Editing Thermal depolymerization (section)

==Ordered depolymerization==
Some materials thermally decompose in an ordered manner to give a single or limited range of products. By virtue of being pure materials, they are usually more valuable than the mixtures produced by disordered thermal depolymerization. For plastics this is usually the starting [[monomer]], and when this is recycled back into fresh polymer, it is called feedstock recycling. In practice, not all depolymerization reactions are completely efficient, and some competitive pyrolysis is often observed.

===Biomass===
[[Biorefinery|Biorefineries]] convert low-value agricultural and animal waste into useful chemicals. The industrial production of [[furfural]] by the acid-catalyzed thermal treatment of [[hemicellulose]] has been in operation for over a century. [[Lignin]] has been the subject of significant research for the potential production of [[BTX (chemistry)|BTX]] and other aromatic compounds,<ref>{{cite journal |last1=Lok |first1=C.M. |last2=Van Doorn |first2=J. |last3=Aranda Almansa |first3=G. |title=Promoted ZSM-5 catalysts for the production of bio-aromatics, a review |journal=Renewable and Sustainable Energy Reviews |date=October 2019 |volume=113 |pages=109248 |doi=10.1016/j.rser.2019.109248|bibcode=2019RSERv.11309248L |s2cid=198328225 }}</ref> although such processes have not yet been commercialized with any lasting success.<ref>{{cite journal |last1=Wong |first1=Sie Shing |last2=Shu |first2=Riyang |last3=Zhang |first3=Jiaguang |last4=Liu |first4=Haichao |last5=Yan |first5=Ning |title=Downstream processing of lignin derived feedstock into end products |journal=Chemical Society Reviews |date=2020 |volume=49 |issue=15 |pages=5510–5560 |doi=10.1039/D0CS00134A|pmid=32639496 |s2cid=220405457 |url=https://eprints.lincoln.ac.uk/id/eprint/46399/1/Lignin%20Valorisation%20Review-Chem.%20Soc.%20Rev.%20Final%20version.docx |url-access=subscription }}</ref>

===Plastics===
{{Main|Plastic recycling}}

Certain polymers like [[PTFE]], [[Nylon 6]], [[polystyrene]], and [[polymethylmethacrylate|PMMA]]<ref>{{cite journal |last1=Kaminsky |first1=W |last2=Predel |first2=M |last3=Sadiki |first3=A |title=Feedstock recycling of polymers by pyrolysis in a fluidised bed |journal=Polymer Degradation and Stability |date=September 2004 |volume=85 |issue=3 |pages=1045–1050 |doi=10.1016/j.polymdegradstab.2003.05.002}}</ref> undergo [[depolymerization]] to give their starting [[monomers]]. These can be converted back into new plastic, a process called chemical or feedstock recycling.<ref>{{cite journal |last1=Kumagai |first1=Shogo |last2=Yoshioka |first2=Toshiaki |title=Feedstock Recycling via Waste Plastic Pyrolysis |journal=Journal of the Japan Petroleum Institute |date=1 November 2016 |volume=59 |issue=6 |pages=243–253 |doi=10.1627/jpi.59.243 |url=https://www.jstage.jst.go.jp/article/jpi/59/6/59_243/_article/-char/en|doi-access=free }}</ref><ref>{{cite journal |last1=Rahimi |first1=AliReza |last2=García |first2=Jeannette M. |title=Chemical recycling of waste plastics for new materials production |journal=Nature Reviews Chemistry |date=June 2017 |volume=1 |issue=6 |pages=0046 |doi=10.1038/s41570-017-0046}}</ref><ref>{{cite journal |last1=Coates |first1=Geoffrey W. |last2=Getzler |first2=Yutan D. Y. L. |title=Chemical recycling to monomer for an ideal, circular polymer economy |journal=Nature Reviews Materials |date=July 2020 |volume=5 |issue=7 |pages=501–516 |doi=10.1038/s41578-020-0190-4|bibcode=2020NatRM...5..501C |s2cid=215760966 }}</ref> In theory, this offers infinite recyclability, but it is also more expensive and has a higher [[carbon footprint]] than other forms of plastic recycling; however, in practice, this still yields an inferior product at higher energy costs than virgin polymer production in the real world because of contamination.