Pyrolysis

(redirected from Biooil)
Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

pyrolysis

[pə′räl·ə·səs]
(chemistry)
The breaking apart of complex molecules into simpler units by the use of heat, as in the pyrolysis of heavy oil to make gasoline. Also known as thermolysis.

Pyrolysis

 

the process by which organic compounds are decomposed by heat. The term “pyrolysis” is usually used in a narrower sense to refer to the high-temperature, extensive thermal conversion of crude oil and natural gas through decomposition, isomerization, and other transformations of the molecules of the raw materials; the term “cracking” is equivalent to “pyrolysis” in this narrower sense.

Pyrolysis is one of the most important industrial methods for producing starting materials for petrochemical synthesis. Its desired product is a gas that is rich in the unsaturated hydrocarbons ethylene, propylene, and butadiene, which are used for making polymers for the production of plastics, synthetic fibers, and synthetic rubbers.

The first pyrolysis plants were constructed in Russia in the 1870’s, in Kiev and Kazan. Primarily kerosine was subjected to pyrolysis, with the aim of producing illuminating gas. Subsequently it was proved feasible to separate aromatic hydrocarbons from the tar that is produced by pyrolysis. Pyrolytic methods were extensively developed during World War I, when a large demand arose for toluene, the starting material for the production of trotyl, or trinitrotoluene (TNT).

A wide variety of raw materials can be subjected to pyrolysis, including crude petroleum, heavy distillates, and such gaseous hydrocarbons as ethane and propane. However, pyrolysis is mostly used to treat gaseous hydrocarbons and gasolines, with which the greatest yields of the desired products are obtained with a minimal formation of coke. In industry, the most common pyrolysis units are of the tube type. The stock, for example, gasoline, is passed through a steam preheater and then mixed with superheated steam before entering a furnace, where it is subjected to further heating and pyrolytic decomposition. The final temperature of the reaction at the furnace exit varies from 750° to 850°C. The high temperatures, the short time that the stock spends in the reaction zone, and the dilution of the stock by water vapor promote decomposition to yield significant amounts of gas. A liquid tar is a by-product of pyrolysis. On the average, stocks of gasoline contain 20 percent tar by weight, while gaseous stock contains 5 percent tar.

To stop the pyrolysis reaction, the steam-gas mixture that exits from the furnace is rapidly cooled in a quencher by direct contact with a water condensate, which evaporates in the process. The mixture undergoes further cooling in a waste-heat boiler, where steam is produced under high pressures. The partially cooled steam-gas mixture exits from the waste-heat boiler and is subject to oil scrubbing to remove particles of soot and coke; the heavy tar fraction separates from the mixture. The scrubbed steam-gas mixture is further cooled with subsequent separation of the water and light-hydrocarbon condensates from the pyrolysis gases, which are transferred to a fractional-distillation unit for the separation of ethylene and propylene.

Pyrolysis tar characteristically contains a high concentration of the aromatic hydrocarbons benzene, toluene, and naphthalene. It also contains unsaturated hydrocarbons, including cy-clopentadiene, which is a starting material in the synthesis of many organic products. The components of the tar are used to manufacture high-octane gasoline, aromatic hydrocarbons, such binders as cumarone-indene resins, and petroleum-coke for electrodes. Table 1 shows the approximate yields of the most valuable gas and tar components from various raw materials.

Table 1. Percent yields for the major products of pyrolysis
 Raw material
 EthanePropaneGasoline (light)Gas oil (light)
Ethylene ............77.742.033.526.0
Propylene ...........2.816.815.516.1
Butadiene, butylene.....2.74.38.89.4
Benzene ...........0.92.56.76.0
Toluene............0.20.53.32.9

Pyrolysis of petroleum and the other heavier stocks is accompanied by considerable deposition of coke and requires specially designed apparatus. Circulating heat carriers are used to accelerate pyrolysis. When solid heat carriers are used, for example, quartz sand or petroleum coke, the reaction is accelerated by burning the coke that is formed within the system. When a gaseous heat carrier is used, for example, steam, acceleration results from minimal deposition of coke. Catalytic processes have been developed to reduce the cost of pyrolysis. The optimal yield in the pyrolysis of gaseous stock is obtained at about 1200°C, in which case the major product is acetylene, a starting material in the production of chloroprene rubber and acetalde-hyde.

REFERENCES

Smidovich, E. V. Destruktivnaia pererabotka nefti i gaza, 2nd ed. Moscow, 1968. (Tekhnologiia pererabotki nefti i gaza, part 2.)
Paushkin, la. M., S. V. Adel’son, and T. P. Vishniakova. Tekhnologiia neftekhimicheskogo sinteza, part 1. Moscow, 1973.

E. V. SMIDOVICH

References in periodicals archive ?
AFS BioOil was formed in 2010 as a spin out of Algae Floating Systems, Inc.
Kingston said the BioOil plants, which are carbon and greenhouse gas neutral, are planned for forestry communities where little or no electricity is available at present.
Heat output for Intermediate BioOil averages 14% higher than the company's standard BioOil, which has up to 55% of the heating value of diesel on a volume basis.
With an energy density 12 times greater than an original wood residue, it means the BioOil can be transported economically over very large distances.
BioOil has yet to replace any fossil fuel, so the municipality would be one of the first commercial organizations to implement such a project.
Testing and evaluation to determine the suitability of DynaMotive BioOil as a mixing (blend) component and/or an alternative fuel in slow and / or medium speed diesel engines at MES facilities.
Vadim Krifuks, CEO of AFS BioOil, says that the team is thrilled to see the results of years of extensive R&D effort put in development and scale up of AFS technologies where algae cultivation and microbial fermentation could be combined in a single system.
We believe we have a great competitive edge in this market as well as being able to target ethanol and syn-diesel production through further processing of our fuel," said Kingston, adding, "We believe that our BioOil and Intermediate BioOils can be shown to be cost competitive with hydrocarbon-based industrial fuels.
Announced in August the receipt of orders of BioOil from a US based client over a period of six months.
Dynamotive's BioOil and Intermediate BioOil can be used in burners, furnaces, and the BioOil also in gas turbines.
According to DynaMotive, the remainder of the plant will be built according to the following schedule: November 22 -- water and sewer excavating and installation completed, BioOil imported into storage tanks; November 30 -- piping/mechanical and electrical installed, commissioning of individual systems in progress and final site work completed; December 5 -- BioOil produced, pending receipt of operation and production permits.