Matar Sami, Hatch Lewis F. Chemistry of petrochemical processes

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17. Rouchaud, J. and Lutete, B., Industrial and Engineering Chemistry,

Product Research Division, Vol. 7, No. 4, 1968, pp. 266–270.

18. Speight, J. G., The Chemistry and Technology of Petroleum, 2nd Ed.,

Marcel Dekker, Inc. New York, 1991, p. 344.

19. Chemical Industries News Letter, April–June, 1998, p.8.

20. Marer, A. and Hussain, M. M., Second Arab Conference on

Petrochemicals, United Arab Emirates, paper No. 6 (p. 3) March

15–23, 1976.

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

11, 1979, p. 186.

22. “Petrochemical Handbook,” Hydrocarbon Processing, Vol. 64, No.

11, 1985, p. 167.

23. Kent, J. A. (ed.) Riegel’s Handbook of Industrial Chemistry, 8th Ed.,

Van Nostrand Reinhold Co. New York, 1983, p. 685.

Ethane and Higher Paraffins-Based Chemicals 187

Chapter 6 1/22/01 11:02 AM Page 187

CHAPTER SEVEN

Chemicals Based on Ethylene

INTRODUCTION

Ethylene is sometimes known as the “king of petrochemicals” because

more commercial chemicals are produced from ethylene than from any

other intermediate. This unique position of ethylene among other hydro-

carbon intermediates is due to some favorable properties inherent in the

ethylene molecule as well as to technical and economical factors. These

could be summarized in the following:

• Simple structure with high reactivity.

• Relatively inexpensive compound.

• Easily produced from any hydrocarbon source through steam crack-

ing and in high yields.

• Less by-products generated from ethylene reactions with other com-

pounds than from other olefins.

Ethylene reacts by addition to many inexpensive reagents such as

water, chlorine, hydrogen chloride, and oxygen to produce valuable

chemicals. It can be initiated by free radicals or by coordination catalysts

to produce polyethylene, the largest-volume thermoplastic polymer. It

can also be copolymerized with other olefins producing polymers with

improved properties. For example, when ethylene is polymerized with

propylene, a thermoplastic elastomer is obtained. Figure 7-1 illustrates

the most important chemicals based on ethylene.

Global demand for ethylene is expected to increase from 79 million

tons in 1997 to 114 million tons in 2005.

In 1998, the U.S. consumption

of ethylene was approximately 52 billion pounds. Figure 7-2 shows the

breakdown of the 1998 U.S. ethylene consumption.

188

Chapter 7 1/22/01 11:04 AM Page 188

OXIDATION OF ETHYLENE

Ethylene can be oxidized to a variety of useful chemicals. The oxida-

tion products depend primarily on the catalyst used and the reaction con-

ditions. Ethylene oxide is the most important oxidation product of

ethylene. Acetaldehyde and vinyl acetate are also oxidation products

obtained from ethylene under special catalytic conditions.

Chemicals Based on Ethylene 189

Figure 7-1. Major chemicals based on ethylene.

Ethylene oxide (EO) is a colorless gas that liquefies when cooled

below 12°C. It is highly soluble in water and in organic solvents.

Chapter 7 1/22/01 11:04 AM Page 189

Ethylene oxide is a precursor for many chemicals of great commercial

importance, including ethylene glycols, ethanolamines, and alcohol

ethoxylates. Ethylene glycol is one of the monomers for polyesters, the

most widely-used synthetic fiber polymers. The current US production of

EO is approximately 8.1 billion pounds.

Production

The main route to ethylene oxide is oxygen or air oxidation of ethylene

over a silver catalyst. The reaction is exothermic; heat control is important:

190 Chemistry of Petrochemical Processes

Figure 7-2. Breakdown of U.S. 1998 ethylene consumption of 52 billion lb.

LLDPE

11%

PVC

15%

HDPE

24%

LDPE

14%

13%

Vinylacetate

Alpha olefins

and linear

alcohols

Styrene

Others

EG = Ethylene glycol

HDPE = High-density polyethylene

LDPE = Low-density polyethylene

LLDPE = Linear low-density polyethylene

PVC = Polyvinyl chloride

Chapter 7 1/22/01 11:04 AM Page 190

A concomitant reaction is the complete oxidation of ethylene to carbon

dioxide and water:

This reaction is highly exothermic; the excessive temperature increase

reduces ethylene oxide yield and causes catalyst deterioration. Over-

oxidation can be minimized by using modifiers such as organic chlorides.

It seems that silver is a unique epoxidation catalyst for ethylene. All

other catalysts are relatively ineffective, and the reaction to ethylene is

limited among lower olefins. Propylene and butylenes do not form epox-

ides through this route.

Using oxygen as the oxidant versus air is currently favored because it

is more economical.

In the process (Figure 7-3), compressed oxygen, ethylene, and recy-

cled gas are fed to a multitubular reactor.

The temperature of oxidation

Chemicals Based on Ethylene 191

Figure 7-3. The Scientific Design Co. Ethylene Oxide process:

(1) reactor,

(2) scrubber, (3,4) CO2 removal, (5) stripper, (6,7) fractionators.

Chapter 7 1/22/01 11:04 AM Page 191

is controlled by boiling water in the shell side of the reactor. Effluent

gases are cooled and passed to the scrubber where ethylene oxide is

absorbed as a dilute aqueous solution. Unreacted gases are recycled.

Epoxidation reaction occurs at approximately 200–300°C with a short

residence time of one second. A selectivity of 70–75% can be reached for

the oxygen based process. Selectivity is the ratio of moles of ethylene

oxide produced per mole of ethylene reacted. Ethylene oxide selectivity

can be improved when the reaction temperature is lowered and the con-

version of ethylene is decreased (higher recycle of unreacted gases).

Derivatives of Ethylene Oxide

Ethylene oxide is a highly active intermediate. It reacts with all com-

pounds that have a labile hydrogen such as water, alcohols, organic acids,

and amines. The epoxide ring opens, and a new compound with a

hydroxyethyl group is produced. The addition of a hydroxyethyl group

increases the water solubility of the resulting compound. Further reaction

of ethylene oxide produces polyethylene oxide derivatives with increased

water solubility.

Many commercial products are derived from ethylene oxide by react-

ing with different reagents. The following reviews the production and the

utility of these chemicals.

Ethylene Glycol (CH

OHCH

OH)

Ethylene glycol (EG) is colorless syrupy liquid, and is very soluble in

water. The boiling and the freezing points of ethylene glycol are 197.2°

and –13.2°C, respectively.

Current world production of ethylene glycol is approximately 15 bil-

lion pounds. Most of that is used for producing polyethylene terephtha-

late (PET) resins (for fiber, film, bottles), antifreeze, and other products.

Approximately 50% of the world EG was consumed in the manufacture

of polyester fibers and another 25% went into the antifreeze.

EG consumption in the US was nearly 1/3 of the world's. The use pat-

tern, however, is different; about 50% of EG is consumed in antifreeze.

The US production of ethylene glycol was 5.55 billion pounds in 1994,

the 30th largest volume chemical.

The main route for producing ethylene glycol is the hydration of eth-

ylene oxide in presence of dilute sulfuric acid (Figure 7-4):

192 Chemistry of Petrochemical Processes

Chapter 7 1/22/01 11:04 AM Page 192

Chemicals Based on Ethylene 193

The hydrolysis reaction occurs at a temperature range of 50–100°C.

Contact time is approximately 30 minutes. Di- and triethylene glycols are

coproducts with the monoglycol. Increasing the water/ethylene oxide

ratio and decreasing the contact time decreases the formation of higher

glycols. A water/ethylene oxide ratio of 10 is normally used to get

approximately 90% yield of the monoglycol. However, the di- and the

triglycols are not an economic burden, because of their commercial uses.

A new route to ethylene glycol from ethylene oxide via the intermedi-

ate formation of ethylene carbonate has recently been developed by

Texaco. Ethylene carbonate may be formed by the reaction of carbon

monoxide, ethylene oxide, and oxygen. Alternatively, it could be

obtained by the reaction of phosgene and methanol.

Ethylene carbonate is a reactive chemical. It reacts smoothly with

methanol and produces ethylene glycol in addition to dimethyl carbonate:

Figure 7-4. The Scientific Design Co. process for producing ethylene glycols from

ethylene oxide:

(1) feed tank, (2) reactor, (3,4,5) multiple stage evaporators, #4

operates at lower pressure than #3, while #5 operates under vacuum, evaporated

water is recycled to feed tank, (6) light ends stripper, (7,8) vacuum distilla-

tion columns.

Chapter 7 1/22/01 11:04 AM Page 193

The reaction occurs at approximately 80–130°C using the proper cat-

alyst. Many catalysts have been tried for this reaction, and there is an

indication that the best catalyst types are those of the tertiary amine and

quaternary ammonium functionalized resins.

This route produces ethyl-

ene glycol of a high purity and avoids selectivity problems associated

with the hydrolysis of ethylene oxide.

The coproduct dimethyl carbonate is a liquid soluble in organic sol-

vents. It is used as a specialty solvent, a methylating agent in organic

synthesis, and a monomer for polycarbonate resins. It may also be con-

sidered as a gasoline additive due to its high oxygen content and its high

octane rating.

Alternative Routes to Producing Ethylene Glycol

Ethylene glycol could also be obtained directly from ethylene by two

methods, the Oxirane acetoxylation and the Teijin oxychlorination

processes. The production of ethylene glycol from formaldehyde and

carbon monoxide is noted in Chapter 5.

In the Oxirane process, ethylene is reacted in the liquid phase with

acetic acid in the presence of a TeO

catalyst at approximately 160° and

28 atmospheres.

The product is a mixture of mono- and diacetates of

ethylene glycol:

The acetates are then hydrolyzed to ethylene glycol and acetic acid. The

hydrolysis reaction occurs at approximately 107–130°C and 1.2 atmos-

pheres. Acetic acid is then recovered for further use:

194 Chemistry of Petrochemical Processes

Chapter 7 1/22/01 11:04 AM Page 194

A higher glycol yield (approximately 94%) than from the ethylene oxide

process is anticipated. However, there are certain problems inherent in

the Oxirane process such as corrosion caused by acetic acid and the

incomplete hydrolysis of the acetates. Also, the separation of the glycol

from unhydrolyzed monoacetate is hard to accomplish.

The Teijin oxychlorination, on the other hand, is considered a modern

version of the obsolete chlorohydrin process for the production of ethyl-

ene oxide. In this process, ethylene chlorohydrin is obtained by the cat-

alytic reaction of ethylene with hydrochloric acid in presence of

thallium(III) chloride catalyst:

=CH

+ TlCl

+ H

ClCH

OH + TlCl + HCl

Ethylene chlorohydrin is then hydrolyzed in situ to ethylene glycol.

Catalyst regeneration occurs by the reaction of thallium(I) chloride

with copper(II) chloride in the presence of oxygen or air. The formed

Cu(I) chloride is reoxidized by the action of oxygen in the presence of HCI:

T1C1 + 2CuC1

TICl

+ Cu

+ 2HCl +

2CuCl

+ H

The overall reaction is represented as:

=CH

+ H

O +

HOCH

Ethoxylates

The reaction between ethylene oxide and long-chain fatty alcohols or

fatty acids is called ethoxylation. Ethoxylation of C

-C

linear alcohols

and linear alkylphenols produces nonionic detergents. The reaction with

alcohols could be represented as:

Chemicals Based on Ethylene 195

Chapter 7 1/22/01 11:04 AM Page 195

The solubility of the product ethoxylates can be varied according to the

number of ethylene oxide units in the molecule. The solubility is also a

function of the chain-length of the alkyl group in the alcohol or in the

phenol. Longer-chain alkyl groups reduce water solubility. In practice,

the number of ethylene oxide units and the chain-length of the alkyl

group are varied to either produce water-soluble or oil-soluble surface

active agents. Surfactants properties and micelle formation in polar and

nonpolar solvents have been reviewed by Rosen.

Linear alcohols used for the production of ethoxylates are produced by

the oligomerization of ethylene using Ziegler catalysts or by the Oxo

reaction using alpha olefins.

Similarly, esters of fatty acids and polyethylene glycols are produced

by the reaction of long-chain fatty acids and ethylene oxide:

The C

-C

fatty acids such as oleic, palmitic, and stearic are usually

ethoxylated with EO for the production of nonionic detergents and emulsifiers.

Ethanolamines

A mixture of mono-, di-, and triethanolamines is obtained by the reac-

tion between ethylene oxide (EO) and aqueous ammonia. The reaction

conditions are approximately 30–40°C and atmospheric pressure:

196 Chemistry of Petrochemical Processes

The relative ratios of the ethanolamines produced depend principally on

the ethylene oxide/ammonia ratio. A low EO/NH

ratio increases

monoethanolamine yield. Increasing this ratio increases the yield of

di-and triethanolamines. Table 7-1 shows the weight ratios of ethanola-

mines as a function of the mole ratios of the reactants.

Ethanolamines are important absorbents of acid gases in natural gas

treatment processes. Another major use of ethanolamines is the produc-

tion of surfactants. The reaction between ethanolamines and fatty acids

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