Pyrolysis is the
chemical decompositionof organic materials by heating in the absence of oxygenor any other reagents, except possibly steam.
It is used in
chemical analysisto break down complex matter into simpler molecules for identification, for example by pyrolysis gas chromatography mass spectrometry.
In industry, it may be used to convert one single chemical; for example,
ethylene dichlorideis pyrolysed to vinyl chlorideto make PVC. It may also be used to convert complex materials such as biomassor wasteinto substances that are either desirable or less harmful (e.g. - syngas).
Extreme pyrolysis, which leaves only
carbonas the residue, is called carbonization. Pyrolysis is a special case of thermolysis.
Some pyrolysis processes are
This phenomenon commonly occurs whenever solid organic material is heated strongly in absence of oxygen, e.g., when
frying, roasting, baking, toasting. Even though such processes are carried out in a normal atmosphere, the outer layers of the material keep its interior oxygen-free (which is why the outer layer oxidizes (burns), but the inside does not).
The process also occurs when burning compact solid fuel, like wood. In fact, the flames of a wood fire are due to combustion of gases released by pyrolysis, not combustion of the wood itself. Thus, the pyrolysis of common materials like wood, plastic, and clothing is extremely important for
fire safetyand fire-fighting.
An ancient industrial use of anhydrous pyrolysis is the production of
charcoalthrough the pyrolysis of wood. In more recent times, pyrolysis has been used on a massive scale to turn coalinto coke for metallurgy, especially steelmaking.
Anhydrous pyrolysis has been assumed to take place during catagenesis, the conversion of
kerogento fossil fuels.
In many industrial applications, the process is done under pressure and at operating temperatures above 430
°C(806 °F). Anhydrous pyrolysis can also be used to produce liquid fuel similar to dieselfrom solid biomassor plastics. [cite web |url=http://www1.eere.energy.gov/biomass/pyrolysis.html |title= US DOE |archiveurl=http://web.archive.org/web/20070814144750/http://www1.eere.energy.gov/biomass/pyrolysis.html |archivedate=2007-08-14] The most common technique uses very low residence times (<2 seconds) and high heating rates using a temperature between 350 and 500 °C and is called either fast or flash pyrolysis.
The term pyrolysis is sometimes used to encompass thermolysis in the presence of water, such as
steam crackingof oil, or more generally hydrous pyrolysis. An example of the latter is thermal depolymerizationof organic waste into light crude oil.
In vacuum pyrolysis, organic material is heated in a
vacuumin order to decrease boiling pointand avoid adverse chemical reactions. It is used in organic chemistryas a synthetic tool. In flash vacuum thermolysis or FVT, the residence time of the substrate at the working temperature is limited as much as possible, again in order to minimize secondary reactions.
Processes for biomass pyrolysis
Fast pyrolysis of biomass feedstocks is required to achieve high yields of liquids. It is characterized by rapid heating of the biomass particles and a short residence time of product vapors (0.5 to 2 s). Rapid heating means that the biomass must be ground into fine particles and that the insulating char layer that forms at the surface of the reacting particles must be continuously removed.
Since pyrolysis is slightly
endothermic, [Fang He, Weiming Yi and Xueyuan Bai, Investigation on caloric requirement of biomass pyrolysis using TG–DSC analyzer, Energy Conversion and Management, Volume 47, Issues 15-16, September 2006, Pages 2461-2469] various methods have been proposed to provide heat to the reacting biomass particles::*Partial combustion of the biomass products through air injection. This results in poor-quality products.:*Direct heat transfer with a hot gas, ideally product gas that is reheated and recycled. The problem is to provide enough heat with reasonable gas flow-rates.:*Indirect heat transferwith exchange surfaces (wall, tubes). It is difficult to achieve good heat transfer on both sides of the heat exchange surface.:*Direct heat transfer with circulating solids: Solids transfer heat between a burner and a pyrolysis reactor. This is an effective but complex technology.
The following technologies have been proposed for biomass pyrolysis: [ Cedric Briens, Franco Berruti and Jan Piskorz, Biomass Valorization for Fuel and Chemicals Production – A Review, IJCRE, vol. 6, R2, Available at: http://www.bepress.com/ijcre/vol6/R2/ ] :*Fixed beds were used for the traditional production of charcoal. Poor, slow heat transfer resulted in very low liquid yields.:*
Augers: This technology is adapted from a Lurgiprocess for coal gasification. Hot sand and biomass particles are fed at one end of a screw. The screw mixes the sand and biomass and conveys them along. It provides a good control of the biomass residence time. It does not dilute the pyrolysis products with a carrier or fluidizing gas. However, sand must be reheated in a separate vessel, and mechanical reliability is a concern. There is no large-scale commercial implementation.:*Ablative processes: Biomass particles are moved at high speed against a hot metal surface. Ablation of any char forming at the particles surface maintains a high rate of heat transfer. This can be achieved by using a metal surface spinning at high speed within a bed of biomass particles, which may present mechanical reliability problems but prevents any dilution of the products. As an alternative, the particles may be suspended in a carrier gas and introduced at high speed through a cyclone whose wall is heated; the products are diluted with the carrier gas. [ [http://www.thw.ctw.utwente.nl/research/Fuelconv/bramer.pdf PowerPoint-presentatie ] ] A problem shared with all ablative processes is that scale-up is made difficult since the ratio of the wall surface to the reactor volume decreases as the reactor size is increased. There is no large-scale commercial implementation.:*Rotating cone: Pre-heated hot sand and biomass particles are introduced into a rotating cone. Due to the rotation of the cone, the mixture of sand and biomass is transported across the cone surface by centrifugal force. Like other shallow transported-bed reactors relatively fine particles are required to obtain a good liquid yield. There is no large scale commercial implementation. [cite web |url=http://www.btgworld.com/technologies/pyrolysis.html |title= BTG Biomass Technology Group b.v. :: Technology:: Pyrolysis |archiveurl=http://web.archive.org/web/20070703000320/http://www.btgworld.com/technologies/pyrolysis.html |archivedate=2007-07-03] :*Fluidized beds: Biomass particles are introduced into a bed of hot sand fluidized by a gas, which is usually a recirculated product gas. High heat transfer rates from fluidized sand result in rapid heating of biomass particles. There is some ablation by attrition with the sand particles, but it is not as effective as in the ablative processes. Heat is usually provided by heat exchanger tubes through which hot combustion gas flows. There is some dilution of the products, which makes it more difficult to condense and then remove the bio-oil mist from the gas exiting the condensers. This process has been scaled up by companies such as Dynamotive and Agri-Therm. The main challenges are in improving the quality and consistency of the bio-oil.:*Circulating fluidized beds: Biomass particles are introduced into a circulating fluidized bed of hot sand. Gas, sand and biomass particles move together, with the transport gas usually being a recirculated product gas, although it may also be a combustion gas. High heat transfer rates from sand ensure rapid heating of biomass particles and ablation is stronger than with regular fluidized beds. A fast separator separates the product gases and vapors from the sand and char particles. The sand particles are reheated in fluidized burner vessel and recycled to the reactor. Although this process can be easily scaled up, it is rather complex and the products are much diluted, which greatly complicates the recovery of the liquid products.
refuse: Pyrolysis is used as a form of thermal treatmentto reduce waste volumes
* waste film plastic: to produce a synthetic diesel fuelcite news | first=Marc | last=Middleton | coauthors= | title=Local recycler ignites Euro fuel market | date=2005-02-06 | publisher=Waste Management & Environment Media Pty Ltd. | url =http://www.wme.com.au/categories/waste_managemt/feb6_05.php | work =Waste Management & Environment | pages = | accessdate = 2008-07-10 | language = ]
* agricultural waste: temperature of 450 to 550 °C
* sawdust and waste woodThere is also the possibility of integrating with other processes such as
mechanical biological treatmentand anaerobic digestion. [Marshall, A. T. & Morris, J. M. (2006) [http://www.alexmarshall.me.uk/index_files/documents/CIWM.pdf A Watery Solution and Sustainable Energy Parks] , CIWM Journal, August p22-23]
* synthetic diesel fuel cannot yet be produced directly by pyrolysis
* bio-oil: can be used as a fuel, after removal of valuable bio-chemicals that can be used as food additives or pharmaceuticals. The bio-oil cannot be used directly in most car engines.
syngas(flammable mixture of carbon monoxide and hydrogen): can be produced in sufficient quantities to both provide the energy needed for pyrolysis and some excess productioncite news | first=Mark | last=Horstman | title=Agrichar – A solution to global warming? | date=2007-09-23 | publisher=Australian Broadcasting Corporation | url =http://www.abc.net.au/catalyst/stories/s2012892.htm | work =ABC TV Science: Catalyst | accessdate = 2008-07-10 ] [cite web |url=http://www.geagroup.com/imperia/md/content/presse/2005.11.30_presentation_dr_plass_e.pdf |title= |archiveurl=http://web.archive.org/web/20061218035002/http://www.geagroup.com/imperia/md/content/presse/2005.11.30_presentation_dr_plass_e.pdf |archivedate=2006-12-18|format=PDF]
* solid char that can either be burned for energy or recycled as a
fertilizer, also known as biochar.
* carbon black
Carbon black is made from heavy oil fractions (mainly) and is an important material used in the rubber industry, where it significantly influences the properties of the final product (hardwearing tread black, soft flexible carcass black).Biochar used as fertilizer is very attractive since it ameliorates the soil texture and releases fertilizer slowly. When compared to chemical fertilizers, it contains oligoelements, such as selenium, which help achieve higher crop yields. When compared to other “natural” fertilizers such as
manureor sewage, it is safer since it has been disinfected at high temperature and, being a solid, greatly reduces any risk of water tablecontamination (inhalation risks remain if the biochar is not properly granulated).cite news | first=Peter | last=Cundall | coauthors= | title=Fact Sheet: Pete’s Patch | date=2007-10-27 | publisher=Australian Broadcasting Corporation | url =http://www.abc.net.au/gardening/stories/s2071694.htm | work =Gardening Australia | pages = | accessdate = 2008-07-10 | language = ] Pyrolytic char is thought to be a major component in the formation of ancient terra pretasoils. Efforts are underway to recreate these soils through the production of biochar, which is designed to promote nutrient retention and enhance soil ecology. Biochar is also being considered for carbon sequestration in the mitigation of global warming. [cite web | url=http://www.css.cornell.edu/faculty/lehmann/biochar/Biochar_home.htm | title=Biochar: the new frontier | author=Johannes Lehmann | accessdate=2008-07-10] cite news | first=Mark | last=Horstman | title=Agrichar – A solution to global warming? | date=2007-09-23 | publisher=Australian Broadcasting Corporation | url =http://www.abc.net.au/catalyst/stories/s2012892.htm | work =ABC TV Science: Catalyst | accessdate = 2008-07-10 ]
firesin buildings will often burn with limited oxygen supply, resulting in pyrolysis reactions. Thus, pyrolysis reaction mechanisms and the pyrolysis properties of materials are important in fire protection engineeringfor passive fire protection. Pyrolytic carbonis also important to fire investigators as a tool for discovering origin and cause of fires.
* [http://www.juniper.co.uk/services/Our_services/P&GFactsheet.html Pyrolysis and Gasification Factsheet]
* [http://www.pyne.co.uk/ The Biomass Pyrolysis Network]
* [http://www.pyrum.net/ Homepage of the project "Pyrum Innovations"]
* [http://www.agri-therm.com/pyrolysis.htm Agri-Therm]
* [http://www.biomatnet.org/secure/Contacts/C1103057.htm Resource Transforms International]
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Look at other dictionaries:
pyrolysis — 1890, from PYRO (Cf. pyro ) + LYSIS (Cf. lysis) … Etymology dictionary
pyrolysis — [pī räl′ə sis] n. [ModL: see PYRO & LYSIS] chemical decomposition of a substance by heat: see CALCINE pyrolytic [pī΄rō lit′ik] adj. pyrolytically adv … English World dictionary
Pyrolysis — The transformation on a compound or material into one or more substances by heat alone (without oxidation). Often called destructive distillation. Pyrolysis of biomass is the thermal degradation of the material in the absence of reacting gases … Energy terms
pyrolysis — Decomposition by the application of or as a result of heat. The breaking apart of complex molecules into simpler units by the use of heat, as in the pyrolysis of heavy oil to make gasoline … Forensic science glossary
pyrolysis — pirolizė statusas T sritis Standartizacija ir metrologija apibrėžtis Medžiagų skaidymas aukštoje temperatūroje be oro. atitikmenys: angl. pyrolysis; thermolysis vok. Pyrolyse, f rus. пирогенное разложение, n; пиролиз, m; термолиз, m pranc.… … Penkiakalbis aiškinamasis metrologijos terminų žodynas
pyrolysis — pirolizė statusas T sritis chemija apibrėžtis Organinių medžiagų skaidymas aukštoje temperatūroje be oro. atitikmenys: angl. pyrolysis; thermolysis rus. пирогенное разложение; пиролиз; термолиз ryšiai: sinonimas – termolizė sinonimas –… … Chemijos terminų aiškinamasis žodynas
pyrolysis — noun Etymology: New Latin Date: circa 1890 chemical change brought about by the action of heat • pyrolytic adjective • pyrolytically adverb … New Collegiate Dictionary
pyrolysis — pyrolytic /puy reuh lit ik/, adj. /puy rol euh sis/, n. Chem. 1. the subjection of organic compounds to very high temperatures. 2. the resulting decomposition. [1885 90; PYRO + LYSIS] * * * … Universalium
pyrolysis — noun /pɪˈɹɒlɪsɪs,paɪˈɹɒlɪsɪs/ The decomposition of a material or compound due to heat in the absence of oxygen or any other reagents See Also: pyrolyse, pyrolyze, pyrolytic, pyrolytically, pyro … Wiktionary
pyrolysis — Decomposition of a substance by heat. [pyro + G. lysis, dissolution] * * * py·rol·y·sis pī räl ə səs n, pl y·ses .sēz chemical change brought about by the action of heat py·ro·lyt·ic .pī rə lit ik adj * * * … Medical dictionary