Basics of Hydrocarbon Chemistry

(https://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.html)

Crude oil is a mixture of hydrocarbon molecules, which are organic compounds of carbon and hydrogen atoms that may include from one to 60 carbon atoms. The properties of hydrocarbons depend on the number and arrangement of the carbon and hydrogen atoms in the molecules. The simplest hydrocarbon molecule is one carbon atom linked with four hydrogen atoms: methane. All other variations of petroleum hydrocarbons evolve from this molecule.

Hydrocarbons containing up to four carbon atoms are usually gases, those with 5 to 19 carbon atoms are usually liquids, and those with 20 or more are solids. The refining process uses chemicals, catalysts, heat, and pressure to separate and combine the basic types of hydrocarbon molecules naturally found in crude oil into groups of similar molecules. The refining process also rearranges their structure s and bonding pattern s into different hydrocarbon molecules and compounds. Therefore it is the type of hydrocarbon (paraffinic, naphthenic, or aromatic) rather than its specific chemical compounds that is significant in the refining process.

Principal groups of hydrocarbon compounds that occur in crude oil:

a. Paraffins. The paraffinic series of hydrocarbon compounds found in crude oil have the general formula CnH2n+2 and can be either straight chains (normal) or branched chain s (isomers) of carbon atoms. The lighter, straight-chain paraffin molecules are found in gases and paraffin waxes. Examples of straight-chain molecules are methane, ethane, propane, and butane (gases containing from one to four carbon atoms), and pentane and hexane (liquids with five to six carbon atoms). The branched-chain (isomer) paraffins are usually found in heavier fractions of crude oil and have higher octane numbers than normal paraffins. These compounds are saturated hydrocarbons, with all carbon bonds satisfied, that is, the hydrocarbon chain carries the full complement of hydrogen atoms.

b. Aromatics are unsaturated ring-type (cyclic) compounds which react readily because they have carbon atoms that are deficient in hydrogen. All aromatics have at least one benzene ring (a single-ring compound characterized by three double bonds alternating with three single bonds between six carbon atoms) as part of their molecular structure. Naphthalenes are fused double-ring aromatic compounds. The most complex aromatics, polynuclears (three or more fused aromatic rings), are found in heavier fractions of crude oil.

c. Naphthenes are saturated hydrocarbon groupings with the general formula CnH2n, arranged in the form of closed rings (cyclic) and found in all fractions of crude oil except the very lightest. Single-ring naphthenes (monocycloparaffins) with five and six carbon atoms predominate, with two-ring naphthenes (dicycloparaffins) found in the heavier ends of naphtha.

Слова для сдачи наизусть:

1. to include - включать
2. to depend on smth. - зависеть от чего-л.
3. arrangement - расположение; структура
4. to ev o lve from - развиваться; формироваться
5. refining process - процесс переработки
6. to rearrange the structure - перестраивать структуру; преобразовывать структуру
7. bonding pattern - связующая часть / звено
8. p a raffin - парафиновый углеводород; углеводород парафинового ряда
9. branched chain - разветвлённая цепь
10. s a turated hydrocarbons - насыщенные углеводороды
11. c o mplement - дополняющее количество
12. aromatics - ароматические нефтепродукты
13. deficient in hydrogen - не имеющий водорода
14. benzene ring - бензольное кольцо; ароматическое кольцо
15. fused compound - конденсированное соединение

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