Diesel fuel is a combination of hydrocarbons derived from crude oil distillation. The cetane number (or cetane index), fuel volatility, density, viscosity, cold behavior, and sulfur concentration are all key characteristics of diesel fuel. Diesel fuel standards fluctuate depending on the gasoline grade and country.
Refining of crude oil
The petrochemical business has been around since the 1850s. Ignacyukasiewicz developed the first modern oil refinery at Jaso, Poland (then under Austrian authority) in 1854–56 [Frank 2005]. The refined products were utilized in the kerosene lamp invented by Ukasiewicz, as well as artificial asphalt, machine oil, and lubricants. Crude oil was discovered in Pennsylvania, the United States, a few years later, in 1859. Kerosene, which was used as lamp oil, was also the first product refined from crude in Pennsylvania [Chevron 1998].
Because only a small portion of the crude could be converted into kerosene, the early refiners were left with a large amount of petroleum waste. Rudolf Diesel, the developer of the compression ignition reciprocating engine, was intrigued by these petroleum by-products. Diesel, whose initial engine concept was based on coal dust as a fuel, realized that liquid petroleum products may be a better alternative to coal. The engine was redesigned to run on liquid fuels, and a working prototype was built in 1895. Diesel is still used for both the engine and the fuel.
Diesel engines provide greater torque than gasoline-powered engines, which is why they employ diesel engines in refuge compactors, and garbage trucks rather than gasoline. In the transportation industry, low-end torque is crucial. The ability of a diesel engine to generate torque and horsepower at low rpm is essential for moving big loads.
Diesel fuel is a combination of hydrocarbons derived from petroleum with boiling temperatures ranging from 150 to 380°C. Hydrocarbons of three primary groups make up petroleum crude oils: paraffinic, naphthenic (or cycloparaffinic), and aromatic hydrocarbons. Olefins (unsaturated hydrocarbons) are uncommon in crude oil. It’s worth noting that the names ‘paraffinic’ and ‘naphthenic’ may appear archaic, yet they’re still used in the petrochemical sector. The two classes of hydrocarbons are known as alkanes and cycloalkanes in contemporary chemistry.
The crude can range in composition from light-colored brownish or greenish crude oils with little viscosity to thick, black oils that resemble molten tar. “High-gravity” crude oils are thin, low-density oils, whereas “low-gravity” crude oils are thick, high-density oils. This practice, which may be perplexing to people outside the petroleum business, is explained by the usage of “API gravity,” a fuel attribute that is inversely related to its density (Equation 1). (5).
Crude oil is refined into transportation fuels like gasoline, jet fuel, and diesel fuel, as well as other petroleum products including liquefied petroleum gas (LPG), heating fuel, lubricating oil, wax, and asphalt. Crude oils with a high gravity include more of the lighter products needed to make transportation fuels and have a reduced sulfur concentration. Modern refining technologies may also transform low-gravity crude oils into lighter products, albeit at the cost of more complicated processing equipment, more processing stages, and energy.
There are three fundamental groups of modern refining processes:
Separation: Based on some physical attribute, the crude is divided into components. Distillation is the most frequent separation method, in which the crude components are divided into multiple streams based on their boiling temperatures. The chemical structure of feedstock components is unaffected by separation techniques.
Conversion involves altering the molecular structure of feedstock components. The most prevalent conversion processes are catalytic cracking and hydrocracking, both of which entail the “cracking” of big molecules into smaller ones, as the names imply.
Upgrading: This process is commonly employed in reformulated fuels to eliminate trace levels of chemicals that give the substance undesirable properties. Hydrotreating, which includes chemical interactions with hydrogen, is the most often used upgrading procedure for diesel fuel.
Figure 1 [Chevron 1998] shows a schematic of a contemporary refinery with the diesel streams indicated. The crude oil feedstock is separated into a series of streams with increasing boiling points in the primary distillation column, which operates at atmospheric pressure. These streams are referred to as straight-run products (e.g., straight-run diesel). The material that is too heavy to evaporate in atmospheric distillation is removed from the column’s bottom (referred to as “atmospheric bottoms”). The atmospheric bottoms are further separated in most refineries by a second distillation under vacuum.
The chemical composition of the crude oil determines the quantity and quality of the streams extracted during distillation. Crude oils also produce quantities of gasoline, diesel, residual fuel oil, and other products that deviate from product demand trends in certain markets. Downstream conversion procedures are the only option to match refinery production patterns with market demands. Large hydrocarbon molecules are broken down into smaller ones using heat, pressure, or catalysts in these conversion processes. Thermal cracking (visbreaking and coking), catalytic cracking, and hydrocracking (using a catalyst but under a high pressure of hydrogen) are all methods used by refineries to maximize the yield of desirable products by cracking undesired heavy fractions. Conversion products (crack components) are blended with primary distillation streams to produce the final products.
To minimize the level of sulfur, nitrogen, and other constituents, both blended and straight-run products may require variable degrees of upgrading. Hydroprocessing is a group of techniques that employ hydrogen in conjunction with a catalyst to improve refinery streams. Hydroprocessing can range from moderate hydrofinishing, which eliminates reactive chemicals such as olefins as well as some sulfur and nitrogen compounds, to more severe hydrotreating, which saturates aromatic rings and removes practically all sulfur and nitrogen compounds.
Diesel fuels utilized in road transportation, as shown in Figure 1, are distillate fuels, meaning they do not include (uncracked) residuum fractions. Heating oils, as well as marine fuels, include petroleum residuum components (also known as bunker fuels). These products generally differ significantly from distillate diesel fuels in terms of characteristics. The chemical composition of the crude oil determines the quantity and quality of the streams extracted during distillation. Crude oils also produce quantities of gasoline, diesel, residual fuel oil, and other products that deviate from product demand trends in certain markets. Downstream conversion procedures are the only option to match refinery production patterns with market demands. Large hydrocarbon molecules are broken down into smaller ones using heat, pressure, or catalysts in these conversion processes. Thermal cracking (visbreaking and coking), catalytic cracking, and hydrocracking (using a catalyst but under a high pressure of hydrogen) are all methods used by refineries to maximize the yield of desirable products by cracking undesired heavy fractions. Conversion products (crack components) are blended with primary distillation streams to produce the final products.
To minimize the level of sulfur, nitrogen, and other constituents, both blended and straight-run products may require variable degrees of upgrading. Hydroprocessing is a group of techniques that employ hydrogen in conjunction with a catalyst to improve refinery streams. Hydroprocessing can range from moderate hydrofinishing, which eliminates reactive chemicals such as olefins as well as some sulfur and nitrogen compounds, to more severe hydrotreating, which saturates aromatic rings and removes practically all sulfur and nitrogen compounds.
Diesel fuels utilized in road transportation, as shown in Figure 1, are distillate fuels, meaning they do not include (uncracked) residuum fractions. Heating oils, as well as marine fuels, include petroleum residuum components (also known as bunker fuels). These products generally differ significantly from distillate diesel fuels in terms of characteristics.