- Email: [email protected]
Hybrid catalysis: Study of a model reaction for one-pot reactor combining an enzyme and a heterogeneous catalyst
Catalysis Today xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Hybrid catalysis: Study of a model reaction for one-pot reactor combining an enzyme and a heterogeneous catalyst Myriam Frey, Laman Seyidova, Dominique Richard, Pascal Fongarland
⁎
Laboratoire de Génie des Procédés Catalytiques (UMR 5285, CNRS, CPE Lyon, UCB Lyon 1), Université de Lyon, 3, rue Victor Grignard, F-69616 Villeurbanne cedex, France
A R T I C LE I N FO
A B S T R A C T
Keywords: Hybrid catalysis Kinetic modelling One-pot reactor Enzymatic isomerisation Heterogeneous catalytic oxidation
The aim of this work is to show the feasibility of a one-pot reaction in three phase hybrid catalysis, one step being an oxidation. The model reaction proposed is a two-step reaction: an enzymatic catalysed isomerisation of fructose to glucose followed by a heterogeneously catalysed oxidation of glucose to gluconic acid. The reaction medium required for the enzymatic step was shown to be compatible with the oxidation catalyst. Kinetic parameters were estimated from experimental data to run simulation using an isothermal one-pot slurry model. Finally, a one-pot test was performed which showed that combining both steps is possible.
1. Introduction The use of enzyme for fine chemical production has been the object of many works during the last decades. Among them, the recent concept of hybrid catalysis emerged, where chemical catalysis (homogeneous or heterogeneous) and enzymatic catalysis are combined [1,2]. One of the first combined use of enzyme and heterogeneous catalysis was reported by Makkee et al. who simultaneously isomerized D-glucose to D-fructose and hydrogenated D-fructose to D-mannitol [3]. They used two catalysts, an immobilized glucose isomerase and a Pt/C catalyst in a one-pot approach. The evolution of this new field called “chemoenzymatic onepot synthesis” since the pioneering work of van Bekkum's group has been reviewed by Gröger et al. [4]. Although the concept existed before, the wording “hybrid catalysis” was first mentioned in the work of Dumeignil and its group at the University of Lille [5–9] who emphasized that such a one-pot synergetic combination encompasses the novel “hybrid catalysis” concept. Indeed, hybrid catalysis in a special case of the orthogonal tandem catalysis class defined by Fogg et al. [10] in which one of the catalyst is an enzyme and the other an heterogeneous catalyst. The pros and cons for the combination of chemo- and biocatalytic reactions have been presented by Rudroff et al. in a recent review [11]. A recent report of the European Cluster on Catalysis, highlights among other emerging issues in the design of catalysts, the combination of different areas of catalysis [12]. Hybrid catalysis has been applied to three areas: kinetic resolution, dynamic kinetic resolution [1,13] and non-stereoselective reactions
⁎
[14]. The aim of the GLYCYBRIDE project is to develop a synergy between enzymatic and heterogeneous catalysis in a one-pot reactor to transform glycerol into value-added chemicals (target reaction). Our aim is to design a one-pot reactor able to perform three phase hybrid catalysis, one step being an oxidation. Knowing that enzyme and heterogeneous catalysis require different reaction conditions, such as temperature, stirring speed, oxygen concentration (oxygen possibly inhibiting the enzymatic reaction) and in order to validate the design of the reactor, we decided to use a model reaction with two well-known steps (mechanism, kinetic parameters). One step requiring an efficient mass transfer of oxygen like the target reaction. Moreover, the media of both step should be compatible. Fig. 1 shows the model reaction selected. The first reaction is an equilibrated enzyme catalysed isomerisation of fructose to glucose. The equilibrium of the first reaction will be shifted by a heterogeneously catalysed oxidation of glucose to gluconic acid. In the present work, we performed a preliminary study to check the compatibility of reaction media. Then we studied separately the kinetics of both steps in order to provide a kinetic model of the reactions to simulate the designed reactor. Then we used a simple approach to build a one-pot isothermal slurry reactor model, which will be considered as a starting point for a more elaborated compartmentalised reactor model.
Corresponding author. E-mail address: [email protected] (P. Fongarland).
https://doi.org/10.1016/j.cattod.2019.04.056 Received 31 October 2018; Received in revised form 11 April 2019; Accepted 17 April 2019 0920-5861/ © 2019 Published by Elsevier B.V.
Please cite this article as: Myriam Frey, et al., Catalysis Today, https://doi.org/10.1016/j.cattod.2019.04.056
Catalysis Today xxx (xxxx) xxx–xxx
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isomerization (mol m−3) maximum apparent reaction rate for forward and reverse isomerization (mol kg −cat1 s−1) equilibrium constant (–) concentration of fructose at the equilibrium (mol m−3) concentration of enzyme (kg m−3) rate constant of oxidation reaction (m3 g −cat1 s−1) adsorption constant for oxidation reaction (m3mol−1) oxidation catalyst concentration (kg m−3)
Nomenclature
vmf , vmr F G GA r1 r2 Vm Km kmf, kmr
fructose glucose gluconic acid apparent reaction rate for step 1 apparent reaction rate for step 2 maximum apparent reaction rate (mol kg −cat1 s−1) apparent Michaelis–Menten constant (mol m−3) Michaelis–Menten constants for forward and reverse
Ke eq Cfructose wenzyme kox KG, KGA wcatalyst
Fig. 1. The model reaction.
2. Experimental section
corresponding maximum apparent reaction rates (vmf , vmr ). The detail of the derivation will not be repeated here but it leads to the following rate laws:
2.1. Experimental procedure As a general procedure, all catalytic tests were performed in a 1 L jacketed glass reactor with counter-blades. The desired amount of substrate is dissolved in a 0.3 M potassium phosphate buffer solution (pH 7.5) in a 0.5 L volumetric flask. The substrate solution is fed in the reactor, already heated up to 50 °C, under a stirring speed of 300 rpm and closed lid. The desired amount of catalyst or catalysts were added when the temperature of the substrate solution reached 50 °C. Samples were taken until the reaction reached equilibrium or was finished and analysed by HPLC (Luna 5 μm NH2 100 Å column from Phenomenex) to monitor the progress of the reaction. In order to estimate kinetic parameters of each reaction step, namely isomerisation and oxidation, two parameters were varied to collect the experimental data required: the initial substrate concentration or the amount of catalyst. For the isomerisation step, first the initial fructose concentration was varied from 0.1 M to 0.75 M with 30 wt% of enzyme Sweetzyme IT extra isomerase from Novozymes, then the amount of catalyst was varied from 10 wt% to 30 wt% with an initial fructose concentration of 0.2 M. For the oxidation step, first the initial glucose concentration was varied from 0.1 M to 0.5 M with 10 wt% of 5 wt% Pt/C from Engelhardt, then the amount of catalyst was varied from 5 wt% to 20 wt% with an initial glucose concentration of 0.2 M.
r1 = Vm·
eq Cfructose − Cfructose eq Km + Cfructose − Cfructose
with
Vm = [1 + K e−1]·
k mf k mr ⎡ 1 K eq ⎤ · 1+⎛ + e ⎞ Cfructose ⎥ k mr − k mf ⎢ k mr ⎠ ⎝ k mf ⎦ ⎣
(4)
Ke =
vmf k mr vmr k mf
(5)
r2 =
⎜
k ox K G Cglucose 1 + K G ·Cglucose + K GA ·Cgluconic acid
dt
dCglucose dt
(6)
= r2·wcatalyst
= r1·wenzyme + r2·wcatalyst
(7) (8) (9)
Since the equilibrium constant can be derived from the fructose and glucose concentrations measured at the end of the isomerization reaction, only three parameters out of the four (kmf, kmr, vmf , vmr ) need to be estimated. The progress of the reaction mixture composition was simulated with an ODE15 solver using Matlab®. Two simulations were run: a first one using kinetic parameters from literature, and a second one using kinetic parameters estimated from our experimental data (LSQNONLIN routine with Matlab®).
To establish the reactor model we combined the isomerization model proposed by Dehkordi et al. [15] and the oxidation model proposed by Dirkx [16]. k−2
·wcatalyst
dCfructose = −r1·wenzyme dt
2.3. Kinetic model
k−1
⎟
The mass balance, assuming that we have an ideal batch reactor is defined by the following equations:
Room temperature powder X-ray diffraction patterns were obtained with a D8 Advanced A25 diffractometer (Bruker) with a Bragg–Brentano configuration and a linear detector. The X-ray source was a copper long fine focused X-ray diffraction tube operating at 40 kV and 30 mA, with an angular step of 0.015° and a time per step of 0.1 s. Chemisorption of H2 were carried out with an ASAP 2020 analyzer (Micromeritics).
k2
(3)
and
2.2. Catalyst characterization
k1
k mr vmf k mf − k mr
Km =
dCgluconic acid
3. Results and discussion 3.1. One-pot slurry simulation (from literature data)
k ox
F + Enz ⇌ Complex ⇌ G + Enz → GA
(2)
(1)
Simulations of each steps based on the reported model were performed using kinetic parameters extracted from the literature [15,16]. They are shown in Fig. 2 and the values of the parameters used reported in Table 1.
Dehkordi et al., starting from glucose established a relation based on Palazzi et al. [17] work, between the observed isomerization rate r1 and the forward and reverse Michaelis–Menten constants (kmf, kmr) and 2
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Fig. 2. Comparison between simulated curves and experimental points (50 °C, 0.2 M substrate, kinetic parameters are from literature).
Fig. 3. Compatibility check of each step with reaction conditions required by the other (0.5 M, 50 °C, 10 wt% of catalyst).
Table 1 Kinetic parameters values from literature and estimated.
3.2. Catalytic tests
Parameter
Literature [15,16]
Estimated from experiment
kmr (mol m−3) kmf (mol m−3)
0.080 0.252 2.1×10−6
0.094 ± 0.011 1.238 ± 0.711 1.49 ± 0.73) ×10−5
8.9×10−6
1.5×10−5
−4
2.2×10−5
1 −1 vmf (mol kg − cat s ) 1 −1 vmr (mol kg − cat s ) 3
1 −1 g− cat s )
k1 (m KG (m3mol−1) KGA (m3mol−1)
2.5×10 13 21
3.2.1. Characterization of the Pt/C catalyst Powder diffraction of the Pt/C catalyst revealed a high dispersion of the metal since the diffraction lines of the metal were too broad to allow for a crystallite size estimation by the Scherrer relation. This observation remained after reaction evidencing the absence of sintering during the course of the reaction. The metallic dispersion (≈50%) measured by H2 chemisorption, only very slightly decreased after the reaction, confirming the previous conclusion.
4.7 84.8
3.2.2. Preliminary test Before collecting experimental data to estimate the kinetic parameters, a series of preliminary tests are necessary, especially to ensure the compatibility of the reaction conditions required for both steps. The blank tests performed confirm that neither the isomerization, nor the oxidation reaction proceeds without a catalyst. For the isomerisation step, a stirring rate of 200–300 rpm is sufficient to prevent diffusion limitation as for the oxidation step, a stirring rate of 1000–1200 rpm is needed. The results of the compatibility tests are presented in Fig. 3. Fig. 3(a), shows that the enzyme does not need to be pre-activated (rehydration in MgSO4 solution) as reported in the literature [18,15]
A comparison of the simulation results with experimental data shows that for Fig. 2(a) and (b), the simulated curves are close to the experimental points. However the isomerisation reaction runs faster than expected by the simulation and the oxidation step slower. As a result the gap between simulated and experimental points is more important when both steps are combined in a one-pot simulation. Those results clearly show that an adjustment of kinetic parameters is necessary to achieve a satisfactory agreement between experimental data and the one-pot slurry simulation.
3
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and that the use of phosphate buffer to ensure stable pH has no significant effect on the reaction rate for the isomerisation step. Fig. 3(b) shows that the presence of air, necessary for the second step (oxidation), does not have a negative effect on the enzymatic step. Fig. 3(c) shows that the presence of MgSO4 has no significant effect on the oxidation step. Meanwhile the presence of buffer seems to have a positive effect on the oxidation step. Indeed without buffer, the reaction rate is the same during the first 40 min then the rate decreases and the conversion almost cease to increase. Whereas in the presence of buffer this phenomenon is not observed. Deactivation of oxidation catalysts such as platinum is well documented in the literature [19–21], for instance poisoning of active sites by side products directly or by CO resulting from decarboxylation of the carboxylic acid produced has been reported. Presence of base such as NaOH has been reported to prevent such poisoning. In our case, the presence of buffer that maintains a steady pH seems to have a similar effect. 3.2.3. Kinetic parameters estimation A comparison of experimental data and simulated ones is presented in Fig. 4 for a set of fructose to glucose isomerisation experiments used to perform the new estimation. The simulated curves (Fig. 4) show a good agreement with the experimental data. Another representation of experimental and simulated data through the parity curve confirms this observation, the difference between experimental and calculated values of the group of points presented is below 10%. The new set of kinetic parameters estimated for our model is presented in Table 1. For the isomerisation step, the values of kmr and νmf are in the same order of magnitude than the ones from the literature, whereas kmf and νmr underwent greater adjustment. Thus changing the Km and Vm values. Vm increases from −9.6 × 10−6 mol kg−1 cat s−1 to −2.9 × 10−6 mol kg−1 cat s−1, which is in correlation with a faster reaction rate. Note that in our case, Vm values are negative, due to the way our kinetic law was constructed. In order to allow direct comparison with the data published by Dehkordi et al. [15,17] who used the same supported enzyme (Sweetzyme IT extra), we reversed the law that was initially used for glucose to fructose isomerisation by the authors. For the oxidation part, the reaction is proceeding slower than estimated with Dirkx et al. [16] parameters, this can be due to different factors, first the catalyst used is less performant, which results in a lower value of k1, which is the case here. But other factors can also be considered, such as a deactivation by adsorption of reaction product as mentioned previously, this can be translated in the kinetic law by a higher adsorption constant value of KAG. The adsorption constant calculated is indeed higher with a value of 84.5 m3 mol−1 in our case against 21 m3 mol−1 reported by Dirkx et al., with stronger adsorption
Fig. 5. One-pot slurry experiment, comparison of experimental data with model.
of products, the desorption is slower and active sites less available for glucose oxidation. Moreover, the adsorption constant value for glucose (KAG) is lower than the one in literature. Both observation are consistent with a slower reaction rate. 3.2.4. One-pot slurry reaction A first one-pot slurry test showed that both steps could be combined (Fig. 5). However, the reaction rates were lower than expected by the
Fig. 4. Isomerization step: experimental and simulated concentration with new kinetic parameters estimated. 4
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slurry model (Fig. 5(a)). This can be due to deactivation or strong inhibition of the catalyst by carboxylic acid groups, a well-known phenomenon. A better curve fitting is indeed achieved (Fig. 5(b)) when considering strong inhibition by products. Further investigation is needed to exclude other additional causes (limitation of oxygen transfer, deactivation, enzyme inhibition, etc.) and optimize the coupling of both steps.
ChemCatChem 7 (24) (2015) 4004–4015. [2] F.R. Bisogno, M.G. López-Vidal, G. de Gonzalo, Organocatalysis and biocatalysis hand in hand: combining catalysts in one-pot procedures, Adv. Synth. Catal. 359 (12) (2017) 2026–2049. [3] M. Makkee, A.P.G. Kieboom, H.V. Bekkum, J.A. Roels, Combined action of enzyme and metal catalyst, applied to the preparation of D-mannitol, J. Chem. Soc., Chem. Commun. (19) (1980) 930–931. [4] H. Gröger, W. Hummel, Combining the ‘two worlds’ of chemocatalysis and biocatalysis towards multi-step one-pot processes in aqueous media, Curr. Opin. Chem. Biol. 19 (2014) 171–179. [5] F. Dumeignil, Hailing the hybrid, Public Serv. Rev. Eur. Union 22 (2011) 528. [6] F. Dumeignil, Chemical catalysis and biotechnology: from a sequential engagement to a one-pot wedding, Chem. Ing. Tech. 86 (9) (2014) 1496. [7] A. Gimbernat, M. Guehl, M. Capron, N. Lopes Ferreira, R. Froidevaux, J.S. Girardon, P. Dhulster, D. Delcroix, F. Dumeignil, Hybrid catalysis: a suitable concept for the valorization of biosourced saccharides to value-added chemicals, ChemCatChem 9 (12) (2017) 2080–2084. [8] M. Guehl, Nouveau concept de catalyse hybride pour la transformation de la biomasse, Ph.D. thesis, Université de Lille, 2017. [9] F.Y. Dumeignil, M. Guehl, A. Gimbernat, M. Capron, N. Lopes Ferreira, R. Froidevaux, J.-S. Girardon, R. Wojcieszak, P. Dhulster, D. Delcroix, From sequential chemoenzymatic synthesis to integrated hybrid catalysis: taking the best of both worlds to open up the scope of possibilities for a sustainable future, Catal. Sci. Technol. (2018) accepted manuscript. [10] D.E. Fogg, E.N. dos Santos, Tandem catalysis: a taxonomy and illustrative review, Coord. Chem. Rev. 248 (2004) 2365. [11] F. Rudroff, M.D. Mihovilovic, H. Gröger, R. Snajdrova, H. Iding, U.T. Bornscheuer, Opportunities and challenges for combining chemo- and biocatalysis, Nat. Catal. 1 (2018) 12–22. [12] S. Perathoner, G. Centi, Science & Technology Roadmap on Catalysis for Europe, Tech. rep. European Cluster on Catalysis, 2016. [13] Y. Wang, H. Zhao, Tandem reactions combining biocatalysts and chemical catalysts for asymmetric synthesis, Catalysts 6 (2016) 194. [14] C.A. Denard, F. Hartwig, H. Zhao, Multistep one-pot reactions combining biocatalysts and chemical catalysts for asymmetric synthesis, ACS Catal. 3 (2013) 2856–2864. [15] A.M. Dehkordi, M.S. Tehrany, I. Safari, Kinetics of glucose isomerization to fructose by immobilized glucose isomerase (Sweetzyme IT), Ind. Eng. Chem. Res. 48 (2009) 3271–3278. [16] J.M.H. Dirkx, H.S. van der Baan, The Oxidation of glucose with platinum on carbon as catalyst, J. Catal. 67 (1981) 1–13. [17] E. Palazzi, A. Converti, Generalized linearization of kinetics of glucose isomerization to fructose by immobilized glucose isomerase, Biotechnol. Bioeng. 63 (3) (1999) 273–284. [18] F. Camacho-Rubio, E. Jurado-Alameda, P. González-Tello, G. Luzón-González, Kinetic study of fructose-glucose isomerization in a recirculation reactor, Can. J. Chem. Eng. 73 (6) (1995) 935–940. [19] T. Mallat, A. Baiker, Oxidation of alcohols with molecular oxygen on solid catalysts, Chem. Rev. 104 (6) (2004) 3037–3058. [20] M. Besson, P. Gallezot, Selective oxidation of alcohols and aldehydes on metal catalysts, Catal. Today 57 (1–2) (2000) 127–141. [21] M.S. Ide, D.D. Falcone, R.J. Davis, On the deactivation of supported platinum catalysts for selective oxidation of alcohols, J. Catal. 311 (2014) 295–305.
4. Conclusion During the present study a model reaction including an oxidation step was proposed for hybrid catalysis for which:
• the medium compatibility for both steps was checked, • the kinetic parameter for each step initially taken from the literature were estimated from the experiments run, • the kinetic laws obtained were used to build a one-pot slurry model of the reactor, • one-pot experiments showed that the fructose to glucose iso•
merisation step and the glucose oxidation to gluconic acid step can be combined as proposed, a slower reaction rate than expected from the model was observed, due to inhibition by the products.
Further investigations are under progress to optimize the one-pot reaction. As a perspective, a more elaborated model, including compartmentalization, will be developed in order to better describe the onepot reactor developed in the project. Acknowlegment This study was carried out in collaboration with SAS PIVERT, as part of the Institute for Energy Transition (ITE) P.I.V.E.R.T (www. institut-pivert.com) selected among the Investments of Future. This study received support from the Investments of Future Program (Reference ANR-001-01). References [1] O. Långvik, T. Saloranta, D.Y. Murzin, R. Leino, Heterogeneous chemoenzymatic catalyst combinations for one-pot dynamic kinetic resolution applications,
5
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Hybrid catalysis: Study of a model reaction for one-pot reactor combining an enzyme and a heterogeneous catalyst Myriam Frey, Laman Seyidova, Dominique Richard, Pascal Fongarland
⁎
Laboratoire de Génie des Procédés Catalytiques (UMR 5285, CNRS, CPE Lyon, UCB Lyon 1), Université de Lyon, 3, rue Victor Grignard, F-69616 Villeurbanne cedex, France
A R T I C LE I N FO
A B S T R A C T
Keywords: Hybrid catalysis Kinetic modelling One-pot reactor Enzymatic isomerisation Heterogeneous catalytic oxidation
The aim of this work is to show the feasibility of a one-pot reaction in three phase hybrid catalysis, one step being an oxidation. The model reaction proposed is a two-step reaction: an enzymatic catalysed isomerisation of fructose to glucose followed by a heterogeneously catalysed oxidation of glucose to gluconic acid. The reaction medium required for the enzymatic step was shown to be compatible with the oxidation catalyst. Kinetic parameters were estimated from experimental data to run simulation using an isothermal one-pot slurry model. Finally, a one-pot test was performed which showed that combining both steps is possible.
1. Introduction The use of enzyme for fine chemical production has been the object of many works during the last decades. Among them, the recent concept of hybrid catalysis emerged, where chemical catalysis (homogeneous or heterogeneous) and enzymatic catalysis are combined [1,2]. One of the first combined use of enzyme and heterogeneous catalysis was reported by Makkee et al. who simultaneously isomerized D-glucose to D-fructose and hydrogenated D-fructose to D-mannitol [3]. They used two catalysts, an immobilized glucose isomerase and a Pt/C catalyst in a one-pot approach. The evolution of this new field called “chemoenzymatic onepot synthesis” since the pioneering work of van Bekkum's group has been reviewed by Gröger et al. [4]. Although the concept existed before, the wording “hybrid catalysis” was first mentioned in the work of Dumeignil and its group at the University of Lille [5–9] who emphasized that such a one-pot synergetic combination encompasses the novel “hybrid catalysis” concept. Indeed, hybrid catalysis in a special case of the orthogonal tandem catalysis class defined by Fogg et al. [10] in which one of the catalyst is an enzyme and the other an heterogeneous catalyst. The pros and cons for the combination of chemo- and biocatalytic reactions have been presented by Rudroff et al. in a recent review [11]. A recent report of the European Cluster on Catalysis, highlights among other emerging issues in the design of catalysts, the combination of different areas of catalysis [12]. Hybrid catalysis has been applied to three areas: kinetic resolution, dynamic kinetic resolution [1,13] and non-stereoselective reactions
⁎
[14]. The aim of the GLYCYBRIDE project is to develop a synergy between enzymatic and heterogeneous catalysis in a one-pot reactor to transform glycerol into value-added chemicals (target reaction). Our aim is to design a one-pot reactor able to perform three phase hybrid catalysis, one step being an oxidation. Knowing that enzyme and heterogeneous catalysis require different reaction conditions, such as temperature, stirring speed, oxygen concentration (oxygen possibly inhibiting the enzymatic reaction) and in order to validate the design of the reactor, we decided to use a model reaction with two well-known steps (mechanism, kinetic parameters). One step requiring an efficient mass transfer of oxygen like the target reaction. Moreover, the media of both step should be compatible. Fig. 1 shows the model reaction selected. The first reaction is an equilibrated enzyme catalysed isomerisation of fructose to glucose. The equilibrium of the first reaction will be shifted by a heterogeneously catalysed oxidation of glucose to gluconic acid. In the present work, we performed a preliminary study to check the compatibility of reaction media. Then we studied separately the kinetics of both steps in order to provide a kinetic model of the reactions to simulate the designed reactor. Then we used a simple approach to build a one-pot isothermal slurry reactor model, which will be considered as a starting point for a more elaborated compartmentalised reactor model.
Corresponding author. E-mail address: [email protected] (P. Fongarland).
https://doi.org/10.1016/j.cattod.2019.04.056 Received 31 October 2018; Received in revised form 11 April 2019; Accepted 17 April 2019 0920-5861/ © 2019 Published by Elsevier B.V.
Please cite this article as: Myriam Frey, et al., Catalysis Today, https://doi.org/10.1016/j.cattod.2019.04.056
Catalysis Today xxx (xxxx) xxx–xxx
M. Frey, et al.
isomerization (mol m−3) maximum apparent reaction rate for forward and reverse isomerization (mol kg −cat1 s−1) equilibrium constant (–) concentration of fructose at the equilibrium (mol m−3) concentration of enzyme (kg m−3) rate constant of oxidation reaction (m3 g −cat1 s−1) adsorption constant for oxidation reaction (m3mol−1) oxidation catalyst concentration (kg m−3)
Nomenclature
vmf , vmr F G GA r1 r2 Vm Km kmf, kmr
fructose glucose gluconic acid apparent reaction rate for step 1 apparent reaction rate for step 2 maximum apparent reaction rate (mol kg −cat1 s−1) apparent Michaelis–Menten constant (mol m−3) Michaelis–Menten constants for forward and reverse
Ke eq Cfructose wenzyme kox KG, KGA wcatalyst
Fig. 1. The model reaction.
2. Experimental section
corresponding maximum apparent reaction rates (vmf , vmr ). The detail of the derivation will not be repeated here but it leads to the following rate laws:
2.1. Experimental procedure As a general procedure, all catalytic tests were performed in a 1 L jacketed glass reactor with counter-blades. The desired amount of substrate is dissolved in a 0.3 M potassium phosphate buffer solution (pH 7.5) in a 0.5 L volumetric flask. The substrate solution is fed in the reactor, already heated up to 50 °C, under a stirring speed of 300 rpm and closed lid. The desired amount of catalyst or catalysts were added when the temperature of the substrate solution reached 50 °C. Samples were taken until the reaction reached equilibrium or was finished and analysed by HPLC (Luna 5 μm NH2 100 Å column from Phenomenex) to monitor the progress of the reaction. In order to estimate kinetic parameters of each reaction step, namely isomerisation and oxidation, two parameters were varied to collect the experimental data required: the initial substrate concentration or the amount of catalyst. For the isomerisation step, first the initial fructose concentration was varied from 0.1 M to 0.75 M with 30 wt% of enzyme Sweetzyme IT extra isomerase from Novozymes, then the amount of catalyst was varied from 10 wt% to 30 wt% with an initial fructose concentration of 0.2 M. For the oxidation step, first the initial glucose concentration was varied from 0.1 M to 0.5 M with 10 wt% of 5 wt% Pt/C from Engelhardt, then the amount of catalyst was varied from 5 wt% to 20 wt% with an initial glucose concentration of 0.2 M.
r1 = Vm·
eq Cfructose − Cfructose eq Km + Cfructose − Cfructose
with
Vm = [1 + K e−1]·
k mf k mr ⎡ 1 K eq ⎤ · 1+⎛ + e ⎞ Cfructose ⎥ k mr − k mf ⎢ k mr ⎠ ⎝ k mf ⎦ ⎣
(4)
Ke =
vmf k mr vmr k mf
(5)
r2 =
⎜
k ox K G Cglucose 1 + K G ·Cglucose + K GA ·Cgluconic acid
dt
dCglucose dt
(6)
= r2·wcatalyst
= r1·wenzyme + r2·wcatalyst
(7) (8) (9)
Since the equilibrium constant can be derived from the fructose and glucose concentrations measured at the end of the isomerization reaction, only three parameters out of the four (kmf, kmr, vmf , vmr ) need to be estimated. The progress of the reaction mixture composition was simulated with an ODE15 solver using Matlab®. Two simulations were run: a first one using kinetic parameters from literature, and a second one using kinetic parameters estimated from our experimental data (LSQNONLIN routine with Matlab®).
To establish the reactor model we combined the isomerization model proposed by Dehkordi et al. [15] and the oxidation model proposed by Dirkx [16]. k−2
·wcatalyst
dCfructose = −r1·wenzyme dt
2.3. Kinetic model
k−1
⎟
The mass balance, assuming that we have an ideal batch reactor is defined by the following equations:
Room temperature powder X-ray diffraction patterns were obtained with a D8 Advanced A25 diffractometer (Bruker) with a Bragg–Brentano configuration and a linear detector. The X-ray source was a copper long fine focused X-ray diffraction tube operating at 40 kV and 30 mA, with an angular step of 0.015° and a time per step of 0.1 s. Chemisorption of H2 were carried out with an ASAP 2020 analyzer (Micromeritics).
k2
(3)
and
2.2. Catalyst characterization
k1
k mr vmf k mf − k mr
Km =
dCgluconic acid
3. Results and discussion 3.1. One-pot slurry simulation (from literature data)
k ox
F + Enz ⇌ Complex ⇌ G + Enz → GA
(2)
(1)
Simulations of each steps based on the reported model were performed using kinetic parameters extracted from the literature [15,16]. They are shown in Fig. 2 and the values of the parameters used reported in Table 1.
Dehkordi et al., starting from glucose established a relation based on Palazzi et al. [17] work, between the observed isomerization rate r1 and the forward and reverse Michaelis–Menten constants (kmf, kmr) and 2
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Fig. 2. Comparison between simulated curves and experimental points (50 °C, 0.2 M substrate, kinetic parameters are from literature).
Fig. 3. Compatibility check of each step with reaction conditions required by the other (0.5 M, 50 °C, 10 wt% of catalyst).
Table 1 Kinetic parameters values from literature and estimated.
3.2. Catalytic tests
Parameter
Literature [15,16]
Estimated from experiment
kmr (mol m−3) kmf (mol m−3)
0.080 0.252 2.1×10−6
0.094 ± 0.011 1.238 ± 0.711 1.49 ± 0.73) ×10−5
8.9×10−6
1.5×10−5
−4
2.2×10−5
1 −1 vmf (mol kg − cat s ) 1 −1 vmr (mol kg − cat s ) 3
1 −1 g− cat s )
k1 (m KG (m3mol−1) KGA (m3mol−1)
2.5×10 13 21
3.2.1. Characterization of the Pt/C catalyst Powder diffraction of the Pt/C catalyst revealed a high dispersion of the metal since the diffraction lines of the metal were too broad to allow for a crystallite size estimation by the Scherrer relation. This observation remained after reaction evidencing the absence of sintering during the course of the reaction. The metallic dispersion (≈50%) measured by H2 chemisorption, only very slightly decreased after the reaction, confirming the previous conclusion.
4.7 84.8
3.2.2. Preliminary test Before collecting experimental data to estimate the kinetic parameters, a series of preliminary tests are necessary, especially to ensure the compatibility of the reaction conditions required for both steps. The blank tests performed confirm that neither the isomerization, nor the oxidation reaction proceeds without a catalyst. For the isomerisation step, a stirring rate of 200–300 rpm is sufficient to prevent diffusion limitation as for the oxidation step, a stirring rate of 1000–1200 rpm is needed. The results of the compatibility tests are presented in Fig. 3. Fig. 3(a), shows that the enzyme does not need to be pre-activated (rehydration in MgSO4 solution) as reported in the literature [18,15]
A comparison of the simulation results with experimental data shows that for Fig. 2(a) and (b), the simulated curves are close to the experimental points. However the isomerisation reaction runs faster than expected by the simulation and the oxidation step slower. As a result the gap between simulated and experimental points is more important when both steps are combined in a one-pot simulation. Those results clearly show that an adjustment of kinetic parameters is necessary to achieve a satisfactory agreement between experimental data and the one-pot slurry simulation.
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and that the use of phosphate buffer to ensure stable pH has no significant effect on the reaction rate for the isomerisation step. Fig. 3(b) shows that the presence of air, necessary for the second step (oxidation), does not have a negative effect on the enzymatic step. Fig. 3(c) shows that the presence of MgSO4 has no significant effect on the oxidation step. Meanwhile the presence of buffer seems to have a positive effect on the oxidation step. Indeed without buffer, the reaction rate is the same during the first 40 min then the rate decreases and the conversion almost cease to increase. Whereas in the presence of buffer this phenomenon is not observed. Deactivation of oxidation catalysts such as platinum is well documented in the literature [19–21], for instance poisoning of active sites by side products directly or by CO resulting from decarboxylation of the carboxylic acid produced has been reported. Presence of base such as NaOH has been reported to prevent such poisoning. In our case, the presence of buffer that maintains a steady pH seems to have a similar effect. 3.2.3. Kinetic parameters estimation A comparison of experimental data and simulated ones is presented in Fig. 4 for a set of fructose to glucose isomerisation experiments used to perform the new estimation. The simulated curves (Fig. 4) show a good agreement with the experimental data. Another representation of experimental and simulated data through the parity curve confirms this observation, the difference between experimental and calculated values of the group of points presented is below 10%. The new set of kinetic parameters estimated for our model is presented in Table 1. For the isomerisation step, the values of kmr and νmf are in the same order of magnitude than the ones from the literature, whereas kmf and νmr underwent greater adjustment. Thus changing the Km and Vm values. Vm increases from −9.6 × 10−6 mol kg−1 cat s−1 to −2.9 × 10−6 mol kg−1 cat s−1, which is in correlation with a faster reaction rate. Note that in our case, Vm values are negative, due to the way our kinetic law was constructed. In order to allow direct comparison with the data published by Dehkordi et al. [15,17] who used the same supported enzyme (Sweetzyme IT extra), we reversed the law that was initially used for glucose to fructose isomerisation by the authors. For the oxidation part, the reaction is proceeding slower than estimated with Dirkx et al. [16] parameters, this can be due to different factors, first the catalyst used is less performant, which results in a lower value of k1, which is the case here. But other factors can also be considered, such as a deactivation by adsorption of reaction product as mentioned previously, this can be translated in the kinetic law by a higher adsorption constant value of KAG. The adsorption constant calculated is indeed higher with a value of 84.5 m3 mol−1 in our case against 21 m3 mol−1 reported by Dirkx et al., with stronger adsorption
Fig. 5. One-pot slurry experiment, comparison of experimental data with model.
of products, the desorption is slower and active sites less available for glucose oxidation. Moreover, the adsorption constant value for glucose (KAG) is lower than the one in literature. Both observation are consistent with a slower reaction rate. 3.2.4. One-pot slurry reaction A first one-pot slurry test showed that both steps could be combined (Fig. 5). However, the reaction rates were lower than expected by the
Fig. 4. Isomerization step: experimental and simulated concentration with new kinetic parameters estimated. 4
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slurry model (Fig. 5(a)). This can be due to deactivation or strong inhibition of the catalyst by carboxylic acid groups, a well-known phenomenon. A better curve fitting is indeed achieved (Fig. 5(b)) when considering strong inhibition by products. Further investigation is needed to exclude other additional causes (limitation of oxygen transfer, deactivation, enzyme inhibition, etc.) and optimize the coupling of both steps.
ChemCatChem 7 (24) (2015) 4004–4015. [2] F.R. Bisogno, M.G. López-Vidal, G. de Gonzalo, Organocatalysis and biocatalysis hand in hand: combining catalysts in one-pot procedures, Adv. Synth. Catal. 359 (12) (2017) 2026–2049. [3] M. Makkee, A.P.G. Kieboom, H.V. Bekkum, J.A. Roels, Combined action of enzyme and metal catalyst, applied to the preparation of D-mannitol, J. Chem. Soc., Chem. Commun. (19) (1980) 930–931. [4] H. Gröger, W. Hummel, Combining the ‘two worlds’ of chemocatalysis and biocatalysis towards multi-step one-pot processes in aqueous media, Curr. Opin. Chem. Biol. 19 (2014) 171–179. [5] F. Dumeignil, Hailing the hybrid, Public Serv. Rev. Eur. Union 22 (2011) 528. [6] F. Dumeignil, Chemical catalysis and biotechnology: from a sequential engagement to a one-pot wedding, Chem. Ing. Tech. 86 (9) (2014) 1496. [7] A. Gimbernat, M. Guehl, M. Capron, N. Lopes Ferreira, R. Froidevaux, J.S. Girardon, P. Dhulster, D. Delcroix, F. Dumeignil, Hybrid catalysis: a suitable concept for the valorization of biosourced saccharides to value-added chemicals, ChemCatChem 9 (12) (2017) 2080–2084. [8] M. Guehl, Nouveau concept de catalyse hybride pour la transformation de la biomasse, Ph.D. thesis, Université de Lille, 2017. [9] F.Y. Dumeignil, M. Guehl, A. Gimbernat, M. Capron, N. Lopes Ferreira, R. Froidevaux, J.-S. Girardon, R. Wojcieszak, P. Dhulster, D. Delcroix, From sequential chemoenzymatic synthesis to integrated hybrid catalysis: taking the best of both worlds to open up the scope of possibilities for a sustainable future, Catal. Sci. Technol. (2018) accepted manuscript. [10] D.E. Fogg, E.N. dos Santos, Tandem catalysis: a taxonomy and illustrative review, Coord. Chem. Rev. 248 (2004) 2365. [11] F. Rudroff, M.D. Mihovilovic, H. Gröger, R. Snajdrova, H. Iding, U.T. Bornscheuer, Opportunities and challenges for combining chemo- and biocatalysis, Nat. Catal. 1 (2018) 12–22. [12] S. Perathoner, G. Centi, Science & Technology Roadmap on Catalysis for Europe, Tech. rep. European Cluster on Catalysis, 2016. [13] Y. Wang, H. Zhao, Tandem reactions combining biocatalysts and chemical catalysts for asymmetric synthesis, Catalysts 6 (2016) 194. [14] C.A. Denard, F. Hartwig, H. Zhao, Multistep one-pot reactions combining biocatalysts and chemical catalysts for asymmetric synthesis, ACS Catal. 3 (2013) 2856–2864. [15] A.M. Dehkordi, M.S. Tehrany, I. Safari, Kinetics of glucose isomerization to fructose by immobilized glucose isomerase (Sweetzyme IT), Ind. Eng. Chem. Res. 48 (2009) 3271–3278. [16] J.M.H. Dirkx, H.S. van der Baan, The Oxidation of glucose with platinum on carbon as catalyst, J. Catal. 67 (1981) 1–13. [17] E. Palazzi, A. Converti, Generalized linearization of kinetics of glucose isomerization to fructose by immobilized glucose isomerase, Biotechnol. Bioeng. 63 (3) (1999) 273–284. [18] F. Camacho-Rubio, E. Jurado-Alameda, P. González-Tello, G. Luzón-González, Kinetic study of fructose-glucose isomerization in a recirculation reactor, Can. J. Chem. Eng. 73 (6) (1995) 935–940. [19] T. Mallat, A. Baiker, Oxidation of alcohols with molecular oxygen on solid catalysts, Chem. Rev. 104 (6) (2004) 3037–3058. [20] M. Besson, P. Gallezot, Selective oxidation of alcohols and aldehydes on metal catalysts, Catal. Today 57 (1–2) (2000) 127–141. [21] M.S. Ide, D.D. Falcone, R.J. Davis, On the deactivation of supported platinum catalysts for selective oxidation of alcohols, J. Catal. 311 (2014) 295–305.
4. Conclusion During the present study a model reaction including an oxidation step was proposed for hybrid catalysis for which:
• the medium compatibility for both steps was checked, • the kinetic parameter for each step initially taken from the literature were estimated from the experiments run, • the kinetic laws obtained were used to build a one-pot slurry model of the reactor, • one-pot experiments showed that the fructose to glucose iso•
merisation step and the glucose oxidation to gluconic acid step can be combined as proposed, a slower reaction rate than expected from the model was observed, due to inhibition by the products.
Further investigations are under progress to optimize the one-pot reaction. As a perspective, a more elaborated model, including compartmentalization, will be developed in order to better describe the onepot reactor developed in the project. Acknowlegment This study was carried out in collaboration with SAS PIVERT, as part of the Institute for Energy Transition (ITE) P.I.V.E.R.T (www. institut-pivert.com) selected among the Investments of Future. This study received support from the Investments of Future Program (Reference ANR-001-01). References [1] O. Långvik, T. Saloranta, D.Y. Murzin, R. Leino, Heterogeneous chemoenzymatic catalyst combinations for one-pot dynamic kinetic resolution applications,
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