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{{Short description|Milligrams of a base needed to neutralize 1 gram of a given acid}}
{{Short description|Milligrams of a base needed to neutralize 1 gram of a given acid}}
{{use mdy dates}}

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In [[chemistry]], '''acid value''' ('''AV''', '''acid number''', '''neutralization number''' or '''acidity''') is a number used to quantify the [[acidity]] of a given [[chemical substance]]. It is the quantity of [[Base (chemistry)|base]] (usually [[potassium hydroxide]] (KOH)), expressed as [[milligram]]s of KOH required to [[Neutralization (chemistry)|neutralize]] the acidic constituents in 1&nbsp;gram of a sample.<ref name="libretext">{{Cite web |date=2016-05-26 |title=14.10.1: Foods- Acid Value and the Quality of Fats and Oils |url=https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_ChemPRIME_(Moore_et_al.)/14%3A_Ionic_Equilibria_in_Aqueous_Solutions/14.10%3A_Titration_Curves/14.10.01%3A_Foods-_Acid_Value_and_the_Quality_of_Fats_and_Oils |df=mdy-all |access-date=2022-10-28 |website=[[LibreTexts|Chemistry LibreTexts]]}}</ref><ref name="Ahuja2015">{{Cite book |last=Ahuja |first=Satinder |url=https://www.google.co.in/books/edition/_/DHKDBAAAQBAJ?hl=en&gbpv=1&dq=acid+number&pg=PA301 |page=301 |oclc=900781294 |title=Food, Energy, and Water: The Chemistry Connection |df=mdy-all |date=2015-01-25 |publisher=Elsevier |isbn=9780128003749}}</ref><ref name="Nielsen2010">{{Cite book |last=Nielsen |first=S. Suzanne |oclc=663096771 |url=https://www.google.co.in/books/edition/_/i5TdyXBiwRsC?hl=en&gbpv=1&dq=acid+value&pg=PA108 |pages=108–109 |title=Food Analysis Laboratory Manual, 2nd Edition |df=mdy-all |date=2010-03-20 |publisher=Springer Science & Business Media |isbn=9781441914637}}</ref><ref>{{Cite book |last=O'Brien |first=Richard D. |pages=220–221 |url=https://www.google.co.in/books/edition/_/3wpHj3mvra8C?hl=en&gbpv=1&dq=acid%20value&pg=PA220 |title=Fats and Oils: Formulating and Processing for Applications, 3rd Edition |oclc=367589246 |df=mdy-all |date=2008-12-05 |publisher=[[CRC Press]] |isbn=9781420061673}}</ref>
In [[chemistry]], '''acid value''' (also '''neutralization number''', '''acid number''', or '''acidity''') is a number used to quantify the [[acidity]] of a given [[chemical substance]]. It is the quantity of [[Base (chemistry)|base]], expressed in [[milligram]]s of [[potassium hydroxide]] (KOH), that is required to [[Neutralization (chemistry)|neutralize]] the acidic constituents in 1&nbsp;gram of sample.


The acid number is a measure of the number of [[carboxylic acid]] groups ({{chem2|\sC(\dO)OH}}) in a chemical compound, such as a [[fatty acid]], or in a [[mixture]] of compounds. In a typical procedure, a known amount of sample dissolved in an [[organic solvent]] (often [[isopropyl alcohol|isopropanol]]) and [[titration|titrated]] with a solution of alcoholic potassium hydroxide (KOH) of known [[concentration]] using [[phenolphthalein]] as a colour indicator.
The acid number is a measure of the number of [[carboxylic acid]] groups ({{chem2|\sC(\dO)OH}}) in a chemical compound, such as a [[fatty acid]], or in a [[mixture]] of compounds.<ref name="Ahuja2015" /> In a typical procedure, a known amount of sample dissolved in an [[organic solvent]] (often [[isopropyl alcohol|isopropanol]]) and [[titration|titrated]] with a solution of alcoholic potassium hydroxide (KOH) of known [[concentration]] using [[phenolphthalein]] as a colour indicator.<ref name="Ahuja2015" />


The acid number for an oil sample is indicative of the age of the oil and can be used to determine when the oil must be changed.<ref name"engineer" />
⚫
For example, the analysis of [[crude oil]]:


A liquid fat sample combined with neutralized 95% ethanol is titrated with standardized sodium hydroxide of 0.1 eq/L [[normality]] to a phenolphthalein endpoint. The volume and normality of the sodium hydroxide are used, along with the weight of the sample, to calculate the free fatty acid value.<ref name="Nielsen2010" />
:<math>AN=(V_{eq}-b_{eq})N\frac{\text{56.1 g/mol}}{W_\text{oil}}</math>


⚫
For example, for analysis of [[crude oil]]:

:<math>AN=(V_{eq}-b_{eq})N\frac{\text{56.1 g/mol}}{W_\text{oil}}</math><ref>{{Cite patent|number=CN103776825A|title=Determining method of acid value of deep-color grease|gdate=2014-05-07|inventor1-first=Ji |inventor1-last=Junmin |inventor2-first=Wang |inventor2-last=Dongmin |inventor3-first=Liu |inventor3-last=Huamin |url=https://patents.google.com/patent/CN103776825A/en}}</ref>

KOH is the [[wikt:titrant|titrant]], wherease crude oil is the [[wikt:titrand|titrand]].
{{mvar|V{{sub|eq}}}} is the volume of titrant (ml) consumed by the crude oil sample and 1&nbsp;ml of [[spiking solution]] at the equivalent point, {{mvar|b{{sub|eq}}}} is the volume of titrant (ml) consumed by 1&nbsp;ml of spiking solution at the equivalent point, and 56.1&nbsp;g/mol is the [[molecular weight]] of KOH. {{math|''W''{{sub|oil}}}} is the mass of the sample in grams.
{{mvar|V{{sub|eq}}}} is the volume of titrant (ml) consumed by the crude oil sample and 1&nbsp;ml of [[spiking solution]] at the equivalent point, {{mvar|b{{sub|eq}}}} is the volume of titrant (ml) consumed by 1&nbsp;ml of spiking solution at the equivalent point, and 56.1&nbsp;g/mol is the [[molecular weight]] of KOH. {{math|''W''{{sub|oil}}}} is the mass of the sample in grams.


The [[molar concentration]] of titrant (N) is calculated as such:
The normality (N) of titrant is calculated as:


:<math>N = \frac{1000 \times W_\text{KHP}}{\text{204.23 g/mol } \times V_{eq}}</math>
:<math>N = \frac{1000 \times W_\text{KHP}}{\text{204.23 g/mol } \times V_{eq}}</math>
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In which {{math|''W''{{sub|KHP}}}} is the mass (g) of [[potassium hydrogen phthalate]] (KHP) in 50&nbsp;ml of KHP standard solution, {{mvar|V{{sub|eq}}}} is the volume of titrant (ml) consumed by 50&nbsp;ml KHP standard solution at the equivalent point, and 204.23&nbsp;g/mol is the molecular weight of KHP.
In which {{math|''W''{{sub|KHP}}}} is the mass (g) of [[potassium hydrogen phthalate]] (KHP) in 50&nbsp;ml of KHP standard solution, {{mvar|V{{sub|eq}}}} is the volume of titrant (ml) consumed by 50&nbsp;ml KHP standard solution at the equivalent point, and 204.23&nbsp;g/mol is the molecular weight of KHP.


An increment in the amount of FFA in a [[fat]] or [[oil]] sample indicates hydrolysis of triglycerides. Such reaction occurs by the action of [[lipase]] [[enzyme]] and it is an indicator of inadequate processing and storage conditions. The source of the enzyme can be the tissue from which the oil or fat was extracted or it can be a contaminant from other cells including microorganisms.<ref name="libretext" />
There are standard methods for determining the acid number, such as [[ASTM]] D 974 and [[DIN]] 51558 (for mineral oils, biodiesel), or specifically for biodiesel using the European Standard EN 14104 and ASTM D664 are both widely used worldwide.{{cn|date=October 2022}}

For determining the acid value of [[mineral oils]] and [[biodiesel]], there are standard methods such as [[ASTM]] D 974 and [[DIN]] 51558, and especially for biodiesel the [[European Standard]] EN 14104 and ASTM D664 are both widely used worldwide.<ref name="Ahuja2015" /> Acid number (mg KOH /g oil) for biodiesel should to be lower than 0.50 mg KOH/g in both EN 14214 and ASTM D6751 standard fuels. This is since the FFA produced may corrode automotive parts and these limits protect vehicle engines and fuel tanks.<ref name"engineer" />

When oils and fats become [[rancidity|rancid]], [[triglyceride]]s are converted into [[fatty acid]]s and [[glycerol]], causing an increase in acid value.<ref>{{Cite journal |last=Fernando |first=Sandun |last2=Karra |first2=Prashanth |last3=Hernandez |first3=Rafael |last4=Jha |first4=Saroj Kumar |date=2007-05-01 |df=mdy-all |title=Effect of incompletely converted soybean oil on biodiesel quality |url=https://www.sciencedirect.com/science/article/pii/S0360544206001496 |journal=Energy |quote=The acid number can become a serious issue when feedstocks with high free fatty acids... |language=en |volume=32 |issue=5 |pages=844–851 |doi=10.1016/j.energy.2006.06.019 |issn=0360-5442}}</ref> A similar situation is observed during aging of biodiesel through analogous [[oxidation]] and when subjected to prolonged high temperatures ([[ester]] [[thermal decomposition|thermolysis]]) or through exposure to acids or bases (acid/base ester [[hydrolysis]]).<ref name"engineer">{{Cite web |title=Acid Value Number or Neutralization Number of Oil |url=https://www.engineersedge.com/lubrication/acid_number_neutralization_number.htm |access-date=2022-10-28 |website=www.engineersedge.com}}</ref>

[[Transesterification]] of waste cooking oil, having high acid value and high water content, can be performed using [[heteropolyacid]]s such as [[dodecatungstophosphoric acid]] (PW12) as a catalyst.<ref>{{Cite journal |last=Cao |first=Fenghua |last2=Chen |first2=Yang |last3=Zhai |first3=Fengying |last4=Li |first4=Jing |last5=Wang |first5=Jianghua |last6=Wang |first6=Xiaohong |last7=Wang |first7=Shengtian |last8=Zhu |first8=Weimin |df=mdy-all |date=2008-09-01 |title=Biodiesel production from high acid value waste frying oil catalyzed by superacid heteropolyacid |url=https://pubmed.ncbi.nlm.nih.gov/18646228/ |journal=Biotechnology and Bioengineering |volume=101 |issue=1 |pages=93–100 |doi=10.1002/bit.21879 |issn=1097-0290 |pmid=18646228}}</ref><ref>{{Cite patent|number=US 8962873 B2|title=Systems And Methods For Making Bioproducts|gdate=2015-02-24|invent1=A|invent2=Rebecca|invent3=Danny|invent4=Barrie|inventor1-first=Summers William|inventor2-first=Williams|inventor3-first=Gulledge|inventor4-first=Tripp Robert|url=https://lens.org/128-931-785-027-93X}}</ref> In 2007, Biodiesel consisted of mono esters made from [[polanga oil]] extract of the plant [[Calophyllum inophyllum]] produced by triple stage transesterification and blended with high speed diesel were tested for their use as a diesel substitute in a single cylinder diesel engine.<ref>{{Cite journal |last=Sahoo |first=P. K. |last2=Das |first2=L. M. |last3=Babu |first3=M. K. G. |last4=Naik |first4=S. N. |date=2007-02-01 |title=Biodiesel development from high acid value polanga seed oil and performance evaluation in a CI engine |url=https://www.sciencedirect.com/science/article/pii/S0016236106003024 |journal=Fuel |language=en |volume=86 |issue=3 |pages=448–454 |doi=10.1016/j.fuel.2006.07.025 |issn=0016-2361}}</ref>


Low Acid value indicates good cleansing by soap.
As oils and fats [[rancidity|rancidify]], [[triglyceride]]s are converted into [[fatty acid]]s and [[glycerol]], causing an increase in acid number. A similar observation is observed with biodiesel aging through analogous oxidation processes and when subjected to prolonged high temperatures (ester [[thermal decomposition|thermolysis]]) or through exposure to acids or bases (acid/base ester [[hydrolysis]]). Low Acid value indicates good cleansing by soap.{{cn|date=October 2022}}


==See also==
==See also==

Revision as of 15:43, 28 October 2022

In chemistry, acid value (AV, acid number, neutralization number or acidity) is a number used to quantify the acidity of a given chemical substance. It is the quantity of base (usually potassium hydroxide (KOH)), expressed as milligrams of KOH required to neutralize the acidic constituents in 1 gram of a sample.[1][2][3][4]

The acid number is a measure of the number of carboxylic acid groups (−C(=O)OH) in a chemical compound, such as a fatty acid, or in a mixture of compounds.[2] In a typical procedure, a known amount of sample dissolved in an organic solvent (often isopropanol) and titrated with a solution of alcoholic potassium hydroxide (KOH) of known concentration using phenolphthalein as a colour indicator.[2]

The acid number for an oil sample is indicative of the age of the oil and can be used to determine when the oil must be changed.Cite error: The opening <ref> tag is malformed or has a bad name (see the help page).

A liquid fat sample combined with neutralized 95% ethanol is titrated with standardized sodium hydroxide of 0.1 eq/L normality to a phenolphthalein endpoint. The volume and normality of the sodium hydroxide are used, along with the weight of the sample, to calculate the free fatty acid value.[3]

For example, for analysis of crude oil:

[5]

KOH is the titrant, wherease crude oil is the titrand. Veq is the volume of titrant (ml) consumed by the crude oil sample and 1 ml of spiking solution at the equivalent point, beq is the volume of titrant (ml) consumed by 1 ml of spiking solution at the equivalent point, and 56.1 g/mol is the molecular weight of KOH. Woil is the mass of the sample in grams.

The normality (N) of titrant is calculated as:

In which WKHP is the mass (g) of potassium hydrogen phthalate (KHP) in 50 ml of KHP standard solution, Veq is the volume of titrant (ml) consumed by 50 ml KHP standard solution at the equivalent point, and 204.23 g/mol is the molecular weight of KHP.

An increment in the amount of FFA in a fat or oil sample indicates hydrolysis of triglycerides. Such reaction occurs by the action of lipase enzyme and it is an indicator of inadequate processing and storage conditions. The source of the enzyme can be the tissue from which the oil or fat was extracted or it can be a contaminant from other cells including microorganisms.[1]

For determining the acid value of mineral oils and biodiesel, there are standard methods such as ASTM D 974 and DIN 51558, and especially for biodiesel the European Standard EN 14104 and ASTM D664 are both widely used worldwide.[2] Acid number (mg KOH /g oil) for biodiesel should to be lower than 0.50 mg KOH/g in both EN 14214 and ASTM D6751 standard fuels. This is since the FFA produced may corrode automotive parts and these limits protect vehicle engines and fuel tanks.Cite error: The opening <ref> tag is malformed or has a bad name (see the help page).

When oils and fats become rancid, triglycerides are converted into fatty acids and glycerol, causing an increase in acid value.[6] A similar situation is observed during aging of biodiesel through analogous oxidation and when subjected to prolonged high temperatures (ester thermolysis) or through exposure to acids or bases (acid/base ester hydrolysis).[7]

Transesterification of waste cooking oil, having high acid value and high water content, can be performed using heteropolyacids such as dodecatungstophosphoric acid (PW12) as a catalyst.[8][9] In 2007, Biodiesel consisted of mono esters made from polanga oil extract of the plant Calophyllum inophyllum produced by triple stage transesterification and blended with high speed diesel were tested for their use as a diesel substitute in a single cylinder diesel engine.[10]

Low Acid value indicates good cleansing by soap.

See also

References

  1. ^ a b "14.10.1: Foods- Acid Value and the Quality of Fats and Oils". Chemistry LibreTexts. May 26, 2016. Retrieved October 28, 2022.
  2. ^ a b c d Ahuja, Satinder (January 25, 2015). Food, Energy, and Water: The Chemistry Connection. Elsevier. p. 301. ISBN 9780128003749. OCLC 900781294.
  3. ^ a b Nielsen, S. Suzanne (March 20, 2010). Food Analysis Laboratory Manual, 2nd Edition. Springer Science & Business Media. pp. 108–109. ISBN 9781441914637. OCLC 663096771.
  4. ^ O'Brien, Richard D. (December 5, 2008). Fats and Oils: Formulating and Processing for Applications, 3rd Edition. CRC Press. pp. 220–221. ISBN 9781420061673. OCLC 367589246.
  5. ^ CN103776825A, Junmin, Ji; Dongmin, Wang & Huamin, Liu, "Determining method of acid value of deep-color grease", issued 2014-05-07 
  6. ^ Fernando, Sandun; Karra, Prashanth; Hernandez, Rafael; Jha, Saroj Kumar (May 1, 2007). "Effect of incompletely converted soybean oil on biodiesel quality". Energy. 32 (5): 844–851. doi:10.1016/j.energy.2006.06.019. ISSN 0360-5442. The acid number can become a serious issue when feedstocks with high free fatty acids...
  7. ^ "Acid Value Number or Neutralization Number of Oil". www.engineersedge.com. Retrieved October 28, 2022.
  8. ^ Cao, Fenghua; Chen, Yang; Zhai, Fengying; Li, Jing; Wang, Jianghua; Wang, Xiaohong; Wang, Shengtian; Zhu, Weimin (September 1, 2008). "Biodiesel production from high acid value waste frying oil catalyzed by superacid heteropolyacid". Biotechnology and Bioengineering. 101 (1): 93–100. doi:10.1002/bit.21879. ISSN 1097-0290. PMID 18646228.
  9. ^ US 8962873 B2, A, Summers William; Rebecca, Williams & Danny, Gulledge et al., "Systems And Methods For Making Bioproducts", issued 2015-02-24 
  10. ^ Sahoo, P. K.; Das, L. M.; Babu, M. K. G.; Naik, S. N. (February 1, 2007). "Biodiesel development from high acid value polanga seed oil and performance evaluation in a CI engine". Fuel. 86 (3): 448–454. doi:10.1016/j.fuel.2006.07.025. ISSN 0016-2361.
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