Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність
Current paper deals with production, purification and oxidative stability enhancement of fuel-grade sunflower oil butyl esters as more ecological alternative of methyl esters as biodiesel. The oil feedstock, used in this study, included refined sunflower oil (acid value – 0.05 mg KOH/g; 25.3 % of ol...
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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_ | 1872009021484957696 |
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| author | Konovalov, S.V. Zubenko, S.O. Patrylak, L.K. Yakovenko, A.V. |
| author_facet | Konovalov, S.V. Zubenko, S.O. Patrylak, L.K. Yakovenko, A.V. |
| author_institution_txt_mv | [
{
"author": "S.V. Konovalov",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine, 1, Murmanska str., Kyiv 02660"
},
{
"author": "S.O. Zubenko",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine, 1, Murmanska str., Kyiv 02660"
},
{
"author": "L.K. Patrylak",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine, 1, Murmanska str., Kyiv 02660"
},
{
"author": "A.V. Yakovenko",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine, 1, Murmanska str., Kyiv 02660,"
}
] |
| author_sort | Konovalov, S.V. |
| baseUrl_str | https://kataliz.org.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2023-09-28T12:18:42Z |
| description | Current paper deals with production, purification and oxidative stability enhancement of fuel-grade sunflower oil butyl esters as more ecological alternative of methyl esters as biodiesel. The oil feedstock, used in this study, included refined sunflower oil (acid value – 0.05 mg KOH/g; 25.3 % of oleic and 61.2 % of linoleic acids) and wasted frying high-oleic sunflower oil (acid value – 1.20 mg KOH/g; 6.1 % of linoleic and 81.7 % of oleic acids). Butanolysis was carried out using potassium butoxide, obtained from KOH and alcohols via original patent-pending method, under mild reaction conditions (alcohol-to-oil molar ratio – 4.5-5.0, 15°C, 1.4-1.6 %еq. KOH of butoxide, 20-30 min). High molar yield of butyl esters (93-96 %) was achieved, while glycerol and vast majority of alkaline catalyst formed the separate reaction products phase mainly in the course of reaction. Ester enriched phases were purified in order to obtain fuel-grade butanol-based biodiesel. Samples after removing of butanol under vacuum followed by water washing and drying were characterized by not enough high butyl esters content (about 94-95 %), as well as higher than allowed content of unconverted glycerides. Vacuum distillation as final purification step allowed fitting butyl esters samples composition within the requirements for biodiesel fuel. Distilled samples contained about 99 % of butyl esters, 0.4-0.5 % of monoglycerides and almost no n-butanol, glycerol, di- and triglycerides. Oxidative treatment (110°C, 6 h, air bubbling) revealed the high oxidation stability of the sample, originated from wasted high-oleic oil, due to the predominance of oleic acid in its fatty acid composition. The sample, obtained from refined sunflower oil (mainly linoleic acid in fatty acid composition), demonstrated very low stability. Addition of at least 2000 mg/kg of antioxidant 2,6-di-tert-butyl-4-methylphenol was shown to be able to improve this characteristic to the level of biodiesel requirements. |
| doi_str_mv | 10.15407/kataliz2021.32.040 |
| first_indexed | 2026-03-12T15:50:10Z |
| format | Article |
| fulltext |
40 Каталіз та нафтохімія, 2021, №32
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
PACS 88.20.fk
https://doi.org/10.15407/kataliz2021.32.040
Fuel-grade sunflower oil butyl esters: synthesis,
purification, oxidation stability
S.V. Konovalov, S.O. Zubenko, L.K. Patrylak, A.V. Yakovenko
V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine,
1, Murmanska str., Kyiv 02660, Ukraine, konovalovserhiy@gmail.com
Current paper deals with production, purification and oxidative stability enhancement of fuel-grade sunflower
oil butyl esters as more ecological alternative of methyl esters as biodiesel. The oil feedstock, used in this study,
included refined sunflower oil (acid value – 0.05 mg KOH/g; 25.3% of oleic and 61.2% of linoleic acids) and wasted
frying high-oleic sunflower oil (acid value – 1.20 mg KOH/g; 6.1% of linoleic and 81.7% of oleic acids). Butanolysis
was carried out using potassium butoxide, obtained from KOH and alcohols via original patent-pending method,
under mild reaction conditions (alcohol-to-oil molar ratio – 4.5-5.0, 15°C, 1.4-1.6%еq. KOH of butoxide, 20-30 min).
High molar yield of butyl esters (93-96%) was achieved, while glycerol and vast majority of alkaline catalyst formed
the separate reaction products phase mainly in the course of reaction. Ester enriched phases were purified in order to
obtain fuel-grade butanol-based biodiesel. Samples after removing of butanol under vacuum followed by water
washing and drying were characterized by not enough high butyl esters content (about 94-95%), as well as higher
than allowed content of unconverted glycerides. Vacuum distillation as final purification step allowed fitting butyl
esters samples composition within the requirements for biodiesel fuel. Distilled samples contained about 99% of butyl
esters, 0.4-0.5% of monoglycerides and almost no n-butanol, glycerol, di- and triglycerides. Oxidative treatment
(110°C, 6 h, air bubbling) revealed the high oxidation stability of the sample, originated from wasted high-oleic oil,
due to the predominance of oleic acid in its fatty acid composition. The sample, obtained from refined sunflower oil
(mainly linoleic acid in fatty acid composition), demonstrated very low stability. Addition of at least 2000 mg/kg of
antioxidant 2,6-di-tert-butyl-4-methylphenol was shown to be able to improve this characteristic to the level of
biodiesel requirements.
Keywords: fatty acid butyl esters, biodiesel, potassium butoxide, oxidation stability, antioxidant
____________________________________________________________________________________________________
Introduction
Biodiesel is alternative biomass-derived fuel for
compression-ignition engines. About its production,
utilization, advantages and disadvantages relative to
traditional petroleum diesel many are told elsewhere
[1-3]. Biodiesel is a mixture of long-chain fatty acids
alkyl esters, which are usually produced via catalytic
transesterification of both fresh and wasted vegetable
oils or animal fats with corresponding monohydric
alcohol. Only fatty acid methyl esters (FAME) have
practical significance as biodiesel fuel. Methanol, used
in FAME production, is known as the most toxic and
dangerous among monohydric alcohols, but it is also
the cheapest one. Besides that, since methanol is
mainly produced from natural gas, FAME cannot be
regarded as fully biorenewable fuel. Also, current
2021th gas crisis in Europe may probably turns the
manufacturers towards the diversification of alcohols
feedstock, used in biodiesel production. Among most
obvious alternatives for methanol are bioalcohols.
After obvious ethanol, biobutanol (n-butanol, obtained
from biomass via biofermentative processes) is the
best candidate. The main advantage of fatty acids butyl
esters (FABE) comparing with FAME is sufficiently
better cold flow properties [4], which makes them
more valuable fuel under cold weather conditions. As
for Ukraine, all the targets to develop the motor
biofuels field (for instance, to produce yearly about 90
mln. tones of biodiesel till 2020 [5]) remained no more
than declarations and there is still no biodiesel
production or using. According to abovementioned,
FAME production in Ukraine, having permanent
problems with natural gas supply and no domestic
methanol production, do not seem to have any real
perspectives in close future.
The common way of biodiesel production via
alkaline-catalyzed transesterification of triglycerides
(TG) is far more complicated in case of methanol
substitution with butanol. This is mainly due to the
lower acidity and polarity of longer-chain monohydric
alcohols comparing with methyl alcohol. Related
issues are discussed in detail in previous works of our
group [6, 7]. There exists the problem with self-
separation of alkaline butanolysis products, as their
mixture forms single phase unlike to the methanolysis
process. Formation of separate glycerol layer,
mailto:konovalovserhiy@gmail.com
Каталіз та нафтохімія, 2021, №32 41
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
containing most of reaction glycerol and also catalyst,
soaps and alcohol, is common for metanolysis. The
absence of self-separation makes downstreaming
processing of biodiesel more complicated.
There are enough examples of effective alkaline
butanolysis of oils using both hydroxide [8, 9] and
alkoxides catalysts [4, 9, 10]. In work [4] butanolysis
of low-acidic rapeseed and wasted frying oil (0.05 and
0.07% of FFA – free fatty acids) was catalyzed by
potassium methoxide and 93-96% molar yields were
achieved in synthesis under optimal reaction
conditions (alchohol-to-oil molar ratio – 6:1, 1 h; 70-
75 °C and 1.2% of catalyst for wasted oil or 90 °C and
1.1-1.15% of catalyst for rapeseed oil). Reaction
products separated after butanol removal by
distillation, obtained butyl esters were washed. Final
product contained 96.64% and 96.85% of FABE,
which fulfills the requirements for biodiesel (at least
96.5%). In work [10] sodium butoxide, obtained by
reaction of Na with alcohol, were used as catalyst of
food grade soybean oil (<0.5% FFA) butanolysis. High
molar yield of FABE was achieved in very short
reaction time (5 min) without heating (22 °C) using
alcohol-to-oil molar ratio 6:1 and 0.66% of catalyst.
Products remained in single phase; their separation
was enforced by removing of butanol by vacuum
distillation. Crude esters were purified via extraction
by deep eutectic solvents (choline chloride with
glycerol or ethylene glycol). Under certain purification
conditions resulting FABE content was in biodiesel
normative range. Effective catalysis of butanolysis by
hydroxides needs higher alcohol excess and longer
reaction time. In work [8] enough high oil conversion
(rapeseed, about 1% of FFA) was achieved using 12-
15:1 alcohol-to-oil molar ratio, 1.2-1.5% KOH at
30 °C or 80 °C after 2-4 h. Separation of reaction
products was enforced by neutralization (strong
mineral acids or CO2 bubbling) followed by removing
of alcohol by vacuum distillation. Neutralization by
strong acids resulted in high acid value of butyl esters.
In case of CO2 final mass yield of crude esters relative
to initial oil was in range 80-100%, while maximal
theoretically possible mass yield of FABE is near 115
% on the oil basis. But these were not biodiesel yet,
since the content of glycerol and soaps was higher then
allowed. In the next paper of the same research group
butanolysis of rapeseed oil (no properties specified)
and separation of products using the same approach
resulted in only 56-66% mass yield of crude butyl
esters relative to oil in case of KOH as catalyst and 79-
89% in case of potassium tert-butoxide as catalyst. In
previous works of our group [6, 7] the high efficiency
of potassium n-butoxide catalytic solution, obtaining
from KOH and n-butyl alcohol only in patent-pending
way [11], was demonstrated. The high yields and
glycerol layer separation were achieved under low
excess of alcohol within short reaction time.
Stability is important criteria concerning any
motor fuel properties. The stability of biodiesel is
known to be one of the problem characteristic, it is
always lower than stability of common mineral diesel
fuel [12]. This is, obviously, due to the presence of the
residues of unsaturated fatty acids, containing highly
reactive olephinic bonds. The formation of deposits
and gum, the darkening of fuel due to contaminants
emergence, including alcohols, acids, aldehydes,
peroxides etc. occurs in course of biodiesel storage
[12-14]. The oxidative stability is one of the major
issues for implementation the use of biodiesel as an
alternative to petrodiesel fuel [12]. Oxidation is
possible both during storage or directly in diesel
engine fuel supply system. In modern diesel engines
with high-pressure fuel pumping, the recirculating fuel
may be heated to 60-150 °C and contact with hot air
and, thus, can be partially oxidized [15-17]. There are
the wide variety of biodiesel stability characterization
techniques, including thermal stability (ASTM D6468-
08), storage stability (ASTM D4625-16, ASTM
D5304-15 and EN 15751) and oxidation stability tests
(ASTM D2274, ASTM D7545-14, and EN 14112)
[15]. The common normative standards for biodiesel
fuel, such as European EN14214, set the requirements
for oxidation stability at 110 °C (at least 6 h),
measuring by accelerated high-temperature oxidation
methods (so-called Rancimat methods).
Oxidation of fatty acids esters forms peroxy
radicals. It is initiated by free radical formation at the
allylic position due to reaction with oxygen [15, 18].
Formed peroxy radicals convert to hydroperoxides and
alkyl radicals. The former may convert to hydroxyl
and alkoxy radicals, which can decompose to alkyl
aldehydes and alkyl radicals, to form acids in result of
oxidation or to polymerize with other alkenes [1, 15,
19-20]. Oxidation of biodiesel is difficult to avoid, the
most effective method for its preventing includes
special approaches for storing, excluding the air, light
and high-temperature exposure etc. However, such
conditions are difficult to achieve, and the most
practically valuable methods is introduction of
antioxidants, extending the oxidation induction period
[12]. Chain breakers (peroxide radical quenchers) and
hydroperoxide decomposers (reducing agents) are the
most common antioxidants [12, 21]. The major widely
used synthetic antioxidants are butylated
hydroxytoluene (BHT), butylated hydroxyanisole
(BHA), tertbutylated hydroquinone (TBHQ),
pyrogallol, i.e., 1,2,3-trihydroxybenzene (PY), and
propylgallate, i.e., propyl 3,4,5-trihydroxybenzoate
(PG) [12, 22].
The general aim of the present work was to
obtain fuel quality butanol-based biodiesel. For such a
purpose a number of tasks was completed: to carry out
effective alkaline butanolysis of fresh and wasted
frying sunflower oil based on earlier developed
42 Каталіз та нафтохімія, 2021, №32
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
approaches, using potassium butoxide catalytic
solution; to develop the purification method of reaction
products; to test the oxidation stability of the latter and
to prove the applicability of common synthetic
antioxidant for enhancement of this characteristic of
sunflower oil butyl esters.
Materials and methods
Chemicals
Refined frozen deodorized sunflower oil sample
(DSTU 4492), having acid value (AV) 0.05 mg KOH/g
and water content – 0.05%) was purchased from local
market. Fatty acid composition was the following:
palmitic acid (С16:0) – 7.0%, stearic acid (С18:0) –
3.7%, oleic acid (С18:1) – 25.3 %, linoleic acid
(С18:2) – 61.2%, other fatty acids (FA) – 2.8%.
Wasted frying high-oleic sunflower oil sample (acid
number – 1.20 mg KOH/g, water content – 0.05 %;
4.4% С16:0, 2.6% С18:0, 81.7% С18:1, 6.1% С18:2,
5.2% other FA) was kindly provided by local reseller.
Fresh high-oleic sunflower oil was produced according
TUU10.4-0033358-004:2016.
n-Butyl alcohol (Turkey, GC area assay –
99.37%, water content about 0.15%), used as
transesterification reagent, was technical grade.
Analytical grade potassium hydroxide (Czech
Republic, 83.0% KOH according to titration of fresh
reagent batch), technical rectified ethyl alcohol,
reagent grade anhydrous i-propyl alcohol, synthetic
zeolite KA-Y/3A (Russian Federation, dynamic water
vapor capacity – 150 mg/cm3) as well as already
mentioned n-butanol were used in preparation of
potassium butoxide (KOBu) catalytic solutions. Also,
technical grade sodium hydroxide (China, 99.8%
NaOH) was the reagent for synthesis of sodium
butoxide for the analytical purposes. Anhydrous
technical grade sodium sulfate was applied in drying of
washed biodiesel.
Reagent grade methylpalmitate (gas
chromatographic (GC) area assay – 98.65%),
pharmaceutical grade glycerol, reagent grade n-
butanol, N-Methyl-N-(trimethylsilyl) trifluoroacet-
amide (MSTFA, for GC derivatization), glyceryl
tridecanoate (≥99%, GC grade) and ASTM D6584
standard solution kit (5 pyridine solutions of 1-
monoolein, 1,3-diolein, triolein and glycerol of various
concentration) were used in gas chromatographic
analyses.
0.1 N HCl water solution (prepared from
fixanale), as well as indicators bromophenol blue and
phenolphthalein were used in acid-base titration.
2,6-Di-tert-butyl-4-methylphenol (also known
as butylated hydroxytoluene – BHT) produced
according TU 38.5901237-90 (Russian Federation)
was used as antioxidant additive.
N,N-dimethylformamide (DMFA, 99.9%),
reagent grade n-hexane, analytic grade anhydrous
pyridine and reagent grade i-propanol were used as
solvents for the analytic purposes.
Gas chromatographic analyses were carried out
using high pure helium and hydrogen gases. Technical
purity argon gas was used in vacuum distillation of
butyl esters.
Synthetic and purification methods
Potassium butoxide catalytic solution in n-
butanol was obtained through the intermediate stage of
potassium ethoxide synthesis from KOH, dissolved in
ethyl alcohol. Synthetic procedure consisted in
repeated drying of ethanol-water azeotrope, condensed
over zeolite KA in Soxhlet extractor, followed by
returning of the dehydrated ethanol in reaction media.
The method is described in detail in patent of Ukraine
[23]. Thereafter, n-butanol was added to resulted
ethoxide solution (1:1 by volume) and ethanol was
removed by distillation with dephlegmator. Samples of
KOBu solutions were also obtained in similar way
from iso-propanol alkali solution.
Transesterification of oil samples was carried
out in 0.5 l conic flask with continuous stirring. At
first, oil was put into reaction flask (100 g of refined
oil or 200 g of wasted frying oil), then the pre-
determined masses of KOBu solution and n-butanol
were quickly added and stirring was started (500 rpm,
magnetic stirrer with triangular anchor). Amount of
loaded alkaline catalyst is presented in %eq. KOH units
relative to mass of oil. Maintaining of the lower-
ambient reaction temperature (15 °C) was provided by
water bath, filled with chilled water. In course of
syntheses dense non-fluent primary glycerol layer
(GL) was deposited on the bottom of reaction flask. It
remained there after transferring the reaction products
into separation funnel, where additional amount of
secondary glycerol layer settled during few next hours
or overnight.
Obtained ester-enriched upper phases (ester
layers – EL) after self-separation was subjected to
successive purification steps. At the first step EL was
placed in round bottom flask and butanol was removed
by distillation under mild vacuum (waterjet pump, 3-
4 kPa) and continuous stirring (500 rpm) with heating
by water bath. The temperature of the latter was
gradually increased from ambient to 90 °C. Resulting
mixture was transferred into separation funnel, where
additional phase separation occurred. The upper of two
obtained phases was repeatedly washed with hot tap
water (60-80 °C, 1:1 by volume each time) until
formation of clear water layer with neutral pH (5-7
successive washing steps). Washed butyl esters were
dried over anhydrous sodium sulfate. Thereafter one
half of washed samples were subjected to batch
vacuum distillation (~0.1-0.3 kPa) under continuous
bubbling of argon gas. Heating was provided by oil
bath (190-260 °C), butyl esters fraction condensed in
temperature range 170-230 °C.
Каталіз та нафтохімія, 2021, №32 43
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
The block-scheme of whole process of FABE
production and purification is given in the Fig. 1.
KOBu preparation is presented by example, which
includes the initial stage of ethoxide preparation from
KOH solution in ethanol. The scheme would be the
same also in the case of iso-propanol alkali solution
utilization on the first stage.
Fig.1. Block-scheme of the lab-scale process of FABE production.
Indicators of efficiency of the butanolysis
process
The main indicator of the efficiency of the oil
transesterification was the effective molar yield of
butyl esters Yef (%) in composition of ester layer:
FABEFFAoil
oilELFABE
ef
M)m(m3
MmC
Y
−
= , (1)
where CFABE is concentration (%) of butyl esters in
ester layer after phase separation; mEL, moil, mFFA are
masses (g) of ester layer, oil and free fatty acids in oil;
Moil, MFABE are molar masses (g/mol) of oil
triglycerides and butyl esters, averaged according to
the fatty acid composition. Term «effective yield»
implies the taking into account only the FABE in
composition of ester layer, since in general case some
fraction of esters may also transfer into glycerol layer.
Also, the mass yields of EL or purified esters
relative to initial oil was calculated:
%100
m
m
Y
oil
prod
mass = , (2)
where mprod is mass (g) of ester layer or purified FABE.
The fraction (%) of the alkaline catalyst, which
remains in composition of ester or glycerol layer or
transforms into soaps, from its loaded amount was
calculated as follows:
%,100
mn
mC
loading fromFraction
oilcat
layerx
= (3)
where Cx is content (%eq.KOH) of catalyst or soaps,
calculated as KOH; mlayer is mass (g) of ester or
glycerol layer; ncat is amount (%eq.KOH) of loaded
catalyst, calculated as KOH, relative to mass of oil.
Oxidation stability determination
Samples of distilled butyl esters, containing 500,
1000, 1500 and 2000 mg/kg BHT antioxidant, were
prepared by simple mixing with magnetic stirrer. 5.0 g
of the sample (containing antioxidant or not) was
placed into the sealed tube and bubbled with
atmospheric air (300 cm3/min) under continuous
heating (110 ºC, oil bath) for 6 h. Such a treatment
procedure is the same as in the standard EN14112
Rancimat method. But instead of the determination of
oxidation induction period by measuring the
conductivity changes, samples of treated butyl esters
were subjected to GC analysis and also titrated to
determine the acid value. In separate case, the samples
for GC analysis were also taken directly in course of
oxidative treatment. If composition of the sample did
not undergo considerable alterations and remained in
the range of the biodiesel normative requirements, it
was regarded as meeting the requirements for
antioxidant stability.
Gas chromatography methods
Butyl esters samples composition was analyzed
using Agilent 7890A Series gas chromatograph
equipped with split/splitless (SS) and cool-on-column
(COC) inlets, flame-ionization detector (FID) and
J&W HP-5 (30 m, 0.32 mm, 0.25 μm) and DB-5HT
(15 m, 0.32 mm, 0.1 μm) capillary columns with ((5%
phenyl)-methyl polysiloxane stationary phase. High-
purity helium was used as carrier gas.
44 Каталіз та нафтохімія, 2021, №32
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
FABE content was measured by modified
method based on standard method of determination of
methyl esters in biodiesel EN14103. Methyl palmitate
(MP) was used as internal standard instead of methyl
heptadecanoate. Sample (0.15-0.20 g) and standard
(about 0.02 g) were weighted with analytic accuracy
and dissolved in 5 cm3 of n-hexane. At least two of
such probes were taken for each FABE sample, each of
them were analyzed twice. Analyses were carried out
under following chromatographic conditions: SS inlet
temperature – 250 °C; constant pressure mode
(82.7 kPa); split ratio 36:1; column (HP-5) temperature
210 °C/27 min, 5 (°C/min)/min up to 320 °C,
280 °C/10 min; FID temperature 250 °C. This method
also was applied to measure the changes in content of
butyl esters of major fatty acids (C16:0, C18:0, C18:1,
C18:2) as well as to monitor the BHT antioxidant
consumption in oxidation stability studies.
Monoglycerides (MG), diglycerides (DG) and
TG concentrations were determined by means of
derivatization with MSTFA followed by
chromatographic analyses (DB-5HT column with 1
m/0.53 mm fused silica retention gap, COC inlet) with
tricaprin as internal standard according ASTMD 6584
standard method. Original ASTMD 6584 method
involves also determination of free glycerol with 1,2,4-
butanetriol as standard, but its delivery in Ukraine is
prohibited. About 0.1 g of FABE sample was weighted
with analytic accuracy in 10 cm3 vial, then tricaprin
solution in pyridine (200 μl, 4000 μg/cm3) and
MSTFA (100 μl) were added. Vial was sealed, shaken,
and left for 20 min at ambient temperature. Then its
content was dissolved in 8 cm3 of n-hexane and
chromatographic analysis was carried out under
conditions described in [24]. MG, DG and TG content
was calculated from calibration, which was built using
ASTM D6584 standard solution kit.
For measurement of low glycerol concentrations
separate analysis was set up. About 0.1 g of FABE
sample was weighted with analytic accuracy in 4 cm3
vial followed by addition of 200 μl of pyridine and
100 μl of MSTFA. Vial was sealed, shaken and left for
20 min at ambient temperature, then 3 cm3 of n-hexane
was added. Resulting solution was analyzed under
such conditions: SS inlet temperature – 300 °C;
constant flow mode (3 cm3/min); split ratio 36:1;
column (HP-5) temperature 110 °C/7 min, 30 °C/min
up to 320 °C, 320 °C/15 min; FID temperature 300 °C.
Concentration of glycerol was calculated from
previously built calibration line.
Concentration of butanol was measured in
another chromatographic analysis. 0.6 cm3 of the
FABE sample was weighted in 10 cm3 vial and
dissolved in 5 cm3 of DMFA, containing 0.230% MP
as internal standard. This solution was also used to
estimate the glycerol concentration higher than 0.5% in
EL (without derivatization), using the same MP in role
of standard. Analyses was carried out under following
conditions: SS inlet temperature – 300 °C; constant
flow mode (3 cm3/min for 9 min, 3 (cm3/min)/min up
to 9 cm3/min and 9 cm3/min to the end of analysis);
split ratio 20:1; column (HP-5) temperature
35 °C/9 min, 10 °C/min up to 80 °C, 80 °C/1 min,
5 °C/min up to 320 °C, 320 °C/7.5 min; FID
temperature 300 °C. n-Butanol and glycerol
concentration were calculated relative to MP peak area
using previously built calibrations.
Another analytic methods
Acid value (AV) of oils and purified butyl esters
was measured by means of titration with sodium
butoxide solution in n-butanol with indicator
bromothymol blue as described in [25]. Alkaline
catalyst and soaps content in the butanolysis products
were determined by two-step acid-base titration
method as described in [26]. Alkali was determined in
a first titration step, using HCl 0.1 N solution as titrant,
iso-propanol as solvent and phenolphthalein as
indicator. In a second titration step, the soap content
was determined using the same titrant and
bromophenol blue as indicator.
Water content in oils samples was determined
by heterogenic azeotrope distillation using benzene to
form heterogeneous azeotrope with water (Dean-Stark
method). Density of butyl esters samples was
measured at 15 °C by means of areometers according
to EN ISO 3675. Kinematic viscosity (KV) of FABE
was determined at 40 °C as described in EN ISO 3104
using glass capillary viscometer.
Results and discussions
FABE synthesis
Butanolysis of refined sunflower oil was carried
using 3 samples of KOBu catalytic solutions, prepared
both from KOH solution in ethanol (KOBu(Et)) and
iso-propanol (KOBu(iPr1) and KOBu(iPr2)). Though
such method of the butoxide synthesis required
additional reagents (ethanol or iso-propanol) and
molecular sieves, it is less time-consuming and energy-
consuming comparing with the earlier used method
[6,7, 11] based on the azeotropic distillation of alkali
metal hydroxide solution in n-butanol. Results of
experiments on transesterification of the refined oil
sample under the same reaction conditions are given in
Table 1 (samples BRSO-1, BRSO-2 and BRSO-3, t =
15 ºC). Such reaction parameters were chosen on the
base of previous studies [6, 7] as providing both high
yield of butyl esters and effective phase separation. In
all three experiments at the same reaction conditions,
but using three different samples of KOBu catalytic
solutions, the very close results were obtained.
Namely, in all syntheses both high FABE yield (93-
94%) and removing of vast majority of glycerol and
alkaline catalyst into separate phase were achieved.
Obtained results demonstrated the good reproducibility
Каталіз та нафтохімія, 2021, №32 45
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of the KOBu preparation methods, using different
alcohols (ethanol or iso-propanol), as well as
reproducibility of KOBu parallel synthesis in case of
the same iso-propanol (KOBu(іPr1) and KOBu(іPr2)
samples). In case of wasted oil butanolysis (BWFO-1)
slightly higher excess of butanol was used, process
was carried out for additional 10 min. Also, additional
KOBu was included for FFA neutralization. As result,
even higher butyl esters yield was achieved, however
ester layer contained more glycerol and potassium. The
latter was almost exclusively in composition of soaps,
as was revealed by acid-base titration with two
indicators. Less effective phase separation of BWFO-1
synthesis product is most likely due to the presence of
FFA in wasted oil, but also higher alcohol-to-oil ratio
and longer reaction time may have some impact.
Table 1. Conditions and results of the experiments on transesterification of oil samples (t = 15°C)
Sample Butoxide
sample
1RAO,
mol/mol
2τ,
min
3ncat,
%eq. KOH
Yef, % Ymass (EL),
%
Concentration in EL, %
FABE n-Butanol Glycerol 4K
BRSO-1 KOBu(Et) 4.5 20 1.40 92.7 128.8 82.5 12.4 0.6 0.05
BRSO-2 KOBu(іPr1) 4.5 20 1.40 92.9 128.9 82.6 12.4 0.6 0.04
BRSO-3 KOBu(іPr2) 4.5 20 1.40 93.7 129.1 83.3 12.3 0.7 0.04
BWFO-1 KOBu(Et) 5.0 30 1.56 95.6 132.9 82.4 14.4 1.7 0.12
1 alcohol-to-oil molar ration
2 reaction time
3 amount of loaded alkaline catalyst, calculated as initial KOH, relative to mass of oil
4 potassium content in EL.
Distribution of alkaline catalyst between the
layers of reaction products and its deactivation due to
saponification reactions (both of acylglycerides and
butyl esters) need separate attention to pay. Previous
studies of our research group [6, 7] revealed the total
difference of the compostion of glycerol layers, formed
during alkaline butanolysis, comparing with that
formed in more common processes of oils
transesterification with methyl or ethyl alcohols. In the
latter cases glycerol layers contain beside glycerol also
the significant fraction of esters and alcohol, some
unconverted acylglycerides as well as soaps and
alkaline catalyst in different proportions. On the
contrary, the GL of butanolysis is composed almost
exclusively of neat glycerol and alkali. Such
observations were never earlier reported in literature
sources.
Data of the Table 2 show the distribution of the
alkali and soaps between ester layers and primary
glycerol layers after refined oil butanolysis. All ester
layers contain no alkaline catalyst and only minor
amount of soaps. Vast majority of loaded catalyst
transfer into the primary GL (settled during synthesis),
whereas soaps are presented in very limited quantities.
The amount of primary GL the latter was 7.4-7.6%
from oil mass, besides that 2.2-2.6% of secondary GL
of close nature formed during settling. It worth be
mentioned, that the maximal possible amount of GL,
containing only glycerol and alkali, in case of full oil
conversion is about 11% from oil mass.
Table 2. Distribution of alkaline catalyst and soaps in refined sunflower oil butanolysis products
Sample Ester layer Primary glycerol layer
Catalyst Soaps Catalyst Soaps
Content,
%eq. KOH
Fraction from
loading, %
Content,
%eq. KOH
Fraction from
loading, %
Content,
%eq. KOH
Fraction from
loading, %
Content,
%eq. KOH
Fraction from
loading, %
BRSO-1 0 0 0.069 6.3 13.71 72.6 0.71 3.8
BRSO-2 0 0 0.063 5.6 13.89 74.8 0.42 2.3
BRSO-3 0 0 0.064 5.9 14.07 75.8 0.38 2.0
The transfer of major part of the catalyst into GL
in course of synthesis from one point of view mostly
prevents the saponification. Soaps formation leads to
the conversion decrease and difficulties with
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separation and purification of esters. At the same time,
the catalyst concentration decreases fast due to its
removing into separate phase. Such the details are
discussed in [7], where also the transformation of
KOBu into potassium glyceroxide in course of
transesterification was grounded. More likely, the
alkali in GL composition is presented by glyceroxide,
which is known as effective transesterification catalyst
[27]. So, preserving the major part of alkaline catalyst
after butanolysis in mixture with glycerol opens
prospects for its reuse in transesterification or for
another purposes.
Isolation of biodiesel-grade butyl esters.
In Table 3 the composition and some properties
of butyl esters samples after different steps of
purification are compared with requirements of
European standard for methanol-based biodiesel. “W”
in the end of the samples name refers to butyl esters
after alcohol removal, washing with water and drying,
while “D” means the distilled butyl esters. Carrying
out the water washing of EL after butanolysis is
strongly complicated by n-butanol with water partial
miscibility. So, the prior butanol removing by
distillation is needed, which also provides its recycling
in the process. Products of refined oil
transesterification were mixed together and then
purified. FABE content after washing in BRSOW
sample was a bit lower, than EN 14214 required,
which mainly due to the presence of unconverted
glycerides. For such cases the higher conversion of oil
in synthesis will provide both increasing the FABE and
decreasing the MG, DG and TG concentrations. This is
easy achievable by increasing alcohol-to-oil molar
ratio up to about 5.0-6.0. This also may decrease to
some extent the fullness of phase separation, however
this is may be the serious problem in case of high-
acidic low-grade oils, but not refined ones.
Table 3. Comparison of composition and physica-chemical properties of purified FABE samples versus
normative requirements
Sample Concentration of components, % AV,
mg KOH/g
KV
(40°C),
mm2/s
Density
(15°C),
kg/m3
Ymass,
%
FABE n-Butanol Glycerol MG DG TG
BRSOW 95.0 0.11 0.041 1.59 1.04 0.33 0.28 5.65 877 93.1
BRSOD 98.9 0.04 0.017 0.45 0.01 0.00 0.26 5.13 873 86.1
BWFOW 93.7 0.28 0.002 0.84 0.23 0.04 0.10 5.90 869 93.5
BWFOD 98.9 0.02 0.005 0.39 0.01 0.00 0.12 5.68 868 89.4
1EN 14214 96.5
(min)
0.20
(max)
0.02
(max)
0.70
(max)
0.20
(max)
0.20
(max)
0.50
(max)
3.5-5 860-900 -
1 Requirements of EN14214 standard for FAME as BD
Sample of washed esters from wasted oil
BWFOW had other features of composition.
Nonetheless some higher conversion, resulting in
lower glycerides content, FABE concentration
appeared to be lower than in BRSOW sample. This is
more likely due to the presence of so-called polar
compounds in wasted oil samples, which includes
oligomerized or polymerized cross-linked
triglycerides, yielding in transesterification heavy
oligomeric esters. The presence of such compounds is
known problem, which complicates the achieving
target 96.5% ester content in wasted oil derived
biodiesel [28, 29]. Some excess content of the alcohol
in BWFOW sample is a result of not enough full
washing, as well as glycerol content in BWFOD
sample. At the same time, water washing is almost
ineffective for removal of MG, DG and TG.
Vacuum distillation of both samples improved
the FABE, MG and DG concentrations, fitting them
within EN 14214 requirements. Moreover, DG and TG
are almost absent in distilled samples composition.
Contents of glycerol and butanol were also within
acceptable limits. As for the kinematic viscosity, it also
decreased after distillation, but remained higher than 5
mm2/s. Such KV values is intrinsic property of FABE
due to the longer alcohol moiety in their molecules
compared with methyl esters. The difference in KV
between BRSOD and BWFOD samples is more likely
caused by their fatty acid composition. It worth
emphasizing, that relatively high FABE viscosity is not
critical for their utilization like biodiesel, as some
national standard, for example ASTM D6751 (USA),
allows higher biodiesel KV (up to 6.0 mm2/s).
Optimization of purified FABE yield was not
the task in the current study. Let us reminded, that
theoretically possible butyl esters mass yield from pure
TG is near 115%. Mass yield of final biodiesel can be
sufficiently improved by reducing product losses in
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intermediate purification steps. For instance, the drying
over Na2SO4 resulted in up to 10% product losses.
Such stage should not be incorporated in a large
production scale, instead of its drying under vacuum is
more rational to use. However, in case of further
vacuum distillation, drying stage is not needed. It is
also possible to refuse from washing step and to carry
out distillation of FABE after butanol removal.
However, in this case the problems with glycerol
content in distillate may arise. It can be resolved by
dry washing step, coupled with vacuum distillation,
which can be realized by condensation of FABE
fraction over the layer of proper adsorbent. This also
may purify the distillate from another relatively light
polar compounds, possibly forming at high
temperatures.
Separate attention should be paid to some non-
fat admixtures, which may originate from initial oil.
Composition of refined oil, mentioned by
manufacturer, included only TG (99.9%), while the
composition of fresh high-oleic oil beside actual
deodorized frozen oil also included additives E320
(antioxidant BHA – butylated hydroxyanisole) and
E900 (defoamer polydimethylsiloxane) in unspecified
amounts. The latter surely should not be present in
biodiesel composition. It cannot be removed by water
washing, but it also cannot be distilled and thus
remained in composition of cube residue.
Oxidative stability of butanol-based biodiesel
Oxidative treatment of distilled butyl esters
revealed the totally different oxidative stability of
BRSOD and BWFOD samples. The former, containing
mostly C18:2 fatty acid residues underwent severe
degradation after 6 h airs bubbling at 110 °C. The
concentration of FABE decreased strongly (Fig. 2a),
while oxidation products appeared in the composition
of the treated sample (Fig. 2b). Acid value also
increased many times (Fig. 2d). Addition of BHT
antioxidant in BRSOD sample decreased the
degradation rate, its concentration 2000 mg/kg
appeared to be enough to protect the sample from
chemical changes. Only at this highest antioxidant
content, some relatively significant amount of BHT
(about 350 mg/kg) remained in the composition of the
sample (Fig. 2c). In other cases, BHT additive was
totally consumed in course of oxidation. As for the
sample BWFOD, which fatty acid composition are
predominantly presented by monounsaturated oleic
acid, no any changes of its composition were observed
even without antioxidant addition.
Fig. 2. Content of FABE (a), volatile oxidation products (b) and antioxidant (c) in butyl esters samples and their
acid value (d): 1 – initial BRSOD; 2 – oxidized BRSOD; 3 – oxidized BRSOD + 500 mg/kg BHT; 4 – oxidized
BRSOD + 1000 mg/kg BHT; 5 – oxidized BRSOD + 1500 mg/kg BHT; 6 – oxidized BRSOD + 2000 mg/kg BHT; 7
– initial BWFOD; 8 – oxidized BWFOD.
Chromatograms of the initial and threated
BWFOD samples (Fig. 3a) are totally identical and
contain the same peaks, having the same relative
intensities comparing with internal standard MP
(retention time about 6 min). The chromatogram of
BRSOD sample after 6 h treatment without antioxidant
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(Fig. 3b) contains, besides peaks of butyl esters of
main fatty acids (C16:0 near 6 min, C18:1 and C18:2
in range near 18-19 min and C18:0 near 20 min), a
wide variety of oxidation products signals. Among
them there is a set of peaks of light oxidation products
(in range about 2.5-8 min and 13-15 min), as well as
peaks, corresponding to oxidized FABE of C18
unsaturated fatty acids (in range about 28-38 min) and
containing the same number of carbon atoms. All such
compounds are referred as «volatile oxidized
products» in Fig. 2b, while FABE content (Fig. 2a)
takes into account only peaks of component, which are
presented both on the initial and oxidized BRSOD
sample chromatograms. The same signals were
presented in chromatograms of oxidized BRSOD
sample, containing 500-1500 mg/kg BHT. The higher
was the antioxidant concentration, the lower was the
fraction of oxidation products. As for the sample,
containing 2000 mg/kg of antioxidant, its
chromatograms almost did not change comparing with
initial BRSOD and FABE content and AV remained in
the range of biodiesel normative. It is worth
emphasizing, that the total concentration of FABE and
volatile oxidation products was substantially lower
than FABE concentration before treatment and no
other signals were presented on the chromatograms.
This is the evidence of the presence of heavier non-
volatile oligomeric components, formed in course of
oxidative treatment. Such components cannot be
revealed via gas chromatographic analyses, and
believed to be of the similar nature as oligomeric or
dimeric esters, which are presented in wasted oils
transesterification products and complicates the
achievement of target 96.5% ester content in wasted
oil based biodiesel [28]. However, the long-chain FFA
are not determined under the used conditions of
chromatographic analysis also.
Fig. 3. Chromatograms of butyl esters samples before and after oxidative treatment (6 h): 1 – initial BWFOD; 2
– oxidized BWFOD; 3 – initial BWFOD; 4 – oxidized BWFOD; 5 – oxidized BWFOD + 2000 mg/kg BHT.
Changing of individual fatty acids esters
concentration in result of oxidation treatment are
presented in the Fig. 4. As clearly seen from given
data, predominantly esters of diunsaturated linoleic
acid underwent the degradation. Their concentration
decreased by about 5 times (Fig. 4d), while lowering
of the oleic acid esters content did not exceed one
quarter from initial content (Fig. 4c). The decreasing of
saturated fatty acids esters content was even less
significant. The same trend was observed in the course
of oxidation of BRSOD sample, containing
1000 mg/kg of antioxidant (Fig. 5). FABE content
began to decrease (predominantly due to C18:2 esters)
after vast majority of antioxidant consuming in course
of first 4 h of treatment (Fig. 6).
It is interesting, that the concentration of C18:2
ester in BWFOD sample, originated from high-oleic
oil, remained unchanged, most likely, due to their
insignificant content (about only 6%). The excellent
oxidation stability of the BWFOD sample is obviously
due to the domination of many times more stable
C18:1 (about 82%) ester in its composition. However,
the presence of the antioxidants in the composition of
initial high-oleic sunflower oil may have separate
influence on the stability of discussed sample.
Tocopherols (vitamin E) are known as the most
powerful natural-occurring fat-soluble antioxidant
[30], their content and isomeric composition have
significant impact on the oxidative stability of
vegetable oils, including high-oleic sunflower oil [31].
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Fig. 4. Content of esters of palmitic (a), stearic (b), oleic (c) and linoleic (d) fatty acids in butyl esters samples:
1 – initial BRSOD; 2 – oxidized BRSOD; 3 – oxidized BRSOD + 500 mg/kg BHT; 4 – oxidized BRSOD + 1000
mg/kg BHT; 5 – oxidized BRSOD + 1500 mg/kg BHT; 6 – oxidized BRSOD + 2000 mg/kg BHT; 7 – initial
BWFOD; 8 – oxidized BWFOD.
Fig. 5. Changing of the content of FABE (1),
FABE and volatile oxidation products content (2),
C18:2 esters (3), C18:1 esters (4), C18:0 esters (5) and
C16:0 esters (6) in BRSOD sample with 1000 mg/kg
BHT concentration in course of oxidative treatment.
Fig. 6. Changing of BHT content (1) and acid
value (2) for the BRSOD sample with initial BHT
concentration 1000 mg/kg in course of oxidative
treatment.
However, the stability of the high-oleic
sunflower oil was shown to be primarily influenced by
its linoleic acid content. Its value lower than 10%
provided excellent frying stability of oil, while C18:2
content higher than named value may be too high to
achieve comparably high performance of oil during
frying [31]. The close trend should be preserved also
for fatty acids esters, namely for BWFOD sample,
containing only about 6% C18:2 ester. The presence of
tocopherols in BWFOD sample is questionable, since
they may be consumed during utilization of initial oil
in frying, as well as remained mainly in cube residue
in course of butyl esters distillation. However, the
presence of tocopherols cannot be surely excluded
50 Каталіз та нафтохімія, 2021, №32
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both for BRSOD and BWFOD samples. The results of
work [32], in which ethyl esters of high-oleic
sunflower oil (78.8% C18:1, 12.5% C18:2) were
synthesized and characterized, looks interesting in this
respect. Ethyl esters samples, purified via water
washing, dry washing and distillation, were all
characterized by unsatisfactory oxidation stability. But
distilled sample has the lowest value of this parameter
(<1 h at 110 °C), which is caused, from our point of
view, by loss of natural antioxidants during distillation.
But, as was mentioned above, initial high-oleic
sunflower oil also contained synthetic antioxidant
BHA (content is not specified), which also may
contribute in the excellent stability of butyl esters. Its
concentration in wasted oil, estimated from
chromatogram, was only about 400 mg/kg. Such a low
content of BHT appeared to be totally ineffective to
prevent degradation of the FABE sample with high
C18:2 ester content. Moreover, BHA was fully
consumed during the oxidation, which did not result in
any changes of the composition of treated BWFOD
sample. At the same time, BRSOD sample began to
degrade before the full consumption of BHT. Thus, the
presence of BHA probably enhanced the oxidative
stability of corresponding FABE sample, in addition to
its high stability due to fatty acid composition.
Nonetheless, the results of current work prove the
wasted frying high oleic sunflower oil as valuable and
very suitable feedstock for biodiesel production. Its
fatty acid composition, free from linoleic acid high
content, provides not only high resistance for biodiesel
oxidative degradation, but also prevents such a
degradation in course of food frying. As result, wasted
oil may contain lesser amount of polar admixtures,
which is favorable for higher biodiesel yield, its easier
purification and higher quality.
As for the chemical composition of the
oxidation products and reaction pathways, leading to
their formation, their elucidation was not the aim of
current study. Much is said on this topic in literature,
but sources mainly deal with FAME [12, 15, 33, 34].
Since the chemical alteration mainly affects the double
bounds in the fatty acids moieties of esters, the nature
of their alcohol moiety should not have the crucial
effect on the oxidation stability. However, the decrease
of induction period of oxidation in row methyl – ethyl
– n-butyl esters were earlier reported [4]. Nonetheless
of the chemical pathways of biodiesel degradation
during oxidation treatment, BHT proved to be efficient
in prevention of formation of both low-molecular
oxidation products and products of oxidative
polymerization. There exists question concerning the
inconsistency of accelerated oxidation tests conditions
to the conditions of long-term biodiesel storage. But
earlier the authors of current work also proved the high
efficiency of BHT antioxidant in preventing the
degradation of butyl esters of linseed and rapeseed oils
during their prolonged storing at ambient temperature
under free access of the air and light exposure [35].
Conclusions
Results of current study have proven the high
efficiency of alkaline-catalyzed route of fatty acid
butyl esters synthesis using potassium butoxide
catalytic solution. The latter may be produced using
only potassium hydroxide and widespread monohydric
alcohols. Transesterification of oils with n-butanol
proceeds under mild reaction conditions (alcohol-to-oil
molar ratio – 4.5-5.0, temperature – 15 °C, butoxide
loading – 1.4-1.6 %еq. KOH) within short reaction time
(20-30 min) and results in 93-96% molar yield of butyl
esters. The reaction products are separated on its own
mainly in course of synthesis, resulting in formation of
primary glycerol layer, which contains predominantly
glycerol and about three-quarters from loading alkali
(more likely as potassium glyceroxide). Such primary
glycerol layer may be useful for reuse in alkaline
catalysis of oil transesterification or in other processes.
Ester phases contains about 82-83% of butyl esters,
only minor amounts of glycerol and soaps and no
alkaline catalyst.
The sequence of purification operations,
enabling to obtain biodiesel grade butyl esters was
proposed. It includes removing of alcohol under
vacuum, followed by additional phase separation,
washing of obtained upper phase with water and
vacuum distillation of washed butyl esters. In case of
full conversion of fresh high-quality oil feedstock, it is
also possible to obtain biodiesel-grade product without
final distillation step.
The approach to the estimation of biodiesel
oxidative stability, grounded on accelerated high-
temperature oxidation with atmospheric air followed
by gas chromatographic and titrimetric analyses, was
developed. High oxidative stability of butyl esters,
obtained from wasted frying high-oleic oil (87.1% and
6.1% of oleic and linoleic acids), and unsatisfactory
low oxidative stability of esters, originated from
refined mid-linoleic sunflower oil (25.3% and 61.2%
of oleic and linoleic acids), were demonstrated.
Addition of at least 2000 mg/kg of antioxidant 2,6-di-
tert-butyl-4-methylphenol was shown to be able to
improve this characteristic to the level of biodiesel
requirements.
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Надійшла до редакції 24.11.2021 р.
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ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність
С.В. Коновалов, С.О. Зубенко, Л.К. Патриляк, А.В. Яковенко
Інститут біоорганічної хімії та нафтохімії ім. В.П. Кухаря НАН України, Україна,
вул. Мурманська, 1, Київ 02660, Україна, konovalovserhiy@gmail.com
Дана робота присвячена одержанню, очищенню та покращенню окисної стабільності паливних
бутилових естерів соняшникової олії як більш екологічної альтернативи метиловим естерам в ролі
біодизелю. Олійна сировина включала зразки рафінованої соняшникової олії (кислотне число – 0,05 мг
КОН/г; 25,3 % і 61,2 % олеїнової та лінолевої кислот) та використаної в смаженні високоолеїнової
соняшникової олії (кислотне число – 1,20 мг КОН/г; 6,1 % і 81,7 % лінолевої та олеїнової кислот). Бутаноліз
проводили за участі бутоксиду калію, одержаного з КОН та спиртів за оригінальним запатентованим
способом, за мʼяких умов (молярне співвідношення спирту до олії – 4,5-5,0, 15 °С, 1,4-1,6 %екв. KOH бутоксиду,
20-30 хв). Було одержано високий молярний вихід бутилових естерів (93-96 %), а гліцерин та основна
частина лужного каталізатора формували окрему фазу продуктів вже переважно в ході реакції. Естерову
фазу піддавали очищенню з метою одержання бутанольного біодизелю паливної якості. Зразки після
видалення бутанолу під вакуумом, наступного розшарування та відмивки і сушіння верхньої з одержаних
фаз характеризувалися дещо заниженим вмістом естерів (94-95 %), а вміст гліцеридів був вище дозволеного
рівня. Вакуумна дистиляція як кінцевий етап очищення дозволила покращити склад продуктів до рівня
вимого до біодизельного палива. Дистиляти містили близько 99 % бутилових естерів, 0,4-0,5%
моногліцеридів, а н-бутанол, гліцерин, ди- та тригліцериди були фактично відсутні. Окисна обробка (110 °С,
6 год барботування повітря) продемонструвала високу окисну стабільність зразка, одержаного з
використаної високоолеїнової олії, завдяки домінуванню в його жирнокислотному складі олеїнової кислоти.
Зразок на основі рафінованої олії (переважно лінолева кислота в жирнокислонтому складі), продемонстрував
дуже низьку стабільність. Було показано, що введення принаймні 2000 мг/кг антиоксиданта 2,6-ди-трет-
бутил-4-метилфенолу сприяє покращенню даної характеристики до рівня вимог до біодизельного палива.
Ключові слова: бутилові естери жирних кислот, біодизель, калію бутоксид, окисна стабільність,
антиоксидант
mailto:konovalovserhiy@gmail.com
|
| id | oai:katalizorgua:article-61 |
| institution | Catalysis and petrochemistry |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-03-12T15:50:10Z |
| publishDate | 2021 |
| publisher | V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | katalizorgua/25/8ed1ad552a5869048a835e47edeed325.pdf |
| spelling | oai:katalizorgua:article-612023-09-28T12:18:42Z Fuel-grade sunflower oil butyl esters: synthesis, purification, oxidation stability Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність Konovalov, S.V. Zubenko, S.O. Patrylak, L.K. Yakovenko, A.V. fatty acid butyl esters biodiesel potassium butoxide oxidation stability antioxidant бутилові естери жирних кислот біодизель калію бутоксид окисна стабільність антиоксидант Current paper deals with production, purification and oxidative stability enhancement of fuel-grade sunflower oil butyl esters as more ecological alternative of methyl esters as biodiesel. The oil feedstock, used in this study, included refined sunflower oil (acid value – 0.05 mg KOH/g; 25.3 % of oleic and 61.2 % of linoleic acids) and wasted frying high-oleic sunflower oil (acid value – 1.20 mg KOH/g; 6.1 % of linoleic and 81.7 % of oleic acids). Butanolysis was carried out using potassium butoxide, obtained from KOH and alcohols via original patent-pending method, under mild reaction conditions (alcohol-to-oil molar ratio – 4.5-5.0, 15°C, 1.4-1.6 %еq. KOH of butoxide, 20-30 min). High molar yield of butyl esters (93-96 %) was achieved, while glycerol and vast majority of alkaline catalyst formed the separate reaction products phase mainly in the course of reaction. Ester enriched phases were purified in order to obtain fuel-grade butanol-based biodiesel. Samples after removing of butanol under vacuum followed by water washing and drying were characterized by not enough high butyl esters content (about 94-95 %), as well as higher than allowed content of unconverted glycerides. Vacuum distillation as final purification step allowed fitting butyl esters samples composition within the requirements for biodiesel fuel. Distilled samples contained about 99 % of butyl esters, 0.4-0.5 % of monoglycerides and almost no n-butanol, glycerol, di- and triglycerides. Oxidative treatment (110°C, 6 h, air bubbling) revealed the high oxidation stability of the sample, originated from wasted high-oleic oil, due to the predominance of oleic acid in its fatty acid composition. The sample, obtained from refined sunflower oil (mainly linoleic acid in fatty acid composition), demonstrated very low stability. Addition of at least 2000 mg/kg of antioxidant 2,6-di-tert-butyl-4-methylphenol was shown to be able to improve this characteristic to the level of biodiesel requirements. Дана робота присвячена одержанню, очищенню та покращенню окисної стабільності паливних бутилових естерів соняшникової олії як більш екологічної альтернативи метиловим естерам в ролі біодизелю. Олійна сировина включала зразки рафінованої соняшникової олії (кислотне число – 0,05 мг КОН/г; 25,3 % і 61,2 % олеїнової та лінолевої кислот) та використаної в смаженні високоолеїнової соняшникової олії (кислотне число – 1,20 мг КОН/г; 6,1 % і 81,7 % лінолевої та олеїнової кислот). Бутаноліз проводили за участі бутоксиду калію, одержаного з КОН та спиртів за оригінальним запатентованим способом, за мʼяких умов (молярне співвідношення спирту до олії – 4,5-5,0, 15°С, 1,4-1,6 %екв. KOH бутоксиду, 20-30 хв). Було одержано високий молярний вихід бутилових естерів (93-96 %), а гліцерин та основна частина лужного каталізатора формували окрему фазу продуктів вже переважно в ході реакції. Естерову фазу піддавали очищенню з метою одержання бутанольного біодизелю паливної якості. Зразки після видалення бутанолу під вакуумом, наступного розшарування та відмивки і сушіння верхньої з одержаних фаз характеризувалися дещо заниженим вмістом естерів (94-95 %), а вміст гліцеридів був вище дозволеного рівня. Вакуумна дистиляція як кінцевий етап очищення дозволила покращити склад продуктів до рівня вимого до біодизельного палива. Дистиляти містили близько 99 % бутилових естерів, 0,4-0,5 % моногліцеридів, а н-бутанол, гліцерин, ди- та тригліцериди були фактично відсутні. Окисна обробка (110 °С, 6 год барботування повітря) продемонструвала високу окисну стабільність зразка, одержаного з використаної високоолеїнової олії, завдяки домінуванню в його жирнокислотному складі олеїнової кислоти. Зразок на основі рафінованої олії (переважно лінолева кислота в жирнокислонтому складі), продемонстрував дуже низьку стабільність. Було показано, що введення принаймні 2000 мг/кг антиоксиданта 2,6-ди-трет-бутил-4-метилфенолу сприяє покращенню даної характеристики до рівня вимог до біодизельного палива. V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine 2021-12-28 Article Article application/pdf https://kataliz.org.ua/index.php/journal/article/view/61 10.15407/kataliz2021.32.040 Catalysis and petrochemistry; No. 32 (2021): Catalysis and petrochemistry; 40-53 Каталіз та нафтохімія; № 32 (2021): Каталіз та нафтохімія; 40-53 2707-5796 2412-4176 10.15407/kataliz2021.32 en https://kataliz.org.ua/index.php/journal/article/view/61/51 Copyright (c) 2021 Catalysis and petrochemistry |
| spellingShingle | бутилові естери жирних кислот біодизель калію бутоксид окисна стабільність антиоксидант Konovalov, S.V. Zubenko, S.O. Patrylak, L.K. Yakovenko, A.V. Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність |
| title | Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність |
| title_alt | Fuel-grade sunflower oil butyl esters: synthesis, purification, oxidation stability |
| title_full | Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність |
| title_fullStr | Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність |
| title_full_unstemmed | Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність |
| title_short | Бутилові естери соняшникової олії: синтез, очищення, окисна стабільність |
| title_sort | бутилові естери соняшникової олії: синтез, очищення, окисна стабільність |
| topic | бутилові естери жирних кислот біодизель калію бутоксид окисна стабільність антиоксидант |
| topic_facet | fatty acid butyl esters biodiesel potassium butoxide oxidation stability antioxidant бутилові естери жирних кислот біодизель калію бутоксид окисна стабільність антиоксидант |
| url | https://kataliz.org.ua/index.php/journal/article/view/61 |
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