One step synthesis of fatty acid diethanolamides and methyl esters from triglycerides using sodium doped calcium hydroxide as a nanocrystalline heterogeneous catalyst

Article abstract of DOI:10.1039/c5nj00388a

Here, we report the preparation of a series of Na⁺-doped Ca(OH)₂ in nanocrystalline form using a very simple method, and investigation of their catalytic activities towards one step aminolysis and transesterification of used cottonseed oil. The catalyst prepared by doping 3.5 wt% Na in Ca(OH)₂ was found to exist in nanocrystalline form (particle size = 25-30 nm) as suggested by TEM and DLS studies and found to have the basic strength of 15.0 < H- < 18.4 as supported by the Hammett indicator test. Na/Ca(OH)₂ was used as a solid catalyst towards the aminolysis and transesterification of used cotton seed oil with diethanolamine and methanol, respectively. The catalyst was found to complete the aminolysis and transesterification of a variety of feedstocks even at room temperature and shows excellent reusability.

Full text of DOI:10.1039/c5nj00388a

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One step synthesis of fatty acid diethanolamides
and methyl esters from triglycerides using sodium
doped calcium hydroxide as a nanocrystalline
heterogeneous catalyst†
Cite this:DOI: 10.1039/c5nj00388a
Dinesh Kumar,*a Soo Min Kima and Amjad Ali*b
Here, we report the preparation of a series of Na+-doped Ca(OH)2 in nanocrystalline form using a very simple
method, and investigation of their catalytic activities towards one step aminolysis and transesterification
of used cottonseed oil. The catalyst prepared by doping 3.5 wt% Na in Ca(OH)2 was found to exist in
nanocrystalline form (particle size = 25–30 nm) as suggested by TEM and DLS studies and found to have
the basic strength of 15.0 o H_ o 18.4 as supported by the Hammett indicator test. Na/Ca(OH)2 was
used as a solid catalyst towards the aminolysis and transesterification of used cotton seed oil with
diethanolamine and methanol, respectively. The catalyst was found to complete the aminolysis and
transesterification of a variety of feedstocks even at room temperature and shows excellent reusability.
Received (in Porto Alegre, Brazil)
13th February 2015,
Accepted 29th June 2015
DOI: 10.1039/c5nj00388a
www.rsc.org/njc
On the other hand due to their industrial applications, fatty
acid amides are produced in thousands of metric tons a year
Introduction
In the development of viable green chemistry, renewable raw from fatty acids by reaction with anhydrous ammonia at
materials play a significant role. In the chemical industry renew- approximately 200 1C and 345–690 kPa.9 Fatty amides can be
able raw materials viz., vegetable oils and fat share the great synthesized from fatty acids or their esters through treatments
proportion of the current consumption.1 Vegetable oil derivatives with amine compounds.10,11 Enzyme catalyzed synthesis of amides
have numerous benefits viz., they are nontoxic, biodegradable from fatty acids or their esters has also been reported.9,12–14
and environmentally friendly. These derivatives have potential Triglycerides can be converted into their fatty acid amides via
industrial applications such as fatty acid methyl esters commonly amidation using ammonia or amine compounds.15,16 The fatty
known as biodiesel, which is a nontoxic, biodegradable, eco- acid amides were synthesized from palm oil using sodium
friendly and renewable substitute for conventional fossil fuel,2 ethoxide as a homogeneous catalyst in the presence of ethanol
and fatty acid amides attract attention due to their biological at 78 1C for 8 h.17 The aminolysis of n-butylamine and methyl
activities and industrial applications in surfactants, lubricants, stearate was performed using sodium methoxide as a homo-
cosmetics, shampoos, foam control agents, fungicides, corrosion geneous catalyst.18 Another method of preparation of fatty acid
inhibitors, water repellents, detergents and anti-blocking agents amides is based on the reaction of fatty acid with ethylene-
in the plastics processing industry.3–5 Owing to their low diamine at 180–185 1C under nitrogen and with continuous
reactivity and thermal properties they are used for the prepara- removal of water. However, high temperature causes self-
tion of anti-slip and anti-block additives in polyethylene films condensation of diethylamine that results in the formation of
and as flow improvers.6 Fatty acid amides also enhance the N,N0-bis(2-hydroxyethyl) piperazine or morpholine instead
ignition quality and characteristics of the fuel. The amide of amide derivatives.19,20
biodiesel should be considered as a good candidate to incor-
The preparation processes for fatty amides utilize the high
porate into the conventional fuels as it increases the cetane temperature and pressure or homogeneous catalysts, which
number of the fuel.7,8
contaminate the product and are required to be washed out
from the product. Thus, the whole process becomes tedious,
lengthy and requires large amounts of water and energy. So, the
heterogeneous catalyst could be the attractive alternative for
such type of reaction due to reusability and easy separation
from the reaction mixture by simple filtration.
a Department of BIN-Fusion Technology, Chonbuk National University,
Jeonju – 561-756, South Korea. E-mail: dinesh.tu@gmail.com; Tel: +82-63-270-2848
b School of Chemistry and Biochemistry, Thapar University, Patiala – 147004, India.
E-mail: amjadali@thapar.edu
† Electronic supplementary information (ESI) available: FT-IR, mass and 1H-NMR
Low cost, ease of availability and non-toxicity have made
calcium oxide as the desired choice for the preparation of a
spectra, and Fig. S1–S6. See DOI: 10.1039/c5nj00388a
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heterogeneous catalyst.21,22 Our research group has previously using Micromerities ASAP 2100 equipment. All samples were
reported calcium oxide based heterogeneous catalysts for trans- degassed at 473 K for 90 min under a nitrogen atmosphere to
esterification reaction of vegetable oils.23,24 But the applica- remove the physisorbed moisture from the catalysts. The basic
tion of heterogeneous catalysts in the aminolysis reaction of strengths of the catalysts (H_) were determined by Hammett
triglycerides has not been explored yet significantly. There are indicators.24 FTIR spectra of triglycerides, biodiesel and corre-
very rare reports available in the literature using heterogeneous sponding amide derivatives have been recorded on a Jasco FTIR-
catalysts for the aminolysis of vegetable oils. Recently, ZnOꢀ 4200 spectrophotometer. Field emission scanning electron
La2CO5ꢀLaOOH was reported as a heterogeneous catalyst for microscopy (FE-SEM) was performed on a Hitachi SU-70 and
complete aminolysis (100% conversion) of triglycerides using transmission electron microscopy (TEM) was performed on a
ethanolamides though it needs long time duration (8 h) for the H-7650, Hitachi to record TEM images. Particle size distributions
completion of reaction.25
of CaO and sodium doped Ca(OH)2 were obtained using a particle
Thus, the objective of the present work is to prepare a size analyzer (90-Plus, Brookhaven Instruments Corporation, USA).
reusable heterogeneous catalyst that could be effective for the Fourier transform-nuclear magnetic resonance (FT-NMR) spectra
single step aminolysis of low quality triglycerides with a short of biodiesel and vegetable oil were recorded on a Bruker Avance-II
reaction time. Present work demonstrated the preparation of (400 MHz) spectrophotometer. Mass spectra of methyl laurate and
Na+ doped Ca(OH)2 in the nano-particle form using a very amide derivatives of methyl laurate were recorded on a Waters
simple chemical method and used as a heterogeneous catalyst Micromass Q-ToF Micro mass spectrophotometer equipped with
for the aminolysis and transesterification of used cotton seed electrospray ionization (ESI) and atmospheric pressure chemical
oil with diethanolamine (DEA) and methanol, respectively. To ionization (APcI) sources having a mass range of 4000 amu in
the best of our knowledge, there is no reported work available in quadruples and 20 000 amu in ToF.
the literature dealing with the preparation of Na doped Ca(OH)2
Preparation of the catalyst
as a heterogeneous catalyst for the aminolysis of triglycerides.
Nanocrystalline sodium metal ion doped calcium hydroxide was
prepared by a chemical method. In a typical preparation, CaO
(10 g) was suspended in 40 mL ethanol and to this 10 mL of
alcoholic solution of sodium nitrate of desired concentration was
added. The concentrations of the sodium nitrate were varied to
obtain Na+ loading in the range of 1.5–5.5 wt% in CaO. The slurry
was stirred for 3 h, then evaporated to dryness and heated at
200 1C for 24 h. The solid thus obtained was characterized by
flame photometry, powder XRD, BET surface area measurements,
Hammett indicator tests, FE-SEM, DLS and TEM techniques.
The prepared catalysts were designated as xx-Na/Ca(OH)2,
where xx represents the sodium concentration (wt%) in Ca(OH)2,
e.g. 3.5-Na/Ca(OH)2 represent the catalyst prepared by doping
3.5 wt% of Na+ (using NaNO3) in Ca(OH)2.
Experimental section
Materials and methods
Sodium nitrate, calcium oxide, methanol (99.8%) and diethanol-
amine (99.8%) used in the present study were obtained from
Merck, India. The mutton fat, virgin cotton seed, soybean,
castor, karanja and jatropha oil were procured from the local
shops located at Patiala. Used cotton seed oil was collected
from the restaurants located at Patiala. Methyl laurate (498%)
was purchased from Sigma-Aldrich, USA.
The free fatty acid (FFA) value, saponification, and the iodine
value of the mutton fat, soybean, virgin cotton seed, used cotton-
seed seed, castor, karanja and jatropha oil were determined by
following the methods as reported in the literature24 and the
moisture content was determined by the Karl Fisher titrimetric
method (Table 1).
Aminolysis reactions
Aminolysis reactions of used cotton seed oil, virgin cotton seed oil,
Sodium ion concentrations in Ca(OH)2 were determined mutton fat, methyl laurate, FAMEs derived from used cotton seed
using a Systronics mediflame 127 flame photometer. The oil, and FAMEs derived from mutton fat have been performed
structural analysis was performed by X-ray diffraction (Rigaku with diethanolamine in the presence of the 3.5-Na/Ca(OH)2
D/MAX 2500 Tokyo, Japan). The surface areas of the catalyst catalyst as shown in Schemes 1 and 2, respectively. All aminolysis
were determined by using the adsorption/desorption method at reactions were performed in a 100 mL, two neck round bottom
77 K by the standard Brunauer–Emmett–Teller (BET) method flask equipped with a water-cooled condenser, an oil bath and a
Table 1 The chemical analysis of vegetable oils used as feedstock in the present study
Free fatty acid
value (wt%)
Moisture
content (wt%)
Saponification
S. no.
Feedstock
value (mg KOH gꢁ1
)
Iodine value
1
2
3
4
5
6
7
Used cotton seed oil
Karanja oil
Jatropha oil
Virgin cotton seed oil
Soybean oil
Mutton fat
1.8
4.2
8.4
0.1
0.2
0.9
2.0
0.36
0.35
0.38
0.31
0.27
0.32
0.34
190.3
184
195.2
188.4
189.6
192.1
180.2
101.3
96.6
101.3
102.4
125.1
46.3
Castor oil
90.5
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In order to test the efficiency of the 3.5-Na/Ca(OH)2 catalyst
with other substrates, the same catalyst has also been employed
for catalyzing the aminolysis reactions of used cotton seed oil
derived biodiesel (as prepared in Section 2.4) and commercially
available methyl laurate using the diethanolamine to FAME
molar ratio of 4 : 1 in the presence of 5 wt% of 3.5-Na/Ca(OH)2
at 110 1C as shown in Scheme 2.
After the completion of the reaction the reaction mixture
was filtered through an ordinary filter paper, washed with water
and an organic layer was dried over sodium sulphate. The
amide product so obtained was further characterized by FTIR
(Fig. S3, ESI†) and 1H-NMR (Fig. S4, ESI†) techniques. The
amide product obtained by the aminolysis of methyl laurate
was also characterized by mass spectrometry (Fig. S5, ESI†)
besides FTIR and proton NMR studies. The FTIR technique has
also been used to monitor the progress of the reaction and
quantify the amide products formed by following the literature
reported procedure.7
Fatty acid amide derivative of used cotton seed oil: yield
499%. FTIR (cmꢁ1): 3397 (nOH), 1615 (nCQO); 1H-NMR (CDCl3,
d ppm): 5.3 (m, –CHQCH–), 3.77 (m, –CH2OH), 3.46 (m, –NCH2–),
2.7 (m, –CHQCH–CH2–CHQCH–), 2.31 (m, –CH2–CO–), 2.0
(m, –CH2–(CH2)n–CH–), 1.6–1.25 (m, –(CH2)n–), 0.95 (m, –CHQ
CH–CH3), 0.87 (m, –CH2–CH3).
Scheme 1 Aminolysis of cotton seed oil in the presence of the 3.5-Na/
Ca(OH)2 catalyst.
Fatty acid amide derivative of used cotton seed oil derived
FAMEs: yield 499%. FTIR (cmꢁ1): 3398 (nOH), 1615 (nCQO);
1H-NMR (CDCl3, d ppm): 5.3 (m, –CHQCH–), 3.78 (m, –CH2OH),
3.48 (m, –NCH2–), 2.7 (m, –CHQCH–CH2–CHQCH–), 2.3
(m, –CH2–CO–), 2.0 (m, –CH2–(CH2)n–), 1.6–1.25 (m, –(CH2)n–),
0.95 (m, –CHQCH–CH3), 0.87 (m, –CH2–CH3).
Fatty acid amide derivative of mutton fat derived FAMEs:
yield 499%. FTIR (cmꢁ1): 3398 (nOH), 1615 (nCQO); 1H-NMR
(CDCl3, d ppm): 5.3 (m, –CHQCH–), 3.75 (m, –CH2OH), 3.47
(m, –NCH2–), 2.3 (m, –CH2–CO–), 2.0 (m, –CH2–(CH2)n–), 1.6–1.25
(m, –(CH2)n–), 0.87 (m, –CH2–CH3).
Fatty acid amide derivative of methyl laurate: yield 499%.
FTIR (cmꢁ1): 3397 (nOH), 1615 (namide–CQO); 1H-NMR (CDCl3, d ppm):
3.8 (m, –CH2OH), 3.5 (m, –NCH2–), 2.3 (m, –CH2–CO–), 1.6–1.25
(m, –(CH2)n–), 0.87 (m, –CH2–CH3); EI-MS (m/z) (intensity
(%), fragment): 287.2 (3, M), 270.3 (100, M–H2O), 227.22 (10,
Scheme 2 Aminolysis of used cotton seed oil derived FAMEs or methyl
laurate in the presence of the 3.5-Na/Ca(OH)2 catalyst.
magnetic stirrer. In a typical aminolysis reaction 10 g of M–CH3(CH2)3), 175.2 (10, M–CH3(CH2)7), 132.2 (12, M–CH3(CH2)10),
vegetable oil was mixed with diethanolamine (DEA) to maintain 114.2 (5, M–CH3(CH2)10OH).
the DEA to oil molar ratio of 6 : 1, in the presence of 5 wt% of
Transesterification reaction
3.5-Na/Ca(OH)2 at 110 1C as shown in Scheme 1. Aminolysis
reactions have been carried out by varying one parameter at a In order to show the efficiency of 3.5-Na/Ca(OH)2 for catalyzing
time in order to establish the best suited reaction conditions the reactions other than aminolysis, the same catalyst has also
for the complete aminolysis of the substrate. After the comple- been used for the transesterification of a variety of triglycerides
tion of the reaction, the reaction mixture was filtered through (virgin cotton seed oil, used cotton seed oil, soybean oil, castor
an ordinary filter paper and was dissolved in 60 mL of hexane oil, karanja oil, jatropha oil and mutton fat) with methanol
and placed in a separatory funnel. The upper hexane layer was as shown in Scheme 3. All transesterification reactions were
separated from the lower glycerol layer, washed with water, performed in a 100 mL, two neck round bottom flask equipped
dried over sodium sulfate and the hexane was rotary-evaporated with a water-cooled condenser, an oil bath and a magnetic
to yield the pure fatty acid amide derivative.
stirrer. In a typical transesterification reaction, triglyceride was
To monitor the progress of the reaction, the samples from mixed in 12 : 1 molar ratio of methanol with 5 wt% (with respect
the reaction mixture have been withdrawn after every 20 min to triglyceride) 3.5-Na/Ca(OH)2 and heated at 65 1C, till the
with the help of a glass dropper, and subjected to FTIR analysis. completion of reaction.
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Results and discussion
Catalyst preparation and characterization
BET surface area and the Hammett indicator test. In the
present study CaO, being less toxic and less expensive, has been
selected as a support for the preparation of the catalyst. The
activity of such a catalyst was found to depend on the basic
strength and the surface area of the catalyst26 and the same has
been tuned by doping calcium oxide with 1.5–5.5 wt% sodium.
The basic strength (H_) of the pure CaO was found to be in the
range of 9.8–10.1. Basic strength was further increased from
10.1–11.1 to 15.1–18.4 as the doping percentage of the sodium
ion was increased from 1.5 to 3.5 wt% as given in Table 2.
A further increase in sodium ion concentration was not found to
increase the basic strength of Na/Ca(OH)2 material. The surface
area of pure calcium oxide and Na/Ca(OH)2 was measured by the
BET method and the same was found to be increased evidently
from 3.7 to 9.6 m2 gꢁ1 after 3.5 wt% doping of sodium as shown
in Table 2. Also, the metal doping increase (from 1.5–5.5 wt%)
has an insignificant effect on the surface area.
Scheme 3 Transesterification of triglyceride (vegetable oil) in the presence
of the 3.5-Na/Ca(OH)2 catalyst.
Powder XRD studies. The comparisons of the powder XRD
patterns of commercially available CaO with 1.5–5.5 wt%
sodium doped Ca(OH)2 are shown in Fig. 1A. CaO shows peaks
at 2y values of 37.371, 53.891 and 32.181 due to the presence of
calcium oxide in the cubic form (JCPDS card no. 821691), as
shown in Fig. 1A(a). The presence of low intensity peaks at 29.41
and at 64.41 reveals the presence of minor amounts of calcium
carbonate as calcite in CaO used as a support (JCPDS 881811).
The powder XRD patterns of Na doped (1.5–5.5 wt%) Ca(OH)2
shows the peaks at 2y values of 34.07, 18.07 and 47.191 to
support the conversion of cubic CaO to hexagonal Ca(OH)2
form as shown in Fig. 1A(c)–(g). The absence of the diffraction
patterns of Na even after 5.5 wt% doping could be due to its
high degree of dispersion on the Ca(OH)2 surface. There was
conversion of CaO to Ca(OH)2 after chemical treatment, as
suggested by XRD analysis, which played an important role in
the basic strength enhancement.
Surface morphology and particle size analysis. The surface
morphology of 3.5-Na/Ca(OH)2 was analyzed by FE-SEM studies
and the images shows that it has mainly hexagonal shaped
2–4 mm sized particles as shown in Fig. 1B. Particle size distribu-
tion analysis (dynamic light scattering analysis, DLS) of CaO
and 3.5-Na/Ca(OH)2 suggested that they have an average parti-
cle size of 112 nm and 28 nm, respectively (Fig. S1, ESI†). The
TEM analysis of the same particles also shows that particles of
After the completion of the reaction, the reaction mixture was
filtered to remove the catalyst, rotary evaporated to recover the
excess methanol and finally kept in a separating funnel for 12 h
to separate the lower glycerol layer from the upper biodiesel
layer. Fatty acid methyl esters (FAMEs), thus obtained, were
1
further characterized and quantified by H-NMR (Fig. S6, ESI†)
by following the literature reported procedure24 as given below:
Yield = {2I(methoxy)/3I(methylene)} ꢂ 100
where I(methoxy) and I(methylene) are the areas of the methoxy and
methylene protons, respectively, in 1H NMR spectra of biodiesel.
Used cotton seed oil derived FAMEs: H-NMR (CDCl3, d ppm): 5.3
(m, –CHQCH–), 3.6 (s, –OCH3), 2.7 (m, –CHQCH–CH2–CHQCH–),
2.3 (m, –CH2–CO–), 2.0 (m, –CH2–CHQCH–), 1.6–1.25 (m,
–(CH2)n–), 0.95 (m, –CHQCH–CH3), 0.87 (m, –CH2–CH3).
Karanja oil derived FAMEs: 1H-NMR (CDCl3, d ppm): 5.34
(m, –CHQCH–), 3.6 (s, –OCH3), 2.75 (m, –CHQCH–CH2–
CHQCH–), 2.3 (m, –CH2–CO–), 2.03 (m, –CH2–(CH2)n–),
1.61–1.25 (m, –(CH2)n–), 0.97 (m, –CHQCH–CH3), 0.88
(m, –CH2–CH3).
1
Jatropha oil derived FAMEs: H-NMR (CDCl3, d ppm): 5.33
(m, –CHQCH–), 3.61 (s, –OCH3), 2.77 (m, –CHQCH–CH2–
CHQCH–), 2.3 (m, –CH2–CO–), 2.02 (m, –CH2–(CH2)n–), 1.61–
1.25 (m, –(CH2)n–), 0.96 (m, –CHQCH–CH3), 0.89 (m, –CH2–CH3).
Soybean oil derived FAMEs: 1H-NMR (CDCl3, d ppm): 5.34
(m, –CHQCH–), 3.6 (s, –OCH3), 2.77 (m, –CHQCH–CH2–CHQCH–),
2.3 (m, –CH2–CO–), 2.03 (m, –CH2–(CH2)n–), 1.6–1.25 (m, –(CH2)n–),
0.95 (m, –CHQCH–CH3), 0.88 (m, –CH2–CH3).
Table 2 Comparison of the BET and single point surface area of CaO with
Na/Ca(OH)2
Castor oil derived FAMEs: 1H-NMR (CDCl3, d ppm): 6.5
(–OH) 5.51 (m, –CH2–CHQCH–), 5.39 (m, –CHQCH–), 3.6
(s, –OCH3), 3.61 (m, –CH–OH), 2.3 (m, –CH2–CO–), 2.20
(m, –CH2–CHQCH–), 2.03 (m, –CH2–(CH2)n–), 1.61–1.30
(m, –(CH2)n–), 0.97 (m, –CHQCH–CH3), 0.88 (m, –CH2–CH3).
Mutton fat derived FAMEs: 1H-NMR (CDCl3, d ppm): 5.34
(m, –CHQCH–), 3.6 (s, –OCH3), 2.3 (m, –CH2–CO–), 2.0
(m, –CH2–(CH2)n–), 1.61–1.25 (m, –(CH2)n–), 0.88 (m, –CH2–CH3).
BET surface
S. no.
Catalyst type
area (m2 gꢁ1
)
Basic strength (H_)
1
2
3
4
5
6
CaO
3.7
9.5
9.6
9.6
9.2
9.3
9.8 o H_ o 10.1
10.1 o H_ o 11.1
11.1 o H_ o 15.0
15.0 o H_ o 18.4
15.0 o H_ o 18.4
15.0 o H_ o 18.4
1.5-Na/Ca(OH)2
2.5-Na/Ca(OH)2
3.5-Na/Ca(OH)2
4.5-Na/Ca(OH)2
5.5-Na/Ca(OH)2
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Optimization of reaction parameters for aminolysis. To deter-
mine the optimum sodium ion concentration in Ca(OH)2 to
achieve the best catalytic activity, a series of Na/Ca(OH)2 catalysts
were prepared by varying the amount of sodium from 0–5.5 wt%.
The aminolysis reaction of used cottonseed oil was performed
with diethanolamine (diethanolamine/oil = 6 : 1; m/m) at 110 1C
in the presence of the 5 wt% catalyst.
The rate of aminolysis was found to increase as the amount
of sodium ion in Ca(OH)2 was increased from 1.5 to 3.5 wt%.
However, a further increase in Na+ ion concentration does not
have an impact on the reaction rate as shown in Fig. 2A and
hence, the 3.5-Na/Ca(OH)2 catalyst was selected for optimizing
the other parameters to achieve the minimum time for the
complete aminolysis of used cotton seed oil. The aminolysis
reaction of used cotton seed oil under the same reaction condi-
tions was also carried out with Ca(OH)2, prepared without Na
metal doping, and found the incomplete conversion even after
4 h of reaction period.
A series of aminolysis reactions of used cottonseed oil with
diethanolamine (1 : 6, m/m) at 110 1C were performed in the
presence of 3.5-Na/Ca(OH)2 by varying its concentration from
1 to 8 wt% (catalyst/oil) in order to find the optimum catalyst
concentration. The rate of reaction increases as the catalyst
concentration was increased from 2 to 5 wt%. A further increase in
catalyst concentration does not change the reaction rate signifi-
cantly as shown in Fig. 2B and hence, the aminolysis reactions
were studied with 5 wt% catalyst concentration for optimiza-
tion of the other parameters. Though the complete aminolysis
(o99% conversion) was possible with 1 wt% of prepared
Fig. 1 (A) Comparative powder XRD patterns of (a) commercial CaO with
(b) 1.5-Na/Ca(OH)2, (c) 2.5-Na/Ca(OH)2, (d) 3.5-Na/Ca(OH)2, (e) 4.5-Na/
Ca(OH)2 and (f) 5.5-Na/Ca(OH)2 where *, E and & represents peaks of
calcium oxide, calcium hydroxide and calcium carbonate, respectively.
(B) FE-SEM and (C) TEM images of 3.5-Na/Ca(OH)2.
3.5-Na/Ca(OH)2 are the clusters of smaller hexagonal and irregular catalyst it required long reaction duration (4 h).
shaped particles with particle sizes in the range of 25–30 nm as A series of aminolysis reactions were conducted in the presence
shown in Fig. 1C. Both DLS and TEM analysis indicated the of the 5 wt% (catalyst/used cottonseed oil) 3.5-Na/Ca(OH)2 catalyst
sharp decrease in particle size of Ca(OH)2 after chemical to find the optimum temperature for aminolysis reaction. The
treatment with sodium doping.
fatty acid amide yield increases as the temperature of the
The characterization studies of 3.5-Na/Ca(OH)2 reveal that it
not only exist in the nanoparticle form but also possesses a
higher basic strength and a higher surface area than pure CaO
and hence, expected to show higher activity than pure CaO
towards the aminolysis and transesterification reaction.
Aminolysis reaction of a variety of triglycerides. The pre-
pared catalysts have been used as catalysts for the aminolysis
of a variety of feedstocks (cotton seed oil, used cotton seed oil,
mutton fat, methyl laurate, and FAMEs derived from used
cotton seed oil and mutton fat) with diethanolamine. However,
used cotton seed oil (1.8 wt% FFAs) has been selected for
optimizing the parameters to achieve the complete aminolysis.
However, as suggested by the literature,27 it’s difficult to
catalyze direct aminolysis of carboxylic acids by using these
kinds of catalysts.
The aminolysis reactions of used cottonseed oil have been
performed by varying one parameter at a time out of the
following parameters (i) sodium ion concentration in Ca(OH)2
(ii) catalyst concentration, (iii) reaction temperature and (iv)
diethanolamine/oil molar ratio. Besides these parameters the
reusability of the selected catalyst and its homogeneous con-
tribution in the catalyst activity have also been studied.
Fig. 2 Effect of (A) sodium ion concentration in Ca(OH)2, (B) catalyst
concentration, (C) reaction temperature, and (D) DEA/Oil molar ratio of
the fatty acid amide (FAA) yield and turn over frequency (TOF) (reaction
time = 1 h). TOF: turn over frequency – moles of substrate converted per
mole of metal (in the solid catalyst) per hour.
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reaction was increased from 35 1C to 110 1C. A further increase 3.5-Na/Ca(OH)2, it was recovered from the reaction mixture by
in reaction temperature was not found to influence the fatty filtration, washed with hexane and dried at 100 1C. The catalyst
acid amide yield significantly as shown in Fig. 2C and hence, thus recovered was used for the six catalytic runs under the
all aminolysis reactions have been performed at 110 1C. Also, same experimental conditions and regeneration method. The
the complete aminolysis (100% m/m) of used cotton seed oil catalyst was able to complete (100%, m/m) the aminolysis of
has been possible at 35 1C though it needed longer reaction used cotton seed oil in six successive cycles as shown in Fig. 3A.
duration (B4 h).
However, the reaction time increases gradually after every
To determine the optimum diethanolamine/used cotton seed successive run, indicating that there is a gradual loss of the
oil molar ratio, the reactions were performed with 3: 1 to 9 : 1 activity. The decrease in catalytic activity after every cycle could
molar ratios at 110 1C using 5 wt% of 3.5-Na/Ca(OH)2 catalyst. be due to the partial leaching of sodium from the calcium oxide
The fatty acid amide yield increases as the diethanolamine/oil support or due to the partial deactivation of the catalytic sites.
molar ratio was increased from 3: 1 to 6: 1. A further increase in
The catalyst reusability study shows the gradual loss of the
diethanolamine/oil molar ratio does not affect the fatty acid catalytic activity and the same could be due to the partial
amide yield significantly as shown in Fig. 2D. The same reaction leaching of the active species from the catalyst support. In
with a low diethanolamine/oil molar ratio (3: 1), which is also order to quantify the homogeneous contribution involved in
a minimum ratio required for aminolysis, also yielded the the catalyst activity, the catalyst, 3.5-Na/Ca(OH)2 (500 mg, equiva-
maximum conversion but in 3 h of reaction duration.
lent to 5 wt% of oil used later for the aminolysis), has been
The necessity of high amount of diethanolamine has been refluxed with diethanolamine for 1 h at 110 1C and then the
described well by Talvik’s hypothesis,28 which stated that catalyst was separated from diethanolamine by filtration. Dietha-
the possibility of formation of a six-membered ring and the nolamine thus obtained was mixed with used cotton seed oil to
importance of an additional molecule of the amine demand the maintain the amine/oil molar ratio of 6 : 1, and the reaction
use of at least two equivalents of diethanolamine to achieve mixture was stirred at 110 1C for 1 h. Under these experimental
high yields of amide.
conditions no conversion of oil to fatty acid amide has been
Effect of feedstock used. In order to determine the effective- achieved. Also, the concentration of Na+ in first and after six
ness of the prepared Na/Ca(OH)2 catalyst towards the amino- catalytic cycles was analyzed using flame photometry and a very
lysis of other substrates than used cotton seed oil, the same little change, from 3.45 wt% to 3.34 wt%, was found. Evidently,
reaction has been performed using methyl laurate (ML), mutton these experiments ruled out the possibility of aminolysis due to
fat (MF), virgin cotton seed oil (CSO), soybean oil (SO), FAMEs of any leached species, and also support the fact that the solid
MF, and FAMEs of UCSO. The catalyst was found to be effective catalyst is stable and responsible for the entire catalytic activity.
for the complete aminolysis of the feedstocks used and in order
Kinetic study. To monitor the progress of the reaction and
to compare the efficiency of the catalyst, the turnover frequency calculate the rate, aminolysis of UCSO with diethanolamine has
(TOF) has been calculated and compared (Table 3). When fatty been performed under the optimized reaction conditions viz.,
acid methyl esters were used as the feedstock of aminolysis
reaction the TOF was found to be B3 times higher than the TOF
obtained in the case of triglycerides as given in Table 3. Also, in
this case a less amount of diethanolamine was required and the
side product was methanol, which was easy to separate. The
chemical structure of FAMEs is quite small as compared to
triglycerides and this could be the reason behind the higher
TOF value or lesser requirement of diethanolamine.
Reusability and homogeneous contribution of the catalyst.
Reusability is one of the most important features of a solid
catalyst for its commercialization. To test the reusability of
Table 3 Comparison of the effect of feedstocks on the amount of
diethanolamine and the turnover frequency (TOF) of the 3.5-Na/Ca(OH)2
catalyst for the complete aminolysis. (Reaction conditions: catalyst amount =
5 wt% of feedstock, temperature = 110 1C, and reaction time = 1 h)
Fig. 3 (A) Reusability studies of the 3.5-Na/Ca(OH)2 catalyst towards the
aminolysis of used cotton seed oil. (B) Plot of ꢁln(1 ꢁ y) vs. time at two
different reaction temperatures for the 3.5-Na/Ca(OH)2 catalyzed amino-
lysis of UCSO. (C) The Eyring plot and the thermodynamics parameters for
the aminolysis of waste cotton seed oil. (D) Effect of change of feedstock
on the catalytic activity of the 3.5-Na/Ca(OH)2 catalyst for transesterifica-
tion reaction; reaction conditions; methanol: feedstock molar ratio = 12 : 1,
catalyst amount = 5 wt% of feedstock, temperature = 65 1C.
DEA : feedstock
molar ratio
S. no.
Type of feedstock
TOF (hꢁ1
)
1
2
3
4
5
6
CSO
SO
MF
FAMEs (UCSO)
FAMEs (MF)
ML
6 : 1
6 : 1
6 : 1
4 : 1
4 : 1
4 : 1
14.6
14.6
15.2
43.8
44.6
45.3
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Table 4 Comparative study of Na/Ca(OH)2 activity towards aminolysis reaction with few literature reported catalysts
Novozym Sodium
Novozym 435 435
Catalyst
methoxidea ZnOꢀLa2CO5ꢀLaOOH CdOb
Na/Ca(OH)2
Substrate
Caffeic acid
methyl ester
Oleic acid Soybean oil Passiflora edulis oil
MO, OA, FA, BA
WO, SO, CO, KO,
JO, MF/methyl laurate
Amine
PEA
4
24 h
EA
30
3 h
NME
1
NR
EA
2.3
8 h
Pyrrolidine
5
24 h for MO, 3 h
for OA, FA, BA
135
DEA
5
1 h
Catalyst amount (wt% of oil)
Reaction time
Reaction temperature (1C)
Amine : feedstock molar ratio 40 : 1
FAA yield (% m/m)
70
65
10 : 1
96.6
60
3 : 1
90
100
3 : 1
100
110
6 : 1/4 : 1
2 : 1
25.5
99 for MO, 95 for OA, 97 499
for FA, 82 for BA
8
32
Reusability of catalyst
Ref.
5
14
NR
31
NR
15
2
25
6
PR
a
b
Homogeneous catalyst. Used ionic liquids as the support, PEA = (R,S)-a-phenylethylamine, NME = N-methyl ethanolamine, EA = ethanolamine,
DEA = diethanolamine, NR = not reported, MO = methyl oleate, OA = oleic acid, FA = fatty acids, BA = benzoic acid, and PR = present report.
using the diethanolamine to oil molar ratio of 6 : 1 in the Transesterification reactions were performed in the presence
presence of the 5 wt% catalyst (3.5-Na/Ca(OH)2) at 110 1C. of the 5 wt% 3.5-Na/Ca(OH)2 catalyst using the methanol to
The samples from the reaction mixture have been withdrawn triglyceride molar ratio of 12 : 1. Different kinds of triglycerides
after every 20 min, centrifuged and rotary evaporated to remove were converted completely into corresponding FAMEs at differ-
the solid catalyst and excess diethanolamine, respectively and ent time intervals. Mutton fat, soybean, cotton seed and used
subjected to FTIR studies to calculate the fatty acid amide yield cotton seed oil required 1 h, castor and karanja oil required 1.5 h
in the reaction mixture.
and jatropha oil required 1.75 h for complete conversion as
The aminolysis reaction of UCSO in the presence of 3.5-Na/ shown in Fig. 3D. A relatively low catalytic activity of the selected
Ca(OH)2 was found to follow the pseudo first-order kinetics and catalyst towards the transesterification of karanja and jatropha
the rate constant (k) for the same reaction could be given as:
oil could be due to the partial deactivation of the catalyst by the
higher concentration of FFAs present in these oils.
k = ꢁln{(1 ꢁ y)/t}
(i)
Comparison of activity with few literature reported catalysts. In
order to show the efficacy and advantages of the 3.5-Na/Ca(OH)2
catalyst over literature reported similar catalysts, a comparison
has been made as shown in Table 4. As evident from the
comparison, the catalyst 3.5-Na/Ca(OH)2, and reaction conditions
optimized in the present study are clearly advantageous than the
literature reported counterparts as the former (i) yielded a higher
FAA yield (499%) than even a homogeneous catalyst, (ii) needed
a shorter reaction duration (1 h) at 110 1C, (iii) effective (FAA
yield 499%) even at room temperature (35 1C), (iv) reusable
(upto 6 catalytic runs), (v) effective for the aminolysis of a variety
of triglycerides, and (vi) equally effective for the transesterifica-
tion of a variety of triglycerides.
where y is the fatty acid amide yield at time t.
The kinetics of the Na/Ca(OH)2 catalyzed aminolysis of
UCSO has been studied at a 6 : 1 diethanolamine to oil molar
ratio at two different temperatures of 35 1C and 110 1C.
The linear nature of ꢁln(1 ꢁ y) vs. t (time) plots (Fig. 3B)
supported that Na/Ca(OH)2 catalyzed reaction follow pseudo
first order kinetics. The rate constants were obtained from
Fig. 3B and found to be 0.077, 0.029, 0.013 and 0.004 minꢁ1
at 110, 95, 65 and 35 1C, respectively.
The Arrhenius model29 was employed to estimate the activa-
tion energy (Ea) and the pre-exponential factor (A) for the same
reaction as given in eqn (ii).
ln k = ꢁEa/RT + ln A
where R is the gas constant (8.31 J Kꢁ1 molꢁ1) and T is the
(ii)
Conclusions
A simple method for the preparation of Na+ doped Ca(OH)2
reaction temperature in Kelvin.
A plot between 1/T and ln k is shown in Fig. 3C, and the values catalysts in nanocrystalline form was employed and its applica-
of Ea and A from the same graph was found to be 54.8 kJ molꢁ1 tion as solid catalyst towards aminolysis and transesterification
and 1.8 ꢂ 109 minꢁ1, respectively. The calculated activation reactions of a variety of feedstocks has been demonstrated. The
energy (54.8 kJ molꢁ1) for the UCSO aminolysis was found to Na/Ca(OH)2 catalyst was found to yield the complete aminolysis
be within the range (33–84 kJ molꢁ1), reported for the hetero- of used cotton seed oil with diethanolamine in 1 h at 110 1C. The
geneous catalysis.30
reaction rate and activation energy were found to be 0.07 minꢁ1
Transesterification of a variety of feedstocks. In order to and 54.8 kJ molꢁ1, respectively, at 110 1C. Th prepared catalyst
show the versatile application of the catalyst, it was used for was also found to complete the transesterification of used cotton
the transesterification of a variety of feedstocks viz., soybean oil seed oil with methanol in 1 h of reaction period at 65 1C.
(SO), mutton fat (MF), cotton seed oil (CSO), used cotton seed The catalyst was found to be equally effective to catalyze trans-
oil (UCSO), castor oil (CO), karanja oil (KO) and jatropha oil (JO). esterification with other feedstocks (viz., mutton fat, soybean,
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Acknowledgements
We are thankful to Center for University-Wide Research Facilities,
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