seen from Table 2 that an increase in reaction temperature has also resulted in increase in the reaction rate constants. Table 2. Forward rate constant kf at different temperatures Temperature (K)

kf kmol/(kg.h)

KB

KW

388.15

0.31

1.210

3.021

403.15

0.38

1.100

2.123

415.65

0.50

1.155

1.899

427.15

0.56

1.090

1.567

439.65

0.71

0.825

1.532

453.15

0.89

0.627

1.321



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Activation energy from the above data was found to be 23.77 x 103 kJ/kmol for the esterification reaction of Valeric acid with glycerol using Eley Rideal model for reactive distillation process. For batch process, the activation energy was 27.37 x 103 kJ/kmol using Eley Rideal model, which is quite higher than obtained in reactive distillation process. The values of rate constants at different temperatures for both of the processes are compared in Table 3. Reactive distillation has found to be prompt as compared to batch process, thus, resulted in high trivalerin selectivity. Table 3. Comparison of rate constants for both batch and reactive distillation process by Eley Rideal model Temperature

Batch process

Reactive distillation

(K)

Activation energy =27.37 x 103

Activation energy =23.77 x 103

kJ/kmol

kJ/kmol

kf

KB

KW

kmol/(kg.h)

kf

KB

KW

kmol/(kg.h)

388.15

0.118

4.023

3.769

0.31

1.210

3.021

415.65

0.136

2.385

3.166

0.50

1.155

1.899

453.15

0.280

1.652

2.850

0.89

0.627

1.321

3.6. Comparison of SBRD with batch process Results obtained from reactive distillation were compared with the batch process for efficiency in terms of both Valeric acid conversion and selectivity of trivalerin, which is desired product. It was found that SBRD has provided enhanced performance with the conversion of 77.4% as compared to batch process i.e. 62% at the reaction temperature of 453.15 K, catalyst loading of 13.0 kg/m3, the molar ratio of 1:3 (Glycerol: Valeric acid) and a stirring speed of 500 RPM after the time of 3 h. This is due to increase in reaction rate in SBRD process due to the removal of water, hence, resulted in an increase in the conversion. Thus, the equilibrium was achieved after the reaction time of 3 h using reactive distillation as compared to batch process i.e. 6 h. Comparison of conversion at different reaction temperatures for both batch and reactive distillation process is shown in Figure 6(a).


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90 Batch

SBRD

80

% Conversion

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70 60 50 40 30 403.15

415.65

427.15 439.65 Temperature (K)

453.15

Figure 6(a). Comparison of percentage conversion obtained from batch and reactive distillation process at the catalyst loading of 13.0 kg/m3, the molar ratio of 1:3 (Glycerol: Valeric acid) and a stirring speed of 500 RPM Selectivity towards mono, di, trivalerin and side product was also compared at the temperature of 453.15 K obtained from both of the processes in Figure 6(b). Reactive distillation has shown substantial high selectivity towards trivalerin of about 95.07% at the temperature of 453.15 K, which is very high as compared to batch process i.e. 74.89%. The formation of n-amyl isovalerate was also suppressed throughout reactive distillation process, consequently, increasing the trivalerin formation. Hence, reactive distillation has provided better selectivity towards trivalerin as compared to batch process at different reaction temperatures as shown in Figure 6(c).


Batch

100 90 80 70 60 50 40 30 20 10 0 MC

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SBRD

DC

TC

AV

Figure 6(b). Comparison of % selectivity of products obtained from batch and reactive distillation process at catalyst loading of 13.0 kg/m3, the molar ratio of 1:3 (Glycerol: Valeric acid), stirring speed of 500 RPM and reaction temperature of 453.15 K (i) 80

Batch-TV

Batch-AV

70 60

% Selectivity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

% Selectivity


50 40 30 20 10 0 403.15

415.65 427.15 439.65 Temperature (K)


453.15

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RD-TV

% Selectivity

(ii) 100

RD-AV

90 80 70 60 50 40 30 20 10 0 403.15

415.65

427.15 439.65 Temperature (K)

453.15

Figure 6(c). Comparison of product selectivity obtained in (i) batch and (ii) reactive distillation process 3.7. Reusability Studies The reusability studies revealed that the catalyst retains the same activity till the six reaction cycles. It was observed that the acidity of the catalyst remains unaffected even after using in six consecutive reactions. After the six cycles, a decline in the activity was observed, which was due to the accumulation of ester on the surface of catalyst as shown in Figure 7. 80 78 76

% Conversion

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74 72 70 68 66 64 62 60 1

2

3

4

5 6 7 Reaction Cycles

Figure 7. Reusability studies of catalyst 17 ACS Paragon Plus Environment

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9

10


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4. CONCLUSIONS The synthesis of trivalerin by reactive distillation has been achieved by the esterification of valeric acid with glycerol over sulfated iron oxide as catalyst. The use of reactive distillation has shown extreme advantage over batch process both in the terms of conversion and trivalerin selectivity. Trivalerin selectivity has achieved to be maximum of 95.07% at the temperature of 453.15 K, entrainer loading of 0.02 m3/m3 of reaction mixture, molar ratio of 1:3 (Glycerol: Valeric acid) and catalyst loading of 13.0 kg/m3 at stirring speed of 500 RPM. However, for batch process, trivalerin selectivity was obtained to be 74.89% at similar reaction conditions. Moreover, the formation of side product i.e. n-amyl isovalerate was also suppressed throughout reactive distillation process, consequently, increasing the trivalerin formation. In addition equilibrium has been achieved promptly in SBRD (3 h) as compared to batch process (6 h). AUTHOR INFORMATION Corresponding Author * Amrit Pal Toor, E-mail: [email protected] Full Mailing address: Dr. SSB University Institute of Chemical Engineering & Technology, Panjab University, Chandigarh, Sector 14, India, Pin: 160014. ACKNOWLEDGEMENTS We acknowledge DST PURSE grant-II, TEQIP-II for financial assistance, SAIF/CIL Panjab University and Mr. Pankaj Samuel for carrying out GC-MS analysis of all the samples. Ms. Kamalpreet Kaur acknowledges UGC-MANF (Government of India: Award number: F117.1/2010/MANF-SIK-PUN-4555) for providing scholarship for the research work. REFERENCES (1) Zhou, C. -H.; Beltramini, J. N.; Fan, Y. -X.; Lu, G. Q. Chemoselective catalytic conversion of glycerol as a biorenewable source to valuable commodity chemicals. Chem. Soc. Rev. 2008, 37, 527.


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(2) Miyazawa, T.; Koso, S.; Kunimori, K.; Tomishige, K. Glycerol hydrogenolysis to 1,2propanediol catalyzed by a heat-resistant ion exchange resin combined with Ru/C. Appl. Catal., A 2007, 329, 30. (3) Bagheri, S.; Julkapli, N. M.; Yehye, W. A. Catalytic conversion of biodiesel derived raw glycerol to value added products. Renew. Sustainable Energy Rev. 2015, 41, 113. (4) Kong, P. S.; Aroua, M. K.; Daud, W. M. A. W. Conversion of crude and pure glycerol into derivatives: A feasibility evaluation. Renew. Sustainable Energy Rev. 2016, 63, 533. (5) Yang, F.; Hanna, M. A.; Sun, R. Value-added uses for crude glycerol--a byproduct of biodiesel production. Biotechnol. Biofuels 2012, 5, 1. (6) Okoye, P. U.; Hameed, B. H. Review on recent progress in catalytic carboxylation and acetylation of glycerol as a byproduct of biodiesel production. Renew. Sustainable Energy Rev. 2016, 53, 558. (7) Calero, J.; Luna, D.; Sancho, E. D.; Luna, C.; Bautista, F. M.; Romero, A.A.; Posadillo, A.; Berbel, J.; Verdugo-Escamilla, C. An overview on glycerol-free processes for the production of renewable liquid biofuels, applicable in diesel engines. Renew. Sustainable Energy Rev. 2015, 42, 1437. (8) Rahmat, N.; Abdullah, A. Z.; Mohamed, A. R. Recent progress on innovative and potential technologies for glycerol transformation into fuel additives: A critical review. Renew. Sustainable Energy Rev. 2010, 14, 987. (9) Zhu, S.; Zhu, Y.; Gao, X.; Mo, T.; Zhu, Y.; Li, Y. Production of bioadditives from glycerol esterification over zirconia supported heteropolyacids. Bioresour. Technol. 2013a, 130, 4. (10) Zhu, S.; Gao, X.; Dong, F.; Zhu, Y.; Zheng, H.; Li, Y. Design of a highly active silverexchanged phosphotungstic acid catalyst for glycerol esterification with acetic acid. J. Catal. 2013b, 306, 155. (11) Zhou, L.; Al-Zaini, E.; Adesina, A. A. Catalytic characteristics and parameters optimization of the glycerol acetylation over solid acid catalysts. Fuel 2013, 103, 617. (12) Kaur, K.; Wanchoo, R. K.; Toor, A. P. Facile Synthesis of Tributyrin Catalyzed by Versatile Sulfated Iron Oxide: Reaction Pathway and Kinetic Evaluation. Ind. Eng. Chem. Res. 2015, 55, 2534. (13) Kaur, K.; Wanchoo, R.K.; Toor, A.P. Elementary Transformation of Glycerol to Trivalerin: Design of an Experimental Approach. ACS Sustain. Chem. Eng. 2017, 5, 802. 19 ACS Paragon Plus Environment


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(14) Hasabnis, A.; Mahajani, S. Entrainer-Based Reactive Distillation for Esterification of Glycerol with Acetic acid. Ind. Eng. Chem. Res. 2010, 49, 9058. (15) Tian, H.; Huang, Z.; Qiu, T.; Wang, X.; Wu, Y. Reactive Distillation for Producing n-Butyl Acetate: Experiment and Simulation. Chin. J. Chem. Eng. 2012, 20, 980. (16) Kumar, R.; Mahajani, S. M. Esterification of Lactic acid with n-Butanol by rReactive Distillation. Ind. Eng. Chem. Res. 2007, 46, 6873. (17) Kumar, R.; Nanavati, H.; Noronha, S. B.; Mahajani, S. M. A continuous process for the recovery of lactic acid by reactive distillation. J. Chem. Technol. Biotechnol. 2006, 81, 1767. (18) Lai, I.-K.; Liu, Y.-C.; Yu, C.-C.; Lee, M.-J.; Huang, H.-P. Production of high-purity ethyl acetate using reactive distillation: Experimental and start-up procedure. Chem. Eng. Process. 2008, 47, 1831. (19) Sandesh, K.; JagadeeshBabu, P. E.; Math, S.; Saidutta, M. B. Reactive Distillation Using an Ion-Exchange Catalyst: Experimental and Simulation Studies for the Production of Methyl Acetate. Ind. Eng. Chem. Res. 2013, 52, 6984. (20) Suman, T.; Srinivas, S.; Mahajani, S. M. Entrainer Based Reactive Distillation for Esterification of Ethylene Glycol with Acetic Acid. Ind. Eng. Chem. Res. 2009, 48, 9461. (21) Ferreira, P.; Fonseca, I. M.; Ramos, A. M.; Vital, J.; Castanheiro, J. E. Glycerol acetylation over dodecatungstophosphoric acid immobilized into a silica matrix as catalyst. Appl. Catal., B 2009b, 91, 416. (22) Canck, E.D.; Dosuna-Rodríguez, I.; Gaigneaux, E.M.; Voort, P.V.D. Periodic Mesoporous Organosilica Functionalized with Sulfonic Acid Groups as Acid Catalyst for Glycerol Acetylation. Materials 2013, 6, 3556. (23) Balaraju, M.; Nikhitha, P.; Jagadeeswaraiah, K.; Srilatha, K.; Prasad, P. S. S.; Lingaiah, N. Acetylation of glycerol to synthesize bioadditives over niobic acid supported tungstophosphoric acid catalysts. Fuel Process. Technol. 2010, 91, 249. (24) Gao, X.; Zhu, S.; Li, Y. Graphene oxide as a facile solid acid catalyst for the production of bioadditives from glycerol esterification. Catal. Comm. 2015, 62, 48.


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(25) Arun, P.; Pudi, S. M.; Biswas, P. Acetylation of Glycerol over Sulphated Alumina: Reaction Parameter Study and Optimization Using Response Surface Methodology. Energy Fuels 2016, 30, 584. (26) Jagadeeswaraiah, K.; Balaraju, M.; Prasad, P. S. S.; Lingaiah, N. Selective esterification of glycerol to bioadditives over heteropoly tungstate supported on Cs-containing zirconia catalysts. Appl. Catal., A 2010, 386, 166. (27) Khayoon, M. S.; Hameed, B. H. Acetylation of glycerol to biofuel additives over sulfated activated carbon catalyst. Bioresour. Technol. 2011, 102, 9229. (28) Kaur, K.; Wanchoo, R. K.; Toor, A. P. Sulfated Iron Oxide: A Proficient Catalyst for Esterification of Butanoic Acid with Glycerol. Ind. Eng. Chem. Res. 2015, 54, 3285. (29) Kaur, K.; Jain, P.; Sobti, A.; Toor, A. P. Sulfated metal oxides: eco-friendly green catalysts for esterification of nonanoic acid with methanol. Green Process. Synth. 2015, 5, 93. (30) Fogler, H.S. Elements of Chemical Reaction Engineering, Prentice-Hall, Englewood Cliffs, New Jersey, 1999, 592 (31) Thomas, J.M.; Thomas, W.J. Heterogeneous Catalysis, VCH Publishers Inc, New York, 1997. (32) Ruthven, D. M. Principles of adsorption and adsorption processes, John Wiley and Sons, New York, 1984.

List of Figure Captions Figure 1. Experimental set up for Semi Batch Reactive distillation process Figure 2. Effect of reaction time on selectivity of products at reaction temperature of 453.15 K, catalyst loading of 13.0 kg/m3, stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid) and entrainer loading of 0.02 m3/m3 of reaction mixture Figure 3(a). Comparison of fractional conversion for batch and reactive distillation process at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3 and a stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid) Figure 3(b). Effect of entrainer loading (m3/m3 of reaction mixture) on fractional conversion at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3, the molar ratio of 1:3 (Glycerol: Valeric acid) and a stirring speed of 500 RPM after the time of 3 h



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Figure 3 (c). Effect of entrainer loading on acid conversion and percentage selectivity of products after the reaction time of 3 h at the reaction temperature of 415.65 K, catalyst loading of 13.0 kg/m3, molar ratio of 1:3 (Glycerol: Valeric acid) and stirring speed of 500 RPM Figure 4. Effect of reaction temperature on acid conversion and percentage selectivity of products at catalyst loading of 13.0 kg/m3, stirring speed of 500 RPM and molar ratio of 1:3 (Glycerol: Valeric acid) after the time of 3 h and entrainer loading of 0.02 m3/m3 Figure 5. Plot of kf versus 1/T for different models Figure 6(a). Comparison of percentage conversion obtained from batch and reactive distillation process at the catalyst loading of 13.0 kg/m3, the molar ratio of 1:3 (Glycerol: Valeric acid) and a stirring speed of 500 RPM Figure 6(b). Comparison of % selectivity of products obtained from batch and reactive distillation process at catalyst loading of 13.0 kg/m3, the molar ratio of 1:3 (Glycerol: Valeric acid), stirring speed of 500 RPM and reaction temperature of 453.15 K Figure 6(c). Comparison of product selectivity obtained in (i) batch and (ii) reactive distillation process


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Table of Contents (TOC) Graphic: Trivalerin Synthesis via Reactive Distillation For Table of Contents only:



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Enhancement in Conversion and Selectivity of Trivalerin Using

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