Cracking is breaking up of large hydrocarbon molecules into smaller ones.
Cracking breaks long chains into short ones
There are several types of cracking:
- hot cracking, large hydrocarbon molecules for high temperature heating (sometimes with high pressure), until they split.
- steam cracking, using high temperature steam (816 ℃) ethane, butane, and decomposition of naphtha to ethylene and benzene (can be used to manufacture chemicals).
- visbreaking, residue of distillation tower heat (482 ℃), and then use diesel oil for cooling and rapidly in a distillation column within the light (make it suddenly burning).This process reduces the viscosity of heavy oil and produces tar.
- coking to the distillation tower, the residual oil heated to 482 ℃ above, cracking of heavy oil, gasoline and naphtha.When this process is completed, a large proportion of almost pure carbon residue (coke) is produced.Coke is sold after being cleaned with coking equipment.
- catalytic cracking, using the catalyst to accelerate the cracking reaction.The catalysts include zeolite, hydrated aluminum silicate, ferroalumina and silicon-alumina.
- fluidized catalytic cracking, a state of fluidized heat (538 ℃), can put the heavy oil cracking catalyst for diesel and gasoline.
- hydrocracking, this method is similar to the fluidized catalytic cracking, but using different catalysts, lower temperature and pressure is higher, also added the hydrogen.It can crack heavy oil into gasoline and kerosene (jet fuel).
After the various hydrocarbons are cracked into smaller ones, the products are separated by another fractionation column.
Sometimes small hydrocarbon molecules need to be combined into larger ones – a process known as association.The main combined process is called catalytic reforming, in which low molecular weight naphtha is converted into aromatic hydrocarbons using a catalyst (platinum, platinum-rhenium alloys) that can be used in chemical manufacturing and gasoline blending.An important by-product of the reaction is hydrogen, which can be used in hydrocracking or sold.