Cracking is what? Cracking of oil, oil products, alkanes. Thermal cracking

It's no secret that gasoline is produced from oil. However, most motorists do not even ask themselves how this process of turning oil into fuel for their favorite vehicles is going on. It is called cracking, with its help refineries receive not only gasoline, but also other petrochemical products necessary in modern life. An interesting story is the origin of this method of oil refining. The inventor of this process and installation is considered to be a Russian scientist, and the installation for this process is very simple and extremely understandable even to a person who does not understand chemistry.

What is cracking?

Why is cracking so called? This word came from English cracking, which means splitting. In fact, this is the process of oil refining, as well as the fractions forming part of it. It is produced in order to obtain products that have a smaller molecular mass. These include lubricating oil, motor fuel and the like. In addition, as a result of this process, the products required in the use of chemical and petrochemical industries are produced.

Cracking of alkanes involves several processes, among them condensation and polymerization of substances. The result of these processes is the formation of petroleum coke and a fraction boiling at a very high temperature and called cracking residue. The boiling point of this substance is more than 350 degrees. It should be noted that, in addition to these processes, there are other - cyclization, isomerization, synthesis.

The invention of Shukhov

The cracking of oil, its history begins in 1891. Then engineer Shukhov VG. And his colleague Gavrilov SP Invented an industrial plant for continuous thermal cracking. This was the first installation of its kind in the world. Inventors in accordance with the laws of the Russian Empire patented it in the authorized body of their country. Of course, this was an experimental model. Later, after almost a quarter of a century, Shukhov's technical solutions were used as the basis for an industrial cracker in the United States. And in the Soviet Union, the first such installations on an industrial scale began to be manufactured and produced at the Sovetskiy Cracking plant in 1934. This factory was located in Baku.

The way of the English chemist Barton

At the beginning of the twentieth century, an invaluable contribution to the petrochemical industry was made by the Englishman Barton, who was looking for ways and solutions for obtaining gasoline from oil. He was found absolutely perfect way, that is, the reaction of cracking, which resulted in the greatest number of lightweight gasoline fractions. Before that, an English chemist was engaged in the processing of petroleum products, including fuel oil, to extract kerosene. Having solved the problem of obtaining gasoline fractions, Barton patented his method of obtaining gasoline.

In 1916, the Barton method was used in industrial conditions, and just four years later, more than eight hundred of its installations were already working hard at the enterprises.

The dependence of the temperature of the boiling of the substance on the pressure on it is well known. That is, if the pressure on some liquid is very high, then, accordingly, the temperature of its boiling will be high. With a decrease in the pressure on this substance, it can boil already at a lower temperature. It was this knowledge that the chemist Barton used, achieving the best temperature for the reaction of cracking. This temperature is from 425 to 475 degrees. Of course, with such a high temperature effect on oil, it will evaporate, and it is rather difficult to work with vaporous substances. Therefore, the main task of the English chemist was to prevent the boiling and evaporation of oil. He began to carry out the whole process under high pressure.

Cracking plant

The Burton device consisted of several elements, including a boiler operating under high pressure. It was made of fairly thick steel, was located above the furnace, which, in turn, was equipped with a smoke pipe. It was directed upwards to the water collector-cooler. Then the entire pipeline was directed to a container for collecting liquid. At the bottom of the tank was a branched pipe, each tube of which had a control valve.

How cracking was performed

The cracking process took place as follows. The boiler was filled with oil, in particular, fuel oil. Gradually, the fuel oil was heated by the furnace. When the temperature reached one hundred and thirty degrees, the water in it was evaporated (evaporated). Passing through the pipe and cooling, this water got into the collecting tank, and from there again through the pipe went down. At the same time, the process continued in the boiler, during which other components, air and other gases, disappeared from the fuel oil. They passed the same path as the water, heading for the pipeline.

Getting rid of water and gases, the oil was ready for subsequent cracking. The stove melted harder, the temperature of her and the boiler slowly rose until it reached 345 degrees. At this time, evaporation of light hydrocarbons occurred. Passing through the pipe to the cooler, they even there remained in a state of gas, unlike water vapor. Once in the collecting tank, these hydrocarbons followed the pipeline, as the exhaust valve was closed and prevented them from leaving the ditch. They returned through the pipe again into the container, and then repeated again all the way, finding no way out.

Accordingly, over time, they became more and more. The result was the growing pressure in the system. When this pressure reached five atmospheres, light hydrocarbons were already unable to evaporate from the boiler. Hydrocarbons, squeezing, maintained a uniform pressure in the boiler, the pipeline, the collection tank and the refrigerator. At the same time, the splitting of heavy hydrocarbons began because of the high temperature. As a result, they turned into gasoline, that is, into a light hydrocarbon. Its formation began to occur at about 250 degrees, light hydrocarbons during the decomposition evaporated, formed a condensate in the cooling chamber, collected in a collection tank. Then, through the pipe, the gasoline flowed into the prepared tanks, in which the pressure was lowered. This pressure facilitated the removal of gaseous elements. With the passage of time, such gases were removed, and the finished gasoline was poured into the necessary reservoirs or tanks.

The more light hydrocarbons evaporated, the more resilient and resistant to temperature effects fuel oil became. Therefore, after turning half the contents of the boiler into gasoline, further work was suspended. Helped in determining the amount of gasoline received specially installed in the installation of the meter. The oven was extinguished, the pipeline was blocked. The pipeline valve that connected it to the compressor, on the contrary, opened, the vapors moved to this compressor, the pressure in it was less. At the same time, the pipe leading to the gasoline was blocked to cut off its connection with the plant. Further actions were to wait for the boiler to cool down, draining the substance out of it. For subsequent use, the boiler was then cleaned of coke deposits, and a new cracking process could be carried out.

Oil refining stages and Barton installation

It should be noted that the possibility of splitting oil, that is cracking alkanes, has long been noticed by scientists. However, it was not used in conventional distillation, since this splitting was undesirable in this situation. For this, overheated steam was used in the process. With its help oil was not split, but evaporated.

Throughout its existence, the oil refining industry has experienced several stages. So, from the sixties of the XIX century to the beginning of the last century, oil was processed for the purpose of obtaining only kerosene. He was then a material, a substance through which people received illumination in the dark. It is noteworthy that during such processing, light-weight fractions obtained from oil were considered waste. They poured into ditches and were destroyed by burning or other means.

The installation of the cracking of Barton and its method served as a fundamental stage in the entire oil refining industry. It was this method of the English chemist that made it possible to achieve a higher result of obtaining gasoline. The yield of this product of oil refining, as well as of other aromatic hydrocarbons, has increased several times.

The need for cracking

In the early twentieth century, gasoline was, you might say, an unnecessary product of oil refining. There was very little motor transport working on this type of fuel at that time, so fuel was not in demand. But over time, the fleet of countries has grown steadily, respectively, and required gasoline. Only in the first ten to twelve years of the twentieth century, the need for gasoline increased by 115 times!

Gasoline obtained by simple distillation, and, more precisely, its volumes did not satisfy the consumer, and even the producers themselves. Therefore, it was decided to use cracking. This allowed us to increase the pace of production. Thanks to this, it was possible to increase the amount of gasoline for the needs of the states.

A little later it was established that the cracking of petroleum products could be carried out not only on fuel oil or diesel oil. As raw material for this, crude oil was also suitable. Also, the manufacturers and specialists in this field determined that the gasoline produced by the cracking method was more qualitative. In particular, when used in cars they worked more regularly and longer than usual. This was due to the fact that the gasoline produced by cracking retained certain hydrocarbons that are burned off during normal distillation. These substances, in turn, when used in internal combustion engines were able to ignite and burn more smoothly, as a result, the engines worked without fuel explosions.

Catalytic cracking

Cracking is a process that can be divided into two types. It is used to produce fuel, for example, gasoline. In some cases, it can be carried out by simple thermal treatment of petroleum products - thermal cracking. In other cases, this process is possible not only with the help of high temperature, but also with the addition of catalysts. Such a process is called catalytic.

Using the last mentioned processing method, manufacturers receive high-octane gasoline.

It is believed that this species is the most important process, which provides the most profound and high-quality processing of oil. The installation of catalytic cracking, introduced into industry in the thirties of the last century, allowed producers to gain undoubted advantages for the whole process. These include operational flexibility, relative ease of alignment with other processes (deasphalting, hydrotreatment, alkylation, etc.). It is thanks to this versatility that a significant share of the use of catalytic cracking in the entire volume of oil refining can be explained.

Raw materials

As a feedstock for catalytic cracking, a vacuum gas oil is used, which is a fraction having a boiling range of 350 to 500 degrees. The final boiling point is set differently and depends directly on the metal content. In addition, this index is also affected by the coking ability of raw materials. It can not be more than three-tenths of a percent.

Preliminary is required and hydrotreated such fraction, as a result of which all kinds of sulfur compounds are removed. Also hydrotreatment allows to reduce coking ability.

At some companies known on the oil refining market, there are several processes that they perform, at which cracking of heavy fractions takes place. They can be coked to six to eight percent fuel oil. In addition, the raw materials may be the residues of hydrocracking. The most probably, rare and, it may be said, exotic raw material is spilled fuel oil. A similar installation (millisecond technology) is available in the Republic of Belarus at the Mozyr Oil Refinery.

Literally until recently, when catalytic cracking of petroleum products was used, an amorphous spherical catalyst was used. It was a three-five-millimeter ball. Now for this purpose cracking catalysts with a volume of no more than 60-80 μm (zeolite-containing microspherical catalyst) are used. They consist of a zeolite element, located on an aluminosilicate matrix.

Thermal method

As usual, thermal cracking is used for the processing of petroleum products, if it is necessary to obtain a product with a smaller molecular weight as a result. For example, such include unsaturated hydrocarbons, petroleum coke, light motor fuels.

The direction of this method of oil processing depends on the molecular weight and nature of the raw materials, and also directly on the conditions under which cracking itself occurs. This was confirmed by chemists over time. One of the most important conditions that affect the speed and direction of thermal cracking is the temperature, pressure and duration of the process. The latter receives a visible phase at three hundred to three hundred and fifty degrees. In describing this process, the first-order cracking kinetic equation is used. The result of cracking, or rather, the composition of its products is influenced by pressure changes. The reason for this is a change in the speed and characteristics of the secondary reactions, which, as mentioned earlier, involve polymerization and condensation, which are accompanied by cracking. The reaction equation for the thermal process is as follows: C20H42 = C10H20 + C10 H22. The effect is on the result and the result is still the volume of reagents.

It should be noted that cracking of oil, carried out by the listed methods, is not the only one. In the production activity, oil refineries use many other types of this process of processing. So, in certain cases, the so-called oxidative cracking, carried out with the use of oxygen, is used. It is used in production and electric cracking. With this method manufacturers get acetylene by passing through electricity methane.