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Fractional distillation of oil, use of alkanes. How does primary oil refining occur? Description of oil fractions

Definitions

Factional composition. For all individual substances, the boiling point at a given pressure is a physical constant. Since oil is a mixture of a large number organic matter, having different saturated vapor pressures, then it is impossible to talk about the boiling point of oil.

Under conditions of laboratory distillation of oil or petroleum products at gradually increasing temperatures, individual components are distilled off in order of increasing boiling points, or, what is the same, in decreasing order of their saturated vapor pressure. Consequently, oil and its products are characterized not by boiling points, but by the temperature limits of the beginning and end of boiling and the yield of individual fractions distilled in certain temperature ranges. Based on the distillation results, the fractional composition is judged.

Faction is the fraction of oil that boils away in a certain temperature range. Oils boil over a very wide temperature range, mainly from 28 to 520-540°C. The fractional composition of oil is determined by the standard method (GOST 2177–82) based on the results of laboratory tests when separating compounds by boiling points by fractionating (distilling) oil, distilling or a mixture of compounds in AVT (atmospheric vacuum tube) installations.

Start of boiling fractions are calculated as the temperature at which the first drop of condensed vapor falls.

End of boil fractions are calculated as the temperature at which the evaporation of a fraction stops.

When studying new oils, the fractional composition is determined using standard distillation apparatuses equipped with distillation columns. This makes it possible to significantly improve the clarity of the separation and build, based on the results of fractionation, the so-called true boiling point curve (TBC) in the coordinates temperature - fraction yield, in % (wt.). Selection of fractions up to 200°C is carried out at atmospheric pressure, and the rest, in order to avoid thermal decomposition, under various vacuums. According to the accepted method, from the beginning of boiling to 300°C, 10-degree and then 50-degree fractions are selected to fractions with a final boiling point of 475-550°C.

Oil fractions

Depending on the boiling temperature ranges, oil fractions (oil separation products) are divided into:

hydrocarbon gas- removed from installations in gaseous and liquid form (“stabilization head”), sent for further processing for gas fractionation plants, used as fuel for oil refinery furnaces;
gasoline fraction- boils away in the range of 50-180°C, is used as a component of commercial motor gasoline, raw material for catalytic reforming and pyrolysis units; exposed secondary distillation to obtain narrow fractions;
kerosene fraction- boils away within the range of 140-220°C (180-240°C), is used as fuel for jet and tractor carburetor engines, for lighting, as a raw material for hydrotreating units;
diesel fraction (light or atmospheric gas oil, diesel distillate)- boils away within the range of 180-350°C (220-350°C, 240-350°C), used as fuel for diesel engines and raw material for hydrotreating units;
fuel oil - residue from atmospheric distillation- boils above 350°C, used as boiler fuel or raw materials for hydrotreating and thermal cracking units;
vacuum distillates (vacuum gas oils)- boil away in the range of 350-500°C, used as raw material for catalytic cracking and hydrocracking;
transformer distillate (light oil fraction)- boils away within 300-400°C (350-420°C);
machine distillate (middle oil fraction)- boils away within 400-450°C (420-490°C);
cylinder distillate (heavy oil fraction)- boils away within 450-490°C;
tar- the residue of atmospheric vacuum distillation of oil, boils away at temperatures above 500°C (490°C), and is used as a raw material for thermal cracking, coking, and production of bitumen and oils.

Determination of fractional composition

The fractional composition is determined by the standard method according to GOST 2177-99 (the method is similar to Engler’s distillation, which is widespread abroad), as well as different ways using laboratory columns. To recalculate boiling points obtained by standard distillation ( T gost) to true boiling temperatures ( T itk) formula proposed:

Start temperatures Tnk and the end T kk boiling point according to ITC can be determined using the formulas:

At determination of fractional composition oil or a petroleum product is distilled in a standard device under certain conditions and a distillation curve is plotted in the coordinate system: the x-axis is the yield of fractions (distillation) in % (vol.) or % (wt.) and the y-axis is the boiling point in °C.

When heating such a complex mixture as oil, low-boiling components with high volatility first pass into the vapor phase. Partially, high-boiling components leave with them, but the concentration of the low-boiling component in the vapor is always greater than in the boiling liquid. As low-boiling components are distilled off, the residue becomes enriched with high-boiling ones. Since the vapor pressure of the high-boiling components at a given temperature is lower than the external pressure, boiling may eventually cease. In order to make the boiling non-stop, the liquid residue is continuously heated. At the same time, more and more new components with ever-increasing boiling points pass into vapor. The exhaust vapors are condensed, and the resulting condensate is selected according to the boiling point ranges of the components in the form of separate oil fractions.

The distillation of oil and petroleum products for the purpose of separation into fractions can be carried out with gradual or single evaporation. During distillation with gradual evaporation, the resulting vapors are continuously removed from the distillation apparatus, they are condensed and cooled in a condenser-refrigerator and collected in a receiver in the form of liquid fractions.

In the case when the vapors formed during the heating process are not removed from the distillation apparatus until a given temperature is reached, at which the vapor phase is separated from the liquid phase in one step (once), the process is called flash distillation. After this, an OI curve is constructed.

It is impossible to achieve a clear separation of petroleum products into narrow fractions either by gradual or even more so by single evaporation, since some of the high-boiling components pass into the distillate, and some of the low-boiling ones remain in the liquid phase. Therefore, distillation with reflux or rectification is used. To do this, oil or petroleum product is heated in a flask; The vapors formed during distillation, almost devoid of high-boiling components, are cooled in a special apparatus - a reflux condenser and turn into a liquid state - phlegm. Phlegm, flowing down, meets the newly formed vapors. As a result of heat exchange, the low-boiling components of the reflux evaporate, and the high-boiling components of the vapor condense. With this contact of vapors, a clearer separation into fractions is achieved than without reflux.

An even clearer separation occurs during distillation with rectification. The apparatus for such distillation consists of a distillation flask, a distillation column, a condenser-refrigerator and a receiver.

Rectification is carried out in distillation columns. During rectification, contact occurs between the upward flow of vapor and the condensate flowing down - reflux. The vapors have a higher temperature than reflux, so heat transfer occurs upon contact. As a result of this, low-boiling components from the reflux pass into the vapor phase, and high-boiling components condense and pass into the liquid phase. To effectively carry out the rectification process, the closest possible contact between the vapor and liquid phases is necessary. This is achieved using special contacting devices placed in the column (nozzles, plates, etc.). The clarity of separation of the components of the mixture mainly depends on the number of contact stages and the amount of reflux (irrigation) flowing towards the vapor. To form reflux, a condenser-refrigerator is placed at the top of the column. Based on the results of clear rectification, a TTC (true boiling point) curve is constructed.

Determination of fractional composition oils and oil fractions is carried out in laboratory conditions. The following types of distillation are most widespread in laboratory practice.

Distillation based on the principle of gradual evaporation: simple distillation of oil and petroleum products boiling up to 350°C:

at atmospheric pressure;
simple distillation of petroleum products boiling above 350°C under reduced pressure (under vacuum);
distillation with reflux;
distillation with clear rectification.

Distillation based on the flash evaporation principle: flash distillation.

Molecular distillation for high molecular weight compounds and resins.

Simulated distillation.

When oil is distilled, based on the difference in boiling points of individual components, fractions or distillates are obtained.
Each of the fractions can be dispersed in narrower temperature ranges. Oil distillation is carried out at atmospheric pressure. The residue after oil distillation - fuel oil - can be subjected to fractionation under vacuum.
In table Table 9.1 shows the main fractions of oil distillation at atmospheric pressure.
The gasoline fraction is used as fuel and can serve as a raw material for the production of individual hydrocarbons.
Table 9.1. Oil fractions (distillates)

Kerosene fraction is used as fuel for jet engines in the form of clarified kerosene and as a raw material for the production of varnishes and paints.
Solar oil and diesel fractions serve as diesel fuel and raw materials for the production of liquid paraffins by dewaxing.
Fuel oil is used as boiler fuel and as a raw material in secondary processing processes. After vacuum distillation of fuel oil, gas oil, oil fractions and tar are obtained. Oil fractions are used as raw materials for secondary oil refining to produce lubricating oils, coke and bitumen. Tar is used in the preparation of asphalt mixtures and in the production of bitumen.
The physical and chemical processes of distillation involve two main steps: heating to high temperatures; product separation.
The main heating equipment is furnaces for heating raw materials and intermediate products, as well as various heat exchangers.
The separation of oil distillation products is carried out in distillation columns.
Tube furnaces are devices designed to transfer the heat generated by burning fuel to the heated product. There are many varieties of tube furnaces used in primary processing, catalytic cracking, catalytic reforming, hydrotreating and other processes.
In Fig. 9.2 and 9.3 show some characteristic types furnaces used in oil refinery installations.
In Fig. Figure 9.2 shows a typical tent-type tubular furnace, which has two combustion chambers separated by overpass walls. Fuel is burned in combustion chambers. Pipes in the form of ceiling and bottom screens are placed along the walls of the chamber. Here, the heat of the burned fuel is transferred to the pipes due to radiation from the torch generated when the fuel is burned. Between the transfer walls there is a convection chamber in which heat is transferred to the product located in the pipes by direct contact of the flue gases. The higher the speed of the flue gases in the furnace and the larger the surface of the convection beam pipes, the more efficient the heat transfer in convection chambers. The raw materials in the furnace are first sent to the convection chamber, and then to the radiation chamber. The main share of heat is transferred to the heated raw material or product in the radiation chamber (70-80%), the convection chamber accounts for 20-25%. Sprayed fuel is fed into the combustion chambers using nozzles.

Rice. 9.2. Typical two-chamber tent-type tube furnace:
1- ceiling screen; 2- convective tube bundle; 3-tube grid of convective bundle; 4- blast window; 5-pipe suspension; 6- furnace frame; 7- inspection hatch; 8- suspended masonry; 9- tunnel for nozzle;
10-hearth screen

light, as well as the air necessary for combustion. The fuel is intensively mixed with air, which ensures its efficient combustion.
The temperature at the inlet of raw materials into the furnace depends on the degree of utilization of the heat of the hot waste products from the distillation columns and is usually 180 - 230 ° C. The temperature at which raw materials leave the furnace depends on the fractional composition of the raw materials. During atmospheric distillation of oil, the temperature is maintained at 330-360 °C, and during vacuum distillation - 410-450 °C. The temperature of the flue gases leaving the furnace and directed into the chimney depends on the temperature of the raw materials entering the furnace and exceeds it by 100-150 ° C. In some cases, the exhaust gases are sent to a heat exchanger to use their thermal energy.
Heat exchangers perform different functions and use different coolants. Heat exchangers account for up to 40% of the metal of all equipment in process plants.
In Fig. 9.4 shows the evaporator heat exchanger. Heat exchangers of this type are used to introduce heat into the lower

a - two-chamber box-type with radiating walls; b - two-chamber box-type with upper combustion gas exhaust -
tions and with double-sided irradiation screens; c - with volumetric combustion of fuel

Rice. 9.4. Heat exchanger with steam space (evaporator):
1- fitting for removing the tube bundle; 2 - bottom; 3 - manhole; 4- body; 5- drain plate; b- “floating head”; 7-tube bundle; 8-distribution chamber

part of the distillation column of those technological installations where heating to high temperatures is not required.
The evaporator heat exchanger consists of a housing 4, in which there is a tube bundle 7 with a “floating head” 6. A drain plate 5 is installed inside the housing. The tube bundle is connected on one side to a distribution chamber, which has a solid horizontal partition inside. The chamber has two fittings for inlet and outlet of coolant (steam or hot oil product). There are three fittings on the body: one for the input of the heated hydrocarbon product, the second for the outlet of the stripped petroleum product after the drain plate, and the third for the release of vapors and directing them to the distillation column.
The product level in the evaporator is maintained by a drain partition 5 so that during normal operation, the bundle 7 is completely covered with the evaporated oil product. The coolant is directed through the tube bundle ( saturated steam or hot oil product). Having given up its heat to the heated medium, the coolant exits through another fitting.
Since the beginning of the 80s of the XX century. At the refineries, a massive replacement of water coolers with air-cooled condensers began. Their use has made it possible to reduce the costs of operating heat exchangers and solve a number of environmental problems. Air coolers (ACO) (Fig. 9.5) are equipped with flat tube bundles through which the cooled flow passes
petroleum products. An air flow forced by a fan is directed through this beam.
Distillation columns are devices for separating products with different boiling points. Most often they are equipped with bubble caps. A distillation column is like several independent installations stacked on top of each other, with sampling along the height of the column. The distillation process is carried out in distillation columns under pressure (Fig. 9.6).
Crude oil is initially heated in a heat exchanger to a temperature of 170-180 °C and sent to a tube furnace, where the oil is under some excess pressure and heated to 300-350 °C. The heated vapor-liquid mixture is fed to the lower part of the distillation column. The pressure decreases, evaporation of light fractions occurs and their separation from the liquid residue - fuel oil. Couples rise into top part columns in contact with the downward flow (reflux). As a result, the lightest substances are concentrated at the top of the column, the heaviest at the bottom, and intermediate products in between. As the products move, they are selected.
Since lighter products (steam) must pass through heavier products (liquid) and be in equilibrium with them anywhere in the column, each stream contains

Rice. 9.5. Air cooler with horizontal sections

Rice. 9.6. Distillation column with side stripping section:
I - heating oven; 2-distillation column

There are very volatile components, the so-called overhead oil.
To remove light fractions from the side stream, a stripping column (section) is sometimes provided. The side stream enters the upper part of the stripping section, the light fractions are stripped off with steam in a countercurrent and again sent to the main column.
There are three types of crude oil fractionation waste: the water removed from the overhead reservoir before recirculation contains sulfides, chlorides, mercaptans and phenol; drainage from oil sampling lines. This water contains a high concentration of oil, sometimes in the form of emulsions; a stable oil emulsion formed in barometric condensers used to create a vacuum.
In modern oil refineries, instead of barometric condensers, surface condensers are used, consisting of a series of shell-and-tube heat exchangers installed in series, in which condensable substances are cooled, and the cooling water does not have direct contact with the condenser.

Vladimir Khomutko

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Description of substances in the fractional composition of petroleum products

The fractional composition of oil is a multicomponent continuous mixture of heteroatomic compounds and hydrocarbons.

Conventional distillation is not capable of separating it into individual compounds, the physical constants of which are strictly defined (for example, the boiling point at a given specific pressure level).

As a result, oil is separated into individual components, which are mixtures of less complexity. These are called distillates or fractions.

In laboratory and industrial conditions, distillation is carried out at an ever-increasing boiling point. This allows fractionation of hydrocarbon gases from oil refining and liquid components, which are characterized not by a specific boiling point, but by a certain temperature range (starting and ending boiling points).

Atmospheric distillation of petroleum feedstock makes it possible to obtain the following fractions, which boil away at temperatures up to 350 degrees C:

petroleum fraction – up to 100 degrees C;
gasoline - boiling point 140 degrees;
naphtha – from 140 to 180;
kerosene - from 140 to 220;
diesel fraction - from 180 to 350 degrees C.

All fractions that boil away to a temperature of 200 degrees C are called gasoline or light. Fractions that boil away in the range from 200 to 300 degrees C are called kerosene or medium.

And finally, the fractions that boil away at temperatures exceeding 300 degrees C are called oil or heavy. In addition, all oil fractions whose boiling point is less than 300 degrees are called light.

The fractions remaining after the selection of light distillates during the rectification process (primary oil refining), which boil away at more than 35 degrees, are called fuel oil (dark fractions).

Further distillation of fuel oil and its advanced processing is carried out under vacuum conditions.

This allows you to get:

vacuum distillate (gas oil) – boiling point from 350 to 500 degrees C;
tar (vacuum residue) – boiling point over 500 degrees C.

The production of petroleum oils is characterized by the following temperature ranges:

In addition, heavy oil components also include asphalt resin-paraffin deposits.

In addition to their hydrocarbon composition, different petroleum fractions also differ in their color, viscosity and specific gravity. The lightest distillates (petroleum) are colorless. Further, the heavier the fraction, the darker its color and the higher the viscosity and density. The heaviest components are dark brown and black.

Description of oil fractions

Petroleynaya

It is a mixture of liquid and light hydrocarbons (hexanes and pentanes). This fraction is also called petroleum ether. It is obtained from gas condensate, light oil fractions and associated gases. Petroleum ether is divided into light (boiling range - from 40 to 70 degrees C) and heavy (from 70 to 100 degrees). Since this is the fastest boiling fraction, it is one of the first to be separated when separating oil.

Petroleum ether is a colorless liquid whose density ranges from 0.650 to 0.695 grams per cubic centimeter. It dissolves various fats, oils, resins and other hydrocarbon compounds well, so it is often used as a solvent in liquid chromatography and in the extraction of oil, hydrocarbons and bitumen from rocks.

In addition, lighters and catalytic heating pads are often refilled with petroleum ether.

Gasoline

This oil and condensate fraction is a complex hydrocarbon mixture of various types of structure. About seventy components of the above mixture have a boiling point of up to 125 degrees C, and another 130 components of this fraction boil away in the range from 125 to 150 degrees.

The components of this carbon mixture serve as materials for the manufacture of various fuels used in internal combustion engines. This mixture contains different types hydrocarbon compounds, including branched and straight-chain alkanes, as a result of which this fraction is often treated with thermal reforming, which converts it into branched, straight-chain molecules.

The composition of gasoline petroleum fractions is based on isomeric and normal paraffin hydrocarbons. Of the naphthenic hydrocarbon group, the most abundant are methylcyclopentane, methylcyclohexane and cyclohexane. In addition, there is a high concentration of light aromatic carbon compounds such as metaxylene and toluene.

The composition of gasoline-type fractions depends on the composition of the refined oil, therefore the octane number, hydrocarbon composition and other gasoline properties vary, depending on the quality and properties of the original petroleum feedstock. In other words, it is not possible to obtain high-quality gasoline from just any raw material. Poor quality motor fuel has an octane number of zero. High quality has this indicator at 100.

The octane number of gasoline obtained from crude oil is rarely more than 60. Of particular value in the gasoline petroleum fraction is the presence of cyclopentane and cyclohexane, as well as their derivatives. It is these hydrocarbon compounds that serve as raw materials for the production of aromatic hydrocarbons, such as benzene, the initial concentration of which in crude oil is extremely low.

Naphtha

This high-octane oil fraction is also called heavy naphtha. It is also a complex hydrocarbon mixture, but consists of heavier components than in the first two fractions. In naphtha distillates, the content of aromatic hydrocarbons is increased to eight percent, which is significantly higher than in gasoline distillates. In addition, the naphtha mixture contains three times more naphthenes than paraffins.

The density of this oil fraction ranges from 0.78 to 0.79 grams per cubic centimeter. It is used as a component of commercial gasoline, lighting kerosene and jet fuel. It is also used as an organic solvent, as well as a filler for liquid-type devices. Before the diesel fraction began to be actively used in industry, naphtha acted as a raw material for the production of fuel used in tractors.

The composition of first distillation naphtha (unrefined, obtained directly from the distillation cube) largely depends on the composition of the crude oil being processed. For example, naphtha obtained from oil with a high paraffin content contains more unbranched saturated or cyclic hydrocarbon compounds. Basically, low-sulfur types of oil and naphtha are paraffinic. On the contrary, oil with a high content of naphthenes contains more polycyclic, cyclic and unsaturated hydrocarbons.

Naphthenic petroleum feedstocks are characterized by a high sulfur content. Purification processes for first distillation naphthas vary depending on their composition, which is determined by the composition of the feedstock.

Kerosene

The boiling point of this fraction during direct atmospheric distillation is from 180 to 315 degrees C. Its density at twenty degrees C is 0.854 grams per cubic centimeter. It begins to crystallize at a temperature of minus sixty degrees.

This oil fraction most often contains hydrocarbons, which contain from nine to sixteen carbon atoms. In addition to paraffins, monocyclic naphthenes and benzene, it also contains bicyclic compounds such as naphthenes, naphtheno-aromatic and aromatic hydrocarbons.

From these fractions, due to the high concentration of isoparaffins in them and the low concentration of bicyclic hydrocarbons of the aromatic group, jet fuel of the most High Quality, which fully meets all modern requirements for promising types of such fuel, namely:

increased density;
moderate content of aromatic hydrocarbons;
good thermal stability;
high low temperature properties.

As in previous distillates, the composition and quality of kerosene directly depend on the original crude oil, which determines the characteristics of the resulting product.

Those kerosene fractions of oil that boil away at temperatures from 120 to 230 (240) degrees are well suited as reactive species fuels, for the production of which (if necessary) so-called demercaptanization and hydrotreating are used. Kerosenes obtained from oil with low sulfur content at temperatures from 150 to 280 degrees or in the temperature range from 150 to 315 degrees are used as lighting. If kerosene boils away at 140 - 200 degrees, it is used to make a solvent known as white spirit, widely used in paint and varnish enterprises.

Diesel

Boils away at temperatures from 180 to 360 degrees C.

It is used as fuel for high-speed diesel engines and as a raw material in other oil refining processes. When it is produced, kerosene and hydrocarbon gases are also produced.

Diesel oil fractions contain few aromatic hydrocarbons (less than 25 percent), and a predominance of naphthenes over paraffins is typical. They are based on derivatives of cyclopentane and cyclohexane, which gives rather low pour points. If diesel components obtained from highly paraffinic oils are distinguished by a high concentration of normal alkanes, as a result of which they have a relatively high pour point - from minus ten to minus eleven degrees C.

In order to obtain winter diesel fuel in such cases, for which the required pour point is minus 45 (and for the Arctic - all minus 60), the resulting components undergo a dewaxing process, which takes place with the participation of urea.

In addition, diesel components contain various types of organic compounds (based on nitrogen and oxygen). These include various types of alcohols, naphthenic and paraffin ketones, as well as quinolines, pyridines, alkylphenols and other compounds.

Fuel oil

This mixture contains:

hydrocarbons with a molecular weight ranging from 400 to 1000 tons;
petroleum resins (weight - from 500 to 3000);
asphaltenes;
carbenes;
carboids;
organic compounds based on metals and non-metals (iron, vanadium, nickel, sodium, calcium, titanium, zinc, mercury, magnesium and so on).

The properties and quality characteristics of fuel oil also depend on the properties and characteristics of the processed crude oil, as well as on the degree of distillation of light distillates.

Main characteristics of fuel oils:

viscosity at a temperature of 100 degrees C – from 8 to 80 millimeters squared per second;
density indicator at 20 degrees - from 0.89 to 1 gram per cubic centimeter;
hardening interval - from minus 10 to minus 40 degrees;
sulfur concentration – from 0.5 to 3.5 percent;
ash – up to 0.3 percent.

Until the end of the nineteenth century, fuel oil was considered an unusable waste and was simply thrown away. Currently, they are used as liquid fuel for boiler houses, and are also used as raw materials for vacuum distillation, since the heavy components of petroleum feedstock normal pressure atmosphere cannot be surpassed. This is due to the fact that in this case, reaching the required (very high) boiling temperature leads to the destruction of the molecules.

Fuel oil is heated to more than seven thousand degrees in special tube furnaces. It turns into steam, after which it is distilled under vacuum in distillation columns and separated into separate oil distillates, and tar is obtained as a residue.

From distillates obtained from fuel oil, spindle, cylinder and machine oils are made. Also, when processing fuel oil at lower temperatures, components are obtained that can be further processed into motor fuel, paraffin, ceresin and various types of oils.

Bitumen is obtained from tar by blowing it with hot air. Coke is obtained from the residues obtained after cracking and distillation.

Boiler fuel oil comes in the following grades:

naval F5 and F12 (refers to light fuel);
combustion M40 (medium type of boiler fuel);
combustion fuel M100 and M200 (heavy boiler fuel).

Naval fuel oil, as the name implies, is used in boilers of sea and river vessels, as well as as fuel for gas turbine engines and installations.

Fuel oil M40 is also suitable for use in marine boilers and is also suitable for use in heating boilers and industrial furnaces.

M100 and M200 fuel oils are usually used at large thermal power plants.

Tar

This is the residue that is formed after all processes of distillation of other oil components (atmospheric and vacuum), which boil away at temperatures below 450 - 600 degrees.

The tar yield ranges from ten to forty-five percent of the total mass of processed petroleum feedstock. It is either a viscous liquid or a solid black product, similar to asphalt, shiny when broken.

Tar consists of:

paraffins, naphthenes and aromatic hydrocarbons – 45-95 percent;
asphaltenes – from 3 to 17 percent;
petroleum resins - from 2 to 38 percent.

In addition, it contains almost all the metals contained in petroleum feedstock. For example, vanadium in tar can be up to 0.046 percent. The density of tar depends on the characteristics of the feedstock and the degree of distillation of all light fractions, and varies from 0.95 to 1.03 grams per cubic centimeter. Its coking capacity ranges from 8 to 26 percent of the total mass, and its melting point ranges from 12 to 55 degrees.

Tar is widely used for the production of road, construction and roofing bitumen, as well as coke, fuel oil, lubricating oils and some types of motor fuel.

Petroleum products. Methods for determining fractional composition

To determine the fractional composition of petroleum products, various types of equipment are used. Basically, these are standardized distillation apparatuses equipped with distillation columns. Such an apparatus for determining the fractional composition is called ARN-LAB-03 (although there are other options).

Such preliminary work using appropriate devices is, firstly, necessary for drawing up technical passport on raw materials, and, secondly, it makes it possible to increase the accuracy of the separation, and also, based on the results obtained, to construct a boiling point (true) curve, where the coordinates are the temperature and yield of each fraction as a percentage of the total mass (or volume).

Crude oil obtained from different fields differs greatly in its fractional composition, and therefore. and by percentage of potential fuel distillates and lubricating oils. Mainly in petroleum raw materials - from 10 to 30 percent of gasoline components, and from 40 to 65 percent of kerosene-gas oil fractions. In the same field, oil layers of different depths can produce raw materials with different characteristics fractional composition.

To determine this important characteristic For oil components, various devices are used, among which the ATZ-01 is the most popular.

into fractions, through repeated evaporation and condensation of vapors, carried out at normal (atmospheric) pressure.

First of two processes primary oil refining .

Technological process

Oil prepared during a special procedure (see. Preparing oil for refining) is heated in a special oven to a temperature of about 380 °C. The result is a mixture of liquid and steam, which is fed to the bottom of the distillation column - the main unit of atmospheric distillation of oil.

The distillation column is an impressively sized (up to 80 meters high and up to 8 meters in diameter) pipe, vertically delimited inside by so-called trays with special holes. When the heated mixture is fed into the column, light vapors rush upward, and the heavier and denser part is separated and sinks to the bottom.

The rising vapors condense and form a layer of liquid about 10 cm thick on each plate. The holes in the plates are equipped with so-called bubble caps, thanks to which the rising vapors bubble through this liquid. In this case, the vapors lose heat, transferring it to the liquid, and some of the hydrocarbons turn into a liquid state. This process“Gurgling” is the essence of rectification. Then the vapors rise to the next plate, where bubbling is repeated. In addition, each plate is equipped with a so-called drain cup, which allows excess liquid to flow onto the lower plate.

Thus, through atmospheric distillation, oil is separated into factions(or shoulder straps). However, for more efficient separation, the following technological methods are used.

To prevent heavy products from entering the upper part of the column, vapors are periodically sent to the refrigerator. The substances condensed in the refrigerators are returned to one of the lower plates. This process is called irrigation distillation column.

On the other hand, some light hydrocarbons may end up in the lower part of the column along with the liquid flow. This problem is solved by passing liquid from the specific place column and re-passing it through the heater. Thus, light hydrocarbons return to the column in the form of steam. The described process is called re-evaporation.

Fractions taken from any part of the column can be subjected to irrigation and re-evaporation. As a result of these processes, some molecules travel all the way through the column several times, evaporating and condensing again. This approach ensures the most efficient separation of oil, and the distillation column is essentially a complex of distillation apparatuses combined together.

Boiling limits of fractions

The fundamentally important and main characteristic of factions is their boiling limits– temperatures at which the distillation products are separated from each other.

Starting Boiling Point (TNK) – temperature at which the fraction begins to boil

Boiling Point (TV) is the temperature at which this fraction has completely evaporated.

Nominally, the boiling point of one fraction should be the initial boiling point of the neighboring, heavier fraction. However, in practice, the rectification process is not ideal and in most cases (if not always) the TV and TNC of neighboring fractions do not coincide. Such overlap is usually called “tails”, and they can be most clearly seen on the acceleration curves.

To simplify, the concept was introduced effective boiling limits, i.e. temperatures at which the fractions are conventionally considered separated.

	Overlapping kerosene and naphtha acceleration curves

The selection of fractions at various levels of the distillation column is carried out through side outlets. Heavy fractions are selected at the bottom of the column, lighter fractions (upper strap) - at the top. In this case, the boiling limits of fractions can be set and adjusted, depending on needs.

	Scheme of separating oil into fractions during atmospheric distillation

Almost all light atmospheric distillation products are immediately sent to recycling, and the straight-run residue (fuel oil) - to

Topic 9 “FUNDAMENTALS OF OIL AND PETROLEUM PRODUCTS PROCESSING TECHNOLOGY”

1. Origin and composition of oil. Oil production and preparation for processing.

3. Fundamentals of technology for the production and processing of polymer materials.

4. Fundamentals of technology for the production of rubber products.

Origin and composition of oil. Oil production and preparation for processing

Of all known types of fuel, the most important is organic fuel, the combustion of which produces thermal energy, and processing - raw materials for chemical industry.

Currently, petroleum products (petroleum products) are the most widely used. They are also produced in our country, so we will consider oil refining technologies in detail.

Oil is a liquid fossil fuel. It usually lies at a depth 1,2 -2 km or more in porous or fractured rocks(sands, sandstones, limestones). Oil is an oily liquid from light brown to dark brown in color with a specific odor, density 0.65-1.05 g/cm 3 . In composition, oil is a complex mixture of hydrocarbons, mainly paraffin and naphthenic, and to a lesser extent aromatic. Its elemental composition (mass fraction, %): carbon (C) - 82-87, hydrogen (H) - 11-14, sulfur (S) - OD-5.5.

Depending on the products obtained from oil, there are three options for its processing:

fuel , used to produce motor and boiler fuel;

fuel and oil , which produce fuel and lubricating oils;

petrochemical (complex), the products of which are not only fuel and oils, but also raw materials for the chemical industry (olefins, aromatic and saturated hydrocarbons, etc.).

Liquid fuel, obtained from petroleum, depending on the use are divided into:

carburetor(aviation and automobile gasolines) - for internal combustion engines;

reactive(kerosene) - for jet and gas turbine engines;

Diz Elnoe(gas oil, diesel distillate) - for diesel engines .

boiler room(fuel oil) - for furnaces of steam boilers, generator sets, metallurgical furnaces. IN general case Processing of oil into petroleum products includes its extraction, preparation and processes of primary and secondary processing.

Oil production carried out by drilling wells.

Preparation extracted from the depths of oil is to remove impurities from it ( associated gas, formation water with mineral salts, mechanical inclusions) and composition stabilization. These operations are carried out both directly at oil fields and at oil refineries.

Primary oil refining, carried out by physical methods (mainly direct distillation), consists of dividing it into separate fractions (distillates), each of which is a mixture of hydrocarbons.

Secondary oil refining represents a variety of processes for processing petroleum products obtained as a result of primary processing. These processes are accompanied by destructive transformations of hydrocarbons contained in petroleum products and are essentially chemical processes.

Direct distillation of oil. Cracking of petroleum products

Process straight distillation based on the phenomena of evaporation and condensation of a mixture of substances with different temperatures boiling.

Boiling of the mixture begins at a temperature equal to the average boiling point of the constituent parts. In this case, predominantly light, low-boiling components (having a lower density and boiling at lower temperatures) pass into the vapor phase, and high-boiling components (having a higher density and boiling at higher temperatures) remain in the liquid phase. If the resulting vapor phase is removed and cooled, a liquid phase condenses from it. Mainly high-boiling (heavy) components will pass into it, and light ones will remain in the vapor phase.

Thus, three fractions are obtained from the initial mixture. One of them, which remains liquid upon boiling, contains predominantly high-boiling components; the second, condensed, has a composition close to the composition of the original mixture; the third, vapor, contains mainly low-boiling components.

Due to single (distillation) or multiple (distillation) processes of boiling and condensation of the resulting fractions, it is possible to achieve a fairly complete separation of low- and high-boiling components.

Technological process direct distillation of oil consists of four main operations: heating the mixture, evaporation, condensation and cooling of the resulting fractions.

Depending on the depth of oil refining, distillation plants are divided into two types:

Single stage, operating at atmospheric pressure (AT);

Two-stage (atmospheric-vacuum) (AVT), in which the first stage, as a rule, operates at atmospheric pressure, and the other at pressure below atmospheric (5-8 kPa) -

In two-stage distillation, the oil is first desalted and dehydrated, then heated in a first-stage tubular furnace to a temperature of 300 - 350 ° C (25 - 30 ° C above the boiling point). The separation of oil into fractions is carried out in a distillation column, which is a cylindrical apparatus with a height of 25 - 55 m and a diameter of 5 - 7 m. Preheated oil is fed to the lower part of the column. Here the oil boils and is divided into two phases: vapor and liquid. Liquid products flow down and vapors rise up the column. A reflux liquid (reflux) is supplied to the top of the column. The vapors rising from below come into repeated contact along the height of the column with the flowing liquid phase. When encountering rising hot vapors, the liquid irrigating the column heats up and partially evaporates. The vapors, giving off heat to it, condense, and the condensate flows into the lower part of the column. As the vapor rises, its temperature decreases, while the phlegm flowing down becomes increasingly enriched in heavy fractions, and the rising vapor in light fractions. At the bottom of the column, liquid containing the heaviest fractions (fuel oil) is collected. Fuel oil is drained from the bottom of the column and cooled in heat exchangers, thereby heating the oil supplied to the column.

To maintain the boiling process, superheated steam is supplied to the distillation column, which carries with it the remnants of light fractions that have not evaporated previously. The lightest gasoline fraction at a temperature of 180 - 200 ° C is removed from the column in the form of vapor into a condenser and separated from the water in a separator. Part of the gasoline fraction is returned to the column for irrigation.

The so-called middle fractions are removed from the intermediate zones of the column: kerosene, boiling at a temperature of 200 - 300 °C, and gas oil (boiling point 300 - 350 °C). Sometimes other fractions are also removed, for example naphtha (160-200 °C), kerosene gas oil fraction (270-320 °C).

The fuel oil obtained after the initial distillation (its yield is about 55% of the original oil) from the first distillation column is pumped into a second-stage tubular furnace, where it is heated to 400 - 420 °C. From the furnace, the fuel oil enters the second distillation column, which operates at a pressure below atmospheric (residual pressure - 5 - 8 kPa). Tar is removed from the lower part of this column, and oil distillates are selected along the height.

The productivity of two-stage units is 8 - 9 thousand tons of oil per day. The yield of gasoline during direct distillation depends on the fractional composition of the oil and ranges from 3 to 1 5%.

Fundamentals of petroleum products cracking technology. The relatively low yield of gasoline (up to 15%) during direct distillation makes it necessary to process other, less valuable fractions obtained during direct distillation of oil and containing heavy hydrocarbon molecules. This processing is called cracking.

Cracking(English, to creak- split, split) - splitting of long molecules of heavy hydrocarbons included in the composition, for example, fuel oil, into shorter light molecules of light low-boiling products.

The main factors influencing the cracking process are temperature and holding time: the higher the temperature and longer duration aging, the more complete the process and the greater the yield of cracking products. Big influence Catalysts influence the course and direction of the cracking process. With the appropriate selection of the catalyst, it is possible to carry out the reaction at lower temperatures, ensuring the production of the necessary products and increasing their yield.

Based on the above, there are two types of cracking: thermal and catalytic.

Thermal cracking conducted at elevated temperatures under high pressure(temperature 450-500 °C and pressure 2-7 MPa). The main purpose of thermal cracking is to obtain light fuel from fuel oil or tar.

Thermal cracking is carried out in tube furnaces in which heavy hydrocarbons are broken down.

Next, the mixture of cracking products and unreacted raw materials passes through an evaporator, in which the creat is separated, i.e. substances that cannot be cracked. Light products enter a distillation column to separate and obtain light commercial fractions. When thermal cracking, for example fuel oil, the approximate composition of the products is as follows: cracked gasoline - 30-35%, cracked gases - 10-15, cracked residue - 50-55%. Cracking gasolines are used as components of motor gasoline; cracking gases are used as fuel or raw material for the synthesis of organic compounds; cracking residue, which is a mixture of resinous, asphaltene substances, is used as boiler fuel or raw material for the production of bitumen.

Thermal cracking can be of two types: low-temperature (visbreaking) and high-temperature (pyrolysis).

Low-temperature cracking is carried out at a temperature of 440-500 °C and a pressure of 1.9-3 MPa, while the process duration is 90-200 s. It is used mainly to produce boiler fuel from fuel oil and tar.

High-temperature cracking occurs at a temperature of 530-600 °C and a pressure of 0.12-0.6 MPa and lasts 0.5-3 s. Its main purpose is to produce gasoline and ethylene. Propylene, aromatic hydrocarbons and their derivatives are formed as by-products.

Catalytic cracking- processing of petroleum products in the presence of a catalyst. IN Lately This method is increasingly used for the production of light petroleum products, including gasoline. Its advantages include:

High speed of the process, 500-4000 times higher than the speed of thermal cracking, and as a result - more mild conditions process and lower energy consumption;

Increasing the yield of commercial products, including gasoline, characterized by a high octane number and greater stability during snoring;

The ability to carry out the process in the right direction and obtain products of a certain composition;

high yield of gaseous hydrocarbons, which are raw materials for organic synthesis;

the use of raw materials with a high sulfur content due to the hydrogenation of sulfur compounds and their release into the gas phase with subsequent disposal.

Synthetic aluminosilicates are used as catalysts in catalytic cracking units.

Catalytic cracking products from the reactor enter the distillation column, where they are separated into gases, gasoline, light and heavy catalytic gas oils. Unreacted feedstock from the bottom of the column is returned to the reactor.

The approximate yield of products during catalytic cracking is as follows: cracked gasoline - 35 - 40%; cracking gas - 15% light cracking gas oil - 35 - 40%, heavy cracking gas oil - 5-8%.

Catalytic cracking gasoline is characterized by good performance properties. Catalytic cracking gases are distinguished by their high content of isobutane and butylene, used in the production of synthetic rubbers.

A type of catalytic cracking is reforming, the course of reactions in which is aimed mainly at the formation of aromatic hydrocarbons and isomers. Depending on the catalyst, the following types of reforming are distinguished:

Platforming (platinum-based catalyst);

Reforming (rhenium-based catalyst).

In practice, the most widespread is platforming, which is a catalytic process for processing gasoline-naphtha fractions of direct distillation, carried out in the presence of hydrogen. If platforming is carried out at 480 - 510 °C and a pressure from 15-10 5 to 3 10 6 Pa, then the result is the formation of benzene, toluene and xylene. At a pressure of 5 10 6 Pa, gasoline is obtained that is characterized by the highest stability and low sulfur content.

Along with liquid products, all catalytic reforming methods produce gases containing hydrogen, methane, propane and butane. Reforming gases are used as raw materials for organic and inorganic synthesis: methanol (ethyl alcohol), ammonia and other compounds. The yield of catalytic reforming gases is 5-15% of the mass of the raw material. The final stage of oil refining is petroleum products purification , which is carried out by chemical and physical-chemical methods. TO chemical methods Purification of petroleum products includes purification with sulfuric acid and with hydrogen (hydrotreating), physico-chemical - adsorption and absorption purification methods.

Sulfuric acid cleaning consists in the fact that the product is mixed with a small amount of 90-93% H 2 SO 4 at normal temperature. As a result chemical reactions a purified product and waste are obtained that can be used to produce sulfuric acid.

Hydrotreating consists in the interaction of hydrogen with the purified product in the presence of aluminum-cobalt-molybdenum catalysts at a temperature of 380-420 ° C and a pressure from 35 10 5 to 4 10 6 Pa and the removal of hydrogen sulfide, ammonia and water.

At adsorption cleaning method petroleum products are treated with bleaching clays or silica gel. In this case, sulfur and oxygen-containing compounds, resins and easily mineralizable hydrocarbons are adsorbed.

Absorption cleaning methods consist in selective (selective) dissolution of harmful components of petroleum products. Liquid sulfur dioxide, furfural, nitrobenzene, dichlorethyl ether, etc. are usually used as selective solvents.

After purification, petroleum products do not always remain stable. In these cases, antioxidants (inhibitors) are added to them in very small quantities, which sharply slow down the oxidation reactions of resinous substances that make up petroleum products. Phenols, aromatic amines and other compounds are used as inhibitors. Oil refining is characterized by a high level of costs for raw materials (50-75% of the cost of refined products), electrical and thermal energy, as well as fixed assets. The level of costs in oil refining significantly depends on the composition of oil, which determines the depth of its refining, the technological scheme of refining, the degree of preparation of raw materials for processing, etc. Thus, when processing high-sulfur oil, additional capital and operating costs for its pumping and preparation are approximately 1.5 higher than when processing low-sulfur oil. In turn, highly paraffinic viscous oil requires additional costs for its dewaxing, pumping and storage.

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