Petroleum Refining: Cracking and Key Products

Petroleum Refining: Cracking Process

Sometimes, crude oil distillation yields only a small percentage of gasoline. To increase this percentage, a secondary distillation process called cracking is used. Cracking breaks down high molecular weight hydrocarbons (such as gas oil and fuel oil) into lower molecular weight compounds (like gasoline). This process always forms hydrogen and carbon compounds. It is very important in petroleum refineries as a way to increase gasoline production at the expense of heavier, less valuable products, such as kerosene and fuel oil.

Types of Cracking

There are two main types of cracking: thermal and catalytic.

• Thermal Cracking: This process involves heating the heavier parts of crude oil to high temperatures under pressure. This divides (cracks) large hydrocarbon molecules into smaller ones, increasing the amount of gasoline produced from a barrel of crude. It uses light liquid or gaseous loads, high temperatures (800-900°C), and low pressures. The process mainly derives naphtha olefins.
• Catalytic Cracking: In this process, heavy fractions like gas oil and fuel oil are heated to 500°C at pressures of 500 atm in the presence of catalysts that speed up the reaction. The process is named after these catalysts.

The best-known catalytic processes, which have largely supplanted the older thermal processes, include the fluidized bed technique and fluid catalytic powder using aluminum-silica gel as catalysts. In the fluidized bed process, oil is passed through a stationary bed of solid particles. In the fluid catalytic process, the particles are mobile and are suspended in a stream of oil vapor at a temperature of 450° to 540°C and a pressure of 2.4 atmospheres.

Impact of Cracking on Gasoline Production

The advantage of cracking is evident in the following statistics: In 1920, a barrel of crude (159 liters) produced 41.5 liters of gasoline, 20 liters of kerosene, 77 liters of diesel oil, and 20 liters of heavier distillates. Today, a barrel of oil produces 79.5 liters of gasoline, 11.5 liters of jet fuel, 34 liters of diesel and distillates, 15 liters of lubricants, and 11.5 liters of heavier waste. This demonstrates that thanks to cracking, naphtha production can increase dramatically.

Major Petroleum Products

Naphtha

Naphtha is a partially refined mixture of hydrocarbons obtained at the top of the atmospheric distillation tower. Refiners generally produce two types of naphtha: light and heavy, distinguished by their distillation range, 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 a solvent and has applications in the paint industry and the production of specific solvents.