Matar Sami, Hatch Lewis F. Chemistry of petrochemical processes

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13. Landau, R. et al., Proceedings of the 7th World Petroleum Congress,

Vol. 5, Petrochemicals, 1967, pp. 67–72.

14. Ainsworth S. J., Chemical and Engineering News, Vol. 70, No. 9,

1992, pp. 9–11.

15. Brownstein, A. M. and List, H., Hydrocarbon Processing, Vol. 56, No.

9, 1977, pp. 159–162.

16. “Petrochemical Handbook,” Hydrocarbon Processing, Vol. 70, No. 3,

1991, p. 185.

17. Hatch. L. F., The Chemistry of Petrochemical Reactions, Gulf

Publishing Co., Houston, 1955, p. 76.

18. Matar, S., “Synfuels; Hydrocarbons of the Future,” PennWell

Publishing Co., Tulsa, OK, 1982, p. 20.

19. “Petrochemical Handbook,” Hydrocarbon Processing, Vol . 58, No.

11, 1979, p. 122.

20. Cornils, B., Hydroformylation, Oxo Synthesis, Roelen Reaction: New

Synthesis with Carbon Monoxide, Springer Verlag, Berlin, New York,

1980, pp. 1–224.

21. “Petrochemical Handbook,” Hydrocarbon Processing, Vol. 70, No. 3,

1991, p. 149.

22. “Petrochemical Handbook,” Hydrocarbon Processing, Vol. 70, No. 3,

1991, p. 158.

23. “Petrochemical Handbook,” Hydrocarbon Processing, Vol . 70, No. 3,

1991, p. 144.

24. Anderson, K. L. and Brown, T. D., Hydrocarbon Processing, Vol. 55,

No. 8, 1976, pp. 119–122.

Chemicals Based on Propylene 237

Chapter 8 1/22/01 11:05 AM Page 237

CHAPTER NINE

Oleffins and Diolefins-

Based Chemicals

INTRODUCTION

The C

olefins produce fewer chemicals than either ethylene or propy-

lene. However, C

olefins and diolefins are precursors for some signifi-

cant big-volume chemicals and polymers such as methyl-ter-butyl ether,

adiponitrile, 1,4-butanediol, and polybutadiene.

Butadiene is not only the most important monomer for synthetic rub-

ber production, but also a chemical intermediate with a high potential for

producing useful compounds such as sulfolane by reaction with SO

, 1,4-

hutanediol by acetoxylation-hydrogenation, and chloroprene by chlori-

nation-dehydrochlorination.

CHEMICALS FROM n-BUTENES

The three isomers constituting n-butenes are l-butene, cis-2-butene, and

trans-2-butene. This gas mixture is usually obtained from the olefinic C

fraction of catalytic cracking and steam cracking processes after separation

of isobutene (Chapter 2). The mixture of isomers may be used directly for

reactions that are common for the three isomers and produce the same inter-

mediates and hence the same products. Alternatively, the mixture may be

separated into two streams, one constituted of l-butene and the other of cis-

and trans-2-butene mixture. Each stream produces specific chemicals.

Approximately 70% of l-butene is used as a comonomer with ethylene to

produce linear low-density polyethylene (LLDPE). Another use of l-butene

is for the synthesis of butylene oxide. The rest is used with the 2-butenes to

produce other chemicals. n-Butene could also be isomerized to isobutene.

238

Chapter 9 1/22/01 11:07 AM Page 238

This section reviews important reactions leading to various chemicals

from n-butenes.

OXIDATION OF BUTENES

The mixture of n-butenes (1- and 2-butenes) could be oxidized to dif-

ferent products depending on the reaction conditions and the catalyst.

The three commercially important oxidation products are acetic acid,

maleic anhydride, and methyl ethyl ketone.

Due to the presence of a terminal double bond in l-butene, oxidation

of this isomer via a chlorohydrination route is similar to that used

for propylene.

Olefins and Diolefins-Based Chemicals 239

Currently, the major route for obtaining acetic acid (ethanoic acid) is

the carbonylation of methanol (Chapter 5). It may also be produced by

the catalyzed oxidation of n-butane (Chapter 6).

The production of acetic acid from n-butene mixture is a vapor-phase

catalytic process. The oxidation reaction occurs at approximately 270°C

over a titanium vanadate catalyst. A 70% acetic acid yield has been

reported.

The major by-products are carbon oxides (25%) and maleic

anhydride (3%):

Acetic acid may also be produced by reacting a mixture of n-butenes

with acetic acid over an ion exchange resin. The formed sec-butyl

acetate is then oxidized to yield three moles of acetic acid:

Chapter 9 1/22/01 11:07 AM Page 239

The reaction conditions are approximately 100–120°C and 15–25 atmos-

pheres. The oxidation step is noncatalytic and occurs at approximately

200°C and 60 atmospheres. An acetic acid yield of 58% could be

obtained.

By-products are formic acid (6%), higher boiling compounds

(3%), and carbon oxides (28%). Figure 9-1 shows the Bayer AG two-step

process for producing acetic acid from n-butenes.

Acetic acid is a versatile reagent. It is an important esterifying agent

for the manufacture of cellulose acetate (for acetate fibers and lacquers),

vinyl acetate monomer, and ethyl and butyl acetates. Acetic acid is used

to produce pharmaceuticals, insecticides, and dyes. It is also a precursor

for chloroacetic acid and acetic anhydride. The 1994 U.S. production of

acetic acid was approximately 4 billion pounds.

240 Chemistry of Petrochemical Processes

Acetic anhydride (acetyl oxide) is a liquid with a strong offensive

odor. It is an irritating and corrosive chemical that must be handled

with care.

The production of acetic anhydride from acetic acid occurs via the

intermediate formation of ketene where one mole of acetic acid loses one

mole of water:

Ketene further reacts with one mole acetic acid, yielding acetic anhydride:

Acetic anhydride is mainly used to make acetic esters and acetyl sali-

cylic acid (aspirin).

Methyl ethyl ketone MEK (2-butanone) is a colorless liquid similar to

acetone, but its boiling point is higher (79.5°C). The production of MEK

from n-butenes is a liquid-phase oxidation process similar to that used to

Chapter 9 1/22/01 11:07 AM Page 240

Olefins and Diolefins-Based Chemicals 241

Figure 9-1. The Bayer AG two-step process for producing acetic acid from n-butenes.

Chapter 9 1/22/01 11:07 AM Page 241

produce acetaldehyde from ethylene using a Wacker-type catalyst

(PdCl

/CuCl

). The reaction conditions are similar to those for ethylene.

The yield of MEK is approximately 88%:

242 Chemistry of Petrochemical Processes

Methyl ethyl ketone may also be produced by the catalyzed dehydro-

genation of sec-butanol over zinc oxide or brass at about 500°C. The

yield from this process is approximately 95%. MEK is used mainly as a

solvent in vinyl and acrylic coatings, in nitrocellulose lacquers, and in

adhesives. It is a selective solvent in dewaxing lubricating oils where it

dissolves the oil and leaves out the wax. MEK is also used to synthesize

various compounds such as methyl ethyl ketone peroxide, a polymeriza-

tion catalyst used to form acrylic and polyester polymers and methyl

pentynol by reacting with acetylene:

Methyl pentynol is a solvent for polyamides, a corrosion inhibitor,

and an ingredient in the synthesis of hypnotics.

Maleic anhydride, a solid compound that melts at 53°C,is soluble in

water, alcohol, and acetone, but insoluble in hydrocarbon solvents.

The production of maleic anhydride from n-butenes is a catalyzed

reaction occurring at approximately 400–440°C and 2–4 atmospheres. A

special catalyst, constituted of an oxide mixture of molybdenum, vana-

dium, and phosphorous, may be used. Approximately 45% yield of

maleic anhydride could be obtained from this route:

Chapter 9 1/22/01 11:07 AM Page 242

Other routes to maleic anhydride are the oxidation of n-butane, a major

source for this compound (Chapter 6), and the oxidation of benzene

(Chapter 10).

Maleic anhydride is important as a chemical because it polymerizes

with other monomers while retaining the double bond, as in unsaturated

polyester resins. These resins, which represent the largest end use of

maleic anhydride, are employed primarily in fiber-reinforced plastics for

the construction, marine, and transportation industries. Maleic anhydride

can also modify drying oils such as linseed and sunflower.

As an intermediate, maleic anhydride is used to produce malathion, an

important insecticide, and maleic hydrazide, a plant growth regulator:

Olefins and Diolefins-Based Chemicals 243

Maleic anhydride is also a precursor for 1,4-butanediol through an ester-

ification route followed by hydrogenation.

In this process, excess ethyl

alcohol esterifies maleic anhydride to monoethyl maleate. In a second

step, the monoester catalytically esterifies to the diester. Excess ethanol

and water are then removed by distillation. The ethanol-water mixture is

distilled to recover ethanol, which is recycled:

Hydrogenation of diethylmaleate in the vapor phase over a nonprecious

metal catalyst produces diethyl succinate. Successive hydrogenation

produces γ-butyrolactone, butanediol, and tetrahydrofuran.

Chapter 9 1/22/01 11:07 AM Page 243

244 Chemistry of Petrochemical Processes

Selectivity to the coproducts is high, but the ratios of the coproducts may

be controlled with appropriate reactor operating conditions. Figure 9-2 is

a block diagram for the butane diol process.

1,4-Butanediol from buta-

diene is discussed later in this chapter.

Figure 9-2. A block diagram for producing 1,4-butanediol from maleic anhydride.

Butylene oxide, like propylene oxide, is produced by the chlorohydri-

nation of l-butene with HOCl followed by epoxidation. The reaction

conditions are similar to those used for propylene:

CH=CH

+ HOCl

CHOHCH

Butylene chlorohydrin

Chapter 9 1/22/01 11:07 AM Page 244

Olefins and Diolefins-Based Chemicals 245

Butylene oxide may be hydrolyzed to butylene glycol, which is used to

make plasticizers. 1,2-Butylene oxide is a stabilizer for chlorinated sol-

vents and also an intermediate in organic synthesis such as in surfactants

and pharmaceuticals.

Hydration of n-Butenes (sec-Butanol [CH

CHOHCH

])

sec-Butanol (2-butanol, sec-butyl alcohol), a liquid, has a strong charac-

teristic odor. Its normal boiling point is 99.5°C, which is near water’s. The

alcohol is soluble in water but less so than isopropyl and ethyl alcohols.

sec-Butanol is produced by a reaction of sulfuric acid with a mixture

of n-butenes followed by hydrolysis. Both 1-butene and cis- and trans-2-

butenes yield the same carbocation intermediate, which further reacts

with the HSO

or SO

ions, producing a sulfate mixture:

The sulfation reaction occurs in the liquid phase at approximately 35°C.

An 85 wt% alcohol yield could be realized. The reaction is similar to the

sulfation of ethylene or propylene and results in a mixture of sec-butyl

hydrogen sulfate and di-sec-butyl sulfate. The mixture is further

hydrolyzed to sec-butanol and sulfuric acid:

The only important by-product is di-sec-butyl ether, which may be recovered.

The major use of sec-butanol is to produce MEK by dehydrogenation,

as mentioned earlier. 2-Butanol is also used as a solvent, a paint remover,

and an intermediate in organic synthesis.

Isomerization of n-Butenes

n-Butene could be isomerized to isobutene using Shell FER catalyst

which is active and selective. n-Butene mixture from steam cracker or

Chapter 9 1/22/01 11:07 AM Page 245

246 Chemistry of Petrochemical Processes

FCC after removal of C

olefins via selective hydrogenation step passes

to the isomerization unit. It has been proposed that after the formation of

a butyl carbocation, a cyclopropyl carbocation is formed which gives a

primary carbenium ion that produces isobutene

=CH—CH

—CH

—CH=CH—CH

[CH

—CH—CH

—CH

]

}

H H

\ /

C——C

/ \

H H

\ /

C——C

/ \

H H

r [CH

—C—CH

] r Isobutene + H

METATHESIS OF OLEFINS

Metathesis is a catalyzed reaction that converts two olefin molecules

into two different olefins. It is an important reaction for which many

mechanistic approaches have been proposed by scientists working in the

fields of homogenous catalysis and polymerization.

5, 6

One approach is

the formation of a fluxional five-membered metallocycle. The interme-

diate can give back the starting material or the metathetic products via a

concerted mechanism:

Another approach is a stepwise mechanism that involves the initial for-

mation of a metal carbene followed by the formation of a four-membered

metallocycle species:

Chapter 9 1/22/01 11:07 AM Page 246