Valorisation of corncob residues to functionalised porous carbonaceous materials for the simultaneous esterification/transesterification of waste oils
ABSTRACT Functionalised porous carbonaceous materials prepared from the controlled pyrolysis of corncobs were found to provide excellent activities in the simultaneous esterification/transesterification of highly acidic waste oils to biodiesel-like mixtures. Materials carbonised at 600 °C (mostly microporous) containing –SO3H groups (ca. 1 wt% S, 0.16 mmol g−1 –SO3H) exhibited the optimum yields (>95%) to fatty acid methyl esters after 6 h of reaction.
Article: New Biofuel Integrating Glycerol into Its Composition Through the Use of Covalent Immobilized Pig Pancreatic Lipase[show abstract] [hide abstract]
ABSTRACT: V.C.); firstname.lastname@example.org (F.M.B.); email@example.com (A.A.R.); firstname.lastname@example.org (C.L.); email@example.com (J.C.) Abstract: By using 1,3-specific Pig Pancreatic lipase (EC 126.96.36.199 or PPL), covalently immobilized on AlPO 4 /Sepiolite support as biocatalyst, a new second-generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol and other alcohols of low molecular weight. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a molar relation 2/1. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuel composition, has similar physicochemical properties compared to those of conventional biodiesel and also avoids the removal step of this by-product. The biocatalyst was found to be strongly fixed to the inorganic support (75%). Nevertheless, the efficiency of the immobilized enzyme was reduced to half (49.1%) compared to that of the free PPL. The immobilized enzyme showed a remarkable stability as well as a great reusability (more than 40 successive reuses) without a significant loss of its initial catalytic activity. Immobilized and free enzymes exhibited different reaction mechanisms, according to the OPEN ACCESS Int. J. Mol. Sci. 2012, 13 10092 different results in the Arrhenius parameters (Ln A and Ea). However, the use of supported PPL was found to be very suitable for the repetitive production of biofuel due to its facile recyclability from the reaction mixture.International Journal of Molecular Sciences 08/2012; 13(08):10091-10112. · 2.60 Impact Factor
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Cite this: Green Chem., 2011, 13, 3162
Valorisation of corncob residues to functionalised porous carbonaceous
materials for the simultaneous esterification/transesterification of waste
Rick Arneil Arancon,*aHiginio R. Barros Jr,aAlina M. Balu,bCarolina Vargascand Rafael Luque*b
Received 26th July 2011, Accepted 30th August 2011
Functionalised porous carbonaceous materials prepared from the controlled pyrolysis of corncobs
were found to provide excellent activities in the simultaneous esterification/transesterification of
highly acidic waste oils to biodiesel-like mixtures. Materials carbonised at 600◦C (mostly
microporous) containing –SO3H groups (ca. 1 wt% S, 0.16 mmol g-1–SO3H) exhibited the
optimum yields (>95%) to fatty acid methyl esters after 6 h of reaction.
Increasingly tighter regulations regarding organic waste, and
the demand for renewable chemicals and fuels, are pushing the
manufacturing industry towards higher sustainability in order
to improve cost-effectiveness and meet customers’ demand.
Waste valorisation is one of the current research areas that has
attracted a great deal of attention over the past few years as a
sound and innovative strategies to process food waste is an area
of increasing importance in our current society. Traditionally,
food waste valorisation strategies have mostly focused on low
these methodologies possess low practical applications, being
environmentally unfriendly and economically unattractive. In
this regard, the valorisation of food waste into high added-value
products (e.g., materials, chemicals and biofuels) could provide
several advantages, and importantly contribute to setting up the
basis of a future bio-based industry that is able to implement
waste valorisation practices.
In any case, the conversion of food waste into valuable
products is highly challenging due to several factors, including
for its processing, the quality of the final products, etc.
Corncobs are a common food waste found in public markets.
Hemicelluloses constitute about 30–40% of a mature cob, with
aXavier University, Ateneo de Cagayan, Philippines.
bDepartamento de Qu´ ımica Org´ anica, Universidad de Cordoba, Campus
de Rabanales, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396,
E14014, Cordoba, Spain. E-mail: firstname.lastname@example.org
cDepartamento de Tecnologia Ambiental, Universidad Rey Juan Carlos,
C/Tulipan s/n, Mostoles, Madrid
†Electronic supplementary information (ESI) available: Experimental
and spectral data. See DOI: 10.1039/c1gc15908a
cellulose and lignin accounting for the remaining 60–70%.3
Upon removal of the maize grains, corncobs are generally
disposed of and/or burnt without finding any alternative use
for them. Previous studies have reported the carbonisation of a
range of biomass feedstocks and residues, including vegetable
shells, fruit stones, woody biomass and waste coffee grounds.
These can generate a family of microporous carbonaceous ma-
terials under different activation conditions.4,5This interesting
characterisation, with most studies related to applications of the
being on the catalytic activity of such materials.7Compara-
tively, analogous polysaccharide-derived porous carbonaceous
materials, denoted as Starbons R ?, are found to have interesting
applications in heterogeneous catalysis upon functionalisation
Following our leading work on functionalised Starbon R ?
acid materials for the simultaneous esterification and trans-
esterification of waste oils and fats,10we envisaged an inte-
grated biorefinery concept on the valorisation of food waste
residues (e.g., corncobs) to porous carbonaceous materials via
simple carbonisation, functionalisation with –SO3H groups
and subsequent utilisation as heterogeneous catalysts in the
transformation of low quality highly acidic waste oils into
fatty acid methyl esters (FAME, biodiesel-like mixtures). The
advantage of the devised strategy is the possibility to carry out
a simultaneous acid-catalysed esterification of free fatty acids as
oils.10This concept has been successfully exploited by other
authors, who have developed shrimp shell5and carbohydrate-
derived solid acid catalysts11,12for biodiesel production. How-
ever, these reported materials are intrinsically non-porous and
the distribution of acid sites (especially with the high –SO3H
loading of >1.5 mmol g-1observed in these materials), as well as
the most important stability and recyclability in the reported
3162 | GreenChem., 2011, 13, 3162–3167This journal is © The Royal Society of Chemistry 2011
biodiesel production, is at least arguable.10,12In most cases,
sulfur and –SO3H loadings were determined neither in the
completion.5,11,12In contrast, porous carbonaceous materials,
having a highly developed mesoporosity and 0.3–0.5 mmol g-1
–SO3H, provided good activities in biodiesel production from
waste oils under similar conditions. However, the materials
generally deactivate through –SO3H poisoning, decomposition
and leaching after each reuse.10
into functionalised biomass-derived carbonaceous solid acids
and their utilisation in the production of biodiesel-like biofuels
from waste oils. The activity of the present system is also
compared to similar reported literature systems.
Materials and methods
Uncooked cobs were sampled from a corn farmer in Misamis
Oriental, Philippines. All cobs utilised in this study were
collected from a single source to ensure sample uniformity.
Cobs were made free from adhering kernels by picking and then
sun-drying them for 48 h. The dried cobs were ground prior
to carbonisation. Waste oil samples were taken from a local
fastfood chain. Mixed methyl ester (C14–C24:1) standard was
purchased from Supelco Chemicals, while the internal standard
(methyl pentadecanoate) was obtained from Sigma-Aldrich.
Other chemicals and instruments were obtained from the
laboratory of the Chemistry Department of Xavier University,
unless otherwise specified.
Lou et al.11The dried and ground cobs (80 g) were carbonised
in a furnace under an N2atmosphere at various temperatures
(400–600◦C) and for different times (5 and 10 h) to yield a
new family of porous carbonaceous materials. The carbonised
materials were then powdered using a mortar and pestle, added
to a solution of concentrated sulfuric acid (7 mL sulfuric acid
per gram of solid), sonicated for 15 min, purged with N2for
15 min and subsequently heated under vigorous stirring for 15
h at 150◦C with the aim of introducing –SO3H groups onto
the material’s surface. The mixture was then cooled to room
temperature and quenched with 500 mL of water. The black
precipitate was then filtered off and washed repeatedly with
hot distilled water (~80◦C) until sulfate ions were no longer
detected in the washings (the presence of sulfate was tested by
the addition of 5 drops of 1.0 M BaCl2to 1 mL of filtrate). The
final carbonaceous solid acids were then dried at 60◦C for 48 h
Y-0 where X00 stands for the carbonisation temperature (400,
500 or 600◦C) and Y for the carbonisation time (5 or 10 h).
The carbonization and sulfonation
Fourier transform infrared spectroscopy (FTIR), thermogravi-
metric analysis (TGA), elemental analysis (EA), X-ray diffrac-
tion (XRD), nitrogen physisorption, scanning electron mi-
croscopy (SEM) and transmission electron microscopy (TEM).
Materials were characterized by
FTIR experiments were conducted using a Perkin-Elmer
Spectrum 100 infrared spectrometer equipped with an atten-
uated total reflectance (ATR) module.
Thermal analysis was performed by a simultaneous TG-
DTA measurement using a Setaram thermobalance Setsys 12.
Samples were heated in the temperature range 20–900◦C at a
heating rate of 10◦C min-1in air.
Nitrogen adsorption measurements were carried out at 77 K
using an ASAP 2000 volumetric adsorption analyzer from
Micromeritics. The samples were outgassed for 2 h at 100◦C
under vacuum (p < 10-2Pa) and subsequently analysed. The
linear part of the BET equation was used for determination
of the specific surface area. The cumulative mesopore volume,
VBJH, was obtained from the PSD curve.
with Cu-Ka (l = 1.5418 A˚) radiation over a 2q range from 2 to
80◦using a step size of 0.018 and a counting time per step of
Elemental analysis (EA) was performed using an Elementar
vario EL b apparatus. The absolute errors were 60.1% (CHS)
and 60.2% (O).
Scanning electron micrographs (SEM) and the elemental
composition of the calcined samples were obtained using a
JEOL JSM-6300 scanning microscope by energy-dispersive X-
a high resolution sputtering SC7640 instrument at a sputtering
rate of 1.5 kV min-1up to a 7 nm thickness.
Transmission electron micrographs (TEM) were collected in
a Philips Tecnai-200 electron microscope operating at 200 kV.
The resolution was around 0.4 nm. Samples were suspended in
ethanol and deposited straight away on a copper grid prior to
method was adapted from the AOAC–IUPAC method (969.33)
for the preparation of methyl esters13and from the method
presented by Lou et al.11with some modifications. In a typical
reaction, a 250 mL three-necked flask equipped with a reflux
condenser was charged with a 32:1 methanol/oil molar ratio
and 3% (w/w) of solid acid catalyst. The mixture was refluxed
for 6 h with constant stirring at 700 rpm. The solid catalyst
was filtered after the reaction and cooled to room temperature.
After filtration, a liquid–liquid extraction was performed using
25 mL of a 20 g/500 mL NaCl solution to remove the glycerol
by-product. The non-polar phase (composed of FAME and
solvent) was then subjected to rotary evaporation under a
reduced pressure. The transesterification was also performed
using a homogeneous acid catalyst (sulfuric acid).
The procedure followed for the reuse of the materials was
as follows: upon reaction completion, the catalyst was filtered
off, washed thoroughly with acetone and ethanol, and dried
reaction was then carried out with fresh reactants, and the
results were analysed by GC and GC-MS using an Agilent 6890
N instrument fitted with a capillary column HP-5 (100 m ¥
0.32 mm ¥ 0.25 mm) and a flame ionisation detector (FID).
Response factors of the reaction products were determined with
respect to the substrates from the GC analysis using standard
compounds in calibration mixtures of specified composition.
◦C overnight prior to its reuse in the reaction. The
This journal is © The Royal Society of Chemistry 2011GreenChem., 2011, 13, 3162–3167 | 3163
Results and discussion
The different carbonised materials were sulfonated and subse-
quently characterised using different techniques prior to their
testing in the production of biodiesel from waste oils.
FT-IR experiments conducted on the carbonaceous materials
(Fig. 1) exhibited the typical bands of carbonyl groups (C
1700 cm-1), characteristic of incompletely carbonised materials
O and C–S groups, respectively.15,16The presence of these
functional groups is largely attributed to the sulfonic group
functionalisation in the materials upon sulfonation. Bands at
with those obtained under 3000 cm-1.
for 10 h (S-400-10-0); B, carbonized at 600◦C for 5 h (S-600-5-0); C,
carbonized at 600◦C for 10 h (S-600-10-0); D, carbonized at 500◦C
for 5 h (S-500-5-0); E, carbonized at 500◦C for 10 h (S-500-10-0); F,
carbonized at 400◦C for 5 h (S-400-5-0)].
IR spectra of the sulfonated samples [A, carbonized at 400◦C
Carbohydrates in the corn cobs were transformed to C
sulfonation via electrophilic aromatic substitution, thus leading
to the presence of –SO3H groups.11
Thermogravimetric data of the carbonised materials revealed
that the samples were mostly degraded at ca. 700◦C. Fig. 2
depicts the thermogravimetric analysis (TGA) of sample S-600-
plot: TG in air; bottom plot: TG in argon).
TGA profile of sample S-600-5-0 with detailed mass loss (top
5-0, both under air and argon. Generally, four mass-losses were
observed. The first mass loss (ca. 4% of total weight), obtained
to the removal of water molecules present and/or trapped in
the materials (physisorbed and constitutional water from the
hydroxyl groups of the polysaccharides).17The second mass
loss (accounting for 1–2%, depending on the sample) could
be correlated to the desorption/decomposition of the sulfonic
groups from the catalyst surface, which was subsequently
confirmed by elemental analysis. The third and four mass
losses corresponded to the carbonization of the samples at
temperatures between 250 to 525◦C, and showed the highest
mass loss (accounting for >80% under air). In these steps,
samples undergo a significant restructuring upon calcination,
reaching a final graphite-like structure at high temperatures.
Desorption at these stages indicated the significant production
of carbon dioxide (as seen by TG/MS, results not shown).18
In principle, we cannot rule out the decomposition of minor
quantities of sulfonated species that were not removed at lower
Very similar results were obtained in all cases for both air
and an inert environment, such as argon, despite the significant
differences in the quantities of mass lost.
Elemental analysis (EA) of the samples revealed the presence
with traces of chlorine and potassium, as well as sodium and
magnesium. The presence of sulfur in the materials could be
largely attributed to the sulfonation reaction. Fig. 3 shows the
sulfur concentration for all samples. S-600-5-0 possessed the
highest sulfur content among all the samples. The EA was
also in good agreement with the assigned –SO3H mass loss
from the TGA data at temperatures <523 K. In all cases, the
sulfur content in the materials corresponded to very low –SO3H
of catalyst) in comparison to other similar literature materials
(>0.5 mmol g-1).10–12
materials. The graph shows from left to right S-400-5-0, S-400-10-0, S-
500-5-0, S-500-10-0, S-600-5-0 and S-600-10-0, respectively. The table
shows the –SO3H loading (measured by TG/MS) in the materials.
Sulfur content (%) in the various synthesized carbonaceous
3164 | GreenChem., 2011, 13, 3162–3167This journal is © The Royal Society of Chemistry 2011
The X-ray diffraction (XRD) patterns show the amorphous
nature of the carbonaceous materials (Fig. 4). All samples
showed broad and weak diffraction bands at 10–30 and 40–
50◦, typical of amorphous carbons. The patterns may suggest
the presence of polycyclic aromatic hydrocarbons oriented in
a random fashion.11All the materials exhibited similar XRD
crystalline substances (from impurities in the corncobs) could
also be observed. In any case, the concentration of such species
was <2%, and thus are unlikely to influence the chemical
properties and/or catalytic activity of the materials.
X-Ray diffraction pattern of S-400-5-0.
N2physisorption experiments showed the inherent microp-
orous nature of the materials, which generally had <2 nm pore
sizes (see the ESI†). A significant interparticular macroporosity
was obtained in the materials. Fig. 5 summarises the main
textural properties in terms of surface area and pore volume.
Material S-400-10-0 exhibited the highest surface area (120 m2
g-1) and pore volume (0.38 mL g-1) among all the samples. In
synthesized functionalised carbonaceous materials. The materials were
essentially microporous in nature (pore size < 2 nm).
Textural properties (surface area and pore volume) of the
range (with the exception of S-500-5-0), with pore volumes
varying between 0.2–0.3 mL g-1.
Scanning electron microscopy (SEM) micrographs of the
different functionalised carbonaceous materials are depicted
in Fig. 6. The SEM images show a very similar layered-
type morphology in the carbonised materials, regardless of
the carbonisation temperature. This implies that the range of
are not necessarily relevant factors affecting the morphology
of the material. In any case, the lower temperature carbonised
aggregate particles (see the ESI†).
◦C) generally showed the presence of large
magnifications (a, carbonized at 400◦C for 10 h (1300¥); b, carbonized
at 500◦C for 5 h (2000¥); c, carbonized at 500◦C for 10 h (700¥); d,
carbonized at 600◦C for 5 h, (900¥)).
Representative SEM images of the catalyst samples at different
Representative TEM micrographs of selected carbonaceous
materials are also included in Fig. 7. These also demonstrate
the typical amorphous structure of the carbonaceous materials,
with the high temperature carbonised samples showing a
structure close to graphite-type materials (Fig. 7B).19From
the different characterisation results, we also did not observe
any significant influence of the carbonisation time (5 to 10 h),
as compared to the expected important differences found for
different carbonisation temperatures.
Upon characterisation, the functionalised carbonised materi-
als were subsequently investigated in the production of biodiesel
from waste oils via the simultaneous esterification of free fatty
acids and transesterification of triglycerides present in the waste
oils. The properties of the utilised waste oils in this work are
summarised in Table 1.
feedstock for biodiesel production
Physico-chemical properties of the waste oils utilised as a
Parameter Value ParameterValue
Acid value/mg KOH g-1
Iodine value/mg I2g-1
Saponification value/mg KOH g-1
This journal is © The Royal Society of Chemistry 2011 GreenChem., 2011, 13, 3162–3167 | 3165
Representative TEM micrographs of S600-5-0 (top) and S400-
The results for the different materials are summarised in
Fig. 8. In general, all the functionalised materials provided
good-to-excellent yields of FAME (sum of esterification +
transesterification) after 6 h of reaction.
by the functionalised carbonaceous materials. Results from blank and
FAME yields from esterification/transesterification catalyzed
Remarkably, almost quantitative conversion to FAME was
obtained for the materials S-600-5-0 and S-600-10-0 under the
investigated conditions, despite their low concentration of acid
acid (utilised in the same concentration as the solid acids)
provided a poor 55% conversion to FAME under identical
These findings demonstrate the high activity and potential of
the low acidic solid acid catalysts in the investigated reaction.
The activity of the materials seem to correlate well with their
with previous literature reports.20
Compared to other literature reported systems, the reported
solid acids provided excellent activities in significantly reduced
reaction times, utilising a third of the catalyst quantity by
mass (Table 2), with materials having at least a 5-times lower
concentration of –SO3H groups.
Finally, the reusability and stability of the carbonaceous solid
acids was investigated under the proposed reaction conditions.
For this purpose, the solid acid catalyst was filtered off upon
prior to its reuse in the process. Fig. 9 depicts the catalyst
first reuse, almost completely deactivating after two reuses (17%
conversion). In principle, deactivation could be attributed to the
removal of the active sites upon recycling and/or poisoning due
to the impurities present in the waste oils. Hot filtration tests
showed the filtrate (upon catalyst separation) did not further
react, increasing the biodiesel yield (60% conversion to FAME
upon catalyst filtration vs. 62% conversion after 12 h leaving the
filtrate reacting with fresh oils and methanol).
80◦C, 6 h.
Reuse of S-600-10-0 in the production of biodiesel from waste
These findings were in good agreement with the lack of
detectable sulfur species (<0.5 ppm) in the filtrate. In any case,
–SO3H loadings of ca. 0.1–0.15 mmol g-1do not seem sufficient
to promote the conversion to FAME under homogeneous
is believed to be due to poisoning of the active acid sites in the
A novel methodology to obtain functionalised catalytically-
active porous materials from food waste valorisation has been
3166 | GreenChem., 2011, 13, 3162–3167 This journal is © The Royal Society of Chemistry 2011
Activity comparison of various carbonaceous solid acid catalysts in the production of biodiesel from waste oils
CatalystReaction conditions FAME yield (mol%) Ref.
Starbon R ? acid
32:1 MeOH/oil ratio, 3 wt% catalyst, 6 h, 80◦C (12 wt% FFA in the oil)
3:1 MeOH/oil ratio, 10 wt% catalyst, 15 h, 80◦C (17 wt% FFA in the oil)
30:1 MeOH/oil ratio, 10 wt% catalyst, 8 h, 80◦C (27.8 wt% FFA in the oil)
1:1 MeOH/oil ratio, 10 wt% catalyst, 12 h, 80◦C (27.8 wt% FFA in the oil)
proposed. Microporous carbonaceous materials were obtained
from corncobs and subsequently sulfonated to render solid
acid catalysts which, despite their low acidity, could efficiently
catalyse the simultaneous esterification of free fatty acids
and the transesterification of triglycerides in waste oils. As a
after 6 h of reaction. Due to their low acidity, the materials
generally deactivated after two reuses, losing almost completely
their activity. In any case, this example highlights the potential
in the conversion of food waste residues to valuable benign
compounds (biomaterials and chemicals) of high importance
for future sustainable goals.
Ateneo de Cagayan and the Kinaadman Research Center
Support for Student Research. R. L. gratefully acknowledges
Ministerio de Ciencia e Innovacion for the concession of a
Ramon y Cajal contract (ref. RYC-2009-04199) and Consejeria
de Ciencia e Innovacion, Junta de Andalucia for funding under
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Rick Arneil Arancon