What is pyrolysis? What does it mean for the modern chemical industry? We will understand 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. Petroleum products, coal, and wood are subject to such decay. Upon completion of the process, synthesis gas is formed, as well as other end products.
Process features
The pyrolysis reaction is carried out at a temperature of from 800 to 900 degrees. This process 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 the processing of oil and gas was patented by A. A. Letnim 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 the chemical industry as acetic acid, charcoal, resin, acetone. Considering that our country is a “storeroom” of forests, large mills operate in Russia to carry out the process of wood pyrolysis.
Garbage pyrolysis
Waste pyrolysis is a special project related to the disposal of household waste. The difficulty of pyrolyzing plastics, tires, and various organic wastes is due to the fact that a different technology is proposed that differs significantly from the processing of other solid materials.
Many wastes contain sulfur, chlorine, phosphorus, which after oxidation (formation of oxides) acquire volatility properties. Pyrolysis products pose a threat to the environment.
When chlorine interacts with organic substances formed after the decomposition process is completed, strong toxic compounds such as dioxins are released. In order to catch such products from the smoke, a special pyrolysis unit is needed. A similar procedure involves significant material costs.
For European countries of great environmental importance is the problem of recycling old car tires, rubber parts that have worked out their useful life. 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 possible.
A huge amount of various substances of organic and inorganic composition can be obtained from household and construction waste, therefore it is so important to develop this industrial area.
Polymers and car tires are excellent raw materials. After its processing by means of low-temperature pyrolysis, it is possible to obtain liquid fractions of saturated hydrocarbons (synthetic oil), combustible gas, carbon residue, and also metal cord. When burning a ton of rubber tires, about 270 kg of soot is released into the atmosphere, as well as about 450 kg of toxic gaseous substances.
Synthesis gas
This is a mixture of hydrogen and carbon monoxide (2). In industrial volumes, it is obtained by conducting steam methane conversion, coal gasification, methane oxidation, and organic waste processing. 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, methanol production and Fischer-Tropsch synthesis occupy a special place. By it is meant 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, cobalt and iron are chosen as catalysts (accelerators) of 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.
The specifics of obtaining
What does the chemistry of the reaction look like? Let's try to find out what it is. The definition of pyrolysis was considered above; now we dwell on the features of the chemical process. The Fischer-Tropsch process involves the interaction of methane with oxygen. The products of interaction are carbon monoxide and hydrogen. As a result of the reaction, we obtain hydrocarbons of a number of alkanes and water vapor. It is the resulting hydrocarbon products after purification that are used to create synthetic oil.
Pyrolysis value
Carbon monoxide and gaseous hydrogen are formed during 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).
With non-oxidative pyrolysis of solid waste, synthesis gas is currently produced in the chemical industry. A certain amount of it is also used in the form of automobile fuel, without being subjected to further processing by the Fischer-Tropsch reaction. If necessary, the use of liquid fuels similar to paraffins and grease uses a simplified chemical technology.
If you want 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 completion of the interaction, hydrogen and carbon dioxide are formed.
Technology improvement
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. Such an indicator existed in 1944.
Modernity
Nowadays, there are two large companies that use the Fischer-Tropsch process in their technology. Most of the South African diesel fuel 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 can cause minimal damage to the environment. For example, American companies currently choose coke or coal as feedstock to produce high-quality liquid hydrocarbons.
Despite the fact that the pyrolysis process is a well-developed technology that can be used on a large scale, it is associated with rather high material costs for the repair and operation of the installation. For many manufacturers, this is a deterrent, because there is a tendency to lower world oil prices.
Conclusion
World reserves of coal are quite large. They can be used as a fuel source 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 for consumers in the price range. In the case of a combination of Fischer-Tropsch synthesis and biomass gasification, we can talk about a promising method of manufacturing a renewable version of automotive fuel.
Synthetic raw materials obtained by coal pyrolysis are competitive only at an oil cost of more than $ 40 per barrel. The production of such a mixture of hydrocarbons requires investments in the range of seven to nine billion dollars 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 in recent years, many developed countries have paid great attention to the development of new methods for producing hydrocarbon fuels, which would allow them to move away from traditional petroleum feedstocks. Thanks to innovations and improvement of the technological chain, the pyrolysis process has become significantly cheaper and more affordable to produce high-quality liquid hydrocarbons. Educated products are used not only as fuel, but also to create a variety of organic substances.