Soybean oil-based monoacylglycerol synthesis using bio-compatible amino acid ionic liquid as a catalyst at low temperature

Article abstract of DOI:10.1016/j.molliq.2021.117231

Monoacylglycerol (MAG) from edible oil is one kind of green and safe food additive. This project mainly focused on a nontoxic and biodegradable catalyst, amino acid-based ionic liquids (AAILs), for the glycerolysis of soybean oil triacylglycerol (TAG) to prepare MAG at low temperature. Seven AAILs, from arginine, lysine, histidine, tryptophan, or glutamic acid and choline hydroxide, tetramethylhydroxide ammonium, or tetrabutylammonium hydroxide, were successfully synthesized in this work. The effects of substrate ratio, AAIL load, temperature, and reaction time on AAIL-catalyzed the glycerolysis of soybean oil were evaluated. Moreover, the activation energy of MAG formation was explored and reaction mechanism was also proposed. Finally, reaction conditions were optimized by response surface methodology. Results showed that, among all tested AAILs, [TMA][Arg] prepared by arginine (Arg) and tetramethylhydroxide ammonium (TMAOH) showed the outstanding catalytic performance for the glycerolysis of soybean oil. The maximum MAG yield (64.89 ± 1.26%) and TAG conversion (86.31 ± 1.68%) were achieved under the optimized conditions: 105 °C, 0.5 h, [TMA][Arg] load 10%, and substrate molar ratio 1:2 (soybean oil/glycerol). Moreover, the activation energies of MAG formation and TAG conversion were 44.22 kJ/mol and 37.58 kJ/mol, respectively.

Full text of DOI:10.1016/j.molliq.2021.117231

Journal of Molecular Liquids 340 (2021) 117231
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Soybean oil-based monoacylglycerol synthesis using bio-compatible
amino acid ionic liquid as a catalyst at low temperature
⇑
Shangde Sun , Yaping Lv, Gaoshang Wang, Xiaowei Chen
Lipid Technology and Engineering, School of Food Science and Engineering, Henan University of Technology, Lianhua Road 100, Zhengzhou 450001, Henan Province, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Monoacylglycerol (MAG) from edible oil is one kind of green and safe food additive. This project mainly
focused on a nontoxic and biodegradable catalyst, amino acid-based ionic liquids (AAILs), for the glycerol-
ysis of soybean oil triacylglycerol (TAG) to prepare MAG at low temperature. Seven AAILs, from arginine,
lysine, histidine, tryptophan, or glutamic acid and choline hydroxide, tetramethylhydroxide ammonium,
or tetrabutylammonium hydroxide, were successfully synthesized in this work. The effects of substrate
ratio, AAIL load, temperature, and reaction time on AAIL-catalyzed the glycerolysis of soybean oil were
evaluated. Moreover, the activation energy of MAG formation was explored and reaction mechanism
was also proposed. Finally, reaction conditions were optimized by response surface methodology.
Results showed that, among all tested AAILs, [TMA][Arg] prepared by arginine (Arg) and tetramethylhy-
droxide ammonium (TMAOH) showed the outstanding catalytic performance for the glycerolysis of soy-
bean oil. The maximum MAG yield (64.89 1.26%) and TAG conversion (86.31 1.68%) were achieved
under the optimized conditions: 105 °C, 0.5 h, [TMA][Arg] load 10%, and substrate molar ratio 1:2 (soy-
bean oil/glycerol). Moreover, the activation energies of MAG formation and TAG conversion were
44.22 kJ/mol and 37.58 kJ/mol, respectively.
Received 11 July 2021
Revised 3 August 2021
Accepted 8 August 2021
Available online 11 August 2021
Keywords:
Monoacylglycerol
Soybean oil
Glycerolysis
Amino acid-based ionic liquid
[TMA][Arg]
Response surface methodology
Ó 2021 Elsevier B.V. All rights reserved.
1. Introduction
Recently, inorganic alkali metal hydroxides or oxides (e.g., KOH
or CaO), bio-enzyme [13,14], or ionic liquids (ILs) [15] have been
Monoacylglycerol (MAG), popular in food, pharmaceutical, and
cosmetic industries, is a safe food additive [1,2]. In food industry,
MAG is commonly used as an emulsifier [3], which thanks to its’
excellent emulsifying properties. For instance, adding MAG into
dairy products and beverages can prevent the sinking of protein
and the floating of oil, and maintain the stability of the product.
However, the content of MAG in nature is low (<5% in edible oil).
To meet the abundant applications and large demands in industry,
MAG is usually obtained by the esterification of fatty acids with
glycerol [4,5], and hydrolysis [6,7] or alcoholysis [8–10] of fats
and oils. With the high value-added utilization of glycerol and
atom effective utilization, MAG synthesis by the glycerolysis of tri-
acylglycerol (TAG) has drawn great attention [11,12].
used as catalysts for MAG synthesis by the glycerolysis of TAG.
Unsatisfactorily, high temperature (e.g., 260 °C) was usually
employed during the alkaline-catalyzed glycerolysis, which
resulted in more energy requirement, undesired odor and taste for-
mation, soap formation, and separation and purification difficulty
[16]. In order to overcome these issues, enzymes have been suc-
cessfully used in glycerolysis process [14]. However, high cost of
enzyme and great mass transfer issues limited their applications
in industry [17]. Compared with the traditional catalysts, the appli-
cations of ionic liquids as catalysts in chemical synthesis have been
attracted more attention in recent years.
Ionic liquids (ILs) consisting entirely of ions are molten salts at
room temperature [18]. Featured by favorable physicochemical
properties, such as non-volatility, good thermal stability, low melt-
ing temperature, and high decomposition temperature, ILs have
been successfully used in some reactions as solvents and promising
catalysts [19–21]. For example, a MAG yield of ~69% can be
obtained by the glycerolysis of soybean oil in the presence of 1-
Butyl-3-methylimidazolium imidazolide ([Bmim]Im) at 200 °C
[16]. However, ILs containing aromatic cations, such as
imidazolium- and pyridinium-based ILs, have the disadvantages
Abbreviations: AAILs, amino acid-based ionic liquids; MAG, monoacylglycerol;
DAG, diacylglycerol; TAG, triacylglycerol; GC, gas chromatography; [Ch][OH],
choline hydroxide; [TBA][OH], tetrabutylammonium hydroxide 30-hydrate;
[TMA][OH], tetramethylammonium hydroxide pentahydrate.
⇑
Corresponding author.
E-mail address: shangdesun@haut.edu.cn (S. Sun).
https://doi.org/10.1016/j.molliq.2021.117231
0167-7322/Ó 2021 Elsevier B.V. All rights reserved.

S. Sun, Y. Lv, G. Wang et al.
Journal of Molecular Liquids 340 (2021) 117231
of expensive cost, complex preparation, toxicity, and non-
biodegradable [22–24]. Therefore, the development of the nontox-
ic, biodegradable and simple preparation IL has been very popular.
Compared with these catalysts, amino acid-based ionic liquids
(AAILs), composed of renewable biomaterial amino acid, have the
merits of simple preparation, nontoxic, and biodegradable
[25,26], which have evoked considerable interest as an efficient
catalyst [23,27] or green solvent [28]. AAILs have been used to pre-
pare biodiesel and showed the best performance for the transester-
ification [27]. However, no information about AAIL as a catalyst for
the glycerolysis of edible oil to prepare food additive MAG was
available.
mixture (0.10 mL) was withdrawn from glycerolysis system peri-
odically for gas chromatography (GC) analysis.
2.4. Determination of acylglycerides by GC.
According to the previous reported method [14], sample analy-
sis was performed by GC (Agilent 7890B, USA). Standards (monoo-
lein, 1,3-diolein, and triolein) were used for the quantification of
the products. Gas chromatography of TAG, DAG, and MAG was
shown in Fig. S1.
The calculations for TAG conversion and MAG yield were as
follows:
The main purpose of this work is to develop an eco-friendly
catalyst-AAIL with high catalytic activity at low temperature to
prepare soybean oil-based MAG by glycerolysis. First, seven AAILs
were synthesized by a two-step strategy. The effect of AAIL struc-
ture on the glycerolysis of soybean oil TAG was evaluated. The
effects of reaction parameters (temperature, substrate ratio, and
AAIL load) on the glycerolysis were investigated and optimized
by the response surface methodology (RSM). Furthermore, reaction
mechanism of the glycerolysis was also proposed.
nMAG þ 2 ꢀ ðnDAG ꢁ nDAG
Þ
0
TAG con
v
ersion ð%Þ ¼
ꢀ 100
ð1Þ
ð2Þ
3 ꢀ nTAG þ 2 ꢀ nDAGþnMAG
nMAG
MAG yield ð%Þ ¼
ꢀ 100
3 ꢀ nTAG þ 2 ꢀ nDAGþnMAG
where nTAG, nDAG, and nMAG are the molar contents of TAG, diacyl-
glycerol (DAG), and MAG, respectively; nDAG is the initial DAG con-
0
tent of the glycerolysis system.
2. Material and methods
2.5. Response surface design
2.1. Materials
Design expert 10.0 software was used to perform the response
surface design and analysis. According to the principle of Box-
Behnken design and the results of single factor experiments, one
RSM design with three factors and three levels was used. MAG
yield (Y1) was selected as the response. The interaction effect of
reaction temperature (A), substrate molar ratio (B), and [TMA]
[Arg] loading (C) on the glycerolysis was explored, and the glyc-
erolysis conditions were optimized.
Refined soybean oil was purchased from a local supermarket.
Physicochemical properties and the fatty acid composition of soy-
bean oil were shown in Tables S1 and S2. Glycerol (G) was from
Tianjin Kermel Chemical Reagent Co. Ltd. (Tianjin, China). Choline
hydroxide ([Ch][OH]), tetrabutylammonium hydroxide 30-
hydrate ([TBA][OH]), and tetramethylammonium hydroxide pen-
tahydrate ([TMA][OH]) were obtained from Sigma-Aldrich (St.
Louis, MO., USA). Arginine (Arg), lysine (Lys), histidine (His), tryp-
tophan (Try), and glutamic acid (Glu) were from Shanghai Macklin
Biochemical Co. Ltd. (Shanghai, China). For GC analysis, standard
glyceryl monooleate, 1,3-diolein, and glyceryl trioleate were also
purchased from Sigma-Aldrich (St. Louis, MO., USA).
3. Results and discussion
3.1. Effect of different AAILs on the glycerolysis of soybean oil
Seven AAILs ([CH][Arg], [CH][Lys], [CH][His], [CH][Trp], [CH]
[Glu], [TMA][Arg], and [TBA][Arg]) prepared by amino acid and
quaternary ammonium hydroxide were used as catalysts for the
glycerolysis of soybean oil, and their catalytic activity were shown
in Table 1 and Fig. 1. As shown in Table 1, among all tested AAILs
with cholinium as cation, [CH][Arg] showed the best catalytic
activity for the glycerolysis of soybean oil. And TAG conversion
(73.54 1.20%) catalyzed by [CH][Arg] was 12 times of other cata-
lysts (less than 6%). These results were ascribed to the presence of
guanidine group in [CH][Arg]. Guanidine group (pKa = 13.8 [29],
Fig. S2) in [CH][Arg] can effectively be combined with H+ dissoci-
ated from glycerol to form a relatively stable protonated nitrogen
atom in the =NH group, which can enhance the glycerolysis reac-
tion. In fact, the outstanding performances of guanidine-based cat-
alysts were also found in other reactions [30–32].
Fig. 1 shows the effect of the cation of AAIL on catalytic activity
and glycerolysis selectivity. The reactions reached equilibrium
within 30 and 60 min under the presence of [TMA][Arg] and
[TBA][Arg], respectively. However, when [CH][Arg] was used as a
catalyst, TAG conversion and MAG yield all increased after 4 h.
Compared with other AAILs, [TMA][Arg] showed the most effective
performance by obtaining high TAG conversion (64.63 2.13%) and
MAG yield (54.85 1.59%) in a short time (30 min). These results
were mainly attributed to the electronic and steric hindrance
effects of alkyl in cations ([TMA]+, [CH]+, and [TBA]+). Therefore,
[TMA][Arg] was selected and used for the next glycerolysis of soy-
bean oil.
2.2. Synthesis of AAIL
The AAILs were synthesized according to the previous report
with some modifications [26]. In a typical preparation, 10 mL of
an aqueous solution of 0.05 mol quaternary ammonium hydroxide
([Ch][OH], [TBA][OH] or [TMA][OH]) was added dropwise into
100 mL aqueous solution of amino acid with a 1:1.1 M ratio of qua-
ternary ammonium hydroxide and amino acid, and stirred at room
temperature and 250 rpm for 48 h. After neutralized, vacuum distil-
lation at 80 °C was employed to remove water. The solvent mixture
was dissolved in acetonitrile/methanol (7:3) to precipitate
unreacted amino acid, and the precipitate was removed by vacuum
filtration. Then, the solvent in AAIL was removed by the evaporation
under vacuum at 60 °C. Finally, the AAIL were further dried in a vac-
uum oven at 90 °C for 0.5 h and stored in a desiccator. The water
content of each AAIL was<0.08%.
2.3. Glycerolysis procedure
The glycerolysis of soybean oil were carried out in 25 mL round-
bottom flasks with a magnetic stirrer bar in an oil bath at 300 rpm.
The heterogeneous reaction mixtures consisted of soybean oil,
glycerol, and AAIL. The effects of molar ratio of soybean oil and
glycerol (2:1, 1:1, 1:2, and 1:4), reaction temperature (80 °C,
90 °C, 100 °C, 110 °C, and 120 °C), and AAIL load (3%, 5%, 8%,
10%, and 12%, w/w, based on oil mass) were investigated. Reaction
2

S. Sun, Y. Lv, G. Wang et al.
Journal of Molecular Liquids 340 (2021) 117231
Table 1
Glyceride content of the reaction catalyzed by AAILs with cholinium as the cation. Glycerolysis conditions: soybean oil/glycerol molar ratio 1:2, 100 °C, 12 h, and 10% catalyst load
(based on soybean oil weight).
Ionic
liquids
Structure of anion
Properties of side chains of the amino acid Isoelectric point of parent amino acid Content (%)
MAG
DAG
TAG
[CH]
Basic
10.76
59.64 1.23 18.56 0.59 21.80 1.01
[Arg]
[CH]
[Lys]
Basic
9.66
5.81 0.96 4.94 1.26 93.25 1.20
[CH]
[His]
Basic
7.60
5.89
3.15
3.95 1.15 2.51 0.69 94.54 1.45
[CH]
[Trp]
Neutral
Acidic
2.18 1.03 2.66 1.02 95.16 2.21
[CH]
[Glu]
2.22 089
2.69 0.39 95.09 1.76
It is worth noting that Arg could not catalyze the glycerolysis
process by itself (Fig. 1), which indicated that the formations of
AAILs enabled Arg to have the catalytic activities for the glyceroly-
sis. Similar finding can also be reported in biodiesel preparation
[26]. Meanwhile, the catalytic activity of each component
([TMA]+ or [TBA]+) has also been improved by the formation of
AAILs with non-catalytic Arg. These AAILs have also been used as
phase transfer catalysts in transesterification or intensification
[33,34].
Compared with the traditional catalysts, for the glycerolysis,
[TMA][Arg] had the advantages of low temperature, high reaction
rate, high MAG yield, and low cost. Especially, compared with
enzyme catalyst, [TMA][Arg] had the advantages of fast reaction
rate and low cost. For examples, the glycerolysis of soybean oil cat-
alyzed by [TMA][Arg] reached equilibrium within 0.5 h, which was
great shorter than the enzymatic glycerolysis (3–8 h) [35,36]. The
prices of the components (arginine and tetramethylammonium
hydroxide pentahydrate) of AAIL [TMA][Arg] are 0.08 $/g and
0.13 $/g, respectively, which were great cheaper than the immobi-
lized enzyme Novozym 435 (2.48 $/g).
[16], and also lower than that of traditional alkane catalyst
(>200 °C) [15].
According to the previous reports [37,38], it is difficult to obtain
a MAG yield of 60% catalyzed by inorganic basic catalysts, such as
KOH, Ca(OH)2, NaOH, and MgO, even though at high temperature
(220–240 °C). Meanwhile, high temperature was responsible for
poor product quality, greater energy consumption, and the forma-
tion of glycerol polymerize [39]. Compared with these traditional
catalysts, [TMA][Arg] exhibited a higher activity for the glyceroly-
sis and higher MAG yield (~65%) at lower temperatures (100 °C).
These phenomena were related to the lower activate temperature
of [TMA][Arg], which was confirmed by the low activation energies
(Ea) of TAG conversion (37.58 kJ/mol) and MAG formation
(44.22 kJ/mol) in the presence of [TMA][Arg] (Fig. 2C).
3.3. Effect of substrate ratio
The glycerolysis of soybean oil catalyzed by alkaline catalyst is
beneficial to the formation of MAG [16,37,38]. In this work, more
glycerol was used to achieve the complete conversion of soybean
oil and high MAG yield. In final MAG product, excessive glycerol
and AAIL [TMA][Arg] can be removed by washing with water. As
shown in Fig. 3, with the increase of glycerol amount, MAG yield
and TAG conversion significantly increased, and reached the max-
imum (64.85 2.13% and 86.11 1.65%, respectively) at 1:2 M
ratio of soybean oil and glycerol, because the increase in the
amount of glycerol can produce more glycerol anion, which is con-
ducive to the glycerolysis of soybean oil and intermediate DAG to
produce more MAG. However, a further increase of glycerol (soy-
bean oil/glycerol molar ratio at 1:4) did not enhance TAG conver-
sion or MAG yield. On the contrary, it decreased the positive
glycerolysis rate, which was due to its high viscosity and great
mass transfer limitation.
3.2. Effect of reaction temperature
Generally, elevating temperature is conducive to the thermody-
namics reaction. To investigate the effect of temperature on the
glycerolysis catalyzed by [TMA][Arg], the experiments were per-
formed under the following reaction conditions: molar ratio of
1:2 soybean oil/glycerol and 10% [TMA][Arg] load (Fig. 2). Results
showed that the glycerolysis rates of soybean oil were accelerated
by increasing temperature in the range of 80–120 °C (Fig. 2C).
Besides, TAG conversion and MAG yield also increased when the
temperature increased from 80 °C to 100 °C. The maximum TAG
conversion (81.11 2.26%, Fig. 2B) and MAG yield (64.85 1.26%,
Fig. 2A) were achieved at 100 °C. Furthermore, when reaction tem-
perature was higher than 100 °C, TAG conversion and MAG yield
did not increase. Therefore, the optimum temperature catalyzed
by [TMA][Arg] was 100 °C, which was great lower than MAG
preparation using ionic liquid [Bmim]Im as a catalyst (200 °C)
3.4. Effect of catalyst [TMA][Arg] load
The effect of [TMA][Arg] load on the glycerolysis reaction was
shown in Fig. 4. The glycerolysis rates increased continuously with
3

S. Sun, Y. Lv, G. Wang et al.
Journal of Molecular Liquids 340 (2021) 117231
Fig. 1. Catalytic activity of synthesized AAILs with selected Arg and their substrates
for the glycerolysis process: (A) MAG yield, (B) TAG conversion. Glycerolysis
conditions: soybean oil/glycerol molar ratio 1:2, 100 °C, and 10% catalyst load
(based on soybean oil weight).
the increase of [TMA][Arg] load in the range of 4–12%. When 10%
[TMA][Arg] load was used, the maximum TAG conversion and
MAG yield were 86.11 1.65% and 64.84 1.56%, respectively.
These were ascribed to the increasing amount of catalytic active
sites with high [TMA][Arg] load, which was favorable for the glyc-
erolysis reaction [40]. In addition, [TMA][Arg] is a liquid catalyst,
which can overcome the mass transfer limitation. With a further
increase of [TMA][Arg] load (>10%), the time to reaction equilib-
rium shortened. However, TAG conversion and MAG yield had no
obvious change. Therefore, 10% catalyst load was enough for this
glycerolysis.
3.5. The glycerolysis mechanism catalyzed by [TMA][Arg]
Fig. 2. Effect of reaction temperature on the process: (A) MAG yield, (B) TAG
conversion. (C) Relationship between the initial glycerolysis rate and temperature.
Glycerolysis conditions: soybean oil/glycerol molar ratio 1:2 and 10% [TMA][Arg]
load (based on soybean oil weight).
According to the GC results, TAG, DAG, and MAG are the main
substances in the product of [TMA][Arg]-catalyzed the glycerolysis
of soybean oil. According to Fig. 5, extending reaction time can
4

S. Sun, Y. Lv, G. Wang et al.
Journal of Molecular Liquids 340 (2021) 117231
Fig. 3. Effect of soybean oil/glycerol molar ratio on the process: (A) MAG yield, (B)
TAG conversion. Glycerolysis conditions: 100 °C and 10% [TMA][Arg] load (based on
soybean oil weight).
Fig. 4. Effect of [TMA][Arg] load on glycerolysis process: (A) MAG yield, (B) TAG
conversion. Glycerolysis conditions: soybean oil/glycerol molar ratio 1:2 at 100 °C.
improve TAG conversion and the formations of MAG and DAG.
Before the reaction reached equilibrium (<0.5 h), TAG conversion,
MAG and DAG contents in the product increased with reaction pro-
cess, which indicated that DAG formation rate was faster than its
consumption rate. The reaction reached equilibrium at 0.5 h.
Meanwhile, TAG conversion, DAG and MAG contents in the product
were 86.11 2.12%, 21.27 2.26%, and 64.84 2.26%, respectively.
When the glycerolysis time was longer than 0.5 h, the contents of
DAG and MAG showed no obvious change.
According to Fig. 5 and the reports of the alkaline-catalyzed
transesterification [2,16,26], the reaction mechanism of the glyc-
erolysis of soybean oil with glycerol to produce MAG catalyzed
by [TMA][Arg] was proposed, and the possible reaction procedure
was illustrated in Scheme 1. Firstly, the guanidine group of Argꢁ
was obtained a proton from the hydroxyl group of glycerol, and
then glycerol was activated to form a glycerol anion (Gꢁ). The car-
bonyl carbon with positive charge of TAG was attacked by the
nucleophiles (Gꢁ) to produce an intermediate [16,41]. After elec-
tron was transferred and the bond was ruptured, the intermediate
was split into diacylglycerol anions (DAGꢁ) and MAG. Then DAGꢁ
was converted into DAG by associating with the protonated guani-
dinium group. And then DAG was reacted with G to produce MAG
in the same way. Meanwhile, the hydrophilic amino moieties favor
the shift of reaction equilibrium towards to MAG formation by
hydrogen-bond in the presence of [TMA][Arg].
3.6. Model fitting and response surface analysis
Response surface design was carried out to optimize the effect
of experimental factors (substrate ratio, temperature, and [TMA]
[Arg] load), and the results were shown in Table 2. The model of
MAG formation was evaluated by multiple regression analysis,
and the results were shown in Table 3 and Fig. 6. By fitting the
experimental data in Table 2, the quadratic polynomial regression
equation of MAG yield was obtained as follows:
MAG yield ð%Þ ¼ 64:47 þ 4:45A ꢁ 10:80B þ 2:31C ꢁ 1:15AB
ꢁ 0:73AC ꢁ 0:50BC ꢁ 5:11A2 ꢁ 24:70B2
ꢁ 2:97C2
ð3Þ
5

S. Sun, Y. Lv, G. Wang et al.
Journal of Molecular Liquids 340 (2021) 117231
Table 2
Response surface design and results of MAG yield.
Trials A: Temperature (°C) B: Substrate C: [TMA][Arg] (%) MAG yield (%)
ratio
(mol/mol)
1
2
3
4
5
6
7
8
0 (100)
1 (120)
ꢁ1 (80)
0 (100)
0 (100)
ꢁ1 (80)
0 (100)
1 (120)
ꢁ1 (80)
0 (100)
0 (100)
1 (120)
0 (100)
0 (100)
0 (100)
ꢁ1 (80)
1 (120)
0 (1:2)
1 (1:3.5)
0 (1:2)
0 (10)
0 (10)
1 (12)
1 (12)
1 (12)
0 (10)
ꢁ1 (8)
ꢁ1 (8)
0 (10)
ꢁ1 (8)
0 (10)
1 (12)
0 (10)
0 (10)
0 (10)
ꢁ1 (8)
0 (10)
64.84 0.91
26.83 0.61
55.00 1.14
50.08 1.27
26.84 1.64
21.54 1.10
45.78 1.40
59.27 0.44
40.20 0.95
24.53 1.92
64.45 1.69
63.75 1.44
63.97 1.72
64.54 0.93
64.56 2.19
47.58 0.69
50.08 1.41
ꢁ1 (2:1)
1 (1:3.5)
1 (1:3.5)
ꢁ1 (2:1)
0 (1:2)
ꢁ1 (2:1)
1 (1:3.5)
0 (1:2)
0 (1:2)
0 (1:2)
0 (1:2)
0 (1:2)
9
10
11
12
13
14
15
16
17
0 (1:2)
ꢁ1 (2:1)
Fig. 5. Changes of components in the product with reaction process. Glycerolysis
conditions: 10% [TMA][Arg] load, soybean oil/glycerol molar ratio 1:2 and 100 °C.
Table 3
ANOVA analysis of glycerolysis variables on MAG yield.
Source
Sum of squares df Mean square F-value
p-value
Table 3 suggested that the model of MAG yield (P < 0.0001) was
extremely significant. The correlation coefficient (R2) was 0.995,
which indicated that the regression equation had a good fitting
and could predict the actual result of the glycerolysis. In the pre-
diction model of MAG yield (Table 3), the effects of three factors
and their quadratic terms were significant, but the interaction
was not significant. According to Table 3 and Fig. 6, the effects of
three factors on MAG yield decreased in the order of substrate
ratio > glycerolysis temperature > [TMA][Arg] load. The optimized
conditions was obtained as: 105 °C, [TMA][Arg] load 10%, and sub-
strate ratio 1:2. Under these optimized conditions, the maximum
MAG yield was 64.89 1.26%, which was higher than those of
NaOH, KOH, Ca(OH)2, or MgO at 240 °C (40–60%) [16].
Model
A-Temperature
B-Substrate ratio
C-[TMA][Arg]
AB
AC
3975.68
158.60
932.98
42.82
5.25
9
1
1
1
1
1
1
1
1
1
7
3
4
16
441.74
158.60
932.98
42.82
5.25
376.50 <0.0001
135.17 <0.0001
795.18 <0.0001
36.49
4.47
1.84
0.84
0.0005
0.0722
0.2172
0.3887
2.16
2.16
BC
0.99
0.99
A2
109.83
2369.09
37.02
8.21
109.83
2569.09
37.02
1.17
93.61 <0.0001
2189.64 <0.0001
31.55
B2
C2
0.0008
Residual
Lack of Fit
Pure Error
Total
R2 = 0.995
7.81
2.60
25.76
0.0045
0.40
0.10
3983.89
Scheme 1. Reaction mechanism of the glycerolysis catalyzed by [TMA][Arg].
6

S. Sun, Y. Lv, G. Wang et al.
Journal of Molecular Liquids 340 (2021) 117231
(64.89
1.26%) were achieved under the optimal conditions of
1:2 M ratio of soybean oil and glycerol and 10% catalyst load at
105 °C for 0.5 h. The activation energies of MAG formation and
TAG conversion were 44.22 kJ/mol and 37.58 kJ/mol, respectively.
Besides these, green sources of raw materials and high catalytic
performance made [TMA][Arg] have great potential in glycerolysis
procedure.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgments
The authors sincerely acknowledge the financial support from
National Natural Science Foundation of China (32072255).
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molliq.2021.117231.
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