produccion de acido acetico a partir de la oxidacion de etileno

8/13/2019 Produccion de Acido Acetico a Partir de La Oxidacion de Etileno

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Catalysis Surveys from Japan 3 (1999) 5560 55

A new process for acetic acid production by direct oxidation ofethylene

Ken-ichi Sano a, Hiroshi Uchida b and Syoichirou Wakabayashi b

a Catalysis Section, Central Research Laboratory, Showa Denko K.K., 5-1 Ogimachi, Kawasaki, Kanagawa 210-0867, Japanb Technology and Development Department, Oita Works, Showa Denko K.K., 2 Nakanosu, Oita 870-0189, Japan

A new process for acetic acid production by direct oxidation of ethylene which was established and commercialized is described.

The catalyst system consisting of Pd and heteropoly acid exhibits excellent activity and selectivity. The addition of Se or Te to the

catalyst system is effective to suppress the formation of carbon dioxide. This new process is applicable to a plant of a wide range of

size corresponding to the local demand. Because this new process produces little waste water, it is very friendly to the environment.

Keywords: acetic acid, oxidation, Pd, heteropoly acid, ethylene

1. Background [1]

1.1. A short history of acetic acid manufacturing

technologies

Among the organic compounds, acetic acid has been

very familiar to mankind since it has been used as vinegar

for a long time. Vinegar was produced by alcohol fermen-

tation before Christ, and even now this brewing method is

used for vinegar production.As the demand for acetic acid grew in a wide range

of fields, pyroligneous acid, which is produced by the dry

distillation of wood, and used by alchemists in medieval

Europe, became a world-wide manufacturing process un-

til the middle of the 20th century. This pyroligneous acid

method was replaced by synthetic processes and is scarcely

used now. In 1914, the acetaldehyde oxidation process was

industrialized in Germany. Acetaldehyde was synthesized

by hydration of acetylene produced from carbide at that

time. The epoch-making process, the so-called Hoechst-

Wacker process which uses ethylene as the raw material,

was developed in 1959. The conventional process for thepreparation of acetaldehyde from acetylene was mostly re-

placed by this process. At the same period, the technology

of hydrocarbon oxidation made progress. Then oxidation

ofn-butane in liquid phase to produce acetic acid was in-dustrialized in 1952, and liquid phase oxidation of naphtha

to produce acetic acid was commercialized in 1956.

In the mean time, the manufacturing process of acetic

acid by the carbonylation of methanol was developed. This

process uses methanol and carbon monoxide as raw ma-

terials which are produced from natural gas, coal, heavy

residual oil, and others. BASF (Germany) industrialized

this process in 1960, and Monsanto (USA) industrialized itin 1970. Especially the latter process, known as Monsanto

process, has become the dominant industrial route for acetic

acid manufacturing.

1.2. Uses of acetic acid

Acetic acid has the demand of about 5.4 million

tons/year in the world in 1997. It is used in vinyl acetate,

solvent for production of pure terephthalic acid (PTA),

acetic anhydride, acetates, and others, as shown in ta-

ble 1 [2].

2. Industrial manufacturing process [1]

2.1. Methanol carbonylation process

This process, which is called Monsanto process, uses

methanol and carbon monoxide as the raw materials to syn-

thesize acetic acid. Because the price of naphtha has risen

and the relatively cheap methanol, produced from off gas,

natural gas, and so on, has been available after the oil cri-

sis, this process has rapidly become prevalent. At present,

this process accounts for 60% of the production capacity of

the world.

CH3OH+ CO

CH3COOH (1)In the Monsanto process, the selectivities to acetic acid

based on methanol and carbon monoxide are 99% and 90%,

respectively, when rhodium is used as a catalyst and iodine

as an activator. These days, most of the methanol carbony-

lation processes have adopted this catalyst system.

Table 1

Demand for acetic acid by applications (1,000 t/y).

1995 1997

Vinyl acetate monomer 1,812 1,996

Acetic anhydride 713 743

PTA 727 955

Acetates 636 661

Others 1,036 1,030

Total 4,924 5,385

Baltzer Science Publishers BV


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56 K.-i. Sano et al. / Acetic acid production by direct oxidation of ethylene

Figure 1. Process flowsheet of Monsantos acetic acid process.

The flowsheet is shown in figure 1 [3]. Methanol and

carbon monoxide are supplied continuously into the reac-

tor. The exhaust gas from the reaction section, together

with exhaust gas from the purification section, are washed

in the scrubber, then the light-ends are recovered and recy-

cled to the reaction section. On the other hand, the reaction

product (crude acetic acid) is sent to the light-ends column,

and acetic acid is taken out as a side-cut. The overhead and

the bottoms including the catalyst are returned to the reac-

tion section. Side-cut acetic acid is sent to the dehydration

column, then the mixture of water and acetic acid is taken

out from the top, and returned to the reaction section. Thebottoms of the dehydration column are sent to the subse-

quent product column. A small amount of the heavy-ends,

which contain propionic acid, is taken out from its bottom.

The overhead is further purified in the next fractionation

column, and purified acetic acid is obtained as a side-cut.

The overhead and the bottoms of the fractionation column

are recycled into the reaction section.

2.2. Acetaldehyde oxidation process

First, ethylene is oxidized into acetaldehyde with a

PdCl2CuCl2 catalyst, which is subsequently oxidized toacetic acid with a manganese acetate catalyst. This process

was prevalent before the appearance of the methanol car-

bonylation process. At present, however, the share of this

process has fallen to 22% of the world production.

C2H4 + (1/2)O2 CH3CHO (2)

CH3CHO+ (1/2)O2 CH3COOH (3)

The flowsheet of this process is shown in figures 2 and

3 [4]. Acetaldehyde vapor produced in the reactor leaves

the gas-liquid separator together with water vapor and un-

reacted gases. After cooling, acetaldehyde is absorbed with

water and the remaining gas is recycled to the reactor. Thelight-ends are removed at the light-ends column. Next, by-

products, such as methyl acetate and crotonaldehyde, are

removed as a side-cut from the product column. Further-

more, by-product acetic acid, together with water, is re-

moved from the bottom, and acetaldehyde is obtained from

the top.

In the oxidation process to acetic acid, acetaldehyde is

supplied near the top of the reactor and oxidized with the

rising oxygen gas introduced from the bottom. The liq-

uid reaction product, which is taken out from the reactor,

contains by-products, such as formic acid, methyl acetate,

ethylidene diacetate and others as well as a small amount

of unreacted acetaldehyde, water, and catalyst. Thus, the

light-ends are removed and the catalyst is recovered in the

purification section. The heavy-ends are removed from thebottom of the fractionation column, then purified acetic acid

is obtained. Acetic acid contained in the bottoms of the

fractionation column is recovered at the recovery column,

and the heavy-ends are removed. The recovered catalyst is

recycled.

2.3. Hydrocarbon (butane, naphtha) oxidation process

Hydrocarbons, such as butane and naphtha, are oxidized

directly into acetic acid, and 9% of the worlds production

capacity owes this process. Acetate catalysts, for exam-

ple, cobalt acetate and manganese acetate, are used. Since

this method uses hydrocarbons with high numbers of car-

bon atom as raw materials, not only acetic acid but acetone,

formic acid, propionic acid, and others are coproduced. Ac-

cordingly, the yield of acetic acid is much lower than those

of the other processes, but this process has advantages when

manufacturing various acids simultaneously is desired.

3. Direct oxidation of ethylene. A new Showa Denko

K.K. process

Showa Denko K.K. has developed a one-stage process

of acetic acid production by direct oxidation of ethylene.In this process, acetic acid is manufactured with high

selectivity from a mixture of ethylene and oxygen in the

vapor-phase at 160210 C over a solid catalyst. The main


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K.-i. Sano et al. / Acetic acid production by direct oxidation of ethylene 57

Figure 2. Process flowsheet of ethylene oxidation to acetaldehyde.

Figure 3. Process flowsheet of acetaldehyde oxidation to acetic acid.

reaction for acetic acid is shown below, together with the

major side-reactions, which are the combustion of ethylene

and the production of acetaldehyde.

In addition, small amounts of several compounds with

low and high boiling points are formed.

A great amount of heat is generated in this reaction, and

it is recovered as steam which is used for the heat source

in the purification section.

(Main reaction) C2H4 + O2 CH3COOH (4)

(Side reactions) C2H4 + 3O2 2CO2 + 2H2O (5)

C2H4 + (1/2)O2 CH3CHO (2)

The flowsheet of this process is shown in figure 4. The

product gas from the reactor is cooled to ambient temper-

ature. Thereby the reaction products such as acetic acid,

organic by-products, and water are condensed and are sep-

arated from un-condensed gas. The condensate is pulled

out of the reaction section and led to the crude acetic acid

tank which is connected to the purification section. The

un-condensed gas is recycled to the reactor after it is pres-

surized by the compressor.

The crude acetic acid stored in the crude acetic acid

tank is sent to the light-ends column. In this column, thelight-end by-products, such as acetaldehyde, ethyl acetate,

ethanol, and others, are removed from acetic acid by dis-

tillation. Then water is separated by extraction.

The acetic acid, free from water and the light-ends,

is sent to the final purification section. In this section,

both trace amounts of impurities and the heavy-ends are

removed, and highly pure acetic acid is obtained as the

product.

The chemical processes are required to be both compet-

itive and environmentally friendly: Showa Denko K.K.s

new process meets these requirements. Usually the pu-

rification of acetic acid is very energy consuming, since a

great amount of water is used in the oxidation reaction. To

solve this problem, Showa Denko K.K. has developed an

energy saving process by combining the extraction and the

distillation operation in which water is efficiently separated

from acetic acid [57]. This process is also very friendly

to the environment, because it generates little waste ow-

ing to the high selectivity of the reaction. No toxic waste,

and only a small volume of waste water were produced.

Moreover, it has a great advantage since no special mate-

rial is required for the construction of plants; adequately

used stainless steel is good enough for the facilities, be-

cause the process does not treat any corrosive compounds

except for acetic acid.

Showa Denko K.K. constructed the first commercial

plant based on the new process. It has the capacity of100,000 tons/year of acetic acid in Oita, Japan. The plant

was completed in August 1997. After the trial run, the plant

has been operated successfully since November 1997 [15].


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Figure 4. Process flowsheet of direct oxidation to ethylene into acetic acid.

Table 2

Proposed catalysts for direct oxidation of ethylene.

Catalyst Temperature Pressure Selectivity STY Ref.

(C) (kg/cm2G) (%) (g/lh)

PdCr/Al2 O3 180 1 60 [5]

PdV2O5 248 1 74 2 [6]

PdV2O5Sb2O5/Al2O3 250 1 84 27 [7]

PdH3PO4/SiO2 150 1 90 56 [8]

PdAuH2SO4/active carbon 150 3.4 85 107 [9]

4. Catalyst development for the direct oxidation

process

Several catalyst systems were proposed in the past for

the direct oxidation of ethylene to acetic acid, as shown

in table 2, for example. However, these catalysts havenot exhibited satisfactory performance for the industrial-

scale production of acetic acid. Here it is noteworthy that

acetic acid is obtained with relatively high selectivity by

the combination of Pd metal and acid catalysts.

4.1. Reaction mechanism

The following two reaction schemes may be considered

for the direct oxidation of ethylene to acetic acid. One

is the route where ethanol is formed by the hydration of

ethylene and then it is oxidized to acetic acid. In this

route, if the ethanol formed is irreversibly oxidized intoacetic acid, these reactions can to proceed under relatively

moderate conditions. It is considered that with catalysts

PdH3PO4/SiO2 and PdAuH2SO4/active carbon shown

in table 2, the reaction mainly proceeds by this mecha-

nism.

C2H4 +H2O CH3CH2OH (6)

CH3CH2OH+O2 CH3COOH+ H2O (7)

The other is the route where ethylene is first converted

into acetaldehyde by the Wacker type reaction, and the ac-

etaldehyde is oxidized into acetic acid. It is considered thatPd2+ basically acts as active species, and consequently the

reoxidation of Pd is necessary to achieve the catalytic reac-

tion. The catalyst systems, for example, PdCr/Al2O3, Pd

Table 3

Combination of Pd and heteropoly acid.a

Catalyst STYb Selectivity (%)

HOAcc

HAcd

CO2

PdH4SiW12O40 93.1 78.5 5.5 14.2

PdH3PW12O40 83.3 78.0 5.0 16.0

PdH4SiMo6W6O40 91.2 77.6 4.4 17.5

PdH3PMo6W6O40 75.1 76.5 4.1 19.2

PdH3PMo12O40 68.5 77.5 4.6 17.8

PdGa0.05H3.85SiW12O40 90.4 80.1 4.1 15.6

PdMg0.05H3.9SiW12O40 90.8 79.7 5.5 14.6

PdGa0.05H2.85PW12O40 75.6 74.8 3.2 21.8

PdLi0.05H3.95SiW12O40 91.0 79.9 3.9 16.1

PdCu0.05H3.9SiW12O40 90.9 78.6 4.9 16.4

Pd 0 0 0 100

H3PW12O40 0 0 0 0

PdH5PMo10V2O40 94.0 61.4 19.4 17.6

a Reaction conditions: reaction pressure = 5 kg/cm2G; reaction

temperature = 150 C; GHSV = 3,000/h; gas component (C2H4/O2/

H2O/inert gas = 50/7/30/13).b STY = space time yield (g/l-catalysth).c HOAc = acetic acid.d HAc = acetaldehyde.

V2O5, or PdV2O5Sb2O5/Al2O3 shown in table 2, mainly

follow this mechanism.

C2H4 + (1/2)O2 CH3CHO (2)

CH3CHO+ (1/2)O2 CH3COOH (3)

In spite of extensive efforts based on the second route,

any industrially promising results have not been obtained.

On the other hand, the first route, via ethanol intermedi-

ate, has at least a high selectivity. Showa Denko K.K.,

therefore, has chosen the R&D strategy based on the first

reaction mechanism, and has made efforts for the improve-

ment of catalyst performance.

4.2. Catalyst systems consisting of Pd and heteropoly

acids

We found that even a simple combination of Pd and a

heteropoly acid shows a relatively high yield of acetic acid,

as shown in table 3 [13].When only Pd was supported on silica, no partial oxida-

tion products of ethylene were obtained, and only carbon

dioxide, a deep oxidation product, was generated. On the


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of carbon monoxide production is also necessary. Conse-

quently the process requires heavy investments in facility

and is hardly profitable unless the production capacity is

equal to or more than 200,000 tons/year. On the other hand,Showa Denko K.K.s new process becomes profitable even

in the case of middle-scale facilities such as about 100,000

tons/year, and the investment can be substantially reduced

as compared with the methanol carbonylation process of

the same capacity. Since the new process is applicable to

a plant of a widely variable size, corresponding to the lo-

cal demand, the plant can be placed near the market. The

variable cost of acetic acid production depends mainly on

the price of methanol or ethylene in each case.

5.2. Comparison with acetaldehyde oxidation process

In the acetaldehyde oxidation process, the reaction is

two-staged, and many kinds of by-products complicate the

purification process. The acetaldehyde production needs

rubber and bricks for the materials of the reactor, because

aqueous hydrochloric acid is used. For these reasons, the

facility cost of the acetaldehyde oxidation process becomes

high. With the new process, the facility cost can be reduced

to 6070% for the same production capacity. Moreover, a

great amount of water is required for the acetaldehyde pro-

duction. This means that a large-scale facility becomes

necessary to treat the waste water. On the other hand, the

waste water from the new process is about 1/15 of that

from the acetaldehyde oxidation process. The new process

is in this respect much more friendly to the environment.

Although the selectivity of each step is high in the acetalde-hyde oxidation process, the overall selectivity of two-stage

oxidation is inferior to that of the new process. As a re-

sult, the unit consumption of ethylene of this new process

is better than that of the acetaldehyde oxidation process.

References

[1] H. Nishino, Kagaku Purosesu (Tokyo Kagaku Do-jin, Tokyo, 1998)

p. 68.

[2] M. Watanabe, Kagaku Keizai Rinji Zo-kan (1998) 64.

[3] H.D. Grove, Hydrocarbon. Process. 51 (1972) 76.

[4] R. Jira, W. Blan and D. Grimm, Hydrocarbon. Process. (March 1976)

97.[5] Showa Denko K.K., Jpn. Kokai Tokkyo Koho, 9-48744 (1997).

[6] Showa Denko K.K., Jpn. Kokai Tokkyo Koho, 9-100254 (1997).


[8] BP Chemicals, GB 1,142,897 (1969).

[9] IFP, FR 1,568,742 (1969).

[10] Nippon Shokubai, Jpn. Kokoku Tokkyo Koho, 46-6743 (1971).

[11] National Distillers, Jpn. Kokai Tokkyo Koho, 47-13221 (1972).

[12] National Distillers, Jpn. Kokai Tokkyo Koho, 51-29425 (1976).



[15] Sekiyu-Kagaku Shinbun (18 December 1997).

produccion de acido acetico a partir de la oxidacion de etileno

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