Matar Sami, Hatch Lewis F. Chemistry of petrochemical processes

Подождите немного. Документ загружается.

Alkylation of benzene using alpha olefins produces linear alkylbenzenes,

which are further sulfonated and neutralized to linear alkylbenzene

sulfonates (LABS). These compounds constitute, with alcohol ethoxy-

sulfates and ethoxylates, the basic active ingredients for household deter-

gents. Production of LABS is discussed in Chapter 10.

Alpha olefins could also be carbonylated in presence of an alcohol

using a cobalt catalyst to produce esters:

RCH=CH

+ CO + RvOH

RCH

COORv

Transesterification with penterithritol produces penterithritol esters and

releases the alcohol.

LINEAR ALCOHOLS

Linear alcohols (C

-C

) are important chemicals for producing vari-

ous compounds such as plasticizers, detergents, and solvents. The pro-

duction of linear alcohols by the hydroformylation (Oxo reaction) of

alpha olefins followed by hydrogenation is discussed in Chapter 5. They

are also produced by the oligomerization of ethylene using aluminum

alkyls (Ziegler catalysts).

The Alfol process (Figure 7-7) for producing linear primary alcohols

is a four-step process.

In the first step, triethylaluminum is produced by

the reaction of ethylene with hydrogen and aluminum metal:

3 CH

=CH

+ 1

+ Al

(CH

)

In the next step, ethylene is polymerized by the action of triethylalu-

minum at approximately 120°C and 130 atmospheres to trialkylalu-

minum. Typical reaction time is approximately 140 minutes for an

average C

alcohol production:

Chemicals Based on Ethylene 207

Chapter 7 1/22/01 11:04 AM Page 207

208 Chemistry of Petrochemical Processes

Figure 7-7. The Alfol process for making even-numbered straight-chain alpha alcohols.

Chapter 7 1/22/01 11:04 AM Page 208

The final step is the hydrolysis of the trialkoxides with water to the cor-

responding even-numbered primary alcohols. Alumina is coproduced and

is characterized by its high activity and purity:

Chemicals Based on Ethylene 209

Linear alcohols in the range of C

–C

are used to make plasticizers.

Those in the range of C

–C

are used for making biodegradable deter-

gents. They are either sulfated to linear alkylsulfates (ionic detergents)

or reacted with ethylene oxide to the ethoxylated linear alcohols (non-

ionic detergents). The C

–C

alcohols are modifiers for wash and wear

polymers. The higher alcohols, C

–C

, are synthetic lubricants and

mold release agents.

BUTENE-l

A new process developed by Institut Francais du Petrole produces

butene-l (l-butene) by dimerizing ethylene.

A homogeneous catalyst

system based on a titanium complex is used. The reaction is a concerted

coupling of two molecules on a titanium atom, affording a titanium (IV)

cyclic compound, which then decomposes to butene-l by an intramolec-

ular β-hydrogen transfer reaction.

The oxidation of triethylaluminum is carried out between 20–50°C with

“bone dry” air to aluminum trialkoxides.

Chapter 7 1/22/01 11:04 AM Page 209

The Alphabutol process (Figure 7–8) operates at low temperatures

(50–55°C) and relatively low pressures (22–27 atm). The reaction occurs

in the liquid phase without a solvent. The process scheme includes four

sections: the reactor, the co-catalyst injection, catalyst removal, and dis-

tillation. The continuous co-catalyst injection of an organo-basic com-

pound deactivates the catalyst downstream of the reactor withdrawal

valve to limit isomerization of l-butene to 2-butene. Table 7-2 shows the

feed and product quality from the dimerization process.

ALKYLATION USING ETHYLENE

Ethylene is an active alkylating agent. It can be used to alkylate

aromatic compounds using Friedel-Crafts type catalysts. Commercially,

210 Chemistry of Petrochemical Processes

Figure 7-8. A flow diagram of the Institute Francais du Petrole process for pro-

ducing 1-butene from ethylene.

Chapter 7 1/22/01 11:04 AM Page 210

ethylene is used to alkylate benzene for the production of ethyl benzene,

a precursor for styrene. The subject is noted in Chapter 10.

REFERENCES

1. Hydrocarbon Processing, Vol. 78, No. 3, 1999, p. 29.

2. Chemical and Engineering News, July 5, 1999, p. 20.

Chemicals Based on Ethylene 211

Table 7-2

Feed and product quality from dimerization

of ethylene to 1-butene

Feed, polymer grade ethylene:

Ethylene, vol% 99.90 min

Ethane + methane, vol% 0.10 max

Impurities, max.

Methane, ppmv 250

and heavier, ppmv 10

Acetylene, H

, H

O, methanol, ppmv 5 each

CO, CO

, O

, ppmv 1 each

Sulfur, chlorine, ppmw 1 each

Product, polymerization grade butene-l:

Butene-l, wt % 99.50 min

Other C

s, wt % 0.30 max

Ethane, wt % 0.15 max

Ethylene, wt % 0.05 max

Impurities, max.

olefins, ppmw 50

Ethers (as DME), ppmw 2

Sulfur, chlorine, ppmw 1

Dienes, acetylenics, ppmw 5 each

CO, CO

, O

, H

O, methanol, ppmw 5 each

By-product, C

cut:

3-Methyl 1-pentene, wt % 23.0

1-Hexene, wt % 5.8

2-Ethyl l-butene, wt % 57.7

Hexadienes, wt % 1.3

Other C

s, wt % 2 5

, wt % 9.7

Properties

Specific gravity, g/cm

0.68

Octane number, RON 95

MON 82

Distillation end point, °C less than 200

Chapter 7 1/22/01 11:04 AM Page 211

3. Matar, S., Mirbach, M. and Tayim, H., Catalysis in Petrochemical

Processes, Kluwer Academic Publishers, Dordrecht, 1989, p. 85.

4. DeMaglie, B. Hydrocarbon Processing, Vol. 55, No. 3, 1976,

pp. 78–80.

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

1991, p. 156.

6. “Olefins Industrial Outlook II,” Chemical Industries Newsletter, SRI

International, Menlo Park, California, July–August 1989, p. 5.

7. Hajjin, J., “Catalytic Cosynthesis Method Developed,” Chemical and

Engineering News, Vol. 70, No. 18, May 4, 1992, pp. 24–25.

8. Brownstein, A. M., Trends in Petrochemical Technology, Tulsa,

Petroleum Publishing Co., 1976, pp. 153–154.

9. Rosen, M. J. “Surfactants: Designing Structure for Performance,”

CHEMTECH, May, 1985, pp. 292–298.

10. Petroleum Refiner, Nov. 1957, pp. 36, 231.

11. Piccolinie R. and Plotkin, J. “Patent Watch” CHEMTECH, April

1999, p. 19

12. Stern, E. W., Catal. Rev., Vol. 73, No. 1, 1967.

13. Hatch, L. F. and Matar, S., “Chemicals from Ethylene,” Hydrocarbon

Processing, Vol. 57, No. 4, 1978, pp. 155–166.

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

1991 p. 192.

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

1991 p. 150.

16. Chemical and Engineering News, July 5, 1999, p. 38.

17. Herron, S., Chemical and Engineering News, July 18, 1994, p. 156.

18. “Petrochemical Handbook,” Hydrocarbon Processing, Vol. 54, No.

11, 1975, p. 110.

19. Oil And Gas Journal, May 26, 1975, pp. 103–108.

20. Commereuc, D. et al., “Dimerize Ethylene to Butene-l,” Hydrocarbon

Processing, Vol. 63, No. 11, 1984, p. 118.

21. Hennico, A. et al., “Butene-l Is Made from Ethylene,” Hydrocarbon

Processing, Vol. 69, No. 3, 1990, pp. 73–75.

212 Chemistry of Petrochemical Processes

Chapter 7 1/22/01 11:04 AM Page 212

CHAPTER EIGHT

Chemicals Based on Propylene

INTRODUCTION

Propylene, “the crown prince of petrochemicals,” is second to ethyl-

ene as the largest-volume hydrocarbon intermediate for the production

of chemicals.

As an olefin, propylene is a reactive compound that can react with

many common reagents used with ethylene such as water, chlorine, and

oxygen. However, structural differences between these two olefins result

in different reactivities toward these reagents. For example, direct oxida-

tion of propylene using oxygen does not produce propylene oxide as

in the case of ethylene. Instead, an unsaturated aldehyde, acrolein, is

obtained. This could be attributed to the ease of oxidation of allylic

hydrogens in propylene. Similar to the oxidation reaction, the direct cat-

alyzed chlorination of propylene produces allyl chloride through substi-

tution of allylic hydrogens by chlorine. Substitution of vinyl hydrogens

in ethylene by chlorine, however, does not occur under normal conditions.

The current chemical demand for propylene is a little over one half

that for ethylene. This is somewhat surprising because the added com-

plexity of the propylene molecule (due to presence of a methyl group)

should permit a wider spectrum of end products and markets. However,

such a difference can lead to the production of undesirable by-products,

and it frequently does. This may explain the relatively limited use of

propylene in comparison to ethylene. Nevertheless, many important

chemicals are produced from propylene.

The 1997 U.S. propylene demand ws 31 billion pounds and most of it

was used to produce polypropylene polymers and copolymers (about 46%).

Other large volume uses are acrylonitrile for synthetic fibers (Ca 13%),

propylene oxide (Ca 10%), cumene (Ca 8%) and oxo alcohols (Ca 7%).

213

Chapter 8 1/22/01 11:05 AM Page 213

Figure 8-1 shows the important chemicals based on propylene. The fol-

lowing discusses the chemistry of the production of these chemicals.

OXIDATION OF PROPYLENE

The direct oxidation of propylene using air or oxygen produces

acrolein. Acrolein may further be oxidized to acrylic acid, which is a

monomer for polyacrylic resins.

214 Chemistry of Petrochemical Processes

Figure 8-1. Important chemicals based on propylene.

Chapter 8 1/22/01 11:05 AM Page 214

Ammoxidation of propylene is considered under oxidation reactions

because it is thought that a common allylic intermediate is formed in both

the oxidation and ammoxidation of propylene to acrolein and to acry-

lonitrile, respectively.

The use of peroxides for the oxidation of propylene produces propy-

lene oxide. This compound is also obtained via a chlorohydrination of

propylene followed by epoxidation.

ACROLEIN (CH

=CHCHO)

Acrolein (2-propenal) is an unsaturated aldehyde with a disagreeable

odor. When pure, it is a colorless liquid, that is highly reactive and poly-

merizes easily if not inhibited.

The main route to produce acrolein is through the catalyzed air or oxy-

gen oxidation of propylene.

CH=CH

+ O

=CHCHO + H

O ∆H= –340.5 KJ/mol

Transition metal oxides or their combinations with metal oxides from

the lower row 5a elements were found to be effective catalysts for the

oxidation of propene to acrolein.

Examples of commercially used cata-

lysts are supported CuO (used in the Shell process) and Bi

/MoO

(used in the Sohio process). In both processes, the reaction is carried out

at temperature and pressure ranges of 300–360°C and 1–2 atmospheres.

In the Sohio process, a mixture of propylene, air, and steam is introduced

to the reactor. The hot effluent is quenched to cool the product mixture

and to remove the gases. Acrylic acid, a by-product from the oxidation

reaction, is separated in a stripping tower where the acrolein-acetalde-

hyde mixture enters as an overhead stream. Acrolein is then separated

from acetaldehyde in a solvent extraction tower. Finally, acrolein is dis-

tilled and the solvent recycled.

MECHANISM OF PROPENE OXIDATION

Much work has been invested to reveal the mechanism by which

propylene is catalytically oxidized to acrolein over the heterogeneous

catalyst surface. Isotope labeling experiments by Sachtler and DeBoer

revealed the presence of an allylic intermediate in the oxidation of propy-

lene to acrolein over bismuth molybdate.

In these experiments, propy-

lene was tagged once at C

, another time at C

and the third time at C

Chemicals Based on Propylene 215

Chapter 8 1/22/01 11:05 AM Page 215

The formed acrolein was photochemically degraded to ethylene and

carbon monoxide. It has been found that radioactivity was exclusively

associated with ethylene when propylene tagged with

C at C

was used.

Also, carbon monoxide was found to be free from radioactivity:

216 Chemistry of Petrochemical Processes

When propylene tagged with

C at either C

or C

was oxidized to

acrolein and then degraded, both CH

=CH

and CO were radioactive,

and the ratio of radioactivity was 1.

A proposed mechanism for the oxidation of propylene to acrolein is by a

first step abstraction of an allylic hydrogen from an adsorbed propylene by

an oxygen anion from the catalytic lattice to form an allylic intermediate:

Chapter 8 1/22/01 11:05 AM Page 216