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Kinetic analysis of a solid base-catalyzed reaction in sub- and supercritical water using aldol condensation with Mg(OH) as a model 2
Makoto Akizuki, Yusuke Nakai, Tatsuya Fujii, and Yoshito Oshima Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b03283 • Publication Date (Web): 03 Oct 2017 Downloaded from http://pubs.acs.org on October 8, 2017
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Kinetic analysis of a solid base-catalyzed reaction in sub- and supercritical water using aldol condensation with Mg(OH)2 as a model Makoto Akizuki,†,* Yusuke Nakai,† Tatsuya Fujii,‡ and Yoshito Oshima† †
Department of Environment Systems, Graduate School of Frontier Sciences, The University of
Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8563, Japan ‡
Research Institute for Chemical Process Technology, National Institute of Advanced Industrial
Science and Technology (AIST), 4-2-1 Nigatake, Miyagino-ku, Sendai, Miyagi 983-8551, Japan *E-mail address:
[email protected]
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ABSTRACT
The kinetics of aldol condensation between acetone and benzaldehyde catalyzed by Mg(OH)2 in sub- and supercritical water at various temperatures (250–450 °C) and pressures (23–31 MPa) was investigated to elucidate the effects of water properties on solid base catalysis. The kinetics obey the Eley-Rideal (ER) mechanism, in which the reaction occurs between acetone enolate adsorbed on the catalyst and benzaldehyde in the bulk phase. Minimal benzaldehyde is adsorbed on the catalyst because of competitive adsorption with water; thus, benzaldehyde in the bulk phase mainly precipitates. The pressure dependence indicates that the reaction rates are affected by the competitive adsorption of water and acetone, as expected from the ER mechanism, and by the change in the solvent properties of supercritical water. The increase in the activation energy and the decrease in the amount of adsorbed acetone with increasing pressure are plausible effects of the solvent properties.
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ABSTRACT GRAPHIC
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1. INTRODUCTION Subcritical water and supercritical water are promising reaction media for organic synthesis, biomass refinery, and waste treatment. The solvent properties of water drastically vary with respect to the temperature and pressure;1–3 therefore, they can be adjusted to suite the characteristics of a reaction. Because of this advantage and the low environmental load of using water as a solvent, many types of organic reactions have been examined in sub- and supercritical water. One of the most widely researched reactions are base-catalyzed reactions. Many kinds of reactions, such as aldol condensation,4–6 Cannizzaro reaction,7 Michael addition,8 benzylic acid rearrangement,9 and hydrolysis,10–12 have been investigated. Recently, the control of basecatalyzed reactions in sub- and supercritical water using solid catalysts has attracted much attention. ZrO2,13–16 Na-ZrO2,15 CaO-ZrO2,17 CeO2,13,16 MgO,16 CaO,16 Na2SiO3,18 and Mg-Al hydrotalcite16,19 have been used as catalysts because of their thermal and chemical stabilities in sub- and supercritical water. In solid catalysis in sub- and supercritical water, the reaction rates and products selectivity change in response to the water properties, such as density and ion product.20–23 Therefore, elucidating the effects of the change in water properties with respect to the temperature and pressure on the catalysis is important to better control these reactions. In this research, the kinetics of solid base catalysis in sub- and supercritical water was investigated using aldol condensation between acetone and benzaldehyde as a model reaction. The aldol condensation was selected as a model for investigating characteristics of the catalysis in sub- and supercritical water because it is a typical base-catalyzed reaction, and the reaction with the solid base catalysts has been well investigated.24–31 Mg(OH)2, which is a simple alkaline earth metal hydroxide and has been used in aldol condensation,24 was used as a catalyst. The purpose of this study is to investigate the effects of the water properties on solid base catalysis in
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sub- and supercritical water through experiments at various temperatures and pressures, and kinetic analysis. 2. EXPERIMENTAL METHODS 2.1. Reagents. Acetone and benzaldehyde were purchased from Wako Pure Chemical Industries Co., Ltd., Japan, and used as received. Distilled water was prepared with distillation equipment (RFD240HA; Advantec Toyo Kaisha, Ltd., Japan) and degassed by bubbling with N2 gas for 30 min prior to the reaction. Magnesium nitrite hexahydrate, sodium hydroxide, and sodium carbonate were purchased from Wako Pure Chemical Industries Co., Ltd. (Japan) and were used for catalyst preparation. 2.2. Catalyst preparation. The Mg(OH)2 catalyst was prepared according to the following precipitation method. Aqueous solutions of sodium hydroxide and sodium carbonate (6:1 by weight) were added slowly to an aqueous manganese nitrite solution at 60 °C, and the mixture was kept in an oven at 80 °C for 24 h. The obtained precipitate was washed with distilled water, dried in an oven at 100 °C, and calcined in a furnace at 550 °C for 8 h. The calcined powder was pressed into a pellet, and it was crushed and then sieved into granular forms of 0.30–0.50 mm in diameter. As described in the latter section, the prepared catalyst was originally MgO; however, it immediately changed to Mg(OH)2 in sub- and supercritical water. 2.3. Experimental procedure. Reactions were performed using a fixed-bed flow reactor, as shown in Figure 1. The mixture of acetone and benzaldehyde was pumped using a syringe pump (260D; Teledyne Isco, Inc., USA). It had been checked that the reaction did not occur only by mixing acetone and benzaldehyde. The distilled water was pumped using a plunger pump (PU2080; JASCO Corp., Japan) and preheated so that the entrance of the reactor (T5 in Figure 1)
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became the predefined reaction temperature. The two streams were mixed and fed into the fixedbed reactor, which was filled with the catalyst. The initial concentrations of acetone (CA0) and benzaldehyde (CB0) at the reactor entrance are summarized in Table 1. The stream emitted from the reactor was cooled using a water-cooled heat exchanger and depressurized using a backpressure regulator (SCF-Bpg; JASCO Corp., Japan). W/F, defined as the weight of the loaded catalyst divided by the volumetric flow rate in the reactor, was used to indicate the reaction time for the catalytic reactions. The volumetric flow rates were calculated using literature values for the water density.1 The density of the mixture was almost the same as that of pure water because the molar ratio of organics to water was small (less than 3.6% for the temperature- and pressuredependent experiments and 6.3% for the acetone concentration-dependent experiments). 2.4. Analysis. The effluent was mixed with methanol so that the water and organics were homogeneous at ambient temperature. The organics in the liquid samples were analyzed using a high-performance liquid chromatography-ultraviolet detector (HPLC-UVD, LC10A Series; Shimadzu Corp., Japan) with a packed column (Finepak SIL C18S; JASCO Corp., Japan). A mixture of a potassium phosphate buffer solution (pH = 2.1) and acetonitrile (4:1 by volume) was used as the mobile phase for HPLC analysis. The catalyst was characterized by X-ray diffraction (XRD, SmartLab, Rigaku Corp., Japan) and by N2 adsorption/desorption (NOVA 2200e; Quantachrome Corp., USA). 2.5. Calculation of the solvent effect on the reaction. To estimate the effect of the dielectric constant of water on the reaction at 400 °C, quantum chemical calculations were conducted. The structures and energies of the reactants, transition state, and product were determined by density functional theory (DFT) calculations using Gaussian 09, revision A.2.32 Calculations were
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performed at the B3LYP/6-311+G(d,p) level of theory. Intrinsic reaction coordinate calculations were conducted to confirm the reaction path from the transition state to the reactants and the product. To consider the solvent effect, geometry optimizations and frequency calculations were performed using the integral equation formalism polarizable continuum model (IEF-PCM), in which the reaction species are surrounded by a continuum medium with a constant dielectric constant. The literature value of the dielectric constant at each pressure3 was used, and other parameters were set to the default values of water in the Gaussian program. Frequency calculations were performed at 400 °C and each pressure using the same basis set and calculation method as for the geometry optimization. A value of 0.987733 was used as a scaling factor. 3. Results and discussion 3.1 Characterization of the catalyst. Figure 2 shows XRD patterns of the catalysts before and after their use in sub- and supercritical water. The prepared catalyst before treatment in sub- and supercritical water is MgO (Figure 2a), and it changes to Mg(OH)2 after less than 5 min in subcritical water (Figure 2b) and supercritical water (Figure 2c). The crystalline structure of Mg(OH)2 does not change after the reaction at 400 °C and 25 MPa for more than 4 h (Figure 2d). Therefore, the crystalline structure of the catalyst during the reactions in sub- and supercritical water can be regarded as Mg(OH)2. The isotherm from the N2 adsorption/desorption analysis and the pore size distribution analyzed by the Barrett-Joyner-Hallender method (BJH) for the catalyst after treatment in water at 400 °C and 25 MPa are shown in Figure 3(a) and (b), respectively, indicating that the catalyst has singly distributed micro to meso pores. The Brunauer-Emmett-Teller (BET) surface area, pore volume, and pore diameter of the catalyst are summarized in Table 2.
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3.2. Reaction rates and products in sub- and supercritical water at 25 MPa. The main product is benzylidene acetone at all examined reaction conditions. It is produced by the aldol reaction of acetone and benzaldehyde, and the successive dehydration of the aldol product (Scheme 1). The aldol product itself is not detected, indicating that the dehydration reaction is fast. In a previous report on aldol condensation between acetone and benzaldehyde with Mg-Al hydrotalcite in excess acetone at 0 °C, the main product is the aldol product.26 In contrast, in the reaction with Mg-Al hydrotalcite in liquid-phase ethanol at 110 °C, the main product is benzylidene acetone and the kinetic constant for the dehydration reaction is 9 times larger than that for the aldol reaction.25 Considering the results of these reports, the dehydration reaction is faster than the aldol reaction at higher temperatures, and the fast dehydration can be explained by our high-temperature reaction conditions. In addition to benzylidene acetone, benzoic acid is also produced as a minor product at high temperatures by the oxidation of benzaldehyde or the Cannizzaro reaction of benzaldehyde. However, the yields of benzoic acid, defined as the molar amount of benzoic acid produced divided by the initial molar amount of benzaldehyde, are at most 2.1% at 450 °C, suggesting that benzaldehyde is mainly consumed by the aldol reaction of acetone and benzaldehyde. The carbon balance of the reactions in this study was in the range of 0.88–1.04 (excluding acetone) or 0.87-1.05 (including acetone). Figure 4 shows the yield of benzylidene acetone (Ybenzylidene acetone), defined as the molar amount of benzylidene acetone produced divided by the initial molar amount of benzaldehyde, with and without a catalyst at 350 °C and 25 MPa. V/F, the volume of the reactor divided by the volumetric flow rate, is used as an indicator of the reaction time in this figure. The reaction with the catalyst is considerably faster than that without the catalyst, suggesting that Mg(OH)2 effectively catalyzes the aldol condensation reaction in water.
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Figure 5 shows pseudo-first-order plots for Ybenzylidene acetone at each temperature and 25 MPa. The plots at each temperature show linear relationships. The concentration of acetone is almost constant during the reaction because the concentration of acetone is more than thirty times larger than that of benzaldehyde. Therefore, the result indicates that the aldol condensation reaction is first order with respect to benzaldehyde. The dependence of the kinetic rate constants on temperature will be discussed in Section 3.4. 3.3. Effect of initial acetone concentration on the reaction rates. To investigate the reaction order of acetone, reactions at different initial concentrations of acetone were conducted at 400 °C and 25 MPa. Figure 6 shows the pseudo-first-order plots for Ybenzylidene acetone. The plots show straight lines because the concentration of acetone is large and remains essentially constant during the reaction. Figure 7 shows the effect of the initial concentration of acetone on the pseudo-first-order kinetic rate constants determined from the slopes of Figure 6. The relationships between the initial concentration of acetone and the kinetic rate constants show linear relationships, indicating that the reaction is first order with respect to acetone under the examined conditions. 3.4. Kinetic analysis of the temperature dependence. In this section, we analyze the kinetics for the temperature-dependent data. Prior to the analyses, we checked that the contribution of the mass transfer processes, which tends to limit the reaction rates of solid-catalyzed reactions, is sufficiently small under our reaction conditions and does not affect the following kinetic analyses. A detailed procedure for the evaluation is provided in the Supporting Information. The rate-determining step of aldol condensation using solid base catalysts has been reported as either the formation of enolate29,30 or the reaction between enolate and aldehyde.25,28 Our
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experimental data in the previous sections suggest that the reaction is dependent on both the concentration of acetone and that of benzaldehyde, which indicates that the reaction between enolate produced from acetone and benzaldehyde is the rate-determining step. The kinetic data for the temperature dependence were analyzed using two models. One model is the Eley-Rideal (ER) mechanism, in which the reaction occurs between acetone enolate adsorbed on the catalyst and benzaldehyde in the bulk phase. The other model is the Langmuir-Hinshelwood (LH) mechanism, in which the reaction occurs between acetone enolate and benzaldehyde, which are both adsorbed on the catalyst. The reaction rate (r) for each model can be represented by eq 1 (ER) and eq 2 (LH): 1 + +
(1)
(1 + + + )
(2)
=
=
where kER and kLH are the kinetic rate constants, Ki is the adsorption equilibrium constant of component i, Ci is the concentration of component i, and the subscripts A, B, and W indicate acetone, benzaldehyde, and water, respectively. Because the concentration of water is considerably larger than that of acetone and benzaldehyde, the term KWCW is larger than the other terms in the denominator, and eq 1 and eq 2 can be simplified to eq 3 (ER) and eq 4 (LH), respectively;
=
=
(3)
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=
= ( )
(4)
where kER’=kERKA/KW and kLH’=kLHKAKB/KW2. Using the assumption that KWCW is large, the reaction order for both acetone and benzaldehyde becomes unity, which is consistent with our experimental findings. Because CA and CW can be regarded as constant during the reaction (CA,0, CW,0), the experimental kinetic rate constant (k) calculated from the slopes of the pseudo-firstorder plots (Figure 5) is expressed using kER′ or kLH′ as follows: = ,⁄ ,
(5)
= ,⁄ ,
(6)
Arrhenius plots for kER′ and kLH′ at 25 MPa are shown in Figure 8. The Arrhenius plot for kER′ is a straight line while that for kLH′ is not. If the heats of adsorption are not largely dependent on temperature, −lnKi becomes proportional to 1/T from the van’t Hoff equation,34 and the Arrhenius plot for kER′ or kLH′ should be a straight line. The apparent activation energy evaluated from the slope of the Arrhenius plot for kER′ is 24.4 ± 2.3 kJ/mol. The reported activation energy for a base-catalyzed aldol condensation between acetone and benzaldehyde with NaOH as the catalyst is 32.6 kJ/mol.35 For the aldol condensation with a solid base catalyst, the apparent activation energy of the reaction between ketones (acetophenone and 2-butanone) and benzaldehyde with the Mg(OH)2 catalyst have been reported as 38 kJ/mol (acetophenone) and 50 kJ/mol (2-butanone),24 and that of the reaction between acetone and citral with Mg-Al hydrotalcite catalyst has been reported as 30 kJ/mol.28 Compared to these values, our value for the apparent activation energy is appropriate as an activation energy for base-catalyzed aldol condensation. From these results, the ER mechanism is thought to be the plausible model for the
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aldol condensation of acetone and benzaldehyde in sub- and supercritical water using the Mg(OH)2 catalyst. In most previous research, the kinetics of the aldol condensation using solid base catalysts in an organic liquid phase have been expressed using the LH mechanism.25–28 An explanation for why the kinetics is expressed by the ER mechanism in sub- and supercritical water is that less benzaldehyde is adsorbed on the catalyst because of the competitive adsorption of water and benzaldehyde; thus, bulk-phase benzaldehyde becomes the main reactant. 3.5. Effect of pressure on the reaction kinetics. To investigate the effect of pressure on the reaction kinetics, reactions were conducted at 400 °C and 23‒31 MPa. Figure 9 shows the W/F dependence of Ybenzylidene acetone. The reaction rates monotonically decrease with increasing pressure. Because the water density, which is proportional to the water concentration (CW), increases with increasing pressure at a constant temperature, the increase of CW suppresses the reaction because water and acetone adsorb competitively on the catalyst surface. Subsequently, we quantitatively examined the dependence on CW. If the reaction is expressed as nth order with respect to water, the slope of a logarithmic plot between k/CA,0 and CW (Figure 10) indicates the apparent reaction order of water (n). From the slope of Figure 10, the apparent reaction order of water is estimated as −1.57 ± 0.17. However, the reaction order of water for the ER mechanism should become −1 from eq 5, indicating that the reaction is more suppressed at higher pressures than when only considering the competitive adsorption effect of water. Because the solvent properties of supercritical water notably change with respect to the pressure, it is thought to affect the reaction. Considering that the solvent properties of water also change with the temperature, this pressure dependence may seem to contradict the fact that the Arrhenius plot in Figure 8a is a straight line. However, the effect of temperature on the reaction rates is
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considerably larger; thus, the temperature dependence can be explained without considering the effect of the solvent properties on the reaction rates, besides the competitive adsorption effect. One possibility is that the change in dielectric constant (ε) of water affects the reaction rate. Solvent effects on the reactions are particularly common in liquid-phase homogeneous reactions, and some cases of heterogeneous-catalyzed reactions have been reported. For example, Mellmer et al. reported that the solvent effect of proton solvation observed for a strong homogeneous Brønsted acid is similarly observed for solid Brønsted acids.36 In addition, concerning the behavior of water molecules on the Mg(OH)2 surface at 300 K, a molecular dynamics simulation showed that Mg(OH)2 does not prevent hydrogen bonds between interfacial water molecules and has a modest effect on the dynamic behaviors of interfacial water compared to other hydrophilic materials even though the density profile and the dipole orientation of water molecules are affected by Mg(OH)2.37 Because the interaction between the Mg(OH)2 surface and water molecules is smaller at higher temperatures, the solvent properties of supercritical water are thought to affect the reaction on the Mg(OH)2 surface in the same manner as that in the bulk phase. The effect of ε on the rate-determining step of the reaction was investigated using DFT calculations. Because the effect of ε is considered to be qualitatively the same on the Mg(OH)2 surface and in the bulk phase from the discussion above, the reaction in the bulk phase was examined, and the Mg(OH)2 surface was not included in the calculation for simplicity. The calculated cartesian coordinates and energies are supplied in the Supporting Information. Figure 11 shows the Gibbs free energy of each chemical species normalized by the energy of the reactants (acetone enolate and benzaldehyde) at each reaction condition. The energy difference between the reactants and the transition state increases with increasing ε because the reactants are
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more stabilized by larger values of ε than the transition state. This dependence of ε on the reaction is consistent with our experimental finding that the reaction is more suppressed at higher pressures. Another possibility for the smaller reaction rates at high pressures is that the change in the affinity between supercritical water and acetone changes the amount of adsorbed acetone on the surface, and it affects the reaction rate. The adsorption of organics to solid materials, such as activated carbon38 and zeolite,39 in supercritical carbon dioxide (scCO2) is decreased with increasing pressure because the larger scCO2 density at higher pressures promotes the partition of organics from the adsorbed phase to the bulk phase. The dielectric constant is one of the most important parameters to discuss the affinities of the chemicals. In addition, Morimoto et al.40 reported that the miscibility of asphaltene with supercritical water can be explained by the dielectric constant and the Hansen solubility parameters. Table 3 shows the dielectric constants3,41 and the Hansen solubility parameters42,43 for acetone and supercritical water. The dielectric constant of supercritical water increases with increasing pressure, and it approaches the dielectric constant of acetone. With respect to the Hansen solubility parameters, the solubility parameter distance (Ra), defined in eq 7, was reported to represent the solubility between chemicals 1 and 2. Ra = 4
,
−
," #
+ $, − $," # + %, − %," #
(7)
As shown in Table 3, the value of Ra decreases with increasing pressure. Therefore, both the dielectric constant and the Hansen solubility parameters indicate that the affinities of acetone and supercritical water increase with increasing pressure. This dependence is also consistent with our experimental finding that the reaction is suppressed at high pressures.
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From these results, the suppression of the reaction at high pressures in addition to the competitive adsorption effect of water can be explained by the change in solvent properties of supercritical water. In the case of the aldol condensation, the change in solvent properties with increasing pressure decreased the reaction rates. However, the fact that the solvent properties of supercritical water affect the reaction rates indicates that reactions having opposite dependence on the solvent properties will be promoted with increasing pressure, and it may counterbalance or even exceed the competitive adsorption effect of water. Further investigations of the effects of sub- and supercritical water on the surface reaction rate and those on the adsorption behavior will help us to quantitatively understand the solvent effects on the solid base catalysis in sub- and supercritical water, which remain topics of future research. 4. CONCLUSIONS The kinetics of a solid base-catalyzed reaction in sub- and supercritical water were investigated using aldol condensation between acetone and benzaldehyde with Mg(OH)2 catalyst as a model. The kinetic analysis of the temperature dependence at 25 MPa indicated that the reaction proceeded according to the ER mechanism, in which the reaction occurred between the acetone enolate adsorbed on the catalyst and benzaldehyde in the bulk phase (benzaldehyde is considered to be less adsorbed on the catalyst because of the competitive adsorption of water and benzaldehyde). The reaction was suppressed with increasing pressure at 400 °C, which can be partly attributed to the competitive adsorption of water promoted by the large water concentration at high pressure. However, the reaction is further suppressed at higher pressures than expected from the ER mechanism, which could be attributed to the increase in the activation energy of the reaction caused by the solvation effects and/or the decrease in the amount of adsorbed acetone because of the increase in the affinity between supercritical water and acetone.
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FIGURES
Figure 1. Schematic diagram for experimental setup.
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Figure 2. XRD patterns for the catalysts. (a) as prepared, (b) after treatment in water at 250 °C and 25 MPa for 5 min, (c) after the treatment in water at 400 °C and 25 MPa for 5 min, (d) after the reaction at 400 °C and 25 MPa, (e) MgO card data (PDF No. 01-075-1525), (f) Mg(OH)2 card data (PDF No. 01-083-0114).
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Figure 3. Results of N2 adsorption/desorption analysis for catalyst after treatment in water at 400 °C and 25 MPa for 2 h. (a) Isotherm, (b) pore size distribution.
Figure 4. Yields of benzylidene acetone with and without catalyst at 350 °C and 25 MPa. (●) with catalyst, (□) without catalyst.
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Figure 5. Pseudo-first-order plot for yields of benzylidene acetone at each temperature and 25 MPa. (●) 250 °C, (▲) 300 °C, (◊) 325 °C, (■) 350 °C, (○) 360 °C, (▼) 400 °C, (♦) 425 °C, (□) 450 °C.
Figure 6. Effect of initial acetone concentration on benzylidene acetone yield at 400 °C and 25 MPa. CA,0 [mol/dm3]: (●) 0.23, (▲) 0.29, (◊) 0.42, (■) 0.50, (○) 0.61.
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Figure 7. Effect of initial acetone concentration on kinetic rate constants at 400 °C and 25 MPa. Error bars indicate standard error.
Figure 8. Arrhenius plots for kinetic rate constants at 25 MPa. (a) Eley-Rideal mechanism, (b) Langmuir-Hinshelwood mechanism. Error bars indicate standard error.
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Figure 9. Pressure dependence of benzylidene acetone yields at 400 °C. (●) 23 MPa, (▲) 25 MPa, (◊) 26.5 MPa, (■) 29 MPa, (○) 31 MPa.
Figure 10. Relationship between ln(k/CA,0) and lnCW at 400 °C. Error bars indicate standard error.
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Figure 11. Relative Gibbs free energy for each chemical species at 400 °C with a B3LYP/6311+G(d,p) level of theory with IEF-PCM. (A-) acetone enolate, (B) benzaldehyde, (TS) transition state, (Aldol-) aldol anion. (―) 23 MPa, ε = 2.106, (- - -) 26.5 MPa, ε = 3.010, (− · − ·) 31 MPa, ε = 6.800.
SCHEMES
Scheme 1. Aldol condensation of acetone and benzaldehyde.
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TABLES Table 1. Initial concentrations of acetone and benzaldehyde in sub- and supercritical water.
Pressure [MPa]
CA0 [mol/dm3]
CB0 [mol/dm3]
Figure #
250
25
1.5
4.6×10−2
5
300
25
1.2
4.1×10−2
5
325
25
1.2
4.0×10−2
5
350
25
1.1
3.4×10−2
4, 5
360
25
1.1
3.4×10−2
5
400
23
0.24
7.7×10−3
9
25
0.23
9.2×10−3
6
0.29
9.5×10−3
5, 6, 9
0.42
9.7×10−3
6
0.50
1.0×10−2
6
0.61
1.0×10−2
6
26.5
0.35
1.2×10−2
9
29
0.54
1.8×10−2
9
31
0.68
2.2×10−2
9
425
25
0.26
6.7×10−3
5
450
25
0.22
5.8×10−3
5
25
1.4
0.10
4
Temperature [°C] with catalyst
without catalyst 350
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Table 2. BET surface area, pore volume, and pore diameter of the catalyst after treatment in water at 400 °C and 25 MPa for 2 h. SBET [m2/g]
pore diameter [nm]
pore volume [cm3/g]
35.9
3.72
0.172
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Table 3. Dielectric constants 3 and Hansen solubility parameters for acetone 42 and supercritical water (SCW) 43.
Hansen solubility parameters [MPa0.5] dispersion (δd)
polar (δp)
hydrogen bonding (δh)
total (δt)
solubility parameter distance (Ra)
21.01
15.5
10.4
7.0
19.9
-
2.11
1.3
5.9
4.9
7.7
28.9
2.50
1.7
6.5
5.6
8.8
28.0
26.5 3.01
2.1
7.2
6.4
9.9
27.0
4.88
3.6
8.9
8.2
12.6
23.9
6.80
4.9
10.1
9.5
14.7
21.4
dielectric constant (ε)
Acetone* SCW (400 °C, 23 MPa) SCW (400 °C, 25 MPa) SCW (400 °C, MPa) SCW (400 °C, 29 MPa) SCW (400 °C, 31 MPa)
*ε is the value at 20 °C and Hansen solubility parameters are the values at 25 °C.
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Supporting Information. Detailed procedure of the evaluation for the mass transfer processes on the reaction rates and the calculated cartesian coordinates and energies of DFT calculation are supplied as the Supporting Information.
ACKNOWLEDGEMENT This work was supported by JSPS KAKENHI (Grant Number 15K18262) and Kurita Water and Environment Foundation Grant (Grant Number 16D018). XRD analyses were performed using facilities at Institute of Solid State Physics, The University of Tokyo. We very much appreciate all of these supports. We also would like to thank Editage for English language editing
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