Лужний синтез ізопропілових естерів жирних кислот
Fatty acid alkyl esters are widely used products. Most of them are used as renewable transport fuel named “biodiesel”. Production of fatty acid iso-propyl esters mainly based on acid process, but using of alkaline catalysts may give good yields also. Alkaline catalysts have some advantageous such as...
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Catalysis and petrochemistry| _version_ | 1872009018645413888 |
|---|---|
| author | Zubenko, S.O. Konovalov, S.V. Denysiuk, B.A. Patrylak, L.K. |
| author_facet | Zubenko, S.O. Konovalov, S.V. Denysiuk, B.A. Patrylak, L.K. |
| author_institution_txt_mv | [
{
"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., 02660 Kyiv"
},
{
"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., 02660 Kyiv."
},
{
"author": "B.A. Denysiuk",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine 1, Murmanska str., 02660 Kyiv"
},
{
"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., 02660 Kyiv"
}
] |
| author_sort | Zubenko, S.O. |
| baseUrl_str | https://kataliz.org.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2023-09-28T12:18:01Z |
| description | Fatty acid alkyl esters are widely used products. Most of them are used as renewable transport fuel named “biodiesel”. Production of fatty acid iso-propyl esters mainly based on acid process, but using of alkaline catalysts may give good yields also. Alkaline catalysts have some advantageous such as low corrosivity and higher reaction rate. In current work the effectivity of potassium hydroxide and treated potassium hydroxide solution as catalyst for transesterification was compared. It was shown that using of KOH solution in iso-propyl alcohol after special treatment gives almost twice higher yields (95-96 %) from refined sunflower oil triglycerides than over KOH under the same conditions. Yield of fatty acids iso-propyl esters from wasted frying oil stabilized after 1-1.5 hours of reaction over both catalysts. Using 1.8 and 2.0 % treated catalyst at 90 °C leads to yield of about 86-88 % at 9:1 alcohol-to-oil ratio. Reaction temperature has significant impact on a yield wich decreases with temperature reduce in the range from 30 to 90 °C. During reaction proceeding the alkali saponification and thus loss the catalytic activity, which displayed in stopping the yield rising. The lower yield of esters from wasted oil comparing to the refined oil may be caused by presence of heavy polymerized triglycerides components formed during frying. Such components cannot be fully converted into monoalkylesters and gives also the oligomerized esters, which is not visible in standard gas chromatographic analysis of biodiesel. Indirect confirmation of the presence of such compounds in wasted frying oil sample is the sufficiently larger mass of the cube residue in vacuum distillation. For refined oil amount of such residue was only 5.4 %, while for wasted oil it was three time higher (14.9 %). In case of wasted frying oil as raw stuff, even after full conversion and effective self-separation conventional purification methods (like water washing or dry washing with adsorbents) may not provide the necessary purity of resulted biodiesel due to the presence of heavy oligomeric admixtures. In such cases vacuum distillation should be included as necessary final purification stage. |
| doi_str_mv | 10.15407/kataliz2021.32.032 |
| first_indexed | 2026-03-12T15:50:10Z |
| format | Article |
| fulltext |
32 Каталіз та нафтохімія, 2021, №32
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
PACS 88.20.fk
https://doi.org/10.15407/kataliz2021.32.032
Alkaline synthesis of fatty acids iso-propyl esters
S.O. Zubenko*, S.V. Konovalov, B.A. Denysiuk, L.K. Patrylak
V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine
1, Murmanska str., 02660 Kyiv, Ukraine., e-mail: S.O.Zubenko@ukr.net
Fatty acid alkyl esters are widely used products. Most of them are used as renewable transport fuel named
“biodiesel”. Production of fatty acid iso-propyl esters mainly based on acid process but using of alkaline catalysts
may give good yields also. Alkaline catalysts have some advantageous such as low corrosivity and higher reaction
rate. In current work the effectivity of potassium hydroxide and treated potassium hydroxide solution as catalyst for
transesterification was compared. It was shown that using of KOH solution in iso-propyl alcohol after special
treatment gives almost twice higher yields (95-96 %) from refined sunflower oil triglycerides than over KOH under
the same conditions. Yield of fatty acids iso-propyl esters from wasted frying oil stabilized after 1-1.5 hours of
reaction over both catalysts. Using 1.8 and 2.0 % treated catalyst at 90 °C leads to yield of about 86-88 % at 9:1
alcohol-to-oil ratio. Reaction temperature has significant impact on a yield which decreases with temperature reduce
in the range from 30 to 90 °C. During reaction proceeding the alkali saponification and thus loss the catalytic
activity, which displayed in stopping the yield rising. The lower yield of esters from wasted oil comparing to the
refined oil may be caused by presence of heavy polymerized triglycerides components formed during frying. Such
components cannot be fully converted into monoalkylesters and gives also the oligomerized esters, which is not visible
in standard gas chromatographic analysis of biodiesel. Indirect confirmation of the presence of such compounds in
wasted frying oil sample is the sufficiently larger mass of the cube residue in vacuum distillation. For refined oil
amount of such residue was only 5.4%, while for wasted oil it was three time higher (14.9%). In case of wasted frying
oil as raw stuff, even after full conversion and effective self-separation conventional purification methods (like water
washing or dry washing with adsorbents) may not provide the necessary purity of resulted biodiesel due to the
presence of heavy oligomeric admixtures. In such cases vacuum distillation should be included as necessary final
purification stage.
Keywords: iso-propyl alcohol, alkaline catalyst, wasted frying oil, transesterification
______________________________________________________________________________________________________
Introduction
Fatty acid alkyl esters are widely used products.
Most of them are used as renewable transport fuel
named “biodiesel”. Biodiesel manufacturing is mainly
based on methanol, utilizing as reagent both in the
triglycerides transesterification and fatty acids
esterification processes. This is due to its lowest price
among the monohydric alcohols, as well as its high
efficiency in this reaction. But methanol using has also
some disadvantageous. First of all, these are high
methanol toxicity and impossibility of “winter
biodiesel” obtaining without using of specific
additives, enhancing methyl esters cold flow
properties. All another aliphatic monohydric alcohols
have much lower toxicity and better low temperature
properties of their fatty acid esters.
Iso-propyl alcohol has good perspectives as
transesterification reagent. First of all, it is widely used
large-scale product of basic organic synthesis, having
relatively low price. It is also known from literature
sources, that fatty acid iso-propyl esters are
characterized by better cold flow properties then
methyl and ethyl esters, obtained from the same raw
materials [1-7].
Effective transesterification of triglycerides by
iso-propyl alcohol, resulting in high conversion of raw
stuff and high yield of iso-propyl esters, is possible in
case of reaction catalysis by strong mineral acids [2, 3,
8]. Alkaline-catalyzed transesterification by iso-propyl
alcohol is strongly influenced by reaction parameters:
temperature, catalyst concentration, molar ratio of
alcohol-to-oil (RAO) and time of reaction. Because of
this, different authors reported different results even at
the same catalyst – KOH. So, authors [9] did not
obtain iso-propyl esters at 25 °C, 1% of catalyst load,
RAO = 6 after 1 hour of reaction. Carrying out
transesterification at higher temperature (45 °C, 0.5%
KOH, RAO = 6, 0.5 hour) resulted in 43 % yield of iso-
propyl esters, while further increasing the temperature
to 60 °C enhanced the yield to about 80% both at 0.5%
and 1.0% KOH and unchanged another reaction
conditions [10]. Under close reaction conditions
(50 °C, 0.5% KOH, RAO = 6:1, 0.5 hour) another
authors achieved 86% yield of iso-propyl esters [11],
however it was not observed any separation of glycerol
layer. Authors [8] failed in preparing iso-propanol-
based biodiesel via alkaline catalysis over KOH even
under unacceptable harsh reaction conditions (77 °C,
mailto:S.O.Zubenko@ukr.net
Каталіз та нафтохімія, 2021, №32 33
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
1.5% KOH, RAO = 70, 48 h) and preferred to carry out
acid-catalyzed process over H2SO4. Low reactivity of
iso-propyl alcohol was attributed to its branched
structure. As generally known, the branched
monohydric alcohols are characterized by far lower
acid strength, than linear once. Namely iso-propanol
has almost two-magnitude weaker acid strength, than
methanol [12]. When catalyzing transesterification
with hydroxides, weaker acidity of the alcohol strongly
suppresses the formation of alkoxide-anion, which acts
as real catalyst in this process. In case of iso-propanol,
its concentration would be very low comparing with
methanol-based process. Another difference from
methanolysis consists in better miscibility of
triglycerides with iso-propanol, which is favorable for
saponification, resulting in catalyst loss. From our
point of view, the difference in results with KOH as
catalyst is first of all due to the inequality of the
hydroxide reagents used in terms of water content. It is
widely known, that KOH reagents may contain about
15% of water. For example, in work [13] 16%
moisture content was revealed in high-pure KOH.
Higher water content during transesterification both
decrease the alkoxide concentration and increase the
saponification rate. Direct utilization of alkoxides
reagents is able to provide the very high concentration
of iso-propoxide anions in reaction media, which is
necessary for the effective transesterification. Earlier it
was described the using of potassium and sodium iso-
propoxides [7]. The former was the commercially
purchased substance, while the later was obtained by
reaction of iso-propanol with metallic Na, which is
non-option on the large production scale. The fullness
of feed-stock conversion was controlled my measuring
total glycerol content in reaction products after
washing. Best results (0.04% total glycerol content)
were obtained in reflux condition at RAO = 20:1 over
potassium iso-propoxide (1.34% in terms of K, or
1.9% in terms of KOH relative to oil mass) after 8
hours of reaction. Utilization of 1-1.5% Na under the
same conditions provided higher total glycerol content
– 0.18-0.34%. Decreasing the alcohol-to-oil ratio (RAO
= 10 or RAO = 6) provided closer result at 1.25% Na
load, but in case of potassium iso-propoxide
conversion was substantially lower (total glycerol
content 0.64-0.70%). However, no phase separation
was observed under any reaction conditions over both
catalysts.
Regardless of relatively lower yields of iso-
propyl esters, than in case of acid catalysis, alkaline-
catalyzed route has some advantageous such as low
corrosivity and high reaction rate. So, we decide to
develop the method of preparing the alkaline catalyst,
which will be free from some disadvantageous, having
alkaline metal hydroxides. Also, we used the really
valuable from practical point of view source of
triglycerides such as wasted frying oil, instead of high-
expensive fresh vegetable oils.
Materials and methods
Chemicals
Oil raw stuff included commercial refined
sunflower oil (Ukraine; acid value 0.07 mg KOH/g and
0.03% of water and fatty acids composition: C16:0 –
6.7%, C18:0 – 2.8%, C18:1 – 33.0%, C18:2 – 54.6%,
others – 2.9%) and wasted frying sunflower oil
(Ukraine: 0.86 mg KOH/g and 0.03% of water and
fatty acids composition: C16:0 – 8.8%, C18:0 – 4.1%,
C18:1 – 35.1%, C18:2 – 47.6%, others – 4.4%).
Another chemicals, used in current study, were the
following: analytical grade KOH (China, 83% KOH;
as catalyst of refined oil transesterification); technical
grade KOH (China, 84% KOH; as catalyst of wasted
oil transesterification); chemical grade iso-propyl
alcohol (Russian Federation); 0.1 N HCl water solution
(prepared from fixanales); indicators bromophenol
blue and phenolphthalein; reagent-grade methyl
palmitate (>97%); reagent-grade n-hexane; synthetic
molecular sieves KA-Y/3A (Russian Federation,
dynamic water vapor capacity – 150 mg/cm3);
technical grade anhydrous calcium chloride.
Experimental
Preparation of catalytic solution
Solution of alkaline catalyst based on KOH and
iso-propyl alcohol (SMC – self-made catalyst) was
prepared by analogous to the method of the
hydroxide/ethanol based alkaline catalyst preparation,
described in patent [14]. Procedure consisted in boiling
of the KOH solution in iso-propanol and selective
dehydration of alcohol water azeotrope, condensed
over the bed of KA-Y/3A molecular sieves in Soxhlet
extractor. Dried iso-propanol was returned into the
alkali solution. The boiling-condensation-drying
sequence was repeated for several times.
Comparison of hydroxide and prepared alkaline
solution
In these series of experiments KOH, previously
dissolved in dried with molecular sieves iso-propyl
alcohol, was used as catalyst. Also, SMC, obtained as
above mentioned from KOH iso-propanol solution,
was utilized. Investigations were carried out using
refined sunflower oil with specified content of
triglycerides about 99.9%. For each synthesis 2%
KOH load (hereinafter catalyst load expressed relative
to mass of oil) was used. Contents of alkali in reagent
(KOH), measured by titration, was about 83%, catalyst
amount is expressed in terms of 100-% КОН. In each
synthesis 100 g of oil was used. In order to compare
the efficiency of the catalysts, the same load of SMC
in equivalent of reagent KOH was used (1.66 %eq. KOH).
RAO ratio was in range of 6-15 mol/mol. Syntheses
were carried out in 500 cm3 round-bottom flask,
34 Каталіз та нафтохімія, 2021, №32
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
equipped with reflux condenser and water trap tube
(filled with CaCl2) in reflux conditions (bath
temperature 120-125 °C) for 2 hours. Heating of the
mixture was provided with oil bath, placed on electric
stove.
Influence of catalyst concentration and reaction
temperature
In this series of experiments only SMC alkaline
catalytic solution was used. It was prepared from KOH
and iso-propyl alcohol. Investigations were carried out
utilizing used frying sunflower oil. Marked
concentration of alkaline catalyst was calculated in
equivalent of KOH (%eq. KOH). Syntheses were carried
out in 250 cm3 two-neck heart-like flask, equipped
with thermometer, reflux condenser and water trap
tube (filled with CaCl2), reaction mixture was stirred
by magnetic stirrer. In each synthesis 70 g of oil was
used. Heating of mixture was provided with oil bath,
placed on the magnetic stirrer. Sampling was carried
out each 0.5 hour, beginning sample was taken
immediately after immersion of the flask into hot oil
bath.
Enlarged synthesis of fatty acid iso-propyl esters
In this process was used SMC alkaline catalytic
solution and wasted frying oil sample. Synthesis was
carried out under next conditions: 2%eq. KOH to oil,
RAO = 9, reaction time – 2 hours, loading of oil –
250 g, bath temperature – water trap tube (filled with
CaCl2) under reflux conditions. Heating of mixture
was provided with oil bath, placed on electric stove.
Analysis
Determination of iso-propyl esters yield
The yield of the iso-propyl esters during and
after syntheses was estimated from the decrease of the
iso-propyl alcohol content in reaction products,
measured by the mass loss of the sample due to
evaporation at room temperature. The sample (5-10 g)
was placed into the open Petri dish and periodically
weighted until the stable mass achievement. All the
mass losses were regarded as evaporated alcohol due
to high boiling temperature of all another reaction
components. Then the theoretically possible mass of
iso-propyl esters, which can be formed from the
alcohol consumed in reaction, was calculated.
In particular case (enlarged synthesis after chose
the reaction parameters), yield of the iso-propyl esters
after finishing synthesis was also calculated from their
known concentrations in reaction products. The latter
was measured by gas chromatographic analysis, using
modified method based on European standard method
of determination of methyl esters in biodiesel
EN14103. When analyzing fatty acid iso-propyl esters
far more affordable methyl palmitate may be used as
internal standard instead of expensive methyl
heptadecanoate. Samples and standard were dissolved
in n-hexane. Analyses were performed on the gas
chromatograph Agilent 7890A Series, equipped with
split/splitless inlet, flame-ionization detector and
Agilent J&W HP-5 capillary column ((5% phenyl)-
methyl polysiloxane, 30 m length, 0.32 mm internal
diameter, 0.25 µm film thickness); high-purity helium
was used as carrier gas. Conditions of analyses were
the following: inlet temperature 250 °C, inlet excess
pressure 82.7 kPa, split ratio 36:1, chromatographic
column oven temperature program 210 °C/27 min –
5 °C/min up to 320 °C, detector temperature 250 °C.
The yield of fatty acid iso-propyl esters was calculated
as the ratio of their total mass in reaction products to
mass, which could be formed when triglycerides fully
convert to esters. After subtraction of free fatty acids,
oil was regarded as pure triglycerides having average
molar mass, calculated from known oil fatty acid
composition.
Estimation of heavy residue in samples of oil
Residue of heavy polymerized compounds in
oils samples, which could not be converted into
compounds, visible in gas chromatographic analyses
was determined by complicated method of successive
treatment of oil samples. It included saponification of
the oil, acid hydrolysis of formed soaps, washing,
drying and vacuum distillation of obtained fatty acids
as described in detail in earlier work [15].
Titration of the reaction products
Alkaline catalyst and soap content in the
reaction products were determined by two-step acid-
base titration method as described in [16]. Alkali was
determined in a first titration step, using HCl 0.1 N
solution as reactant, 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.
Results and Discussions
After transesterification of refined sunflower oil
both over KOH and SMC solutions one-phase clear
mixtures of reaction products, showing no tends for
phase separation, were formed. Yield of fatty acids iso-
propyl esters over KOH appeared to be not higher,
than 53% at highest excess of alcohol used (Fig. 1,
yield values, estimated from the alcohol content
decrease, are given). Using of SMC was remarkably
more efficient and resulted in yield of about 92% at
RAO = 6 and about 95-96% at higher excess of iso-
propanol.
For further investigation of transesterification of
wasted oil sample over SMC reagents ratio RAO = 9,
which was the lowest among that providing enough
high fullness of refined oil transformation (see Fig. 1),
was chosen. Yield of iso-propyl esters stabilized after
1-1.5 hours of reaction at 90 ºC (Fig. 2, yield values,
estimated from the alcohol content decrease, are
given).
.
Каталіз та нафтохімія, 2021, №32 35
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
Fig. 1. Yield of iso-propyl esters in refined sunflower oil transesterification over KOH and SMC
(reflux – 90 ºC, 2 h, 2% KOH or 1.66%eq. KOH SMC).
0
20
40
60
80
100
0 1 2 3
is
o
-p
ro
p
yl
e
st
er
s
yi
el
d
.
%
Reaction time. h
1
2 3
Fig. 2. Changing of iso-propyl esters yield in course of wasted sunflower oil transesterification using different load
(1 – 2.0, 2 – 1.8, 3 – 1.6%eq. KOH) of SMC (90 ºC, RAO = 9).
Using of 1.8 and 2.0%eq.KOH catalyst load
provided almost the same yield of esters about 86-
88%, while decreasing of the catalyst load to 1.6%eq.
KOH resulted in reducing the yield by about 15%.
Further attempts to gradually decrease the
reaction temperature under the unchanged other
conditions (SMC load – 2%eq. KOH, RAO = 9) in order to
provide more environmental friendly energy-saving
process resulted in regular decreasing of the iso-propyl
esters yield (Fig. 3, yield values, estimated from the
alcohol content decrease, are given). It is interesting to
mentioned, that the temperature impact on the alkaline
iso-propanolysis appeared to be totally different from
that observed in our previous studies for butanolysis
using the similar approaches for the alkaline catalytic
solution preparing [17, 18]. Namely, alkaline-synthesis
of n-butyl esters proceeds very fast even at 15 ºC and,
moreover, carrying out reaction without heating
provides the effective phase self-separation. Another
synthesis with larger mass of oil loaded was carried
out under reaction conditions, which was chosen as
most efficient on the base of discussed results (2%eq
KOH SMC, reflux, 2 hours, RAO – 9:1). In these cases
iso-propyl esters yield was determined both from the
alcohol losses due to evaporation and from the results
of gas chromatographic analysis.
Both values were enough close – 72 and 74%
respectively. However, these values are some lower,
than achieved in smaller synthesis (see Fig. 2 and
Fig. 3). Probably, this is due to faster saponification
under reflux conditions than during mechanical stirring
at close temperature.
36 Каталіз та нафтохімія, 2021, №32
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
Fig. 3. Changing of iso-propyl esters yield in course of wasted sunflower oil transesterification over SMC at
different reaction temperatures: 1 – 90, 2 – 70, 3 – 50, 4 – 30 °C (2%eq. KOH, RAO = 9).
It should be emphasized, that titration of
reaction mixture after 2 hours of synthesis revealed the
absence of the alkaline catalyst due its full
saponification. Only saponified alkali was determined
via titration with bromophenol blue (concentration of
soaps – more than 10% in whole mixture). This may
explain stopping rising of esters yield at some stable
level before reaching full conversion of the oil or
reaction equilibrium (see Fig. 2 and Fig. 3).
There arise the question concerning the reasons
of the higher catalytic efficiency of SMC comparing
with ordinary KOH, dissolved in iso-propyl alcohol.
The answer is first of all the difference in water
content in the alkaline catalytic solution, and thus in
reaction medium during the process. In homogeneous
alkaline catalysis of transesterification water content is
known to be a critical factor [19-22]. Water leads to
secondary hydrolysis and saponification reactions
which cause a drop in yield and consume part of the
catalyst. Although there are no official specifications,
one can be met information about maximum water
content in the reaction medium about 0.1% for
biodiesel applications [19]. In case of trans-
esterification with branched alcohols, such as iso-
propanol, the water content influence may be even
more critical.
The preparing procedure of SMC consisted in
selective water removal from initial KOH alcohol
solution. The main source of the water was the
potassium hydroxide reagents, containing only 83-84%
of KOH (water was the main admixture). Some water
also where present in the iso-propanol. The removing
of this water leads to the shift of the equilibrium of
alcohol reaction with alkali towards the alkoxide
formation:
(1)
Also, additional water, formed in reaction (1)
may be removed as process goes on. This may result in
further growth of the alkoxide content. As was already
mentioned, the alkoxide is the real active catalytic
specie in alkaline transesterification. As generally
known, alkoxide-anions play a role of nucleophile
particles attacked the carbonyl groups of glycerides on
each of three successive stages of triglycerides
transesterification [23]. The water impact on the
equilibrium (1) should be far more pronounced, than in
case of methanol with alkali reaction due to difference
in acid strength between branched and linear alcohols.
Thus, it may be assumed, that in case ordinary
KOH solution the alkali was consumed in sapo-
nification reactions before the target transesterification
had time to pass sufficiently. In case of SMC both
higher saponification reaction rate in presence of water
and lower transesterification reaction rate (during to
the lower alkoxide-anions content) may be assumed.
As result, the higher yield of iso-propyl esters may be
achieved before the moment of total loss of alkaline
catalyst due to soaps formation.
As for the lower yield of esters from wasted oil
comparing to the refined oil, this is may be due to
presence of heavy polymerized triglycerides
components formed during frying [24, 25]. Such
components cannot be fully converted into monoalkyl
esters and gives also the oligomerized esters, which is
not visible in standard gas chromatographic analysis of
biodiesel. Indirect confirmation of the presence of such
compounds in wasted frying oil sample, used in
current study, is the sufficiently larger mass of the
cube residue in vacuum distillation of fatty acids,
Каталіз та нафтохімія, 2021, №32 37
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
obtained from oil samples. In case of refined oil
amount of such residue was only 5.4%, while in case
of wasted oil it was three times higher (14.9%).
Cleaning of reaction products to obtain
biodiesel-grade iso-propyl esters from resulting
mixture will be complicated problem till glycerol self-
separation achieved. However, in case of wasted frying
oil as raw-stuff, even after full conversion and
effective self-separation conventional purification
methods (like water washing or dry washing with
adsorbents) may not provide the necessary purity of
resulted biodiesel due to the presence of heavy
oligomeric admixtures. In such cases vacuum
distillation should be included as necessary final
purification stage.
Conclusions
Obtained results showed that KOH solution in
iso-propyl alcohol after special treatment (SMC) gives
almost twice higher yield of esters from refined
sunflower oil triglycerides than at KOH under same
conditions. Using both 1.8 and 2.0%eq. KOH amount of
SMC gives same highest yield (about 86-88%) of iso-
propyl esters from wasted frying oil. Enough high
yields iso-propyl esters yield is achieved only at
maximum reaction temperature (90 °C), which is
possible to maintain in unpressurized conditions. It
was also shown, that stopping of yield rising during
iso-propanolysis is due to full alkali saponification, but
not due to achievement of reaction equilibrium.
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Надійшла до редакції 11.11.2021 р.
Каталіз та нафтохімія, 2021, №32 39
ISSN 2707-5796. Kataliz ta naftohimia. 2021, 32
Лужний синтез ізопропілових естерів жирних кислот
С.О. Зубенко*, С.В., Коновалов, Б.А. Денисюк, Л.К. Патриляк
Інститут біоорганічної хімії та нафтохімії ім. В.П. Кухаря НАН України,
Україна, 02660 Київ, вул. Мурманська, 1. e-mail: S.O.Zubenko@ukr.net
Алкілестери жирних кислот є широко використовуваними продуктами. Більшість із них застосовують як
відновлюване паливо для транспорту, яке називають «біодизелем». Виробництво ізопропілових естерів
жирних кислот в основному базується на кислотному процесі, але з використанням лужних каталізаторів
також можна отримати хороші виходи. Лужні каталізатори мають деякі переваги, такі як низька корозійна
активність та вища швидкість реакції. У даній роботі було порівняно ефективність гідроксиду калію та
додатково обробленого розчину гідроксиду калію як каталізаторів переестерифікації. Показано, що розчин
KOH в ізопропіловому спирті після спеціальної обробки сприяє одержанню майже вдвічі вищого виходу (95-
96%) естерів з тригліцеридів рафінованої соняшникової олії, ніж на KOH за тих же умов. Вихід ізопропілових
естерів жирних кислот з відпрацьованої олії після фритюру стабілізується через 1-1,5 години реакції на обох
каталізаторах. З використанням 1,8 і 2,0% обробленого каталізатора за 90°C було одержано виходи близько
86-88 % за співвідношення спирту до олії 9:1. Встановлено, що температура реакції має суттєвий вплив на
вихід, який спадає із пониженням температури від 30 до 90 °C. Впродовж реакції луг омилюється і втрачає
каталітичну активність, що проявляється у зупинці зростання виходу. Нижчий вихід естерів з відпрацьованої
олії порівняно з рафінованою олією може бути спричинений присутністю важких полімеризованих
компонентів тригліцеридів, які формуються впродовж смаження. Такі компоненти не можуть бути повністю
перетворені в моноалкілестери та утворюють олігомеризовані естери, які не фіксуються при стандартному
газохроматографічному аналізі біодизелю. Непрямим підтвердженням присутності таких сполук у зразку
відпрацьованої олії після фритюру є значно більша маса кубового залишку, одержаного при вакуумній
перегонці. Для рафінованої олії кількість такого залишку становила лише 5,4%, а для фритюрної втричі
більше – 14,9%. У разі використання як сировини фритюрної олії навіть за повного перетворення та
ефективного саморозділення загальноприйняті методи очищення (промивання водою або сухе очищення із
застосуванням адсорбентів) можуть не забезпечити необхідної чистоти отриманого біодизеля через наявність
важких олігомерних домішок. У таких випадках необхідною кінцевою стадією очищення має бути вакуумна
перегонка.
Ключові слова: ізопропіловий спирт, лужний каталізатор, використана олія після смаження,
переестерифікація
|
| id | oai:katalizorgua:article-60 |
| 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/88/1a0ab3c90ed91967648a9313f3d0c688.pdf |
| spelling | oai:katalizorgua:article-602023-09-28T12:18:01Z Alkaline synthesis of fatty acids iso-propyl esters Лужний синтез ізопропілових естерів жирних кислот Zubenko, S.O. Konovalov, S.V. Denysiuk, B.A. Patrylak, L.K. iso-propyl alcohol alkaline catalyst wasted frying oil transesterification ізопропіловий спирт лужний каталізатор використана олія після смаження переестерифікація Fatty acid alkyl esters are widely used products. Most of them are used as renewable transport fuel named “biodiesel”. Production of fatty acid iso-propyl esters mainly based on acid process, but using of alkaline catalysts may give good yields also. Alkaline catalysts have some advantageous such as low corrosivity and higher reaction rate. In current work the effectivity of potassium hydroxide and treated potassium hydroxide solution as catalyst for transesterification was compared. It was shown that using of KOH solution in iso-propyl alcohol after special treatment gives almost twice higher yields (95-96 %) from refined sunflower oil triglycerides than over KOH under the same conditions. Yield of fatty acids iso-propyl esters from wasted frying oil stabilized after 1-1.5 hours of reaction over both catalysts. Using 1.8 and 2.0 % treated catalyst at 90 °C leads to yield of about 86-88 % at 9:1 alcohol-to-oil ratio. Reaction temperature has significant impact on a yield wich decreases with temperature reduce in the range from 30 to 90 °C. During reaction proceeding the alkali saponification and thus loss the catalytic activity, which displayed in stopping the yield rising. The lower yield of esters from wasted oil comparing to the refined oil may be caused by presence of heavy polymerized triglycerides components formed during frying. Such components cannot be fully converted into monoalkylesters and gives also the oligomerized esters, which is not visible in standard gas chromatographic analysis of biodiesel. Indirect confirmation of the presence of such compounds in wasted frying oil sample is the sufficiently larger mass of the cube residue in vacuum distillation. For refined oil amount of such residue was only 5.4 %, while for wasted oil it was three time higher (14.9 %). In case of wasted frying oil as raw stuff, even after full conversion and effective self-separation conventional purification methods (like water washing or dry washing with adsorbents) may not provide the necessary purity of resulted biodiesel due to the presence of heavy oligomeric admixtures. In such cases vacuum distillation should be included as necessary final purification stage. Алкілестери жирних кислот є широко використовуваними продуктами. Більшість із них застосовують як відновлюване паливо для транспорту, яке називають «біодизелем». Виробництво ізопропілових естерів жирних кислот в основному базується на кислотному процесі, але з використанням лужних каталізаторів також можна отримати хороші виходи. Лужні каталізатори мають деякі переваги, такі як низька корозійна активність та вища швидкість реакції. У даній роботі було порівняно ефективність гідроксиду калію та додатково обробленого розчину гідроксиду калію як каталізаторів переестерифікації. Показано, що розчин KOH в ізопропіловому спирті після спеціальної обробки сприяє одержанню майже вдвічі вищого виходу (95-96 %) естерів з тригліцеридів рафінованої соняшникової олії, ніж на KOH за тих же умов. Вихід ізопропілових естерів жирних кислот з відпрацьованої олії після фритюру стабілізується через 1-1,5 години реакції на обох каталізаторах. З використанням 1,8 і 2,0 % обробленого каталізатора за 90°C було одержано виходи близько 86-88 % за співвідношення спирту до олії 9:1. Встановлено, що температура реакції має суттєвий вплив на вихід, який спадає із пониженням температури від 30 до 90 °C. Впродовж реакції луг омилюється і втрачає каталітичну активність, що проявляється у зупинці зростання виходу. Нижчий вихід естерів з відпрацьованої олії порівняно з рафінованою олією може бути спричинений присутністю важких полімеризованих компонентів тригліцеридів, які формуються впродовж смаження. Такі компоненти не можуть бути повністю перетворені в моноалкілестери та утворюють олігомеризовані естери, які не фіксуються при стандартному газохроматографічному аналізі біодизелю. Непрямим підтвердженням присутності таких сполук у зразку відпрацьованої олії після фритюру є значно більша маса кубового залишку, одержаного при вакуумній перегонці. Для рафінованої олії кількість такого залишку становила лише 5,4 %, а для фритюрної втричі більше – 14,9 %. У разі використання як сировини фритюрної олії навіть за повного перетворення та ефективного саморозділення загальноприйняті методи очищення (промивання водою або сухе очищення із застосуванням адсорбентів) можуть не забезпечити необхідної чистоти отриманого біодизеля через наявність важких олігомерних домішок. У таких випадках необхідною кінцевою стадією очищення має бути вакуумна перегонка. 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/60 10.15407/kataliz2021.32.032 Catalysis and petrochemistry; No. 32 (2021): Catalysis and petrochemistry; 32-39 Каталіз та нафтохімія; № 32 (2021): Каталіз та нафтохімія; 32-39 2707-5796 2412-4176 10.15407/kataliz2021.32 en https://kataliz.org.ua/index.php/journal/article/view/60/50 Copyright (c) 2021 Catalysis and petrochemistry |
| spellingShingle | ізопропіловий спирт лужний каталізатор використана олія після смаження переестерифікація Zubenko, S.O. Konovalov, S.V. Denysiuk, B.A. Patrylak, L.K. Лужний синтез ізопропілових естерів жирних кислот |
| title | Лужний синтез ізопропілових естерів жирних кислот |
| title_alt | Alkaline synthesis of fatty acids iso-propyl esters |
| title_full | Лужний синтез ізопропілових естерів жирних кислот |
| title_fullStr | Лужний синтез ізопропілових естерів жирних кислот |
| title_full_unstemmed | Лужний синтез ізопропілових естерів жирних кислот |
| title_short | Лужний синтез ізопропілових естерів жирних кислот |
| title_sort | лужний синтез ізопропілових естерів жирних кислот |
| topic | ізопропіловий спирт лужний каталізатор використана олія після смаження переестерифікація |
| topic_facet | iso-propyl alcohol alkaline catalyst wasted frying oil transesterification ізопропіловий спирт лужний каталізатор використана олія після смаження переестерифікація |
| url | https://kataliz.org.ua/index.php/journal/article/view/60 |
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