What is pyrolysis? What is its significance for the modern chemical industry? Let's look into this issue together.
About the 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. Oil products, coal, wood are exposed to such disintegration. 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 feedstock for the production of various organic compounds: benzene, divinyl, propylene.
Wood pyrolysis
Arguing over what pyrolysis is, we note that for the first time this chemical technology for processing oil and gas raw materials was patented by A. A. Letny in 1877. What is wood pyrolysis? 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. Considering that our country is a "pantry" of forests, large plants operate in Russia for the process of wood pyrolysis.
Trash pyrolysis
Waste pyrolysis is a special project related to the destruction of household waste. The complexity of the pyrolysis of plastics, tires, various organic wastes is due to the fact that a different technology is assumed, which is significantly different from the process of processing other solid materials.
Many wastes contain sulfur, chlorine, phosphorus, which, after oxidation (formation of oxides), acquire the properties of volatility. Pyrolysis products pose a threat to the environment.
When chlorine interacts with organic substances formed after the completion of the decomposition process, strong toxic compounds such as dioxins are released. In order to capture such products from the emitted smoke, a special pyrolysis unit is needed. Such a procedure involves significant material costs.
For European countries, the problem of recycling old car tires, rubber parts that have worked out their service life is of great environmental importance. Due to the fact that natural oil raw materials are an irreplaceable type of minerals, it is necessary to use secondary resources to the maximum extent.
From household and construction waste, you can get a huge amount of various substances of organic and inorganic composition, so it is so important to developthis industry.
Polymers and car tires are excellent valuable raw materials. After its processing by low-temperature pyrolysis, it is possible to obtain liquid fractions of saturated hydrocarbons (synthetic oil), combustible gas, carbon residue, and metal cord. Burning a ton of rubber tires releases about 270 kg of soot into the atmosphere, as well as about 450 kg of toxic gaseous substances.
Syngas
This is a mixture of hydrogen and carbon monoxide (2). In industrial volumes, it is obtained during the steam reforming of methane, coal gasification, methane oxidation, and processing of organic waste. Depending on the technology used to produce 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, a special place is occupied by the production of methanol, as well as the Fischer-Tropsch synthesis. It is understood as a chemical reaction that occurs in the presence of a catalyst. It consists in the conversion of carbon monoxide and hydrogen into a variety of liquid hydrocarbons. Basically, cob alt and iron are chosen as catalysts (accelerators) for this interaction.
The specificity of this process is the possibility of producing synthetic materials for use in the form of synthetic lubricating oil or fuel.
Receiving specifics
What does the chemistry of a reaction look like? Let's try to find out what it is. The definition of pyrolysis was discussed above, now let's dwell on the features of the chemical process. The Fischer-Tropsch method involves the interaction of methane with oxygen. The reaction products are carbon monoxide and hydrogen. As a result of the reaction, we get hydrocarbons of a number of alkanes and water vapor. It is the resulting hydrocarbon products after purification that are used to create synthetic oil.
Meaning of pyrolysis
Carbon monoxide and hydrogen gas are produced by the partial oxidation of wood fuel and coal. The significance of such a process lies in 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 it is also used in the form of automotive fuel, without further processing by the Fischer-Tropsch reaction. If it is necessary to use liquid fuels similar to paraffins and lubricants, a 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 is shifted in this equation. In this case, after the interaction is completed, hydrogen and carbon dioxide are formed.
Improving technology
After the discovery made in 1920 by German researchers Hans Tropsch and Franz Fischer, the technology has been repeatedly modernized and improved. Gradually quantitySynthetic fuel created by pyrolysis reached 124,000 barrels per day in Germany. Such an indicator existed in 1944.
Modernity
Today, there are two large companies that use the Fischer-Tropsch process in their technology. Most of the diesel fuel in South Africa is produced by pyrolysis, followed by oxidation of the forming products.
This chemical technology gained particular attention after scientists began to look for ways to produce diesel low-sulfur substances that could cause minimal environmental damage. For example, American companies are currently choosing coke or coal as feedstock, producing high quality liquid hydrocarbons.
Despite the fact that the pyrolysis process is a mature 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 producers, this is a deterrent, because there is a downward trend in world oil prices.
Conclusion
World coal reserves are quite large. They can be used as a source of fuel due to significant oil depletion. 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 resulting fuel not only has higher environmental performance compared to petroleum fuel, but is also quite acceptable to consumers.by price range. In the case of a combination of Fischer-Tropsch synthesis and biomass gasification, we can talk about a promising way to produce a renewable version of automotive fuel.
Synthetic feedstock, obtained by pyrolysis of coal, is competitive only if the cost of oil is more than $40 per barrel. The production of such a mixture of hydrocarbons requires investments ranging from seven to nine billion dollars for eighty thousand barrels of synthetic fuel. Technologies associated with the pyrolysis process are recognized by environmentalists as one of the safest for the environment. That is why recently many developed countries have been paying great attention to the development of new methods for producing hydrocarbon fuels, which would allow them to move away from traditional oil feedstock. Thanks to innovations and improvement of the technological chain, the pyrolysis process has become much cheaper and more accessible for obtaining high-quality liquid hydrocarbons. Educated products are used not only as fuel, but also to create a variety of organic substances.
