Editing Pyrolysis (section)

=== Coke, carbon, charcoals, and chars ===
[[File:BurningOgatan(JapaneseBriquetteCharcoal).theora.ogv|thumb|[[Charcoal briquette]]s, often made from compressed sawdust or similar, in use.]]

Carbon and carbon-rich materials have desirable properties but are nonvolatile, even at high temperatures. Consequently, pyrolysis is used to produce many kinds of carbon; these can be used for fuel, as reagents in steelmaking (coke), and as structural materials.

[[Charcoal]] is a less smoky fuel than pyrolyzed wood.<ref>{{cite journal |last1=Sood |first1=A |title=Indoor fuel exposure and the lung in both developing and developed countries: an update. |journal=Clinics in Chest Medicine |date=December 2012 |volume=33 |issue=4 |pages=649–65 |doi=10.1016/j.ccm.2012.08.003 |pmid=23153607 |pmc=3500516 }}</ref> Some cities ban, or used to ban, wood fires; when residents only use charcoal (and similarly treated rock coal, called ''coke'') air pollution is significantly reduced. In cities where people do not generally cook or heat with fires, this is not needed. In the mid-20th century, "smokeless" legislation in Europe required cleaner-burning techniques, such as [[coke (fuel)|coke]] fuel<ref name="zones">{{cite journal |title=SMOKELESS zones. |journal=British Medical Journal |date=10 October 1953 |volume=2 |issue=4840 |pages=818–20 |doi=10.1136/bmj.2.4840.818 |pmid=13082128 |pmc=2029724 }}</ref> and smoke-burning incinerators<ref>{{Cite web|url=https://www.freepatentsonline.com/3881430.html|title=Two-stage incinerator, United States Patent 3881430 |work=www.freepatentsonline.com |access-date=11 February 2023}}</ref> as an effective measure to reduce air pollution<ref name="zones" />

[[File:Coal-forge-diagram.svg|thumb|right|upright=1.25|A blacksmith's forge, with a blower forcing air through a bed of fuel to raise the temperature of the fire. On the periphery, coal is pyrolyzed, absorbing heat; the coke at the center is almost pure carbon, and releases a lot of heat when the carbon oxidizes.]]

[[File:CoalPyrolysisProducts.png|thumb|upright=1.25|Typical organic products obtained by pyrolysis of coal (X = CH, N).]]
The coke-making or "coking" process consists of heating the material in "coking ovens" to very high temperatures (up to {{convert|900|C|F|disp=or|sigfig=2}}) so that the molecules are broken down into lighter volatile substances, which leave the vessel, and a porous but hard residue that is mostly carbon and inorganic ash. The amount of volatiles varies with the source material, but is typically 25–30% of it by weight. High temperature pyrolysis is used on an industrial scale to convert [[coal]] into [[Coke (fuel)|coke]]. This is useful in [[metallurgy]], where the higher temperatures are necessary for many processes, such as [[steelmaking]]. Volatile by-products of this process are also often useful, including [[benzene]] and [[pyridine]].<ref>{{cite encyclopedia|author=Ludwig Briesemeister |author2=Andreas Geißler |author3=Stefan Halama |author4=Stephan Herrmann |author5=Ulrich Kleinhans |author6=Markus Steibel |author7=Markus Ulbrich |author8=Alan W. Scaroni |author9=M. Rashid Khan |author10=Semih Eser |author11=Ljubisa R. Radovic |pages=1–44|chapter=Coal Pyrolysis|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|year=2002|publisher=Wiley-VCH|place=Weinheim| doi=10.1002/14356007.a07_245.pub2|isbn=978-3-527-30673-2}}</ref>  Coke can also be produced from the solid residue left from petroleum refining.

The original [[xylem|vascular structure]] of the wood and the pores created by escaping gases combine to produce a light and porous material. By starting with a dense wood-like material, such as [[nutshell]]s or [[peach]] [[endocarp|stone]]s, one obtains a form of charcoal with particularly fine pores (and hence a much larger pore surface area), called [[activated carbon]], which is used as an [[adsorption|adsorbent]] for a wide range of chemical substances.

[[Biochar]] is the residue of incomplete organic pyrolysis, e.g., from cooking fires.  It is a key component of the [[terra preta]] soils associated with ancient [[indigenous peoples of Brazil|indigenous]] communities of the [[Amazon basin]].<ref name="lehmann1">
  {{cite web 
  | url=http://www.css.cornell.edu/faculty/lehmann/biochar/Biochar_home.htm 
  | title=Biochar: the new frontier 
  | author=Lehmann, Johannes 
  | access-date=2008-07-10 |archive-url = https://web.archive.org/web/20080618231424/http://www.css.cornell.edu/faculty/lehmann/biochar/Biochar_home.htm <!-- Bot retrieved archive --> |archive-date = 2008-06-18}}
</ref> Terra preta is much sought by local farmers for its superior fertility and capacity to promote and retain an enhanced suite of beneficial microbiota, compared to the typical red soil of the region. Efforts are underway to recreate these soils through [[biochar]], the solid residue of pyrolysis of various materials, mostly organic waste.
[[File:Carbon fibers from silk cocoon.tif|right|thumb|Carbon fibers produced by pyrolyzing a silk cocoon. Electron micrograph, scale bar at bottom left shows 100 [[Micrometre|μm]].]]
[[Carbon fiber]]s are filaments of carbon that can be used to make very strong yarns and textiles. Carbon fiber items are often produced by spinning and weaving the desired item from fibers of a suitable [[polymer]], and then pyrolyzing the material at a high temperature (from {{convert|1500|-|3000|°C|F|disp=or|sigfig=3}}).  The first carbon fibers were made from [[rayon]], but [[polyacrylonitrile]] has become the most common starting material. For their first workable [[electric lamp]]s, [[Joseph Wilson Swan]] and [[Thomas Edison]] used carbon filaments made by pyrolysis of [[cotton]] yarns and [[bamboo]] splinters, respectively.

Pyrolysis is the reaction used to coat a preformed substrate with a layer of [[pyrolytic carbon]]. This is typically done in a fluidized bed reactor heated to {{convert|1000|-|2000|°C|F|disp=or|sigfig=3}}. Pyrolytic carbon coatings are used in many applications, including [[artificial heart valve]]s.<ref name="ratner">Ratner, Buddy D. (2004). Pyrolytic carbon. In ''[https://books.google.com/books?id=Uzmrq7LO7loC&dq=discovery%20of%20pyrolytic&pg=PA171 Biomaterials science: an introduction to materials in medicine] {{webarchive|url=https://web.archive.org/web/20140626221658/http://books.google.com/books?id=Uzmrq7LO7loC&lpg=PA172&ots=zcTbDBKgU-&dq=discovery%20of%20pyrolytic&pg=PA171 |date=2014-06-26 }}''. Academic Press. pp. 171–180. {{ISBN|0-12-582463-7}}.</ref>