Petroleum Distillation and Gasoline Properties

Posted on Sep 4, 2024 in Technology

REDUCED PRESSURE DISTILLATION

Distillation is a process designed to separate liquids by boiling point. After fractional distillation or topping, a material called petroleum spirit is obtained and must be further distilled for use. The problem is that if it is distilled in the same way as crude oil, its high boiling point would cause much of the material to evaporate or burn. The decomposition temperature of the material is less than the boiling point. At 350 °C the carbon chains begin to decompose. This temperature is not enough to distill the material. For this, a solution was discovered… reduced pressure distillation.

Reduced pressure distillation reduces the pressure at which the liquid is subjected to distillation. Normal pressure is 760 millimeters of mercury, but in this process, the pressure is reduced to approximately 40 millimeters of mercury. This reduction in pressure also decreases the boiling point, and the distilling material is not lost through evaporation.

After reduced pressure distillation, materials such as heavy gas oil, lubricating oils (light, medium, and heavy), bitumen (tar), petrolatum, and paraffin, among others, are extracted.

Vacuum Distillation

Vacuum distillation towers provide the necessary reduced pressure to avoid thermal cracking by distilling the residue, or reduced crude, which reaches the atmospheric tower at higher temperatures. The internal designs of some vacuum towers are different from atmospheric towers in that instead of filling dishes, they use random and air particle separator pads. Larger diameter towers are sometimes also used to reduce speeds.

A regular vacuum tower produces diesel, base material for lubricating oil, and heavy residues for propane deasphalting. A second-phase tower, which operates at a lower vacuum level than the atmospheric distillation tower, is not used for processing lubricants, and the residue left over from the first vacuum tower is not used for deasphalting.

Usually, vacuum towers are used to separate catalytic cracking residue. Also, waste from the vacuum towers can be sent to a coker, used as material for lubricants and asphalt, or desulfurized and mixed to obtain low sulfur fuel.

NAPHTHA

Naphtha is a mixture of hydrocarbons that are refined, partially achieved in the top of the atmospheric distillation tower. Different companies and refiners produce generally two types of gasoline: light and heavy. Both are distinguished by the range of distillation, which is then used to produce different types of gasoline. Gasoline, or petrol, is highly flammable, so its handling and storage require extreme care. Naphtha is also used in agricultural areas as solvents and has applications in the paint industry and the production of specific solvents.

GASOLINE

Gasoline, like all petroleum products, is a blend of hydrocarbons. The properties of octane and volatility provide the vehicle engine with easy starting in cold weather, peak power during acceleration, non-oil dilution, and silent operation under normal engine operating conditions. It is mainly used in vehicle engines, marine engines, and work tools such as trimmers, cutters, or saws.

We have three types of commercial gasoline:

  1. Regular Unleaded or regular gasoline has an octane rating that is the average of the Research Octane Number (RON) and Motor Octane Number (MON). It has a minimum octane rating of 89. Unleaded gasoline is equivalent to regular unleaded. This gasoline may not give the engine peak performance, but it does not contain lead, making it much cleaner and relatively less corrosive to the motor vehicle and its parts.
  2. Normal Petrol or Leaded Petrol has an octane rating of about 82. Leaded petrol has a far greater pollution index than any other type of gasoline because of its high content of toxic and environmentally harmful substances in its exhaust. Besides being heavily polluting, it is also very corrosive to the motor vehicle. The substances present in the fuel damage the engine, causing mechanical problems.
  3. Premium or Super Gasoline has a minimum octane rating of 96. It is a reformulated fuel with an oxygen-containing component known as methyl tert-butyl ether (MTBE). MTBE improves combustion and thereby protects the environment. Because of its high octane, it is recommended for vehicles with a high compression ratio. Super petrol’s composition, including additives, ensures that the engine runs without leaving deposits in the fuel intake system. This keeps the carburetor, injector, and intake valves free of deposits, allowing them to continue operating as designed and prolonging engine life.

Other more specialized types of gasoline have octane ratings higher than 98, giving the motor vehicle more power, performance, and speed. A clear example is Ultra or Super Premium, which has an octane rating of 98.

Octane Number

The octane number in gasoline is not always the same. It should be measured in two ways:

  • RON: Research Octane Number is measured at maximum load and low engine speeds, at the moment of peak power.
  • MON: Motor Octane Number is measured at high speed and low load, during acceleration on the road.

Properties of Gasoline

Gasoline has four main properties:

  1. Octane Rating is the main property of gasoline and is highly related to the performance of the vehicle engine. The octane rating refers to the measure of gasoline’s resistance to knocking or detonating when compressed in the engine. This is measured by comparing the knock or detonation that gasoline produces with known reference standards of isooctane and n-heptane, which have octane numbers of 100 and zero, respectively. Under normal conditions, combustion occurs quickly and quietly, but when the octane is inadequate for the engine’s operation, combustion occurs violently, causing an explosion or detonation that can seriously damage the vehicle engine.
  2. Distillation Curve is related to the composition of gasoline, its volatility, and its vapor pressure. It indicates the temperature at which a certain percentage of gasoline evaporates from a reference sample.
  3. Volatility is measured as vapor pressure. This indirectly records the content of volatile components that provide product safety during transportation and storage. This property must, in turn, be related to the characteristics of high ambient temperature and humidity for the storage of the product design.
  4. Sulfur Content is highly related to the amount of sulfur (S) contained in the product. The amount of sulfur in gasoline is limited because it can have a corrosive effect on metal parts of the engine and exhaust pipes. When it leaves the exhaust pipe, it contributes to air pollution, producing acid rain.

AVIATION GASOLINE (AVGAS)

Aviation gasoline, or AVGAS, is composed of a mixture of hydrocarbons, mainly isoparaffins and a small amount of aromatics, to which certain additives are added, such as:

  • Tetraethyl lead to bring the product to the required octane levels
  • Antioxidants
  • Antifreeze

Its formulation and volatility characteristics are quite different from those used in gasoline for motor vehicles. Its main use is in aircraft that operate with piston engines.

There are currently two types of aviation fuel that differ in lead content and color:

  • Grade 100LL (blue) has a lower lead content than Grade 100/130.
  • Grade 100/130 (green)

The process of obtaining these gasolines differs from the process to obtain gasoline and bio gasoline, as it occurs by synthesis using the alkylation method.

Main Properties

  1. Octane Number in AVGAS varies between 100 and 130 according to the requirements of the piston engine used in the aircraft. This octane is achieved with lead-based additives, making AVGAS the only gasoline containing this antiknock additive. The measurement of octane in AVGAS is completely different from the method used for gasoline for motor vehicles.
  2. Reid Vapor Pressure is a measure of the tendency of the more volatile components to evaporate. The maximum value is 80 kPa. This prevents the formation of vapor pockets in the fuel system, which could prevent normal fuel flow.
  3. Present Gums relate to the extent of a fuel’s stability. This corresponds to accelerated oxidation, resulting in the formation of coatings and polymers, which can form deposits in the combustion system. The gums in AVGAS are relatively low compared to the specified requirement.
  4. Density is used to calculate the weight of fuel. It is especially important for cargo planes to determine the limits of their load.
  5. Volatility is obtained by the balance of light and heavy compounds and by its distillation range. This measure differs considerably from that set for gasoline engine vehicles.

CONTAMINATION OF PETROL

Lately, gasoline contamination of the environment has decreased due to the reduced use of lead in fuel and by limiting the content of aromatics and olefins. The addition of oxygenates also reduces pollution. As a result, combustion gases are less toxic. The addition of oxygen enables more complete combustion, abruptly decreasing the formation of carbon monoxide.