Definition of Cracking (of Oil)

Main types of cracking: thermal and catalytic

Thermal cracking is a process that is carried out thanks to a temperature and a certain pressure, around 800ºC and 2 to 8 kg/cm2, respectively. When the molecules are subjected to such temperatures they break down and form lower molecular weight compounds.

Instead, catalytic cracking meant a change in the paradigm of hydrocarbons since it introduced a new concept to the process, the use of catalysts in this reaction. These catalysts seek to accelerate the reaction speed, without the need for such a significant increase in temperature. In these cases, the temperatures are around 400ºC and the catalytic substance is an inert compound, which does not take part in the reaction itself. In general, oxides such as Al

₂OR₃, since this type of clay allows the reaction to be directed in one direction, avoiding unwanted products, which is why they are called selective reactions. In this sense, olefins are obtained (products that are used as raw material in other petrochemical processes), gasoline of high quality and LPG (Liquefied Petroleum Gas).

How does the catalytic cracking process work?

It can occur in different ways, although, for the most part, the catalyst flows in contact with the hydrocarbon continuously, which is known as fluidized catalytic cracking. Likewise, there is also fixed bed catalytic cracking, by Thermofor or moving bed.

In fluidized catalytic cracking, the catalyst is placed in the reactor suspended in an ascending stream of the hydrocarbon to be cracked in a fluidized bed. It should be noted that, in this type of cracking, the catalyst is exhausted after a certain amount of cycles, so that carbon or coke is deposited on them and its selectivity is reduced, decreasing so the effectiveness of process.

The basic parts of fluidized catalytic cracking are: firstly, a reactor, where the actual reaction takes place, that the catalyst is perfectly distributed in order to come into contact with the entire load and, with the addition of steam, the Energy necessary. The mixture then reaches the degasser where the catalyst is stripped of hydrocarbons and vapors. However, coke is deposited on the catalyst and must be removed for regeneration, so it goes through a regenerator where different techniques can be used. Typically, a stream of air hot burns the coke. Finally, once regenerated, the catalyst is returned to the reactor for its next use and the liquid products of the reactor process are sent to a fractionator for cooling. This process allows to recover the desired products and fine parts of the catalyst that have passed.

Many times we hear about hydrocracking and it has to do with the addition of hydrogen in the catalytic cracking process. That is, hydrogen results in an additional reactant (high pressures and temperatures) that is added onto the catalyst arranged in a fixed bed in the cracking reactor.

The advantages that accompany the practice

Thanks to cracking, the world of hydrocarbons has been able to significantly increase its production, since from the same volume of oil, more gasoline is obtained than that obtained by simple refining processes such as distillation. Currently, we hear that gasolines with better octane rating and quality are being produced, which is closely linked to this technology.

This process opened new horizons in the hydrocarbon industry, since cracking is what many authors call: secondary distillation. With a fractional distillation, the percentages of low molecular weight hydrocarbons (of greater demand in the market) that can be obtained are limited.

From cracking it is possible to divide high molecular weight compounds, such as fuel oil, into smaller compounds such as gasoline and naphtha. Moreover, it is an economically profitable process, since many heavy hydrocarbons do not have a great economic value such as naphtha, for therefore, being able to obtain naphtha from, for example, kerosene without having to go through distillation is a very important discovery. valuable. In this way, cracking became a necessary process in oil refineries.

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