Coal is one of the oldest types of fuel known to man. And even today it occupies a leading position in terms of volume of use. The reason for this is its prevalence, ease of extraction, processing and use. But what is he like? What is the chemical formula of coal?
In fact, 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, by the chemical formula of coal in this article we will mean rather 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 for many years due to exposure to high temperature and pressure. And since plants are organic in nature, organic matter will dominate in coal.
Depending on the age and other conditions of origin of coal, it is divided into several types. Each species differs in elementary composition, the presence of impurities and other important characteristics.
Brown coal
It is the youngest type of coal. It even has a vegetative woody structure. It is 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 it gets into the air, it evaporates, and the coal crumbles into powder. Further, we will focus on the chemical composition of this particular dry residue. The amount of inorganic impurities in brown coal is also large and amounts to 20-45%. As 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
By the time of formation, this type of coal goes next after brown. It has a black or gray-black color, as well as a tarry, sometimes metallic sheen.
The 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 it can also reach values similar to brown coal (up to 48%). The elemental 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 this we can conclude that the chemical formula of coal coal consists of a greater amount of carbon than brown. This makes this type of coal a better fuel.
Anthracite
Anthracite is the oldest form of fossil coal. It is characterized by a dark black color, and it has a characteristic metallic luster. This is the best coal in terms of the amount of heat that it emits during combustion.
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 more than 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 fossil, therefore, it has some features of its composition. It is produced by heating dry wood to a temperature of 450-500 o C without access of 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, wood burning is also pyrolysis, but due to the presence of oxygen in the air, the evolved gases ignite. This is what determines the presence of flames during combustion.
Wood is not homogeneous, there are a lot of pores and capillaries in it. A similar structure is partially preserved by the coal obtained from it. For this reason, it has good adsorption capacity and is used along with activated carbon.
Humidity of this type of coal is very small (about 3%), but with prolonged 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 be no more than 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 coal with a high specific pore surface, which is why it has even greater adsorption capacity than wood. As raw materials for its production, charcoal and hard coal, as well as coconut shells are used. The starting material is subjected to an activation process. Its essence is to open the clogged pores by the action of high temperature, electrolyte solutions or water vapor.
During the activation process, only the structure of the substance changes, therefore, the chemical formula of activated carbon is identical to the composition of the raw material from which it was made. The moisture content of activated carbon depends on the specific surface of the pores and is usually less than 12%.