Editing Glycerol (section)

==Production==
===Natural sources===
Glycerol is generally obtained from plant and animal sources where it occurs in [[triglyceride]]s, [[ester]]s of glycerol with long-chain [[carboxylic acids]]. The [[hydrolysis]], [[saponification]], or [[transesterification]] of these triglycerides produces glycerol as well as the fatty acid derivative:
<div style="display: flex; max-width: 100%; overflow-x: auto">
{{Biochem reaction subunit |compound=Triglyceride |class=skin-invert-image|image=Fat_structural_formulae_V3.svg |imagesize=150px}}
{{Biochem reaction subunit |direction=forward |title=3 [[NaOH]] / {{H2O-nl}} |title_lower={{abbr|Δ|heating}}}}
{{Biochem reaction subunit |n=3 |compound=soap |class=skin-invert-image|image=General sodium carboxylate.svg}}
{{Biochem reaction subunit |compound=glycerol |class=skin-invert-image|image=Glycerine Structural Formula V1.svg}}
</div>
Triglycerides can be saponified with [[sodium hydroxide]] to give glycerol and fatty sodium salt or [[soap]].

Typical plant sources include [[soybeans]] or [[Arecaceae|palm]]. Animal-derived [[tallow]] is another source. From 2000 to 2004, approximately 950,000 tons per year were produced in the United States and Europe; 350,000 tons of glycerol were produced in the U.S. alone.<ref>{{cite web |title= A Glycerin Factor |author= Nilles, Dave |url= https://www.biodieselmagazine.com/article.jsp?article_id=377 |publisher= Biodiesel Magazine |year= 2005 |access-date= 21 February 2022 |archive-date= 8 November 2007 |archive-url= https://web.archive.org/web/20071108114027/http://www.biodieselmagazine.com/article.jsp?article_id=377 |url-status= live }}</ref> Since around 2010, there is a large surplus of glycerol as a byproduct of [[biofuel]], enforced for example by [[Directive on the Promotion of the use of biofuels and other renewable fuels for transport|EU directive 2003/30/EC]] that required 5.75% of petroleum fuels to be replaced with biofuel sources across all [[Member state of the European Union|member states]].<ref name="Ullmann">{{cite encyclopedia |encyclopedia= Ullmann's Encyclopedia of Industrial Chemistry |last1= Christoph |first1= Ralf |last2= Schmidt |first2= Bernd |last3= Steinberner |first3= Udo |last4= Dilla |first4= Wolfgang |last5= Karinen |first5= Reetta |year= 2006 |doi= 10.1002/14356007.a12_477.pub2 |chapter= Glycerol |isbn= 3527306730}}</ref>
Crude glycerol produced from triglycerides is of variable quality, with a selling price as low as US$0.02–0.05 per kilogram in 2011.<ref>{{cite journal |last1 = San Kong |first1 = Pei |last2 = Kheireddine Aroua |first2 = Mohamed |last3 = Ashri Wan Daud |first3 = Wan Mohd |year = 2016 |title = Conversion of crude and pure glycerol into derivatives: A feasibility evaluation |journal = Renewable and Sustainable Energy Reviews |volume = 63 |pages = 533–555 |doi = 10.1016/j.rser.2016.05.054 |bibcode = 2016RSERv..63..533K }}</ref> It can be purified in a rather expensive process by treatment with [[activated carbon]] to remove organic impurities, alkali to remove unreacted glycerol esters, and [[ion exchange]] to remove salts. High purity glycerol (greater than 99.5%) is obtained by multi-step distillation; a [[vacuum chamber]] is necessary due to its high boiling point (290&nbsp;°C).<ref name=Ullmann/>

Consequently, glycerol recycling is more of a challenge than its production, for instance by conversion to glycerol carbonate<ref>{{Cite journal |last1=Das |first1=Arpita |last2=Kodgire |first2=Pravin |last3=Li |first3=Hu |last4=Basumatary |first4=Sanjay |last5=Baskar |first5=Gurunathan |last6=Rokhum |first6=Samuel Lalthazuala |date=2023 |title=Recent Advances in Conversion of Glycerol: A Byproduct of Biodiesel Production to Glycerol Carbonate |journal=Journal of Chemistry |language=en |volume=2023 |issue=1 |pages=8730221 |doi=10.1155/2023/8730221 |doi-access=free |issn=2090-9071}}</ref> or to synthetic precursors, such as [[acrolein]] and epichlorohydrin.<ref>{{cite journal |title= Glycerol|last= Yu|first= Bin|journal= Synlett|volume= 25|issue= 4|pages= 601–602|doi= 10.1055/s-0033-1340636|year= 2014|doi-access= free}}</ref>

===Synthetic glycerol===
Although more expensive than production from plant or animal triglycerides, glycerol can be synthesized by various routes.  During [[World War II]], synthetic glycerol processes became a national defense priority because it is a precursor to [[nitroglycerine]]. Epichlorohydrin is the most important precursor. [[Chlorination reaction|Chlorination]] of propylene gives [[allyl chloride]], which is oxidized with [[hypochlorite]] to [[dichlorohydrin]], which reacts with a strong base to give [[epichlorohydrin]]. Epichlorohydrin can be hydrolyzed to glycerol. [[Chlorine]]-free processes from propylene include the synthesis of glycerol from [[acrolein]] and [[propylene oxide]].<ref name="Ullmann" />
: [[File:Synthetic routes to glycerol.png|class=skin-invert-image|600px]]