Catalytic cracking of oil (in English - splitting) is a technological process aimed at increasing the yield of gasoline by special processing of components of heavy oil fractions. During the initial processing of the product an average of 5-14% of the total mass of gasoline is obtained. The quality of the resulting fuel after direct distillation does not meet the requirements of modern technology.
Catalytic cracking increases the yield of gasoline and improves its quality.
There are two types of thermal (catalytic) cracking: liquid and gas phase. For the first, the raw material is fuel oil, which is fed in an oven at 600-625 ° C under atmospheric pressure. Gas-phase catalytic cracking is carried out under the same conditions, but the oil is gas oil (solar oils). During thermal cracking in the structure of high molecular alkanes, carbon bonds are broken and molecules of low molecular weight carbons entering the gasoline fraction are formed:
1022 - 512 + 510.
Thus, two substances (saturated and unsaturated hydrocarbons) with a lower molecular weight are formed from high molecular weight decane .
Catalytic cracking is carried out in the presence of catalysts (activated clay or aluminosilicates) at a temperature of 470-530 degrees under pressure from 70 to 370 kPa. The main raw material for the process is gas oil, the yield of gasoline from the total mass of oil can reach 30-40%. Therefore, the production of gasoline is a difficult and time-consuming process. To improve the quality of the product, alkenes and alkynes, which sometimes occupy up to 30% of the total mass, are removed from its composition.
Thanks to the use of innovative technologies, the yield of gasoline in the process of oil distillation can be up to 80 percent. To assess the quality of liquid fuels, an octane rating is used. Isooctane or 2,2,4-trimethylpentane was chosen as a fuel sample with high antiknock properties.
Its octane number is considered equal to 100. As a sample with the lowest antiknock properties, take n-heptane: 716, the octane number (OCh), which is considered equal to 0. To determine this indicator, the detonation properties of gasoline are compared with the properties of a mixture of isooctane and n-heptane.
For example, a product with an octane rating of 80 has the same detonation properties as a mixture of 80% isooctane and 20% n-heptane. The higher the octane number, the higher the fuel quality. Increasing this indicator saves fuel and saves the power of internal combustion engines. Other components are added to the product, including synthetic carbons, and antiknock agents (these are substances that, at minimum concentrations (not more than 0.5%) improve the antiknock properties of the fuel). Previously, tetraethyl plumbum was used for these purposes. Due to the fact that this substance is very toxic, it was replaced with other antiknock agents, which are made from manganese-organic compounds. These substances are less toxic to our body and make it possible to obtain fuel with an OCh of one hundred twenty five to one hundred thirty units.
Gasoline production technology
By direct distillation of oil , gasoline is obtained with an OCh up to 91. The indicated method for today is an impermissible luxury, since the output of gasoline itself is small. To increase the fuel yield and improve its quality, re-distillation, catalytic, thermal cracking, reforming, etc. are used.
These methods increase the cost of labor, time and money, however, only they allow you to get less harmful gasoline for the environment. To increase OCh today, very often use a variety of chemicals (alcohols, organometallic compounds, esters, etc.).