- Email: [email protected]
Kinetics of methanol homologation
Journal of Molecular Catalysis,
58 (1990) 43-52
43
KINETICS OF METHANOL HOMOLOGATION PART II. BEHAVIOUB OF COBALT-PHOSPHINE-IODINE CATALYSTS PLUS OTHER METALS AS COCATALYSTS E. SANTACESARIA*,
M. DI SERIO
Cattedra di Chimica Industriale, Dipartimento Mezzocanrwne 4, 80134 Naples (Italy) D. GELOSA
di Chimica dell Universitd
di Napoli, Via
and S. Cm
Cattedra di Chimica Fisica, Dipartimento di Chimica Fisica Applicata o!.elPolitecnico, Piazza Leonardo da Vinci 32, 20133 Milan (Italy) (Received January 2,1989;
accepted April 3,1989)
Summary By employing the kinetic model developed in a previous work, the kinetic behaviour of cobalt/phosphine/iodine catalysts has been compared with that of several metals mixed with cobalt, by taking the molar ratio between cobalt and the added metal equal to 1. It has been concluded that other metals generally have a deactivating effect on the homologation reaction. In particular, manganese completely inhibited activities. As expected, ruthenium mixed with cobalt shows a high selectivity to ethanol. The catalytic behaviour of Ru/Co catalysts is the most interesting. Therefore, we have extended our investigations to the kinetic behaviour of Ru/Co catalysts at different molar ratios of the two metals from 0 to 1. A strong synergic effect has been observed for low ruthenium amounts, while selectivities to ethanol strongly increase only for a Ru content of at least 20% with respect to cobalt. Reflections on these findings conclude the paper.
Introduction The homologation of methanol is a very interesting reaction for producing acetaldehyde or ethanol from synthesis gas. For this reason, the process has been carefully studied in the last few years; many papers, reviews, books and patents have recently been published. The reaction occurs in the homogeneous phase, and the most frequently employed catalysts are cobalt-phosphine-iodine and cobalt-ruthenium-phosphine-iodine for the production of acetaldehyde and ethanol 11-51, respectively. Some papers have also been published devoted to the influence of metals other than ruthenium as cocatalysts l&6-83, but in all cases experimental data have been interpreted by comparing the compositions of the liquid mixtures *Author to whom correspondence 0304-5102/90/$3.50
should be addressed. @ Elsevier Sequoia/Printed
in The Netherlands
44
obtained at the end of the reaction, that is, by comparing activity and selectivity data at a 6xed time without any kinetic analysis. Very recently, we studied the kinetics of the reactions occurring in the homologation of methanol 191. Normally the reaction pattern is the following: CHBOH+ CO + Hz
w
CH&HO + HZ0
(1)
CH&HO + Hz0 + Hz __* CH3CH20H CH&HO + 2CHBOH w 2CHSOH + CO
w
CH&H(OCH&
(2) + Hz0
CH&OOCH3 + Hz0
(3) (4)
The relevant kinetic equations are:
(5) r2 =
k2c2p9
(6) (7)
r4 =
k4csa
(8)
where the subscripts indicate: 1 = methanol, 2 = acetaldehyde, 3 = ethanol, 4 = acetal, 5 = acetate, 6 = water, 7 = dioxan, 8 = carbon monoxide, 9 = hydrogen. As explained in our previous paper 191, for determining kinetic parameters for this type of reaction, it is necessary to consider the evolution with time of the reaction composition affected by both reaction rates and vapour-liquid partition equilibria. Details of the mathematical model for this are reported in the above-mentioned paper 191. In the present paper, the kinetic analysis previously performed on the cobalt/phosphine/iodine catalytic system has been extended to mixtures of cobalt with many other metals, by taking in all cases a molar ratio of 1 between the two metals. In particular, the behaviour of ruthenium as cocatalyst has been analyzed in detail, since this metal shows a very interesting kinetic behaviour. For this purpose, kinetic runs were performed and interpreted for different Ru/Co ratios. In all the above cases, kinetic parameters were determined by fitting experimental runs.
Experimental Methods, techniques and reagents All kinetic runs were performed in a magnetically stirred 11 autoclave made from stainless steel, which was equipped with an injection gas burette and a syngas storage. A pressure regulator allowed constant pressure to be maintained throughout the reaction. A typical kinetic run was performed by introducing in the autoclave 300 cm3 of methanol, 70 cm3 of dioxan and the
45
catalyst. The autoclave was closed, the liquid was flushed with nitrogen and then with synthesis gas for the time necessary to remove oxygen. The closed autoclave was then heated at the reaction temperature (normally 185 “C) while the pressure was successively adjusted by injecting synthesis gas in the autoclave, using a gas burette. The gas burette allowed direct evaluation of both the amount of synthesis gas initially injected and the consumption of synthesis gas with time. The pressure was kept constant, normally at 190 atm. The synthesis gas (CO/H2 with a ratio normally equal to 1) was fed when necessary from a bomb. Liquid was withdrawn from the autoclave at different reaction times, and conveyed to a frozen test tube, kept at -20 “C, equipped with a refluxing cooler. Analysis of the collected liquid samples was made by gas chromatography. The employed column was 2 m long of Chromosorb 102. Helium was employed as carrier gas and HWD as detector. The analysis of the vapour phase was made only occasionally by conveying vapours in a sampling valve kept at the reaction temperature and injecting into another gas chromatograph. CO, Hz and CH4 were analyzed with a 1 m long molecular sieve column using argon as carrier gas. Reagents and standards for chromatography were all from Carlo Erba Co. at the highest purity available. Synthesis gas was furnished by SIAD SpA as a mixture of pure hydrogen and carbon monoxide. Cobalt acetate was employed (CO(AC)~*~H~O)as reference catalyst, together with triphenylphosphine and methyl iodide. Cocatalysts were normally added with a molar ratio equal to 1, except for ruthenium. In Tables 1 and 2 are summarized the catalyst mixtures tested.
TABLE 1 List of cocatalysts used; in all cases 6.7 mm01 P(Ph), and 4.78 mm01 CH,I were added Number of runs
Catalyst
Cocatalyst (mm011
(mmol) Co(CH,C001,.4H,O Co(CH,C001,.4H,O Co(CH,C00),.4H,O Co(CH,COO),.4H,O Co(CHsCOOl,.4H,O Co( CHaCOO ),.4H,O Co(CH&00),.4H,O Co(CH,COO)a.4H,O Co(CHaC00),.4H,O
(2) (2) (2) (2) (2) (2) (2) (21 (2)
Fe(CO), Cu(CH&OO), Zn(CH,COO), WOCl* Mo(THFl,Cl, SnCl, Cr(CH,COO), PdCl, 0
10 11 12 13
Co(CHJ!0012.4H,0 Co(CH,COO),.4H,O Co(CH,COO)a~4H,O Co(CH,COO),.4H,O
(2) (2) (2) (2)
II VO ( CH,-G-CH=CMn(CH&OOl, Ni(CH,COO)a.4H,O RuCl,P(Ph),
(2) (2) (2) (2) (2) (2) (2) (2) 0
I
*I-W,
(2) (2) (2) (2)
46 TABLE
2
Kinetic parameters Number of run 1 2 3 4 5 6 7 8 9 10 11 12
obtained by fitting experimental
runs
Catalyst
K, x 10m5
K, x 1O-4
K3 x 1O-3
K4 x lo-’
K,
axlO6
co
2.7 1.8 2.5 0.8 1.0 2.7 1.2 2.7 1.6 2.0 0. 2.7
0.20 0.07 0.15 0.03 0.02 0.10 0.20 0.20 0.02 0.10 -
2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 -
12 12 12 12 12 12 12 12 12 12 -
4.8 38. 8.8 180. 180. 30. 35. 35. 9.8 4.8 -
0.20
2.5
1.4 1.2 1.4 0.6 0.7 1.4 1.0 1.4 1.4 2.4 0. 1.4
12
18.
Co-Fe Co-Cu Co-Zn co-w
CO-MO CO-h Co-0 Co-Pd co-v Co-Mll Co-Ni
Results
Kinetic runs performed with the catalysts described in detail in Table 1, under the operative conditions also reported in the same table, have been interpreted with the mathematical model reported elsewhere [91. The kinetic parameters obtained are reported in Table 2. Figure 1 illustrates the fit obtained using the parameters of Table 2 for the reference run (11, in the presence of cobalt alone. Figures 2 and 3 show, as examples, the fits obtained in runs 2 and 3, respectively, corresponding to Co-Fe and Co-Cu. o Methanol
(moles.
2)
o Acetal
40 36
OAcetaldehyde
o Methanol
A Acetate
40
. Ethanol
36
0Acetatdehyde
. Ethanol
24
24 z 6
20
I =
o Acetat A Acetate
3.2
3.2
z 6
(moles’2)
1.6
2.0 16
12 08 04 0.0
00
40
60 TIME
120 (MIN.)
160
00
80
160. TIME
240
(MIN.)
1. Kinetic run performed at 185 “C, 190 atm, with catalyst 2 mm01 Co(Ac),.4H,O, 6.7 mmol P(Ph),, 4.78 mm01 CH,I. Initial reaction mixture: 7.414 mol methanol and 0.821 mol dioxan. Curve fits were obtained by calculation using the parameters reported in Table 2 (run 1). Fig.
Fig. 2. Kinetic run performed in the same conditions described in the legend to Fig. 1, but in the presence of 2 mmol Fe(CO), as cocatalyst. Kinetic parameters employed for fitting experimental data are those reported in Table 2 (run 2).
47 o Methanol 4.0 3.6 A
z I
(moles’
2)
q
A&al
. water
n Acetate
0 Acetaldehyde
. Ethanol
20 16
00
0.0
80
160 TIME
(MIN
240 1
Fig. 3. Kinetic run performed in the presence of 2mmol Cu(Ac), as cocatalyst. Other experimental conditions are the same described in the legend to Fig. 1. Kinetic parameters employed for fitting experimental data are those reported in Table 2 (run 3).
In Table 3, kinetic parameters related to the Co/Ru system, at different molar ratios are reported. Figures 4,5 and 6 show the fits obtained, using the kinetic parameters of Table 3, for interpreting the experimental kinetic runs performed at different Co/Ru ratios. In Fig. 7 the kinetic behaviour of ruthenium alone as catalyst is reported.
Discussion
and conclusions
As previously mentioned, many data reported in literature regarding the behaviour of two mixed metals in catalyzing homologation reaction are based on the observation of the liquid compositions obtained after a fixed reaction time. This can lead to erroneous conclusions about the true activity and selectivity of the examined catalyst, above all in the presence of deactivating effects in the kinetics. If we observe the kinetic parameters reported in Tables 1 and 3, we note that (Y, the deactivating parameter, changes by many orders of magnitude according to the metal employed as TABLE 3 Kinetic parameters obtained for different ruthenium amounts in the catalyst Number of run
Catalyst
K, x 1O-5
K, x 1O-4
KS x lo3
K,xlO-=
K,
(rx1O6
1 13 14 15 16
co Ru/Co = 1 Ru/Co = l/20 Ruf Co = l/5 Ru
2.7 2.2 4.0 4.0 0.12
0.2 2.9 0.2 0.4 9.0
2.5 2.5 2.5 2.5 2.5
1.4 1.9 5.4 5.4 0.4
12 12 12 12 12
4.8 0. 2.0 2.0 0.
o Methanol 40 36 A
(moles
2)
0 Methanol
o Acetal
. water
A Acetate
0 Acetaldehyde
. Ethanol
(moles.
2)
LI Acetal
4.0
. Water
b Acetate
3.6
OAcetaldehyde
. Ethanol
3.2 20 24 B 6
20
*
1.6 1.2
0.0 0.0
80
240
160 TIME
TIME
WIN.)
(MIN.)
Fig. 4. Kinetic run performed in the presence of 2mmol RuCl,(Ph)S as cocatalyst. Other experimental conditions are the same described in the legend to Fig. 1. Kinetic parameters employed for fitting experimental data are those reported in Table 3 (run 13). Fig. 5. Kinetic run performed as described in the legend of Fig. 1, but in the presence of 0.1 mm01 RuCl,(Ph)s as cocatalyst. Data are fitted by employing the parameters reported in Table 3 (run 14).
o Methanol 4or 36
(mOles.2)
q
o Methanol
Acetal
. water
D Acetate
0 Acetaldehyde
. Ethanol
1: [
::y
(moles.
o Acetal
2)
ldeh y de
:
:::::I
32 20 0.6 t: 2 0.4 -
L
12
ijg_+&, 00
160
60. TIME
(MIN)
240
::h 00
40.
60.
TIME
(MIN.)
Fig. 6. Kinetic run performed as described in the legend to Fig. 1, but in the presence of 0.4 mm01 RuCl,(Ph), as cocatalyst. Curve fits were obtained by employing kinetic parameters reported in Table 3 (run 15). Fig. 7. Behaviour of pure RuCl,(PhjB as catalyst. III this case CO(AC)~.~H~Owas replaced by 2 mmoi of the mentioned ruthenium complex. Other conditions are as in the legend to Fig. 1. Parameters employed for fitting experimental data are reported in Table 3 (Run 16).
49
cocatalyst. The parameter (Yseems to be related to the hydrogenating power of the complex HyMeL which is useful in the elementary step of acetaldehyde formation. Indeed, in a previous work, we suggested oxidative addition of CHJ to be the more reliable mechanism, occurring through the following steps: HCoL,
e
HCoL, + CO
HCoL3 + CH31
=
CH&oHLJ
(10)
CH&oHLJ
e
CH&oL, + HI
(11)
CH$oL,
=
CH,CoL,
(12)
CH&oL,
e
CH,COCoL,
(13)
CH&OCoL3 + CO
=
CH,COCoL4
(14)
CH&HO + Co2LB
(15)
+ CO
CH,COCoL, + HCoL, _
(9)
Co2L8+ H2
=
2HCoL,
(16)
CHBOH+ HCoL,
e
CH,OH,+ + CoL,-
(17)
Hz0 + HCoL,
=
H,O+ + CoL,-
(18)
CH,OH + HI
=
CH,OH,+ + I-
(19)
Hz0 + HI
=
H,O+ + I-
(20)
CH,OH,+ + I-
=
CHJ + Hz0
(21)
By assuming the CO insertion as the rate-determining step, as already discussed in the previous paper, the kinetic eqn. (5) resulted with cr inversely proportional to the equilibrium constant, related to the hydrogenation of the CH,COCoL, complex. Obviously, in our case, this proportionality can be proposed only as a rough and qualitative interpretation of the phenomenon, because metals can form clusters and (Y depends on other parameters, too. However, in the case of ruthenium (Ru/Co = 1) (Y= 0, this fact indicates that the equilibrium (15) is completely shifted to the right. On the contrary, zinc and tungsten show the maximum value of (Y, that is, the maximum deactivating effect, which would be related to the poor hydrogenating power of the coresponding complex formed in the reaction system. When examining the parameters reported in Table 1, it is possible to generally conclude that almost all the metals have a deactivating effect with respect to cobalt alone by the depressing reactions (1,2 and 3). In particular, manganese, known as an effective CO insertion catalyst [ 101, in the presence of cobalt eliminates any kind of activity. This fact can be interpreted as the consequence of the formation of a very stable cluster in which the steric positions of the mononuclear complexes responsible for the insertion activity are blocked. Another interesting observation is that vanadium deactivates the catalyst in the homologation reaction but promotes carbonylation.
60
0.0
0.
15
50
25
loo
Fig. 8. Effects of 8 ruthenium in the Co-Ru catalyst mixture on the kinetic parameters k,, k,, k, and a, obtained by fitting experimental data.
Finally, if the kinetic parameters reported in Table 3 and related to Co/Ru catalysts, at different molar ratios, are plotted as in Fig. 8, it is possible to observe a strong synergic effect in acetaldehyde and methyl acetate formation when small amounts of ruthenium are present. At a higher ruthenium percentage, the global activity decreases while ethanol selectivity strongly increases. This behaviour is in agreement with the observations by Hidai et al. [51 according to whom a maximum of ethanol productivity can be observed for a Ru/Co molar ratio of about 0.3. These authors do not report any maximum in the production of acetaldehyde as, on the contrary, clearly appears in our case. This fact is probably due to the fact lOO-
00
160.
60. TIME
240.
(MIN.)
Fig. 9. Evolution with time of selectivities to acetaldehyde + acetal for different Ru/Co ratios.
51 100
60 I
z =
60c, co
5 .
Ru/Co~1/20
5
0
Ru/C0=1/5
3Y
q
Ru/Co=l/l
40.
.
Ru/Co.l/2O
0
RU/CO.l/5
D
RU/CO.l/l
20 .
160
60 TIME
(MIN)
240
*p I
00 00
I
I
60
I
I
160 TIME
I
1
240
(MINI
Fig. 10. Evolution with time of selectivities to ethanol for different Ru/Co ratios. Fig. 11. Evolution with time of selectivities to methyl acetate for different Ru/Co ratios.
that Hidai et al. made kinetic runs by stopping the reaction after 2.5 h. Under these conditions, it is impossible to reliably compare activity and selectivity as in our case. Another important observation is related to the behaviour of (Y in Fig. 8. For low ratios of Ru/Co, (Y consistently decreases with respect to Co alone, and consequently the acetaldehyde yields increase at the end of the reaction. This positive effect must be added to the synergic one. The trends of selectivities with Ru/Co ratio are reported in Figs. 9, 10, 11. In Fig. 9 a small decrease in acetaldehyde selectivities appears for small amounts of ruthenium in the catalyst, to which a high increase in productivity (see Fig. 8) corresponds. In Fig. 10 it appears that selectivities to ethanol increase on increasing the amount of ruthenium. The selectivities to acetate are doubled for low amounts of ruthenium in the catalyst (R&o = l/5 and l/20), while for Co alone and for the catalyst R&o = 1 they are about equal. The evolution of selectivities with time normally shows an increase for ethanol and a decrease for acetaldehyde in any case, while it is constant for acetate. This fact confirms that acetaldehyde is an intermediate compound in ethanol formation.
Acknowledgements
Thanks are due to the Consiglio Nazionale delle Ricerche, Piano Finalizzato Energetica 2, Minister0 Pubblica Instruzione, Fund 40%, SISAS SpA for financial support.
52
References 1 J. Gauthier-Lafaye and R. Perron, Methanol et Curbonylution, Rhone Poulenc Recherches, Saint-Fons, 1986. 2 M. Roper and H. Loevenich, in W. Kein (ed.) Catalysis in C, Chemistry, Reidel, Dordrecht, 1983. 3 H. Loevenich and M. Roper C, Mol. Chem., 1 (1984) 155. 4 M. E. Fakley and R. A. Head, AppZ. CutuZ., 5 (1983) 3. 5 M. Hidai, M. Orisaku, M. Ue, Y. Koyasu, T. Kodama and Y. Uchide, OrgunometuZZics, 2 (1983) 292. 6 G. Doyle, J. Mol. Cutal., 13 (1981) 237. 7 M. Hidai, M. Orisatu, M. Ue, Y. Uehida, K. Yasufutu and H. Yamazati, C&m. Lett., 1 (1981) 143. 8 K. Kudo and N. Sugita, Nippon Keg&u Ibishi, 3 (1982) 462. 9 E. Santacesaria, D. Gelosa, M. Di Serio and S. Carra, J. Mol. Cutal., 58 (1990). 10 F. Calderazzo, Angew. Chem., Znt. Ed. EngZ., 16 (1977) 299.
58 (1990) 43-52
43
KINETICS OF METHANOL HOMOLOGATION PART II. BEHAVIOUB OF COBALT-PHOSPHINE-IODINE CATALYSTS PLUS OTHER METALS AS COCATALYSTS E. SANTACESARIA*,
M. DI SERIO
Cattedra di Chimica Industriale, Dipartimento Mezzocanrwne 4, 80134 Naples (Italy) D. GELOSA
di Chimica dell Universitd
di Napoli, Via
and S. Cm
Cattedra di Chimica Fisica, Dipartimento di Chimica Fisica Applicata o!.elPolitecnico, Piazza Leonardo da Vinci 32, 20133 Milan (Italy) (Received January 2,1989;
accepted April 3,1989)
Summary By employing the kinetic model developed in a previous work, the kinetic behaviour of cobalt/phosphine/iodine catalysts has been compared with that of several metals mixed with cobalt, by taking the molar ratio between cobalt and the added metal equal to 1. It has been concluded that other metals generally have a deactivating effect on the homologation reaction. In particular, manganese completely inhibited activities. As expected, ruthenium mixed with cobalt shows a high selectivity to ethanol. The catalytic behaviour of Ru/Co catalysts is the most interesting. Therefore, we have extended our investigations to the kinetic behaviour of Ru/Co catalysts at different molar ratios of the two metals from 0 to 1. A strong synergic effect has been observed for low ruthenium amounts, while selectivities to ethanol strongly increase only for a Ru content of at least 20% with respect to cobalt. Reflections on these findings conclude the paper.
Introduction The homologation of methanol is a very interesting reaction for producing acetaldehyde or ethanol from synthesis gas. For this reason, the process has been carefully studied in the last few years; many papers, reviews, books and patents have recently been published. The reaction occurs in the homogeneous phase, and the most frequently employed catalysts are cobalt-phosphine-iodine and cobalt-ruthenium-phosphine-iodine for the production of acetaldehyde and ethanol 11-51, respectively. Some papers have also been published devoted to the influence of metals other than ruthenium as cocatalysts l&6-83, but in all cases experimental data have been interpreted by comparing the compositions of the liquid mixtures *Author to whom correspondence 0304-5102/90/$3.50
should be addressed. @ Elsevier Sequoia/Printed
in The Netherlands
44
obtained at the end of the reaction, that is, by comparing activity and selectivity data at a 6xed time without any kinetic analysis. Very recently, we studied the kinetics of the reactions occurring in the homologation of methanol 191. Normally the reaction pattern is the following: CHBOH+ CO + Hz
w
CH&HO + HZ0
(1)
CH&HO + Hz0 + Hz __* CH3CH20H CH&HO + 2CHBOH w 2CHSOH + CO
w
CH&H(OCH&
(2) + Hz0
CH&OOCH3 + Hz0
(3) (4)
The relevant kinetic equations are:
(5) r2 =
k2c2p9
(6) (7)
r4 =
k4csa
(8)
where the subscripts indicate: 1 = methanol, 2 = acetaldehyde, 3 = ethanol, 4 = acetal, 5 = acetate, 6 = water, 7 = dioxan, 8 = carbon monoxide, 9 = hydrogen. As explained in our previous paper 191, for determining kinetic parameters for this type of reaction, it is necessary to consider the evolution with time of the reaction composition affected by both reaction rates and vapour-liquid partition equilibria. Details of the mathematical model for this are reported in the above-mentioned paper 191. In the present paper, the kinetic analysis previously performed on the cobalt/phosphine/iodine catalytic system has been extended to mixtures of cobalt with many other metals, by taking in all cases a molar ratio of 1 between the two metals. In particular, the behaviour of ruthenium as cocatalyst has been analyzed in detail, since this metal shows a very interesting kinetic behaviour. For this purpose, kinetic runs were performed and interpreted for different Ru/Co ratios. In all the above cases, kinetic parameters were determined by fitting experimental runs.
Experimental Methods, techniques and reagents All kinetic runs were performed in a magnetically stirred 11 autoclave made from stainless steel, which was equipped with an injection gas burette and a syngas storage. A pressure regulator allowed constant pressure to be maintained throughout the reaction. A typical kinetic run was performed by introducing in the autoclave 300 cm3 of methanol, 70 cm3 of dioxan and the
45
catalyst. The autoclave was closed, the liquid was flushed with nitrogen and then with synthesis gas for the time necessary to remove oxygen. The closed autoclave was then heated at the reaction temperature (normally 185 “C) while the pressure was successively adjusted by injecting synthesis gas in the autoclave, using a gas burette. The gas burette allowed direct evaluation of both the amount of synthesis gas initially injected and the consumption of synthesis gas with time. The pressure was kept constant, normally at 190 atm. The synthesis gas (CO/H2 with a ratio normally equal to 1) was fed when necessary from a bomb. Liquid was withdrawn from the autoclave at different reaction times, and conveyed to a frozen test tube, kept at -20 “C, equipped with a refluxing cooler. Analysis of the collected liquid samples was made by gas chromatography. The employed column was 2 m long of Chromosorb 102. Helium was employed as carrier gas and HWD as detector. The analysis of the vapour phase was made only occasionally by conveying vapours in a sampling valve kept at the reaction temperature and injecting into another gas chromatograph. CO, Hz and CH4 were analyzed with a 1 m long molecular sieve column using argon as carrier gas. Reagents and standards for chromatography were all from Carlo Erba Co. at the highest purity available. Synthesis gas was furnished by SIAD SpA as a mixture of pure hydrogen and carbon monoxide. Cobalt acetate was employed (CO(AC)~*~H~O)as reference catalyst, together with triphenylphosphine and methyl iodide. Cocatalysts were normally added with a molar ratio equal to 1, except for ruthenium. In Tables 1 and 2 are summarized the catalyst mixtures tested.
TABLE 1 List of cocatalysts used; in all cases 6.7 mm01 P(Ph), and 4.78 mm01 CH,I were added Number of runs
Catalyst
Cocatalyst (mm011
(mmol) Co(CH,C001,.4H,O Co(CH,C001,.4H,O Co(CH,C00),.4H,O Co(CH,COO),.4H,O Co(CHsCOOl,.4H,O Co( CHaCOO ),.4H,O Co(CH&00),.4H,O Co(CH,COO)a.4H,O Co(CHaC00),.4H,O
(2) (2) (2) (2) (2) (2) (2) (21 (2)
Fe(CO), Cu(CH&OO), Zn(CH,COO), WOCl* Mo(THFl,Cl, SnCl, Cr(CH,COO), PdCl, 0
10 11 12 13
Co(CHJ!0012.4H,0 Co(CH,COO),.4H,O Co(CH,COO)a~4H,O Co(CH,COO),.4H,O
(2) (2) (2) (2)
II VO ( CH,-G-CH=CMn(CH&OOl, Ni(CH,COO)a.4H,O RuCl,P(Ph),
(2) (2) (2) (2) (2) (2) (2) (2) 0
I
*I-W,
(2) (2) (2) (2)
46 TABLE
2
Kinetic parameters Number of run 1 2 3 4 5 6 7 8 9 10 11 12
obtained by fitting experimental
runs
Catalyst
K, x 10m5
K, x 1O-4
K3 x 1O-3
K4 x lo-’
K,
axlO6
co
2.7 1.8 2.5 0.8 1.0 2.7 1.2 2.7 1.6 2.0 0. 2.7
0.20 0.07 0.15 0.03 0.02 0.10 0.20 0.20 0.02 0.10 -
2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 -
12 12 12 12 12 12 12 12 12 12 -
4.8 38. 8.8 180. 180. 30. 35. 35. 9.8 4.8 -
0.20
2.5
1.4 1.2 1.4 0.6 0.7 1.4 1.0 1.4 1.4 2.4 0. 1.4
12
18.
Co-Fe Co-Cu Co-Zn co-w
CO-MO CO-h Co-0 Co-Pd co-v Co-Mll Co-Ni
Results
Kinetic runs performed with the catalysts described in detail in Table 1, under the operative conditions also reported in the same table, have been interpreted with the mathematical model reported elsewhere [91. The kinetic parameters obtained are reported in Table 2. Figure 1 illustrates the fit obtained using the parameters of Table 2 for the reference run (11, in the presence of cobalt alone. Figures 2 and 3 show, as examples, the fits obtained in runs 2 and 3, respectively, corresponding to Co-Fe and Co-Cu. o Methanol
(moles.
2)
o Acetal
40 36
OAcetaldehyde
o Methanol
A Acetate
40
. Ethanol
36
0Acetatdehyde
. Ethanol
24
24 z 6
20
I =
o Acetat A Acetate
3.2
3.2
z 6
(moles’2)
1.6
2.0 16
12 08 04 0.0
00
40
60 TIME
120 (MIN.)
160
00
80
160. TIME
240
(MIN.)
1. Kinetic run performed at 185 “C, 190 atm, with catalyst 2 mm01 Co(Ac),.4H,O, 6.7 mmol P(Ph),, 4.78 mm01 CH,I. Initial reaction mixture: 7.414 mol methanol and 0.821 mol dioxan. Curve fits were obtained by calculation using the parameters reported in Table 2 (run 1). Fig.
Fig. 2. Kinetic run performed in the same conditions described in the legend to Fig. 1, but in the presence of 2 mmol Fe(CO), as cocatalyst. Kinetic parameters employed for fitting experimental data are those reported in Table 2 (run 2).
47 o Methanol 4.0 3.6 A
z I
(moles’
2)
q
A&al
. water
n Acetate
0 Acetaldehyde
. Ethanol
20 16
00
0.0
80
160 TIME
(MIN
240 1
Fig. 3. Kinetic run performed in the presence of 2mmol Cu(Ac), as cocatalyst. Other experimental conditions are the same described in the legend to Fig. 1. Kinetic parameters employed for fitting experimental data are those reported in Table 2 (run 3).
In Table 3, kinetic parameters related to the Co/Ru system, at different molar ratios are reported. Figures 4,5 and 6 show the fits obtained, using the kinetic parameters of Table 3, for interpreting the experimental kinetic runs performed at different Co/Ru ratios. In Fig. 7 the kinetic behaviour of ruthenium alone as catalyst is reported.
Discussion
and conclusions
As previously mentioned, many data reported in literature regarding the behaviour of two mixed metals in catalyzing homologation reaction are based on the observation of the liquid compositions obtained after a fixed reaction time. This can lead to erroneous conclusions about the true activity and selectivity of the examined catalyst, above all in the presence of deactivating effects in the kinetics. If we observe the kinetic parameters reported in Tables 1 and 3, we note that (Y, the deactivating parameter, changes by many orders of magnitude according to the metal employed as TABLE 3 Kinetic parameters obtained for different ruthenium amounts in the catalyst Number of run
Catalyst
K, x 1O-5
K, x 1O-4
KS x lo3
K,xlO-=
K,
(rx1O6
1 13 14 15 16
co Ru/Co = 1 Ru/Co = l/20 Ruf Co = l/5 Ru
2.7 2.2 4.0 4.0 0.12
0.2 2.9 0.2 0.4 9.0
2.5 2.5 2.5 2.5 2.5
1.4 1.9 5.4 5.4 0.4
12 12 12 12 12
4.8 0. 2.0 2.0 0.
o Methanol 40 36 A
(moles
2)
0 Methanol
o Acetal
. water
A Acetate
0 Acetaldehyde
. Ethanol
(moles.
2)
LI Acetal
4.0
. Water
b Acetate
3.6
OAcetaldehyde
. Ethanol
3.2 20 24 B 6
20
*
1.6 1.2
0.0 0.0
80
240
160 TIME
TIME
WIN.)
(MIN.)
Fig. 4. Kinetic run performed in the presence of 2mmol RuCl,(Ph)S as cocatalyst. Other experimental conditions are the same described in the legend to Fig. 1. Kinetic parameters employed for fitting experimental data are those reported in Table 3 (run 13). Fig. 5. Kinetic run performed as described in the legend of Fig. 1, but in the presence of 0.1 mm01 RuCl,(Ph)s as cocatalyst. Data are fitted by employing the parameters reported in Table 3 (run 14).
o Methanol 4or 36
(mOles.2)
q
o Methanol
Acetal
. water
D Acetate
0 Acetaldehyde
. Ethanol
1: [
::y
(moles.
o Acetal
2)
ldeh y de
:
:::::I
32 20 0.6 t: 2 0.4 -
L
12
ijg_+&, 00
160
60. TIME
(MIN)
240
::h 00
40.
60.
TIME
(MIN.)
Fig. 6. Kinetic run performed as described in the legend to Fig. 1, but in the presence of 0.4 mm01 RuCl,(Ph), as cocatalyst. Curve fits were obtained by employing kinetic parameters reported in Table 3 (run 15). Fig. 7. Behaviour of pure RuCl,(PhjB as catalyst. III this case CO(AC)~.~H~Owas replaced by 2 mmoi of the mentioned ruthenium complex. Other conditions are as in the legend to Fig. 1. Parameters employed for fitting experimental data are reported in Table 3 (Run 16).
49
cocatalyst. The parameter (Yseems to be related to the hydrogenating power of the complex HyMeL which is useful in the elementary step of acetaldehyde formation. Indeed, in a previous work, we suggested oxidative addition of CHJ to be the more reliable mechanism, occurring through the following steps: HCoL,
e
HCoL, + CO
HCoL3 + CH31
=
CH&oHLJ
(10)
CH&oHLJ
e
CH&oL, + HI
(11)
CH$oL,
=
CH,CoL,
(12)
CH&oL,
e
CH,COCoL,
(13)
CH&OCoL3 + CO
=
CH,COCoL4
(14)
CH&HO + Co2LB
(15)
+ CO
CH,COCoL, + HCoL, _
(9)
Co2L8+ H2
=
2HCoL,
(16)
CHBOH+ HCoL,
e
CH,OH,+ + CoL,-
(17)
Hz0 + HCoL,
=
H,O+ + CoL,-
(18)
CH,OH + HI
=
CH,OH,+ + I-
(19)
Hz0 + HI
=
H,O+ + I-
(20)
CH,OH,+ + I-
=
CHJ + Hz0
(21)
By assuming the CO insertion as the rate-determining step, as already discussed in the previous paper, the kinetic eqn. (5) resulted with cr inversely proportional to the equilibrium constant, related to the hydrogenation of the CH,COCoL, complex. Obviously, in our case, this proportionality can be proposed only as a rough and qualitative interpretation of the phenomenon, because metals can form clusters and (Y depends on other parameters, too. However, in the case of ruthenium (Ru/Co = 1) (Y= 0, this fact indicates that the equilibrium (15) is completely shifted to the right. On the contrary, zinc and tungsten show the maximum value of (Y, that is, the maximum deactivating effect, which would be related to the poor hydrogenating power of the coresponding complex formed in the reaction system. When examining the parameters reported in Table 1, it is possible to generally conclude that almost all the metals have a deactivating effect with respect to cobalt alone by the depressing reactions (1,2 and 3). In particular, manganese, known as an effective CO insertion catalyst [ 101, in the presence of cobalt eliminates any kind of activity. This fact can be interpreted as the consequence of the formation of a very stable cluster in which the steric positions of the mononuclear complexes responsible for the insertion activity are blocked. Another interesting observation is that vanadium deactivates the catalyst in the homologation reaction but promotes carbonylation.
60
0.0
0.
15
50
25
loo
Fig. 8. Effects of 8 ruthenium in the Co-Ru catalyst mixture on the kinetic parameters k,, k,, k, and a, obtained by fitting experimental data.
Finally, if the kinetic parameters reported in Table 3 and related to Co/Ru catalysts, at different molar ratios, are plotted as in Fig. 8, it is possible to observe a strong synergic effect in acetaldehyde and methyl acetate formation when small amounts of ruthenium are present. At a higher ruthenium percentage, the global activity decreases while ethanol selectivity strongly increases. This behaviour is in agreement with the observations by Hidai et al. [51 according to whom a maximum of ethanol productivity can be observed for a Ru/Co molar ratio of about 0.3. These authors do not report any maximum in the production of acetaldehyde as, on the contrary, clearly appears in our case. This fact is probably due to the fact lOO-
00
160.
60. TIME
240.
(MIN.)
Fig. 9. Evolution with time of selectivities to acetaldehyde + acetal for different Ru/Co ratios.
51 100
60 I
z =
60c, co
5 .
Ru/Co~1/20
5
0
Ru/C0=1/5
3Y
q
Ru/Co=l/l
40.
.
Ru/Co.l/2O
0
RU/CO.l/5
D
RU/CO.l/l
20 .
160
60 TIME
(MIN)
240
*p I
00 00
I
I
60
I
I
160 TIME
I
1
240
(MINI
Fig. 10. Evolution with time of selectivities to ethanol for different Ru/Co ratios. Fig. 11. Evolution with time of selectivities to methyl acetate for different Ru/Co ratios.
that Hidai et al. made kinetic runs by stopping the reaction after 2.5 h. Under these conditions, it is impossible to reliably compare activity and selectivity as in our case. Another important observation is related to the behaviour of (Y in Fig. 8. For low ratios of Ru/Co, (Y consistently decreases with respect to Co alone, and consequently the acetaldehyde yields increase at the end of the reaction. This positive effect must be added to the synergic one. The trends of selectivities with Ru/Co ratio are reported in Figs. 9, 10, 11. In Fig. 9 a small decrease in acetaldehyde selectivities appears for small amounts of ruthenium in the catalyst, to which a high increase in productivity (see Fig. 8) corresponds. In Fig. 10 it appears that selectivities to ethanol increase on increasing the amount of ruthenium. The selectivities to acetate are doubled for low amounts of ruthenium in the catalyst (R&o = l/5 and l/20), while for Co alone and for the catalyst R&o = 1 they are about equal. The evolution of selectivities with time normally shows an increase for ethanol and a decrease for acetaldehyde in any case, while it is constant for acetate. This fact confirms that acetaldehyde is an intermediate compound in ethanol formation.
Acknowledgements
Thanks are due to the Consiglio Nazionale delle Ricerche, Piano Finalizzato Energetica 2, Minister0 Pubblica Instruzione, Fund 40%, SISAS SpA for financial support.
52
References 1 J. Gauthier-Lafaye and R. Perron, Methanol et Curbonylution, Rhone Poulenc Recherches, Saint-Fons, 1986. 2 M. Roper and H. Loevenich, in W. Kein (ed.) Catalysis in C, Chemistry, Reidel, Dordrecht, 1983. 3 H. Loevenich and M. Roper C, Mol. Chem., 1 (1984) 155. 4 M. E. Fakley and R. A. Head, AppZ. CutuZ., 5 (1983) 3. 5 M. Hidai, M. Orisaku, M. Ue, Y. Koyasu, T. Kodama and Y. Uchide, OrgunometuZZics, 2 (1983) 292. 6 G. Doyle, J. Mol. Cutal., 13 (1981) 237. 7 M. Hidai, M. Orisatu, M. Ue, Y. Uehida, K. Yasufutu and H. Yamazati, C&m. Lett., 1 (1981) 143. 8 K. Kudo and N. Sugita, Nippon Keg&u Ibishi, 3 (1982) 462. 9 E. Santacesaria, D. Gelosa, M. Di Serio and S. Carra, J. Mol. Cutal., 58 (1990). 10 F. Calderazzo, Angew. Chem., Znt. Ed. EngZ., 16 (1977) 299.