STUDYING THE ABSORPTION OF A MIXTURE OF GASES CONTAINING SULFUR OXIDES IN AN ALKALINE MEDIUM

ABSTRACT

In the article, the absorption of a mixture of gases containing sulfur dioxide and sulfur trioxides in an alkaline environment is considered. In the mixture of gases consisting of sulfur oxides, good absorption of sulfur trioxide in solutions was determined, and it was shown that the problem requires a deeper study of the laws of absorption of sulfur dioxide in solutions. Accordingly, it is recommended to use an alkaline medium for better absorption of sulfur dioxide in solutions.

АННОТАЦИЯ

В статье рассмотрено поглощение смеси газов, содержащих диоксид серы и триоксиды серы, в щелочной среде. В смеси газов, состоящей из оксидов серы, установлено хорошее поглощение сернистого ангидрида в растворах и показано, что проблема требует более глубокого изучения закономерностей поглощения сернистого ангидрида в растворах. Соответственно, рекомендуется использовать щелочную среду для лучшего поглощения диоксида серы в растворах.

Keywords: sulfur gases, sulfur dioxide, sulfur trioxide, utilization, absorption, alkaline medium.

Ключевые слова: сернистые газы, диоксид серы, триоксид серы, утилизация, абсорбция, щелочная среда.

The disposal of sulfur dioxide (SO₂) and sulfur trioxide (SO₃) gases emitted from metallurgical plants is necessary because these gases are harmful to both human health and the environment [1]. SO₂ is a highly reactive gas that can cause respiratory problems such as bronchitis, asthma and emphysema when inhaled in large quantities. It can also contribute to the formation of acid rain, which damages crops, forests and buildings. In addition, SO₂ emissions can negatively affect local air quality and contribute to smog [2-3].

SO₃ is also a highly reactive gas that can cause similar health problems when inhaled and is even more dangerous than SO₂. It can react with water to form sulfuric acid, which is highly corrosive and can damage infrastructure and buildings. In addition, it contributes to the formation of acid rain [4-5]. Sulfur gases are often released during the production of non-ferrous metals and are released into the atmosphere due to improper absorption in the chimneys of metallurgical furnaces.  

To reduce these negative effects, metallurgical plants should take measures to control and eliminate SO₂ and SO₃ gases. The most common method of disposal is to convert SO₂ to sulfuric acid through a contact process. In this, SO₂ is reacted with oxygen in the presence of a catalyst, resulting in the formation of SO₃, which is then hydrated to form sulfuric acid. This process not only eliminates harmful gases, but also helps in the production of valuable industrial chemicals [6].

The absorption coefficient of SO₂ and SO₃ gases in water indicates the rate of dissolution of these gases in water. This coefficient depends on several factors, including temperature and pressure [7]. At a given pressure, the absorption coefficient of SO₃ gas in water generally increases with increasing temperature. This is because higher temperatures generally increase the kinetic energy of gas molecules, making them more likely to collide with water molecules and dissolve in solution. In addition, SO₃ gas has a high activity and reacts with water to form sulfuric acid, and this process continues until there are no excess water molecules left in the solution. But due to weak interaction of SO₂ gas with water, its solubility in water can be determined [8]. The volume (m₃) of SO₂ gas absorbed by 1m₃ of water at a gas partial pressure of 101325 kPa changes depending on the temperature. This can be clearly seen from the graph depicted in Figure 1.

However, the relationship between temperature and absorption coefficient is not linear, and other factors such as gas concentration and solution pH can also affect the coefficient. In addition, with an increase in the concentration of SO₂ or SO₃ in the gas phase, the absorption coefficient can be saturated, that is, further increases in concentration do not significantly increase the absorption rate [7]. The concentration of the gas in the water affects the Henry’s law constant because the solubility of a gas in water is directly proportional to its partial pressure in the gas phase. The pH of the solution also affects the Henry’s law constant because it can alter the chemical properties of the gas and the water molecules.

Due to the fact that the absorption of SO₃ gas in the mixture of SO₃ and SO₂ gases from the metallurgical industry is very good, the absorption of the mixture of these gases was considered only on the example of SO₂. When SO₂ gas is absorbed into an alkaline solution, it reacts with hydroxide ions (OH^-) to form sulfite and bisulfite ions.

Figure 1. Solubility of SO₂ gas in water with increasing temperature

The degree of absorption of SO₂ in solution depends on several factors, such as the concentration, temperature, pressure and gas flow of the alkaline solution. The dependence of SO₂ gas absorption on alkaline environment can be described by the following equations:

1. Absorption rate equation:

The absorption rate of SO₂ in an alkaline solution is expressed by the following equation:

r = K₁ * C_SO2 * C_OH-                                              (1)

Here: r is the rate of absorption, K₁ is the rate constant, C_SO2 is the concentration of SO₂ in the gas phase, C_OH-  is the concentration of hydroxide ions in the solution.

2. Equilibrium equation:

Absorption of SO₂ in solution reaches equilibrium when the rate of absorption is equal to the rate of desorption. The equilibrium state can be expressed by the following equation:

K_eq = C_sulfit * C_OH- / C_SO2                                           (2)

Here: K_eq is the equilibrium constant, C_sulfite is the concentration of sulfite ions, C_SO2 and C_OH- are the concentrations of SO₂ and hydroxide ions, respectively.

3. Equation of dependence on pH:

The pH of the solution affects the absorption of SO₂ gas because it affects the concentration of hydroxide ions. The dependence of absorption rate on pH can be described by the following equation:

r = K₂ * C_SO2 * (1 - 10^{(pH - pKa)})                                      (3)

Here: K₂ is the rate constant, pH is the hydrogen indicator of the solution, pKa is the acidic dissociation constant of sulfuric acid.

In conclusion, the absorption of SO₂ and SO₃ gases in water can have significant effects on the environment and health. SO₂ is a major contributor to acid rain and can cause respiratory problems in humans, while SO₃ can react with water to form sulfuric acid, which is highly corrosive and can damage buildings and other structures.

The disposal of SO₂ and SO₃ gases from metallurgical plants is important for the protection of human health, the environment and infrastructure. Converting SO₂ to sulfuric acid through a contact process is an efficient and sustainable way to achieve this. However, there is no practical possibility to process the sulfurous gases released directly around the metallurgical plants by the contact method. This made it necessary to dispose of the mixture of sulfur gases by soaking them in alkaline solutions.

The absorption of SO₂ gas in an alkaline solution depends on the concentration of hydroxide ions, which in turn depends on the pH level of the solution. The equilibrium constant is also affected by the concentration of sulfite ions and the concentration of SO₂ in the gas phase.

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