Fatty acid eutectic mixtures and derivatives from non-edible animal fat as phase change materials

Article abstract of DOI:10.1039/c7ra03845c

A set of compounds from non-edible fat waste was prepared and their thermal behavior was studied. The fat was hydrolyzed and crystallized in a simple and robust process to yield palmitic acid-stearic acid (PA-SA) mixtures. The PA-SA mass ratios determined by GC-FID (gas chromatography-flame ionization detection) were similar to those reported for eutectic mixtures of PCMs (phase change materials). DSC (differential scanning calorimetry) results indicated that the melting and solidification temperatures were around 55 °C and 52 °C and the latent heat of the crystallized fractions measured was around 180 kJ kg^-1. The thermal cycling reliability of the eutectic mixtures was also tested during 1000 melting/freezing cycles. The loss in melting and solidification enthalpies was below 14% in all mixtures showing a promising behavior for PCM applications. Additionally, the unsaturated fatty acids were recovered and transformed to threo-9,10-dihydroxystearic acid (DHSA) and some of their inorganic salts, which were analyzed by FT-IR (Fourier transform-infrared spectroscopy) and tested for the first time using the DSC technique.

Full text of DOI:10.1039/c7ra03845c

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PAPER
Fatty acid eutectic mixtures and derivatives from
non-edible animal fat as phase change materials†
Cite this: RSC Adv., 2017, 7, 24133
a
b
a
a
Pau Gallart-Sirvent,
Marc Martın,
Gemma Villorbina,
Merce Balcells,
`
´
c
bd
b
*
Aran Sole,
Camila Barrenche,
and Ramon Canela-Garayoa
Luisa F. Cabeza
´
a
*
A set of compounds from non-edible fat waste was prepared and their thermal behavior was studied. The fat
was hydrolyzed and crystallized in a simple and robust process to yield palmitic acid–stearic acid (PA–SA)
mixtures. The PA–SA mass ratios determined by GC-FID (gas chromatography-flame ionization detection)
were similar to those reported for eutectic mixtures of PCMs (phase change materials). DSC (differential
scanning calorimetry) results indicated that the melting and solidification temperatures were around
55 ꢀC and 52 ꢀC and the latent heat of the crystallized fractions measured was around 180 kJ kgꢁ1. The
thermal cycling reliability of the eutectic mixtures was also tested during 1000 melting/freezing cycles.
The loss in melting and solidification enthalpies was below 14% in all mixtures showing a promising
behavior for PCM applications. Additionally, the unsaturated fatty acids were recovered and transformed
to threo-9,10-dihydroxystearic acid (DHSA) and some of their inorganic salts, which were analyzed by
FT-IR (Fourier transform-infrared spectroscopy) and tested for the first time using the DSC technique.
Received 4th April 2017
Accepted 26th April 2017
DOI: 10.1039/c7ra03845c
rsc.li/rsc-advances
are partially hydrogenated soy-wax6,7 or saturated fatty esters
resulting from the hydrogenation of unsaturated fatty acid ob-
tained from several sources.5,8,9 The hydrogenation process is
1. Introduction
Animal fats are triacylglycerols containing saturated and
unsaturated fatty acids. Nowadays, enormous amounts of
animal fat are produced annually as a co-product of agro-
industrial practices generating crude fatty materials that are
difficult to treat and valorize.1,2 Since fatty acids present high
thermal and chemical stability and high heat capacity, TES
(thermal energy storage) applications are considered as
a potential solution to revalorize these materials. Thermal
energy is stored and released during the phase change process
by fatty acids, acting as PCMs, when the surrounding temper-
ature increases or decreases.3 Indeed, fatty acids and fatty acid
derivatives are considered an alternative to other PCMs, such as
paraffin and salt products, with the improvement of being
sustainable bio-based materials.3,4
essential in these bio-based PCMs whereby they can remain
stable during phase change cycles with no risk of oxidation.8,10
Unfortunately, the unsaturated fatty acids are converted to the
corresponding saturated fatty acids, losing the opportunity of
use them in other potential applications. On the other hand,
eutectic mixtures of fatty acids have also been prepared from
pure commercial fatty acids and have shown satisfactory
performance as phase change materials.3,11–13 However, no study
has addressed the preparation of PCMs based on eutectic
mixtures directly recovered from acylglycerols as feedstock.
Indeed, near eutectic mixtures of PA–SA and unsaturated fatty
acids can be separated hydrolyzing animal fat waste with
biocatalysts.14
The remaining unsaturated fatty acids could be an excellent
starting material to prepare high-value molecules.15 In that way,
oleic acid has been epoxidated, hydroxylated, and cleaved
oxidatively to azealic acid.16–18 One of the intermediates of this
process, DHSA, also plays an important role as a building block.
Recently, it has been used as an ionizable molecule in water-
borne polyurethane dispersions19 and as a starting material for
the preparation of lubricants,20 estolides,21 soaps,21 deodorant
sticks21 and shampoos.21
Recently, various studies of bio-based organic PCMs from
feedstocks have appeared. Such studies were based on
commercially available organic compounds.5–9 These products
aDepartment of Chemistry-DBA Center, University of Lleida-Agrotecnio, Av. Rovira
Roure 191, 25198, Lleida, Spain. E-mail: canela@quimica.udl.cat
b
´
GREA Innovacio Concurrent, INSPIRES Research Centre, University of Lleida, Pere de
Cabrera s/n, 25001, Lleida, Spain. E-mail: lcabeza@diei.udl.cat
cDepartment of Mechanical Engineering and Construction, Universitat Jaume I,
The aim of the present study is to determine the actual
thermal energy storage capacity as PCM of eutectic mixtures of
PA–SA prepared from non-edible animal fat through a simple
process involving hydrolysis and crystallization steps.
´
Campus del Riu Sec s/n, 12071 Castello de la Plana, Spain
dDepartment of Material Science and Physical-Chemistry, Universitat de Barcelona,
´
´
Martı i Franques 1-11, Barcelona 08028, Spain
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra03845c
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Fig. 1 Synthesis afforded in this study. The triglyceride represents the three fatty acids usable to prepare the products studied.
Moreover, the remaining unsaturated fatty acids were trans- Stirring was performed using a stirring glass rod with three
formed to pure DHSA. DHSA and some of it inorganic salts Teon baffles. The reactor temperature was regulated using
(Fig. 1) have also been analyzed by FT-IR and tested using a DSC regular motor antifreeze heated using a B. Braun Thermomix
technique to study their potential as PCM.
1441 Recirculating Bath Pump.
2.2. Synthesis pretreatments
2. Experimental
2.1. Materials
2.2.1. Non-edible animal fat hydrolysis. Ethanol (1000 mL)
was added to the mechanically stirred cylindrical jacketed glass
Animal fat was a kind gi from Subproductos Carnicos Eche- reactor (5 L) containing 1000 g of animal fat at 80 ꢀC. The
varria y Asociados S.L (Cervera, Spain). This fat was composed of mixture was stirred at 300 rpm. Aerwards, 2000 mL of 14.2%
non-edible fatty pig and chicken parts. It consisted mainly of NaOH solution at 60 ꢀC were added drop wise and the reaction
triglycerides and had a saponication value (SV) of 196. The mixture was reuxed for 30 min under stirring. The reaction
percentage of unsaturated fatty acids was 55.14%, in which mixture was driven at pH ¼ 2 by adding drop wise 250 mL of
monounsaturated and polyunsaturated fatty acids accounted a 98% H2SO4. This addition should be performed carefully and
for 40.50% and 14.64%, respectively, as determined by a chro- drop wise during at least 30 min to avoid as much as possible
matographic method.22 Of all the unsaturated fatty acids in the the overheating and the organic matter oxidation. Finally, the
animal fat, oleic acid was the most abundant, accounting for aqueous layer was discarded and the organic phase was washed
´
ꢀ
about 36.97% of the total fatty acids present. Saturated fatty twice with 2000 mL of a 20% NaCl aqueous solution at 60 C.
acids accounted for 43.99% of the total fatty acids and palmitic The upper phase was recovered yielding 944 g of crude free fatty
and stearic acids for 24.57% and 14.05% of this total, acids (99% yield).
respectively.
Crystallization of hydrolyzed animal fat to prepare PA–SA
Animal fat hydrolysis and DHSA synthesis were conducted in eutectic mixtures and a high unsaturated fatty acid mixture.
a mechanically stirred cylindrical jacketed glass reactor (5 L). Crystallization studies were performed by dissolving under
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reux 5 g of the hydrolyzed animal fat using various common was stirred under reux for 30 min and aerwards driven at pH
solvents according the procedure already described.14 The ¼ 2 by adding drop wise 25 mL of 98% H2SO4. The aqueous
crystallization process was performed at ꢁ20 ꢀC using a solute/ layer was discarded and the organic phase was washed twice
solvent ratio of 1 : 6 (w/v). Recovered solids were analyzed for with 300 mL of a 20% NaCl aqueous solution at 60 ꢀC. The crude
their PCMs properties. These solid fatty acids were also DHSA was recovered yielding 106 g (95% yield). The crude was
analyzed by GC-FID22 and FT-IR. To prepare DHSA the crystal- dissolved in hot ethyl acetate (1 g of solute : 1 mL of solvent) and
lization process was scaled up to 200 g of free fatty acids using let to crystallize for 24 h at 4 ꢀC. The resulting white powder was
methanol at ꢁ20 ꢀC. The mother liquor was concentrated under recovered by ltration under vacuum in a Pyrex crucible no. 3
vacuum to achieve a high unsaturated fatty acid mixture.
and then washed three times with cold ethyl acetate (74% iso-
2.2.2. Synthesis of DHSA from the high unsaturated fatty lated yield). Mp: 94.5 ꢀC (DSC rst cycle). The nal white powder
1
acid mixture. The synthesis of DHSA has been widely described was analyzed by FT-IR and H NMR (see ESI†):
appearing as early as end 19th and early 20th.21 Swern described
1H NMR (400 MHz, CDCl3) d ppm: 0.88 (t, J ¼ 6.9 Hz, CH3),
on 1959 the synthesis of DHSA from commercial oleic acid.23 In 1.19–1.55 (m, CH2), 1.63 (m, bCH2), 2.34 (t, J ¼ 7.4 Hz, aCH2),
this procedure, a high amount of hazardous formic acid and 3.40 (m, HCOH).
hydrogen peroxide are mixed with oleic acid producing a high
2.2.3. Synthesis of DHSA salts. To a solution containing 1 g
exothermic reaction. Once the formic acid is removed by (3.16 mmol) of DHSA in 10 mL of methanol, 3.32 mmol of NaOH
distillation, sodium hydroxide is added to hydrolyze the ester or LiOH$H2O in 10 mL of water were added under high stirring
moiety and hydrochloric acid is nally added to liberate the free speed. Aerwards, the reaction temperature was increased until
fatty acids. Recently, the epoxidation and hydrolysis of tri- the solution became transparent and then let it cold until
acylglycerols24,25 has been described and patented.26 These precipitated appeared. The calcium and magnesium salts were
publications studied and optimized the amount of reactants prepared from the sodium salt solution by adding drop wise
and the conditions to achieve the products using less amounts 3.48 mmol of CaCl2 or MgCl2 in 10 mL of water. The precipitates
of reactants and also involving milder conditions. Even though were recovered by ltration under vacuum in a Pyrex crucible
the preparation of crude DHSA from animal sources is claimed, no. 3. All the products were analyzed by FT-IR.
the patented procedure is described and preferred for palm oil-
based oleic acid.26 These last decades palm oil production has
been revised and reviewed due to their contribution in defor-
2.3. Characterization
estation and their affect in biodiversity.27–29 Malaysia and FT-IR spectroscopy was performed in order to identify the
Indonesia produce more than the 80% of all palm oil.28 characteristic structure of PA–SA eutectic mixture, DHSA and
Unfortunately, 55–59% of oil palm expansion in Malaysia, and DHSA salts. FT-IR spectra were recorded with a Jasco 6300 FT-IR
at least 56% of that in Indonesia occurred at the expense of spectrometer coupled with an ATR accessory.
1
forests during the period 1990–2005.29 Besides, demand of palm
The DHSA structure and purity was determined by H NMR
oil is predicted to continue increasing30 with potentially suitable spectroscopy. This technique allowed the evaluation of the
areas for oil palm cultivation in Southeast Asia, Latin America purity of this product by comparing the signals related to H–
and Central Africa.28,29 In opposite, this study uses non-edible COH (hydrogen bonded to a secondary alcohol) and R1CH2-
animal fats as a source to prepare DHSA. As a summary, the COOH (hydrogen bonded to the a-carbon of the carboxylic
mixture of high unsaturated fatty free acids recovered from the acid).31 Moreover, this technique was also used to evaluate the
mother crystallization liquor was mixed with moderate DHSA content aer this product was analyzed by DSC tech-
1
amounts of formic acid and then hydrogen peroxide was added nique. H NMR spectra were recorded with a MERCURY plus
drop wise.24–26 Once the double bonds were epoxied, the NMR Spectrometer Systems VARIAN Imant AS operating at 400
temperature was increased to lead all the epoxide groups react MHz.
with the free fatty acids and formic acid yielding the corre-
GC-FID is commonly used on the analysis of mixtures of free
sponding esters. Subsequently, sodium hydroxide was added to fatty acids to determine the percentage of each fatty free acid.
hydrolyze the ester groups and sulfuric acid was nally added to GC-FID was used to characterize the fatty acid contents in the
liberate the free fatty acids.23 Finally, the crude mixture of non-edible animal fat, the PA–SA eutectic mixtures and the high
reaction was crystallized to recover pure DHSA.
unsaturated fatty acid mixture. These fatty maters were
Thereby, 8.32 mL (208.1 mmol) of formic acid were added to analyzed in triplicate using a ThermoQuest series 2000 chro-
a mechanically stirred cylindrical jacketed glass reactor (5 L) matograph equipped with a FID detector, an EEP system
containing 100 g of the high unsaturated fatty acids previously (Fisons, Barcelona, Spain), a split/split-less injection system and
obtained from the mother liquor. The mixture was stirred at an autosampler. The analytical column (Supelco, Madrid,
300 rpm. Aerwards, 130 mL of 30% H2O2 (1.141 mol) solution Spain) was a 30 m ꢂ 0.25 mm fused-silica capillary coated with
ꢀ
were added drop wise at 4 C. Once the addition was nished, 0.25 mm lm thickness of poly(80% biscyanopropyl–20% cya-
the temperature was driven up to 60 ꢀC and the reaction mixture nopropylphenyl siloxane) (SP-2330), and was temperature pro-
was stirred for 18 h at 60 ꢀC. The resulting epoxide groups were grammed from 150 ꢀC to 220 ꢀC at 5 ꢀC minꢁ1 then held at
hydrolyzed for 3 h at 100 ꢀC. Ethanol (100 mL) was added to the 220 C for 6 min.
ꢀ
reactor, and esters were hydrolyzed by a drop wise addition of
100 mL of 20% NaOH solution at 60 C. The reaction mixture differential scanning calorimetry (DSC 822e from Mettler
Thermophysical characterization was performed with
ꢀ
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Toledo) in order to analyze the phase change temperature and shows a band signal at 2955 cmꢁ1 associated to the asymmet-
phase change enthalpies (melting and solidication). rical stretching vibration of –CH3 while the bands at 2917 cmꢁ1
Measurements were conducted using a three cycle program and 2845 cmꢁ1 responds to the symmetrical and asymmetrical
repetitions. The rst cycle was disregarded and, thus, the mean stretching modes of –CH2 group, respectively. A characteristic
value of the two following cycles was calculated and the results band at 1697 cmꢁ1 represents the asymmetrical stretching
were presented in a condence interval of 95%. The second and vibration (u2) of C]O. The band at 1460 cmꢁ1 is the –CH2
the third cycle were performed at 0.5 ꢀC minꢁ1 under owing 80 deformation while 1409 cmꢁ1 has its origin in the C]O
mL minꢁ1 nitrogen gas. The DSC analyses were performed symmetrical stretching vibration (u1). The band at 1295 cmꢁ1
between 30 ꢀC and 250 ꢀC depending on the melting point of the represents –CH2 twist and wag and the band at 935 cmꢁ1
product studied. The mass of sample used was around 5 mg and responds to C]O deformation (u3). The –CH2 rocking vibration
the samples were located into 40 mL aluminum crucibles. The and bending is associated to a band at 721 cmꢁ1
.
equipment accuracy was ꢃ0.1 ꢀC for temperature and ꢃ3 kJ
The bands at 3332 cmꢁ1 and 3244 cmꢁ1 correspond to DHSA
(O–H stretching vibration). A characteristic band signal at 2952
kgꢁ1 for enthalpy results.
The thermal cycling reliability is crucial for the application of cmꢁ1 responds to the asymmetrical stretching vibration of –CH3
PCMs, in fact only a thermal stable phase change temperature while the bands at 2910 cmꢁ1 and 2848 cmꢁ1 are associated
and latent heat of PCMs aer a large number of thermal cycles with the symmetrical and asymmetrical stretching modes of
makes possible the PCMs purpose. To study the thermal cycling –CH2 group, respectively. The band at 1704 cmꢁ1 is the char-
reliability, an accelerated thermal cycle experiment was per- acteristic absorption band for asymmetrical stretching vibra-
formed to analyze the changes of the phase change temperature tion (u2) of C]O. The band at 1468 cmꢁ1 corresponds to the
and latent heat of the PA–SA eutectic mixtures aer 1000 –CH2 deformation while 1411 cmꢁ1 respond to the C]O
thermal cycles. In order to study the thermal cycling stability symmetrical stretching vibration (u1). The bands at 1331 cmꢁ1
and reliability, new material samples were cycled in a thermal and 1295 cmꢁ1 have its origins on the –OH bending and –CH2
cycler Bioer Gene Q T-18. A tube volume of 0.5 mL was used for twist and wag, respectively. The –OH stretching is associated
each compound. A dynamic method was established using with a band at 1078 cmꢁ1. At 923 cmꢁ1 and 721 cmꢁ1 are
ꢁ1
ꢀ
ꢀ
a temperature range between 30 and 70 C and at 4 C s for observed the C]O deformation (u3) and –CH2 rocking vibra-
cooling and 5 ꢀC sꢁ1 for heating. A total of 1000 cycles were tion and bending, respectively.
performed under the described conditions. Finally, the
The broad absorption band of O–H stretching vibration band
compounds were recovered and a new DSC test was performed. is present in all the salts within 3300 cmꢁ1 and 3266 cmꢁ1
Notice that this study presents results when performing 1000 depending on the salt. The band corresponding to the asym-
cycles, which would be around 3 years of operation if the PCM metrical stretching vibration of –CH3 is only observed in
implemented in a system cycled once per day.32
calcium (2952 cmꢁ1) and sodium (2950 cmꢁ1) spectra salts.
Otherwise, the bands at ꢄ2920 cmꢁ1 and ꢄ2850 cmꢁ1 associ-
ated to the symmetrical and asymmetrical stretching modes of
–CH2 group are present in all spectra. The band at 1704 cmꢁ1
characteristic for asymmetrical stretching vibration (u2) of
C]O previously observed in DHSA spectra can now be found at
the region around 1600–1535 cmꢁ1 upon formation of the
carboxylate anion. Moreover, calcium salt spectra presents two
3. Results and discussions
3.1. FT-IR characterization of the PA–SA eutectic mixture,
DHSA and their salts
Table 1 shows the assigned wave number (cmꢁ1) of the
compounds synthesized. PA–SA eutectic mixture FT-IR spectra
Table 1 Absorption maxima (cmꢁ1) in the FT-IR spectra of PA–SA eutectic mixture, DHSA and their salts (see ESI)
Wave number (cmꢁ1
)
PA–SA
Lithium salt
of DHSA
Sodium salt
of DHSA
Calcium salt
of DHSA
Magnesium salt
of DHSA
`
eutectic
DHSA
Assignment
—
3332, 3244
2952
2910
2848
1704
1468
1411
1331
1295
1078
923
3284
—
3290
2950
2917
2848
1558
1463
1435–1415
1328
—
3266
2952
2917
2848
1571, 1535
1464
1428
1325
—
3300
—
Broad absorption of O–H stretching vibration
CH3, C–H asymmetrical stretching
CH2, C–H asymmetrical stretching
CH2, C–H symmetrical stretching
C]O asymmetrical stretching vibration (u2)
CH2 deformation
C]O symmetrical stretching vibration (u1)
O–H bending
–CH2 twist and wag
2955
2917
2845
1697
1460
1409
—
1295
—
935
721
2916
2847
1562
1463
1399
1335
—
1078
—
718
2920
2852
1600
1468
1399
1335
—
1078
—
721
1078
—
718
1078
—
718
O–H stretching
C]O deformation (u3)
–CH2 rocking and bending
721
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bands for the asymmetrical stretching vibration (u2) of C]O 58.7 : 41.3 in the case of the methanol crystallization. Similar
(1571 and 1535 cmꢁ1). The band at around 1460 cmꢁ1 charac- compositions as 62 : 38 (ref. 3) or 64.2 : 35.8 (ref. 36) were
teristic for the –CH2 deformation and the band at around 1400– described in the preparation of eutectic mixtures starting from
1430 cmꢁ1 for the C]O symmetrical stretching vibration (u1) commercially pure palmitic and stearic acids. The DSC curve of
are present in all the spectra. As the –OH bending and –OH the bio-based mixtures prepared from non-edible fats showed
stretching, which have its origins in bands at ꢄ1330 cmꢁ1 and one sharp endothermic peak during the melting process and
1078 cmꢁ1, respectively. Finally, the band corresponding to the one sharp exothermic peak on the solidication process, which
C]O deformation (u3) observed in the previous fatty free acids indicates that only one real eutectic mixture has been obtained
analyzed disappears in all the salts but the –CH2 rocking aer crystallization. The melting and solidication tempera-
vibration and bending is maintained at ꢄ720 cmꢁ1
.
tures around 55 C and 52 C, respectively, measured by DSC
analysis were lower than the melting points of the pure palmitic
or stearic acids.3 These results were close to those reported on
the preparation of PA–SA eutectic mixtures of commercial pal-
ꢀ
ꢀ
3.2. Composition, thermal properties and reliability of the
PA–SA eutectic mixture prepared by crystallization
ꢀ
mitic and stearic acids, with melting points of 53.89 C (ref. 3)
The preparation of a eutectic mixture from PA–SA allows of the
preparation of PCMs useful in applications such as to improve
the thermal comfort in buildings through heating applications,
to improve domestic hot water (DHW) tanks efficiency,33,34 air
conditioning condensation heat recovery systems,3 and low
temperature industrial waste heat (IWH) recovery.35 Depending
on the application, palmitic acid and stearic acid present too
high phase change temperatures (Tm). Eutectic mixtures allow
the decrease of the Tm. In this case, the animal fat used showed
a 3 : 2 palmitic/stearic acid ratio (w/w). This ratio is very close to
the palmitic/stearic acid ratio showing eutectic properties,
which can lead to the PCM indicated above.3,36 Hence, authors
realized that by an optimal crystallization, the unsaturated fatty
acids and the saturated fatty acids could be separated with the
advantage of prepare in the crystallization process an eutectic
PA–SA mixture.14 Table 2 shows the thermal properties of the
PA–SA eutectic mixtures. The solute/solvent ratio and crystalli-
zation temperature implied higher saturated fatty acid recovery
with no presence of unsaturated fatty acids. In these conditions,
between 76 to 90% of the palmitic and stearic acids present in
the starting hydrolyzed animal fat were recovered in form of
eutectic mixtures.
and 52.3 ꢀC (ref. 36) and a solidication temperature of
54.37 C.3 The latent heats of melting of the eutectic mixtures
ꢀ
prepared ranged from 183 kJ kgꢁ1 to 176 kJ kgꢁ1 and the
solidication latent heats from 181 kJ kgꢁ1 to 172 kJ kgꢁ1
depending on the mixture achieved (see ESI†). Similar results of
latent solidication heat, 177.67 kJ kgꢁ1 (ref. 3) and 181.7 kJ
kgꢁ1 36 were described in the PA–SA eutectic mixtures prepared
,
from commercial palmitic and stearic acids.
In general terms, aer thermal cycling, solidication and
melting enthalpies present similar reduction in their values
with a maximum decrease of 14% (Table 2). These loses are
below 15% aer thermal cycling, which indicated that the
material shows good thermal cycling stability.37 Moreover,
phase change temperature (i.e. melting and solidication) does
not present outstanding changes, ranging from ꢁ1.8 to 1.1%.
According to the distinct mixtures prepared, the product crys-
tallized in methanol presented the best thermal cycling stability
since melting enthalpy only decreased by 9% and solidication
enthalpy by 11% while the ones crystallized in ethanol present
the worst (14% reduction). Moreover, the mixtures crystallized
in methanol showed the highest latent heat aer 1000 heating/
cooling cycles of the whole materials under study: 164 kJ kgꢁ1
(melting enthalpy), 158 kJ kgꢁ1 (solidication enthalpy). Thus,
The palmitic/stearic acid ratios determined by GC-FID22
ranged from 63.2 : 36.8 for the ethyl acetate crystallization to
Table 2 Thermal properties of the various PA–SA eutectic mixtures prepared from the hydrolyzed animal fat waste by crystallization with various
solvents
Crystallization solvent
Ethyl acetate
Cycling aspects
Hmelting (kJ kgꢁ1
)
Hsolidication (kJ kgꢁ1
)
Tmelting (ꢀC)
Tsolidication (ꢀC)
Not-cycled
182 ꢃ 8
161 ꢃ 3
11
183 ꢃ 5
161 ꢃ 3
12
183 ꢃ 8
158 ꢃ 2
14
176 ꢃ 6
157 ꢃ 1
11
181 ꢃ 14
160 ꢃ 1
11
181 ꢃ 5
158 ꢃ 2
13
180 ꢃ 8
155 ꢃ 2
14
172 ꢃ 10
153 ꢃ 1
11
54.9
54.9
ꢁ0.1
54.1
54.8
ꢁ1.2
55.2
55.0
0.4
53.4
54.3
ꢁ1.8
55.0
55.0
0.0
52.0
52.2
ꢁ0.3
52.5
52.3
0.5
52.3
52.2
0.1
52.1
51.5
1.1
52.1
52.6
ꢁ1.1
Cycled (1000)
Property loss (%)
Not-cycled
Cycled (1000)
Property loss (%)
Not-cycled
Cycled (1000)
Property loss (%)
Not-cycled
Cycled (1000)
Property loss (%)
Not-cycled
Acetone
Ethanol
Hexane
Methanol
179 ꢃ 11
164 ꢃ 2
9
178 ꢃ 10
158 ꢃ 2
11
Cycled (1000)
Property loss (%)
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Table 3 Thermal properties of DHSA and their salts
Product
Hmelting (kJ kgꢁ1
)
Hsolidication (kJ kgꢁ1
)
Tmelting (ꢀC)
Tsolidication (ꢀC)
DHSA
161 ꢃ 11
236
82
76 ꢃ 2
151 ꢃ 7
—
—
68 ꢃ 4
93.8
82.8
—
—
127 ꢃ 1
Lithium salt of DHSA
Sodium salt of DHSA
Calcium salt of DHSA
231.6
204.7
160 ꢃ 1
these mixtures prepared in an easy and robust process can be mixtures of PA–SA showed good performance as PCMs. The
considered as potential PCM candidates due to their thermal melting and solidication temperatures of the various PA–SA
performance and thermal cycling stability and reliability.
PCM prepared were around 55 ꢀC and 52 ꢀC, respectively.
Moreover, the latent heats of the crystallized fractions ranged
172 to 181 kJ kgꢁ1. Thermal cycling test results indicated a good
thermal cycling reliability of PA–SA because the melting and
solidication temperatures of PA–SA PCM oscillated only up to
1.8% and 1.1%, respectively. Concerning the melting and
solidication latent heats of the eutectic PCM, they decreased
up to 14% aer 1000 thermal cycles in the most pronounced
case. Moreover, DHSA was synthesized from non-edible animal
fat. This dihydroxy fatty acid was prepared from the unsaturated
fatty acids present in the mother crystallization liquor, which
evidences the opportunity of provide distinct applications to
animal fat. The DSC analysis performed for rst time on DHSA
and their salts revealed no potential use as PCM. Nevertheless,
a good melting enthalpy and a phase change temperature
higher than common fatty acids could be promising for PCM
interests. The modication of DHSA to new phase change
materials with improved cycling stability is now undergone.
3.3. Determination of the thermal properties of DHSA and
their salts
Table 3 shows the thermal properties of DHSA and their salts
prepared from the animal fat waste. The variation of enthalpy
and melting point observed along the two recorded cycles
announced the poor cycling stability of DHSA. Presumably, the
diol and carboxylic acid moieties present in DHSA reacted
forming an estolide with a decreasing response on the
enthalpies as well as a modication on the phase change
temperature. To conrm this hypothesis, the content in the DSC
1
crucible was recovered and analyzed by H NMR spectroscopy
(see ESI†). Two new signals appeared at 3.58 ppm and 4.83 ppm,
which can be assigned to H–COH (hydrogen bonded to
a secondary alcohol) and R1COOCHR2 (hydrogen bonded to
a secondary alcoxyester), respectively. These signals are char-
acteristics of a DHSA-estolide.38 Nevertheless, the rst DSC
analysis cycle recorded a melting temperature of 94.5 ꢀC (ref. 39)
and also the narrow enthalpy peaks observed made patent that
the developed process allowed the preparation of pure DHSA.
Therefore, the worthy melting enthalpy on the rst recorded
cycle (168 kJ kgꢁ1) and a phase change temperature higher than
common fatty acids are remarkable. These values are promising
for PCM interests but the low cycling stability makes patent the
need of avoid the formation of the detected DHSA-estolides.
The DHSA salts were synthesized presupposing the mainte-
nance of the good enthalpy values of DHSA and trying to
improve the poor cycling stability. Nevertheless, Table 3 shows
that none of the salts synthesized presented a suitable behavior
to be used as PCMs. Only calcium diol salt shows melting and
solidication, but with a low phase change enthalpy value,
whereas magnesium salt does not show melting process.
Unfortunately, lithium salt, which showed a very promising
melting enthalpy value (236 kJ kgꢁ1), did not shown solidica-
tion capability.
Abbreviations
ATR
Attenuated total reectance
threo-9,10-Dihydroxystearic acid
Domestic hot water
Differential scanning calorimeter
Fourier transform-infrared spectroscopy
Gas chromatography-ame ionization detector
Industrial waste heat
DHSA
DHW
DSC
FT-IR
GC-FID
IWH
PA–SA
PCM
TES
Palmitic acid–stearic acid
Phase change material
Thermal energy storage
Acknowledgements
GREA and DBA are certied agents TECNIO in the category of
technology developers from the Government of Catalonia. We
´
thanks to Subproductos Carnicos Echevarria y Asociados S.L
4. Conclusion
(Cervera, Spain) for supplying the non-edible fat. Moreover, the
This paper shows new applications to non-edible animal fat research leading to these results has received funding from the
waste by preparing eutectic mixtures of PA–SA. These European Commission Seventh Framework Programme (FP/
compounds were achieved from animal fat by a conventional 2007–2013) under grant agreement no. PIRSES-GA-2013-610692
hydrolysis (99% yield) process. Various solvents can be used to (INNOSTORAGE) and from the European Union's Horizon 2020
perform the crystallization process. This let to recoveries up to research and innovation program under grant agreement no.
90% of the PA–SA content in the animal fat. These eutectic 657466 (INPATH-TES). The authors would like to thank the
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Catalan Government for the quality accreditation given to their 18 V. Benessere, M. E. Cucciolito, A. De Santis, M. Di Serio,
research groups GREA (2014 SGR 123), Agricultural Biotech-
nology Research Group (2014 SGR 1296) and DIOPMA (2014
R. Esposito, F. Ruffo and R. Turco, J. Am. Oil Chem. Soc.,
2015, 92, 1701–1707.
SGR 1543). This work has been partially funded by the Spanish 19 P. P. KosheelaDevi, T. I. Tuan Noor Maznee, S. S. Hoong,
government
(CTQ2015-70982-C3-1-R
(MINECO/FEDER),
H. Nurul'Ain, S. M. Norhisham, M. N. Norhayati,
A. Srihanum, S. K. Yeong, A. H. Hazimah, V. Sendijarevic
and A. Sendijarevic, J. Appl. Polym. Sci., 2016, 133, 1–10.
ENE2015-64117-C5-1-R (MINECO/FEDER) and ENE2015-64117-
C5-2-R (MINECO/FEDER)). Dr Camila Barreneche would like
˜
to thank Ministerio de Economia y Competitividad de Espana 20 J. Filley, Bioresour. Technol., 2005, 96, 551–555.
´
for her grant Juan de la Cierva FJCI-2014-22886. Aran Sole would 21 G. F. L. Koay, T. Chuah, S. Zainal-abidin, S. Ahmad and
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like to thank Ministerio de Economıa y Competitividad de
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Espana for Grant Juan de la Cierva, FJCI-2015-25741.
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23 D. Swern, J. T. Scanlan and G. B. Dickel, Org. Synth., 1959, 39,
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