Lecture 5

General characteristics of the aromatic hydrocarbon content in the oil properties and path selection. Hydrocarbon hybrid and mixed structure. Content in petroleum fractions, their influence on the properties of oil.

Plan of the lecture

1. Characteristics of unsaturated hydrocarbons

2. Recycling of oil - the source of unsaturated hydrocarbons

3. Characteristics of diolefins

1. The chemical properties of unsaturated hydrocarbons. The main structural element defining reactivity alkene is a double bond. The double bond is much shorter and stronger than the single bond. However, the energy of the double bond is less than the energy of the single at 92.1 kJ/mol. Therefore the double bond proceeds readily in two single δ-bond. Consequently alkenes are extremely reactive. The following are the most important reactions in which they enter.

Addition of hydrogen:

RCH = CH₂ + H₂ RCH₂CH₃

The polymerization to low molecular weight oligomers of alkenes (dimers, trimers, tetramers) is an industrial method of producing alkenes C6 -C15, as well as high octane component of gasoline:

4С₃Н₆ С₁₂Н₂₄

Polymerization of alkenes to high molecular weight polymers gives valuable polymeric materials - polyethylene, polypropylene polyisobutylene.

And the dehydrogenation of isoamylenes formed butylene, 1,3-butadiene and isoprene - basic monomers for the synthesis of rubber:

СН₂=СНСН₂СН₃ СН₂=СНСН=СН₂

СН₂ = СНСН(СН₃)₂ → СН₂ = СНС(СН₃) = СН₂

Chlorination and hydrochlorination of ethylene and propylene are important processes for preparing certain intermediates and solvents.

Alkylation. The term usually refers to the alkylation of olefin to join the branched hydrocarbon chain. Branched hydrocarbon typically is isobutane, and olefins, propylene and butylene. Alkylation of branched alkanes alkenes gives a high octane motor fuel:

С₄Н₈ + (СН₃)₃СН изо-С₈Н₁₈

Alkylation of alkenes monocyclic arenes get alkylbenzenes:

C_nH_2n + C₆H₆ C_nH_2n+1C₆H₅

Alkylbenzenes are valuable raw materials base organic synthesis.

When attached to the sulfuric acid higher alkenes (sulphation) formed acidic sulfuric acid esters - alkylsulphates used for detergents:

OSO₂OH

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СНз(СН₂)_nСН = СН₂ + H₂SO₄ → СН₃(СН₂)_nСНСН₃

The reaction of alkenes with carbon monoxide and hydrogen in the presence of a cobalt catalyst (oxo synthesis) is important for the production of aldehydes:

СН₂ = СН₂ + СО + Н₂ → СН₃СН₂СНО

Further reduction of the aldehyde produces the corresponding primary alcohols.

2. Unsaturated hydrocarbons contained in the liquid product of thermal and catalytic refining. Thus, the content of unsaturated compounds in gasoline is% petrol liquid phase thermal cracking - 30-35; gasoline steam cracking 40 -45; gasoline catalytic cracking≈ 10.

The first four terms homolytic number of alkenes (C 1 -C 4) - gases. C5 -C17 - alkenes are liquid higher molecular weight alkenes - solids.

In industrial processes of petroleum refining obtained alkenes with alkanes in the mixture. Their properties are markedly different, which is used for the separation and isolation of the individual compounds.

Alkenes with straight chain of carbon atoms boil at higher temperatures than their branched chain isomers. Moving the center of the double bond in the molecule causes an increase in the boiling temperature of unsaturated hydrocarbons.

Among unsaturated hydrocarbons in the petrochemical industry the most important are ethylene, propylene, butadiene and benzene. On their basis, produce most of all petrochemicals.

Dominant scale of production and consumption is ethylene. The main method of production of ethylene is pyrolysis of hydrocarbons.

The content of unsaturated compounds in the liquid phase thermal cracking of gas (470-520°C; 5.2 MPa) is approximately 20% (vol.), in the vapor phase thermal cracking of gas (530-600°C, 0.1-0.5 MPa) and pyrolysis (670-900°C, 0.1 MPa) 30-50% (vol.). As follows from the data which presented in Table. 7.30 alkenes include thermal processes dominate ethylene and propylene; in appreciable amounts present butylene and butadiene. In the gas of catalytic cracking content of alkene is up to 25% (vol.) or more. Alkanes have a high content of iso-butane - up to 25% (vol.)

3. In the products of the steam cracking pyrolysis and contains from 5 to 10% (wt.) of dialkadienes. This is mainly conjugated alkadienes (conjugated) double bonds: 1,3-butadiene, 1,3-pentadiene (piperylene) cyclopentadiene.

The most important feature of the compounds with conjugated bonds is their higher reactivity compared with compounds having isolated double bonds. Two conjugated double bonds, in some cases, act as a single system is unsaturated; for example, joining the conjugated bonds usually occurs at the ends of 1.4, and the provisions of 2.3 there is a new double bond:

СН₂ = СНСН = СН₂ Н₂ССlСН = СНСН₂Сl

Only a small portion of butadiene reacts like alkenes:

СН₂ = СНСН = СН₂ Н₂СС1СНС1СН = СН₂

Specific reaction of alkadienes with conjugated bonds is diene synthesis (Diels-Alder reaction). It is believed that this reaction is the basis for the formation of arenes in the thermal processing of alkanes.

To quantify alkadienes used in petroleum condensation reaction of dienes and maleic anhydride.

A very important feature of dienes with conjugated double bonds is the extreme ease of polymerization. In the polymerization of dienes obtained some very long chain:

n СН₂ = СНСН = СН₂ → [ –СН₂СН = СНСН₂ – ]_п

Reactions of this type are based synthetic rubber. The greatest industrial importance are two alkadienes, 1,3-butadiene and its homologue 2-methyl-1,3-butadiene (isoprene).

The control questions

1. What refining processes unsaturated hydrocarbons are formed?

2. Which of the unsaturated hydrocarbons are the most important in the petrochemical industry?

3. The main method of ethylene production

4. What kind of reaction is used for the quantitative determination of alkadienes in petroleum products?