Hydrocarbon

Introduction to Hydrocarbons

Hydrocarbons are organic compounds composed of hydrogen and carbon. They can be classified into two main categories: saturated and unsaturated hydrocarbons. They are also commonly divided into two groups among chemists: aliphatic hydrocarbons (alkanes, alkenes, and alkynes) and aromatic hydrocarbons. Light and heavy hydrocarbons are simply trade names that may result from blending, refining, distillation, or sweetening processes.

The main source of heavy and light hydrocarbons is crude oil. Crude oil consists of various hydrocarbon compounds with different chemical and physical properties. Crude oil composition varies depending on the extraction region. Although the specific amounts of hydrocarbon components in crude oil differ, the types of hydrocarbons that make up crude oil remain constant.

In general, crude oil is predominantly carbon-based, accounting for about 85% by weight, with the remaining portion usually being hydrogen. Crude oil contains significant amounts of sulfur, oxygen, nitrogen, and trace amounts of unusual metals such as vanadium and nickel. Sulfur, nitrogen, and oxygen atoms are typically present in hydrocarbons as substitutes for carbon. The presence of more sulfur in hydrocarbon compounds leads to increased corrosion and greater physical changes. Heavier compounds result in more challenging oil refining processes. The lighter and purer the crude oil, the fewer substitute elements are present in hydrocarbons.

Methods of Hydrocarbon Production include:

– Production from crude oil

– Extraction from coal mines

– Production of light and heavy hydrocarbon compounds based on primary raw materials.

Structural Characteristics of Hydrocarbon Products:

– Non-polar

– Flammable

– Soluble in non-polar solvents and insoluble in water

– Low to high boiling range (for heavy and light hydrocarbons respectively).

Light Hydrocarbons:

Light hydrocarbons are substances with a density below 0.8 g/cm³ in a temperature range of 270°C to -40°C. They are mainly used as solvents and diluents. Light hydrocarbons include hydrocarbon chains of 5 to 12 carbons and are commonly used in the petrochemical industry for the production of aromatic compounds and high-octane gasoline through catalytic reforming processes. These hydrocarbons can also be used as a primary material in the chemical and petrochemical industries to produce olefins through steam cracking and as solvents. They are also used as feedstock in the production of various petrochemical products, including solvents and diluents. Other diverse applications of these hydrocarbons include raw materials for various plastics, synthetic fibers, industrial alcohols, paint thinners and lacquers, heating and cooking fuel (similar to liquefied petroleum gas and kerosene), and major components of paint thinners. Additionally, they can be transformed into high-octane gasoline and other petroleum fuels using catalytic processes.

Another type of light hydrocarbons is a mixture of paraffinic and aromatic hydrocarbons with carbon ranges of 9 to 12 and a distillation range of 200°C to 142°C. These compounds are used as solvents or generally as paint thinners. These solvents are clear liquids with a water-like color, have a mild odor, chemical stability, and do not cause corrosion. They are used as extraction solvents, cleaning solvents, fat solvents from metal surfaces, aerosol solvents, color dryers, solvents in fabric printing, solvents in specialized household items such as furniture, floor coverings, varnishes, and waxes. They are also used in shoe polish, dry cleaning, and as solvents for asphalt products. The primary application of 9-12 carbon light hydrocarbons is in paints and lacquers, making them common solvents in the paint industry and as solvents in paints, lacquers, and alcohols. Additionally, they play a role in diamond turning, a machining process, and are therefore known as DIAMOND TURNING.

Heavy Hydrocarbons:

Heavy hydrocarbons are compounds with a density higher than 81.0 g/cm³, primarily used as marine fuel, tank cleaning agents, and for industrial and domestic purposes. The flash point of these hydrocarbons is at least 40°C, and they are categorized as heavy industrial compounds. The chain length of heavy hydrocarbons generally ranges from C12 and above. The distillation range of these hydrocarbons is 385°C to 150°C. These compounds are obtained from intermediate distillates of oil refineries, which consist of a heterogeneous mixture of major compounds, including alkyls, resins, and asphaltenes, and can form a significant part of crude oil depending on their origin. They are used in diesel engines, heavy fuels, domestic and industrial burners, and lubricating oils.

Given that heavy hydrocarbons are derived from heavier cuts of crude oil and gas, their prices are adjusted based on their applications using cuts and petroleum compounds. These hydrocarbons mainly include oils and are known by names such as diesel fuel or diesel oil.

Heavy hydrocarbons are environmentally stable, but they can potentially harm human health, the environment, and water resources. It is expected that the demand for heavy hydrocarbons will increase in the future due to the growing global energy demand, leading to the increasing exploitation of heavy oil reserves.

Introduction to the main components of crude oil:

The components of crude oil are numerous and have various chemical formulas. In engineering sciences, they are classified into groups for simplicity. For example, compounds containing 1 carbon atom are represented as C1C1, and so on up to C7C7. Compounds containing more than 7 carbon atoms are represented as C7+C7+ for easier analysis. The main components of crude oil are discussed below.

1- Paraffins (Alkanes):

These compounds in organic chemistry are represented by the general formula CnH2n+2 and are classified into two groups: normal and iso. Saturated hydrocarbons with a linear chain are called normal paraffins, and hydrocarbons with branches are called iso-paraffins. These two compounds are chemically identical but differ in structure, which affects their physical properties. In crude oil, normal paraffins with straight chains are more common than branched iso-paraffins. Although these two compounds are chemically identical, their structural differences affect their physical properties. For example, normal paraffins with straight chains have a higher boiling point compared to branched iso-paraffins.

Paraffins are the primary components of natural gas hydrocarbons. They are also abundant in white oil and gasoline, which constitute more than 3% of crude oil.

The simplest molecule in the paraffin group is alkanes, which are saturated hydrocarbons with a simple bond and a linear molecular structure. They can have side branches or be without branches. Light paraffins are specific to natural gases, while heavier types are found in crude oil. The simplest of them is methane (CH4).

Usually, hydrocarbons with 5 carbon atoms or less are in gaseous state, while those with 10 to 15 carbon atoms are in liquid form. Methane, ethane, propane, and butane, which are the primary members of this group, are in the form of gas, while the remaining compounds from pentane to heptane are liquid.

2- Naphtenes (Cycloalkanes):

The second major group of hydrocarbons in crude oil is naphtenes, with a molecular formula of CnH2n, consisting of one or more cyclic rings of carbon atoms. These compounds are an important part of petroleum refining products and can be converted into diesel fuel through a simpler process. The simplest cyclic hydrocarbons are saturated with a simple bond and can also have side branches. The amount of naphtenes is less in gases and more in crude oil. Crude oil has a higher concentration of naphtenes compared to other components.

Naphtenes can have a minimum of 3 to more than 30 carbon atoms arranged in their rings. Cyclopentane with a five-carbon ring and cyclohexane with a six-carbon ring are common naphtenes in various types of crude oil. Similar amounts of naphtenes and paraffins are present in different types of crude oil. Overall, saturated hydrocarbons make up about 60% of most crude oil varieties.

Aromatic Hydrocarbons:

These compounds are present in almost all types of crude oil and consist of cyclic hydrocarbons with alternating double bonds, unlike alkanes and paraffins. Their structure is based on a six-carbon ring, and the simplest member of this family, benzene, is named after the benzene ring. In benzene, the only atom bonded to the carbon ring is hydrogen. Aromatics are formed by the substitution of paraffin molecules with hydrogen in the benzene ring. This group includes toluene, ethylbenzene, naphthalene, and anthracene. Aromatic hydrocarbons are liquid at normal pressure and temperature. They are present in a lesser amount in light crude oil but are abundant in heavy crude oil. Toluene is the most common aromatic in crude oil. Other important aromatics include xylene and benzene. Benzene, toluene, and xylene are liquid aromatic compounds, while compounds with an increased number of carbon atoms, such as naphthalene, become solids.

Polyaromatic compounds with high molecular weight present in crude oil contain heteroatoms such as sulfur, nitrogen, and oxygen.

Olefins:

Olefins with the molecular formula CnH2n are produced during crude oil refining. These compounds, due to their double bond, are highly reactive and easily undergo oxidation and polymerization.

Asphaltenes:

The fourth important group of compounds in crude oil is resins and asphaltenes. Resins and asphaltenes are complex compounds consisting of a combination of numerous aromatic ring molecules along with sulfur, nitrogen, and oxygen elements. They are heavy and unsaturated, with no specific general formula. These hydrocarbons are often found in heavy, viscous crude oil or in solid forms like natural asphalt. These impure hydrocarbons are often referred to as NSO compounds because they contain sulfur, nitrogen, and oxygen atoms, some of which replace carbon in aromatic rings. NSO compounds, with the highest molecular weight, are the heaviest components in various types of crude oil. In most cases, resins and asphaltenes are found in heavy aromatic crude oil.

Lower Economic Value of Heavy Hydrocarbons Compared to Light Ones:

Considering that a significant portion of the extracted oil from Iranian oil wells is of heavy type, the conversion of heavy hydrocarbon compounds into lighter ones with higher economic value is important. These compounds have challenges in terms of transportation (due to high viscosity, high density, etc.) and have low economic value due to difficulties in processing and using them in energy production processes. These products, which are mostly used in the production of bitumen and waxes, can be converted into lighter products with higher value through the processing and breaking of larger hydrocarbon chains.

Therefore, the development of alternative methods that can reduce energy consumption in these processes can pave the way for the development of processes for producing lighter petroleum compounds from heavy ones, which have higher economic value.