Coal is one of the oldest fuels known to man. And even today it occupies a leading position in terms of usage. The reason for this is its prevalence, ease of extraction, processing and use. But what is he? What is the chemical formula of coal?
Actually, this question is not entirely correct. Coal is not a substance, it is a mixture of various substances. There are a lot of them, so it is impossible to completely determine the composition of coal. Therefore, under the chemical formula of coal in this article, we will rather mean its elemental composition and some other features.
But what can we learn about the state of this substance? Coal is formed from the remains of plants over many years due to exposure to high temperature and pressure. And since plants are organic in nature, organic substances will predominate in the composition of coal.
Depending on the age and other conditions of the origin of coal, it is divided into several types. Each species is distinguished by its elemental composition, the presenceimpurities and other important characteristics.
Brown coal
Is the youngest type of coal. It even has a vegetal woody structure. Formed directly from peat at a depth of about 1 kilometer.
This type of coal contains a fairly large amount of moisture: from 20 to 40%. When exposed to air, it evaporates, and the coal crumbles into powder. Next, we will talk about the chemical composition of this particular dry residue. The amount of inorganic impurities in brown coal is also high and amounts to 20-45%. These impurities are silicon dioxide, oxides of aluminum, calcium and iron. It may also contain alkali metal oxides.
There are a lot of volatile organic and inorganic substances in this coal. They can be up to half the mass of this type of coal. The elemental composition minus inorganic and volatile substances is as follows:
- Carbon 50-75%.
- Oxygen 26-37%.
- Hydrogen 3-5%.
- Nitrogen 0-2%.
- Sulfur 0.5-3%.
Coal
According to the time of formation, this type of coal comes next after brown. It has a black or gray-black color, as well as a resinous, sometimes metallic sheen.
Humidity of coal is much less than brown: only 1-12%. The content of volatile substances in coal varies greatly depending on the place of extraction. It can be minimal (from 2%), but can also reach values similar to brown coal (up to 48%). The elementary composition is as follows:
- Carbon 75-92%.
- Hydrogen 2, 5-5, 7%.
- Oxygen 1, 5-15%.
- Nitrogen up to 2.7%.
- Sulfur 0-4%.
From here we can conclude that the chemical formula of hard coal consists of more carbon than brown coal. This makes this type of coal a better quality fuel.
Anthracite
Anthracite is the oldest form of fossil coal. It is dark black in color and has a characteristic metallic sheen. This is the best coal in terms of the amount of heat it releases when it burns.
The amount of moisture and volatile substances in it is very small. About 5-7% for each indicator. And the elemental composition is characterized by an extremely high carbon content:
- Carbon over 90%.
- Hydrogen 1-3%.
- Oxygen 1-1, 5%.
- Nitrogen 1-1, 5%.
- Sulfur up to 0.8%.
More coal is contained only in graphite, which is a further stage of coalification of anthracite.
Charcoal
This type of coal is not a fossil, so it has some peculiarities in its composition. It is produced by heating dry wood to a temperature of 450-500 oC without air. This process is called pyrolysis. During it, a number of substances are released from wood: methanol, acetone, acetic acid and others, after which it turns into coal. By the way, the combustion of wood is also pyrolysis, but due to the presence of oxygen in the air, the released gases ignite. This is what causes the existenceflames when burning.
Wood is not homogeneous, it has a lot of pores and capillaries. A similar structure is partly preserved in the coal obtained from it. For this reason, it has good adsorption capacity and is used along with activated carbon.
The moisture content of this type of coal is very low (about 3%), but during long-term storage it absorbs moisture from the air and the percentage of water rises to 7-15%. The content of inorganic impurities and volatile substances is regulated by GOSTs and should not exceed 3% and 20%, respectively. The elemental composition depends on the production technology, and approximately looks like this:
- Carbon 80-92%.
- Oxygen 5-15%.
- Hydrogen 4-5%.
- Nitrogen ~0%.
- Sulfur ~0%.
The chemical formula of charcoal shows that in terms of carbon content it is close to stone, but in addition it has only a small amount of elements unnecessary for combustion (sulfur and nitrogen).
Activated carbon
Activated carbon is a type of carbon with a high specific pore surface area, which makes it even more absorbent than wood. Charcoal and coal, as well as coconut shells are used as raw materials for its production. The starting material is subjected to an activation process. Its essence is to open clogged pores with high temperature, electrolyte solutions or water vapor.
During the activation process, only the structure of the substance changes, so the chemical formula of activated carbonidentical to the composition of the raw materials from which it was made. The moisture content of activated carbon depends on the specific surface area of the pores and is usually less than 12%.
