Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів
Acid value is one of the key technical characteristic of vegetable oils and oleochemicals, obtaining on its basis. The existing standard methods of acid value measurement are relatively complicated and have some disadvantages. There are including utilization of the significant amounts of solvents, t...
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V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine
2021
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Catalysis and petrochemistry| _version_ | 1872008956635774976 |
|---|---|
| author | Zubenko, S.O. |
| author_facet | Zubenko, S.O. |
| author_institution_txt_mv | [
{
"author": "S.O. Zubenko",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry NAS of Ukraine 1, Murmanska str."
}
] |
| author_sort | Zubenko, S.O. |
| baseUrl_str | https://kataliz.org.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2021-12-10T12:37:13Z |
| description | Acid value is one of the key technical characteristic of vegetable oils and oleochemicals, obtaining on its basis. The existing standard methods of acid value measurement are relatively complicated and have some disadvantages. There are including utilization of the significant amounts of solvents, throwing out as wastes, and necessity in special equipment for determination. Also, a special issue is visual indication of the equivalence point of indicator transfer from acid to alkali form for intensive colored oils’ samples. Visual indication of the color transfer of phenol-phthalein as indicator (from colorless to pink) is quite difficult. The color transfer of thymolphthalein (from yellow to green) in such condition is not determined. Using of alkali blue 6B is complicated by the necessity of use ethanol and aromatic compounds mixture.
In current work the rapid and simple method of acid value determination was proposed. It consists in alkaliacid titration of the sample by sodium butoxide solution in n-butanol with bromothymol blue, n-butanol is also using as solvent. The method was tested on 3 series of the mixtures of the refined sunflower oil and free fatty acids (distilled fatty acids of sunflower and rapeseed oils and chemical grade oleic acid). The fatty acid content in tested mixtures was in range 1-50 % wt. Some disadvantages of traditional methods, such as the necessity of mixed solvents’ and relatively complicated laboratory equipment use, titration in a hot state, effect of temperature changes in the laboratory and difficulties with visual indication of color transfer, were overcame. Proposed method requires only the simplest laboratory glassware (conic flasks, non-calibrated pipettes, hermetically sealed glass vessels for titrant) and technical laboratory scales (weighting accuracy ±0.01 g). The method allows to determine the acid value in wide range of samples, including the samples with intense coloration. The relatively high accuracy of acid value determination was shown. The method sensitivity is 0.02-0.10 mg KOH/g. The time for analyze is enough short (about 5-15 minutes). |
| doi_str_mv | 10.15407/kataliz2021.31.069 |
| first_indexed | 2026-03-12T15:49:45Z |
| format | Article |
| fulltext |
Каталіз та нафтохімія, 2021, 31 69
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 31
The simple method of vegetable oils and oleochemical products
acid value determination
S.O. Zubenko
V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry NAS of Ukraine
1, Murmanska str., 02660 Kyiv, Ukraine., tel./fax: (044) 559-98-00, S.O.Zubenko@ukr.net
Acid value is one of the key technical characteristic of vegetable oils and oleochemicals, obtaining on its basis.
The existing standard methods of acid value measurement are relatively complicated and have some disadvantages.
There are including utilization of the significant amounts of solvents, throwing out as wastes, and necessity in special
equipment for determination. Also, a special issue is visual indication of the equivalence point of indicator transfer
from acid to alkali form for intensive colored oils’ samples. Visual indication of the color transfer of phenol-phthalein
as indicator (from colorless to pink) is quite difficult. The color transfer of thymolphthalein (from yellow to green)
in such condition is not determined. Using of alkali blue 6B is complicated by the necessity of use ethanol and
aromatic compounds mixture.
In current work the rapid and simple method of acid value determination was proposed. It consists in alkali-
acid titration of the sample by sodium butoxide solution in n-butanol with bromothymol blue, n-butanol is also using
as solvent. The method was tested on 3 series of the mixtures of the refined sunflower oil and free fatty acids (distilled
fatty acids of sunflower and rapeseed oils and chemical grade oleic acid). The fatty acid content in tested mixtures was
in range 1-50 % wt. Some disadvantages of traditional methods, such as the necessity of mixed solvents’ and relatively
complicated laboratory equipment use, titration in a hot state, effect of temperature changes in the laboratory and
difficulties with visual indication of color transfer, were overcame. Proposed method requires only the simplest
laboratory glassware (conic flasks, non-calibrated pipettes, hermetically sealed glass vessels for titrant) and technical
laboratory scales (weighting accuracy ±0.01 g). The method allows to determine the acid value in wide range of
samples, including the samples with intense coloration. The relatively high accuracy of acid value determination was
shown. The method sensitivity is 0.02-0.10 mg KOH/g. The time for analyze is enough short (about 5-15 minutes).
Key words: acid value, vegetable oils, biodiesel, titration, n-butanol
______________________________________________________________________________________________________
Introduction
Acid value, or free fatty acids (FFA) content is
one of the key technical characteristic of vegetable oils
as the raw materials for the production of fatty acid
alkyl esters (biodiesel) or another oleochemical
purposes. Raw materials used for fatty acids esters
production is often characterized by significant FFA
content due to partial oil degradation or different other
causes. In biodiesel production it is desirable to use
non-food grade raw material [1]. The latter includes
oils of technical cultures or oils, which not corresponds
quality requirements for food grade products (wasted
frying oils, oils with expired term of use, technological
wastes etc.). One of the main parameters, determining
the unsuitability for use as edible oils is fatty acids
content, which is displayed as acid value. The latter
usually must be lower than 0.3% (counted as oleic
acid) [2].
Moreover, commercial biodiesel must correspond
to requirements of free fatty acids content (lower than
0.25 % count as oleic acid) [3, 4]. Also, acid value is
main parameter, controlling in the course of the reaction
of fatty acids esterification with alcohols over acid
catalysts, which is main route for synthesis of fatty
acids esters from raw materials with significant content
of FFA.
Therefore, in biodiesel fuel manufacturing and in
quality control of obtained intermediate products and
final products the acid value determination is very
necessary.
The methods of acid value determination
Acid value is amount of alkali (potassium
hydroxide), which is needed to spend for neutralization
of acids in 1 g of mixture subjected to analysis. In case
of oils and fatty acids esters, acid value reflects the
amount of fatty acids. The products of the fatty acids
neutralization with alkali are soaps. Formed soaps in
water media hydrolyze and form acids and alkali, which
leads to alkali reaction in water solution. Therefore, the
titration of FFA by alkali water solutions leads to
understatement of resulted acid value.
For overcoming the hydrolysis variety of
methods was developed. One of them is utilization of
saturated water solution of sodium chloride, which used
in mixture with sample analyzed. Obtained mixture is
UDC 543.635.35
https://doi.org/10.15407/kataliz2021.31.069
70 Каталіз та нафтохімія, 2021, № 31
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 31
titrated by alkali water solution with phenol-phthalein
as indicator [5].
Using of supporting co-solvents such as
chloroform or diethyl ether with ethyl alcohol leads to
formation of large amounts of organic wastes, which
difficult to separate or regenerate for reuse. In this
method phenol-phthalein is used as indicator. For
colored samples thymolphthalein is recommended to use
as indicator. In the latter case, titration is carried out
using special flask with external glass branch pipe to
observe the color transfer of the mixture from yellow to
green [5].
Another method of acid value determination
consists in titration of hot solution of the oil sample in
ethanol by alkali ethanol solution, using phenol-
phthalein or thymolphthalein as indicators [5].
Analysis may be carried out without heating of the
mixture using isopropyl alcohol as solvent and, alkali
ethanol solution as titrant and phenol-phthalein or
thymolphthalein as indicators [6].
The method of acid value determination of
colored petrol products, including diesel fuels, is based
on using of ethanol-aromatic (benzene, toluene or
xylene) solution of indicator alkali blue 6B as co-
solvent. The sample is dissolved in the latter and then
titration by alkali ethanol solution is performed,
observing the color transfer from blue to red [7].
In another method [8, 9] iso-propanol/toluene
mixture as solvent, KOH solution in iso-propanol as
titrant and p-naphtholbenzein as indicator (color transfer
from orange to green) are used. In method [10], which is
relies on potentiometric titration, the same solvent and
titrant are used.
Listed methods have a number of disadvantages,
including utilization of the significant amounts of
solvents, throwing out as wastes, and necessity in special
equipment for determination.
Also, a special issue is visual indication of the
equivalence point of indicator transfer from acid to alkali
form. First of all, these applies the acid value
determination of the reaction mixtures during acid-
catalyzed esterification of fatty acids and in case of the
intensive colored oils’ samples, such as not refined oils
of technical cultures, wasted cooking oils etc. The latter
may have color from mild-brown to almost black. Visual
indication of the color transfer of phenol-phthalein as
indicator (from colorless to pink) is quite difficult. The
color transfer of thymolphthalein (from yellow to green)
in such condition is not determined. Using of alkali blue
6B is complicated by the necessity of use ethanol and
aromatic compounds mixture. Also, the significant
amount of such a mixture of solvents is needed to fully
dissolve the analyzed oil sample.
Moreover, titration by alkali ethanol or iso-
propanol solutions is related with practical difficulties.
At-first, alkali solutions can’t be kept for a long time.
At-second, alkali alcohol solutions can dissolve rubber
parts of burette or jamming of glass tap due to carbonate
formation. At-third, such alkali solutions leach the
surface of the glass vessel, in which it is stored. This
also results in the contamination of titrant. At-fourth,
high volatility of both ethyl and iso-propyl alcohols
leads to distortion of results of analysis, especially at
high room temperature in summer. At-fifth,
determination of alkali molar concentration in mol/dm3
is not comfortably, because of the possible deviation of
temperature in laboratory from 20 °С. The concentration
in this case may change significantly, which leads to
distortion of the determination results too.
This article deals with developing of the simple
alternative method of vegetable oils’ and oleochemical
products’ acid number determination, which is able to
overcome most of the listed disadvantages. The method
consists in the titration of the oils by sodium butoxide
solution in butanol in the medium of n-butyl alcohol.
Materials and methods
Chemicals
Analytical grade NaOH (China; for preparation of
sodium butoxide); chemical grade n-butyl alcohol
(Czech; for preparation of sodium butylate), technical
grade n-butyl alcohol (Turkey; as solvent in titration);
food grade H3PO4 (for preparation of fatty acids from
vegetable oils); technical grade KOH (China; for
preparation of fatty acids from vegetable oils), technical
grade EtOH (Ukraine, for preparation of fatty acids from
vegetable oils); commercial refined sunflower oil
(Ukraine; as base oil for preparation of oil/fatty acids
mixtures for titration); not refined rapeseed oil (Ukraine;
as raw material for preparation fatty acids); not refined
sunflower oil (Ukraine; as raw material for preparation
of fatty acids); chemical grade oleic acid (Czech; for
preparation of oil/fatty acids mixtures for titration),
analytical grade HCl (Ukraine; 14 % solution in water),
chemical grade bromothymol blue (indicator).
Alkali titrant solution preparation
Sodium butoxides solution, used in current study
as titrant solution, was prepared from n-butanol and
sodium hydroxide according to well-known method [11]
using Dean-Stark trap. Obtained solution was diluted by
n-butyl alcohol to the concentration of alkali around 1
%wt. (calculated in terms of initial NaOH). The exact
concentration was determined by means of titration by
0.1 N HCl in water.
Potassium butoxide solution also can be used for
titration. But it preparation is complicated by higher
moisture content in reactive KOH of the same class of
purity (about 14-16 %). As result, its production of
potassium butoxide is significantly longer.
Fatty acid preparation
Fatty acids of rapeseed or sunflower oil were
prepared by saponification of the corresponding oil
triglycerides followed by transformation of obtained
potassium soaps to fatty acids by means of treatment
with H3PO4.
For this purpose, to the round bottom flask
equipped with Liebig condenser was loaded with 100 g
Каталіз та нафтохімія, 2021, № 31 71
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 31
rapeseed of oil and 33 g of KOH dissolved in 140 g
rectified ethyl alcohol (94.6 %wt.). Mixture was heated
by oil bath (120 °C) throughout 3 hours and then 900
cm3 of distilled water was added. Obtained products
were fully dissolved in water, which gives evidence the
high oil saponification level. Then about 300 cm3 of
water-ethanol mixture was separated by distillation. The
residue mixture was poured to separation funnel,
followed by addition of H3PO4 and shaking. After that,
the formation of two layers was observed. The top layer
was the fatty acids. It was treated by phosphoric acid in
the same way one more time and thoroughly washed by
water using separation funnel. Obtained cloudy fatty
acids were dried several days over calcined sodium
sulfate until clear liquid was formed. The last one was
filtered through paper filter. Brown colored dried and
filtered fatty acids was distilled under vacuum. As result
light-yellow clear distillate was obtained light-yellow
distillates.
Preparation of the fatty acids/oil mixtures
The solutions of fatty acids in refined sunflower
oil (approximately 1, 2, 5, 10, 15, 20 and 50 %wt.) were
prepared using distilled fatty acids of rapeseed and
refined sunflower (marked as FA-1 and FA-2 series
correspondingly), as well as commercial oleic acid
(marked as FA-3 series). Approximately 100 g of each
solution was prepared by mixing of fatty acids with oil
in conic flask with magnetic stirrer (1 h, ambient
temperature). Components were weighted on technical
scales (accuracy ±0.01 g), the exact concentration of
fatty acids were calculated using the weighting data.
Methodology of titration
The sample (10-15 g) was put into pre-weighed
flask and weighted on technical scales with accuracy
±0.01 g. Then, 15-20 g of n-butanol (technical or higher
purity grade) and 5-10 drops of 0.5 % bromothymol blue
solution in n-butanol were added as solvent and
indicator respectively. Before analysis n-butanol
(solvent) was also titrated in order to determine its
acidity for the accounting in the calculating of fatty acids
content in sample analyzed. Obtained mixture after
addition of the solvent and indicator was weighted, its
color was brown. Then the titration by sodium butoxide
solution in butanol (about 1 % of alkali in terms of
NaOH), using non-calibrated pipette, was carried out
until the changing of the mixture color to deep blue. The
color transfer in equivalent point occurs at several drops
of solution, thus operator should be carefully. After that
mass of the obtained mixture was measured and FFA
content was calculated. Titration of each mixture was
repeated three times and the confidence interval of fatty
acid content (p = 0.95) was calculated. The results of the
analyses can be expressed as acid value (mg KOH/g) or
as the fatty acid concentration itself. The latter may be
counted as oleic acid or, if the fatty acid composition of
the sample is known, as the mass concentration of all
presented acids.
Results and discussions
The results of the titration of prepared series of
fatty acids/oil mixtures are given in Table below. First of
all, it should be emphasized the quite narrow confidence
interval (p = 0.95, 3 parallel analyses). This indicates a
good reproducibility of the titration results. However,
noticeable deviation from the actual concentration of
FFA in prepared mixtures, changing linearly with its
concentration, was observed (see Fig.). There are some
insignificant overestimation at low FFA contents (in
case of series FA-1 and FA-2) and more significant
underestimation at higher FFA contents, growing
linearly with its concentration. The underestimation
reaches about 0.6-1.4 % for different mixtures’ series at
the maximum FFA content. The deviation values are
higher, than the confidence interval wide, thus they can’t
be explained by the scattering of the titration results. In
addition, the reason of the deviation can’t be result of the
expression of FFA content as oleic acid. The difference
between the latter and real FFA content, calculated on
the basis average molecular weight of fatty acid, taking
into account the fatty acid composition of fatty acids
(not shown in article), is insignificant or even negligible
(see Table). The linear growth of absolute error with
FFA content, in our opinion, can be explained by the
partial formation of fatty acid salts associated with free
fatty acids. In such case it may be assumed, that using
the lower mass of the sample and/or higher amount of
the solvent (n-butanol) will minimize such a systematic
error of proposed method.
The proposed method is applicable for acid value
determination of the wide variety of the samples’ types,
including refined and not refined oils and fats from
different sources, wasted frying oils, fatty acids alkyl
esters, fatty acids, products of fatty acidsʼ esterification
by different alcohols, etc. Even in case of titration of the
samples, having intense dark-brown and almost black
color, the color transfer is easily indicated visually.
Another advantage of the method is using of n-
butanol as solvent. It is able to efficiently dissolve petrol
products, vegetable oils, fats, monoalkyl esters, fatty
acids, soaps and another alcohols. Due to the low
toxicity and the possibility of the n-butanol production
by biotechnological fermentation of various sugar-
containing raw-stuff, it is considered as green solvent.
Moreover, n-butanol can be easily recovered by
distillation and reused in analyses repeatedly.
When the titration is holding by the operator, the
method sensitivity is 0.01-0.05 % of free fatty acids
(depending on sample amount and titrant concentration),
which equivalent of acid value about 0.02-0.10 mg
KOH/g. The time for analyze is enough short (about 5-
15 minutes).
The proposed method is also able to overcome
some disadvantages of the standard methods of acid
value determination.
72 Каталіз та нафтохімія, 2021, № 31
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 31
Table. Results of titration
FFA content in
mixture, %wt.
FFA content by titration, %wt.
Confidence interval of
FFA content, ±%
Counted as oleic acid
Counted for real fatty
acids’ composition
FA-1 (fatty acids of rapeseed oil)
1.08 1.17 1.17 0.01
2.14 2.24 2.23 0.05
5.23 5.21 5.19 0.01
10.11 10.00 9.97 0.07
14.97 14.70 14.65 0.04
20.17 19.80 19.73 0.04
50.07 48.85 48.68 0.31
FA-2 (fatty acids of sunflower oil)
1.07 1.17 1.16 0.03
2.07 2.16 2.15 0.03
5.04 5.10 5.07 0.06
10.05 10.03 9.97 0.08
15.04 14.88 14.80 0.09
19.99 19.74 19.63 0.11
50.00 49.18 48.90 0.70
FA-3 (reagent grade oleic acid, Czech)
1.03 1.04 1.03 0.01
2.11 2.06 2.05 0.01
5.06 4.92 4.89 0.07
10.09 9.80 9.73 0.11
15.06 14.65 14.55 0.08
19.94 19.47 19.33 0.36
49.81 48.35 48.01 0.78
Fig. The absolute error of the FFA content determination.
Каталіз та нафтохімія, 2021, № 31 73
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 31
Titrant (sodium butoxide solution in butanol) in case of
its storing in tightly closed bottle can be used with the
same efficiency after the year or longer, as the
concentration of the alkali doesn’t change. Also, the
long-term storing of the titrant anhydrous alkali solution
doesn’t result in any leaching of the glass tare even in
case of not chemical resistant glass. Proposed method
requires only the simplest laboratory glassware (conic
flasks, non-calibrated pipettes, hermetically sealed glass
vessels for titrant) and technical laboratory scales
(weighting accuracy ±0.01 g). Used glassware can be
easily washed with only water. The dosage of the sample
and titrant not by volume, but by mass is easy and rapid.
It also eliminates the distortion of the results due to the
titrant volume change with temperature in laboratory.
Additionally, the relatively low volatility of the n-
butanol (117 °С boiling temperature) excludes the
meaningful evaporation during the analysis, and
therefore minimizes the error of determination.
Practical application of the method
This method of acid value determining was tested
on a number of refined and unrefined natural oils
(including strongly colored mustard oil), waste edible
oils, as well as on technical fats with high acidity
(chicken fat, beef fat, etc.). (More than 80 samples).
Also, this method has been successfully used to
control the process during the esterification of fatty acids
derived from natural oils and oils with high acidity
(unrefined mustard oil, waste cooking oil, etc.) on acid
heterogeneous and homogeneous catalysts with methyl,
ethyl, iso-propyl, n-propyl, iso-butyl, n-butyl, heptyl,
decyl and cetyl alcohols. It should be noted that the
products of acid synthesis have an intense dark brown
color. (More than 150 definitions).
In addition, this method has been successfully
used to determine the acid value of purified fatty acid
esters (methyl, ethyl, iso-propyl, n-propyl, iso-butyl, n-
butyl, n-amyl and n-heptyl), as well as intermediate
determinations during the purification process. (More
than 300 samples).
Conclusions
The rapid and simple method of acid value
determination using alkali-acid titration by butoxide
solution and butyl alcohol as solvent was developed. The
method allows to determine the acid value in wide range
of samples, including the samples with intense
coloration. The relatively high accuracy of acid value
determination was shown. Some disadvantages of
traditional methods of acid value determination were
overcame.
References
1. Elgharbawy A.S., Sadik W.A., Sadek O.M.,
Kasaby M.A. A review on biodiesel feedstocks and
production technologies. Journal of Chilean Chemical
Society. 2021. 66. 5098-5109. [In English].
2. DSTU 4492. Oil sunflouer. Specifications. [In
Ukraine].
3. DSTU 6081. Automotive fuels. Fatty acid methyl
esters of fat and oil for diesel engines. Technical
requirements. [In Ukraine].
4. DSTU 7178. Alternative fuel. Fatty acid ethyl
esters of fat and oil for diesel engines. Technical
requirements and test methods. [In Ukraine].
5. GOST 31933. Vegetable oils. Methods for
determination of acid value. [In Russian].
6. GOST R 52110. Vegetable oils. Methods for
determination of acid value. [In Russian].
7. GOST 5985. Petroleum products. Method for
determination of acidity and acid number. [In Russian].
8. ASTM D 3339. Standard test method for acid
number of petroleum products by semi-micro color
indicator titration. [In English].
9. ASTM D 974. Standard test method for acidand
base number by color-indicator titration. [In English].
10. ASTM D 664. Standard test method for acid
number of petroleum products by potentiometric titration.
[In English].
11. Zubenko S.O., Konovalov S.V., Patrylak L.K.,
Okhrimenko M.V. Peculiarities of potassium butylate
preparation as a catalyst for the transesterification process.
Kataliz i neftekhimia. 2017. 26. 36-39. [In English].
Надійшла до редакції 14.05.2021 р.
74 Каталіз та нафтохімія, 2021, № 31
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 31
Простий метод визначення кислотного числа рослинних олій та
олеохімічних продуктів
С.О. Зубенко
Інститут біоорганічної хімії та нафтохімії ім. В.П. Кухаря НАН України, Україна,
02660 Київ, вул. Мурманська, 1, тел./факс: (044) 559-98-00, S.O.Zubenko@ukr.net
Кислотне число – це одна з ключових технічних характеристик рослинних олій та олеохімікатів,
одержаних на цій основі. Існуючі стандартні методи визначення кислотного числа відносно складні та мають
деякі недоліки. В даній роботі було запропоновано швидкий та простий метод визначення кислотного числа.
Він полягає у кислотно-лужному титруванні зразка бутанольним розчином бутилату натрію з використанням
бромтимолового синього, а також використання н-бутанолу в ролі розчинника. Метод тестувався на трьох
серіях сумішей рафінованої соняшникової олії та вільних жирних кислот (дистильованих жирних кислот
соняшникової та ріпакової олій та хімічно чистої олеїнової кислоти). Вміст жирних кислот в тестових сумішах
був у межах 1-50 % мас. Метод дозволяє визначати кислотне число у широкому асортименті зразків, який
включає зразки з інтенсивним забарвленням. Було показано порівняно високу точність визначення кислотного
числа. Деякі недоліки традиційних методів, такі як необхідність використання змішаних розчинників та
порівняно складне використання лабораторного обладнання, титрування в гарячому стані, вплив
температурних змін у лабораторії та труднощі з візуальною індикацією передачі кольору, були подолані.
Ключові слова: кислотне число, рослинні олії, біодизель, титрування, н-бутанол
|
| id | oai:katalizorgua:article-16 |
| institution | Catalysis and petrochemistry |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-03-12T15:49:45Z |
| publishDate | 2021 |
| publisher | V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine |
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| resource_txt_mv | katalizorgua/a5/cf2da78dc2864bdf6f50d6ce0cad0ba5.pdf |
| spelling | oai:katalizorgua:article-162021-12-10T12:37:13Z The simple method of vegetable oils and oleochemical products acid value determination Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів Zubenko, S.O. acid value vegetable oils biodiesel titration n-butanol кислотне число рослинні олії біодизель титрування н-бутанол Acid value is one of the key technical characteristic of vegetable oils and oleochemicals, obtaining on its basis. The existing standard methods of acid value measurement are relatively complicated and have some disadvantages. There are including utilization of the significant amounts of solvents, throwing out as wastes, and necessity in special equipment for determination. Also, a special issue is visual indication of the equivalence point of indicator transfer from acid to alkali form for intensive colored oils’ samples. Visual indication of the color transfer of phenol-phthalein as indicator (from colorless to pink) is quite difficult. The color transfer of thymolphthalein (from yellow to green) in such condition is not determined. Using of alkali blue 6B is complicated by the necessity of use ethanol and aromatic compounds mixture. In current work the rapid and simple method of acid value determination was proposed. It consists in alkaliacid titration of the sample by sodium butoxide solution in n-butanol with bromothymol blue, n-butanol is also using as solvent. The method was tested on 3 series of the mixtures of the refined sunflower oil and free fatty acids (distilled fatty acids of sunflower and rapeseed oils and chemical grade oleic acid). The fatty acid content in tested mixtures was in range 1-50 % wt. Some disadvantages of traditional methods, such as the necessity of mixed solvents’ and relatively complicated laboratory equipment use, titration in a hot state, effect of temperature changes in the laboratory and difficulties with visual indication of color transfer, were overcame. Proposed method requires only the simplest laboratory glassware (conic flasks, non-calibrated pipettes, hermetically sealed glass vessels for titrant) and technical laboratory scales (weighting accuracy ±0.01 g). The method allows to determine the acid value in wide range of samples, including the samples with intense coloration. The relatively high accuracy of acid value determination was shown. The method sensitivity is 0.02-0.10 mg KOH/g. The time for analyze is enough short (about 5-15 minutes). Кислотне число – це одна з ключових технічних характеристик рослинних олій та олеохімікатів, одержаних на цій основі. Існуючі стандартні методи визначення кислотного числа відносно складні та мають деякі недоліки. В даній роботі було запропоновано швидкий та простий метод визначення кислотного числа. Він полягає у кислотно-лужному титруванні зразка бутанольним розчином бутилату натрію з використанням бромтимолового синього, а також використання н-бутанолу в ролі розчинника. Метод тестувався на трьох серіях сумішей рафінованої соняшникової олії та вільних жирних кислот (дистильованих жирних кислот соняшникової та ріпакової олій та хімічно чистої олеїнової кислоти). Вміст жирних кислот в тестових сумішах був у межах 1-50 % мас. Метод дозволяє визначати кислотне число у широкому асортименті зразків, який включає зразки з інтенсивним забарвленням. Було показано порівняно високу точність визначення кислотного числа. Деякі недоліки традиційних методів, такі як необхідність використання змішаних розчинників та порівняно складне використання лабораторного обладнання, титрування в гарячому стані, вплив температурних змін у лабораторії та труднощі з візуальною індикацією передачі кольору, були подолані. V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine 2021-11-01 Article Article application/pdf https://kataliz.org.ua/index.php/journal/article/view/16 10.15407/kataliz2021.31.069 Catalysis and petrochemistry; No. 31 (2021): Catalysis and petrochemistry; 69-74 Каталіз та нафтохімія; № 31 (2021): Каталіз та нафтохімія; 69-74 2707-5796 2412-4176 10.15407/kataliz2021.31 en https://kataliz.org.ua/index.php/journal/article/view/16/8 |
| spellingShingle | кислотне число рослинні олії біодизель титрування н-бутанол Zubenko, S.O. Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів |
| title | Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів |
| title_alt | The simple method of vegetable oils and oleochemical products acid value determination |
| title_full | Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів |
| title_fullStr | Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів |
| title_full_unstemmed | Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів |
| title_short | Простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів |
| title_sort | простий метод визначення кислотного числа рослинних олій та олеохімічних продуктів |
| topic | кислотне число рослинні олії біодизель титрування н-бутанол |
| topic_facet | acid value vegetable oils biodiesel titration n-butanol кислотне число рослинні олії біодизель титрування н-бутанол |
| url | https://kataliz.org.ua/index.php/journal/article/view/16 |
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