Kinetics and mechanism of esterification of palmitic acid with ethanol in the presence of Brønsted acidic ionic liquids as catalyst

Author Notes

Abstract

The present work is focused on the kinetics and mechanisms of palmitic acid and ethanol esterification reaction using Brønsted acidic ionic liquids (BAILs) as catalysts. The experiments were performed in an isothermal batch reactor and progress of reaction has been monitored by measuring the water content using Karl Fischer Titrator. The experimental data has been investigated by integral method of data analysis to determine the kinetics. The kinetics from the experimental data revealed that the reaction is non-elementary, and a suitable mechanism was proposed. The importance of activity coefficients was also studied using UNIFAC and modified UNIFAC programme.

esterification, Brønsted acidic ionic liquids, kinetics, mechanisms, activity coefficients

Issue Section:

Research article

Introduction

Esterification of carboxylic acids with alcohol is one of the most important industrial reactions which has been widely studied [1–3]. Organic esters find applications in the manufacturing of flavours, pharmaceuticals, solvents, plasticizers, emulsifiers, and cosmetic industries. Long chain fatty acid methyl or ethyl esters can be used as biofuels [1–5]. Generally, esterification reactions are very slow and reversible in nature, which are conventionally carried out by homogeneous and heterogeneous catalysts [3, 5, 6]. Overcoming the drawbacks of conventional methods of catalysis lead to the exploration of an alternative to initiate the esterification reaction. In recent times, researchers are focusing on more environmentally friendly organic synthesis geared towards green chemistry. In this context, ionic liquid, especially room temperature ionic liquids (RTILs) are receiving more attention because of its applications in the versatile fields such as catalyst, separation, electrolyte, heat storage, lubricants, and additive, liquid crystal [7, 8].

Literatures [5, 9–11] showed that Brønsted acidity of ionic liquid has an important role in catalysis to enhance reaction rate. Therefore, SO₃H-functionalised ionic liquids were selected as catalyst for the study, 1-(4 Sulphonic acid) butyl-3 methyl imidazolium hydrogen sulphate, 1-(4 Sulphonic acid) butyl-3 methyl imidazolium trifluoromethane sulphonate, 1-(4 Sulphonic acid) butyl-3 methyl imidazolium hydrogen phosphate, 1-(4 Sulphonic acid) butyl pyridinium hydrogen sulphate, 1-(4 Sulphonic acid) butyl triethyl ammonium hydrogen sulphate.

Additionally, the kinetics of esterification reactions in the presence of homogeneous and heterogeneous catalysts has been widely studied. But the kinetics of these reactions in the presence of BAILs as catalyst is yet to be studied. The present work mainly focuses on the investigation of kinetics of esterification of palmitic acid and ethanol in the presence of BAILs as catalyst and proposes a mechanism for the above reaction, a series of steps of reactions in molecular level before reaching the final product. In the case of ideal system, the reaction rate depends only on the concentration of components of reaction mixture [12], but the selected system of study shows a strong non-ideality due to the presence of polar compounds such as water and ethanol [13]. A higher order fatty acid, palmitic acid was selected to ascertain the efficiency of IL in the process of esterification.

Experimental

Chemicals

Palmitic acid (99–100%, synthesis grade, SDFCL) and ethyl alcohol (99.9 wt.%, Jiangsu Huaxi International) were used without further purification. The BAILs such as 1-(4 Sulphonic acid) butyl-3 methyl imidazolium hydrogen sulphate, 1-(4 Sulphonic acid) butyl-3 methyl imidazolium trifluoromethane sulphonate, 1-(4 Sulphonic acid) butyl-3 methyl imidazolium hydrogen phosphate, 1-(4 Sulphonic acid) butyl pyridinium hydrogen sulphate, 1-(4 Sulphonic acid) butyl triethyl ammonium hydrogen sulphate was synthesized and used as catalyst for the present study. Karl Fischer Solution (Merck Specialties Pvt. Limited) and methanol (99.8 wt.% HPLC grade, Thomas Baker) were used for the analysis.

Esterification

Known quantity of alcohol and acid were added into a reactor and the contents were stirred to reach the desired temperature. Upon reaching the set temperature of the reaction mixture, known amounts of catalyst were added into the reactor, which was considered the zero time (t_o). Temperature and stirring speed were constant throughout the experiment. The reaction continued until equilibrium was reached. At different time intervals, small amounts of reaction samples were collected from the reactor and analysed using the Karl Fischer titrator. In the titrator, water content was recorded being one of the products of the reaction. By measuring the amount of water in the reaction, the reaction progress was monitored. The Karl Fischer titrator (Model no. 870KF Titino plus, Metrohm, Switzerland) having a drift range of 1–999 μl/min and results display resolution as 0.00001.

Results and discussion

Kinetics of reactions

A reaction kinetics model was derived from experimental data conducted at different reaction conditions such as molar ratios of reactants, temperatures, and catalyst concentrations. The order of reactions was determined using the integral method of analysis. To fit batch reactor data, all possible forms of models were used, including first-order irreversible, first-order reversible, second-order irreversible, second-order reversible, and first-order forward and second-order backward. Data for analysis were obtained at the experimental conditions of palmitic acid and ethanol in the presence of FIL1 with temperature as 81.5°C, initial mole ratio M = 6.4 and catalyst concentration, 1.29 g.

First order reversible reaction,

- \ln (1 - \frac{X_{A}}{X_{A e}}) = \frac{k_{1} (M + 1)}{(M + X_{A e})} t

(1)

where M = C_R0/C_A0 = 0, reduces Equation (1) to Equation (2)

- \ln (1 - \frac{X_{A}}{X_{A e}}) = \frac{k_{1}}{X_{A e}} t

(2)

In these models, the forward reaction kinetic constant is k₁, while the backward reaction kinetic constant is k₂. Figure 1 confirms that the reaction is first order reversible. The kinetics of palmitic acid with ethanol in the presence of other FILs shown in Fig. 2 also confirms that the reaction is first order reversible.

Figure 1.

Esterification of palmitic acid and ethanol at optimized conditions in the presence of FIL1 described by a model fitted to a first order reversible reaction.

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Figure 2.

The reversible first order rate equation tested at different temperatures and constant mole ratio of M = 4 and 0.75 g of catalyst for esterification of palmitic acid and ethanol in the presence of FIL1.

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According to Table 1, due to the increase in collision rate between reactant molecules that results in increase in reaction rate, equilibrium conversion, velocity constants, and equilibrium constants also increase with temperature. The increment in the catalyst amount also exhibits the same trend as that of temperature (all the parameter listed in Table 1 increases). The catalyst makes the reactant molecules more energy-efficient by altering their energy level. By increasing the amount of catalyst, the energy barrier reduces, which increases the reaction rate. By increasing the mole ratio, equilibrium conversion and equilibrium constants increase, while velocity constants decrease.

Table 1.

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The equilibrium conversion X_ae, rate constants, and equilibrium constants for ethanol and palmitic acid reactions in the presence of FIL1 under various experimental conditions

Term	Equilibrium conversion, X_ae	k₁, min⁻¹	k₂, min⁻¹	Equilibrium constant, K_act
At different temperatures, at a constant catalyst amount of 0.75 g and a mole ratio of M = 4
81.5^oC	0.614	0.043	0.027	1.59
72.5^oC	0.566	0.033	0.026	1.31
62.5^oC	0.538	0.017	0.015	1.165
At different catalyst amounts, at a constant temperature of 80ºC and a mole ratio of M = 6
1.2 g	0.816	0.058	0.013	4.435
0.3 g	0.624	0.017	0.01	1.66

Term	Equilibrium conversion, X_ae	k₁, min⁻¹	k₂, min⁻¹	Equilibrium constant, K_act
At different temperatures, at a constant catalyst amount of 0.75 g and a mole ratio of M = 4
81.5^oC	0.614	0.043	0.027	1.59
72.5^oC	0.566	0.033	0.026	1.31
62.5^oC	0.538	0.017	0.015	1.165
At different catalyst amounts, at a constant temperature of 80ºC and a mole ratio of M = 6
1.2 g	0.816	0.058	0.013	4.435
0.3 g	0.624	0.017	0.01	1.66

Table 1.

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The equilibrium conversion X_ae, rate constants, and equilibrium constants for ethanol and palmitic acid reactions in the presence of FIL1 under various experimental conditions

Term	Equilibrium conversion, X_ae	k₁, min⁻¹	k₂, min⁻¹	Equilibrium constant, K_act
At different temperatures, at a constant catalyst amount of 0.75 g and a mole ratio of M = 4
81.5^oC	0.614	0.043	0.027	1.59
72.5^oC	0.566	0.033	0.026	1.31
62.5^oC	0.538	0.017	0.015	1.165
At different catalyst amounts, at a constant temperature of 80ºC and a mole ratio of M = 6
1.2 g	0.816	0.058	0.013	4.435
0.3 g	0.624	0.017	0.01	1.66

Term	Equilibrium conversion, X_ae	k₁, min⁻¹	k₂, min⁻¹	Equilibrium constant, K_act
At different temperatures, at a constant catalyst amount of 0.75 g and a mole ratio of M = 4
81.5^oC	0.614	0.043	0.027	1.59
72.5^oC	0.566	0.033	0.026	1.31
62.5^oC	0.538	0.017	0.015	1.165
At different catalyst amounts, at a constant temperature of 80ºC and a mole ratio of M = 6
1.2 g	0.816	0.058	0.013	4.435
0.3 g	0.624	0.017	0.01	1.66

Activation energy and frequency factor

Arrhenius equation is used for calculation of activation energy as well as frequency factor of the reaction. Based on the already determined forward and reverse reaction rate constants, Arrhenius plot was constructed. Figure 3 illustrates values of activation energy determined from Arrhenius plot in the case of palmitic acid and ethanol reaction with FIL1 as catalyst. Table 2 shows values for forward and backward reaction activation energies as well as frequency factors in both directions. In addition, it gives coefficient of determination for palmitic acid esterification with different FILs as catalyst. The activation energy of forward reaction for palmitic acid falls in the range of 50–60 KJ/mol like other FILs.

Figure 3.

The Arrhenius plot shows palmitic acid esterification in the presence of FIL1.

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Table 2.

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Activation energy and frequency factor for palmitic acid esterification with FILs as catalyst.

Palmitic acid-ethanol system
Catalyst	E₁, kJ/mol	E₂, kJ/mol	k₁₀, s⁻¹	k₂₀, s⁻¹	$R_{1}^{2}$	$R_{2}^{2}$
FIL1	60.58	39.39	1.47 × 10⁻⁶	2.6 × 10⁻³	0.987	0.971
FIL2	60.99	50.38	6.81 × 10⁻⁷	1.39 × 10⁻⁴	1	1
FIL5	57.566	22.17	0.832	2.298	0.977	0.935

Palmitic acid-ethanol system
Catalyst	E₁, kJ/mol	E₂, kJ/mol	k₁₀, s⁻¹	k₂₀, s⁻¹	$R_{1}^{2}$	$R_{2}^{2}$
FIL1	60.58	39.39	1.47 × 10⁻⁶	2.6 × 10⁻³	0.987	0.971
FIL2	60.99	50.38	6.81 × 10⁻⁷	1.39 × 10⁻⁴	1	1
FIL5	57.566	22.17	0.832	2.298	0.977	0.935

Table 2.

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Activation energy and frequency factor for palmitic acid esterification with FILs as catalyst.

Palmitic acid-ethanol system
Catalyst	E₁, kJ/mol	E₂, kJ/mol	k₁₀, s⁻¹	k₂₀, s⁻¹	$R_{1}^{2}$	$R_{2}^{2}$
FIL1	60.58	39.39	1.47 × 10⁻⁶	2.6 × 10⁻³	0.987	0.971
FIL2	60.99	50.38	6.81 × 10⁻⁷	1.39 × 10⁻⁴	1	1
FIL5	57.566	22.17	0.832	2.298	0.977	0.935

Palmitic acid-ethanol system
Catalyst	E₁, kJ/mol	E₂, kJ/mol	k₁₀, s⁻¹	k₂₀, s⁻¹	$R_{1}^{2}$	$R_{2}^{2}$
FIL1	60.58	39.39	1.47 × 10⁻⁶	2.6 × 10⁻³	0.987	0.971
FIL2	60.99	50.38	6.81 × 10⁻⁷	1.39 × 10⁻⁴	1	1
FIL5	57.566	22.17	0.832	2.298	0.977	0.935

Mechanism of reaction

The esterification reaction of any fatty acid with ethanol in the presence of catalyst can be written as

$Fatty acid + Alcohol ⇌ Fatty acid ester + water$

According to batch reactor data analysis, the reaction follows first-order behavior in both forward and backward directions almost under all operating conditions. Furthermore, the experimental data supports first order irreversibility when the reaction is at complete conversion. In view of this observation, the reaction is not elementary, and the mechanism of the reaction must be clarified.

Currently, on using FIL catalysts that are more acidic and capable of generating H⁺ ions from cationic material. The decomposition of FILs can be represented as

FIL ⇄ {FIL}^{-} + H^{+}

As FILs act as catalyst, the H⁺ ions initiate the esterification reaction. To develop kinetic expressions for the esterification of fatty acids by extending the existing mechanisms, few assumptions were used.

Decomposition of FILs produces H⁺ ions
The reaction involves only elementary and reversible steps. The detailed mechanism is shown below.

{C H}_{3} - {(C H_{2})}_{n} - COOH + {C H}_{3} - {C H}_{2} - O H \overset{Catalyst}{\to} {C H}_{3} - {(C H_{2})}_{n} - COO - {C H}_{2} - {C H}_{3}

(3)

FIL ⇌ F I L^{-} + H^{+}

(4)

C H_{3} - {(C H_{2})}_{n} - COOH + H^{+} ⇌ C H_{3} - {(C H_{2})}_{n} - CHO - O H

(5)

C H_{3} - {(C H_{2})}_{n} - CHO - O H + C H_{3} - C H_{2} - O H ⇌ C H_{3} - {(C H_{2})}_{n} - C {(O H)}_{3} - C H_{2} - C H_{3}

(6)

C H_{3} - {(C H_{2})}_{n} - C {(O H)}_{3} - C H_{2} - C H_{3} ⇌ C H_{3} - {(C H_{2})}_{n} - COOH - C H_{2} - C H_{3}

(7)

C H_{3} - {(C H_{2})}_{n} - COOH - C H_{2} - C H_{3} ⇌ C H_{3} - {(C H_{2})}_{n} - COO - C H_{2} - C H_{3} + H^{+}

(8)

F I L^{-} + H^{+} ⇌ FIL

(9)

where

\begin{matrix} {A = C H}_{3} - {(C H_{2})}_{n} - COOH \\ \begin{matrix} A^{*} = C H_{3} - {(C H_{2})}_{n} - CHO - O H \\ \begin{matrix} B = {C H}_{3} - {C H}_{2} - O H \\ \begin{matrix} C = {C H}_{3} - {(C H_{2})}_{n} - COO - {C H}_{2} - {C H}_{3} \\ C^{*} = {(C H_{2})}_{n} - COOH - C H_{2} - {C H}_{3} \end{matrix} \end{matrix} \end{matrix} \end{matrix}

For a simplified version of the above mechanism, rewrite it as follows:

A + H^{+} \leftrightarrow A^{*}; k_{1} and k_{- 1} = forward and backward reaction constant

(10)

A^{*} + B \leftrightarrow C^{*} + D; k_{2} and k_{- 2} = forward and backward reaction constant

(11)

C^{*} \leftrightarrow C + H^{+}; k_{3} and k_{- 3} = forward and backward reaction constant

(12)

Protonation of fatty acids is assumed to determine the rate (Equation 10) and the other reactions (Equations 11 and 12) are in equilibrium, hence, the rate of reaction derived from the rate limiting step can be expressed as:

- r_{A} = k_{1} C_{A} C_{H}^{+} - k_{- 1} C_{A}^{*}

(13)

Applying the steady state approximation rule, the concentration of the intermediate is computed from Equations (11) and (12).

From Equations (11) and (12),

k_{2} = \frac{C_{C}^{*} C_{D}}{C_{A}^{*} C_{B}} and k_{3} = \frac{C_{C} C_{H}^{+}}{C_{C}^{*}}

By solving Equations (13) and

C_{A}^{*} = \frac{C_{C} C_{C} C_{C}^{+}}{K_{K} K_{3} C_{B}}

(14)

The substitution of Equation (14) into Equation (12) yield

{- r}_{A} = k_{1} C_{A} C_{H}^{+} - K_{- 2} \frac{C_{C} C_{D} C_{H}^{+}}{C_{B} K_{2} K_{3}}

(15)

where $K_{1} = \frac{k_{1}}{k_{- 1}}, k_{1}^{'} = k_{1} C_{H}^{+}$ and $K_{E} = K_{1} K_{2} K_{3}$

Considering K₁, k₁′ and K_E, the overall rate equation can be written as

{- r}_{A} = k_{1}^{'} (C_{A} - \frac{C_{C} C_{D}}{K_{E} C_{B}})

(16)

Equation (16) shows first order kinetics in both forward and backward directions, which agrees with data derived from batch reactor analysis. According to the rate expression, the rate of reaction depends on all the reaction components.

Fit of the kinetic model

The experimental data of palmitic esterification with FILs catalyst and parameters from Table 3 were fitted into the model (Equation 16). Figure 4 shows the resultant fit of palmitic acid in the presence of FIL1.

Figure 4.

Model fit at T = 81.5°C, CMi = 6.4 and 1.29 g catalyst for palmitic acid esterification with FIL1 as catalyst.

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Table 3.

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Rates and equilibrium constants for palmitic acid and ethanol reactions in the presence of different FILs.

Catalyst	Temperature, °C	Initial mole ratio	Catalyst amount, g	k₁, min⁻¹	k₂, min⁻¹	K_act
FIL1	81.5	6.4	1.29	0.0804	0.0134	5.896
FIL2	80	6	0.75	0.079	0.015	5.28
FIL2	80	4	1.2	0.153	0.025	6.09
FIL5	80	6	1.2	0.12	0.015	8.09

Catalyst	Temperature, °C	Initial mole ratio	Catalyst amount, g	k₁, min⁻¹	k₂, min⁻¹	K_act
FIL1	81.5	6.4	1.29	0.0804	0.0134	5.896
FIL2	80	6	0.75	0.079	0.015	5.28
FIL2	80	4	1.2	0.153	0.025	6.09
FIL5	80	6	1.2	0.12	0.015	8.09

Table 3.

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Rates and equilibrium constants for palmitic acid and ethanol reactions in the presence of different FILs.

Catalyst	Temperature, °C	Initial mole ratio	Catalyst amount, g	k₁, min⁻¹	k₂, min⁻¹	K_act
FIL1	81.5	6.4	1.29	0.0804	0.0134	5.896
FIL2	80	6	0.75	0.079	0.015	5.28
FIL2	80	4	1.2	0.153	0.025	6.09
FIL5	80	6	1.2	0.12	0.015	8.09

Catalyst	Temperature, °C	Initial mole ratio	Catalyst amount, g	k₁, min⁻¹	k₂, min⁻¹	K_act
FIL1	81.5	6.4	1.29	0.0804	0.0134	5.896
FIL2	80	6	0.75	0.079	0.015	5.28
FIL2	80	4	1.2	0.153	0.025	6.09
FIL5	80	6	1.2	0.12	0.015	8.09

Activity coefficients

The kinetics of the esterification reaction in the presence of FILs demonstrated the reversible nature and can be formulated as follows:

r = k^{'} [C_{A} - \frac{C_{C} C_{D} .}{K_{E} C_{B}}]

(17)

The equilibrium constants provided in the rate expression (Equation 17) are based on the concentration of the reactants and products. Only ideal systems can use concentration-based equilibrium constants. It is important to note that in non-ideal cases, equilibrium constants are dependent on the conditions in the liquid phase, such as concentration of species and ionic strength. The equilibrium constant calculated based on the concentration (K_C) is related to true thermodynamic constant (K_act) through activity based constant (K_γ). For instance, a reaction with two reactants giving out two different products, can be represented as

A + B \leftrightarrow C + D

The true thermodynamic constant K_act is defined by

K_{act} = \frac{C_{C} C_{D} γ_{C} γ_{D}}{C_{A} C_{B} γ_{A} γ_{B}}

(18)

K_C and K_γ are defined as

K_{C} = \frac{C_{C} C_{D}}{C_{A} C_{B}} and K_{γ} = \frac{γ_{C} γ_{D}}{γ_{A} γ_{B}}

(19)

K_{act} = K_{C} {. K}_{γ} .

(20)

The concentration based rate constant, K_c is obtained by K_c = K_act/K_γ. K_act is determined from experimental data and K_γ is to be calculated using an approximate theory. The insertion of K_c in the rate expression (Equation 17) yields the concentration-based model.

In the present case, the reaction system consists of different components CH₃(CH₂)₁₄COOH, CH₃CH₂OH, CH₃(CH₂)₁₄COOCH₂CH₃ and H₂O for palmitic acid esterification. The calculations of activity coefficient were done by using UNIFAC program. Two models such as UNIFAC and modified UNIFAC were used to establish the values. By these models, the activity coefficient of a species γ_i consists of combinatorial (C) and residual (R) parts [14–16].

l n γ_{i} = l n γ_{i}^{C} + l n γ_{i}^{R}

(21)

Temperature and composition of the mixture affect the activity coefficient, so, UNIFAC program was used to calculate activity coefficients for various experimental temperatures and compositions from the beginning of the reaction to the complete conversion of the reactants. K_act, Kγ_UNIFAC and Kγ_mod.UNIFAC values at different temperatures and initial molar ratios used in the model prediction are summarized in Table 4.

Table 4.

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Actual, activity and concentration-based equilibrium constants for palmitic esterification system at different experimental conditions.

Palmitic acid—ethanol system
Catalyst	X_Ae	K_act	K_γunifac	K_{γ mod.unifac}	K_{C unifac}	K_{C mod.unifac}
FIL1	0.85	5.896	11.452	9.71	0.515	0.6073
FIL2	0.84	5.28	11.43	9.65	0.462	0.547
FIL2	0.85	6.09	10.77	9.04	0.565	0.673
FIL5	0.88	8.09	11.45	9.59	0.707	0.844

Palmitic acid—ethanol system
Catalyst	X_Ae	K_act	K_γunifac	K_{γ mod.unifac}	K_{C unifac}	K_{C mod.unifac}
FIL1	0.85	5.896	11.452	9.71	0.515	0.6073
FIL2	0.84	5.28	11.43	9.65	0.462	0.547
FIL2	0.85	6.09	10.77	9.04	0.565	0.673
FIL5	0.88	8.09	11.45	9.59	0.707	0.844

Table 4.

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Actual, activity and concentration-based equilibrium constants for palmitic esterification system at different experimental conditions.

Palmitic acid—ethanol system
Catalyst	X_Ae	K_act	K_γunifac	K_{γ mod.unifac}	K_{C unifac}	K_{C mod.unifac}
FIL1	0.85	5.896	11.452	9.71	0.515	0.6073
FIL2	0.84	5.28	11.43	9.65	0.462	0.547
FIL2	0.85	6.09	10.77	9.04	0.565	0.673
FIL5	0.88	8.09	11.45	9.59	0.707	0.844

Palmitic acid—ethanol system
Catalyst	X_Ae	K_act	K_γunifac	K_{γ mod.unifac}	K_{C unifac}	K_{C mod.unifac}
FIL1	0.85	5.896	11.452	9.71	0.515	0.6073
FIL2	0.84	5.28	11.43	9.65	0.462	0.547
FIL2	0.85	6.09	10.77	9.04	0.565	0.673
FIL5	0.88	8.09	11.45	9.59	0.707	0.844

Using Equation (18) and the parameters from Table 4, the concentration-based models were developed. Figure 5 shows the resultant concentration-based models for palmitic acid esterification in the presence of FIL1 by UNIFAC and modified UNIFAC. Experimental and concentration-based curves show significant differences in the above plot. Therefore, the activity of the system is an important factor in determining rate equations. For plotting concentration-based rate curves, both UNIFAC and modified UNIFAC models were used. A modified UNIFAC model approaches experimental conditions for palmitic acid-ethanol esterification. Therefore, the palmitic acid—ethanol—ethyl palmitate—water system is not ideal. For an improved understanding of the system, the incorporation of the activity coefficient into the rate equation is essential.

Figure 5.

Concentration based model fit at T = 81.5°C, CMi = 6.4 and 1.29 g catalyst for palmitic acid and ethanol reaction in the presence of FIL1.

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Conclusions

A batch reactor was used for experiments to determine fatty acid kinetics, and Karl Fischer titrators were used for analysis of the samples. To analyse the kinetics of the reaction, integral method of analysis was used. The experimental data fit well with the first order reversible reaction. The kinetic constants were determined at various temperatures and activation energies were calculated using Arrhenius plot. The batch reactor data revealed that the fatty acid esterification is non-elementary, as a result, a mechanism needs to be determined. An elementary series of reversible reactions has been proposed, with protonation of fatty acids as the rate determining step. The rate expression developed for esterification reaction through the proposed mechanism is first-order in both forward and backward direction. The experimental data fit very well into the rate expression derived from the mechanism. Based on UNIFAC and modified UNIFAC program, the reaction system activity coefficients were calculated. Using the activity coefficients, the concentration-based model was developed, resulting in a plot indicating the existence of non-ideality in the fatty acid esterification system.

Data availability

All the data required to reproduce the work are presented in the manuscript.

Authors’ contributions

Beula C (Conceptualization [equal], Data curation [equal], Formal analysis [equal], Funding acquisition [equal], Project administration [equal], Supervision [equal], Writing—original draft [equal], Writing—review & editing [equal]), Srilekshmi Muraleedharan (Conceptualization [equal], Data curation [equal], Formal analysis [equal], Investigation [equal], Methodology [equal], Validation [equal], Writing—original draft [equal], Writing—review & editing [equal]), and Gokul Chandran (Writing—original draft [equal], Writing—review & editing [equal])

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflict of interest statement: None declared.

References

Ronnback

Salmi

Vuori

et al.

Development of a kinetic model for the esterification of acetic acid with methanol in the presence of a homogeneous catalyst

Chem Eng Sci

1997

;

3369

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Article Contents

Kinetics and mechanism of esterification of palmitic acid with ethanol in the presence of Brønsted acidic ionic liquids as catalyst

Abstract

Introduction

Experimental

Chemicals

Esterification

Results and discussion

Kinetics of reactions

Activation energy and frequency factor

Mechanism of reaction

Fit of the kinetic model

Activity coefficients

Conclusions

Data availability

Authors’ contributions

Funding

References

Author notes

Citations

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