Acetaldehyde Production by Reductive Carbonylation of Methanol

Chapter 9

Acetaldehyde Production by Reductive

Carbonylation of Methanol, Methyl Ketals, and Methyl Esters Richard W. Wegman, David C. Busby, and John B. Letts Downloaded by TUFTS UNIV on October 17, 2014 | http://pubs.acs.org Publication Date: December 16, 1987 | doi: 10.1021/bk-1987-0328.ch009

Union Carbide Corporation, P.O. Box 8361, South Charleston, WV 25303 Acetaldehyde is obtained from the reaction of synthesis gas with methanol, methyl ketals or methyl esters. The reactions are carried out with an iodide-promoted Co

catalyst at 180-200 °C and 2000-5000 psig. In compar-

ing the various feedstocks, the best overall process to make acetaldehyde involves the reductive carbonylation of methyl esters. In this case, acetaldehyde selec-

tivities are > 95% at acceptable rates and conversion. The reductive carbonylation (Equation 1) and homologation (Equation 2) of methanol are reactions of considerable interest to the

chemical industry (_]_) .

These reactions provide a route to

CH OH + CO + H2 CH OH + CO + 2H2

>

CH C(0)H + H20 > CH CH20H + H20

acetaldehyde and ethanol from non-petroleum-derived synthesis gas.

Acetaldehyde can be used as a building block for numerous

chemicals, for instance (i) condensation to higher aldehydes and alcohols, (ii) esters via the Tischenko reaction, specifically formation of ethyl acetate which can be readily cracked to ethylene and acetic acid, and (iii) vinyl ethers from various acetal derivatives. The main thought with ethanol is that it would provide a synthesis gas based route to ethylene. The homologation reaction was first reported nearly 40 years

ago (2) .

The catalyst precursor was Co (C0)~.

Subsequent work-

ers utilized cobalt catalysts but also employed iodide promoters

(_3,_4), a Ru co-catalyst (5) , and trivalent phosphines (_5) to

increase the yield.

The reaction is carried out at 180-200 °C

and 4000-8000 psig. In the better cases, the ethanol rate and selectivity are 1-6 M/hr and 50-80 %• Unsatisfactory conversion,

selectivity, and the required high operating pressure have prevented commercialization of the current homologation technology. Additionally, fermentation routes to ethanol have now 0097-6156/87/0328-0125$06.00/0

© 1987 American Chemical Society In Industrial Chemicals via C1 Processes; Fahey, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

(1) (2)

1 26

INDUSTRIAL CHEMICALS VIA C , PROCESSES

become economically competitive with a synthesis gas-based pro-

cess (2>__).

Less attention has been given to the reductive carbonylation reaction in the literature. The reaction is catalyzed, at least to some extent, by most Group VIII metals used in conjunction

with an iodide promoter (_} ) .

The highest rates and selectivities

are obtained with cobalt-based catalysts. In addition to Co-I, promoters of the form ER (E = N, P, As, Sb, Bi; R = organic moiety) are frequently used. Several studies have been published that describe the effect of catalyst concentration, solvent, temperature, and pressure on the C0-I-ER3 catalyzed reaction (6,1013) . In general, reasonable rates are obtained when the reaction

is carried out at 160-180 °C and 3000-5000 psig. A simplified

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version of the generally accepted mechanism leading to the forma-

tion of acetaldehyde is shown in Equations 3-5 (J_4) .

CH OH + CH I

+

HI "cat"

> +

CH I

CO

CH C(0)-cat-I + H2

+ >

>

H20 CH C(0)-cat-I

CH C(0)H + HI + "cat"

"Cat" represents the catalyst and is thought to be a cobalt compound containing iodide, CO, and, if applicable, ER ligands. The homologation reaction proceeds via a similar mechanism except acetaldehyde is further reduced in situ to ethanol.

We have studied the Co-I-PPh catalyzed reductive carbonylation of methanol, dimethyl ketals, dimethyl carbonate and methyl

esters (J_0 »_1_5,_1_6) .

Our goal was to achieve high acetaldehyde

selectivity while maintaining a reasonable rate of product formation. The effect of reaction variables and the advantages and disadvantages of each feedstock are discussed. Experimental

All chemicals were reagent grade and used without further purification. The batch experiments were carried out in a 300 ml Hastelloy C autoclave. In a typical experiment Co(OAc) 4H 0 (8.0 mmol), I (14.0 mmol) and PPh (30.8 mmol) are charged under N' to a clean reactor containing I5O ml CH OH. The reactor is sealed, purged with synthesis gas and pressured to 2000 psig with synthesis gas. Agitation (750 rpm) is begun and the reactor heated to the desired temperature in 40 min. At reaction temperature the reactor is pressured to 5250 psig. The reaction is allowed to consume gas until the pressure has fallen to 4750 psig. The reactor is repressured to 5250 psig and cycled in this manner for 10000 psi total uptake.

The reactor contents are then

cooled via internal cooling coils to 10 C. A vapor phase sample is taken for analysis, and the liquid contents are placed in a chilled bottle. A similar procedure was utilized with dimethylketals, dimethyl carbonate, and methyl ester feedstocks. The liquid products obtained in the batch and semicontinuous experiments were analyzed with a Hewlett-Packard Model 5880 gas

Chromatograph equipped with two 1/8 in x 10 ft 60/70 mesh

Chromasorb 101 columns connected in series.

In Industrial Chemicals via C1 Processes; Fahey, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

(3) (4)

(5)

9. WEGMAN ET AL.

Acetaldehyde Production

1 27

Hates and selectivities were calculated as previously described ( 10) . Discussion

Reductive Carbonylation of Methanol. The reductive carbonylation of methanol (solvent free) was studied at variable I/Co, PPh,/I,

temperature, pressure, synthesis gas ratio and methanol conver-

sion (gas uptake) in the batch reactor. A summary of the results is given in Table I. In general, the acetaldehyde rate and selectivity increase with increasing I/Co. The PPh /I ratio has little effect except in run #7 where the rate is drastically reduced at I/Co =3.5 and PPh /I = 2.

A good set of conditions


is I/Co =3.5 and PPh /I = 1.T where the acetaldehyde rate and

selectivity is 7.6 M/ttr and 76% at 170 °C and 5000 psig.

The

effect of methanol conversion at these conditions is obtained by comparing runs 13, 1, 14, and 15. The gas uptake was varied from 14000 to 4000 psi, which corresponds to observed methanol conversions of 68% to 38%.

The most notable feature about the data is the acetaldehyde rate, which increases with decreasing methanol conversion. For example, a rate of 17.5 M/hr is obtained at a conversion of 38%.

There are numerous explanations for this trend, including product inhibition of the catalyst or rate dependence on methanol concentration. However, the important point is that when comparing any data dealing with this reaction, the conversions must be similar

in order to draw meaningful conclusions.

Increasing the temperature from 170-210 °C at I/Co =3.5,

PPh /I = 1.1 and H /CO = 1.5 results in lower acetaldehyde rate

and^selectivity.

St 170 °C acetaldehyde and methyl acetate

account for 91% of the products. Other products include ethanol (4%), dimethyl ether (2%), methane (1%), and trace amounts of crotonaldehyde, n-butanol and other minor components. At the higher temperatures, dimethyl ether and methane markedly

increase.

For example, at 210 °C their selectivities are 30 and

20%, respectively.

This change in selectivity to less desirable

products is accompanied by a reduction in the overall rate of

conversion of methanol.

Similar results were reported by Roper,

Loevenich, and Korff for Co(OAc) /I /PPh

and cobalt-phosphine

complexes such as Col ( PPh ) (_jj) . Our^investigation of cobalt complexes Col (PPh ) f CoI^OPPh ) , and [MePPh ] [Col.] also found declining activity as temperature increased above 190 °C,

but the effect was more severe with the latter two indicating

catalyst instability is a likely cause (_H)) .

The formation of

cobalt metal would explain the increased production of methane observed.

Reaction pressure is also a significant variable. The reaction is best carried out at 5000 psig but will proceed at 3000 psig with reduced acetaldehyde rate and the same overall response to the reaction variables reported in Table I for 5000 psig. Below 2000 psig the acetaldehyde rate is less than 1.0 M/hr. Methyl acetate is the principal by-product in the reductive carbonylation of methanol.

As indicated in Table I, decreasing

the Hp/C0 increases the methyl acetate selectivity. In the limit

of pure CO, methyl acetate is obtained in 90-95% selectivity.


128

INDUSTRIAL CHEMICALS VIA Ci PROCESSES

Carbonylation of methanol, Equation 6, is a well-known reaction.

2CH30H + CO

> CH C(0)OCH + H20

> CH C(0)OH + CH OH (6)

BASF operates a commercial process with a Co-1 catalyst at 210 °C and 10000 psig (_1j_) .

The main product is acetic acid with rates

and selectivities of 1-4 M/hr and 90-93%.

In the late 1960s,

Monsanto developed a Rh- I catalyst that operates at significantly lower pressure (18) . In their process, the reaction is carried out at 180-200 C and 500 psig with acetic acid rates and selectivities of 10- j0 M/hr and 95-99%.

Since there is little known about Co-I-PPh

as a carbonyla-

tion catalyst, we studied the reaction of methanol with CO in Downloaded by TUFTS UNIV on October 17, 2014 | http://pubs.acs.org Publication Date: December 16, 1987 | doi: 10.1021/bk-1987-0328.ch009

some detail.

A summary of the results is given in Table II.

The overall response to the reaction variables is very simi-

lar in the carbonylation and reductive carbonylation reactions. This may indicate similar catalysts and reaction mechanisms. In the carbonylation reaction Co(C0)~ was identified by its charac-

teristic CO stretching frequency U(C0) = 1890 cm" ) as the dom-

inant species present in high pressure infrared experiments car-

ried out at 170 °C and 5000 psig. Similar results were obtained in the reductive carbonylation of methanol.

It is known that

Co(C0)4" rapidly reacts with CH I to yield CH C(0)Co(C0)4 (J_9) ; however, in the carbonylation and reductive carbonylation reactions acyl-cobalt complexes are not observed by infrared under catalytic conditions. This indicates that once formed, the acyl complex rapidly reacts as outlined by Equations 7 and 8. CH OH

CH C(0)Co(C0) I 6

X Y

.

1

>

CH C(0)0CH

I

H_ -

>

CH C(0)H

5

(7)

5

(8)

Methyl acetate probably originates from the reaction of methanol

with the intermediate cobalt-acyl complex.

The reaction leading

to the formation of acetaldehyde is not well understood.

Equation 8, H

In

is shown as the reducing agent; however, metal

carbonyl hydrides are known to react with metal acyl complexes

(20-22) .

For example, Marko et al. has recently reported on the

reaction of n-butyryl- and isobutyrylcobalt tetracarbonyl com-

plexes with HCo(C0)4 and H (^3). They found that at 25 °C rate constants for the reactions with HCo(C0K are about 30 times larger than those with H ; however, they observed that under hydrof ormylation conditions, reaction with Yi is the predominant pathway because of the greater concentration of H

and the

stronger temperature dependence of its rate constant. The same considerations apply in the case of reductive carbonylation.

Additionally, we have found that CH C(0)Co(C0) L (L = PBu^, PPh CH ) reacts with H

(Equation 87 but not with the correspond-

ing HCÖ(C0)L and that the reaction of CH C(0)Co(C0) PPh with

HCo(C0)4 and HCo(CO) PR (R = Bu, The Ph) results only in the decomreaction of

position of the cobalt hydrides.

CH C(0)Co(C0) PPh with HSiR , HSnR or H yields acetaldehyde according to the following postulated mechanism (X = SiR~, SnR , H) (24).


9. WEGMAN ET AL.

Table I.


1 29

The Effect of Reaction Variables in the Reductive

__________________ Carbonylation of Methanol


Run//

I/Co

P/I

Temp.,°C.

1 2 3

1.0 1.0 2.0

0.5 2.0 0.5

170 170 170

H /CO

Uptake, psi

1:1 1:1 1:1

10000 10000 10000

AcH rate

Sei % AcH MeOAc

4.2 3.8 5.4

68 73 79

20 17 14

14

4

2.0

2.0

170

1:1

10000

5.3

78

5

3.5

0.5

170

1:1

10000

6.1

74

18

6

3.5

1.1

170

1:1

10000

7.6

76

15

7

3.5

2.0

170

1:1

10000

0.9

76

15

8

3.5

1.1

170

1.5:1

10000

6.1

83

9

9 10 11 12 13

3.5 3.5 3.5 3.5 3.5

1.1 1.1 1.1 1.1 1.1

170 170 190 210 170

0.75:1 0.5:1 1.5:1 1.5:1 1:1

10000 10000 10000 10000 14000

11.4 10.1 1.2 0.5 3.8

72 52 48 23 75

20 41 16 14 17

14

3.5

1.1

170

1:1

7000

12.2

76

13

15

3.5

1.1

170

1:1

4000

17.5

76

13

All runs at 5000 psig with [Co] = 0.052 M, P = PPh , and I = total iodide charged. Rates are reported as M/hr.

Table II.

The Effect of Reaction Variables in the

__________________ Carbonylation of Methanol CH OH

I/Co

P/I

Temp.,°C

2.0 2.0 3.5 3.5 3.5 3.5 3.5 3.5 3.5

0.5 1.1 0.5 1.1 1.1 1.1 1.1 1.1 1.1

170 170 170 170 170 170 170 210 180

Cortv.,% 60.7 61.6 60.2 61.5 25.1 47.2 83.4 59.5 61.7

MeOAc

Rate Sel.,% 2.0 2.9 1.7 4.0 7.4 5.3 2.6 4.7 3.2

93-3 92.8 87.7 94.1 95.7 95.4 93.2 93.5 93-9

All runs = 5000 psig CO; [Co]=0.052M, P=PPh , and I = total iodide. Rates are reported as M/nr.


1 30

INDUSTRIAL CHEMICALS VIA C, PROCESSES

CH3C(0)Co(C0) PPh CH3C(0)Co(CO)2PPh + HX

>

CH C(0)Co(C0)2(H)(X)PPh + CO

CH C(0)Co(C0)2PPh + CO > CH C(0)Co(C0>2(H)(X)PPh > CH C(0)H + XCo(CO) PPh

(9) (10) (11)


At constant CO partial pressure, the rate determining step is a function of the HX bond strength. In the case of HSnR , the rate determining step is CO dissociation, Equation 9. For HSiR and H , it is the oxidative addition step, Equation 10. Assuming the reductive carbonylation of methanol proceeds according to the generalized Equations 3-5 and 7-8, then we can speculate on the nature of the acetaldehyde producing step under catalytic conditions. According to high-pressure infrared (170

C and 5000 psig) Co(C0) ~ accounts for approximately 95% of the charged cobalt in the Co-I-PPh catalyzed reaction (J_0) . Trace

amounts of HCo(CO). are observed with no indication of a cobalt

acyl complex. If we assume that the upper limit concentrations of the cobalt-acyl species and HCo(CO). are 1 and 4% of the total cobalt charged (0.053 M) , then, with a partial pressure of 2500

psi H , concentrations will vary as [H ] (0.9 M) » [HCo(C0)a] (0.002 M) » [cobalt-acyl] (0.00053 M)7

H

and possibly HCoCCOK

are in relatively large excess so that once formed, the cobaltacyl complex is rapidly cleaved. This step may occur as outlined in Equations 9-11. Based on the reported work of Marko et al. (23) , cleavage should be at least an order of magnitude faster

with HCo(CO)^; however, the H :HCo(C0K mole ratio is at least 100:1 so it is more likely that cleavage via H , as shown in Equation 8, is the dominant reaction. Therefore, H competes with methanol for reaction with the cobalt-acyl complex. Decreasing the [H ] by decreasing the H /CO ratio increases the amount of methyl acetate formed. In the absence of added H , methyl acetate is the sole product. The methyl acetate forming reaction can be suppressed by

increasing the H? partial pressure or by decreasing the initial

methanol concentration.

Increasing the H

partial pressure

requires an overall increase in the operating pressure and also increases the amount of by-product ethanol. A significant gain in acetaldehyde selectivity is not observed. Decreasing the methanol concentration is readily accomplished by utilizing a solvent. In this case the acetaldehyde selectivity is improved. The results of experiments carried out with various solvents are given in Table III.

In general, the best acetaldehyde rates and selectivities, typically 3-5 M/hr and 80-90%, are obtained in ethers and polyethers. Relative to the solvent-free case (methanol only) the rate is somewhat lower and the selectivity is normally 10% higher.

The problem with solvents is that in most cases they decompose under the reaction conditions used in the reductive carbonylation reaction. Solvent decomposition can occur in a variety of ways including (i) acid cleavage of ether linkages by HI and HCo(C0K, (ii) well known hydrolysis and halogenation reactions,


9. WEGMAN ET AL.


131

(iii) participation in condensation reactions with acetaldehyde or other products produced in the reaction, and (iv) conversion by hydrogénation, reductive carbonylation, homologation or carbonylation. A good illustration is tetraglyme. With this sol-

vent the acetaldehyde rate is 6.6 M/hr at 170 °C, 5000 psig and a

methanol conversion of 61%; however, tetraölyme rapidly decomposes to triethylene glycol and methoxytetraethylene glycol. Triethylene glycol is a reasonably good solvent, but it eventually decomposes to ethylene glycol and diethylene glycol. Ethylene glycol is a poor solvent giving acetaldehyde rate and selectivity of 0.2 M/hr and 45%. Ester, alcohol, and most ketone solvents also decompose. For example, with the Co-I-PPh catalyst, methyl acetate reacts Downloaded by TUFTS UNIV on October 17, 2014 | http://pubs.acs.org Publication Date: December 16, 1987 | doi: 10.1021/bk-1987-0328.ch009

with synthesis gas to form ethyl acetate.

All of the primary and

secondary alcohols tested (Cp thru Cr) decompose during long-term

operation.

The major decomposition products include aldehydes,

alkyl iodides, and ethers. Ketones are readily hydrogenated and the resulting alcohols decompose. Good solvents in terms of stability are diphenyl ether and alkanes. The acetaldehyde rate is somewhat low (1.8 M/hr) in diphenyl ether, and the selectivity is low in alkanes. In addition, these solvents do not have good solubility properties, especially in product refining. Reductive Carbonylation of Dimethoxy Ketals and Dimethyl Carbonate. Acetaldehyde is obtained via the reductive carbonylation of

dimethyl ketals, Equation 12, and dimethyl carbonate, Equation 13

(15).

R2C(0CH ) + H2 + CO

> CH C(0)H + RC(0)R + CH OH

(12)

(CH 0)2C0 + H2 + CO — -> CH C(0)H + C02 + CH OH

(13)

In each case, the products other than acetaldehyde must be recy-

cled to reform the substrate.

For example, 2,2-dimethoxypropane

yields acetaldehyde, acetone, and methanol according to Equation

12. The reaction is carried out at 135 °C and 2250 psig with a

cobalt catalyst. Iodide promoters are not required. The acetaldehyde rate is typically 4.0 M/hr and the selectivity is 60-70%. The co-produced acetone and methanol are recycled in a separate

step via the equilibrium represented by Equation 14.

2CH OH + CH C(0)CH

~~? CH C(0CH )2CH + H20

(14)

Relative to the reductive carbonylation of methanol, the added recycle step is a disadvantage with dimethyl ketals. This disadvantage is offset by the lower pressure of operation and the noncorrosive halide-free catalyst, which permits cheaper materials of construction.

The reaction of dimethyl carbonate with synthesis gas

requires a cobalt-iodide catalyst and operating conditions of 180 C and 4000 psig. The acetaldehyde rate approaches 30 M/hr with selectivities greater than 85%. The productivities are much better than with methanol; however, recycle of the CO and methanol back to dimethyl carbonate is very difficult.


132

INDUSTRIAL CHEMICALS VIA C, PROCESSES

Reductive Carbonylation of Methyl Esters. The best alternative, and in our opinion, the best reported synthesis gas based process to produce acetaldehyde, is the reductive carbonylation of methyl esters, Equation 15 ( 16) .

RC(0)OCH + CO + H2

>

CH C(0)H + RC(0)OH

(15)

For example, the reaction of methyl acetate and synthesis gas at

170 °C and 5000 psig with a Co-Lil-NPh catalyst results in the


formation of acetaldehyde and acetic acid. The rate of acetaldehyde formation is 4.5 M/hr, and the yield based on Equation 15 is nearly 100%. Methane (1-2%) and ethyl acetate (1-2%) are the only by-products. The product mixture does not contain water, methanol or 1 , 1-dimethoxyethane. The acetic acid can easily be recycled by esterification with methanol in a separate step.

Thus, the overall acetaldehyde selectivity approaches 98%.

The

utility of methyl acetate as an alternative feedstock has been

previously illustrated by the reported carbonylation to acetic

anhydride (25) and homologation (^6) to ethyl acetate via reac-

tion with synthesis gas. A summary of the results we have obtained for the reductive carbonylation of methyl acetate is given in Table IV.

Amine promoters tend to give higher acetaldehyde rates relative to phosphines. Increasing the temperature to 200 C increases the rate to 7.1 M/hr whereas decreasing the pressure to 2000 psig markedly lowers the rate. Lil is a critical component

of the catalyst.

Substituting Lil with Nal , KI, Ip or CH I

results in a substantial loss in catalytic activity. A key step in the postulated reaction mechanism, as outlined in Equations

16-18, is cleavage of methyl acetate by Lil to yield CH I and

LiOAc (27).

5

CH C(0)0CH

+ Lil

>

CH I + CO + H2 HI + LiOAc

CH I + LiOAc

(16)

> CH C(0)H + HI >

(17)

Lil + CH C(0)0H

(18)

Other alkali/alkaline earth metal iodides either cleave esters

less efficiently or form insoluble carboxylate salts and are

therefore not as effective as Lil.

Addition of Li

and I" com-

pounds capable of forming Lil under reaction conditions works as

well as initially charging Lil (Table IV).

The acetaldehyde pro-

ducing step, Equation 17, is carried out with the cobalt-based catalyst. Since the carboxylate half of the ester is not

involved with the cobalt center, any methyl ester which can be cleaved by Lil should also show activity. We have found that methyl isobutyrate, dimethyl malonate, methyl propionate, and

dimethyl succinate yield acetaldehyde and the corresponding carboxylic acids in high yield under the same conditions utilized with methyl acetate. Summary and Conclusions Acetaldehyde is obtained from the reaction of methanol, methyl


9. WEGMANETAL.

Table III.


133

The Use of Solvents in the Reductive Carbonylation


____________________________ of Methanol Rx. MeOH AcH Solvent Time Conv. Rate Sei

Et OH Rate Sei

MeOAc Rate Sel

nonane toluene

1.68 0.91

56 62

3.1 4.2

84 86

0.2 0.2

4.8 3-7

0.2 0.2

2,5-hexanedione methyl ethyl ketone diphenyl ether THF 2-ethoxyethyl ether 1,4-dioxane n-propanol

0.82 0.51 1.15 0.38 0.48 0.51 0.45

66 52 66 45 64 71 56

1.9 4.4 1.8 3.6 5.4 3-5 1 .8

74 86 88 90 86 87 73

0.03 0.06 0.07 0.0 0.2 0.09 0.2

1.2 1.0 3.4 0.0 2.5 2.3 7.1

0.4 2.1 0.3 8.0 0.05 3.5 0.2 4.0 0.2 5.9 trace a

iso-propanol ethylene glycol

0.58 1.23

53 45

3.9 89 0.2 low

0.3 6.6 0.03 7.5

0.03 3.0 0.1 3.6

1 ,4-butanediol

0.98

72

1 .9

25

2,5-hexanediol

0.53

65

3.8

87

b

0.1

5.8 5.6

b

4.3

0.1

3.6

All runs at 170 °C and 5000 psig with [Co] = 0.052 M, I/Co = 4, and I/P = 2.

Rates reported as M/hr and the reaction time is hr.

a = not well resolved via GC.

b = complex reaction mixture due to solvent decomposition.

_____ Table IV.

Col ÊFL mmol mmol 8

NBu

(16)

Reductive Carbonylation of Methyl Acetate

Ï

Temp . , °C Pressure ÄcH C psig Rate, M/hr

Lil (32)

180

5000

Lil (32)

180

5000

180

2000

200

5000

8 NPh^ (16) Li0Ac(32)+CH 1(32) 200

5000

8 NPh^ (16)

Lil (32)

8

PPh;? (16)

Lil (32)

8 NPh^ (16)

Lil (32)

200

KI (32)

200

8 PCy^ (16)

8 PPh^ (16) 8 NPh^ (16)

8 NPh^ (16)

Lil (32)

Nal (32)

180

180

8 NPh^ (16) Li2C0 ( 16)+l|( 16) 200

4.7

5000

4.5

5000

2.7

5000

7.1

5000

0.2

5000

3.6

3-9

0.2 0.5

7.4

All runs = 150 mL methyl acetate


1 34

INDUSTRIAL CHEMICALS VIA C , PROCESSES

ketals, dimethyl carbonate or methyl esters with synthesis gas and a cobalt-based catalyst. Each feedstock has its advantages and disadvantages. Ketals suffer from low acetaldehyde selectivity and dimethyl carbonate requires a difficult recycle step. Good acetaldehyde rates and selectivities are obtained with

methanol; however, achieving high selectivity (>90% while maintaining adequate methanol conversion) requires the use of a solvent. The solvent must be recycled, and that may require an additional refining step. The major problem with most solvents is that they eventually decompose which requires additional refining of the product and the costly replacement of the sol-


vent.

Overall, the best process is based on methyl esters.

Good

rates and, more importantly, high selectivity (>95%) are obtained in the absence of a solvent. In the case of methyl acetate, product refining consists of separating acetaldehyde from acetic acid and unreacted methyl acetate. An important feature of the methyl ester system is the absence of water and methanol in the product mixture. In contrast, with methanol the minimum separa-

tion involves acetaldehyde, methanol, dimethyl acetal, methyl acetate, acetic acid and water.

The benefits obtained from the

high acetaldehyde selectivity and the easy product refining more than compensate for the additional esterification step required with a methyl ester feedstock. Acknowledgments

We thank Union Carbide Corporation for permission to publish this information. Literature Cited

1.

Bahrmann, H.; Cornils, B.

In New Syntheses with Carbon

Monoxide; Falbe, J., Ed.; Springer-Verlag: New York, 1980; Chap. 2.

2. 3. 4.

Wender, I.; Levine, R.; Orchin, M.

J. Am. Chem. Soc. 1949,

71, 4160.

Berty, J.; Marko, L.; Kallo, D. Chem. Tech. 1956, 3, 3260. Mizorogi, T.; Nakayoma, N. Bull. Chem. Soc. Jpn. 1964, 37, 236.

5.

Schultz, H. F.; Bellstdt, F. Dev.

6.

Ind. Eng. Chem. Prod. Res.

1973, 12, 176.

Pretzer, W.; Kobylinski, T.

Ann. N. Y. Acad. Sci. 1980,

333, 58.

7. 8.

9.

Dale, B. E. Swodenk, W.

Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 466. Chem. Eng. Tech. 1983, 55, 683.

Deluzarche, A.; Jenner, G.; Kiennemann, A.; Samra F. A.

Erobel Kohle Endgass. Petrochem. 1979, 32, 436.

10. 11.

Wegman, R.; Busby, D. C. J. Mol. Catal. 1985, 32, 125. Doyle, G. J. Organomet. Chem. 1981, 13, 237.

12.

Roper, M.; Lovevenich, H.; Korff, J. J. Mol. Catal. 1982, 17, 315. Steinmetz, G. R.; Larkins, T. H. Organometallics 1983, 2,

13. 14.

1879.

Slocum, D. W. In Catalysis in Organic Chemistry; Jones, W. H. Ed.; Academic Press: New York, 1980; p. 245.


9. WEGMAN ET AL.


15. Wegman, R.; Letts, J. B. 16. Wegman, R.; Busby, D. C.

J. Mol. Catal. 1985, 33, 357. J. Chem. Soc., Chem. Commun. 1986,

332.

17. 18.

Reppe, W.; Friederich, H. U.S. Patent 2 727 902, 1955. Eby, R. T.; Singleton, T. C. In Applied Industrial Catalysis; Leach. B. E. Ed.; Academic Press: New York, 1983;

19.

Galamb, V.; Palyi, G.

20.

Orchin, M.

Chap. 10.

21. 22.

Coord. Chem. Rev. 1984, 59, 203.

Acc. Chem. Res. 1981, 14, 259.

Ungvary, M.; Marko, L. Organometallics 1983, 2, 1608. Martin, J. T.; Baird, M. C. Organometallics 1983, 2, 1073.

23. Kovacs, I,; Ungvary, F.; Marko, L. Organometallics 1986, 5, 209.


24.

25.

Wegman, R. W.

Organometallics 1986, 5, 707.

Larkins, T. H.; Polichnowski, S. W.; Tustin, G. C.; Young, D. A.

U.S. Patent 4 374 070, 1983.

26.

Braca, G.; Sbrana, G.; Valentini, G.; Andrich, G.; Gregorio, G. J. Am. Chem. Soc. 1978, 100, 6238. 27. Shina, H.; Hashimoto, T. Yukagaku 1980, 29, 901.

RECEIVED August 14, 1986


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Acetaldehyde Production by Reductive Carbonylation of Methanol

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