What are the types of hydrocarbons?

What are hydrocarbons?

Hydrocarbons are compounds made up of carbon and hydrogen atoms that play a very important role in human life. Contrary to popular belief, which limits the application of hydrocarbons only to fuel, these compounds are used in various fields. For example, isobutane is one of the widely used hydrocarbons that is utilized as a refrigerant gas in refrigerators. Of course, this is only one of the applications of isobutane.

In this article, we aim to introduce and review the different types of hydrocarbons in the oil industry and crude oil refining. Please note that Kian Petroleum is not a supplier of hydrocarbons; this company operates in the field of gas supply and transportation. In relation to oil products, Kian Petroleum only provides brokerage services for purchasing from the energy exchange for its customers.

Types of Hydrocarbons

Classification of Hydrocarbons Based on Molecular Structure

There are various methods for classifying hydrocarbons. In one of these classifications, hydrocarbons are divided into two categories: aliphatic and aromatic. This classification is based on the presence or absence of a benzene ring in their structure. Aromatic hydrocarbons have at least one benzene ring, which gives them specific chemical and physical characteristics such as greater stability and a distinct odor.

Classification of Hydrocarbons Based on the Number of Carbon Atoms

This type of classification holds special importance in the oil industry, as these compounds are divided into two main categories based on molecular weight and the number of carbon atoms: light hydrocarbons and heavy hydrocarbons. The main focus of this article is also on this type of classification, as it plays a significant role in the understanding and optimal utilization of these compounds in oil and refining processes.

What are light hydrocarbons?

When talking about light hydrocarbons, you might first think of gases like propane and butane, which is entirely correct; these gases are also considered light hydrocarbons. However, in the oil industry, when referring to light hydrocarbons in oil fractions, it means compounds with carbon chains ranging from 5 to 12 carbon atoms. These compounds, recognized as one of the valuable components of crude oil, include substances like naphtha, gasoline, kerosene, and other similar materials.

These hydrocarbons, due to their high volatility and relatively low boiling point, are extracted from the upper sections of the atmospheric distillation column in refineries. Oil fractions containing light hydrocarbons are usually distilled within the temperature range of 40 to 200 degrees Celsius, and their density ranges between 660 to 890 kilograms per cubic meter. Applications of these compounds include their use as solvents and in the production of light fuels with high octane numbers.

Specifically, in the oil refining process, light hydrocarbons play a key role in the production of gasoline and other high-quality fuels. These compounds are also used in petrochemical processes to produce aromatic substances such as benzene and toluene, as well as other compounds. Since light hydrocarbons are among the essential and primary components in the oil refining industry, upgrading them to higher-quality fuels through processes like catalytic reforming is one of the main tasks of modern refineries.

What are heavy hydrocarbons?

Heavy hydrocarbons refer to a category of hydrocarbons that have longer carbon chains, consisting of more than 12 carbon atoms. These compounds have a higher density compared to light hydrocarbons, and their boiling point ranges between 150 to 380 degrees Celsius. Due to their more complex molecular structure, these materials have higher viscosity, making them thicker and heavier than light hydrocarbons.

The applications of heavy hydrocarbons include their use as heavy fuels in ships, large diesel engines, and industrial furnace heating. These hydrocarbons consist of substances like fuel oil (mazut) and heavy fuels, which, due to their high density and viscosity, are suitable for industrial applications.

Some heavy hydrocarbons may also be referred to as industrial diesel, but these compounds should not be confused with regular diesel used in vehicles. Due to their low octane rating (a measure of fuel combustion quality) and specific physical characteristics, heavy hydrocarbons are not suitable for use as gasoline. Instead, heavy fuels are often used in applications that require slower combustion and long-term energy production.

Production of Hydrocarbons from Crude Oil

The production of light and heavy hydrocarbons from crude oil is one of the key steps in the oil refining process. This process is carried out to separate and purify the various components of crude oil so that these compounds can be utilized in various industries. However, before the distillation process, crude oil undergoes a pre-processing stage. The purpose of pre-processing is to remove impurities such as salts, sulfur, and other contaminants. Once pre-processing is complete, the crude oil is ready for distillation.

Crude Oil Distillation

Pre-heating of Crude Oil

The first stage in atmospheric distillation is the pre-heating of crude oil. In this step, the crude oil is heated to a temperature of approximately 350 to 400 degrees Celsius before entering the atmospheric distillation column. This pre-heating is carried out using heat exchangers and furnaces to provide the necessary thermal energy for the distillation process. At this stage, the components of the crude oil with lower boiling points are converted into gas.

Entering the Atmospheric Distillation Column

After pre-heating, the crude oil enters the atmospheric distillation column. This column contains multiple trays, each operating at a specific temperature. Due to the environmental temperature and pressure, different hydrocarbon molecules either turn into gas or remain in liquid form, depending on their boiling points, and are collected on different trays. Compounds with higher boiling points collect in the lower sections of the column, while those with lower boiling points accumulate in the upper sections.

Separation of Hydrocarbons

In the crude oil distillation process, various hydrocarbon gases are separated based on their boiling points and the position of the trays within the distillation column. Each type of hydrocarbon gas is collected on a specific tray according to its boiling point. For instance, methane and ethane, which have very low boiling points, accumulate at the top of the column, while gases like propane and butane, with higher boiling points, are collected on lower trays.

After the light gases, which are distilled first due to their high volatility and low boiling points, light and heavy hydrocarbons are separated from crude oil in the middle stages. As the gases are separated in the upper parts of the distillation column, the liquid phase of hydrocarbons remains at the bottom. These substances, due to their high boiling points, do not vaporize during distillation and remain in liquid form. This liquid phase, known as heavy residue, includes heavier materials such as bitumen.

Collection and Cooling

The vapors produced at each stage of the distillation column are cooled using heat exchangers, condensing them into liquids. These liquids are then collected in separate storage tanks. Each product, depending on its type and quality, is sent to subsequent units in the refinery for further processing or is prepared as a final product to be delivered to the market.

Disadvantages of Using Hydrocarbons

• Combustion of these compounds leads to the emission of greenhouse gases like CO2 and pollutants such as nitrogen oxides (NOx) and sulfur oxides (SOx).
• Pollutants resulting from the burning of hydrocarbons contribute to an increase in respiratory diseases, cardiovascular issues, and premature death rates.
• Oil spills and leaks from tankers or offshore oil rigs can cause widespread damage to marine ecosystems, leading to the mass death of marine animals, plants, and coral reefs.
• Excessive use of fossil fuels and hydrocarbon extraction processes can lead to soil erosion and the destruction of natural habitats.
• Hydrocarbons are non-renewable resources, and with their heavy consumption, the reserves of oil and natural gas are steadily depleting.

Conclusion

Ultimately, while hydrocarbons play a vital role in providing energy and raw materials for modern industries, excessive dependence on these non-renewable resources and their widespread environmental impact indicates that the future of global energy requires innovation and transformation in consumption and production methods. The development of cleaner technologies, reduction of fossil fuel consumption, and utilization of renewable resources are essential steps in protecting the environment and ensuring the sustainability of life for future generations.