Synthesis of Petrochemicals

8/6/2019 Synthesis of Petrochemicals

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Petrochemical Synthesis

the synthesis of chemical products from petroleum and hydrocarbon gases. Hydrocarbons of

petroleum, natural gases, casinghead gases, and petroleum refining gases are the main raw

materials for the manufacture of the most important high-volume synthetic productsplastics,rubbers and fibers, nitrogen fertilizers, surface-active agents, detergents, lubricants and lubricant

additives, plasticizers, fuels, solvents, and extractants. All these products are widely used in

various branches of industry and in the household, and the development of many new areas of

technology, such as space exploration and atomic power engineering, is related to them.

In the industrially developed countries, petrochemical synthesis has made possible the

establishment of a large and rapidly expanding petrochemical industry. The hydrocarbons of

petroleum and gases, which are readily available, cheaper, and more technologically efficient

raw materials, are replacing other types of raw materials (coal, oil shale, vegetable oil, and

animal fat) in almost all processes of organic synthesis.

Petrochemical synthesis is based on advances in organic chemistry, catalysis, physical chemistry,

and chemical engineering and is related to the extensive study of the composition of petroleum

and the properties of its components. Numerous reactions of organic chemistry, including

pyrolysis, oxidation, alkylation, dehydrogenation and hydrogenation, halogenation,

polymerization, nitration, and sulfonation, are the basis of the processes for converting

hydrocarbon raw materials into finished products. Catalytic reactions are the most important of

these reactions. The preparation of the hydrocarbon raw material and the production of primary

initial hydrocarbons, including alkanes (paraffins), unsaturated hydrocarbons (olefins, dienes,

and acetylene), aromatics, and naphthenes, are of great importance in the production of

petrochemical products. Most of these primary products are converted into derivatives with

functional groups containing oxygen, nitrogen, chlorine, fluorine, sulfur, and other elements.

Alkanes. Alkanes are important because of the large volume of their use in petrochemical

synthesis. The lower gaseous hydrocarbons (methane, ethane, propane, butane, and the pentanes)

and the liquid or solid paraffins (from C 6 to C 40) are used to make various chemical products. The

lower paraffin hydrocarbons are isolated from natural and casinghead gases. Petroleum by-

product gases and gases produced by petroleum stabilization contain C 2-C 5 alkanes in amounts


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from 83 to 97 percent by volume. The ethane-propane fraction, isobutane, N-butane, and pentane

are isolated from the gases. Natural gas containing 9697 percent methane is used as industrial

methane, primarily for the production of ammonia, acetylene, methanol, chlorine derivatives,

carbon disulfide, and hydrocyanic acid. Liquid and solid normal C 6-C40 paraffins are obtained

from products of petroleum refining (gasoline-kerosine, diesel, and oil distillates) by

crystallization upon cooling, by carbamide deparaffination, and by means of molecular sieves.

The refining of paraffin raw materials satisfies the ever-increasing demand of petrochemical

synthesis for unsaturated hydrocarbons (olefins, dienes, and acetylene). The main method for the

production of olefins (ethylene, propylene, and butylenes) is high-temperature pyrolysis of

various raw materials, from ethane and natural gasoline to heavy petroleum fractions and crude

petroleum. Olefins are also obtained as by-products in petroleum refining. Catalytic

dehydrogenation is used for the conversion of butane into butadiene and of isopentane intoisoprene. Butadiene and isoprene are the main monomers used in the production of synthetic

rubbers.

The conversion of paraffin hydrocarbons into producer gas (a mixture of carbon monoxide and

hydrogen) has great industrial importance. The raw material may be natural gases, casinghead

gases, petroleum refining gases, or any petroleum fraction. Low-cost hydrogen, which is

consumed in large quantities for the production of ammonia, for hydrorefining of petroleum

products, and for hydrocracking, is obtained from producer gas. Ammonia is the raw material for

the preparation of fertilizers (ammonium nitrate and urea) and hydrocyanic acid. The two-stage

conversion of methane also yields concentrated carbon monoxide, which is used in many

processes of petrochemical synthesis. Producer gas is widely used in the oxo process, which is

based on the reactions of olefins with carbon monoxide and hydrogen. Methanol, which is the

raw material for the production of formaldehyde, an important product in the manufacture of

plastics, varnishes, and adhesives, is produced from carbon monoxide and hydrogen.

A wide variety of products is produced from paraffins by oxidation, halogenation, nitration, and

sulfonation. Acetic acid is produced in large quantities by direct liquid-phase air oxidation of the

light fractions of direct-distillation gasoline (boiling limits, 30-90C) at 150-210C and 4

meganewtons per sq m (40 technical atmospheres) in the presence of cobalt acetate or

manganese acetate. Liquid-phase air oxidation of solid normal paraffins to higher fatty acids


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(C10-C20) is a large-scale process. The oxidation of N-paraffins (C 10-C 20) is used in industry for

the production of higher alcohols, which are converted into surface-active agents and detergents

of the alkyl sulfate type.

Halogen derivatives of paraffins are produced on an industrial scale. Methyl chloride, methylene

chloride, chloroform, and carbon tetrachloride are produced from methane. Methylene chloride

and carbon tetrachloride are good solvents. Chloroform is used in the synthesis of

tetrachloroethylene, chlorofluorine derivatives, and the valuable monomer tetrafluoroethylene.

Chlorination of ethane yields hexachloroethane and other chloro derivatives. Chloroparaffin-40

(about 40 percent CI), a product of chlorination of solid paraffins, is used as a plasticizer;

chloroparaffin-70 (about 70 percent CI) is used for the impregnation of fire-resistant paper and

fabrics. Products of the complete fluorination of narrow fractions of kerosine and gas oil arevaluable lubricants and hydraulic fluids with high thermal and chemical stability. They can

perform for extended periods at 250-300C in highly aggressive media. Freonschlorofluorine

derivatives of methane and ethaneare used as refrigerants. A mixture of nitroparaffins is

obtained by nitration with nitric acid of propane and paraffins that boil above 160-180C. Such

mixtures are used as solvents and intermediates in the production of nitro alcohols, amino

alcohols, and explosives. Surface-active agents of the alkylsulfonate type are obtained by

sulfochlorination and sulfoxidation of kerosine fractions and N -paraffins from C 12 to C 20.

Unsaturated hydrocarbons . Because of their great reactivity, unsaturated hydrocarbons are

widely used in petrochemical synthesis. Many products are synthesized from olefins, diene

hydrocarbons, and acetylene.

OLEFINS. Ethylene occupies first place among the olefins in terms of industrial use. Propylene

and butenes are being used in increasing quantities. The most important higher olefins are

straight-chain -olefins obtained by thermal cracking of solid or soft paraffin at about 550C and

by catalytic oligomerization of ethylene using organoaluminum catalysts. Macromolecular

substances such as polyethylene and polypropylene are obtained by polymerization of olefins.

Polyethylene is the plastic produced in greatest quantities. Its production is increasing very

rapidly, and it is widely used in all sectors of industry. The production of vinyl chloride by

oxidative chlorination of ethylene or a mixture of ethylene with acetylene is expanding rapidly.


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Vinyl chloride is widely used for the production of many polymer materials. Polyvinyl chloride

is used for making films and tubes.

Ethylene oxide and propylene oxide have acquired great importance in petrochemical synthesis;

they are used for the production of glycols, surface-active agents, and ethanolamines. A

considerable quantity of ethylene is consumed in the alkylation of benzene for the production of

styrene and oxidation to acetaldehyde and acetic acid, and also for the production of vinyl acetate

and ethyl alcohol. The oxo process is used for the preparation of alcohols and aldehydes. Many

important solvents and insecticides are produced by chlorination of olefins. Alkyl sulfates and

petroleum product additives are produced from higher olefins.

DIENES. The main monomers in the production of synthetic rubbers are 1, 3-butadiene and 2-

methyl-l, 3-butadiene (isoprene). In industry, butadiene is obtained as a by-product of the

pyrolysis of petroleum products and dehydrogenation of butane, the butylene fraction of the

pyrolysis of petroleum raw material in the production of ethylene. The dehydrogenation of

isoamy-lenes isolated from light cracked gasoline and the dehydrogenation of isopentane

contained in casinghead gases and obtained by the isomerization of N -pentane are promising

methods of producing isoprene. Part of the butadiene produced is used in making chloroprene

and 1, 5, 9-cyclododecatriene, an intermediate in the production of polyamide fibers.

ACETYLENE. Large quantities of acetylene are produced from methane and other paraffin

hydrocarbons by oxidizing pyrolysis, electrocracking, and pyrolysis of various petroleum raw

materials in hydrogen plasma. Dimerization of acetylene in the presence of cuprous chloride

yields vinylacetylene, which is mainly used for the production of chloroprene. Acrylonitrile,

vinyl chloride, and acetaldehyde are also obtained from acetylene, but in these cases acetylene is

gradually being replaced by cheaper ethylene and propylene.

AROMATIC HYDROCARBONS. Benzene, toluene, xylenes, trimethylbenzene andtetramethylbenzene, and naphthalene are valuable raw materials for the synthesis of many

products. Aromatic hydrocarbons are formed by catalytic re-forming of gasoline and ligroin

fractions. Such compounds are obtained in considerable quantities as by-products in the pyrolytic

production of ethylene. Benzene and naphthalene are also obtained by dealkylation of their alkyl


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derivatives in the presence of hydrogen. For this method of producing benzene, alkyl aromatic

hydrocarbons (toluene, xylenes, and higher alkyl derivatives) and pyrolytic gasolines are used.

Heavy re-forming fractions and gas oil obtained by catalytic cracking are raw materials for the

production of naphthalene. Alkylation of benzene by ethylene yields ethylbenzene, and

alkylation by propylene yields isopropylbenzene; ethylbenzene and isopropylbenzene are

converted by dehydrogenation into styrene and -methylstyrene, which are valuable monomers

for the production of rubber. Air oxidation of isopropylbenzene yields phenol and acetone in

large quantities. Alkyl aromatic compounds are the basis for the synthesis of plasticizers,

lubricants, lubricant additives, and surface-active agents. Oxidation of aromatic hydrocarbons

yields terephthalic acid, which is used in the production of fibers (lavsan) , and maleic and

phthalic anhydrides, which are valuable plasticizers and components of heat-resistant plastics,

such as polyimides. Chlorination and nitration of aromatic hydrocarbons are used to a lesser extent. Effective herbicides, solvents, and insulating oils for transformers are produced from

chlorophenols and chloro-naphthalenes. Benzyl chloride is used in the production of a number of

compounds containing the benzyl group (benzyl alcohol and its esters).

Naphthenes . Of the naphthenes, only cyclohexane has acquired great importance in

petrochemical synthesis. Cyclohexane is isolated in small quantities by careful rectification of

the gasoline fractions of petroleum (which contain 17 percent cyclohexane and 15 percent

methylcyclopentane). Methylcyclo-pentane is converted into cyclohexane by isomerization with

aluminum chloride. The industrial demand for cyclohexane is satisfied mainly by hydrogenation

of benzene in the presence of a catalyst. Oxidation of cyclohexane by atmospheric oxygen yields

cyclohexanone and adipic acid, which are used in the synthesis of synthetic polyamide fibers

(kapron and nylon).

Adipic acid and the other dicarboxylic acids obtained in the oxidation of cyclohexane are used

for the preparation of esters that serve as lubricants and plasticizers. Cyclohexanone is used as a

solvent, and also as a camphor substitute.

A great deal of attention is being devoted to the development of microbiological synthesis using

petroleum raw material. Concentrates containing protein and vitamins are produced from

paraffin hydrocarbons and are used in feeding livestock.


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Synthesis of Petrochemicals