Cracking
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules (e.g. light hydrocarbons) by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of any catalysts. Cracking, also referred to as pyrolysis, is the breakdown of a large alkane into smaller, more useful alkanes and an alkene. Simply put, hydrocarbon cracking is the process of breaking long chain hydrocarbons into short ones.
History and patents
The thermal cracking method (also known as "Shukhov cracking process") was invented by Russian engineer Vladimir Shukhov and patented in 1891 in the Russian empire, Patent No. 12926, November 27, 1891. This process was modified by the American engineer William Merriam Burton and patented as U.S. Patent 1,049,667 on January 7, 1913.
In 1924 the delegation of the American "Sinckler Oil" paid a visit to Shukhov. The "Sinckler Oil" firm protested the personal right appropriated by the Rockefeller "Standard Oil" concern on the discovery of oil cracking. It indicated that the patent of Burton used by the "Standard Oil" concern was the modified patent of Shukhov. Shukhov proved Americans that the Burton method was just the slightly changed modification of his 1891 patents. However an agreement of lawsuit between the American companies finally was made, in order not to buy the patent from Soviet Russia.[1]
Applications
Oil refinery cracking processes allow the production of "light" products such as liquified petroleum gas (LPG) and gasoline from heavier crude oil distillation fractions such as gas oils and residues. Fluid catalytic cracking produces a high yield of gasoline and LPG, while hydrocracking is a major source of jet fuel, diesel, naphtha, and LPG.
Thermal cracking is currently used to "upgrade" very heavy fractions ("upgrading", "visbreaking"), or to produce light fractions or distillates, burner fuel and/or petroleum coke. Two extremes of the thermal cracking in terms of product range are represented by the high-temperature process called "steam cracking" or pyrolysis (ca. 750 to 900 °C or more) which produces valuable ethylene and other feedstocks for the petrochemical industry, and the milder-temperature delayed coking (ca. 500 °C) which can produce, under the right conditions, valuable needle coke, a highly crystalline petroleum coke used in the production of electrodes for the steel and aluminium industries.