What is pyrolysis? The definition, the concept of the process

What is pyrolysis? What does it mean for the modern chemical industry? We will together understand this issue.

About pyrolysis of hydrocarbons

So what is pyrolysis? The definition of this process involves the thermal decomposition of an organic compound without the presence of oxygen. Such decomposition of oil products, coal, timber. After the process is completed, synthesis gas is formed, as well as other end products.

Process Features

The pyrolysis reaction is carried out at a temperature of 800 to 900 degrees. It is this process that is considered the main option for the formation of ethylene. This unsaturated hydrocarbon is an important starting material for the preparation of a variety of organic compounds: benzene, divinyl, propylene.

Pyrolysis of wood

Arguing over what is pyrolysis, we note that for the first time this chemical technology of processing oil and gas was patented by A. A. Letnim in 1877. What is pyrolysis of wood? This reaction is carried out at a temperature of about 500 degrees. It is associated with the formation of such important components of chemical production as acetic acid, charcoal, resin, acetone. Given that our country is a "pantry" of forests, in Russia there are large mills to carry out the process of pyrolysis of wood.

Pyrolysis of garbage

Pyrolysis of waste is a special project associated with the destruction of domestic garbage. The complexity of pyrolysis of plastics, tires, various organic wastes is due to the fact that a different technology is expected, which differs substantially from the processing of other solid materials.

In the composition of many wastes there is sulfur, chlorine, phosphorus, which after oxidation (formation of oxides) acquire the properties of volatility. Pyrolysis products pose a threat to the environment.

In the interaction of chlorine with organic substances formed after the completion of the decomposition process, the release of strong toxic compounds, such as dioxins. In order to catch these products from the emitted smoke, a special pyrolysis unit is needed. Such a procedure involves substantial material costs.

For European countries, the problem of recycling old car tires, rubber parts, which have fulfilled their operational life, is of great ecological importance. Due to the fact that natural oil is an irreplaceable type of minerals, it is necessary to use secondary resources to the maximum extent.

From household and construction garbage it is possible to receive a huge quantity of various substances of organic and inorganic composition, that is why it is so important to develop this industrial direction.

Polymers and car tires are an excellent valuable raw material. After its processing by low-temperature pyrolysis, liquid fractions of saturated hydrocarbons (synthetic oil), combustible gas, carbonaceous residue, and also metal cord can be obtained. When burning a ton of rubber tires, about 270 kg of soot are released into the atmosphere, as well as about 450 kg of toxic gaseous substances.

Synthesis gas

It is a mixture of hydrogen and carbon monoxide (2). In industrial volumes, it is produced by steam methane conversion, gasification of coal, methane oxidation, processing of organic waste. Depending on the technology used to produce the synthesis gas, the ratio of carbon monoxide and hydrogen in it can vary from 1: 1 to 1: 3.

Among the main areas of application of this raw material, the production of methanol, as well as the synthesis of Fischer-Tropsch, takes a special place. It is understood as a chemical reaction that occurs when a catalyst is present. It consists in the conversion of carbon monoxide and hydrogen into a variety of liquid hydrocarbons. In general, cobalt and iron are chosen as catalysts (accelerators) for this interaction.

The specificity of this process in the possibility of producing synthetic materials for application in the form of lubricating synthetic oil or fuel.

Specificity of receipt

What does the reaction chemistry look like? Let's find out what it is. The definition of pyrolysis was discussed above, now let us dwell on the features of the chemical process. The Fischer-Tropsch method implies the interaction of methane with oxygen. The products of interaction are carbon monoxide and hydrogen. The reaction produces hydrocarbons of a number of alkanes and water vapor. It is the resulting hydrocarbon products, after purification, used to create synthetic oil.

The importance

Carbon monoxide and gaseous hydrogen are formed during the partial oxidation of wood fuel and coal. The significance of this process is the formation of hydrogen or liquid hydrocarbons from solid raw materials (hydrocarbon waste or coal).

In the non-oxidative pyrolysis of solid waste, synthesis gas is currently produced in the chemical industry. Some of its amount is also used in the form of automobile fuel, not subject to subsequent processing by the Fischer-Tropsch reaction. If it is necessary to use liquid fuel similar to paraffins and lubrication, simplified chemical technology is used.

If it is necessary to increase the amount of hydrogen produced, by changing the volume of water vapor, the chemical equilibrium in this equation is shifted. In this case, after completion of the interaction, hydrogen and carbon dioxide are formed.

Improvement of technology

After the discovery, made in 1920 by German researchers Hans Tropsch and Franz Fischer, the technology was repeatedly modernized and improved. Gradually, the amount of synthetic fuel created by pyrolysis reached 124 thousand barrels per day in Germany. This indicator existed in 1944.

Modernity

Nowadays, there are two large companies that use the Fischer-Tropsch process in their technology. Most of South Africa's diesel fuel is produced by pyrolysis, followed by oxidation of the forming products.

Special attention was paid to this chemical technology after scientists began to look for ways to obtain diesel low-sulfur substances, capable of causing minimal damage to the environment. For example, American companies currently use coke or coal as feedstock to produce liquid hydrocarbons of high quality.

Despite the fact that the pyrolysis process is a proven technology that can be used on a large scale, it is associated with rather high material costs for the repair and operation of the plant. For many manufacturers, this is a deterrent, because there is a tendency to reduce world oil prices.

Conclusion

World reserves of coal are large enough. They can be used in the form of a fuel source in connection with a significant depletion of oil. Analysts involved in the oil and gas industry are convinced that it is through pyrolysis that high-quality hydrocarbons can be produced. They note that the fuel produced not only has higher environmental performance than oil fuels, but is also quite acceptable for consumers over the price range. In the case of a combination of Fischer-Tropsch synthesis and biomass gasification, it is possible to talk about a promising way of making a renewable version of automobile fuel.

Synthetic raw materials, obtained by pyrolysis of coal, are competitive only at an oil price of more than $ 40 per barrel. To produce such a mixture of hydrocarbons, investments in the range of seven to nine billion dollars are needed for eighty thousand barrels of synthetic fuel. Technologies associated with the pyrolysis process are recognized by ecologists as one of the safest for the environment. That is why recently many developed countries pay much attention to the development of new ways of obtaining hydrocarbon fuel, which would allow them to move away from traditional oil raw materials. Thanks to innovations and improvement of the technological chain, the pyrolysis process became much cheaper and more affordable for obtaining high-quality liquid hydrocarbons. Educated products are used not only as a fuel, but also for the creation of a variety of organic substances.