Industrial Chemicals via C1 Processes

Chapter 12

Vapor-Phase Carbonylation of Dimethyl Ether and Methyl Acetate with Supported Transition Metal Catalysts Downloaded by PENNSYLVANIA STATE UNIV on April 16, 2013 | http://pubs.acs.org Publication Date: December 16, 1987 | doi: 10.1021/bk-1987-0328.ch012

Tsutomu Shikada, Kaoru Fujimoto, and Hiro-o Tominaga Department of Synthetic Chemistry, Faculty of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan It

was

found

catalyst was

that

a

effective

nickel-activated

carbon

for vapor phase carbonyl-

ation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250°C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250°C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of

acetic acid was methyl acetate.

is

discussed.

formed in the carbonylation of The route of acetic acid formation

A

molybdenum-activated

carbon

catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. The synthesis of acetic acid (AcOH) from methanol (MeOH) and carbon

monoxide has been performed industrially in the liquid phase using a

rhodium

complex

catalyst and an

iodide promoter

(.1^4) .

The

selectivity to acetic acid is more than 99% under mild conditions

(175 C, 28 atm) . The homogeneous rhodium catalyst is also effective for the synthesis of acetic anhydride (Ac O) by the carbonylation of dimethyl ether (DME) or methyl acetate (AcOMe) (5-13) . However, rhodium is one of the most expensive metals , and its " proved reserves are quite limited. It is highly desirable, therefore, to develop a new catalyst as a substitute for rhodium. We have already reported that nickel supported on activated

carbon exhibits an excellent activity for the vapor phase carbonylation of methanol in the presence of methyl iodide (Mel) at moderate pressures (14-16) . In addition, corrosive attack of iodide compounds on reactors is expected to be minimized in the vapor phase system.

We

have

tried

to

explore

the

catalytic

capabilities

0097-6156/87/0328-0176$06.00/0

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

of

1 2. SHIKADA ET AL.

Carbonylation of Dimethyl Ether and Methyl Acetate

1 77

transition metals supported on activated carbon for the carbonylation of dimethyl ether and methyl acetate (17-19) . It was found that nickel and molybdenum gave methyl acetate from dimethyl ether and acetic anhydride from methyl acetate with high selectivities. In the present work, catalytic features of nickel-activated carbon (Ni/A.C) and molybdenum-activated carbon (Mo/A.C.) for the carbonylation of dimethyl ether and methyl acetate were studied together with

the

effects

of

several

factors

that controlled the rate of

carbonylation .

Downloaded by PENNSYLVANIA STATE UNIV on April 16, 2013 | http://pubs.acs.org Publication Date: December 16, 1987 | doi: 10.1021/bk-1987-0328.ch012

CH OCH

CH COOCH

+ CO

+ CO

9> CH COOCH

(1)

> (CH CO) 0

(2)

Experimental

Nickel-activated

carbon catalysts were prepared by impregnating

commercially available activated carbon granules (Takeda Shirasagi C, 20-40 mesh) with aqueous solutions of nickel chloride or nickel acetate, followed by drying in air at 120 C for 24 h and then activating in a stream of hydrogen at 400 C for 3 h. Molybdenumactivated carbon catalysts were prepared by the same procedure but using an aqueous solution of ammonium molybdate and activating in flowing hydrogen at 450 C for 3 h. A continuous-flow reactor with a fixed catalyst bed was employed at pressurized conditions. Gaseous dimethyl ether was supplied to the reactor at its vapor pressure with carbon monoxide while liquid reactants such as methyl acetate, methyl iodide, and water were fed with microfeeders. Methyl acetate used in this experiment was dehydrated by Molecular Sieve 5A before use. A part of the reaction mixture was sampled with a heated syringe and was analyzed by gas chromatography. The product yields were calculated by the following equation. Yield = (nr /2r )100

(3)

where n is the number of methyl groups in a molecule, r formation rate of product (mol/g» h) , and r dimethyl ether or methyl acetate (mol/g«h) .

is the

is the feed rate of

Results and Discussion

Carbonylation of Dimethyl Ether on Ni/A.C. Catalysts. The main product of this reaction was methyl acetate. Small amounts of acetic acid, acetic anhydride, methane and CO were formed as by-products . Figure 1 shows the product yields and the selectivity to methyl acetate as a function of reaction temperature. The yield of methyl acetate increased with a rise in the temperature up to 250 C and then decreased, while those of acetic acid and methane

increased to lower the selectivity to

methyl acetate.

A trace

amount of acetic anhydride was formed at around 250 C. Figure 2 shows the effect of operational pressure on the product yields and the selectivity to methyl acetate. Methyl acetate was formed with a

yield of 14.2% and a selectivity of 95.3% at 10 atm. methyl

acetate

increased monotonically

with

an

The yield of

increase in the

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

178

INDUSTRIAL CHEMICALS VIA C, PROCESSES

30 r^ — f / ^"^^V?^/ / ^Aç0MeVl*K^C


J 20 " / rH •H >^

^^- 60 a
ü

/ /

Aco0 CH ^ 2

200

250

«u . 20 w

300

Temperature (°C) Figure 1. Effect of reaction temperature on DME carbonylation. 2.5wt%Ni/A.C. , 10 atm, W/F (Weight of catalyst/Flow rate)=5

g-h/mol, CO/DME/Mel = 100/9.5/1.

50 |

—

» 100

40 -

^ 30 -

*-*~" — "-Q- — - 80 g

^ AcOMe

o 20 -

- 60

/

o

^X

m

*

>^

u

or 10 -

ol

0

ii

X

^AcOH

/

\

- 20

«

w

nv — ^rr^— f— 10

10

20

30

40

50

Pressure (atm)

Figure

2.

Effect of reaction pressure on DME carbonylation.

2.5wt%Ni/A.C. , 250°C, W/F=2.5 g«h/mol, CO/DME/MeI=60/9. 5/1 . 0.


1 2. SHIKADA ET AL.


1 79

pressure, while its selectivity decreased gradually. Small amounts of acetic acid and acetic anhydride were found in the products and their selectivities increased with increasing pressure suggesting that they were formed successively from methyl acetate. The fact that higher pressure is suitable for the formation of acetic anhydride agrees with the results in the carbonylation of methyl


acetate mentioned later.

Table I shows the effects of Mel /DME and CO/DME ratios in the feed gas on product yields. With increasing Mel/DME ratio both methyl acetate yield and selectivity increased. The yield of methyl acetate increased with an increase in the CO/DME ratio whereas its selectivity decreased. In the case of methanol carbonylation on

Ni/A.C. catalyst, the product yield and selectivity were strongly affected by CO/MeOH ratio but not by Mel/MeOH ratio (14-16) . The promoting effect of methyl iodide on the methanol carbonylation reached a maximum at a very low partial pressure, that is 0.1 atm or lower. However, both CO/DME and Mel/DME ratios were important for regulating the product yield and selectivity of the dimethyl ether carbonylation. This suggests that the two steps, namely, the

dissociative adsorption of methyl iodide on nickel (Equation 4) and the insertion of CO (Equation 5) are slow in the case of dimethyl ether reaction.

CH3l + Ni/

«

0.03

\/

°

X A 0M

/ \ ACUiie ^

«

- 20

/ \>

y' /co / o 0I

- 30 |

1

12

eg e

-2

\ - io f 1

1

3

-^0 5

4

Partial pressure of CO (atm) I

I

I

I

I

I

0

0.2

0.4

0.6

0.8

1.0

Partial pressure of AcOMe (atm)

Figure 8.

Effect of partial pressures of CO, Mel and AcOMe on

the

of

rate

AcOH

formation

in

the

presence

of

water.

2.5wt%Ni/A.C. , 250°C, 10 atm, (#) P^QMe"0'6 atm? PMeI=0'01 atm? P„ =0.6 atm, (O ) P, _ =0.6 atm; CpL ®=2. 8 atm; Pu =0.6 atm, Vfo) P -7.4 atm; PAC°^f).02 atm; P„C°=1.8 atm. CO

Mel

HO

«2°


1 86

INDUSTRIAL CHEMICALS VIA C , PROCESSES

(CH3CO)20 + H20

* 2CH3COOH

(6)

On the other hand, the reaction order with respect to methyl acetate was -1.7. The strong self-inhibition effect of methyl acetate should be noted, because of stronger adsorption of methyl acetate on Ni/A.C. than other reactants.


Carbonylation of Dimethyl Ether and Methyl Acetate on Mo/A.C. Catalyst. In this section, the carbonylation of dimethyl ether and methyl acetate on Mo/A.C. catalyst was investigated. To our knowledge, molybdenum has never been reported to catalyze carbonylation reactions.

Table V shows the results obtained for the carbonylation of

dimethyl

ether

and

methyl

acetate

with

molybdenum

catalysts

supported on various carrier materials. In the case of dimethyl ether carbonylation, molybdenum-activated carbon catalyst gave methyl acetate with an yield of 5.2% which was about one-third of the activity of nickel-activated carbon catalyst. Silica gel- or y-alumina-supported catalyst gave little carbonylated product.

Similar

results

were

obtained

in

the

carbonylation

of

methyl

acetate. The carbonylation activity occured only when molybdenum was supported on activated carbon, and it was about half the activity of nickel-activated carbon catalyst.

Figure 9 shows the product yields as a function of operational pressure in the carbonylation of methyl acetate. The yield of acetic anhydride increased monotonically with increasing pressure, while that of methane was almost unchanged. The yield of acetic acid increased up to 30 atm and then decreased above that pressure. Acetic anhydride was formed with a yield of 15% and a selectivity of 83% at 45 atm, indicating that high operational pressure was favorable for the selective formation of acetic anhydride on the Mo/A.C. catalyst. Table V.

Reactant

Carbonylation Activities of Supported Molybdenum and Nickel-Activated Carbon Catalysts

Catalyst0 Temp Press. (°C)

Product yield (%)

CO /CH.

(atm)

AcOMe

Ac 0

AcOH

CH

DME

Mo/A.C.

300

11

5.2

0

0

2.7

0.1

DME DME

Mo/Si02 Mo/y-Al20

300 300

11 11

0.6 0.4

0 0

0 0

0.2 1.1

0.1 0.1

DME AcOMe AcOMe

Ni/A.C. Mo/A.C. Mo/SiO

300 250 250

11 15 15

15.2 -

tr 4.5 0

7.4 6.6 0

3.2 1.3 0.1

0.8 0.4 -

AcOMe

Mo/y-Al20

250

15

0

0

tr

-

AcOMe

Ni/A.C.

250

15

-

10.3

9.9

2.6

0.5

^/F, 10 g-h/mol. bC0/DME/MeI, 240/100/9 molar ratio; CO/AcOMe/Mel, 100/9/1 molar ratio. cMetal loading, 2.5 wt% . ^lolar ratio. Reproduced with permission from reference 18. Copyright 1985, The Chemical Society of Japan.


1 2. SHIKADA ET AL.


15 -

1 87

^/^


Ac2°~~\y'

Industrial Chemicals via C1 Processes

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