The study of the structure of organic compounds, the chemical properties shown by them in the reactions, allow the release of various types of products and goods from the same raw materials. The processing of produced hydrocarbons solves many problems. To the question: “How to get alkane from alkane?” Chemical science and oil cracking practice give comprehensive answers. Let us examine the problem of the relationship between different classes of hydrocarbons, as well as their derivatives. We will focus on industrial methods for processing carbon-containing raw materials.
Genetic affinity of organic substances
In the early stages of the study and production of hydrocarbons and derivatives, it seemed to chemists that these groups were isolated from each other. Gradually accumulated information shedding light on the genetic relationship of the main classes of substances. The main efforts were aimed at finding ways to change the structure, increase the frequency of communication. The most important problems of theoretical research and experimentation:
- how to get alkane from alkane;
- how to process coal, crude oil and natural gas;
- how to carry out dehydrogenation of saturated hydrocarbons;
- how to get alkine from alkane (acetylene).
Researchers and practitioners have become convinced that there are many reciprocal transitions from one hydrocarbon to another.
The practical significance of the genetic relationships of the main types of compounds
The unity of hydrocarbon compounds has been proven in the process of establishing organic chemistry as a science and industry. Russian and Soviet organic chemists made a significant contribution to the development of this problem — how to get alkane from alkane. Many reactions-transformations used for these purposes are catalytic processes and are carried out using complex technologies. Close bonds and mutual transformations of organic compounds are used to solve a variety of practical problems, including:
- obtaining from one type of raw material of different types of substances;
- production of complex products from simple compounds and vice versa;
- production of various goods in high demand;
- saving heavily depleted natural hydrocarbon resources;
- rational use of oil and gas bearing strata, coal tar, oil shale, peat.
Composition of natural carbon sources
Hydrocarbons of all types are found in nature in significant quantities. They serve as starting materials for the processing and preparation of organic compounds of various compositions. The most important sources of alkanes and alkenes:
- Natural gas. The content of saturated methane hydrocarbon in different deposits reaches 80–98%. Other compounds: nitrogen, carbon dioxide, ethane, propane, butane.
- Oil. The natural mixture of isomeric hydrocarbons from different fields differs in composition. In some types of "black gold" alkanes prevail, while others consist of cycloparaffins and arenas. Domestic associated petroleum gases also contain paraffins.
- Coke. The production of coal necessary for metallurgy is accompanied by the production of coal tar containing over 400 components, the main of which are arenas.
- Plant and food raw materials are a large and diverse group, which includes wood, seeds and fruits of industrial crops, animal fats.
Possible transitions between organic compounds
In the composition of deposits of "black gold" are often cycloalkanes or naphthenes. Processing of raw materials gives the limiting cyclic hydrocarbons containing 5–7 C atoms in the ring, they have the greatest practical value. How to get cycloalkane from alkane if naphthenes are depleted? To obtain saturated cyclic hydrocarbons from saturated acyclic compounds, a dehydrocyclization method is used. Chains of 4 or more C atoms are closed, a stable cycle occurs. Other typical conversions of organic substances can be reflected in simple schemes:
- Oil → hydrocarbons → alkanes → carboxylic acids.
- Natural gas → saturated hydrocarbons → carboxylic acids.
- Coal → hydrocarbons → alkanes → unsaturated hydrocarbons → polymers.
- Oil → hydrocarbons → arenas → benzene → isopropyl-benzene → acetone, phenol.
- Natural gas → unsaturated hydrocarbons → ethanol.
- Coal → methanol.
- Oil → hydrocarbons → alkenes → butadiene and isoprene.
Let us consider in more detail what chemical compounds can be obtained due to the genetic relationship of organic substances.
How to get alkane from alkane
In industry, almost all types of saturated hydrocarbons are obtained from oil and gas raw materials. Oil refining is a modern method for producing alkanes from alkanes:
A) Liquid saturated hydrocarbons gives direct distillation of oil (low yield of target products).
B) Thermal and catalytic cracking of oil is used to increase the percentage of light fractions, improve the quality of the resulting hydrocarbons (gasoline, kerosene). Hexadecane is present in the oil fraction of the oil, which upon decomposition produces dodecane and butylene. Dodecane already in the kerosene fraction undergoes further decomposition, from it the saturated hydrocarbon nonane and propene (alkene) are obtained. Continued cracking can lead to the formation of heptane and ethylene.
Isomerization and alkylation
The catalytic isomerization reactions make it possible to obtain branched alkanes from normal alkanes: 3— (2) 3 — 3 → (3) 2 — 2 — 3. The product of this process is isopentane. Normal butane, which is contained in cracking gases, is converted to isobutane in the catalytic isomerization reaction. The resulting product can be alkylated with isobutylene in the presence of a catalyst and get isooctane - a high-quality fuel. If we take ethylene as the alkylating agent, then in the reaction with isobutane, synthetic fuel neohexane is obtained.
How to get alkene and alkadiene from alkane
In industry, unsaturated acyclic hydrocarbons with one double bond are obtained by cracking oil. At high temperatures, alkanes decompose (pyrolysis). Alkenes are isolated from the total mass of intermediate and final reaction products. Ethylene is obtained by dehydrogenation of ethane on a nickel catalyst: C2H6 → C2H4 + H2 ↑. Butane under such conditions gives 2-butene, while ethane and ethylene are formed. Dehydrogenation allows you to find solutions to the problem of how to get alkadiene from alkane. With the stepwise removal of two hydrogen molecules from a hydrocarbon of 4 carbon atoms, the following transformations occur: butane → butene → butadiene. The final product is important for the production of synthetic rubber. Similar to butadiene, another polymer is obtained that mimics the valuable qualities of a natural analogue: isopentane → isoprene → isoprene rubber.
How to get acetylene from alkane
A hydrocarbon with one triple bond - acetylene - is very important in the industrial sector, construction and other areas of economic activity. The oldest way to produce this simplest alkyne is through the action of water on solid pieces of calcium carbide. This method was replaced by cracking of natural gas. Now, in the chemical industry, they know how to get alkine from alkane at the lowest cost. In special technological devices at high temperature or under the influence of an electric discharge, methane is dehydrogenated - the predominant natural gas substance: 2CH4 → HC →CH + 3H2. Acetylene is widely used, acetaldehyde is obtained from it, which is then used in the production of acetic acid, artificial resins, plastics, synthetic fibers, rubbers and rubbers.
How to get arenas from saturated hydrocarbons
From paraffins, transformation chains lead to benzene and its derivatives. The aromatization process was studied by Russian and Soviet chemists in the 20th century. The essence of their work on the topic “How to get benzene and its homologues from alkane” boils down to the dehydrocyclization of hexane, heptane and other saturated hydrocarbons: 614 → 66 + 42; 716 → 65 — 3 + 42. Another way is to synthesize cycloparaffins from acyclic hydrocarbons followed by dehydrogenation: hexane → cyclohexane → benzene.
How to get ethyl and other alcohols from alkanes
In ancient times, they did not reflect on the question “How to get alcohol from alkane?”, Our ancestors used only the method of alcoholic fermentation of sugar-containing products under the action of yeast enzymes. The growing technical importance of ethyl alcohol led to the search for new types of non-food raw materials for the production of ethanol. In the first half of the last century, the substance became an indispensable raw material for the production of rubber according to the Lebedev method. One of the methods was predicted by A. M. Butlerov, who dreamed that a cheap method of producing ethylene would open the way "for the extraction of alcohol." Sources of unsaturated hydrocarbons are oil cracking products and catalytic dehydrogenation of alkanes. Ethylene is obtained from ethane, which is oxidized in the presence of sulfuric acid: C2H6 → C2H4 → C2H5OH. Hydration of other alkenes, which are also obtained during oil refining, gives homologues of synthetic ethyl alcohol. The disadvantages of the method are expressed in the cost of the regeneration of the acid and the protection of the apparatus from its corrosive effects. The industry has switched to the direct hydration of alkenes, which uses solid catalysts. Methanol is obtained by the oxidation of methane. Ethylene and its homologues serve as raw materials for the production of alcohols.
How to get aldehydes and carboxylic acids from alkanes
After solving the problem of cheap raw materials for the alcohol industry, chemists know how to get aldehyde from alkane at the lowest cost. One way to get acetaldehyde is to hydrate acetylene. The whole process goes according to the scheme: natural gas → 4 → 22 → 3 — . The use of natural hydrocarbons for the production of ethyl alcohol has increased. The substance is a raw material for the production of carbonyl and carboxyl compounds. Acetaldehyde can be obtained by dehydrogenation of ethane, followed by the formation of ethanol in the reaction, its oxidation or dehydrogenation. One option is the oxidation of ethylene: C2H6 → C2H4 → C2H4O. How to get carboxylic acid from alkane? A question that has long been in the category of problematic ones. Acetic acid is formed during the fermentation of food raw materials, during the dry distillation of wood. The availability of available alkane sources allows the oxidation of butane and the production of cheap acetic acid: 410 + 2 ½ 2 → 23 + 2. The release of other carboxylic acids from saturated and unsaturated hydrocarbons has been established.
It is hard to imagine a modern world economy without natural gas, oil and coal raw materials. Various alkanes are isolated from these natural mixtures, which are used to produce a large number of organic synthesis products.