LiquidâLiquidâSolid Model for the Epoxidation of Soybean Oil

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A liquid-liquid-solid model for the epoxidation of soybean oil catalysed by Amberlyst-16 Martino Di Serio, Vincenzo Russo, Elio Santacesaria, Riccardo Tesser, Rosa Turco, and Rosa Vitiello Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 28 Apr 2017 Downloaded from http://pubs.acs.org on April 29, 2017

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Industrial & Engineering Chemistry Research

A liquid-liquid-solid model for the epoxidation of soybean oil catalysed by Amberlyst-16 Martino Di Serio1,*,Vincenzo Russo1, Elio Santacesaria2, Riccardo Tesser1, Rosa Turco1, Rosa Vitiello1 1Università

degli Studi di Napoli ‘Federico II’, IT-80126 Napoli, Italy.

2Eurochem

Engineering srl, IT-20138 Milano, Italy. * [email protected]

Abstract The epoxidation of soybean-oil is a hot topic for biorefinery. The process is nowadays performed in the presence of a strong mineral acid (H2SO4, H3PO4), that catalyze both the epoxidation and the oxirane ring opening reactions, leading to high conversions and low selectivity. Moreover, the separation of such a catalyst need neutralization steps, thus operation units. Previous studies revealed that Amberlyst-16, an acid exchange resin, is a stable and active catalyst in the epoxidation of soybean oil, showing high selectivity. In the present paper, a rigorous liquidliquid-solid kinetic model has been proposed to interpret the kinetics of the soybean oil epoxidation reaction catalyzed by Amberlyst-16. The intrinsic kinetics of the overall reaction network has been investigated by taking into account all the occurring chemical and physical phenomena, overall dealing with the intraparticle diffusion limitations. From the data elaboration, it has been demonstrated that the unique role of the resin is to catalyze the formic to performic acid step. Formic acid shown a higher rate in decomposing the oxirane ring respect to performic, this was justified by its higher acidity. The high selectivity is due to the fact that the resin has no action in catalyzing the ring opening reactions, because of its high hydrophilicity. The obtained results are a good starting point for designing a continuous reactor. Keywords: three-phase model, liquid-liquid-solid system, soybean oil epoxidation kinetics, heterogeneous catalysts, Amberlyst-16.

1

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1 Introduction The epoxidation of vegetable oil is a hot-topic for the chemical industry, being the obtainable epoxides useful to produce a wide range of products, such as plasticizers and stabilizers of polyvinyl chloride (PVC)1. Currently, these products are synthesized by using a peracid formed in situ, from the reaction between a carboxylic acid, either formic or acetic, and hydrogen peroxide2,3, in the presence of soluble mineral acid catalysts such as sulfuric or phosphoric acid. Being the reaction extremely exothermic4-6, one of the main drawbacks of the process is the heat removal, to keep the operation isothermal and safe7-8. Another important drawback is related to the use of mineral acid. Such strong acids promote undesirable side reactions, responsible of the oxirane ring opening resulting in a dramatic decrease in the oxirane selectivity, thus on the product specimen3. Despite these drawbacks, industrial plants are running with the described technology. The reaction is performed in jacketed batch reactors, equipped with very efficient heat exchangers to keep the reaction temperature under control. The mineral catalysts are neutralized after the reaction by adding NaOH, leading to the formation of soaps, by triglyceride hydrolysis, leading to problems in separating the product from the aqueous phase, that is normally made by decantation. It is evident that finding an alternative to soluble mineral catalysts is of uppermost importance to optimize the process. For this reason, the research moved to the screening of heterogeneous catalysts characterized by high stability, conversion and oxirane selectivity. Heterogeneous acidic ionic exchange resins shown high selectivity and reasonable double bonds conversion at low reaction times1. These catalysts are macroporous polymeric resins, characterized by the presence of strong isolated acid sites. These sites are located inside the polymeric matrix, thus it is very difficult that organic molecules characterized by long chain and high steric hindrance, such as vegetable oil, would access to them easily. This peculiar structure solves one of the main drawback of the use of mineral acids that is the promotion of ring opening reactions. As a result, these resins show relatively high selectivity to epoxidized soybean oil. On the contrary, the high acidity of the resin promotes the formation of performic acid starting from formic acid and hydrogen peroxide. Performic acid migrates in the oil phase, reacting with the oil double bonds, giving place to the oxirane ring. Consequently, the overall conversion of the system increases. A sketch of the overall mechanism, taking into account the action of the resins is shown in Scheme 1. 2


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Aqueous phase

Solid phase CO2 + H2O

O

+ H2O2 H

r1,W

OH

r2,W

O

H+

O

+ H2O2

+ H2 O

O H

CO2 + H2O

H

H

O

OH

r1,S

r2,S

O

H+

+ H2O

O H

O

H

Aqueous/organic interf ace

O

+ H

O

R1

OH

C

R2

R3 C

+

O R4

+FA r2,O

R1

O

r1,O H

O

H

R3 C

R2

C R4

+PFA r3,O D1

D2

Organic phase

Scheme 1 – Overall reaction network of the soybean oil epoxidation in the presence of ion exchange resins as heterogeneous catalyst. It is important to underline that several side reactions can occur. Firstly, both in the liquid phase and in the liquid inside the resin pores, performic acid can decompose. It was shown that this reaction is independent on the acidity of the system9,10, occurring spontaneously. As a consequence, a certain amount of performic acid, thus formic acid, is consumed, leading to a lowering of the reaction yield. Hydrogen peroxide decomposition was demonstrated to be stabilized by the acid environment11-13. This side reaction normally occurs at relatively high temperature (greater than 90°C). It is strongly suggested to avoid to work at so high temperature in synthesizing epoxidized soybean oil in order to avoid possible runaway reactions, due to the thermal decomposition of the peracids. For this reason, the reaction was not included in Scheme 1. Finally, being these systems not characterized by full selectivity to oxirane, it is evident that the acidity of formic and performic acid dissolved in the organic phase is responsible of the oxirane ring attack, reaction that leads to the formation of un-desirable side products. For the mentioned reasons, several polystyrene sulfonic resins with different amounts of divinylbenzene as a cross-linking agent were tested for the epoxidation of vegetable oils14,15, demonstrating that resins characterized by lower degrees of crosslinking were more porous, allowing the access of the oil molecules to the sulfonic acid groups, thus low selectivity is 3



Page 4 of 27

achieved14. The most commonly used sulfonic acid resin is Amberlite IR-120 (a gel type resin containing 8% divinylbenzene), showing high selectivity to epoxidized soybean oil, using peracetic acid16. However, this resin shows low reaction rates and high breakage due to pressure drops when using it in continuous reactors17. Other efforts have been recently reviewed by Milchert et al.16, showing the advantages of using Amberlite IR-120 as catalyst. The authors shown that the catalyst can be reused four times keeping almost the same conversion working at 50°C with a CH3COOH/H2O/double bonds=0.5:1.5:1. In 2013, Turco et al. demonstrated that by using Amberlyst-16 as catalyst, it is possible to obtain products of high quality level, working under isothermal conditions8. The catalyst is macroreticular, keeping its shape under moderate pressure drop, thus solving the reactors plugging when using it in continuous reactors. This catalyst shows a relatively high hydrophilicity, protecting the epoxidized product (dissolved in the oil phase) from an acid attack, solving the mentioned selectivity problems8. Moreover, the catalyst has shown high activity and stability in re-use tests. Even if the experiments show a promising application, an effort must be made to scale-up the process. For this reason, the experimental data must be interpreted with a kinetic model that would take into account all the chemical and physical phenomena involved in the reaction network. At this purpose, a comprehensive kinetic model was developed, studying each step of the overall reaction network separately. In particular, formic to performic acid synthesis experimental data were directly taken from literature, while the epoxidation tests performed in the presence/absence of resin either from literature or with new tests. A particle model was developed to test the influence of the intraparticle mass transfer limitations. The data interpretation was able to reveal the catalytic role of the catalyst, that is uniquely the promotion of the performic acid synthesis, giving negligible influence on the ring opening reactions. The importance of the present investigation is to give a good starting point for the reactor design of continuous tubular reactors for the epoxidation of vegetable oils in the presence of acid resins.

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2 Materials, Experiments and Methods 2.1 Materials Materials Amberlyst 16 was purchased from Rohm and Haas (Rohm and Haas Italia S.R.L., Milano, Italy capacity 3.9 meq/g of dry resin, pore diameter of 250Å, specific area 30m2/s). Hydrogen peroxide (60 wt% in water) was kindly provided by Solvay Italia. Soybean oil with an iodine number of 128 (128 gI consumed per 100 gsample) was purchased in a local food store. Formic acid (96%, w/w) and all other reagents were supplied by Sigma Aldrich (Milano, Italy) at the highest level of purity available ( > 99.9%) and were used as received without further purification. 2.2 Experiments Resin liquid uptake and repartition of reagents Because the composition inside the resin can be strongly different from the bulk one and this can have strong consequences on the kinetic interpretation, some liquid uptake and partition experiments have been performed18. Liquid uptake experiments have been performed by putting in contact a fixed amount of Amberlyst-16 dried at 80°C with a fixed volume of a certain reactant in a graduated cylinder. The increase of the overall volume observed after a sufficient time is clearly an indication of the resin liquid uptake. The results are reported in Table 1. Table 1 – Liquid uptake tests experimental conditions and obtained results. Liquid mixture H2O2 (20 wt.%) H2O2 (40 wt.%) H2O2 (60 wt.%) H2O HCOOH H2O/HCOOH (1:1) H2O2/HCOOH (1:1) H2O2/soybean oil (1:1) Soybean oil Epoxidized soybean oil

Vinitial [cm3] 5.0 5.0 5.0 5.0 1.4 1.2 1.2 1.8 1.0 1.2

Vfinal [cm3] 10.5 10.5 10.5 10.5 2.0 2.2 2.4 3.8 1.0 1.2

Liquid uptake [%] 110 110 110 110 43 83 100 111 -

As it can be seen, no liquid uptake has been observed by placing in contact the oil-based compounds with the resin. This means that no intraparticle diffusion occurs for these 5



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components. Water and hydrogen peroxide solutions show the same behavior in the resin liquid uptake, showing roughly a double value respect to formic acid. As all the epoxidation of soybean oil catalyzed by Amberlyst-16 experiments have been performed with an excess of hydrogen peroxide, we assumed that the contribution of the liquid uptake is given principally by the water and hydrogen peroxide interaction. Moreover, the epoxidation of soybean oil experiments, catalyzed by Amberlyst-16, have been performed with an excess of both hydrogen peroxide and formic acid, so their presence does not give great influence on the resin liquid uptake. Thus, we can consider constant the mean radius of resin particles that resulted equal to be RP=0.3·10-3 m. The partition experiments have been performed by putting in contact a fixed amount of Amberlyst-16 with either a solution of H2O2 (20wt.%) or formic acid in water (3:1 by weight). Liquid samples have been withdrawn periodically and analyzed respectively by iodometric analysis19 or formic acid analysis to determine the residual hydrogen peroxide or formic acid concentrations. Along the time, the concentration of hydrogen peroxide and formic acid remains the same in absence and in presence of resin. This means that the intraparticle diffusion can be explained by concentration gradients considering equal to 1 the partition coefficients between the bulk aqueous solution and the resin particles. Epoxidation reactions The epoxidation of soybean oil experiments in the absence of heterogeneous catalyst have been performed following the same procedure reported in the literature8, by using a fed-batch reactor where the aqueous solution is pumped with a fixed flow rate for a fixed time (necessary to feed a tank with the compositions reported in Table 2), to a pre-heated amount of oil. All the other experiments have been directly taken from the literature8,20. The main operative conditions, useful for the parameter estimation analysis, are listed in Table 2. The reaction occurred in a 0.5L jacketed reactor, mechanically stirred at 750 rpm by a two-blades impeller, by using baffles to warrantee a good mixing. For the same reason, an impeller to vessel ratio was choose to be 0.6.

6


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Table 2 – Operative conditions adopted for the experiments used for the parameter estimation analysis. Test

T [K]

wOIL [kg]

nFA,feed [mol]

nOX,feed [mol]

nW,feed [mol]

Qfeed [m3/s]

wAmberlyst-16 [kg]

D-1 D-2 D-3 D-4

303 313 323 333

-

0.20 0.20 0.20 0.20

0.31 0.31 0.31 0.31

0.51 0.51 0.51 0.51

-

-

B-1

328

0.05

0.091

0.28

0.35

-

8

B-2

323

0.2

0.225

1.31

1.67

-

-

B-3

333

0.2

0.225

1.31

1.67

-

-

R-1

328

0.05

0.091

0.28

0.35

2.5·10-3

8

R-2

328

0.05

0.091

0.28

0.35

1.25·10-3

8

R-3

328

0.05

0.091

0.28

0.35

10·10-3

8

R-4

328

0.05

0.046

0.28

0.35

5·10-3

8

R-5

328

0.05

0.183

0.28

0.35

5·10-3

8

R-6

318

0.05

0.091

0.28

0.35

5·10-9 for 3279s 1.22·10-8 for 5898s 1.22·10-8 for 5898s 5·10-9 for 3279s 5·10-9 for 3279s 5·10-9 for 3279s 5·10-9 for 3279s 5·10-9 for 3279s 5·10-9 for 3279s

20 20 20 20

5·10-3

8

Reference

2.3 Modeling procedure The coupled ordinary differential equations (ODEs), the liquid phase mass balance equations, and partial differential equations (PDEs), the intraparticle mass balance, system was solved numerically by using gPROMS Model Builder v.4 software21. The PDEs were solved by choosing a fourth order centered finite difference formula for the spatial derivatives (discretization points=40). All the physical properties adopted for the calculations have been taken from CHEMCAD v.5.0 database software22.

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3 Results and Discussion 3.1 Performic acid synthesis and decomposition In order to investigate the intrinsic kinetics of the soybean oil epoxidation reaction, it is necessary to evaluate all the possible reactions included in the overall reaction network. The performic acid synthesis is the first step of the overall mechanism. This reaction has been widely investigated in the literature. Recently, De Filippis et al.20 published a paper concerning the synthesis and decomposition of the performic acid in autocatalytic conditions. The authors proposed that the performic acid is an equilibrium reaction catalyzed by the proton concentration (see Eq. 1).  C PFA,W CW ,W r1,W  k1,W C H  ,W  C FA,W C OX ,W  K 1,W 

   

(1)

The proposed reaction rate expression is widely accepted and lead to a satisfactory interpretation of the collected experimental data. The proton concentration has been evaluated by using the analytical solution used by Sun et al.9. The authors evaluated that the main contribution to the acidity of the system is given by the formic acid, thus the proton concentration is mainly dependent with the formic acid concentration and its pKa (see Eq. 2). C H  ,W  1000 10  pK a C FA,W / 1000 , pK a  57.528  2773.9 / T  9.1232 ln(T )

(2)

Concerning the performic acid decomposition, the authors proposed a reaction rate expression dependent on both the performic acid and the proton concentration. The dependence with the acidity of the system is in strong disagreement with the experimental observations reported in the literature9,10,23, where a decomposition rate following a first-order irreversible reaction expression respect to the performic acid concentration is suggested (see Eq. 3). r2,W  k 2,W C PFA,W

(3)

By considering that De Filippis et al. reported experimental results in a wide range of operative conditions, we decided to interpret their experimental data by applying the rate expressions above mentioned. The classical Arrhenius and Van’t Hoff equations have been used to include the temperature dependence of respectively the kinetic and the equilibrium constants. In order to interpret the data, the O.D.E. system reported in Eq. 4 has been solved. dni ,W dt



N . Re actions

  j 1

r VW

(4)

ij j

The obtained results are reported in Figure 1, while in Table 3 the obtained parameters are listed. 8


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Table 3 – List of the parameters estimated on the formic to performic experimental data collected by De Filippis et al. C.I.: 95% confidence intervals. Value

95% C.I.

Units

k1,W(55°C)

1.85·10-9

0.02·10-9

(m3/mol)2/s

k2,W(55°C)

3.59·10-10

0.10·10-10

s-1

K1,W(55°C)

2.50

0.25

-

Ea1,W

44270

5450

J/mol

Ea2,W

77716

7850

J/mol

∆H

-581.6

2.5

J/mol

As it can be seen, a good agreement between the experimental and the calculated data has been obtained. The parameters show confidence intervals in the range of the 10%. Moreover, a slight temperature influence on the equilibrium constant has been observed, as reported by Santacesaria et al.10. The obtained kinetic and equilibrium parameters are in the same order of magnitude than the ones reported in the literature (Santacesaria et al.10 reported Ea1,W=45000J/mol and Ea2,W=78000J/mol; Wu et al.24 reported Ea1,W=46000J/mol and Ea2,W=42000J/mol). Thanks to the obtained agreements, we can feel confident that the formic to performic reaction rate expressions, with the related parameters, can be applied to our reaction network.

3.2 Liquid-liquid soybean oil epoxidation The second step of our study was to evaluated separately the epoxidation of soybean oil reaction, together with the related oxirane ring opening, in the absence of heterogeneous reactions. The mentioned reaction occurs as the performic acid migrates from the aqueous, where it is formed, to the organic phase. The system needs to be described by a liquid-liquid kinetic model (see fragment of the sketch in Figure 2). Performic acid synthesis and decomposition kinetic rate expressions have been obviously fixed. The epoxidation and ring opening reactions have been interpreted by using the reaction rate expressions reported in Eqs. 5-7, related to the oil phase. r1,O  k1,O C PFA,O C DB ,O

(5)

r2,O  k 2,O C E ,O C FA,O

(6) 9



r3,O  k 3,O C E ,O C PFA,O

Page 10 of 27

(7)

The epoxidation step follows a bi-molecular second order reaction rate as reported in the literature1-3,24,25. The oxirane ring opening reaction, has been considered dependent on either the formic or the performic acid concentrations. We considered that the rate-determining step of the ring opening reaction is the protonation of the oxirane oxygen. This aspect can be considered acceptable, by considering that both formic and performic acid show acidity, thus they are responsible of the ring opening reaction. Being the reaction mechanism the same, we imposed the same activation energy for both the ring opening reactions. The system is biphasic; thus, it is necessary to write the mass balances equations for both the aqueous and the organic phases. Formic and performic acid partition has been taken directly from the literature3 (see Eqs. 8-9). H FA 

CFA,W  (9  10 7 T (C ) 2 5  10 5 T (C )  0.0046) 1 CFA,O

H PFA 

CPFA,W  (4 10 6 T (C ) 2 4 105 T (C )  0.0402)1 CPFA,O

(8) (9)

The liquid-liquid mass transfer resistance has been considered negligible as it was previously demonstrated3. The resulting mass balances equations are reported in Eqs. 10-11. dni ,W dt dni ,O dt



N . Re actions

  j 1



N . Re actions

  j 1

r V   (Ci ,W  H i Ci*,O )VW

(10)

r VO   (Ci*,O  Ci ,O )VO

(11)

ij j W

ij j

Where the interface concentration has been calculated assuming that no accumulation is present at the interface, thus the mass transfer flux can be equalized. The parameters, reported in Table 4, have been calibrated on both the experimental data reported by Turco et al.8 (test B-1 of Table 2) and on two new experiments (tests B-2 and B-3 of Table 2). The results of the parameter estimation activity are reported in Figure 3.

10


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Table 4 – List of the parameters estimated on the soybean oil epoxidation tests performed in the absence of heterogeneous catalysts C.I.: 95% confidence intervals. Value

95% C.I.

Units

k1,O(55°C)

5.37·10-6

0.12·10-6

m3/(mol·s)

k2,O(55°C)

2.28·10-6

0.10·10-6

m3/(mol·s)

k3,O(55°C)

0.25·10-6

0.02·10-6

m3/(mol·s)

Ea1,O

40285

3958

J/mol

Ea3,O=Ea4,O

56975

9442

J/mol

Also in this case, a good agreement has been obtained and the confidence intervals on the parameters are acceptable. The epoxidation activation energy is of the same order of magnitude respect to the ones reported in the literature (Ea1,O=47656J/mol reported by Santacesaria et al.3; Ea1,O=41000J/mol reported by Wu et al.24). It is not possible to make a straight comparison concerning the ring opening parameters because we assumed a different rate-determining step in respect to the cited literature. By observing the kinetic constant values, it is possible to observe that the formic acid ring opening reaction is roughly 9 times faster than the performic acid one (k2,0/k3,0=9). This fact can be explained by considering that formic acid acidity is higher than performic one (pKa,FA=3.77, pKa,PFA=7.1). This means that as the performic acid synthesis reaction occurs, the pH of the solution increases and there is a decrease in the ring opening reaction activity.

11



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3.3 Liquid-liquid-solid soybean oil epoxidation catalyzed by Amberlyst-16 The experimental tests performed in the presence of Amberlyst-16 as catalyst, have been interpreted by adopting a liquid-liquid-solid kinetic model. By considering the collected evidences, it is possible to sketch the three-phases model reported in Figure 2. Being the catalyst wetted only by the aqueous phase, it is evident that the epoxidation reaction cannot be influenced directly by the resin itself. Anyway, its acidity catalyzes the formic to performic acid synthesis. For this reason, we scaled the performic acid formation kinetic constant by the aqueous proton concentration and we multiplied it for the equivalent proton concentration inside the resin. Concerning the equilibrium constant, we have verified that it is not possible to use directly the values obtained on De Filippis et al. experiments20. It has been demonstrated that the equilibrium constant for this reaction strongly depends on the environment. As a matter of fact, in aqueous phase it can range between 0.8-2.5 depending on the pH of the solution10. As inside the resin the equivalent proton concentration is very high (it can be calculated from the acidity, see 2.1 Materials), it can be reasonable to assume that the equilibrium constant is different. For this reason, we decided to adjust this parameter on the collected experimental data. Finally, the performic acid decomposition can obviously occur also inside the particle. In this case, being the reaction independent on the media, we assumed the same parameters obtained from the parameter estimation activity performed on De Filippis et al. experimental data20. The formic acid partition coefficient has been considered equal to one. The same was assumed for performic acid. A summary of the adopted assumptions is reported below: (i) The particle phase is wetted only by the aqueous phase. (ii) The formic to performic acid synthesis and related performic acid decomposition occurs both in the water and in the particle. (iii) The equilibrium constant of the performic acid synthesis reaction inside the resin can be different from the one determined in the aqueous phase. (iv) The soybean oil epoxidation and related ring opening occur in the oil phase. (v) Liquid-liquid and external liquid-solid mass transfer limitations have been considered negligible due to the well mixing of the system.

12


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Concerning the formic acid synthesis, we decided to use proton concentration in rate equations instead of Hammett acidities, assuming a rapid protonation of the reactants versus protonation as a rate-determining step. The mass balances equations governing the reaction network can be written as a mixed O.D.E. – P.D.E. system. The O.D.E. are already listed in Eqs.10-11, while the intraparticle mass balance equation is reported in Eq. 12. 1 ni ,S Deff ,i   VS t

  2 Ci ,S s C i ,S  1 N . Re actions      ij r j , S 2  r    r  r j  1 P P  P 

(12)

To solve Eq. 12, it is necessary to define a set of boundary conditions. Eq. 13 represents the symmetry conditions inside the particle, while Eq. 14 the flux from the aqueous phase to the particle surface.

1 ni ,S VS rP

0

(13)

rP  0

Deff ,i 1 ni ,S  VS rP

 k m (C i ,W  C i , S rP  RP

rP  RP

)

(14)

The effective diffusivities have been calculated correcting the molecular diffusivities estimated with the Wilke-Chang correlation modified for multicomponent mixtures (Eq. 15) by the porosity and tortuosity of the catalyst, whose ratio was approximated to be 1/10 (Eq. 16). Di , M  7.4 E  12

N M T (C ) ,  M  x j j M j   M  v i0.6 j 1 c

(15)

j A

Deff ,i 

1  Di , M  Di ,M  10

(16)

Being the catalyst in spherical form, a shape factor of s=2 has been adopted. By solving the coupled O.D.E. – P.D.E. system, it is possible to evaluate the evolution with time of both the double bonds conversion and the oxirane yield for the experiments performed in the presence of Amberlyst-16 (R-1 to R-6 of Table 2). The equilibrium constant of the performic acid synthesis reaction occurring inside the resin has been obtained by parameter estimation analysis on the experimental data, resulting to be 14.90±0.36 at 55°C. The results of the simulations are reported in Figures 4-6. 13



Page 14 of 27

As it can be seen, the developed model properly describes all the experimental data reported in the literature. As an example, the solution of the P.D.E. system of the R-1 simulation is reported in Figure 7. The model is able to predict the concentration of all the components present in the aqueous phase inside the catalyst particle. As expected, by increasing the time, there is a decrease of both the hydrogen peroxide and the formic acid concentrations. Performic acid is firstly formed and then decomposes. Each component shows gradients in the particle radius coordinate. This fact can be even better appreciated by calculating the effectiveness factor as in Figure 7 for both the performic acid synthesis (η1) and decomposition reactions (η2), defined as in Eq. 17. RP

rr

s 1

i P

i 

drP

0

(17)

RP

ri

rP  RP

r

P

s 1

drP

0

The performic acid decomposition reaction is always slower inside the particle than on the surface, because performic acid is already present in the bulk phase catalyzed by the acid environment. Performic synthesis effectiveness factor changes with time. This can be considered reasonable because the reactants need first to migrate inside the particle and then react.

14


Page 15 of 27 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


4 Conclusions In the present paper, a detailed investigation of the soybean oil epoxidation reaction in the presence of Amberlyst-16 as heterogeneous catalyst has been performed. All the key steps that constitute the overall reaction mechanism has been studied independently. In particular, the formic to performic acid synthesis, with related performic thermal decomposition has been investigated by re-interpreting literature data with a more reliable model, obtaining good results. The liquid-liquid epoxidation reaction has been investigated with dedicated experiments, partially already published. The reaction has been considered occurring between the performic acid dissolved in the oil phase with the double bonds. As the oxirane ring is highly reactive, a proton attack has been considered as the rate-determining step for the ring opening reactions. It has been demonstrated that the decomposition due to the formic acid attack to the ring opening is about 9 times faster than the performic acid one, fact due to their different acidity. Some dedicated experiments have been performed to investigate the interaction between the resin and all the chemical specie constituting the system. The resin shown a highly hydrophilic behavior and no different affinity for the reactants present in the liquid phase. This fact can explain the high selectivity of the system. As a matter of fact, the resin has no catalytic action for the ring opening reactions, due to its low affinity with the organic phase. Starting from these preliminary investigation, it has been possible to interpret the epoxidation of soybean oil experiments performed in the presence of the solid catalyst. It has been demonstrated that the unique role of the resin is to catalyze the formic to performic acid synthesis. The good agreements make us confident of the fact that the puzzle can be considered completed. We can conclude that the developed model is a good starting point for the industrial reactor optimization.

15



Page 16 of 27

Notation C

concentration, mol/m3

C*

interface concentration, mol/m3

D1, D2

oxirane ring opening products

Deff,i

effective diffusivity, m2/s

Di,M

molecular diffusivity in a mixture, m2/s

E

oxirane ring

Ea

activation energy, J/mol

Hi

partition coefficient expressed as water/oil solubility, -

k1,O

kinetic constant, m3/(mols)

k2,O


k3,O


k1,W

kinetic constant, (m3/mol)2/s

k2,W

kinetic constant, 1/s

km

mass transfer coefficient, m/s

K

equilibrium constant, -

M

molecular mass, g/mol

n

amount of substance, mol

Q

volumetric flow rate, m3/s

r

reaction rate, mol/(m3s)

rP

particle coordinate, m

RP

particle radius, m

s

shape factor, - for a sphere = 2

t

time, s

T

temperature, K

V

volume, m3

w

weight, kg

x

association factor, -

XDB

double bonds conversion, -

YE

oxirane yield, -

16


Page 17 of 27 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


Greek letters β

liquid-liquid mass transfer coefficient, 1/s

ΔH

enthalpy, J/mol

ε

porosity, -

η

effectiveness factor, -

μ

viscosity, Pa s

ν

stochiometric matrix, -

τ

tortuosity, -

φ

volumetric fraction, -

Subscripts and superscripts DB

double bonds

FA

formic acid

O

organic phase

OIL

soybean oil

OX

hydrogen peroxide

PFA

performic acid

S

solid phase

W

water/water phase

Acknowledgements The authors are grateful to Solvay for having provided hydrogen peroxide. Thanks due to the Finanziamento della Ricerca di Ateneo Federico II (000023-ALTRI_DR_3450_2016_Ricerca di Ateneo- CA_BIO) for financial support.

17



Page 18 of 27

References (1) Goud, V.V.; Patwardhan, A.V.; Dinda, S.; Pradhan, N. Kinetics of Epoxidation of Jatropha Oil with Peroxyacetic and Peroxyformic Acid Catalysed by Acidic Ion Exchange Resin. Chem. Eng. Sci. 2007, 62, 4065. (2) Campanella, A.; Fontanini, C.; Baltanas, M.A. Degradation of the Oxirane Ring of Epoxidized Vegetable Oils with Hydrogen Peroxide using an Ion Exchange Resin. Catal. Today 2005, 107, 208. (3) Santacesaria, E.; Tesser, R.; Di Serio, M.; Turco, R.; Russo, V.; Verde, D. A Biphasic Model describing Soybean Oil Epoxidation with H2O2 in a Fed-Batch Reactor. Chem. Eng. J. 2011, 173, 198. (4) Russo, V.; Tesser, R.; Santacesaria, E.; Di Serio, M. Chemical and Technical Aspects of Propene Oxide Production via Hydrogen Peroxide (HPPO Process). Ind. Eng. Chem. Res. 2013, 52, 1168. (5) Russo, V.; Tesser, R.; Santacesaria, E.; Di Serio, M. Kinetics of Propene Oxide Production via Hydrogen Peroxide with TS-1. Ind. Eng. Chem. Res. 2014, 53, 6274. (6) Salzano, E.; Agreda, A.G.; Russo, V.; Di Serio, M.; Santacesaria, E. Safety Criteria for the Epoxydation of Soybean Oil in Fed-Batch Reactor. Chem. Eng. Transactions 2012, 26, 39. (7) Salzano, E.; Russo, V.; Tesser, R.; Di Serio, M. Facing the Hazard of Biphasic, Unstable, Highly Exothermic Process: the Case of Epoxidation of Vegetable Oils. Chem. Eng. Transactions 2016, 48, 493. (8) Turco, R.; Vitiello, R.; Russo, V.; Tesser, R.; Santacesaria, E.; Di Serio, M. Selective Epoxidation of Soybean Oil with Performic Acid Catalyzed by Acidic Ionic Exchange Resins. Green Process. Synth. 2013, 2, 427. (9) Sun, X.; Zhao, X.; Du, W.; Liu, D. Kinetics of Formic Acid-Autocatalyzed Preparation of Performic Acid in Aqueous Phase. Chinese J. Chem. Eng. 2011, 19, 964. (10) Santacesaria, E.; Russo, V.; Tesser, R.; Turco, R.; Di Serio, M. Kinetics of Performic Acid Synthesis and Decomposition. Submitted for publication in Ind. Eng. Chem. Res. 2017. (11) Spalek, O.; Balej, J.; Paseka, I. Kinetics of the Decomposition of Hydrogen Peroxide in Alkaline Solutions. J. Chem. Soc., Faraday Trans. 1 1982, 78, 2349. (12) Rice, F.O.; Reiff, O.M. The Thermal Decomposition of Hydrogen Peroxide. J. Phys. Chem. 1927, 31, 1352. 18


Page 19 of 27 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


(13) Santacesaria, E.; Tesser, R.; Di Serio, M.; Russo, V.; Turco, R. A New Simple Microchannel Device to Test Process Intensification. Ind. Eng. Chem. Res. 2011, 50, 2569. (14) Chadwick, A.F; Barlow, D.O.; Wallace, A.A.; D’Addieco. Theory and Practice of ResinCatalyzed Epoxidation. J.G. J. Am. Oil Chem. Soc. 1958, 35, 355. (15) Tan, S.G.; Chow, W.S. Biobased Epoxidized Vegetable Oils and its Greener Epoxy Blends: a Review. Polym.-Plast. Technol. Eng. 2010, 49, 1581. (16) Milchert, E.; Malarczyk-Matusiak, K.; Musik, M. Technological Aspects of Vegetable Oils Epoxidation in the Presence of Ion Exchange Resins: a Review. Pol. J. Chem. Technol. 2016, 18, 128. (17) Rios, L.A.; Echeverru, D.A.; Franco, A. Epoxidation of Jatropha Oil using Heterogeneous Catalysts Suitable for the Prileschajew Reaction: Acidic Resins and Immobilized Lipase. Appl. Catal. A 2011, 394, 132. (18) Tesser, R.; Di Serio, M.; Casale, L.; Carotenuto, G.; Santacesaria, E. Absorption of Water/Methanol Binary System on Ion-Exchange Resins. Can. J. Chem. Eng. 2010, 88, 1044. (19) Kolthoﬀ, I.M.; Sandell, E.B.; Meehan, E.J. Treatise on Analytical Chemistry; John Wiley & Sons: New York, 1993; Vol. 2, 888. (20) De Filippis, P.; Scarsella, M.; Verdone, N. Peroxyformic Acid Formation: a Kinetic Study. Ind. Eng. Chem. Res. 2009, 48, 1372. (21)

gPROMS

Model

Builder,

Process

System

Enterprise

Home

Page,

https://www.psenterprise.com/ (accessed April 2017). (22) CHEMCAD, Chemstations Home Page, http://www.chemstations.com/ (accessed April 2017) (23) Leveneur, S.; Thones, M.; Hebert, J.P.; Taouk, B.; Salmi, T. From Kinetic Study to Thermal Safety Assesment: Application to Peroxyformic Acid Synthesis. Ind. Eng. Chem. Res. 2012, 51, 13999. (24) Wu, Z.; Nie, Y.; Chen, W.; Wu, L.: Chen, P.; Lu, M.; Yu, F.; Ji, J. Mass Transfer and Reaction Kinetics of Soybean Oil Epoxidation in a Formic Acid-Autocatalyzed Reaction System. Can. J. Chem. Eng. 2016, 94, 1576. (25) Santacesaria, E.; Renken, A.; Russo, V.; Turco, R.; Tesser, R.; Di Serio, M. Biphasic Model Describing Soybean Oil Epoxidation with H2O2 in Continuous Reactors. Ind. Eng. Chem. Res. 2012, 51, 8760. 19



14000

T [K] 303.15 313.15 323.15 333.15 PFA OX

12000

Ci,W [mol/m3]

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

Page 20 of 27

10000 8000 6000 4000 2000 0 0

2000 4000 6000 8000 10000 12000 14000 16000

t [s] Figure 1 – Experimental data and related simulations for the formic to performic experiments performed at different temperatures by De Filippis et al. Full symbols are related to hydrogen peroxide profiles, while empty symbols to performic acid.

20


Page 21 of 27 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


Particle

Water phase

Oil phase

Ci,W Ci,O

Ci,S 1. FA + H 2 O 2 n PFA + H 2 O 2. PFA g CO 2 + H 2 O

0

1 . FA + H 2 O 2 n PFA + H 2 O 2. PFA g CO 2 + H 2O

1. PFA + DB g E + FA 2. E + FA g D 1 3. E + PFA g D 2

RP rP Figure 2 – Soybean oil epoxidation scheme in the presence of Amberlyst-16.

21



1.0

1.0

B-1

0.9

XDB, YE, [-]

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

0.9

1.0

B-2

0.9

0.8

0.8

0.8

0.7

0.7

0.7

0.6

0.6

0.6

0.5

0.5

0.5

0.4

0.4

0.4

0.3

0.3

Page 22 of 27

B-3

0.3

0.2

XDB

0.2

XDB

0.2

XDB

0.1

YE

0.1

YE

0.1

YE

0.0 0

0.0 2000 4000 6000 8000 10000 12000 0

t [s]

0.0 2000 4000 6000 8000 10000 12000 0

t [s]

2000 4000 6000 8000 10000 12000

t [s]

Figure 3 – Soybean oil epoxidation reaction results performed in the absence of heterogeneous catalysts.

22


1.0

1.0

0.8

0.8

0.6

0.6

YE [-]

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


XDB [-]

Page 23 of 27

0.4

0.2

R-1 R-4 R-5

0.0

0.4

0.2

R-1 R-4 R-5

0.0 0

3000

6000

9000

12000

0

t [s]

3000

6000

9000

12000

t [s]

Figure 4 – Effect of the formic acid/double bonds molar ratio for soybean oil epoxidation reaction results performed in the presence of Amberlyst-16.

23


1.0

1.0

0.8

0.8

0.6

0.6

YE [-]

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

XDB [-]


0.4

0.2

Page 24 of 27

0.4

0.2 R-1 R-6

0.0

R-1 R-6

0.0 0

3000

6000

9000

12000

0

t [s]

3000

6000

9000

12000

t [s]

Figure 5 – Temperature effect of the formic acid/double bonds molar ratio for soybean oil epoxidation reaction results performed in the presence of Amberlyst-16.

24


1.0

1.0

0.8

0.8

0.6

0.6

YE [-]

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


XDB [-]

Page 25 of 27

0.4

0.2

R-1 R-2 R-3

0.0

0.4

0.2

R-1 R-2 R-3

0.0 0

3000

6000

9000

12000

0

t [s]

3000

6000

9000

12000

t [s]

Figure 6 – Catalyst concentration effect of the formic acid/double bonds molar ratio for soybean oil epoxidation reaction results performed in the presence of Amberlyst-16.

25



3

CFA,s [mol/m ]

9000 8000

0 500 1000 1500 2000 2500 3000

t [s]

7000 6000 5000 4000

10000

7000 6000 5000 4000 3000

2000

2000

1000

1000 0.2

0.4

0.6

0.8

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

8000

3000

0 0.0

3

COX,s [mol/m ]

9000

t [s]

10000

0 0.0

1.0

0.2

rP/RP [-] 3

8000

0 500 1000 1500

7000 6000 5000

2000 2500 3000

4000 3000 2000

j

CPFA,s [mol/m ]

9000

0.6

0.8

1.0

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2  

0.019 0.018 0.017

1000 0 0.0

0.4

rP/RP [-]

10000

t [s]

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

Page 26 of 27

0.016

0.2

0.4

0.6

rP/RP [-]

0.8

1.0

0.015 0

2000

4000

6000

8000

10000

12000

t [s]

Figure 7 – Concentration profiles for: hydrogen peroxide, formic acid and performic acid. Effectiveness factor for the performic acid synthesis and decomposition reactions occurring inside the catalyst particle.

26


For Table of Contents Only CPFA,s 1.0

time

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


Conversion, yield [-]

Page 27 of 27

0.8 0.6 0.4

Particle radius 0.2 0.0

Double bonds conversion Oxirane yield 0

2000

4000

6000

8000

10000 12000

time [s]

27


LiquidâLiquidâSolid Model for the Epoxidation of Soybean Oil

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