Matar Sami, Hatch Lewis F. Chemistry of petrochemical processes

Подождите немного. Документ загружается.

HEXAMETHYLENEDIAMINE (H

N-(CH

)

-NH

)

Hexamethylenediamine (1,6-hexanediamine) is a colorless solid, sol-

uble in both water and alcohol. It is the second monomer used to produce

nylon 6/6 with adipic acid or its esters.

The main route for the production of hexamethylene diamine is the

liquid-phase catalyzed hydrogenation of adiponitrile:

NC—(CH

)

—CN + 4H

N—(CH

)

—NH

The reaction conditions are approximately 200°C and 30 atmospheres

over a cobalt-based catalyst.

ADIPIC ACID (HOOC(CH

)

COOH)

Adipic acid may be produced by a liquid-phase catalytic carbonylation

of butadiene.

A catalyst of RhCl

and CH

I is used at approximately

220°C and 75 atmospheres. Adipic acid yield is about 49%. Both α-gul-

taric acid (25%) and valeric acid (26%) are coproduced:

=CH—CH=CH

+ 2CO + 2H

HOOC(CH

)

COOH

BASF is operating a semicommercial plant for the production of adipic

acid via this route.

A new route to adipic acid occurs via a sequential

carbonylation, isomerization, hydroformylation reactions.

The follow-

ing illustrates these steps:

=CH–CH= CH

+ CO + CH

CH=CH–CH

COCH

OOO

|| || ||

CH=CHCH

COCH

+ 2CO + 3H

C(CH

)

COCH

+ H

Olefins and Diolefins-Based Chemicals 257

Chapter 9 1/22/01 11:07 AM Page 257

OO OO

|| || || ||

–C–(CH

)

–C–OCH

+ O

HOC(CH

)

–COCH

Hydr.

Adipic

acid

The main process for obtaining adipic acid is the catalyzed oxidation of

cyclohexane (Chapter 10).

BUTANEDIOL (HO-(CH

)

-OH)

The production of 1,4-butanediol (1,4-BDO) from propylene via the

carbonylation of allyl acetate is noted in Chapter 8. 1,4-Butanediol from

maleic anhydride is discussed later in this chapter. An alternative route

for the diol is through the acetoxylation of butadiene with acetic acid fol-

lowed by hydrogenation and hydrolysis.

The first step is the liquid phase addition of acetic acid to butadiene.

The acetoxylation reaction occurs at approximately 80°C and 27 atmos-

pheres over a Pd-Te catalyst system. The reaction favors the 1,4-addition

product (1,4-diacetoxy-2-butene). Hydrogenation of diacetoxybutene at

80°C and 60 atmospheres over a Ni/Zn catalyst yields 1,4-diacetoxybu-

tane. The latter compound is hydrolyzed to 1,4-butanediol and acetic acid:

258 Chemistry of Petrochemical Processes

Acetic acid is then recovered and recycled. Butanediol is mainly used for

the production of thermoplastic polyesters.

Chloroprene (2-chloro 1,3-butadiene), a conjugated non-hydrocarbon

diolefin, is a liquid that boils at 59.2°C and while only slightly soluble

in water it is soluble in alcohol. The main use of chloroprene is to poly-

merize it to neoprene rubber.

Chapter 9 1/22/01 11:07 AM Page 258

Butadiene produces chloroprene through a high temperature chlorina-

tion to a mixture of dichlorobutenes, which is isomerized to 3,4-dichloro-

l-butene. This compound is then dehydrochlorinated to chloroprene:

Olefins and Diolefins-Based Chemicals 259

Sulfolane (tetramethylene sulfone) is produced by the reaction of

butadiene and sulfur dioxide followed by hydrogenation:

Optimum temperature for highest sulfolene yield is approximately 75°C.

At approximately 125°C, sulfolene decomposes to butadiene and SO

This simple method could be used to separate butadiene from a mixture

of C

olefins because the olefins do not react with SO

Sulfolane is a water-soluble biodegradable and highly polar com-

pound valued for its solvent properties. Approximately 20 million

pounds of sulfolane are consumed annually in applications that include

delignification of wood, polymerization and fiber spinning, and electro-

plating bathes.

It is a solvent for selectively extracting aromatics from

reformates and coke oven products.

CYCLIC OLIGOMERS OF BUTADIENE

Butadiene could be oligomerized to cyclic dienes and trienes using

certain transition metal complexes. Commercially, a mixture of TiCl

and Al

)

is used that gives predominantly cis, trans, trans-

1,5,9-cyclododecatriene along with approximately 5% of the dimer

1,5-cyclooctadiene

Chapter 9 1/22/01 11:07 AM Page 259

1,5,9-Cyclododecatriene is a precursor for dodecane-dioic acid through a

hydrogenation step followed by oxidation. The diacid is a monomer for

the production of nylon 6/12.

Cyclododecane from cyclododecatriene may also be converted to the

lactam, which is polymerized to nylon 12.

REFERENCES

1. Chemical and Engineering News, Oct. 25, 1993, p. 30.

2. Brockhaus, R., German Patent, 1279, 011, 1968.

3. “Petrochemical Handbook,” Hydrocarbon Processing, Vol. 58, No. 11,

1979, p. 120.

4. Harris, N. and Tuck, M. W., “Butanediol via Maleic Anhydride,”

Hydrocarbon Processing, Vol. 69, No. 5, 1990, pp. 79–82.

5. Grubbs, R. H. et al., J. Am. Chem. Soc., Vol. 98, 1976, p. 3478.

6. Katz, T. J. Adv. Organomet. Chem., Vol. 16, 1977, p. 283.

7. Herisson, J. L. and Chaurin, Y., Makromol. Chem., 141, 1970, p. 161;

Tsonis, C. P., Journal of Applied Polymer Science, Vol. 26, 1981,

pp. 3525–3536.

8. Stinson, S., “New Rhenium Catalyst for Olefin Chemistry,” Chemical

and Engineering News, Vol. 70, No. 6, 1992, p. 29.

9. Cosyns, J. et al., Hydrocarbon Processing, Vol. 77, No. 3, 1998, p. 61.

10. Patton, P. A. and McCarthy, T. J., “Running the Impossible Reaction,

Metathesis of Cyclohexene,” CHEMTECH, July 1987, pp. 442–446.

11. Amigues, P. et al., “Propylene From Ethylene and Butene-2,”

Hydrocarbon Processing, Vol. 69, No. 10, 1990, pp. 79–80.

12. Nierlich, F. “Oligomerize for Better Gasoline,” Hydrocarbon

Processing, Vol. 71, No. 2, 1992, pp. 45–46.

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

1991, p. 166.

14. Hucknall, D. J., “Selective Oxidation of Hydrocarbons,” Academic

Press Inc., New York 1974, pp. 55–69.

15. British Patent, 1, 182, 273 to Tejin.

16. West German Offen, 2, 354, 331 to Atlantic Richfield.

17. Unzelman, G. H., “U.S. Clean Air Act Expands Role for Oxygenates,”

Oil and Gas Journal, April 15, 1991.

18. Iborra, M., Izquierdo J. F., Tejero, J. and Cunil, F., CHEMTECH,

Vol. 18, No. 2, 1988, pp. 120–122.

260 Chemistry of Petrochemical Processes

Chapter 9 1/22/01 11:07 AM Page 260

19. Abraham, O. C. and Prescott, G. F., “Make Isobutene from TBA,”

Hydrocarbon Processing, Vol. 71, No. 2, 1992, p. 51.

20. Hatch, L. F., The Chemistry of Petrochemical Reactions, Houston,

Gulf Publishing Co., 1955, p. 149.

21. Belgian Patent 770, 615 to BASF, 1971.

22. CHEMTECH, April 1999, p. 19.

23. Heaton, C. A., ed. “An Introduction to Industrial Chemistry,” 2nd ed.

Blacki and Son Ltd., London, 1991, p. 395.

24. Parshall, G. W. and Nuget, W. A., “Functional Chemicals via

Homogeneous Catalysis,” CHEMTECH, May 1988, pp. 314–320.

25. Chemical and Engineering News, Sept 5, 1994, p. 26.

Olefins and Diolefins-Based Chemicals 261

Chapter 9 1/22/01 11:07 AM Page 261

CHAPTER TEN

Chemicals Based on Benzene,

Toluene, and Xylenes

INTRODUCTION

The primary sources of benzene, toluene, and xylenes (BTX) are refin-

ery streams, especially from catalytic reforming and cracking, and pyrol-

ysis gasoline from steam cracking and from coal liquids. BTX and ethyl

benzene are extracted from these streams using selective solvents such as

sulfolene or ethylene glycol. The extracted components are separated

through lengthy fractional distillation, crystallization, and isomerization

processes (Chapter 2).

The reactivity of C

, C

aromatics is mainly associated with the

benzene ring. Aromatic compounds in general are liable for electrophilic

substitution. Most of the chemicals produced directly from benzene are

obtained from its reactions with electrophilic reagents. Benzene could be

alkylated, nitrated, or chlorinated to important chemicals that are precur-

sors for many commercial products.

Toluene and xylenes (methylbenzenes) are substituted benzenes.

Although the presence of methyl substituents activates the benzene ring for

electrophilic attack, the chemistry of methyl benzenes for producing com-

mercial products is more related to reactions with the methyl than with the

phenyl group. As an electron-withdrawing substituent (of methane), the

phenyl group influences the methyl hydrogens and makes them more avail-

able for chemical attack. The methyl group could be easily oxidized or

chlorinated as a result of the presence of the phenyl substituent.

REACTIONS AND CHEMICALS OF BENZENE

Benzene (C

) is the most important aromatic hydrocarbon. It is the

precursor for many chemicals that may be used as end products or inter-

262

Chapter 10 1/22/01 11:08 AM Page 262

mediates. Almost all compounds derived directly from benzene are con-

verted to other chemicals and polymers. For example, hydrogenation of

benzene produces cyclohexane. Oxidation of cyclohexane produces

cyclohexanone, which is used to make caprolactam for nylon manufac-

ture. Due to the resonance stabilization of the benzene ring, it is not eas-

ily polymerized. However, products derived from benzene such as

styrene, phenol, and maleic anhydride can polymerize to important com-

mercial products due to the presence of reactive functional groups.

Benzene could be alkylated by different alkylating agents, hydrogenated

to cyclohexane, nitrated, or chlorinated.

The current world benzene capacity is approximately 35 million tons.

The 1994 U.S. production of benzene was about 14.7 million pounds.

The chemistry for producing the various chemicals from benzene is

discussed in this section. Figure 10-1 shows the important chemicals

derived from benzene.

ALKYLATION OF BENZENE

Benzene can be alkylated in the presence of a Lewis or a Bronsted acid

catalyst. Olefins such as ethylene, propylene, and C

–C

alpha olefins

are used to produce benzene alkylates, which have great commercial

value. Alkyl halides such as monochloroparaffins in the C

–C

range

also serve this purpose.

The first step in alkylation is the generation of a carbocation (carbo-

nium ion). When an olefin is the alkylating agent, a carbocation interme-

diate forms.

Chemicals Based on Benzene, Toluene, and Xylenes 263

Carboncations also form from an alkyl halide when a Lewis acid cat-

alyst is used. Aluminum chloride is the commonly used Friedel-Crafts

alkylation catalyst. Friedel-Crafts alkylation reactions have been

reviewed by Roberts and Khalaf:

RCI + AlCl

_ _ _ _ AlCl

–

]

The next step is an attack by the carbocation on the benzene ring,

followed by the elimination of a proton and the formation of a ben-

zene alkylate:

Chapter 10 1/22/01 11:08 AM Page 263

264 Chemistry of Petrochemical Processes

Figure 10-1. Important chemicals based on benzene.

Chapter 10 1/22/01 11:08 AM Page 264

Ethylbenzene (EB) is a colorless aromatic liquid with a boiling point

of 136.2°C, very close to that of p-xylene. This complicates separating it

from the C

aromatic equilibrium mixture obtained from catalytic reform-

ing processes. (See Chapter 2 for separation of C

aromatics). Ethylben-

zene obtained from this source, however, is small compared to the syn-

thetic route.

The main process for producing EB is the catalyzed alkylation of ben-

zene with ethylene:

Chemicals Based on Benzene, Toluene, and Xylenes 265

Many different catalysts are available for this reaction. AlCl

-HCl is

commonly used. Ethyl chloride may be substituted for HCI in a mole-

for-mole basis. Typical reaction conditions for the liquid-phase AlCl

catalyzed process are 40–100°C and 2–8 atmospheres. Diethylbenzene

and higher alkylated benzenes also form. They are recycled and dealky-

lated to EB.

The vapor-phase Badger process (Figure 10-2), which has been com-

mercialized since 1980, can accept dilute ethylene streams such as those

produced from FCC off gas.

A zeolite type heterogeneous catalyst is

used in a fixed bed process. The reaction conditions are 420°C and

200–300 psi. Over 98% yield is obtained at 90% conversion.

4,5

Poly-

ethylbenzene (polyalkylated) and unreacted benzene are recycled and

join the fresh feed to the reactor. The reactor effluent is fed to the ben-

zene fractionation system to recover unreacted benzene. The bottoms

Chapter 10 1/22/01 11:08 AM Page 265

containing ethylbenzene and heavier polyalkylates are fractionated in

two columns. The first column separates the ethylbenzene product, and

the other separates polyethylbenzene for recycling. An optimization

study of EB plants by constraint control was conducted by Hummel et al.

They concluded that optimum operation could be maintained through a

control system when conditions such as catalyst activity and heat trans-

fer coefficients vary during operation.

Ethylbenzene is mainly used to produce styrene. Over 90% of the 12.7

billion pounds of EB produced in the U.S. during 1998 was dehydro-

genated to styrene.

266 Chemistry of Petrochemical Processes

Figure 10-2. The Badger process for producing ethylbenzene:

(1) reactor, (2)

fractionator (for recovery of unreacted benzene), (3) EB fractionator, (4) poly-

ethylbenzene recovery column.

Styrene (vinylbenzene) is a liquid (b.p. 145.2°C) that polymerizes

easily when initiated by a free radical or when exposed to light. The

1998 U.S. production of styrene was approximately 11 billion pounds.

Dehydrogenation of ethylbenzene to styrene occurs over a wide

variety of metal oxide catalysts. Oxides of Fe, Cr, Si, Co, Zn, or their

mixtures can be used for the dehydrogenation reaction. Typical reaction

Chapter 10 1/22/01 11:08 AM Page 266