Over the past decades, humanity has reached the highest level of technology for the production of hydrocarbons and their processing.
Technologies
On the purification and processing of oil
Conventional crude oil produced from a well is a greenish-brown, flammable, oily liquid with a pungent odor.
At the fields, it is stored in large tanks, from where it is transported by tankers or through pipelines to the tanks of processing plants.
In many refineries, different types of crude oil are separated according to their properties according to the results of preliminary laboratory processing.
It indicates the approximate amount of gasoline, kerosene, lubricating oils, paraffin and fuel oil that can be produced from this oil.
are different and range from paraffinic, which consists mainly of paraffinic hydrocarbons, to naphthenic or asphalteneic, which contains mainly cycloparaffinic hydrocarbons; there are many intermediate or mixed types.
compared to naphthenic or asphaltene oil, contains more gasoline and less sulfur and is the main raw material for the production of lubricating oils and paraffins.
Naphthenic types of crude oil contain less gasoline, but more sulfur and fuel oil, as well as asphalt.
contains some dissolved gas, which is similar in composition and structure to natural gases and consists of light paraffinic hydrocarbons.
The liquid phase of crude oil contains hundreds of hydrocarbons and other compounds having a boiling point of 38° C. to about 430° C., the percentage of each of which is small.
For example, a gasoline fraction can contain up to 200 individual hydrocarbons, but typical gasoline contains only about 60 hydrocarbons – from methane with a boiling point of -161 ° C to mesitylene (aromatic hydrocarbon), with a boiling point of 165 ° C.
They include paraffins, cycloparaffins and aromatics, but no olefins. The enormous amount of work required to analyze the composition of gasoline hydrocarbons makes it practically impossible to carry out these studies with conventional template determinations.
With regard to compounds boiling at temperatures above 165°C, present in kerosene and high boiling distillates and residues, the difficulty of identifying individual components increases due to the large number of compounds, the overlap of their boiling points and the increasing tendency of high boiling compounds to break down when heated.
Therefore, all combustible petroleum products are divided into fractions according to the temperature limits of their boiling and density, and not according to their chemical composition.
The compounds present in asphalts and similar heavy residue products are extremely complex.
Analyzes show that they are polycyclic compounds.
Distillation
Periodic distillation.
In the early stages of the development of the petrochemical industry, crude oil was subjected to the so-called periodic distillation in a vertical cylindrical distillation apparatus.
The distillation processes were inefficient because there were no distillation columns and no clean separation of the distillates was obtained.
Tubular distillation apparatuses.
The development of the batch distillation process led to the use of a common distillation column, from which distillates with different boiling points were taken from different levels.
This system is still in use today.
The incoming oil is heated in a coil to approximately 320°C, and the heated products are fed to intermediate levels in the distillation column.
Such a column may have 30 to 60 spaced trays and chutes, each with a bath of liquid.
Rising vapors pass through this liquid, which are washed by condensate flowing down.
With proper control of the runoff rate (i.e. the amount of distillates pumped back to the refractionation column), it is possible to produce top-of-column gasoline, kerosene and light combustible distillates with precisely defined boiling ranges at successively decreasing levels.
Usually, in order to improve further separation, the distillation residue from the distillation column is subjected to vacuum distillation.
The design of distillation columns in the oil refining industry becomes a work of art in which no detail is left without attention.
By very precise control of temperature, pressure, and the flow of liquids and vapors, ultrafine fractionation methods have been developed.
These columns reach a height of 60 m and more and allow the separation of chemical compounds whose boiling point differs by less than 6 ° C. They are isolated from external atmospheric influences, and all stages of distillation are automatically controlled.
Processes in some of these columns occur at high pressures, in others – at pressures close to atmospheric; similarly, temperatures vary from extremely high to below -18°C.
Thermal cracking
The propensity for further decomposition of heavier fractions of crude oil when heated above a certain temperature has led to a very important success in the use of the cracking process. When high-boiling oil fractions decompose, carbon-carbon bonds are broken, hydrogen is stripped from hydrocarbon molecules and thus a wider range of products is obtained compared to the composition of the original crude oil. For example, distillates boiling in the temperature range of 290-400 ° C, as a result of cracking, give gases, gasoline and heavy tar-like residual products. The cracking process improves the yield of gasoline from crude oil by breaking down heavier distillates and residues from primary distillation.
The output of coke is determined by the nature of the processed raw materials and the degree of recycling of the heaviest fractions.
Typically, approximately 15–25% naphtha and 35–50% gas oil (i.e. light diesel oil) are formed from the initial cracked volume, along with cracking gases and coke. The latter is used mainly as a fuel, excluding the resulting special types of coke (one of them is a roasting product and is used in the production of carbon electrodes). Coking is still popular mainly as a process for preparing feedstock for catalytic cracking.
catalytic cracking
A catalyst is a substance that speeds up a chemical reaction without changing the nature of the reactions themselves. Many substances have catalytic properties, including metals, their oxides, and various salts.
Goodry process. E. Goodry’s studies of refractory clays as catalysts led to the creation in 1936 of an effective catalyst based on aluminosilicates for the cracking process.
Medium-boiling distillates of oil in this process were heated and transferred to a vapor state; to increase the rate of cleavage reactions, i.e. cracking process, and changing the nature of the reactions, these vapors were passed through the catalyst bed. The reactions took place at moderate temperatures of 430–480°C and atmospheric pressure, in contrast to thermal cracking processes where high pressures are used.
The Goodry process was the first catalytic cracking process successfully commercialized.
The goal of most cracking processes is to achieve optimum gasoline yield. During cracking, heavy molecules break down, as well as complex processes of synthesis and restructuring of hydrocarbon molecules. The effect of different catalysts is different. Some of them, such as chromium and molybdenum oxides, accelerate the dehydrogenation reaction (hydrogen removal). Clays and special aluminosilicate compounds used in industrial catalytic cracking contribute to the accelerated breaking of carbon-carbon bonds more than the removal of hydrogen. They also promote the isomerization of linear molecules into branched ones. These compounds slow down polymerization (see below) and the formation of tar and asphalt, so that oils are not only destructured, but enriched with useful components.
Reforming
Reforming is the process of converting linear and non-cyclic hydrocarbons into benzene-like aromatic molecules. Aromatic hydrocarbons have a higher octane number than other hydrocarbon molecules and are therefore preferred for modern high octane gasoline production.
In thermal reforming, as in catalytic cracking, the main goal is to convert low octane gasoline components to higher octane ones. The process is usually applied to straight-run paraffin cuts boiling between 95-205°C. Lighter cuts are rarely suitable for such conversions.
There are two main types of reforming – thermal and catalytic. In the first, the corresponding fractions of the primary distillation of oil are converted into high-octane gasoline only under the influence of high temperature; in the second, the transformation of the initial product occurs under the simultaneous action of both high temperature and catalysts. The older and less efficient thermal reformer is still used in some places, but in developed countries almost all thermal reformers have been replaced by catalytic reformers.
If gasoline is the preferred product, then almost all reforming is carried out on platinum catalysts supported on an alumina or aluminosilicate carrier.
Most reforming units are fixed bed units. (A catalytic reforming process that uses a stationary catalyst is called platforming.) But under pressure of about 50 atm (when producing gasoline with a moderate octane rating), the activity of the platinum catalyst remains for about a month. Units that use a single reactor have to be shut down for several days to regenerate the catalyst. In other installations, several reactors are used with one additional one, where the necessary regeneration is carried out. The life of a platinum catalyst is reduced in the presence of sulfur, nitrogen, lead and other „poisons“. Where these components are a problem, usually before entering the reactor, the mixture is pre-treated with hydrogen (the so-called hydrotreatment, when, before feeding into the reactor, petroleum distillates – straight-run gasolines – are passed through hydrogen-containing gases, which bind harmful components and reduce them content up to acceptable limits). Some fixed bed reactors are being replaced by continuous catalyst regeneration reactors. Under these conditions, the catalyst moves through the reactor and is continuously regenerated.
Reactions that increase octane during catalytic reforming include:
– dehydrogenation of naphthenes and their transformation into the corresponding aromatic compounds;
– conversion of linear paraffinic hydrocarbons into their branched isomers;
– hydrocracking of heavy paraffinic hydrocarbons into light high-octane fractions;
– formation of aromatic hydrocarbons from heavy paraffinic hydrocarbons by elimination of hydrogen.
Most of the hydrogen-rich gases emitted from these units are used in hydrocracking and the like.
Other gasoline production processes
In addition to cracking and reforming, there are several other important processes in the production of gasoline. The first of these to become economically viable on an industrial scale was the polymerization process, which made it possible to obtain liquid gasoline cuts from olefins present in cracked gases.
Polymerization of propylene, an olefin containing three carbon atoms, and butylene, an olefin of four carbon atoms, produces a liquid product that boils within the same range as gasoline and has an octane rating of 80 to 82. Refineries using polymerization processes , typically operate on fractions of cracked gases containing olefins with three and four carbon atoms.
In this process, isobutane and gaseous olefins react under the action of catalysts and form liquid isoparaffins having an octane number close to that of isooctane. Instead of polymerizing isobutylene to isooctene and then hydrogenating it to isooctane, in this process isobutene reacts with isobutylene to form isooctane directly.
All alkylation processes for the production of motor fuels are carried out using either sulfuric acid or hydrofluoric acid as catalysts at temperatures initially of 0-15°C and then 20-40°C.
Another important way to obtain high-octane feedstock for adding to motor fuels is the isomerization process using aluminum chloride and other similar catalysts.
Isomerization is used to increase the octane number of natural gasoline and straight chain naphthenes. The improvement in antiknock properties occurs as a result of the conversion of normal pentane and hexane to isopentane and isohexane. Isomerization processes are becoming important, especially in those countries where catalytic cracking to improve the yield of gasoline is carried out in relatively small quantities. With additional ethylation, i.e. the introduction of tetraethyl lead, the isomers have octane numbers from 94 to 107 (at present, this method has been abandoned due to the toxicity of the resulting volatile alkyl lead compounds that pollute the natural environment).
Hydrocracking
Early work on the production of liquid fuels from coals by high-pressure hydrogenation (the Bergus process) was carried out mainly in Germany using very strong catalysts, such as molybdenum oxides, which are either insensitive to the presence of sulfur or retain their activity to a large extent after the last sulfation. For this, the following parameters were required: pressure up to 280 atm, temperature about 450 ° C and a catalyst.
Pressures used in modern hydrocracking processes range from about 70 atm to convert crude oil to liquefied petroleum gas (LP-gas) to over 175 atm when full coking and high yield conversion of vapor oil to gasoline and jet fuel occurs. The processes are carried out with fixed beds (rarely in a fluidized bed) of the catalyst. The fluidized bed process is used exclusively for oil residues – fuel oil, tar. Other processes also used residual fuels, but mainly high-boiling oil fractions, as well as light-boiling and medium-distillate straight-run fractions. The catalysts in these processes are sulfided nickel-aluminum, cobalt-molybdenum-aluminum, tungsten materials and noble metals such as platinum and palladium on an aluminosilicate basis.
Where hydrocracking is combined with catalytic cracking and coking, at least 75–80% of the feedstock is converted to gasoline and jet fuel. The production of gasoline and jet fuels can easily change depending on seasonal needs. With a high hydrogen consumption, the product yield is 20–30% higher than the amount of raw material loaded into the plant. With some catalysts, the plant operates efficiently for two to three years without regeneration.
The need to reduce air pollution in industrial areas causes a significant increase in the use of hydrogenation processes for the desulphation of distillates and residual fuels. Hydrocracking processes designed primarily to remove sulfur with low yield requirements are known as „hydrotreating“.
The gaseous light ends first pass through a vacuum liquefaction unit, then the resulting gas oil undergoes a hydrotreating desulfurization before being remixed with some vacuum residues and other low sulfur light ends of the crude oil.
Cleaning of light products
Hydrotreating is currently the most common method for hydrogenating olefins and upgrading light products by removing sulfur and other impurities. For economic reasons, as well as problems associated with air and water impurities, other methods are used, such as the use of lead sulfide as a catalyst in regenerative solvents and pre-refining using high-voltage electric furnaces to better separate the cleaning agent from the resulting product.
Oils and lubricants
The oil industry supplies oils and lubricants ranging in viscosity from liquid, almost like water, to the consistency of molasses. As in the case of other petroleum fractions and products, new methods of their production have appeared – extraction and deasphalting with solvents, etc.
As a result of the introduction of VHVI technology, deep purification of oil fractions of oil occurs with their subsequent processing by the process of catalytic hydrocracking. As a result, the structure and properties of the base oil change at the molecular level. Such oil is called hydrocracking and is classified as a synthetic product. Engine oils produced by VHVI hydrocracking technology have a very high viscosity index, providing reliable protection for any engine.
Solvent extraction.
Industrial solvents include chlorex, furfural (a by-product of oat husk processing), nitrobenzene, phenols, methyl ethyl ketones, etc. Solvent extraction is usually carried out in countercurrent mode (oil flows in one direction, and solvent flows in the opposite direction), which allows selective dissolution and deeper cleaning. With an even more selective procedure, the column is filled with a porous medium (performed, for example, in the form of perforated plates).
Liquefied propane.
Lubricating oil treatment efficiency is enhanced by the use of pressurized LPG. This paraffinic hydrocarbon (boiling point –42°C) has practically no solvent effect on asphalts and very slightly dissolves solid paraffins at low temperatures. However, by adjusting and selecting temperature and solvent/oil ratios, asphalt and wax waxes can be successfully removed.
Solvent dewaxing. Solvent dewaxing is an important step in the production of lubricating oils. Dewaxing crude or refining lubricating oils produces a variety of products ranging from light spindle oils to heavy vacuum greases and commercial waxes. Most widely used for dewaxing a mixture of methyl ethyl ketone and toluene or benzene and acetone.
Cracking gas
Secondary gaseous products are obtained from oil as a result of various cracking processes. Heavy fractions during cracking give gasoline, and gasoline fractions are moderately cracked with an increase in octane number. The gases resulting from these processes can be 2–10% (wt.) of the cracked oil; they differ markedly from natural petroleum gases. Their main feature is the presence of olefins, which are completely absent in natural gases. High temperature cracking gases may contain 50% olefins, including ethylene, propylene and butylenes. As a rule, olefins make up more than 10–25%. Cracking gases usually also contain a small amount of hydrogen. Cracking temperatures of 540°C or higher at low pressure are favorable for ethylene formation, while more moderate temperatures of 455–480°C and high pressure are favorable for the formation of less ethylene and proportionately more propylene and butylenes.
Petrol
Gasoline is the most important product of oil refining; crude oil produces up to 50% of gasoline. This value includes natural gasoline, cracked gasoline, polymerization products, liquefied petroleum gases and all products used as industrial motor fuels. Each oil refining process has requirements for the quantity and quality of gasoline produced.
Composition. Industrial gasoline is a mixture of hydrocarbons with a boiling point range of 30–200°C. Some butanes, boiling below 38°C, have high vapor pressures. Hydrocarbons in gasoline include many isoparaffins as well as aromatics and naphthenes, and cracked gasolines contain 15 to 25% olefins. The octane number of hydrocarbons decreases in the following order: isoparaffins > aromatics > olefins > naphthenes > n-paraffins. There are differences between the components of each of these groups, depending on the structure of the molecules and the boiling point. Various components contribute to the octane number of gasoline blends.
Cracked gasolines contain a significant percentage of those components, when mixed, motor fuel is formed. However, their direct use is legally restricted in many countries because they contain significant amounts of olefins, and olefins are one of the main causes of photochemical smog.
Classification of gasoline.
Gasolines are classified on various bases, including boiling point ranges, octane rating, and sulfur content.
Boiling temperature ranges. Most gasolines boil in the range of 30–200°C. The 50% point, i.e. the temperature at which half of the components of the mixture boils and which determines the composition of the mixture during engine warm-up, and partly during acceleration of the vehicle, is in the range of 98–104 ° C. The high content of low-boiling components, such as butanes and pentanes, causes an exceptionally high vapor pressure in warm weather is also the cause of the formation of vapor locks, when gas bubbles prevent the flow of fuel through the narrow pipes of engines and thermal installations. At the same time, the lack of low-boiling components causes difficulties in starting the engine in winter. The 90% boiling point of gasoline determines engine warm-up time and fuel efficiency.
Octane number.
Octane number is the most important characteristic of gasoline. It is usually determined in a single-cylinder stationary unit equipped with various knock propensity instruments. Normal heptane (seven carbons in a linear chain) detonates very easily; it has a zero octane rating. Isooctane (eight branched carbons) does not detonate until extreme pressure, temperature and load conditions are reached; it is arbitrarily set to an octane rating of 100. When testing gasoline with unknown knock properties, it is compared to a mixture of heptane and iso-octane, which has the same knock ability as the test gasoline; The octane number of gasoline is the percentage of isooctane in such a mixture. The octane number determined in this way does not always correspond to the performance in a multi-cylinder engine under road conditions under varying speeds, loads and accelerations.
Kerosene
Kerosene is the lightest and most volatile liquid heating fuel. Originally used only for lighting, kerosene is now used as a fuel in bakeries, heating and heating appliances, farm equipment, and as a motor fuel component. Good kerosene should have a specific color (approximately 250-300 mm on the Stammer scale for petroleum products), sufficient viscosity to ensure stable and uniform impregnation of the wick, should burn with a clear, high flame without soot or solid carbon deposits on the wick, soot in chimneys and on lamp glass . The safety of kerosene when used in lighting lamps is determined by the standard flash test. Kerosene is heated slowly in a small glass or metal cup and the surface is periodically touched with a flame until a small amount of smoke appears, corresponding to the flash point.
Other products
Intermediate petroleum distillates, boiling at temperatures higher than kerosene but lower than lubricating oils, are fuels for medium and high speed diesel engines.
Diesel fuels are rated by their cetane number, a real measurement of flammability under temperature and pressure, not combustion ability. In this case, the fuel is compared with a mixture of cetane – a paraffinic hydrocarbon with 16 carbon atoms, which ignites easily under pressure, and a-methylnaphthalene, which does not ignite. The percentage of cetane in a mixture that shows the same flammability as diesel fuel under standard test conditions is called the cetane number. Paraffin fuels are more suitable for diesel engines because they ignite easily under pressure without an additional ignition spark. However, due to the increasing demand for straight distillates for purposes other than diesel, the use of lower cetane heavy distillates from catalytic cracking is increasing. Improving the ignition reliability of low quality diesel fuels, improving flammability, better known as increasing the cetane number, is achieved by adding special oils. They include components such as organic oxides and peroxides. Small additions of amyl nitrate satisfactorily improve fuel quality.
Jet fuel oil can be kerosene or naphthenic.
Consists primarily of straight-run gasoline or kerosene in kerosene-type fuel or No. 1 naphthenic-type fuel.
The use of light distillates as domestic fuels is constantly increasing, as they are more convenient and cleaner than, for example, coal. They compete with natural gas and electricity.
Most industrial boilers and thermal power plants use black viscous residues of oil refining – fuel oil as fuels. In most cases, these are cracked products, although there are also products of direct distillation.
They are the main means for protecting equipment from the action of water. All of them have a water-white color and a melting point in the range of 50-95 ° C.
They are used as insulation in a wide variety of industries such as the electrical and communication industries, as well as in printing, engraving, etc.
consisting of heavy oil residues and paraffin waxes, is produced by filtering cylinder distillates and is used in technology (as an anti-corrosion lubricant, etc.) and medicine (mainly for the manufacture of ointments).
Obtaining petroleum products by fractionation.
The oil industry is the main producer of chemicals.
Its first successes in the separation of individual hydrocarbons were achieved in the fractionation of natural gas and natural gasoline.
The first components isolated in this way were methane, ethane, propane, normal butane, isobutane, and pentines.
Appropriately designed distillation columns make it possible to separate from cracking gases small fractions with a narrow boiling point range, which serve as primary raw materials for chemical production, these are hydrocarbons having from 1 to 5 carbon atoms (both paraffins and olefins).
A large number of chemicals are produced commercially by the oxidation of natural gas.
They include methyl (wood) alcohol, ethyl (food) alcohol, propyl alcohol (with 3 carbon atoms), formaldehyde, acetone, methyl ethyl ketone, formic acid, acetic acid.
From these components, primarily containing oxygen, many other products are produced, well known in organic chemistry.
Ammonia is synthesized from hydrogen obtained by cracking natural gas and nitrogen extracted by distillation from liquefied air. Nitric acid and ammonium nitrate, used to make fertilizers and explosives, are also made from ammonia.