Sylvie Willis
Fossil fuels are created from fossilized plant and animal remnants that existed millions of years ago. The fossil fuels we use today, such as oil, natural gas, and coal, are formed through a process that involves heat and pressure acting on these ancient fossils. The process of refining fossil fuels involves separating them into various components, which are then transformed into different products. This separation is achieved through methods like distillation, where the fossil fuels are heated and separated into fractions based on their boiling points. These fractions are then used for various purposes, including fuels, lubricants, and even road tar.
| Characteristics | Values |
|---|---|
| Fossil fuels are separated by | Fractional distillation |
| Cracking | |
| Reforming | |
| Refining | |
| Heat and pressure | |
| Selective reconfiguration | |
| Fossil fuels are separated into | Petroleum components |
| Gases | |
| Liquids | |
| Gummy solids |
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Cracking
Fossil fuels are compound mixtures made of fossilised plant and animal remnants from millions of years ago. The creation of fossil fuels (oil, natural gas, or coal) from these fossils is determined by the type of fossil, the amount of heat, and the amount of pressure. As the fossil material gets buried deeper underground, it is subjected to increased heat and pressure. As the heat rises, the fossil molecules begin to break apart.
One method of separating fossil fuels is through a process called cracking. Cracking involves breaking down larger and heavier hydrocarbons in kerosene and higher-boiling-point fractions by heating them to temperatures as high as 900°C. This high-temperature reaction causes the carbon-carbon bonds to break, converting the compounds into lighter molecules similar to those in the gasoline fraction. This process is particularly useful in converting a straight-chain alkane with a number of carbon atoms corresponding to the kerosene fraction into a mixture of hydrocarbons with a number of carbon atoms corresponding to the lighter gasoline fraction.
There are several variants of thermal cracking methods, including the Shukhov cracking process, the Burton cracking process, the Burton-Humphreys cracking process, and the Dubbs cracking process. The first thermal cracking process was invented and patented by Russian engineer Vladimir Shukhov in 1891. However, it was not widely adopted, and American engineers William Merriam Burton and Robert E. Humphreys later independently developed a similar process in 1908.
One of the earliest thermal cracking processes, the Burton process, operates at temperatures between 700-750°F (370-400°C) and an absolute pressure of 90 psi (620 kPa). This process is used to "'upgrade'" very heavy fractions or produce light fractions, distillates, burner fuel, or petroleum coke.
Another type of cracking is catalytic cracking, which involves the presence of solid acid catalysts, typically silica-alumina and zeolites. This process promotes the formation of carbocations, which undergo rearrangement and the scission of C-C bonds. Catalytic cracking operates at milder temperatures compared to thermal cracking, saving energy and reducing the yield of undesirable alkenes that cause instability in hydrocarbon fuels. Fluid catalytic cracking, a commonly used process, yields a high amount of petrol and LPG.
Methane cracking is a process that separates the molecular components of methane (hydrogen and carbon) at high temperatures (750°C and above) without releasing harmful emissions. This process has been explored as a way to produce energy from fossil fuels without generating carbon dioxide.
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Reforming
Fossil fuels are compound mixtures made of fossilized plant and animal remnants from millions of years ago. The fossil fuels that are used today, such as oil, natural gas, or coal, are determined by the type of fossil, the amount of heat, and the amount of pressure. The energy in fossil fuels comes from the sun, which drives photosynthesis to change carbon dioxide and water into the molecular building blocks of ancient plants and animals.
There are four widely used reforming processes for hydrogen production: Steam Methane Reforming (SMR), Partial Oxidation (POX), Auto-thermal Reforming (ATR), and Dry reforming (DR). All these methods produce carbon monoxide as a byproduct, so one or more chemical reactors are installed to convert carbon monoxide into CO2 through the water-gas shift reaction (WGS) and methanation processes. Steam reforming has a lower operating temperature and a greater H2/CO ratio compared to partial oxidation and autothermal reforming. It is also considered the least expensive and most effective technique for H2 production.
The advancement and use of carbon capture and sequestration technologies ensure the CO2 formed during reforming can be easily captured and stored. This has led to the development of hydrogen fuel cell-based cars, which have practically zero GHG emissions during their use. The use of solar energy to reform hydrogen has also been gaining prominence, as it increases the efficiency of hydrogen conversion and further decreases GHG emissions.
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Fractional distillation
Fossil fuels are compound mixtures made of fossilized plant and animal remnants from millions of years ago. Crude oil is separated into its various components through a process called fractional distillation. This process involves heating the oil to vaporize it and then feeding it into the bottom of a distillation tower. As the vapour rises through the vertical column, its temperature decreases, causing certain hydrocarbons to condense and run off at different levels. This separation occurs due to the different boiling points of the hydrocarbons, with the most volatile components having the lowest boiling points and condensing at the top of the column, while the less volatile components condense nearer the bottom.
The fractions that condense at each level contain hydrocarbon molecules with a similar number of carbon atoms. These fractions are then drawn off separately, resulting in products such as gases used in natural and bottled gas, liquids used as fuels and lubricants, and gummy solids used as tar. Light distillate, with boiling points around 70-200°C, includes products like gasoline, kerosene, jet fuel, and paraffin. Medium distillate, with boiling points of 200-350°C, includes diesel fuel and gas oil. Heavy distillate, with boiling points above 350°C, includes fuel oil and may be solid or semi-solid.
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Petroleum refining
Petroleum, or crude oil, is a fossil fuel composed of thousands of different chemical compounds called hydrocarbons, each with a different boiling point. Crude oil is classified by density, sulfur content, and acidity, and these factors determine how it is refined.
Crude oil is transformed into useful products through a variety of processes, including distillation, cracking, and reforming. During distillation, the crude oil is heated and separated into different petroleum components, called fractions, according to their boiling points. The lightest fractions, including gasoline and liquefied refinery gases, rise to the top of the distillation tower, while medium-weight liquids like kerosene and distillates remain in the middle. Heavier liquids, such as gas oils, separate lower down, and the heaviest fractions settle at the bottom.
After distillation, the heavier and lower-value fractions can be further processed through cracking, where they are heated to extremely high temperatures to break down the carbon-carbon bonds, converting them into lighter molecules similar to those in the gasoline fraction. Reforming is another process used to increase the value of the product, where straight-chain alkanes are chemically converted into branched-chain alkanes or mixtures of aromatic hydrocarbons using metals like platinum as catalysts.
The final stage involves carefully combining the streams from the processing units to create the desired product, such as gasoline, diesel, or jet fuel. The composition of these blends is carefully controlled, taking into account factors such as octane level and vapor pressure ratings. The final products are stored temporarily in large tanks near the refinery before being distributed.
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Distillation columns
The process of fractional distillation is used to separate the various lengths of hydrocarbon chains found in petroleum fuel products, which are known as alkanes or paraffins. Alkanes are stable and versatile, making them safe for use and storage as fuel products. By breaking down and altering the mixtures of distillates, fractional distillation can create a range of petroleum products such as petrol, diesel, kerosene, and lubricants.
Fractional distillation is also used in the separation and characterization of biofuels, where it can improve the properties of organic liquid products (OLPs) obtained from thermal-catalytic cracking of vegetable oils and crude palm oil. By adjusting the distillation temperature range, biofuels with better physical, chemical, and compositional qualities can be produced. Additionally, distillation columns are used in chemical production to purify and separate various chemicals, as well as in environmental cleanup to separate pollutants from water or solvents.
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Frequently asked questions
Fossil fuels are separated into petroleum components, also known as fractions, based on their boiling points. The most volatile components condense at the top of the distillation column, while the least volatile components condense at the bottom.
The different fractions of fossil fuels include gases used in natural and bottled gas, liquids used as fuels and lubricants, and gummy solids used as tar on roads and roofs.
The process of separating fossil fuels is called fractional distillation. It involves introducing a mixture called the feedstock into a refining tower or distillation column. The components then condense at different temperatures depending on their boiling points and are drawn off separately.
Separating fossil fuels allows for the production of a range of valuable products with specific compositions. For example, converting less volatile, lower-value fractions into more volatile, higher-value mixtures can increase the profitability of petroleum refining.
