Gasoline is a combustible mixture of light hydrocarbons with a boiling point of +33 to 205°C (depending on additives). Density of about 0,71 g/cm³. The calorific value of about 10,200 kcal/kg (46 MJ/kg to 32,7 MJ/liter). The freezing point of -72°C in the case of use of special additives.
Gasolines are used as a fuel and a raw material in industrial organic synthesis.
Directly Distilled Gasolines
For a long time, gasoline was produced by rectification (distillation) and stripping of oil fractions boiling away within certain temperature range (up to 100°C - gasoline grade I, up to 110°C - special gasoline, up to 130°C - gasoline grade II). However, a common property of those gasolines was low octane number. In general, getting straight-run gasoline with an octane rating above 65 by motor method is rare and is only possible for the oil of Azerbaijan, Central Asia, Krasnodar Territory and Sakhalin. However, even for distillates of those grades of petroleum, a sharp decrease in octane number with increasing temperature in the end of stripping, was characteristic. Thus the entire gasoline fraction (180°C) is seldom used. For the oil from Ural-Volga basin, Kazakhstan, as well as that from West Siberia oilfields, it is characterized by the predominance of normal paraffinic hydrocarbons, thus straight-run gasoline from those is exemplified by low octane numbers. This prompted refiners to strip the fraction below 90-95°C as far back as 1930-ies , so that n-heptane would not interfere, or include heavier fractions into the yield, with its subsequent positive distillation to remove normal paraffins. Such "denormalization" of straight-run gasoline affords to increase its octane number up to 74-76 points with, nevertheless, substantial decrease in output. At the present time, they distill NK 180°C fraction from oil, which is then divided into two fractions - NK-62°C or NK-85°C. Those latter distillates are used as components of commercial gasoline or sent to upgrading (isomerization).
Alkyl-gasoline is a mixture of hydrocarbon isomers of S7 and S8 and is produced by way of alkylation of isobutane with butenes. Alkyl-gasoline is widely used as a component of automotive and aviation gasolines and has high RON of 90-93. Alkyl-gasoline may be produced by engaging propylene and amylenes in raw material alkylation.
The leader in the production of alkyl-gasoline is the United States (more than 40 million ton/year). In Russia, they produce less than 1 million tons/year of alkyl-gasoline due to lack of resources of butane-butylene fraction, which is produced in the course of catalytic cracking process, which is not widespread in Russia. Besides, the alkylation process itself in Russia is technically obsolete and inefficient, which results in firing of excess raw materials.
In the first half of the XX century, they started using cracking and reforming to convert linear chains of normal alkanes - the main component of straight-run gasoline - to branched alkanes and aromatic compounds, respectively, to improve octane number.
The Russian automobile gasolines are produced in compliance with GOST 2084-77, GOST 51105-97 and GOST R 51866-2002, and following TU 0251-001-12150839-2015 Gasoline RON 92, 95 (Alternative).
Motor gasolines are divided into summer and winter (winter gasolines contain more low-boiling hydrocarbons).
Basic grades of motor gasoline by GOST 51105-97:
- Normal-80 (AI-80) - with an octane number RON of at least 80;
- Regular-92 (AI-92) - octane RON of at least 92;
- Premium 95 (AI-95) - with an octane number RON of at least 95;
- Extra-98 (AI-98) - with an octane number RON of at least 98;
- EKTO-100 (AI-100) - octane RON of at least 100.
Compliant with the GOST R 54283-2010, motor gasolines are marked with three groups of characters separated by a hyphen (e.g., "AI-92-4"):
- AI indicates motor gasoline with an octane number by RON;
- numerical designation of octane number determined by research method (e.g., 80, 92, 95 or 98);
- the number 2, 3, 4 or 5 - gasoline class in accordance with the technical regulations; number matches a number of environmental standard of the "Euro" series, which the gasoline should match (2 for Euro 2, 3 for Euro 3, etc.).
For example: AI-92-4 stands for motor gasoline with an octane rating of 92, measured by research method corresponding to the fourth environmental class (Euro-4 standard).
Since 2003, Russia officially discontinued production of harmful leaded gasoline, all gasoline is considered unleaded, and that fact does not appear in the identification whatsoever.
In the US, they use "octane index" calculated by the formula "motor" plus "research" divided by two. Following that parameter, American gasoline 87 matches the Russian AI-92, gasoline 89 corresponds to AI-95 while gasoline 91 corresponds to AI-98.
Aviation gasoline is different from motor fuel by higher quality requirements, it usually has a higher octane number (which is characterized by its antiknock rating in lean mix) and is subdivided by "grade of quality" (which characterizes its antiknock rating in rich mix).
The main indicators of quality for aviation fuel are:
- detonation resistance (determines gasoline suitability for use in engines with a high compression ratio of the working mixture without causing detonation combustion);
- fractional composition (indicative of gasoline evaporation discharge, which is necessary to determine its ability to form a working fuel-air mix - it is characterized by boiling temperature envelope (40-180°C) and saturated vapor pressure (29-48 kPa));
- chemical stability (the ability to resist changes in chemical composition during storage, transport and application).
The main methods of production of aviation gasolines are direct oil distillation, catalytic cracking or reforming without additives or with the addition of high-quality components, ethyl fluid and various additives.
Classification of aviation gasolines is based on their anti-knock properties, expressed in octane numbers and grading units. Grades of Russian aviation gasoline are marked following GOST 1012-72, usually as a fractional number: the numerator - octane or grade for lean mix, the denominator - grade in rich mix, e.g., B-91/115 and B-95/130. Labeling of aviation gasoline using octane numbers would also take place, for example, B-70 (produced following TU 38.101913-82) and B-92 (produced following TU 38.401-58-47-92 ).
Gasoline B-91/115 B-95/130 and B-92 are leaded, while gasoline B-70 is not (it is mostly used as solvent).
Dedicated low boiling products of catalytic reforming (BR-2) or those of sweet crude oil direct distillation (BR-1) (GOST 443-76) are used as a solvent for the preparation of rubber adhesives in the manufacture of printing inks, mastics; for degreasing electrical equipment, fabrics, leather, metal surfaces before the application of metal coatings; flushing bearings, fittings before conservation, in the production of artificial fur; for the manufacture of quick-drying oil paints and insulating varnishes; to extract colophony from timber, preparation of alcohol-gasoline mixture for washing printed circuit boards in the electrical industry.
Extraction gasolines (boiling temperature of 70-95°C) of direct distillation of sweet crude oil are used to extract vegetable oils, extracting fat from bones, nicotine from caporal leaves, as a solvent in the rubber and paint and coatings industries.
Low sulfur dearomatized extraction gasoline (boiling point 70 to 85°C) is used to produce oil in hot climates (high evaporative power).
The BLKh solvent produced from raffinate of catalytic reforming (boiling temperature of 105-125°C) that mainly contains paraffinic hydrocarbons of linear and isomeric structure, is produced specifically for dendrochemical industry and is used to extract colophony from wood chips, sometimes in preparation of rubber adhesives and printing lacquer formulation paints.
The narrow straight distillation fraction (boiling temperature of 110-185°C) (ozocerite solvent) is used for the extraction of ozocerite from ores.
Nefras S 50/170 (GOST 8505-80) (a broad fraction of direct distillation of sweet oil or catalytic reforming raffinate) as a solvent in the production of artificial leathers, for chemical cleaning of fabrics, flushing parts before repair, for washing anti-corrosion coatings away from parts, etc. attained broad applicability.
Xylene raffinate of catalytic reforming and toluene with aromatic content of up to 30% - Nefras SAR is used in the manufacture of monolithic capacitors.
Particularly widespread gasoline-solvent for the paint and coatings industry is the white spirit.
Nefras S 150/200 of narrow fractions of direct distillation of sour oil is similar in properties and is used in a similar manner as the white spirit, however, it contains more sulfur and has a pungent odor.
In the vernacular, low-boiling gasoline solvents for domestic use are often called "Gumshoes" - besides, a Nefras C2 80/120 product similar in composition to the BR1 and the trade name "Gumshoes" may be encountered in the Russian market.
Naphtha (petrochemical gasoline)
Naphtha is a petroleum fraction with the limits of boiling points of up to 180 degrees Celsius, it is composed predominantly of normal paraffins S5 to S9. Those are produced by direct distillation of crude oil with addition of a small amount of secondary fractions. It is used as raw material for ethylene pyrolysis in petrochemical industry, for blending and for export. The following trade names of naphtha are known In Russia:
- Stable casing head gasoline (BGS);
- Gasoline for chemical industry;
- Straight-run gasoline (BP);
- Light distillate of gas condensate (DGKl);
- Other similar products.