The industrial hydroformylation of olefins with a rhodium-based supported liquid phase catalyst

The Chemical Engineering

Journal, 32 (1986) 101 - 110

101

The Industrial Hydroformylation of Olefins with a Rhodium-based Supported Liquid Phase Catalyst I: Description of the Catalyst System, Catalyst Characterization and Preparation, together with some Orienting Hydroformylation Experiments with Propylene J. M. HERMAN, P. J. VAN DEN BERG and J. J. F. SCHOLTEN Laboratory of Chemical (The Netherlands)

Technology,

Delft University of Technology,

Julianalaan

136, 2628

BL Delft

(Received May 14, 1984; in final form August 18,1985)

ABSTRACT

1. INTRODUCTION

Hydridocarbonyltris(triphenylphosphine)rhodium(I) (RhHCO(PPh,),), dissolved in liquid triphenylphosphine and immobilized in a porous support by strong capillary forces, is applied as a heterogeneous catalyst for the hydroformylation of olefins. The hydroformylation reaction proceeds in the following way for propylene:

Generally speaking, a serious problem in the technical application of homogeneous catalysts is the occurrence of entrainment of the catalyst by the product stream. Rhodium is an extremely rare metal, and so this problem needs special attention. Moreover, the metal and/or ligands contaminate the product mixture and always necessitate a cumbersome separation. In heterogeneous catalysis this problem does not exist. Finally, the large-scale application of homogeneous catalysts may entail serious corrosion problems as, for example, in Wacker-type processes [ 11. In view of this problem it is logical that the heterogenization of rhodium-based catalysts has received much attention in recent years [2 - 51. The application of a supported liquid phase catalyst (SLPC) is a way to reach this goal. An SLPC consists of a liquid catalyst solution which is impregnated into the pores of a porous support material. The immobilization of the catalyst solution is caused by strong capillary forces. The catalytically active solution may consist of a molten salt, a liquid metal, an acid or a liquid mixture of an organometallic complex and a high boiling solvent. In order to prevent high evaporation losses and concomitant drying-up of the solution, the volatility of the solvent should be as low as possible. Figure 1 shows a schematic diagram of an SLPC system. Such a system has been used for the hydrogenation of acetylenes [6]. It was shown that with a chlororhodium catalyst the results are in agreement with those of Rony [7] and Rony and Roth [8]. Further, it was concluded that,

CH,-CH=CH,

+ CO + Hz +

CH$H,CH,CHO

and/or CH,CH=CH,

+ CO + Hz __f

CH&H(CH,)CHO

In order to assess the industrial applicability of the above-mentioned catalyst a number of support materials were investigated. The influence of the rhodium concentration and the influence of the total degree of conversion on catalyst performance were also studied. It is concluded that supports based on a-alumina show the best results if these are pure and have an inert surface. SCS9 and SA5202 and also an experimental silica are suitable. After 24 h, catalysts based on these supports are stable for a further 1500 h. In the range 25 - 100 (mol Rh) (m3 PPh,)- ’ the reaction rate is first order with respect to the rhodium concentration. The selectivity is high. The degree of propylene conversion can be as high as 16.8% without an adverse effect on the catalyst performance. In this range of degrees of conversion the reactor behaves differentially. The rate is4.93 (cm3 propylene) (g Rh)-’ s-l. 0300-9467/86/$3.50

@ Elsevier Sequoia/Printed in The Netherlands

102 AC

Fig. 1. Schematic diagram of an SLPC system: A, liquid film of catalyst solution; B, catalyst support; C, gas-liquid interface; D, pore; E, plug of catalyst solution.

if molten triphenylphosphine is used as the ligand as well as the solvent, an excess of PPha is necessary. The rate of the reaction is a linear function of the rhodium concentration [ 61. For hydroformylation, Gerritsen [ 21 found that an SLPC, in which RhHCO(PPhs)s is dissolved in PPh, and immobilized, could be an attractive alternative to the homogeneous rhodium-based low pressure OX0 (LPO) process of Union Carbide [9]. The first to apply a rhodium-based SLPC to the hydroformylation of propylene with a gaseous reaction mixture was Rony [7]. The IIbutyraldehyde-to-isobutyraldehyde ratio obtained, however, was only 2. Also, information about the catalyst stability was scarce [8]. Gerritsen’s SLPC proved to exhibit the following features. (1) A time-independent n-butyraldehydeto-isobutyraldehyde ratio as high as 35 was observed at a sufficiently low CO pressure. Tjan’s physically adsorbed rhodium-based catalyst [ 41 and Rony’s rhodium-based SLPC [ 71 yield n-butyraldehyde-to-isobutyraldehyde ratios of only 2, whereas the LPO process (the state of the art in rhodium-based industrial hydroformylation) exhibits an nbutyraldehyde-to-isobutyraldehyde ratio of 12 [lo, 111. The value of the n-butyraldehydeto-isobutyraldehyde ratio has a major impact on the overall economics of the process. (2) 99.5 mol.% of the olefin is converted to aldehydes. (3) An excellent catalyst stability was obtained. Gerritsen’s SLPC shows no sign of deactivation after use for 800 h. The physically adsorbed catalyst employed by Tjan [4] deactivates to 10% of the initial activity in the first 150 h. The homogeneous rhodium

catalyst applied in the LPO process deactivates at a rate of 3% day-l based on its initial activity [ 121. In view of the extremely low physical availability of rhodium, such deactivation constitutes a serious problem. (4) An overall catalyst activity per mole of rhodium was obtained that is six times higher than that of Tjan’s catalyst but which is appreciably lower than that of the LPO catalyst under the same reaction conditions. Several investigators [6] used a large excess of PPh3. It has been proved that the function of such a large excess is sevenfold [2]. (1) Immobilization of the rhodium complex on the support is achieved. The immobilization of the catalyst solution is caused by strong capillary suction forces. (2) Improvement of the selectivity occurs [13] and a large excess of PPh3 leads to a high n-butyraldehyde-to-isobutyraldehyde ratio. (3) PPh, is a very good solvent for RhHCO(PPhs)s. Moreover, PPh, shows a vapour pressure of only 1.15 Pa at 90 “C [ 141. Such a low volatility results in a very low degree of contamination of the produced aldehydes with PPh, [15]. (4) Stabilization of the rhodium complex is effected. In the absence of PPh3 and CO the complex RhHCO(PPhs)s undergoes the following reaction [ 161: RhHCO(PPh& I

RhHCO(PPh3)T + PPhs

(1) RhHCO(PPh,), , in turn, reacts in the following way [16] : 2RhHCO(PPh& _

[ RhCO(PPh,),] 2 + Hz

(2) [RHCO(PPh&12 was found to be completely inactive [ 171. Moreover, the above-mentioned two equilibria proved to be shifted to the left by the addition of excess PPhs or by the presence of H,. A twofold excess of PPh3 at 8 MPa of Hz and at 20 “C resulted in a complete regeneration of RhHCO(PPh& [ 171. Dilution with benzene resulted in a higher degree of dimer formation [17]. When CO is added in the absence of free PPh3, another dimer is formed [ 161: [ RhCO(PPh,),] 2 + 2C0 =

[Rh(COMPPhd,12

(3)

103

Kastrup et al. [18] thoroughly studied the dissociation reaction of RhHCO(PPh,), in the presence of PPhs: RhHCO(PPh,),

+ nPPhsZ

RhHCO(PPh&

+

+ (n +l)PPh, (4) where n = 6 - 140. This reaction was studied in toluene solution by 3’P nuclear magnetic resonance (NMR) in the temperature range from -5 to +105 “C!.In all cases (even when IZ= 6) the equilibrium concentration of RhHCO(PPh3)2 was too low for 31P NMR detection. The latter complex is a key intermediate in both the associative and the dissociative mechanism proposed by Wilkinson and coworkers [19, 201. According to Wilkinson and coworkers, the presence of a threefold excess of PPh, inhibits dimerization

[201.

Finally, a study of the influence of the rhodium concentration on catalyst performance is presented.

(5) Suppression of hydrogenation [20 - 221 is observed. In the LPO process, in which excess PPh3 is employed, only 5 mol.% of the olefin feed is hydrogenated to the corresponding paraffin [23], whereas no alcohols are formed. (6) Double-bond isomerization is also suppressed, although this is irrelevant for the hydroformylation of ethylene and propylene. (7) Suppression of the rate of hydroformylation [20] also occurred, and this adverse effect cannot be avoided because of the need for a large excess of PPh3. Clearly, an SLPC cannot be applied to liquid phase reactions because the catalyst would be leached out by the liquid reaction mixture. In the present paper a study of the influence of the type of support on catalyst performance is reported. According to Gerritsen [2], a support should be chosen that shows a highly inert surface and no strong acidic or basic sites in order to suppress aldol condensation. A high degree of aldol condensation may lead to the condensation of the aldol products formed, and this in turn will entail a considerable leaching-out of the catalyst solution. Therefore, if an alumina support is to be chosen, its o-alumina content should be as high as possible. For silica [2] it was found that a positive correlation exists between the sodium content of a given support and the extent of aldol condensation. For this reason, only sodium-poor silica supports should be employed.

2. EXPERIMENTAL

DETAILS

2.1. Materials used In Table 1 the names of the suppliers of the chemicals used are listed. The data regarding purity were given by the suppliers. Nz, ethylene, propylene, HZ, CO and helium were freed from oxygen and water by passing them over finely divided copper on a support material (BASF R 3-l 1 catalyst) and molecular sieve 3A respectively. Additionally, traces of CO, were removed from CO by passing it over NaOH on asbestos (Ascarit). Immediately before use, n-butyraldehyde and isobutyraldehyde were purified by distillation in order to remove aIdol products and then stored at -20 “C. All other chemicals were used without further purification. 2.2. Description and characterization of the rhodium-based supported liquid phase catalyst The rhodium-based SLPC consists of three components: (1) RhHCO(PPh3)3, i.e. the rhodium complex; (2) PPh,, the solvent and ligand; (3) the support. The rhodium complex is dissolved in liquid PPh3. The porous support is impregnated with the resulting catalyst solution. Gerritsen [2] and Gerritsen et al. [24] showed most of the catalyst solution to be present in the smallest pores of the support, in accordance with the theory of capillary condensation [25,26]. Additionally, they showed the PPh, to be homogeneously distributed over the particles; hence the catalyst is not a mantle type. An SLPC can be fully characterized by the following parameters: the type of support; its chemical composition (bulk and surface composition); the texture; the crystal structure; the mechanical strength; the particle size; the degree 6 of liquid loading, i.e. the volumetric fraction of the total pore volume of the support filled up with catalyst solution; the molar rhodium complex concentration [ Rh] in the catalyst solution at 90 “C in moles of rhodium per cubic metre of catalyst solution; the liquid density of PPh3 at 90 “C which is 1.07 X lo3 kg me3 [ 271; the molar phosphorusto-rhodium ratio (in this ratio the amount of

104 TABLE 1 Suppliers of the materials used (the purity is given in parentheses) Material

Supplier

RhC1s*H20 PPhs (99.5 wt.%) Benzene (99.5 wt.%) KOH (87 wt.%) Ethanol (99.5 wt.%) Formaldehyde (35 wt.%, solution in water) Nz (99.98 vol.%) Ethylene (99.8 vol.%) Propylene (99.5 vol.%) Hz (99.5 vol.%) CO (99.62 vol.%) He (99.995 vol.%) Alumina SA6190 (99.2 wt.% AlzOa) Alumina HY343 (99.9 wt.% AlzOs) Alumina SA5202 (99.6 wt.% AlzOs) Alumina SCS9 (99.8 wt.% AlzOs) Alumina KlO (99.5 wt.% AlzOs) Silica 1 (99.9 wt.% SiOZ)

Johnson Matthey Chemicals Ltd., Gt. Britain Fluka, Switzerland J. F. Baker Chemicals BV, The Netherlands J. F. Baker Chemicals BV, The Netherlands J. F. Baker Chemicals BV, The Netherlands Merck, F.R.G. Air Products, U.S.A. Air Products, U.S.A. Air Products, U.S.A. Air Praducts, U.S.A. Air Products, U.S.A. Union Carbide Benelux NV, Belgium Norton Ltd., Gt. Britain Norton Ltd., Gt. Britain Norton Ltd., Gt. Britain Rhone Poulenc Industries, France Dr. C. Otto & Comp. G.m.b.H., F.R.G. DSM, The Netherlands (research sample)

phosphorus present in the rhodium complex is included); the molecular mass of RhHCO(PPhs)s which is 918, and that of PPh, which is 262. 2.3. Catalyst prepara tion The catalyst preparation, carried out according to Gerritsen’s procedure [2, 241, consisted of the four following steps. (1) Preparation of RhHCO(PPh3)3 from RhCl,-H,O. This was carried out according to the method of Ahmad et al. [ 281. (2) Drying of the catalyst support. The support was dried in uacuo (0.1 kPa), first at 150 “C for 3 h and then at 500 “C for 16 h. (3) Impregnation of the support with the catalyst solution. This step was carried out in the apparatus shown in Fig. 2. A weighed quantity of support was placed in the support holder B under flowing Nz . Weighed quantities of RhHCO(PPh& and of PPh3, corresponding to the desired rhodium complex concentration and to the desired degree of liquid loading, were dissolved in benzene at 70 “C in vessel A, under flowing N,. In principle, the total solution volume was taken to equal the total pore volume, and hence the method of dry impregnation was applied. In practice a very small additional quantity of benzene was added to the solution, in order to compensate for evaporation losses during impregnation. The solution was added dropwise to the

Fig. 2. Catalyst preparation apparatus: A, catalyst solution holder; B, support holder; C, magnetic stirrer; D, oil bath.

magnetically stirred support at 70 “C under flowing Nz . Blanketing with N, was necessary in order to prevent PPhs from oxidizing to OPPhs .

(4) Drying of the impregnated support. The impregnated support, still present in the support holder, was slowly dried at room temperature under flowing Nz for 3 h. After that, the catalyst was removed from the support holder and dried at 90 “C for 16 h under flowing N,, allowing the catalyst

105

solution to be redistributed in the pores. During this procedure, benzene was completely removed from the catalyst. The resulting dry, free-flowing and slightly yellow catalyst was stored at -20 “C. The above method of preparing the SLPC was found to be completely reproducible. It was shown that two different batches with the same specifications exhibit the same catalytic performance. 2.4. Description of the hydroformylation equipment The rhodium-catalysed hydroformylation was investigated in a continuous flow apparatus, suitable for absolute total pressures up to 2 MPa and for reactor temperatures up to 200 “C. A schematic diagram of the equipment is shown in Fig. 3. It was employed for the hydroformylation of both propylene and ethylene. Hz, helium, CO, propylene and ethylene were purified in the way described in Section 2.1. These gases were metered from gas cylinders, the two propylene cylinders being placed in a thermostatted water bath at 50 “C, in order to attain a vapour pressure that was sufficiently high for proper metering at absolute total reactor pressures up to 2 MPa. Beyond the purification section A, the pressures of the above-mentioned gases were reduced by pressure regulators (Veriflo-type

IR 502 S 4 PMR) to an absolute pressure of 2.1 MPa, except for propylene which had an absolute metering pressure of 2.05 MPa that was controlled by the thermostatted water bath. From the water bath, propylene vapour was passed through heated tubes and the heated purification section A. The four metering sections had to be thermostatted for proper metering at 35 “C for Hz, helium and CO (thermostat D) and at 65 “C for propylene (thermostat C). Beyond the pressure regulators, each gas was passed subsequently through a thermal mass flowmeter (Brooks model 5810) and through a flow controller (Brooks model 8744 B). The metering accuracy was 1% for each component. Beyond the metering sections the gases were mixed in a heated mixing chamber F in order to prevent the occurrence of stratified flow in the reactor. The resulting gas mixture was led through a heated tube to a stainless steel fixed-bed reactor 0.25 m long (inner diameter, 0.025 m). The fixed-bed reactor J was placed in an air thermostat K permitting isothermal operation to within 1 “C. The reactor temperature was measured with three chromel-alumel thermocouples to within 0.5 “C. The reactor pressure was measured to within 0.01 MPa, by means of a precision pressure gauge (Econosto type

Fig. 3. Continuous flow apparatus for the hydroformylation experiments: A, purification section; B, vent; C, thermostat for the metering section of propylene; D, thermostat for the metering sections of hydrogen, helium and CO; E, emergency vent; F, mixing chamber; G, thermostat for the mixing chamber; H, fan; I, air intake; J, tubular reactor; K, air thermostat; L, sampling bottle ; M, vent; N, soap film meter; 0, vent of the product mixture ; P, pneumatically actuated Carle sampling valve; Q, Porapack-PS column with catharometer ; R, microcomputer ; S, recorder; T, mercury O-ring meter; U, vent of the carrier gas; FC, flow controller; FI, flow indicator; PA, pressure alarm; PC, pressure controller; PI, pressure indicator; TC, temperature controller; TI, temperature indicator; Sl, S2, S3, S4, S5, S6 and S7, solenoid valves.

106

347, DIN class 0.6). Ambient pressure was recorded continuously with a barograph (Wilhelm Lambrecht type 293) to within 10 Pa. In this way, ambient pressure fluctuations could be taken into account. These fluctuations proved to be negligible with respect to the absolute total reactor pressure. The gaseous product mixture was passed from the reactor through a heated tube to a heated back-pressure regulator (Veriflo type BPR 40-300-l-K-PBK), by which it was throttled. The back-pressure regulator controlled the reactor pressure to within 1%. From the back-pressure regulator the product mixture, then at atmospheric pressure, was passed through a heated tube to a gas chromatograph (GSC) containing a PorapackPS column Q from Waters Ass. Inc. U.S.A., having an inner diameter of 0.0021 m and a total length of 3 m. The analysis was performed isothermally at a column temperature of 170 “C and a carrier gas flow of 0.33 cm3 s-i (20 “C; 0.1 MPa). The carrier gas was helium. The column temperature was controlled to within 1 “C. Sampling was effected automatically using a pneumatically actuated Carle sampling valve P with a sampling volume of approximately 1 cm3. The analysis signals were detected catharometrically. The peak areas were noted on the recorder S and integrated with a microcomputer R (Tracer Instruments). After the total volumetric flow had been measured at a known pressure by means of a soap film meter N, the product mixture was vented to the atmosphere at 0. All temperatures were measured with chromel-alumel thermocouples to within 0.5 “C. As a thermocouple reference system an automatic ice bath (Kaye Instruments) was employed. The read-out of the signals from the thermocouples and of those from the thermal mass flowmeters was effected with a data acquisition system consisting of a Numation digital indicator (model 914), a digital printer (model 2730), a scannerprogrammer (model 2740) and a digital clock (Leeds and Northrup Company). 2.5. Calibration procedures 2.5.1. Calibration of the thermal mass flowmeters The thermal mass flowmeters were calibrated by means of a mercury O-ring meter connected to an electronic stopwatch (Heuer

Microsplit, reference number 840.7). Calibration accuracy was 1%. 2.5.2. Calibration of the gas chromatograph As aldehydes were the only products detected [ 151, the total degree &= of conversion of propylene was calculated as follows:

EC,=

AnPn+ AiPi AnPn+ AiPi + Ao

(5)

where A,, Ai and A,, are the integrated peak areas for n-butyraldehyde, isobutyraldehyde and propylene respectively, whereas /_?,and pi are the molar internal normalization factors of n-butyraldehyde and isobutyraldehyde respectively with respect to propylene. The n-butyraldehyde-to-isobutyraldehyde ratio S was calculated from S=_n

&&I AdA

(6)

In order to determine /3, and pi, gaseous calibration mixtures of propylene and n-pentane and liquid mixtures of n-butyraldehyde, isobutyraldehyde and n-pentane were made. For /3, and pi the same value, i.e. 0.80 (+0.03), was found; this is plausible since the thermal conductivities of gaseous n-butyraldehyde and isobutyraldehyde are equal. 2.6. Data processing of the hydroformylation experiments The reactor was operated differentially; therefore the total reaction rate r can be expressed as r=

tc,

(7) m,,iFq where msh (g) is the mass of rhodium present in the reactor and Fcr (cm3 s-i (0.1 MPa; 20 “C)) is the propylene flow. Consequently, r is given in cubic centimetres of propylene converted (0.1 MPa; 20 “C) per gram of rhodium per second. Only n-butyraldehyde and isobutyraldehyde were produced in significant amounts. Consequently, the following equation applies: r, + ri = r

(8)

where r, and ri are the reaction rates of formation of n-butyraldehyde and isobutyraldehyde respectively. Therefore, r, and ri can be calculated in the following way:

107

with a correlation coefficient of 0.999. Consequently, in the interval from 0 to 16.8 mol.% conversion the total reaction rate can be calculated from eqn. (7). In this case, r was 4.93 (cm3 CT) (g Rh)-’ s-i.

Sr

rn= 1+s and

r

(10)

ri = 1+s

The data processing of the hydroformylation experiments was implemented with an ALGOL-60 computer program on the Amdahl 470V/7B computer of the Delft University Computing Centre. 2.7. Starting-up procedure At the start of each experiment the reactor temperature was raised stepwise to its final value in a period of approximately 2 h.

3. RESULTS

3.1. Some orienting hydroformylation experiments 3.1.1. Relation between the total degree of conversion and the total rate of reaction In order to determine the range of differential operation of the experimental reactor, the total degree ,&= of conversion of propylene was measured as a function of the reactor space time m&F,,. The results are shown in Table 2. By means of a linear regression analysis using the data presented in Table 2, the .& versus mRhIFc= curve was fitted to a straight line through’the origin, TABLE 2 The total degree of conversion of propylene as a function of the reactor space time

tc=

(m301.%C;)

(m&F&X lo2 ((g Rh) s tcm3 C,)-r

16.82 12.31 9.49 6.90 6.05 4.27 3.18 2.57

3.46 2.47 1.92 1.44 1.15 0.864 0.691 0.576

s ) 8.4 8.6 8.5 8.6 8.4 8.2 8.5 8.7

P = 1.62 MPa; propylene:Hz:CO feedstream ratio, 1:l:l; t = 90 “C. Catalyst support: alumina KlO; 6 = 0.60; [Rh] = 75 mol rnP3., molar phosphorus-to-rhodium ratio, 57.4. Cylindrical particles: d, = 4.6 mm; I, = 9.7 mm.

3.1.2. Influence of the type of support A number of commercially available supports were tested in the hydroformylation of propylene; only silica 1 is not yet commercially available [29] but is a research sample from DSM, Geleen, The Netherlands. In each case the degree of liquid loading was approximately 0.20. The catalytic performance of the impregnated catalysts is presented in Table 3. In each case, after approximately 24 h on-stream time, stable final activity and selectivity levels were reached. From Table 3 it can be concluded that alumina SA6190 must be ruled out completely. Moreover, the n-butyraldehydeto-isobutyraldehyde ratio in these experiments is rather low; this is caused by the relatively high CO pressure of 0.540 MPa. For unknown reasons, alumina HY343 yields a very low n-butyraldehyde-toisobutyraldehyde ratio, which means that the expensive feedstock is not converted efficiently. Therefore, on the basis of the data presented in Table 3, the choice is reduced to alumina SCSS, alumina SA5202, alumina KlO and silica 1. 3.1.3. Influence of the rhodium concentration The influence of the rhodium concentration was investigated using alumina KlO as a support. The rhodium concentration was varied between 25 and 100 mol (m3 PPh3)-l. The information obtained in these experiments is presented in Table 4. After approximately 24 h, the activity and selectivity reached a stable level. From Table 4 it appears that the rhodium concentration affects neither catalyst activity per gram of rhodium nor selectivity in the 25 - 100 mol (m3 PPh3)-’ range. This means that the total rate of reaction is first order in the rhodium concentration, which is in accordance with Gerritsen’s findings [ 21. In addition, the catalyst stability is not adversely affected when the rhodium concentration is increased from 25 to 100 mol (m3 PPh3)-‘.

108 TABLE 3 Performance of supported liquid phase catalysts applying various supports Catalyst support

Alumina Alumina Alumina Alumina Alumina Silica 1

SCS9 SA6190 HY343 SA5202 KlO

Particle shape

Spherical Cylindrical Cylindrical Spherical Cylindrical Irregular

Particle size *, (mm)

1, (mm)

2.8 - 3.4 3.4 2.5 6.3 4.6 1-2

3.6 Variable 9.7 -

6

(m&kg-) x 102 ((g Rh) s (cm3 CT)-l)

EC= (mol.% Cf)

r ((cm3 CT) (g Rh)-’ s-’ )

s

0.16 0.20 0.20 0.20 0.20 0.20

1.25 1.25 1.25 1.24 1.27 0.609

10.3 3.11 9.97 9.64 12.2 4.20

8.23 2.49 7.99 7.17 9.62 6.90

7.9 7.7 4.9 7.8 7.2 7.3

P = 1.62 MPa; propylene:H2:C0 feedstream ratio, 1:l:l; t = 90 “C. [Rh] = 100 mol mp3; molar phosphorus-to-rhodium ratio, 43.8.

TABLE 4 Influence of the rhodium concentration

on catalyst performance s

((mol Rh) me3 )

WI

Molar phosphorusto-rhodium ratio

(m&F& X lo= ((g Rh) sqcm3 C,)-l)

k=

(mol.% CT)

;(cm3 CT) (g Rh)-’

25.0 50.0 75.0 100

166 84.7 57.4 43.8

1.25 1.25 1.92 1.21

6.29 5.14 9.50 6.03

5.03 4.59 4.95 4.98

s-l) 9.2 9.6 8.5 8.8

P = 1.62 MPa; propylene:Hz:CO feedstream ratio, 1:l:l; t = 90 “C. Catalyst support: alumina KlO. Cylindrical particles: d, = 4.6 mm; 1, = 9.7 mm; 6 = 0.60.

4. DISCUSSION

4.1. The supports According to Gerritsen [2], a high surface area at the gas-PPh, interface results in a high activity which, according to this same researcher, is due to the exclusive activity of the rhodium complexes in the meniscus. However, the question of whether this statement is still valid under the condition of a higher total conversion might be raised. In that case, larger amounts of products are likely to dissolve in PPh, and, because of this, rhodium complexes become accessible for the catalytic reactions [ 301. All the activities found in the present experiments are of the same order of magnitude. In addition, these results are comparable with the activities found elsewhere, in which supports were used with both high and low surface areas [ 2,6].

A complicating factor is the varying adsorbability of the rhodium complexes on the different support materials. Of course, adsorptive withdrawal of complexes at the support-PPh, interface will decrease the amount of complexes in the solution and at the gas-PPh, interface and hence will lower the catalytic activity [ 301. For silica a positive correlation was found to exist between the sodium content and the extent of aldol condensation [ 21. The adverse effect of sodium contamination emphasizes the indispensability of detailed information on the degree of contamination of all supports involved. Therefore, this matter was studied in detail [15]. It was found that alumina SCSS, alumina HY343, alumina 5202 and silica 1 show a very low degree of contamination whereas alumina SA6190 and alumina KlO exhibit a somewhat higher degree of contamination.

109

Furthermore, a support should be chosen that exhibits a very inert surface in order to suppress aldol condensation, i.e. for alumina supports the a-alumina content should be as high as possible. Qualitative determination of the crystal structure of the alumina supports showed that alumina KlO, alumina SA5202 and alumina SCS9 are mainly composed of a-alumina, whereas alumina SA6190 and alumina HY343 also contain considerable quantities of &alumina [ 151. On the basis of all results obtained in the characterization of the supports it can be concluded that alumina SCSS, alumina SA5202 and silica 1 are superior to the other supports as far as inertness of the surface and degree of contamination are concerned. 4.2. The hydroformylation experiments From the hydroformylation experiments presented in Section 3, two important conclusions can be drawn. (1) The total degree of conversion of propylene can be raised to 16.8% without an adverse effect on activity, stability and selectivity. In previous experiments [2] the total degree of conversion was of the order of only 5%. For the industrial application of the SLPC a high total degree of conversion is imperative; otherwise the recirculation costs of unreacted reactants become very high. (2) The increase in the particle size of the SLPC to approximately 5 mm does not influence catalyst performance. Gerritsen used particles of about 0.5 mm which, in view of the pressure drop, are too small for application in a large-scale fixed-bed reactor. Generally speaking, it is not wise to specify particle sizes below 3 mm [31] for a largescale fixed-bed reactor, since smaller particles cause a high pressure drop across the reactor. It might seem surprising that the experimental reactor operates differentially even at a total degree of conversion of propylene as high as 16.8 mol.%, but it should be remembered that, at a molar propylene:H2:C0 feedstream composition of l:l:l, the fractional change E in total volumetric flow between zero conversion and complete conversion is -2/3. The definition of E is given by the following equation : e=

FI -Fo Fo

where F, and FI are the total volumetric flows at zero and complete conversion respectively of propylene. From this it follows that under isothermal and isobaric conditions the decrease in pc= at E = -2/3 and EC, = 16.8 mol.% is only36.3%. This fact explains the wide range of differential behaviours of the reactor. From the performance presented in Table 3 it can be deduced that alumina SCSS, alumina SA5202, alumina K10 and silica 1 yield the best results as far as activity and selectivity are concerned. Therefore the choice of support can be narrowed down to alumina SCSS, alumina SA5202, alumina KlO and silica 1. If the data presented in Section 4.1 are also considered, it follows that alumina SCSS, alumina SA5202 and silica 1 are to be preferred to the other supports. Catalyst activity per gram of rhodium and selectivity are not influenced by a change in the rhodium concentration from 25 to 100 (mol Rh) mF3, corresponding to molar phosphorus-to-rhodium ratios in the range 43.8 - 166. Kastrup et al. [18] found that in the temperature range from -5 to +105 “C and for molar phosphorus-to-rhodium ratios of 9 - 143 the complex RhHCO(PPh3)3 does not show any significant dissociation to RhHCO(PPh3)2. By far the most of the rhodium involved is therefore present as RhHCO(PPh3)3. This conclusion fits in with the experimental results given in Table 4. Catalyst performance does not change in the range of molar phosphorus-to-rhodium ratios investigated. In addition, no deactivation was found. The explanation for this result is obvious. As RhHCO(PPh3)3 does not show any significant dissociation under the abovementioned conditions, the formation of inactive dimers is most unlikely. A lower molar phosphorus-to-rhodium ratio decreases the reactor volume required for a given production of n-butyraldehyde under given reaction conditions. With respect to this fact it should be realized that there are limits to decreasing the phosphorus-torhodium ratio. Firstly, there is the danger of dimerization of the rhodium complex to catalytically inactive species if the ratio becomes smaller than 9. Secondly, a higher rhodium concentration will aggravate the heat disposal problem of this highly exothermic

110

reaction. The heat disposal problem will be treated in considerable detail in the final part of this series of papers [32].

Plants, Vol. 1, Principles and Techniques, Wiley, New York, 1st edn., 1977, p. 493. 32 J. M. Herman, P. J. van Krugten, A. P. A. F. Rocourt, P. J. van den Berg and J. J. F. Scholten, Chem. Eng. Sci., to be published.

REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

25 26

27 28 29

30 31

D. M. Fenton,J. Org. Chem., 38 (1973) 3192. L. A. Gerritsen, Ph.D. Thesis, Delft, 1979. N. A. de Munck, Ph.D. Thesis, Delft, 1980. P. H. W. L. Tjan, Ph.D. Thesis, Delft, 1976. Th. G. Spek, Ph.D. Thesis, Delft, 1976. J. M. Gil Figueroa and J. M. Winterbottom, J. Chem. Tech. Biotechnol., 32 (1982) 857. P. R. Rony, J. Catal., 14 (1969) 142. P. R. Ronyand J. F. Roth,J. Mol. Catal., 1 (19751976) 13. R. Fowler, H. Connor and R. A. Baehl, Chem. Eng. (N.Y.), 84 (2) (1977) 110. G. Wilkinson, Johnson Matthey, Ger. Patent 1,939,322, 1970. G. Wilkinson, Johnson Matthey, Br. Patent 1,338,225, 1973. E. Billig, Union Carbide Corporation, Eur. Patent Appl. 28,378, 1981. D. Evans, J. A. Osborn and G. Wilkinson, J. Chem. Sot. A, (1968) 3133. C. G. de Kruif, J. M. Herman and P. J. van den Berg, J. Chem. Eng. Data, 26 (1981) 359. J. M. Herman, Ph.D. Thesis, Delft, 1983. D. Evans, G. Yagupsky and G. Wilkinson, J. Chem. Sot. A, (1968) 2660. M. Yagupsky, C. K. Brown, G. Yagupsky and G. Wilkinson, J. Chem. Sot. A, (1970) 937. R. V. Kastrup, J. S. Merola and A. A. Oswald, Adv. Chem. Ser., 196 (1982) 43. G. Yagupsky, C. K. Brown and G. Wilkinson, J. Chem. Sot. A, (1970) 1392. C. K. Brown and G. Wilkinson, J. Chem. Sot. A, (1970) 2753. W. Strohmeier and A. Kuhn, J. Organomet. Chem., 110 (1976) 265. J. A. Osborn, F. H. Jardine, J. F. Young and G. Wilkinson, J. Chem. Sot. A, (1966) 1711. E. A. V. Brewster and R. L. Pruett, Union Carbide Corporation, U.S. Patent 4,247,486,1981. L. A. Gerritsen, A. van Meerkerk, M. H. Vreugdenhil and J. J. F. Scholten, J. Mol. Catal., 9 (1980) 139. R. Zsigmondy, 2. Anorg. Chem., 71 (1911) 356. P. H. Emmett, Catalysis, Fundamental Principles (Part I), Vol. 1, Reinhold, New York, 1st edn., 1961, p. 22. M. V. Forward, S. T. Bowden and W. J. Jones, J. Chem. Sot., 5 (1949) S121. N. Ahmad, S. D. Robinson and M. F. Uttley, J. Chem. Sot., Dalton Trans., (1972) 843. J. J. F. Scholten and A. van Montfoort, DSM, Geleen, The Netherlands, Dutch Patent Appl. 8,201,925,1982. H. L. Pelt, Ph.D. Thesis, Delft, 1984. H. F. Rase, Chemical Reactor Design for Process

APPENDIX A: NOMENCLATURE

Fe,

1, mRh

n P r

integrated peak area for isobutyraldehyde (-) integrated peak area for n-butyraldehyde (-) integrated peak area for propylene (-) diameter of the catalyst particle (mm) total volumetric flow rate at zero conversion of propylene (cm3 s-l (0.1 MPa; 20 “C)) total volumetric flow at complete conversion of propylene (m3 s-l (0.1 MPa; 20 “C)) propylene flow at the inlet of the reactor ((cm3 CT) s-l (0.1 MPa; 20 “C!)) length of the catalyst particle (mm) mass of rhodium present in the reactor (g) number of free PPh, molecules per rhodium complex (-) absolute total pressure in the reactor (MPa) total reaction rate ((cm3 Cr) (g Rh)-’ S-l)

ri

rn

[Rhl s t

reaction rate of formation of isobutyraldehyde (( cm3 Cc) (g Rh)- ’ s-l) reaction rate of formation of n-butyraldehyde ((cm3 CT) (g Rh)-’ s-l) rhodium concentration in the catalyst solution ((mol Rh) m-3) n-butyraldehyde-to-isobutyraldehyde ratio in the product stream (-) temperature in the reactor (“C)

Greek symbols molar internal normalization factor of isobutyraldehyde with respect to propylene (-) molar internal normalization factor of P, n-butyraldehyde with respect to propylene (-) fractional degree of liquid loading (-) 6 (FI - F,)lFo (-) total degree of conversion of propylene F,, (mol.% Cf or fractional) 6