Editing Ethanol (section)

== Purification ==
Ethylene hydration or brewing produces an ethanol–water mixture. For most industrial and fuel uses, the ethanol must be purified. [[Fractional distillation]] at atmospheric pressure can concentrate ethanol to 95.6% by weight (89.5 mole%). This mixture is an azeotrope with a boiling point of {{convert|78.1|C|F}}, and ''cannot'' be further purified by distillation. Addition of an entraining agent, such as benzene, [[cyclohexane]], or [[heptane]], allows a new ternary azeotrope comprising the ethanol, water, and the entraining agent to be formed. This lower-boiling ternary azeotrope is removed preferentially, leading to water-free ethanol.<ref name="ullmann">{{cite book | first1=Naim | last1=Kosaric | first2=Zdravko | last2=Duvnjak | first3=Adalbert | last3=Farkas | first4=Hermann | last4=Sahm | first5=Stephanie | last5=Bringer-Meyer | first6=Otto | last6=Goebel | first7=Dieter | last7=Mayer | name-list-style=vanc | chapter=Ethanol | title=Ullmann's Encyclopedia of Industrial Chemistry | pages=1–72 | year=2011 | publisher=Wiley-VCH | location=Weinheim | doi=10.1002/14356007.a09_587.pub2 | isbn=978-3-527-30673-2}}{{subscription required}}</ref>

Apart from distillation, ethanol may be dried by addition of a [[desiccant]], such as [[molecular sieves]], cellulose, or [[cornmeal]]. The desiccants can be dried and reused.<ref name="ullmann" /> [[Molecular sieve]]s can be used to selectively absorb the water from the 95.6% ethanol solution.<ref>{{Cite book | url={{google books | plainurl=y | id=4iEhAQAAMAAJ}} | title=Advances in Cereal Science and Technology | last=Chemists | first=American Association of Cereal | date=1986 | publisher=American Association of Cereal Chemists, Incorporated | isbn=978-0-913250-45-7 | language=en}}</ref> Molecular sieves of pore-size 3&nbsp;[[Angstrom|Å]], a type of [[zeolite]], effectively sequester water molecules while excluding ethanol molecules. Heating the wet sieves drives out the water, allowing regeneration of their desiccant capability.<ref>{{citation | url=https://www.bio.umass.edu/microscopy/mol_sieves.htm | title=Molecular Sieve Information | author=Dale Callaham}}</ref>

Membranes can also be used to separate ethanol and water. Membrane-based separations are not subject to the limitations of the water-ethanol azeotrope because the separations are not based on vapor-liquid equilibria. Membranes are often used in the so-called hybrid membrane distillation process. This process uses a pre-concentration distillation column as the first separating step. The further separation is then accomplished with a membrane operated either in vapor permeation or pervaporation mode. Vapor permeation uses a vapor membrane feed and pervaporation uses a liquid membrane feed.

A variety of other techniques have been discussed, including the following:<ref name="ullmann" />
* Salting using [[potassium carbonate]] to exploit its insolubility will cause a phase separation with ethanol and water. This offers a very small potassium carbonate impurity to the alcohol that can be removed by distillation. This method is very useful in purification of ethanol by distillation, as ethanol forms an [[azeotrope]] with water.
* Direct [[electrochemical reduction of carbon dioxide]] to ethanol under ambient conditions using [[copper nanoparticle]]s on a carbon nanospike film as the catalyst;<ref>{{cite journal | last1=Song | first1=Yang | last2=Peng | first2=Rui | last3=Hensley | first3=Dale K. | last4=Bonnesen | first4=Peter V. | last5=Liang | first5=Liangbo | last6=Wu | first6=Zili | last7=Meyer | first7=Harry M. | last8=Chi | first8=Miaofang | last9=Ma | first9=Cheng | last10=Sumpter | first10=Bobby G. | last11=Rondinone | first11=Adam J. | name-list-style=vanc | date=2016 | title=High-Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle/N-Doped Graphene Electrode | journal=[[ChemistrySelect]] | issue=Preprint | doi=10.1002/slct.201601169 | volume=1 | pages=6055–6061 | doi-access=free}}</ref>
* Extraction of ethanol from grain mash by [[supercritical carbon dioxide]];
* [[Pervaporation]];
* [[Fractional freezing]] is also used to concentrate fermented alcoholic solutions, such as traditionally made [[Applejack (beverage)]];
* [[Pressure swing adsorption]].<ref>{{cite journal | doi=10.1016/j.renene.2011.09.027 | title=Production of anhydrous ethanol using various PSA (Pressure Swing Adsorption) processes in pilot plant | year=2012 | last1=Jeong | first1=Jun-Seong | last2=Jeon | first2=Hyungjin | last3=Ko | first3=Kyung-mo | last4=Chung | first4=Bongwoo | last5=Choi | first5=Gi-Wook | name-list-style=vanc | journal=Renewable Energy | volume=42 | pages=41–45 | bibcode=2012REne...42...41J}}</ref>

=== Grades of ethanol ===
{{Further|Denatured alcohol}}
Pure ethanol and alcoholic beverages are heavily [[Sin tax|taxed]] as psychoactive drugs, but ethanol has many uses that do not involve its consumption. To relieve the tax burden on these uses, most jurisdictions waive the tax when an agent has been added to the ethanol to render it unfit to drink. These include [[bitterant|bittering agents]] such as [[denatonium benzoate]] and toxins such as methanol, [[naphtha]], and pyridine. Products of this kind are called ''denatured alcohol.''<ref>{{cite web | url=http://www.procurement.umich.edu/Contracts/Denatured_Alchohol.pdf | title=U-M Program to Reduce the Consumption of Tax-free Alcohol; Denatured Alcohol a Safer, Less Expensive Alternative | publisher=University of Michigan | access-date=29 September 2007 | url-status=dead | archive-url=https://web.archive.org/web/20071127095510/http://www.procurement.umich.edu/Contracts/Denatured_Alchohol.pdf | archive-date=27 November 2007 | df=dmy-all}}</ref><ref>Great Britain (2005). ''[http://www.opsi.gov.uk/si/si2005/20051524.htm The Denatured Alcohol Regulations 2005] {{Webarchive|url=https://web.archive.org/web/20091209162605/http://www.opsi.gov.uk/si/si2005/20051524.htm |date=9 December 2009 }}.'' Statutory Instrument 2005 No. 1524.</ref>

Absolute or anhydrous alcohol refers to ethanol with a low water content. There are various grades with maximum water contents ranging from 1% to a few parts per million (ppm). If [[azeotropic distillation]] is used to remove water, it will contain trace amounts of the material separation agent (e.g. benzene).<ref>{{cite book | first1=Raj K. | last1=Bansal | last2=Bernthsen | first2=August | name-list-style=vanc | title=A Textbook of Organic Chemistry | url={{google books | plainurl=y | id=1B6ijcTkD5EC | page=402}} | year=2003 | publisher=New Age International Limited | isbn=978-81-224-1459-2 | pages=402–}}</ref> Absolute alcohol is not intended for human consumption. Absolute ethanol is used as a solvent for laboratory and industrial applications, where water will react with other chemicals, and as fuel alcohol. Spectroscopic ethanol is an absolute ethanol with a low absorbance in [[ultraviolet]] and visible light, fit for use as a solvent in [[ultraviolet-visible spectroscopy]].<ref>{{cite book | last1=Christian | first1=Gary D. | name-list-style=vanc | chapter=Solvents for Spectrometry | title=Analytical chemistry | date=2004 | publisher=John Wiley & Sons | location=Hoboken, NJ | isbn=978-0-471-21472-4 | edition=6th | volume=1 | page=[https://archive.org/details/analyticalchemis00chri_0/page/473 473] | chapter-url=https://archive.org/details/analyticalchemis00chri_0/page/473}}</ref> Pure ethanol is classed as 200 [[proof (alcohol)|proof]] in the US, equivalent to 175 degrees proof in the UK system.<ref name="Andrews2007">{{cite book | first=Sudhir | last=Andrews | name-list-style=vanc | title=Textbook Of Food & Bevrge Mgmt | url={{google books | plainurl=y | id=HfHtaq1GWUcC& | page=268}} | date=1 August 2007 | publisher=Tata McGraw-Hill Education | isbn=978-0-07-065573-7 | pages=268–}}</ref> Rectified spirit, an azeotropic composition of 96% ethanol containing 4% water, is used instead of anhydrous ethanol for various purposes. Spirits of wine are about 94% ethanol (188 proof). The impurities are different from those in 95% (190 proof) laboratory ethanol.<ref>{{cite journal | vauthors=Kunkee RE, Amerine MA | title=Sugar and alcohol stabilization of yeast in sweet wine | journal=Applied Microbiology | volume=16 | issue=7 | pages=1067–1075 | date=July 1968 | doi=10.1128/AEM.16.7.1067-1075.1968 | pmid=5664123 | pmc=547590}}</ref>