Hydroformylation of 1-Butene on Rh Catalyst - American Chemical

Dec 29, 2008 - Kinetics of homogeneously catalyzed hydroformylation of 1-butene was studied in a pressurized semibatch autoclave reactor. Kinetics was...
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Ind. Eng. Chem. Res. 2009, 48, 1325–1331

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Hydroformylation of 1-Butene on Rh Catalyst Tapio Salmi,† Johan Ahlkvist,† Andreas Bernas,† Johan Wa¨rnå,† Pa¨ivi Ma¨ki-Arvela,† Cecilia Still,† Juha Lehtonen,‡ and Dmitry Yu. Murzin*,† Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo Akademi, FI-20500 Åbo/Turku, Finland, and Technology Centre, Perstorp Oy, P.O. Box 350, FI-06101 Borgå/PorVoo, Finland

Kinetics of homogeneously catalyzed hydroformylation of 1-butene was studied in a pressurized semibatch autoclave reactor. Kinetics was determined for a reaction mixture, which consisted of 1-butene, carbon monoxide, hydrogen, a rhodium-based catalyst, and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate as a solvent. The following reaction parameters were investigated: temperature (70-100 °C), total pressure (1-3 MPa), catalyst concentration (100-200 ppm), catalyst (Rh)-to-ligand ratio, and the initial ratio of the synthesis gas (hydrogen and carbon dioxide) components. The solubility of 1-butene, carbon monoxide, and hydrogen in the solvent was determined by precise pressure and weight measurements and modeled mathematically. The main reaction products were pentanal (P) and 2-methylbutanal (MB), while trace amounts of cis-2- and trans-2-butene were detected as reaction intermediates. The ratio of the main products (P and MB) was practically independent of temperature, but the ligand-to-Rh ratio affected considerably the product distribution: an increasing ratio preferred the formation of pentanal (P). Increasing total pressure diminished the yield of pentanal (P). On the basis of the experimentally recorded kinetic data, a stoichiometric scheme was constructed and simplified. The kinetic data were combined with solubility models, and the parameters of an empirical power-law rate model were determined by nonlinear regression analysis. The kinetic parameters were well identified and physically reasonable being in accordance with qualitative observations. 1. Introduction Hydroformylation is the oldest and in production volume the largest homogeneously catalyzed industrial process. The hydroformylation reaction was discovered by Otto Roelen in 1938; the reaction is also called oxosynthesis and Roelen’s reaction.1-4 The catalysts used in hydroformylation are typically organometallic complexes. Cobalt-based catalysts dominated hydroformylation until the 1970s; thereafter, rhodium-based catalysts were commercialized. Synthesized aldehydes are typical intermediates for the chemical industry.5 Hydroformylation catalysts are used in the excess of a ligand, e.g., triphenylphoshine. In the recent years, a lot of effort has been put into the ligand chemistry to find new ligands for tailored processes.7-9 In the present study phosphine-based rhodium catalysts were used for hydroformylation of 1-butene. Despite intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and the kinetics are not in most cases clear. Both associative and dissociative mechanisms have been proposed.5,6 The discrepancies in mechanistic speculations have also lead to a variety of rate equations for hydroformylation processes. The concentrations of the reactant (substrate) alkene, the catalyst, and H2 and CO are included in the kinetic expressions, but very little quantitative information on the effect of the ligands is available. Typically increase in the alkene and catalyst concentrations as well as H2 pressure is beneficial for the reaction rate, while an inhibitory effect of CO is characteristic for many rate equations proposed hitherto.10 The general feature of previous studies has been that the partial pressures of H2 and CO have not been screened systematically, thus the exact form of the rate equation remains obscured; for instance, the dependence of the rate on CO cannot always be pCO-1 as proposed in some rate equations, but a zero * To whom correspondence should be addressed. Tel.: +358 2 215 4985. Fax: +358 2 215 4479. E-mail: [email protected]. † Åbo Akademi. ‡ Perstorp Oy.

order or higher order behavior might become visible at lower CO pressures.10 A lot of research has been published on hydroformylation of alkenes, but the vast majority of the effort has been focused on the chemistry of various metal-ligand systems. Quantitative kinetic studies including modeling of rates and selectivities are much scarcer. Even if this aspect of oxo-synthesis has been much less investigated with respect to the mechanism of the reaction or the molecular design of the catalyst, an extended kinetic modeling approach was recently done by Chauhari et al.11 In this work, we present the approach to modeling of hydroformylation kinetics and gas solubility. Hydroformylation of 1-butene with a rhodium-based catalyst was selected as a case study. 2. Experimental Section Both gas solubility measurements and hydroformylation experiments were carried out in a pressurized autoclave (Parr 4561, 150 mL) at various pressures and temperatures. The method for solubility measurements of 1-butene, hydrogen, and carbon monoxide in 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate is described in detail by Still et al. in ref 12. In a typical experiment, the catalyst precursor carbonylhydridotris(triphenylphosphine)rhodium (I) (97%, Aldrich) and the ligand triphenylphosphine (TPP, 99%, Acros Organics) were dissolved in 100 mL (94 g) of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate in a vessel under nitrogen bubbling on a heating plate equipped with magnetic agitation at a temperature slightly less than the reaction temperature. After a period of 20 to 30 min the ligand-modified complexes were formed. All chemicals were nitrogen treated and stored under nitrogen to avoid any contact with air to prevent oxidation. The experiments were carried out in a stirred and pressurized 300-mL Parr 4561 stainless steel reactor, which was designed to withstand a pressure of 300 bar at 350 °C. It had an internal

10.1021/ie800215t CCC: $40.75  2009 American Chemical Society Published on Web 12/29/2008

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cooling loop and was equipped with an automatic temperature control system consisting of an external electric heating jacket coupled to a steering unit (Parr 4843), which was also used to control the stirring speed. The temperature could be maintained within (1 °C. The reactor had facilities for sampling of the liquid phase as well as the gaseous content, and it was connected to reservoirs of 1-butene (99.5%, AGA) and nitrogen (99.999%, AGA). Synthesis gas containing a H2/CO mixture of the composition 50.5 mol % CO and 49.5 mol % H2 (99.995%, AGA) or 45.0 mol % CO and 55.0 mol % H2 (99.995%, AGA) was fed at a constant pressure to the reactor with a pressure controller (Brooks 5866, Brooks 0154). The reactor was equipped with transducers for online measurements of temperature and pressure (Keller type PA21 SR/80520.3-1), which was followed up on a PC for continuous data logging. After charging the catalyst solution, the reactor was sealed tight and the heating jacket was attached. Gases fed into the reactor were dispersed in the liquid phase by the aid of a sinter. Initially, the PC logging of temperature and pressure was started and the reactor was pressurized with 6 bar (overpressure) of nitrogen with all valves closed to check for leakage. Thereafter, the agitation was switched on at 1000 rpm, and nitrogen was flushed through the reactor for 3 min at atmospheric pressure to remove any residues of oxygen prior to the experiment. The pressure was increased to 10 bar and kept at this level for 10 min. After reaching equilibrium between gas and liquid phases the outlet was carefully opened. Thereafter the reactor was exposed to vacuum for 10 min. 1-Butene was loaded into the reactor from a gas bottle that was on a scale at room temperature under stirring at 400 rpm. The reactor was kept closed for 25 min to await gas-liquid equilibrium. The amount of 1-butene was measured to 9.5 g. The system was heated to the reaction temperature while the pressure increased at the same time. The stirring was kept on during this entire procedure. The first sample was withdrawn, after which the synthesis gas (CO/H2) was introduced into the system. The reaction time was initialized to zero as soon as the reactor was pressurized with hydrogen-carbon monoxide mixture. Samples of 1 mL were withdrawn from the liquid phase at certain time intervals. Waste samples of ∼1 mL were also taken prior to sampling. The weight was measured for all samples, and the loss of the total liquid volume was taken into account in the calculations of the concentration profile. After the run, the outlet was opened carefully, and after reaching atmospheric pressure the reactor was cooled by the aid of cooling water and nitrogen flushing. The reactor was washed first with water and technical acetone, following this with acetone and methanol of PA grade. Between some 5 to 10 experiments, blank runs were performed to check for catalysis of metal residues in the reactor. No catalytic activity was ever detected in these runs. Analyses of hydroformylation products for reaction followup were carried out by an internal standard method using a gas chromatographic technique. Because of evaporation of 1-butene from the samples, the required initial amount of 1-butene was calculated from the aldehyde products since no side reactions were detected. A Hewlett-Packard 5890 series II gas chromatograph with flame ionization detector operating at 300 °C and split/splitless injector with HP GC Chem Station Rev. A.06.03 509 electronic integrator using a J&W Scientific DB-1 capillary column of 60 m length and 0.25 mm inner diameter with 1 µm film thickness was used. The injector operated in the split mode at 250 °C and 1.93 bar, the oven temperature program was 30 °C (0 min):1 °C/min:60 °C (0 min), 15 °C/min:300 °C (40 min),

Table 1. Experimental Matrix for Hydroformylation of 1-Butene experiment no.

temperature [°C]

P [MPa]

c(Rh) [ppm]

L/Rh [mol/mol]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

70 70 70 70 70 70 70 85 100 100 100 100 100 100 100 100

1 1 1 2 2 3 3 1 1 1 1 2 3 3 3 3

100 200 200 100 200 100 200 100 100 200 200 100 100 150 200 200

10 55 100 100 10 10 100 10 100 10 100 10 100 100 10 100

and the gas flow rates of 3 mL/min carried gas helium, 28 mL/ min makeup gas helium, 245 mL/min air, 41 mL/min hydrogen, and 202 mL/min split were applied. 3. Results and Discussion 3.1. Solubility of 1-Butene in 2,2,4-Trimethyl-1,3-pentanediol Monoisobutyrate. The solubility data were first modeled with the empirical equation13 giving mole fraction of dissolved gas (xi) ln xi ) A ′ +

B′ + C ln(T, K) (T, K)

(1)

where i is the component index, T is the absolute temperature (in K) and A′, B′, and C′ are coefficients determined from the data by regression analysis. Data of the mol fraction xi are at 1 atm partial pressure of each component. According to Henry’s law the concentration is given by cLi ) pixicL

(2)

where cL is the total concentration of the liquid. The solubility of 1-butene decreases with increasing temperature as expected. As a next step, the empirical equation (eq 1) was fitted to the data by regression giving the following result 6438.5 + 12.039 ln(T, K) (3) (T, K) The equation is valid at 297-373 K. The fit is very good as shown in ref 12. The regression factor was 99.8%. The solubility of CO and H2 were reported elsewhere.12 3.2. Kinetic Measurements. All the kinetic experiments were carried out with 1-butene, CO, H2, and carbonylhydridotris(triphenylphoshine)rhodium(I), RhH(CO)(TPP)3 as the rhodium precursor, and triphenylphoshine, TPP, as the ligand. H2 and CO were fed as 1:1 mixture in most experiments. Few experiments were carried out with a slight excess of H2 (H2:CO ) 55:45). The following process parameters were investigated: temperature, pressure, ligand-rhodium ratio (L/ Rh), and rhodium concentration. A list of the experiments is displayed in Table 1. On the basis of the experiments, some general statements can be made. Pentanal and 2-methylbutanal were the absolutely dominating products; just trace amounts of plausible reaction intermediates, cis-2-butene and trans-2-butene, were detected. In experiments carried out with a stoichiometric feed of H2 and CO, no butane was formed, while trace amounts of butane became visible in experiments performed with an excess of H2. ln xg ) -91.417 +

Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009 1327

Figure 1. Product distribution at temperatures 70 and 100 °C under 3 MPa, concentration of rhodium was 200 ppm, and L/Rh-ratio 100.

Figure 2. Product distribution at the temperature 100 °C under 3 MPa a of total pressure, rhodium concentrations 100 ppm, 150 ppm, and 200 ppm, and L/Rh-ratio 100.

The effects of various process parameters are discussed in detail in the following sections. 3.3. Temperature. The experiments revealed that the initial rate increases as a function of temperature. A product distribution plot is provided in Figure 1. The product ratio of pentanal to 2-methylbutanal is approximately 4. Figure 1 indicates that the product distribution is practically independent of the temperature. The activation energies of the main reactions seem to be rather equal. 3.4. Catalyst Concentration. The effect of the catalyst concentration on the product distribution is displayed in Figure 2, which gives the constant product ratio of 3.5. 3.5. Ligand Concentration. The ligand concentration had a considerable effect on the selectivity. Experiments were carried out with different ligand concentrations. The product distribution is given in Figure 3, while the time dependent product formation results are displayed in Figure 5. A higher ligand concentration retards the overall rate and increases the selectivity to pentanal. At the lowest L/Rh ratio (10), the ratio pentanal-to-2-methylbutanal ratio was about 3.6, while it became about 6 for the highest L/Rh ratio (100). The reaction rate was retarded when the ligand concentration was increased. 3.6. Pressure. The effect of the total pressure (1 and 3 MPa) on the product distribution is illustrated by Figure 4. As follows from Figure 4, the total pressure does not have any significant effect on the product distribution. The pentanal-to-2-methylbutanal ratio was about 3.6 in both experiments. Also the rate was rather pressure independent in the investigated pressure range.

Figure 3. Product distribution at temperature 100 °C, pressure 1 MPa, rhodium concentration 200 ppm, and L/Rh-ratios 10 and 100.

Figure 4. Product distribution at 70 °C, pressure 1 and 3 MPa, catalyst concentration 100 ppm, and L/Rh-ratio 10.

A similar system has recently been studied in ref 14. The kinetics of homogeneously catalyzed hydroformylation of propene to isobutyraldehyde and n-butyraldehyde was studied in semibatch mode over rhodium/cyclohexyldiphenylphosphine (Rh/CHDPP) and rhodium/triphenylphosphine (Rh/TPP) catalyst using 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate solvent. The rate was temperature dependent and pressure dependent at low pressures, while the Rh concentration or syngas composition did not have any significant impact on the rate. The n/i ratio was always independent of the conversion but dependent on the ligand concentration: higher ligand concentration promoted isobutyraldehyde formation. The ligand CHDPP showed lower hydroformylation rate and n/i ratio than that for TPP. The n/i ratio versus conversion always showed a linear dependence, which was on a lower level for CHDPP than that for TPP at similar conditions. The hydroformylation rate versus ligand concentration dependence passed a maximum at rather low ligand amount. The ligand concentration was the only variable affecting the n/i ratio versus conversion dependence. Rate increased and n/i ratio decreased when the ligand concentration was decreased for both investigated ligands. 3.7. Kinetic Modeling Principles. Modeling of the hydroformylation kinetics was started by constructing a stoichiometric scheme for the process. A detailed reaction pattern is shown in Scheme 1. Experimental data, however, indicated that just trace amounts of cis-2-butene and trans-2-butene appeared in the experiments; the concentrations of these compounds were typically less than 3 mol %. This implied that their impact on the total balance was very minimal, particularly considering the general accuracy of the data. In the experiments where the

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Figure 5. Fitting of the model for the following process parameters. (a) T ) 70 °C, p ) 1 MPa, c(Rh) ) 100 ppm, L/Rh-mole ratio ) 10, (b) T ) 70 °C, p ) 1 MPa, c(Rh) ) 200 ppm, L/Rh-mole ratio ) 55, (c) T ) 70 °C, p ) 1 MPa, c(Rh) ) 200 ppm, L/Rh-mole ratio ) 100, (d) T ) 70 °C, p ) 2 MPa, c(Rh) ) 100 ppm, L/Rh-mole ratio ) 100. The experimental values are depicted as symbols, whereas model fits are shown as lines. Symbols: (O) pentanal, (+) 2-methylbutanal, and (3) 1-butene.

stoichiometric ratio H2:CO ) 1:1 was used, no butane was detected. Thus, in the mathematical modeling of kinetic data, it is possible to use a considerably simplified scheme (1)

Scheme 1. Reaction Scheme for Hydroformylation of 1-Butene

(2)

pentanal r 1-butene f 2-methylbutanal (P)

(A)

(MB)

The generation rates of the components (A ) 1-butene, P ) pentanal, and MB ) 2-methylbutanal), thus, according to the stoichiometry, become rA ) -r1 - r2

(4)

rP ) r1

(5)

rMB ) r2

(6)

The next step is to find suitable expressions for r1and r2. They could in principle be derived from reaction mechanisms proposed in the literature. However, due to complexity of such a mechanism, in practice it is extremely difficult. Considerable simplifications are in any case needed. Because of these reasons, the empirical expressions for r1 and r2 listed below were used as a starting approach (L ) ligand), m3 m4 m5 r1 ) k1cAmicmcat2 cCO cH2cL

(7)

n cHn42cnL5 r2 ) k2cAn1cncatcCO

(8)

where the parameters to be calculated are k1 and k2 as well as the exponents (m, n). The ratios of the exponents can be preliminarily obtained by checking the product distribution plots (Figures 1-4). Essentially the product distribution depended on the ligand concentration (Figure 3) only, while it was rather independent of the catalyst concentration (Figure 2) and total

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pressure (Figure 4). The change of total pressure (10 MPa, 30 MPa) also implied the change of the partial pressures of CO and H2 and thus their concentration in the liquid phase. This implies that m2 ) n2, m3 ) n3, and m4 ) n4 in eqs 7 and 8. Consequently, we remain at the first stage with the parameters m1, m2, m3, m4, m5, and n5. To progress with parameter estimation, the mass balances in the reactor were considered. 3.8. Mass Balances for the Reactor. The reactor system, where the kinetic experiments were carried out, can be described as a semibatch reactor. Only the synthesis gas (H2 and CO) was fed into the reactor continuously during the experiments, while 1-butene and the solvent were in the batch mode. All reactions took place in the liquid phase. The mass balance for an arbitrary component in the gas is given by n˙0Gi ) NiAm +

dnGi dt

(9)

dnLi (10) NiAm + riVL ) dt For components which are in batch (1-butene and reaction products), n˙0Gi is zero. By introducing the concentrations (nLi ) ciVL and ni ) cGiVG) and adding together the balances for case n0Li ) 0, we get (11)

Here the fluxes were considered to be equal. No reactions are assumed to take place in the liquid film at the gas-liquid interface; therefore, eqs 9 and 10 can be added together. As the agitation of the reaction mixture was very intensive, interfacial mass transfer resistance is suppressed, and the concentration in gas and liquid are related by the phase equilibrium cGi ) Ki w cGi ) KicLi cLi

(12)

This is inserted in the balance equation, which gets its final form ri dcLi ) dt VG K +1 VL i

(13)

(14)

where cL is the total concentration of the liquid. Henry’s constant (Pi*/xLi*) was obtained from the solubility model.12 The concentration of 1-butene in the liquid phase was calculated from the overall balance, cAL(VL + KAVG) ) n0A - nP - nMB

where ∞ denotes the asymptotic concentration of the products. The concentration of 1-butene in the liquid phase is then obtained (cLA ) cA) by cA )

cP∞ + cMB∞ - (cP + cMB) 1 + KAVG ⁄ VL

(17)

This expression was used in the parameter estimation, that is, just the concentrations cP and cMB were used in the data fitting, and cA was calculated from eq 17. The rate constants included in the model were described by the modified Arrhenius equation k ) krefe(-Ea/R)[(1/T)-(1/Tref)] kref ) Ae-(Ea/RTref)

(18)

(15)

that is, consumed butene is equal to formed products (the concentrations of the products were zero at t ) 0). The amounts of P and MB are expressed with concentrations nP ) cPLVL and nMB ) cMBLVL. In case that all 1-butene (A) was reacted, we get the balance

(19)

Tref was 358.15 K. The transformation (eq 18) was used to suppress the correlation between A and Ea. 3.9. Parameter Estimation. In the parameter estimation, the product components P and MB were included. The objective function was defined as Q)

∑ ∑ (c

2 it - citexp)

t

(20)

i

where cit denotes the modeled liquid-phase concentration at time t and citexp is the corresponding experimental concentration. The objective function was minimized with a hybrid Simplex-Levenberg-Marquardt method by using Modest software.15 The regression analysis revealed that the original rate equations can be considerably simplified. Parameters m1, n1, m2, and n2 get the value 1, while m3 ) n3 ) m4 ) n4 ) 0 in the rate expressions (eqs 7and 8). This is in accordance with many previous investigations of hydroformylation. It should be noted, however, that in our previous investigation of propene hydroformylation14 the reaction rate was first order in alkene and negative in ligand concentration in agreement with the present data, while first order kinetics in CO and hydrogen was determined for propene, showing an influence of the substrate nature on kinetic regularities. Since -(dcA)/ (dt) ) rA ) r1 + r2, the regression procedure ended up with two simple rate equations r1 ) rP )

For nonvolatile components, Ki ) 0. The equilibrium parameter (Ki) is expressed by Henry’s constant as follows Hi Ki ) RTcL

(16)

where kref was calculated from

where n˙0Gi is the inlet flow, Ni the interfacial flux, and Am the interfacial area. For the liquid phase, the corresponding balance equation is written as

VG dcGi dcLi + ) ri VL dt dt

n0A ) cPL∞ + cMBL∞ VL

dcP cAccat ) k1 δ dt c

(21)

dcMB cAccat ) k2 γ dt c

(22)

L

r2 ) rMB )

L

where δ ) 0.28 and γ ) 0.44. The parameters obtained from the parameter estimation are collected in Table 2. As revealed by Table 2, the parameters are very well identified and thus statistically relevant. The obtained modeling results can be compared with preliminary results obtained just by checking kinetic data. The product plots cP versus cMB should according to the model be linear, which also is the case. The ratio between the rate constants (k1/k2) is ∼5, according to the plots in Figures 1–4 which agrees with modeling. Furthermore, the difference between the activation energies Ea2 - Ea1 is about 11 kJ/mol, which is a small value. Thus the temperature dependence of the rate constants is very weak, which is confirmed, for example, by Figure 1. The modeling results are

1330 Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009 Table 2. Kinetic Parameters for Hydroformylation parameter

calculated parameter value

calculated standard deviation

calculated relative standard deviation [%]

standard deviation of the parameters

k1 [mol-0.72 L0.72 min-1] k2 [mol-0.72 L0.72 min-1] Ea1 [J/mol] Ea2 [J/mol] δ γ

8.51 × 10-3 1.43 × 10-3 6.49 × 104 7.55 × 104 0.278 0.439

3.93 × 10-4 1.02 × 10-4 1.34 × 103 1.88 × 103 1.48 × 10-2 2.11 × 10-2

4.6 7.1 2.1 2.5 5.3 4.8

21.7 14.1 48.3 40.1 18.8 20.8

displayed by Figure 5 and Supporting Information. In general the modeling results follow the experimental curves of pentanal (P) and 2-methylbutanal (MB) rather well with the exception of a few cases. The predicted 1-butene concentration is typically slightly higher than the experimental one, as it should be because of volatilization during the sampling. In addition, the concentration of the mass balances of P and MB gives k1 dcP ) Cγ-δ dcMB k2 L

(23)

During an experiment, the liquid concentration is constant, and thus an integration of the above equations gives the product distribution (cP ) 0 and cMB ) 0 at t ) 0), cP k1 ) Cγ-δ cMB k2 L

As mentioned above the kinetic regularities for propene were somewhat different compared to those for 1-butene. In this context the literature studies on kinetics of ethylene and 1-hexene hydroformylation should be mentioned.16,17 In the case of ethylene, the reaction order close to 1.5 was observed, as at the same time strong inhibition by ethylene and by CO at higher CO pressures was reported.16 Similar dependencies (e.g., the rate maxima as a function of alkene and CO partial pressures) were also observed with 1-hexene, pointing out that the nature of the precursor and the substrate has a strong influence on kinetics. 3.10. Analytical Solution of the Balance Equations. Since the rate expressions became simple, a further development is possible. By inserting the rate expressions in the balance we get

(24)

( )

γ-δ

(25)

where (cP/cMB)1 and (cP/cMB)2 is the regioselectivity for the two experiments, correspondingly. The term (cL1/cL2) is the ratio between the ligand amounts in the two experiments. In the experiments in Figure 3, the ratio was 100/10 and γ - δ ) 0.161. Thus, we get (cP/cMB)1/(cP/cMB)2 ) 100.161 ) 1.45. This can be directly compared to Figure 3. The experiment with L/Rh ) 100 gives a product ratio of pentanal-to-2-methylbutanal of 6. The experiment with L/Rh ) 10, on the other hand, gives a product ratio of pentanal-to-2-methylbutanal of 3.6. Thus, (cP/ cMB)1/(cP/cMB)2 is equal to 6/3.6 ) 1.67, and the model predicts nicely the dependence of the product distribution on the liquid concentration. The regression factor became 97-99%, which is very satisfactory. It can be concluded the product-oriented modeling approach worked very well. Contour plots of the parameters (not shown) also revealed that the correlation between the parameters is on an acceptable level. The kinetics of hydroformylation of propene to isobutyraldehyde and n-butyraldehyde was studied more in detail by Bernas et al. in semibatch mode over rhodium/cyclohexyldiphenylphosphine (Rh/ CHDPP) and rhodium/triphenylphosphine (Rh/TPP) catalyst using 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate solvent in ref 14. The parameters of kinetic models were calculated for both catalysts. In ref 14 the kinetic models showed the R2 value of more than 0.9 and reasonably small estimated relative standard errors of the parameters. Independent variable variation was indicated by a correlation coefficient matrix of values close to zero, and it was possible to find minima of the objective function for the parameters. As showed by sensitivity analysis, the kinetic parameters were well identified, physically reasonable, and in accordance with qualitative observations. The models predicted the propene hydroformylation kinetic system very well.

(26)

dcMB k2 ′cA ) γ dt c

(27)

L

By combining two experiments under identical conditions but different ligand concentrations we obtain cL1 (cP/cMB)1 ) (cP/cMB)2 cL2

dcP k1 ′cA ) δ dt c

L

where k1′ ) k1ccat and k2′ ) k2ccat. The stoichiometric relation between A, P, and MB is inserted, dcP R1(c∞ - (cP + cMB)) ) (28) dt (β + 1) dcMB R2(c∞ - (cP + cMB)) ) (29) dt (β + 1) where R ) k1ccat/cLδ, R2 ) k2ccat/cLγ, β ) KAVL/VG, and c∞ ) cP∞ + cMB∞. Division of the differential equation and integration with the limits [0, cP] and [0, cMB] give cMB )

R2 c R1 P

(30)

which is inserted in the balance equation of P, from which cP is solved by separation of variables and integration (at t ) 0, cP ) 0). Summing, we get for cP and cMB, R1 cP ) (1 - e-(R1+R2)t/(β+1)) c∞ R1 + R2

(31)

cP R2 ) (1 - e-(R1+R2)t/(β+1)) c∞ R1 + R2

(32)

where c∞ ) cP∞ + cMB∞. The concentration of A in the liquid bulk can now be calculated from cMB 1 - (cP ⁄ c∞ + cMB ⁄ c∞) ) c∞ β+1

(33)

4. Conclusions Hydroformylation of 1-butene in the presence of the Rh catalyst in the temperature and pressure ranges 70-100 °C and 1-3 MPa gave pentanal (P) and 2-methylbutanal as the main products. Just trace amounts of cis- and trans-2-butene were

Ind. Eng. Chem. Res., Vol. 48, No. 3, 2009 1331

detected as byproduct. No butane was detected in experiments, where a stoichiometric ratio of CO and H2 were used. On the basis of preliminary considerations of product distributions, a kinetic model was developed. The kinetic parameters obtained from the model were well identified and physically reasonable. The product concentrations are predicted very well by the kinetic model. The kinetic model can be further refined by considering detailed reaction mechanisms and extending it to the domain of lower partial pressures of CO and H2. Acknowledgment This work is a part of Finnish Centre of Excellence Programs (2000-2011) financed by Academy of Finland. Financial support from Perstorp is gratefully acknowledged. Notation A ) frequency factor A ) gas-liquid interfacial area A′, B′, C′ ) parameters in gas solubility model c ) concentration Ea ) activation energy H ) Henry’s constant K ) gas-liquid equilibrium ratio k ) rate constant k′ ) transformed rate constant m, n ) empirical exponents in rate expressions N ) interfacial (gas-liquid) flux n ) amount of substance n˙ ) flow of amount of substance P ) total pressure p ) partial pressure Q ) objective function R ) gas constant () 8.314 J mol-1 K-1) r ) rate T ) absolute temperature (K) t ) time x ) mole fraction V ) volume R1, R2, β1 ) lumped parameters γ, δ ) empirical exponents in rate expressions (Table 2) Subscripts and Superscripts G ) gas L ) liquid i ) component index AbbreViations A ) 1-butene cat ) catalyst L ) ligand MB ) 2-methylbutanal P ) pentanal

ref ) reference ∞ ) asymptotic value

Supporting Information Available: Comparison between experimental and calculated values is provided. This information is available free of charge via the Internet at http://pubs.acs.org. Literature Cited (1) Cornils, B.; Herrmann, W. A. Concepts in Homogeneous Catalysis: The Industrial View. J. Catal. 2003, 216, 23. (2) The Catalyst Technical Handbook; Johnson Matthey: 2001. http:// www.jmcatalysts.com/pharma/pdfs-uploaded/Catalyst%20Handbook%20EU. pdf (accessed Nov 2008). (3) Cornils, B.; Herrmann, W. A. Introduction. In Applied Homogeneous Catalysis with Organometallic Compounds: A ComprehensiVe Handbook In Three Volumes; Cornils, B., Herrmann, W. A., Eds; Wiley-VCH: Weinheim, 2002; Vol. 1, pp 1-2. (4) Sheldon, R. A. Chemicals from Synthesis Gas: Catalytic Reaction of CO and H2; Reidel: Dordrecht, 1983. (5) Frohning, C. D.; Kohlpaintner, C. W.; Bohnen, H. In Hydroformylation (Oxo Synthesis, Roelen Reaction), 2nd ed.; Cornils, B., Herrmann, W. A., Eds; Wiley-VCH: Weinheim, 2002; Vol. 1, pp 31-104. (6) Bohnen, H. W.; Cornils, B. Hydroformylation of Alkenes: An Industrial View of the Status and Importance. AdV. Catal. 2002, 47, 1. (7) Stanley, G. G. Organometallic Chemistry, May 28, 2003. http:// chemistry.lsu.edu/stanley/webpub/4571-chap16-hydroformylation.pdf, (accessed Oct 2004). (8) Pruett, R. L.; Smith, J. A. Low-Pressure System for Producing Normal Aldehydes by Hydroformylation of R Olefins. J. Org. Chem. 1969, 34, 327. (9) Beller, M.; Cornils, B.; Frohning, C. D.; Kohlpaintner, C. W. Progress in Hydroformylation and Carbonylation. J. Mol. Catal. A: Chem. 1995, 104, 17. (10) Chaudhari, R. V.; Seayad, A.; Jayasree, S. Kinetic Modeling of Homogeneous Catalytic Processes. Catal. Today 2001, 66, 371. (11) Diwakar, M. M.; Deshpande, R. M.; Chaudhari, R. V. Hydroformylation of 1-Hexene Using Rh/TPPTS Complex Exchanged on Anion Exchange Resin: Kinetic Studies. J. Mol. Catal. A: Chem. 2005, 232, 179. (12) Still, C.; Salmi, T.; Ma¨ki-Arvela, P.; Era¨nen, K.; Murzin, D. Yu.; Lehtonen, J. Solubility of Gases in a Hydroformylation Solvent. Chem. Eng. Sci. 2006, 61, 3698. (13) Fogg, P. G. T.; Gerrard, W. Solubility of Gases in Liquids: A Critical EValuation of Gas/Liquid Systems in Theory and Practice; Wiley: Chichester, 1991. (14) Bernas, A.; Ma¨ki-Arvela, P.; Lehtonen, J.; Salmi, T.; Murzin, D. Yu. Kinetic Modeling of Propene Hydroformylation with Rh/TPP and Rh/ CHDPP Catalysts. Ind. Eng. Chem. Res. 2008, 47, 4317. (15) Haario, H. ModEst, 6.1; Software for Kinetic Modeling; ProfMath: Helsinki, 2002. (16) Deshpande, R. M.; Bhanage, B. M.; Divekar, S. S.; Kanagasabapathy, S.; Chaudhari, R. V. Kinetics of Hydroformylation of Ethylene in a Homogeneous Medium: Comparison in Organic and Aqueous Systems. Ind. Eng. Chem. Res. 1998, 37, 2391. (17) Deshpande, R. M.; Chaudhari, R. V. Kinetics of Hydroformylation of 1-Hexene using Homogeneous HRh(CO)(PPh3)3 Complex Catalyst. Ind. Eng. Chem. Res. 1988, 27, 1996.

ReceiVed for reView February 6, 2008 ReVised manuscript receiVed November 23, 2008 Accepted November 26, 2008 IE800215T