Green bioprocesses in sponge-like ionic liquids

Article abstract of DOI:10.1016/j.cattod.2014.08.025

Abstract Ionic liquids (ILs) are a new class of liquid solvent, whose use has led to a green chemical revolution because of their unique array of physico-chemical properties, headed by their negligible vapour pressure and their exceptional ability to stabilize biocatalysts. Hydrophobic ILs based on cations with long alkyl side-chains, e.g. N,N,N,N-hexadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([C₁₆tma][NTf₂]), are temperature switchable ionic liquid/solid phases that behave as sponge-like systems (sponge-like ionic liquid, SLILs). Based on this new property, SLILs have been used to develop straightforward and clean approaches for producing nearly pure synthetic compounds with added value (e.g. geranyl acetate, anisyl acetate, methyl oleate, etc.) in two steps: an enzymatic synthetic step as liquid phase, and then a product separation step involving simple centrifugation as a solid phase.

Full text of DOI:10.1016/j.cattod.2014.08.025

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Green bioprocesses in sponge-like ionic liquids
Pedro Lozanoa,∗, Juana M. Bernala, Celia Gómeza, Eduardo García-Verdugob,
M. Isabel Burgueteb, Gregorio Sánchezc, Michel Vaultierd, Santiago V. Luisb
a Departamento de Bioquímica y Biología Molecular B e Inmunología, Facultad de Química, Universidad de Murcia, Campus de Excelencia Internacional
Regional “Campus Mare Nostrum”, E-30100 Murcia, Spain
b Departamento de Química Inorgánica y Orgánica, Universidad Jaume I, Avda. Sos Baynat s/n, 12071 Castellon, Spain
c Departamento de Química Inorgánica, Facultad de Química, Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain
d Institut des Sciences Moléculaires, Université Bordeaux-1, CNRS-UMR 5255, Groupe Phoenics, F-33405 Talence Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 July 2014
Received in revised form 11 August 2014
Accepted 20 August 2014
Available online xxx
Ionic liquids (ILs) are a new class of liquid solvent, whose use has led to a green chemical revolu-
tion because of their unique array of physico-chemical properties, headed by their negligible vapour
pressure and their exceptional ability to stabilize biocatalysts. Hydrophobic ILs based on cations with
long alkyl side-chains, e.g. N,N,N,N-hexadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide
([C16tma][NTf2]), are temperature switchable ionic liquid/solid phases that behave as sponge-like systems
(sponge-like ionic liquid, SLILs). Based on this new property, SLILs have been used to develop straight-
forward and clean approaches for producing nearly pure synthetic compounds with added value (e.g.
geranyl acetate, anisyl acetate, methyl oleate, etc.) in two steps: an enzymatic synthetic step as liquid
phase, and then a product separation step involving simple centrifugation as a solid phase.
© 2014 Elsevier B.V. All rights reserved.
Keywords:
Ionic liquids
Sponge-like ionic liquids
Biocatalysis
Green processes
Methyl oleate
Flavour synthesis
1. Introduction
properties, headed by their very low vapour pressure. Besides, ILs
have recently emerged as exceptionally interesting non-aqueous
Green Chemistry is based on the use of safer solvents and reac-
tion conditions, and encourages the use of environmentally benign
non-aqueous solvents and efficient catalysts for chemical reactions
and/or processes [1,2]. Enzymes, as catalysts of living systems,
clearly constitute powerful green tools for chemical processes,
since their activity and selectivity (stereo-, chemo- and region-
selectivity) for catalyzed reactions are far-ranging [3]. Furthermore,
solvents are key elements in chemical processes, where they act as
media for mass-transport, reaction and product separation. They
are responsible for a major part of the environmental impact of
processes in the chemical industry and have a great impact on
cost, safety and health. The search for new environmentally benign
non-aqueous solvents or green solvents, being able to be easily
recovered/recycled and allowing enzymes to operate efficiently in
them, is a priority in the development of integral green chemi-
cal processes [4]. In this context, the recent introduction of ionic
liquids (ILs) in Chemistry could lead to a green revolution in indus-
trial processes, because of their unique array of physico-chemical
reaction media for enzymatic transformations [2,5,6], which can
be improved by the assistance of microwave irradiation [7,8].
The use of ILs, based on cation with short alkyl-side chains
(e.g. 1-butyl-3-methylimidazolium), as reaction media for lipase-
catalyzed biodiesel synthesis provided moderate catalytic activity
because of the resulting biphasic reaction media, formed by an
alcohol-IL phase immiscible with an vegetable oil phase [9,10].
In this context, among the 23 ILs tested for immobilized lipase-
catalyzed biodiesel synthesis, the best yield (80%) was achieved
in the 1-ethyl-3-methylimidazolium trifluoroacetate IL after 12 h
at 50 ◦C, which did not increase at longer reaction times [9].
These results were clearly improved by using the hydrophobic
IL [Bmim][NTf2] as reaction medium, which permitted to 96%
biodiesel yield after 48 h at room temperature [10]. However, the
efficient recovery of the IL for further reuse remains as an impor-
tant problem of this approach. In this context, reaction systems
based on reduced amounts of ILs is another interesting approach.
By using ILs for coating heterogeneous catalysts, also named sup-
ported ionic liquid phases, SILPs, the performance of catalysts
(e.g. activity, stability and selectivity, etc.) are greatly improved
[6,11,12]. Biocatalysis in SILP/scCO2 biphasic systems is another
efficient tool for designing continuous clean biocatalytic processes
∗
Corresponding author. Tel.: +34 868 887392; fax: +34 868 884148.
E-mail address: plozanor@um.es (P. Lozano).
http://dx.doi.org/10.1016/j.cattod.2014.08.025
0920-5861/© 2014 Elsevier B.V. All rights reserved.
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Fig. 1. (A) Structure of the IL [C18tma][NTf2], as an example of sponge-like ionic liquids (SLILs). (B) Scheme of the immobilized lipase-catalyzed synthesis of both methyl
oleate by transesterification and flavour esters by esterification approaches.
that directly provide pure products [2,3]. The clean and continuous
biocatalytic synthesis of biodiesel in SILP/scCO2 (18 MPa and 60 ◦C)
reached up to 95% yield by using packed bed reactors containing
immobilized enzyme particles coated with ILs (e.g. 1.methyl-
3-octadecylimidazolium bis(trifluoromethylsulfonyl)imide, etc.)
[13].
containing nylon membranes (0.2 ␮m pore size) were obtained
from VWR Int. (Barcelona, Spain). Microwave-assisted reactions
were performed in a Microwave Discover System (CEM Corpo-
ration Model 908010, USA) using high purity quartz vials (10 mL
capacity).
Hydrophobic ILs based on cations with long alkyl side-
chains, e.g. N,N,N,N-octadecyltrimethylammonium bis(trifluoro-
methylsulfonyl)imide [C18tma][NTf2], see Fig. 1A), are tempera-
ture switchable ionic liquid/solid phases that behave as sponge-like
systems (sponge-like ionic liquid, SLILs) [14,15], which represent
an interesting way for developing integral green processes. As liq-
uid phases, these SLILs are excellent monophasic reaction media
for lipase-catalyzed synthetic reactions that provided exceptional
enzyme activity and stability [13,16]. As solid phases, the reaction
mixture can easily be fractionated by iterative centrifugations at
controlled temperatures into different phases, allowing straight-
forward product separation and the recovery of the SILLs [17].
The aim of this work was to demonstrate the exceptional suit-
ability of SLILs as a new green platform for performing both the
enzymatic synthesis of high added value products (e.g. flavour
esters and methyl oleate) by means of esterification or transes-
terification (see Fig. 1B), and subsequent separation of the product
as a nearly pure fraction using straightforward clean methodolo-
gies (e.g. centrifugation,). The influence of the nature of the SLILs
and microwave-assistance on the biotransformation yield, as well
as the use of different physical strategies for product separation,
were studied.
2.2. Lipase-catalyzed synthesis of flavour esters in sponge-like
ionic liquid (SLILs)
Three mmol of citronellol, geraniol, nerol or anisyl alcohol, and
1, 2 or 3 mmol of acetic acid were added to 3 mL screw-capped
vials with teflon-lined septa. Then, the corresponding amount of
[C16tma][NTf2] was added to reach a final IL concentration of 60
or 70% (w/w) with respect to the mass substrates. Reaction mix-
tures were pre-incubated at 50 ◦C for 10 min, resulting in fully
clear monophasic systems. Then, 80 mg of MS13× per mmol of car-
boxylic acid were also added. The reaction was started by adding
Novozym 435 (40 mg/mmol of carboxylic acid) and the reaction
was incubated for 4 h at 50 ◦C while shaking (300 rpm), or under
4 W microwave irradiation (which provided a 50 ◦C constant tem-
perature). For products analysis, aliquots (20 ␮L) were taken at
selected times and suspended in 500 ␮L octane, and the resulting
biphasic mixture was shaken to extract the products. The result-
ing mixture was centrifuged at 14,000 rpm for 10 min. Finally,
300 ␮L of the octane extract were added to 100 ␮L of a 100 mM
ethyl propionate (internal standard) solution in octane, and the
final solution was analyzed by CG. For full recovery of the flavour
ester products at 4 h, the reaction mixtures were consecutively
centrifuged four times at 14,000 rpm (15 min) and at room tem-
perature, 21, 10 and 4 ◦C, which resulted in a top liquid phase of
flavour ester and a bottom solid phase containing the SLIL. For
the case of anisyl acetate, the reaction mixture was cooled in an
ice bath for 3 h, and the resulting solid mixture was placed in a
centrifugal filter, then centrifuged at 16,000 rpm (10 min) and at
0 ◦C. This resulted in a top SLIL solid phase, which was retained
inside the filter, and a bottom liquid phase of anisyl acetate. For
all cases, a sample (10 ␮L) of the resulting flavour ester phase
was dissolved in 1 mL acetone-ı6, then analyzed by 300 MHz 1H
NMR and 282 MHz 19F NMR, in a Brucker AC 300E spectrometer
for SLIL detection. All experiments were carried out in dupli-
cate.
2. Materials and methods
2.1. Materials
Immobilized Candida antarctica lipase B (Novozym 435, EC
3.1.1.3) was from Novozymes S.A. (Spain). The SLILs, dode-
cyltrimethylammonium
bis(trifluoromethylsulfonyl)imide
([C12tma][NTf2], 99% purity), tetradecyltrimethylammonium
bis(trifluoromethylsulfonyl)imide ([C14tma][NTf2], 99% purity),
hexadecyltrimethylammonium bis(trifluoromethylsulfonyl)imide
([C16tma][NTf2], 99% purity) and octadecyltrimethylammonium
bis(trifluoromethylsulfonyl)imide ([C18tma][NTf2], 99% purity)
were obtained from IoLiTec GmbH (Germany). Centrifugal filters
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Fig. 2. Green approach for the biocatalytic synthesis of flavour esters in sponge-like ionic liquid (SLILs), and product separation by cooling and centrifugation, including full
recovery and reuse of the enzyme – SLIL system.
2.3. Lipase-catalyzed methyl oleate synthesis in switchable ILs
3. Results and discussion
For each IL (i.e. [C12tma][NTf2], [C14tma][NTf2], [C16tma][NTf2],
or [C18tma][NTf2]), triolein (0.36, 0.23 or 0.11 mmol) was added
into three different screw-capped vials (1.0 mL total capac-
ity) containing SLIL and methanol (2.18, 1.37 or 0.69 mmol).
The resulting mixtures at a 1/6 (mol/mol) triolein–methanol
ratio gave the following SLIL/triolein/methanol ratios (w/w/w):
16.4/68.7/14.9; 47.7/43.0/9.3; 73.9/21.4/4.7, respectively. For each
case, the mixture was previously incubated for 30 min at 60 ◦C,
resulting in fully clear monophasic liquid systems. The reaction
was started by adding Novozym 435 (18% w/w with respect
to the amount of triolein) and the reaction mixture was main-
tained at 60 ◦C for 8 h. At selected times, 20 ␮L aliquots were
taken and suspended in 480 mL of a dodecane/isopropanol (95/5,
v/v) solution, and the resulting biphasic mixtures were shaken
for 3 min, and then centrifuged at 15,000 rpm for 10 min to
extract methyl oleate. Finally, 350 mL of dodecane/isopropanol
extracts (upper phase) were added to 150 mL of a 100 mM ethyl
decanoate and 100 mM tributyrin (internal standards) solution
in dodecane/isopropanol (95/5, v/v), and the final solution was
analyzed by CG. All experiments were carried out in dupli-
cate.
3.1. Biocatalytic production of flavour esters in sponge-like ionic
liquids
Flavour esters of short-chain carboxylic acids (e.g. geranyl
acetate, etc.) are among the most important fragrance compounds
used in the food, cosmetic and pharmaceutical industries. Inter-
national legislations means that “natural” flavour substances can
only be prepared either by physical processes (e.g. extraction) from
natural sources, or by enzymatic or microbial transformation of
precursors isolated from nature, without the use of organic sol-
vents. In this context, enzyme-catalyzed direct esterification of a
flavour alcohol and acetic acid in solvent-free media is the clearest
way to obtain “natural” products. However, this approach provides
moderate results because of the usual enzymes deactivation that
occurs by direct contact with concentrated acids [18].
The suitability of the SIIL [C16tma][NTf2] as reaction medium
for carrying out the enzymatic synthesis of different terpene esters
(e.g. neryl acetate, geranyl acetate and citronellyl acetate) by direct
esterification of acetic acid and the corresponding alcohol was stud-
ied at 50 ◦C, following the operation protocol depicted in Fig. 2. All
the reactions were assayed at 60% (v/v) SLIL concentration, and at
three different acetic acid/flavour alcohol molar ratios (1/3, 2/3 and
3/3 mol/mol). Product yields in the range 90–100% were obtained
at all cases after 4 h reactions. Using the case of geranyl acetate
as example (see Fig. 3A), it can be observed how reaction medium
was fully clear monophasic systems during the enzymatic reac-
tion at 50 ◦C, and then became a monophasic solid system after
cooling to room temperature. Finally, the solid phase could be sep-
arated into two phases, an upper SLIL-free liquid (as determined
by 19F-NMR), and another bottom solid phase containing the IL by
following the iterative centrifugation protocol detailed above (see
Section 2). Fig. 3B shows the resulting product concentration in the
upper SLIL-free phase for each assayed reaction medium, which
was practically independent of the nature of the terpene alcohol in
all the assayed conditions [14].
2.4. GC analysis
GC analysis of the ester flavours reactions was performed
with a Shimadzu GC-17A (Shimadzu Europe, Germany) equipped
with an FID detector. Samples were analyzed on a SupraWax-280
capillary column (30 m × 0.32 mm × 0.5 ␮m, Teknockroma, Spain),
using ethyl propionate as an internal standard, under the following
conditions: carrier gas (He) at 1.1 mL/min; inlet split ratio, 1:20;
temperature programme, 60 ◦C, 4 min, 10 ◦C/min, 240 ◦C, 12 min
[14]. GC analysis of methyl oleate reactions was performed with
a Shimadzu GC-2010 (Shimadzu Europe, Germany) equipped with
an FID detector. Samples were analyzed on a TRB-BIODIESEL capil-
lary column (10 m × 0.28 mm × 0.1 mm, Teknokroma, Spain), using
both ethyl decanoate and tributyrin as internal standards, under
the following conditions: carrier gas (He) at 28.6 kPa (40 mL/min
total flow); temperature programme: 100 ◦C, 10 ◦C/min, 200 ◦C,
15 ◦C/min, 370 ◦C; variable split ratio (80:1–10:1); detector, 320 ◦C
[16].
Fig. 4A depicts the time courses of the Novozym 435-catalyzed
esterification of acetic acid with anisyl alcohol in 70% (w/w)
[C16tma][NTf2] SLIL for a 1/1 (mol/mol) acetic acid/anisyl alcohol
ratio concentration by using either MW irradiation (4 W power)
or conventional heating (50 ◦C). The enzyme was able to synthe-
size anisyl acetate in both cases, reaching an up to 82% yield (with
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Fig. 4. Novozym 435-catalyzed synthesis of anisyl acetate by direct esterification
between acetic acid and anisyl alcohol in 70% (w/w) [C16tma][NTf2] SLIL at 50 ◦C.
(A) Time-course profiles shown by Novozym 435-catalyzed anisyl acetate synthesis
by direct esterification of acetic acid with anisyl alcohol (1:1 molar ratio) in 70%
(w/v) [C16tma][NTf2] SLIL at 50 ◦C conventional heating (white), or at 4 W microwave
irradiation (black). (B) Phase behaviour of the reaction mixture containing the anisyl
acetate product at 50 ◦C (1), 0 ◦C (2), 0 ◦C using a centrifugal filter (0.25 ␮m pore size),
and after centrifugation at 16,000 rpm (10 min) and at 0 ◦C (3).
Fig. 3. Novozym 435-catalyzed synthesis of neryl acetate (NA), geranyl acetate
(GA) and citronellyl acetate (CA) by direct esterification between acetic acid and
the corresponding flavour alcohol in 60% (w/w) [C16tma][NTf2] SLIL at 50 ◦C. (A)
Phase behaviour of the reaction mixture containing geranyl acetate product at 50 ◦
C
(1), 25 ◦C (2), and after centrifugation at 14,000 rpm (30 min) and at 10 ◦C (3). (B)
Effect of the acetic acid/flavour alcohol molar ratio on the terpene ester product
obtained through the esterification reaction catalyzed by Novozym 435 in 60% (w/w)
[C16tma][NTf2] SLIL in a 4 h reaction at 50 ◦C.
ILs here considered is their ability to behave as sponge-like sys-
tems in solid phase, where products can easily separate from the
IL by centrifugation. These features could be explained by refer-
ence to the solid/liquid structural organization of ILs, which possess
analogous structural patterns in both solid and liquid phase, as a
result of the ionic network formed by monomeric units of a cation
surrounded by three anions and vice versa. The incorporation of
molecules into this IL network leads to changes in their physico-
chemical properties, and even the formation of polar and non-polar
regions. Thus, ILs are described as nano-structured materials, which
permits neutral molecules to reside in less polar regions, while
ionic or polar species undergo faster diffusion in the more polar
regions [19,20]. For the case of pyrrolidinium-based ILs, it has been
reported that these ILs are organized as an intricately nanostruc-
tured net, where the ILs containing cations with shorter alkyl chain
substituents form alternating cation–anion monolayer structures
on confinement to a thin film, whereas a cation with a longer
alkyl chain substituent leads to bilayer formation [21]. In agree-
ment with these studies, the nanostructural organization of the
[C16tma][NTf2] SLIL, as temperature switchable liquid/solid phase,
may be described in terms of ordered layers in which the alkyl side
chains of the cations provide hydrophobic holes appropriate for
“housing” flavour molecules in the solid phase. Then, centrifuga-
tion of the solid mixture across the filter allowed the “wet sponge”
to be “wrung”, and the product to be recovered. In this context,
the ability of these SLILs to melt at temperatures compatible with
enzyme catalysis permitted the development of a straightforward
and green method for flavour ester production based on two-steps:
respect to the initial acetic acid) in 1 h under MW irradiation. The
assistance with MW irradiation provided a slightly better anisyl
acetate profile than conventional heating, which reached a similar
product concentration as MW after 4 h. Fig. 4B shows that the final
reaction mixture was a fully clear monophasic system, and once
again, it became solid after cooling to room temperature. Apply-
ing the above centrifugation protocol at controlled temperatures to
the solid reaction mixture did not permit the physical separation
of both phases for product recovery because the solid SLIL phase
rapidly re-dissolved into the anisyl acetate phase. Thus, a new frac-
tionation approach based on the use of a centrifugal nylon filter
(0.2 ␮m pore size) was assayed at 0 ◦C. Using this new approach,
the SLIL solid was retained by the nylon membrane, while the
liquid anisyl acetate phase crossed the membrane to the bottom
tube, similarly to the way in which a wet sponge can be wring-
ing. In this case, the synergism observed between MW irradiation
and biocatalysis agreed with the results obtained for a variety of
synthetic reactions, where improvements in the reaction rate have
been attributed to both thermal and non-thermal effects of this
irradiation [7,8].
The excellent suitability of water-immiscible ILs for carrying
out biocatalytic synthetic reactions has been widely reported in
the literature. This property has been attributed to the native con-
formation of the proteins being maintained, as demonstrated by
spectroscopic techniques, thus protecting them against the usual
unfolding that occurs in non-aqueous environments [2–4]. Never-
theless, the most exciting and intriguing feature of the hydrophobic
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Fig. 5. Green approach for the biocatalytic synthesis of methyl oleate in sponge-like ionic liquids (SLILs), and product separation by addition of water followed by cooling
and centrifugation.
(i) lipase-catalyzed direct esterification, and (ii) clean separation of
the reaction product by cooling/centrifugation [14,17].
3.2. Biocatalytic production of methyl oleate in sponge-like ionic
liquids
One of the most important limitations in the catalytic pro-
duction of methyl oleate (biodiesel) by transesterification of
triacylglycerides with methanol can be directly attributed to the
non-miscibility of the substrates, leading to a two-phase system
that reduces process efficiency and, for the case of biocatalysts,
results in full enzyme deactivation through direct contact with
methanol. It has been demonstrated how highly hydrophobic ILs
based on an imidazolium cation with a long alkyl-side chain (e.g.
[C18mim][NTf2]) are able to dissolve both triolein and methanol
at any concentration, providing one-phase reaction media that
showed excellent suitability for the biocatalytic synthesis of methyl
oleate (up to 96% yield in 6 h at 60 ◦C). Furthermore, the excellent
suitability of the enzyme-IL system for methyl oleate synthesis was
also demonstrated by the total preservation of the catalytic activ-
ity for subsequent reuse [2,16]. However, any industrial application
of this approach should involve a clean approach so that the syn-
thesized methyl oleate can be extracted and the IL be recovered
and reused (e.g. by using immobilized enzymes onto covalently
attached IL phases and continuous scCO2 flow) [13,22]. However,
despite the greenness of supercritical fluids, their industrial appli-
cation for biodiesel production may be doubtful mainly because of
the excessive cost of high-pressure equipment.
In agreement with the schematic protocol of Fig. 5, the bio-
catalytic synthesis of methyl oleate was carried out through
methanolysis of triolein, using a 1/6 triolein/methanol molar ratio
Fig. 6. (A) Effect of the alkyl chain length of the [1-alkyltrimethylammonium] cation
of the SLIL on the methyl oleate yield obtained by Novozym 435-catalyzed methanol-
ysis of triolein (1/6 triolein/methanol mol ratio) in an 8 h reaction at 60 ◦C and at
three different SLIL concentrations. (B) Phase behaviour of the reaction mixture con-
taining both methyl oleate and glycerol products at 60 ◦C (1), 60 ◦C after addition of
water (2), 25 ◦C (3), and after three consecutive centrifugation steps at 15,000 rpm
(1 h) at room temperature, 23 and 15 ◦C, respectively (4).
as substrate, in four different [Cntma][NTf2] (n = 12, 14, 16 or 18,
respectively) SLILs as reaction media for an 8 h of reaction period at
60 ◦C, and at different SLIL concentrations. As can be seen in Fig. 6A,
regardless of the nature of the ILs, methyl oleate yields close to 100%
were obtained at SLIL concentrations higher than 40% (w/w), which
could be related with the fact that a minimum IL content in the reac-
tion medium is necessary to achieve full miscibility between the
substrates as a monophasic system (see Fig. 6B) [13]. Furthermore,
an increase in the alkyl chain length of cation slightly improves
the catalytic efficiency of the system, and so [C18tma][NTf2] was
selected as the most suitable SLIL for performing methyl oleate
synthesis [17].
temperature, separation was achieved after three consecutive cen-
trifugation steps at 15,000 rpm (15 min) at room temperature,
23 and 15 ◦C. This resulted in a three phases system: an upper
methyl oleate phase, a middle liquid aqueous phase containing the
glycerol by-product, and a bottom solid containing the SLIL (see
Fig. 6B). Additionally, the presence of water, a green solvent that
is not miscible with methyl oleate or SLIL, improved the separa-
tion between phases, ordered in agreement with their respective
densities (methyl oleate < water < SLIL) [17]. The suitability of the
proposed methodology for clean methyl oleate separation was thus
To separate of both the methyl oleate and glycerol products from
the reaction medium containing SLIL, a new cooling/centrifugation
approach, based on the prior addition of hot water (60 ◦C), was
developed (see Fig. 6B). By cooling the resulting mixture to room
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demonstrated. Increasing the centrifugation time and/or speed of
the protocol might improve the extraction yields, although the tem-
perature at which centrifugation can be carried out is limited by
the melting point of the fatty acid methyl esters present in the
methyl oleate. Furthermore, this approach also includes an easy
way to separate both methyl oleate and glycerol into different frac-
tions. Other proposed approaches based on liquid–liquid extraction
with organic solvents (e.g. hexane), or supercritical fluids are less
interesting for industrial application, both from the economic and
technical standpoint [2,15,17].
Acknowledgements
This work was partially supported by Ministry of Economy and
Competitiveness (MINECO), Spain (Ref: CTQ2011-28903) grant.
We thank Ramiro Martinez (Novozymes Espan˜a. S.A.) for a gift of
Novozym 435.
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applied for classical separation processes in Chemical Engineering
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value compounds (flavour esters, methyl oleate, etc.). The protocol
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hydrophobic compounds like methyl oleate or esters flavours as
a liquid phase, and then to be “wrung out” by centrifugation at
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Please cite this article in press as: P. Lozano, et al., Green bioprocesses in sponge-like ionic liquids, Catal. Today (2014),
http://dx.doi.org/10.1016/j.cattod.2014.08.025