New Hydroformylation Technology with Cobalt Carbonyls - Advances

2 New Hydroformylation Technology with

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 2, 2016 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0132.ch002

Cobalt Carbonyls R. KUMMER, H. J. NIENBURG, H. HOHENSCHUTZ, and M. STROHMEYER BASF, Ludwigshafen, Germany In the classical oxo process the catalyst cobalt carbonyl is formed i n situ by introducing divalent cobalt into the reactor. High temperature is required for this catalyst formation that gives a mixture of aldehydes and alcohols containing only 60-70% of linear product. A new BASF process using cobalt carbonyl hydride shows improved selectivity and efficient catalyst recovery. The catalyst is prepared by passing an aqueous solution of cobalt salt over a promoter and extracting the catalyst from the water phase with olefin. The olefin is then hydroformylated at low temperatures (90°-120°C) to yield 72-80% of linear aldehydes. The catalyst is recovered by mixing the product with air in an aqueous solution of cobalt formate.

T h e hydroformylation reaction or oxo synthesis has been used on an industrial scale for 30 years, and during this time it has developed into one of the most important homogeneously-catalyzed technical proc esses ( 1 ). A variety of technical processes have been developed to pre pare the real catalyst cobalt tetracarbonyl hydride from its inactive pre cursors, e.g., a cobalt salt or metallic cobalt, to separate the dissolved cobalt carbonyl catalyst from the reaction products ( decobaltation ) and to recycle it to the oxo reactor. The efficiency of each step is of great economical importance to the total process. Therefore many patents and papers have been published concerning the problem of making the cata lyst cycle as simple as possible. Another important problem i n the oxo synthesis is the formation of undesired branched isomers. Many efforts have been made to keep the yield of these by-products at a minimum. A l l technical processes now i n operation offer at best a satisfactory solution to only one of these two problems. Processes with a simple and 19 Forster and Roth; Homogeneous Catalysis—II Advances in Chemistry; American Chemical Society: Washington, DC, 1974.


20

HOMOGENEOUS CATALYSIS

II

efficient catalyst cycle, especially those which recycle an aqueous solution of a cobalt salt after decobaltation by oxidation with air, require relatively high reaction temperatures to form the catalyst in situ from the cobalt salt. These high reaction temperatures increase the yield of the less desir able branched reaction products, and in the case of long chain olefins an inseparable mixture of aldehydes and alcohols is obtained. Other techni cal processes yielding predominantly straight chain products use a cobalt compound soluble in an organic solvent or a cobalt carbonyl catalyst modified by phosphines. The number of steps required and the loss of modifier through oxidation add to the cost of the process. The phosphine process which produces primarily alcohols is therefore less suited for technical purposes if aldehydes are desired. OLEFIN AQUEOUS SOLUTION OF HCo(CO)

OFF GAS

4

AIR

OLEFIN Co (CO)

^

2

8

DEC0BALTED ALDEHYDE

fcoo C0/H

WATER

2

AQUEOUS FORMATION

OF HCo(C0U

SOLUTION OF Co ( I I ) - S A L T

EXTRACTION

Figure 1.

HYDROFOLMYLATION

DECOBALTATION

Flow sheet of new oxo process

In recent years B A S F has developed an effective method which uses a simple and very economical catalyst cycle to produce predominantly straight chain aldehydes. A n important feature of the new process ( F i g ure 1 ) is a small separate reactor to prepare the cobalt carbonyl catalyst from an aqueous solution of cobalt salt outside the hydroformylation reactor. Extracting the catalyst with the olefin from the aqueous solution gives a homogeneous solution of cobalt carbonyls in the hydrocarbon for use in the oxo reaction. The oxo reaction itself is carried out in the absence of water or any additional solvent permitting low reaction tem peratures and thus improving the yield of straight chain aldehydes. Finally the catalyst is removed quantitatively by mixing air with the reaction product in the presence of an aqueous solution of cobalt formate. Two phases separate with the cobalt catalyst remaining entirely in the aqueous phase. The aqueous phase containing the cobalt salt is recycled to the carbonyl regeneration reactor.

Forster and Roth; Homogeneous Catalysis—II Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

KUMMER ET AL.

New Hydroformylation Technology

21

The Four Main Steps of the New Process


Step 1: Formation of the Active Cobalt Carbonyl Catalyst. Many efforts have been made (2, 3, 4) to prepare carbonyl catalyst by treating metallic cobalt or cobalt compounds at high temperatures ( 1 5 0 ° - 2 0 0 ° C ) and pressures with carbon monoxide and hydrogen (Reactions 1 and 2). 2 Co

m e t

+ 8 C O + H *=> C o ( C O ) + H 2 H C o ( C O ) 2

2

8

2

(1)

4

H 0 2

2 Co

2 +

+ 4 X - + 8 C O + 3 H 6 H 0 + + 4 X ~ + 2 C o ( C O ) r 2

3

(2)

Even at 180 °C, however, Reaction 2 proceeds very slowly and de composition to metallic cobalt (Reaction 1) is significant. The use of a palladium catalyst to promote Reaction 2 has recently (5) been sug gested, but it is economically less suitable. A number of simple and inexpensive materials catalytically promote the cobalt-carbonylation (Reaction 2) in aqueous solution. These in clude ion-exchange resins, zeolites, or special types of activated carbon. Formation of the active catalyst in a separate reactor is thus economically feasible. The mechanism of this catalysis has not yet been elucidated and seems to differ for each promoter mentioned. After an induction period during which the cobalt fed to the reactor is partially retained by the promoter, fully active materials have absorbed cobalt carbonyl anion C o ( C O ) ~ (ion exchange resins), C o cation (zeolites), or a mixture of C o , cobalt carbonyl hydride, and cluster-type cobalt carbonyls ( activated carbon). This can be shown by analytical studies (extraction, titration, and IR studies ) of active material withdrawn from the reactor. Figure 2 shows the influence of temperature on the reaction time of a 70% conversion of C o in Reaction 2a. 2+

4

2+

2+

H 0 2 Co(OOCCH ) + 8 C O + 3 H < = ± 2 H Co(CO) + 4 C H C O O H 2

3

2

2

4

(2a)

3

A 70% conversion of C o to H C o ( C O ) , which means a 1:2 ratio of Co to Co ( C O ) " or formation of the compound C o [ C o ( C O ) ] 2 is sufficient to carry out the next step of the process. Step 2: Extraction of the Catalyst from the Aqueous Solution. It is not feasible technically to charge the aqueous solution of cobalt car bonyl hydride directly into the hydroformylation reactor because two phases may form, especially with the long chain olefins. The most direct and most efficient way to eliminate water while permitting full use of the carbonyl catalyst is to extract it from the water phase with the olefin intended for hydroformylation. The extraction is carried out between 2+

2+

4

4


4

22

HOMOGENEOUS

°C £200

ι

ι

ι

II

I

PRECIPITATION OF METALLIC COBALT

*180

CATALYSIS

-

LU Ω

Σ


^ 160

I

I

30

I

I

60 REACTOR

90 120 SPACE TIME MIN.

Figure 2. Influence of temperature on reactor space time for 70% conversion of an aqueous solution of cobalt acetate (1% Co ); activated carbon as promoter, 280 atm, CO:H = 1:1 2+

2

2 0 ° - 1 0 0 ° C and a total pressure of 1-300 atm (the pressure of the hydro formylation reaction), depending on the reactivity of the olefin. After the cobalt carbonyl hydride has passed from the aqueous phase into the organic phase (Reaction 3 ) , stoichiometric hydroformylation (6, 7, 8) takes place (Reactions 4 - 8 ) . H 0 + + C o ( C O ) - in H 0 H C o ( C O ) in olefin 3

4

2

R

HCo(CO)

4

+

RCH=CH

4

H

\

/

C

CoH(CO)

2

/

C

3

+ CO

(4)

\

H H

(3)

H

H

\

/ c; * CoH(CO), ^ Z Î

RCH CH Co(CO) 2

2

3

C H

/

\

H


(5)

2.

KUMMER ET A L .


RCH CH Co(CO) 2

2

3

+ C O τ± R C H C H C O C o ( C O )

RCH CH COCo(CO) 2

2

RCH CH COCo(CO)


2

2

4

2

3

2

23

+ C O R C H C H C O C o ( C O ) 2

(6)

3

2

+ H C o ( C O ) τ± R C H C H C H O + C o ( C O ) 4

2

2

(7)

4

2

8

(8)

After extraction the catalyst remains i n the olefin phase as shown by IR analysis either as an acyl complex, as dicobalt octacarbonyl, or (at low C O pressure) as tetracobalt dodecacarbonyl. The extraction may be carried out in a countercurrent or concurrent extraction column. If there is sufficient mixing of the two phases, a veryshort contact time even for long chain olefins is adequate to ensure com plete transfer of the catalyst from the aqueous phase into the olefin. After extraction the two phases are separated and the olefin phase containing the active catalyst is fed to the hydroformylation reactor. LU

Τ

Ο c/)

n-octene-1 non-terminal octene

3 r

80

100

120

160 °C

140

Figure 3. Isomer distribution in the hydroformylation of octene. total pressure 280 atm, curve 1,2, CO:H = 1:1, curve 3,4, CO:H = 1:3 2

2

Step 3 : Hydroformylation with Pre-Formed Homogeneous Catalyst. The goal is to improve the ratio of straight chain to branched chain products (n:iso ratio) and to keep the hydrogénation of olefin to paraffin and aldehyde to alcohol as low as possible. A l l hydroformylation experiments were performed i n a continuously operated reactor. The concentration of the catalyst was varied from 0.1 to 0.4 wt % to keep olefin conversion at the same level (80—90% ) for a l l reaction temperatures. The total pressure for a l l experiments was 280 atm, and n-octene was used as typical straight chain olefin of medium chain length. Forster and Roth; Homogeneous Catalysis—II Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

24


Improvement in the isomer distribution can be achieved by lowering the hydroformylation temperature from the range 150°-170 °C, now used industrially, to 100°C. Figure 3 shows an almost constant 2 % increase in yield of straight chain products for each 10° decrease i n reaction temperature. This increase becomes even more pronounced ( 4 - 5 % ) at higher hydrogen partial pressure ( C O : H = 1:3). A n increase i n hydrogen partial pressure increases reaction velocity (9, 10); thus it could be desirable to use a higher ratio of H : C O than the usual 1:1. Figure 3 also shows the isomer distribution resulting from the hydro formylation of a mixture of straight chain octenes with predominantly internal double bond ( 2 % 1-octene, 37% 2-octene, 36% 3-octene, and 23% 4-octene). In this case the n:iso ratio did not change for the range of temperatures examined. The conclusion is that increased rate of olefin isomerization to 1-octene resulting from increased temperature or higher hydrogen partial pressure is compensated for by a decrease i n the n:iso ratio. Therefore no advantage can be seen in hydroformylating internal olefins using a low-temperature process. Another important economic problem in industrial processes con cerns losses through side reactions, especially the hydrogénation of start ing material to paraffin and the conversion of aldehydes to alcohols. Figure 4 shows the effect of temperature and partial pressure varia tions on the product yield from the hydrogénation of octene. Equimolar 2


II

2

% YIELD 5

/ /

^Nonanol

/

3/Octane Nonanol

1 . Octane

80

100

120

140

160 °C

Figure 4. Influence of temperature on hydrogénation of olefin and aldehyde; total pressure 280 atm, curve 1,2, CO:H = 1:1, curve 3,4, CO:H =1:3 2

2


2.

K U M M E R ET A L .


25

amounts of C O and H give less than 1% direct hydrogénation below 130°C, but even lower temperatures ( 8 0 ° - 1 0 0 ° C ) are required to reduce the alcohol formed to 2 % . The results compare favorably with the more than 5% of paraffin and 10% of alcohol produced in older industrial processes using reaction temperatures above 150°C. Though the decrease in the rate of hydrogénation is substantially greater with the 3:1 H> to C O mixture than that with the 1:1 mixture, the curves in Figure 4 show that more than 2% alcohol and 1% paraffin are obtained at reaction temperatures above 85 °C. Another side reaction of hydroformylation is formate ester formation (11). The 4% yield of formates d i d not change in the temperature range examined or with lower C O partial pressure. Reaction products obtained by low-temperature hydroformylation ( 1 0 0 ° - 1 2 0 ° C ) of linear α-olefins with an equimolar amount of C O and Ho at 280 atm were ( % ) : aldehyde, 94 ± 1 (n:iso ratio 2, 56 to 3, 16); formate, 4 ± 0.5; alcohol, 2 =b 0.5. Furthermore, 1% of the olefin feed is hydrogenated to paraffin and 2 - 3 % is converted to high boiling products (aldols, ketones, and acetals). Step 4: Decobaltation of the Reaction Product. The product of the hydroformylation reactor containing the catalyst as a mixture of cobalt carbonyl hydride and dicobalt octacarbonyl is fed to the decobalting sec tion. Mixing the product at 120 °C and 10 atm with a dilute formic a c i d / cobalt formate solution in the presence of air decomposes the catalyst (Reaction 9) (12).


2

Co (CO) + 0 2

8

2

+ 4 H 0 + + 4 H C O O - -> 3

2 Co + + 4 H C O O - + 6 H 0 + 8 C O 2

2

(9)

The reaction conditions ensure that all cobalt catalyst remains in the aqueous phase and that only Co -compounds that are soluble in water are formed. The aqueous phase, after dilution with the water from the extraction section (Figure 1), is recycled partially to the decobalting tube and partially to the catalyst formation section where the active catalyst is regenerated. 2+

Summary The five important advantages of the new process are then: 1. The process has an absolutely closed catalyst cycle; no losses occur during the cycle. The catalyst always remains in liquid phase eliminating the handling of solid materials. 2. Only air is needed as an auxiliary chemical. Waste streams which might cause a pollution problem or effect the commercial feasibility are excluded.



26


II

3. N o water or any organic solvent is fed to the hydroformylation reactor. 4. The catalyst is always fed as the true active cobalt carbonyl catalyst to the reactor, and its concentration in the reactor may be varied within a wide range. 5. Carrying out the hydroformylation reactions at low temperatures significantly improves the yield of straight chain aldehydes and reduces losses by olefin hydrogénation. Literature Cited 1. Falbe, J., "Carbon Monoxide in Organic Synthesis," Springer-Verlag, Berlin, 1970. 2. Nienburg, H . J., Hauber, H . , Hagen, W., German Patent 843,848 (7-141952, appl. 7-1-1950). 3. Nienburg, H . J., Hauber, H . , Hagen, W., German Patent 849,103 (9-111952, appl. 8-1-1950). 4. Mertzweiler, J. K., Smith, W. M . , U.S. Patent 2,725,401 (11-29-1955, appl. 11-19-1948). 5. Usami, S., Nishimura, K., Koyama, T., Fukushi, S., Bull. Chem. Soc. Jap. (1969) 42, 2966. 6. Heck, R. F., Breslow, D. S., J. Amer. Chem. Soc. (1961) 83, 4023. 7. Karapinka, G. L., Orchin, M . , J. Org. Chem. (1961) 26, 4187. 8. Rupilius, W., Orchin, M . , J. Org. Chem. (1972) 37, 936. 9. Martin, A. R., Chem. Ind. (London) (1954) 1536. 10. Natta, G., Ercoli, R., Castellano, S., Chim. Ind. Milan (1955) 37, 6. 11. Marko, L . , Szabo, P., Chemische Technik (1961) 13, 482. 12. Moell, H . , Eckert, E., Kerber, H . , Appl, M . , Hohenschutz, H . , Walz, H . (BASF), German Patent 1,272,911 (7-18-68, appl. 4-5-66). RECEIVED July 20, 1973.


New Hydroformylation Technology with Cobalt Carbonyls - Advances

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