Catalytic synthesis of glycerol tert-butyl ethers as fuel additives from the biodiesel by-product glycerol

Article abstract of DOI:10.1155/2015/763854

Glycerol is a major by-product in the biodiesel production process. Every 100 kg of biodiesel produced generates approximately 10 kg of crude glycerol. As the biodiesel industry has expanded rapidly in recent years, finding new uses of the excess crude glycerol is important. Many studies have examined alternative uses of crude glycerol. One of them is the use of glycerol derivatives, such as glycerol tert-butyl ethers as fuel additives. In this paper, the etherification kinetics of glycerol with tert-butyl alcohol to glycerol tert-butyl ethers was studied using an Amberlyst catalyst. The influences of the catalyst type and loading, reaction time, molar ratio, and temperature were investigated in detail.

Full text of DOI:10.1155/2015/763854

Hindawi Publishing Corporation
Journal of Chemistry
Volume 2015, Article ID 763854, 6 pages
http://dx.doi.org/10.1155/2015/763854
Research Article
Catalytic Synthesis of Glycerol tert-Butyl Ethers as Fuel
Additives from the Biodiesel By-Product Glycerol
Rui Huang and Eui Yong Kim
Department of Chemical Engineering, University of Seoul, Seoulsiripdaero 163, Dongdaemun-gu, Seoul 130-743, Republic of Korea
Correspondence should be addressed to Eui Yong Kim; eykim@uos.ac.kr
Received 26 January 2015; Revised 2 April 2015; Accepted 7 April 2015
Academic Editor: Yiannis Kourkoutas
Copyright © 2015 R. Huang and E. Y. Kim. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Glycerol is a major by-product in the biodiesel production process. Every 100 kg of biodiesel produced generates approximately
10 kg of crude glycerol. As the biodiesel industry has expanded rapidly in recent years, finding new uses of the excess crude glycerol
is important. Many studies have examined alternative uses of crude glycerol. One of them is the use of glycerol derivatives, such
as glycerol tert-butyl ethers as fuel additives. In this paper, the etherification kinetics of glycerol with tert-butyl alcohol to glycerol
tert-butyl ethers was studied using an Amberlyst catalyst. e influences of the catalyst type and loading, reaction time, molar ratio,
and temperature were investigated in detail.
1. Introduction
the production of GTBEs at low cost and high yield is
an important research topic. By reacting of glycerol with
isobutene could be obtained GTBEs in the presence of acid
catalysts [7, 8]. On the other hand, its boiling point is −6.9∘C,
which means high pressure conditions are necessary to keep
it in the liquid state. e most commonly used reactor is an
autoclave, which can be adjusted to a high pressure about
1.5 MPa to keep isobutene in the liquid state. Despite this,
the performance of the etherification process is strongly
dependent on mass transfer between the two materials [9].
Compared to isobutene, tert-butyl alcohol (TBA) is more
attractive for producing GTBE by the glycerol etherification
reaction in a solid-liquid catalytic process [10]. TBA is a
useful reactant in the etherification reaction to overcome the
technological problems arising from the need to use solvents
to dissolve glycerol. e etherification reaction is carried
out at atmospheric pressure to optimize the reaction con-
ditions. When the etherification reaction between glycerol
and TBA takes place in the presence of an acid catalyst,
some or all of the hydroxyl groups in the glycerol molecule
are reacted to form five different types of alkyl glycerol
ethers, as shown in Figure 1. Among the ethers, 3-tert-
butoxy-1,2-propanediol and 2-tert-butoxy-1,3-propanediol
have relatively high water solubility and are unsuitable as
Biodiesel is a renewable, clean-burning diesel replacement
from biological sources that it is produced widely around
the world. On the other hand, every 100 kg of biodiesel pro-
duced generates approximately 10 kg of crude glycerol. e
glycerol market is influenced by the commercial availability of
biodiesel. erefore, how to use the surplus glycerol profitably
is an important problem to solve in biodiesel production.
Many applications of glycerol have been developed over
the past few decades [1–4]. Despite these, new fields of
glycerol use are needed to improve the economics of biodiesel
production. Among the derivatives, glycerol tertiary butyl
ethers (GTBEs) are excellent additives with large potential for
diesel and biodiesel reformulation. In particular, a mixture of
1,3-di-, 1,2-di-, and 1,2,3-tri-tert-butyl glycerol, when incor-
porated in standard 30–40% aromatic-containing diesel fuel,
leads to a significant decrease in the emissions of particulate
matter, hydrocarbons, carbon monoxide, and unregulated
aldehydes [5, 6]. e addition of glycerol ether additives
results in a slight increase in NO emissions; however, the
ꢀ
use of sufficient known cetane improvers to increase the fuel
cetane value by 5 to 10 units will reduce the NO emissions
ꢀ
to well below the level of the base reference fuel. erefore,

2
Journal of Chemistry
H3C
CH3
CH3
OH
OH
CH3
OH
OH
H+
O
H3C
H3C
O
HO
OH
+
+
H3C
O
HO
+
H
H
OH
CH3
CH3
TBA
H2O
Glycerol
MTBG 1
MTBG 2
H3C
H3C
O
CH3
CH3
CH3
CH3
CH3
O
CH3
H+
O
MTBG 1
MTBG 2
HO
+
+
+
H3C
OH
H3C
O
H
H
O
OH
CH3
CH3
CH3
TBA
CH3
H3C
H2O
DTBG 1
H3C
DTBG 2
CH3
CH3
O
CH3
OH
CH3
CH3
H+
DTBG 1
DTBG 2
+
+
H3C
H3C
O
O
H
H
CH3
O
CH3
CH3
H3C
TTBG
H2O
TBA
Other possible side reactions
(1) TBA
Isobutene + H2O
(2) DTBG + DTBG
(3) MTBG + MTBG
MTBG + TTBG
G + DTBG
Figure 1: Tert-butylation of glycerol and side reactions.
diesel-blending agents whereas the higher ethers of glyc-
erol, such as 1,3-di-tert-butoxy-2-propanol (DTBG1), 1,2-di-
tert-butoxy-3-propanol (DTBG2), and 1,2,3-tri-tert-butoxy-
2-propane (TTBG), have good solubility in biofuel, a high
flash point, low water affinity, and negligible cetane reduction,
making them a potential candidate fuel additive [10]. In
this study, the etherification kinetics of glycerol with tert-
butanol to glycerol tert-butyl ethers was examined using an
Amberlyst catalyst. Amberlyst is a strongly acidic, sulfonic
acid, macroreticular polymeric resin based on cross-linked
styrene divinylbenzene copolymers. It is used in catalytic
processes including etherification reaction. e influences of
the catalyst type and loading, reaction time, molar ratio, and
temperature were investigated in detail. e present study
aims to produce as much DTBGs and TTBG as possible while
minimizing the production of MTBGs.
2. Experimental
2.1. Materials. Glycerol (Extra Pure) and tert-butyl alcohol
(Extra Pure) were used as the reactants in the etherifica-
tion reaction. Both reagents were purchased from Duksan
Reagents of Korea. Acetone (99.5%) (Duksan Chem. Co.,
Korea) was used as the analysis reagent. Industrial-grade,
strongly acidic ion-exchange resins, such as Amberlyst 15
(Sigma-Aldrich Co.), Amberlyst 35 wet (Dow Chem. Co.),
and Amberlyst 35 dry (Dow Chem. Co.) were used as the
catalysts. Table 1 lists the typical properties of the catalysts
used in this study.
2.2. Experiment and Analysis Method. e reactions were
carried out in 150 mL glass reactors equipped with Graham
condensers under pressure. All the reactors were settled in
a water channel that was equipped with two temperature

Journal of Chemistry
3
100
80
60
40
20
0
Table 1: Characteristics of catalysts of catalysts used in this study.
Amberlyst 35 Amberlyst 35
Characteristics
Physical form
Amberlyst 15
Opaque beads
dry
wet
Opaque
Opaque
beads
beads
Concentration
(eq/kg)
≥4.7
≥5.0
50
≥1.9
50
Surface area (m2/g)
Average pore
53
300
300
300
˚
diameter (A)
Total pore volume
(mL/g)
0.40
0.35
0.35
0
1
2
3
4
5
6
Table 2: GC retention time of each peak.
Time (h)
Amberlyst 35 wet
Amberlyst 35 dry
Amberlyst 15
Peak name
TBA
TTBG
Retention time (min)
2.41 0.05
6.31 0.05
DTBG 1
DTBG 2
MTBG 1
MTBG 2
Glycerol
7.46 0.05
8.20 0.05
10.21 0.05
11.26 0.05
15.35 0.05
Figure 2: Influence of the different catalysts on glycerol conversion.
Reaction conditions: 70∘C, TBA to glycerol molar ratio = 4 : 1,
catalyst loading = 7.5 wt.% to glycerol, and 8 hours.
chosen as an indicator of reaction conversion. e glycerol
conversion was defined as follows [13]:
controllers. In a typical experiment, sufficient water was
added to the water channel and the temperature was set
using a temperature controller. e reactants, catalysts, and
stirring bar were placed in the reactors. TBA was first placed
in the reactor followed by glycerol because the density of TBA
was smaller than that of glycerol. By doing so the sequential
reactant addition method can provide good mixing of the
two reactants (stirring velocity 1000 min−1). e samples
obtained from the experiment were first treated by centrifugal
separation to separate the catalyst from the reaction mixture.
e reaction mixture was then diluted and mixed with the
Glycerol conversion (%)
(MTBGs + DTBGs + TTBG) mmol/L
=
(1)
(Glycerol remaining + MTBGs + DTBGs + TTBG) mmol/L
× 100.
3. Results and Discussion
3.1. Selection of Reaction Catalyst. A number of Amberlyst
catalysts are active in the reaction because of its large
average pore diameter or in other words, its high cross-linked
macroreticular structure. e large pore diameters allow rel-
atively large glycerol molecules to access the inner surface of
the catalyst to undergo a transformation. Klepa´cˇova´ et al. [12]
and Ozbay et al. [14] examined various kinds of Amberlyst
type catalysts, such as Amberlyst 15, Amberlyst 16, Amberlyst
31, Amberlyst 35, Amberlyst 36, Amberlyst 39, and Amberlyst
119; both wet and dry forms were examined if they existed.
e main difference between wet and dry form of Amberlyst
35 is the concentration of acid sites. e best results were
obtained using Amberlyst 15 and Amberlyst 35, which are
commonly used as catalysts for the transformation reaction
of aliphatic ether oxygenates. ey have a prominent large
average pore diameter and surface area compared to the
others.
To select the most efficient catalyst, comparative exper-
iments were conducted under the same reaction conditions
using Amberlyst 15, Amberlyst 35 dry and wet forms; the
glycerol conversion from each reaction with the different
catalysts was obtained. Although the mean pore diameters
of these catalysts were the same, the surface area and pore
volume of Amberlyst 15 are larger than those of dry and wet
organic solvent, acetone ((CH ) CO), and 1 ꢀL was injected
3 2
into a gas chromatograph for quantitative analysis [11].
e reaction samples were analyzed by gas chromatography
(GC) using a DB-WAX column and a FID detector. Five
abbreviations of the products are defined as follows: 3-tert-
butoxy-1,2-propandiol or mono-tert-butyl ether of glycerol
1 (MTBG 1), 2-tert-butoxy-1,3-propandiol, or mono-tert-
butyl-ether of glycerol 2 (MTBG 2), 1,3-di-tert-butoxy-2-
propanol, or di-tert-butyl ethers of glycerol 1 (DTBG 1), 1,2-
di-tert-butoxy-3-propanol, or di-tert-butyl ether of glycerol 2
(DTBG 2), and tri-tert-butoxy-propane or tri-tert-butyl ether
of glycerol (TTBG). As shown in Table 2, retention times for
the compounds are different, so they can be well separated.
Since the area of each peak indicates concentration, the con-
centration of each compound could be calculated accurately
with reference to its calibration data. Because MTBG1 and
MTBG2 are isomers, it is possible to use the same calibration
data to calculate their concentrations. In the case of DTBG
and TTBG, response factors were extrapolated from that of
MTBG [12]. TBA should be present in excess to glycerol
because each step of the reaction consumes it, so glycerol was

4
Journal of Chemistry
100
98
96
94
92
90
88
86
100
90
80
70
60
50
40
30
20
10
84
0
2.5
5.0
7.5
10.0
12.5
0
5
10 15 20 25 30 35 40 45 50 55 60
Time (h)
Catalyst loading (wt.%)
×10−3
4.0
Figure 3: Influence of the catalyst loading on glycerol conversion.
Reaction conditions: 70∘C, TBA to glycerol molar ratio = 4 : 1, and 8
hours.
×10−3
3.0
3.2
3.0
2.8
2.6
2.4
2.2
2.0
0.0
2.0
1.0
0.0
0
5
10 15 20 25 30 35 40 45 50 55 60
Time (h)
DTBGs
MTBGs
2
3
4
5
6
7
8
9
10 11 12 13
Figure 5: Glycerol conversion and products yields as a function of
time. Reaction conditions: 70∘C, TBA to glycerol molar ratio = 4 : 1;
Amberlyst 15 catalyst = 7.5 wt.% to glycerol.
Catalyst loading (wt.%)
MTBGs
DTBGs + TTBG
Figure 4: Influence of catalyst loading on product yield. Reaction
conditions: 70∘C, TBA to glycerol molar ratio = 4 : 1, and 8 hours.
is in accordance with the previously published results [15].
On the other hand, the differences in conversion between
5.0% or 10.0% and 7.5% were not so significant; the highest
glycerol conversion was 96% at 7.5 wt.% and around 94%
at 5.0 wt.% and 10.0 wt.%. Similarly, the desired product
(DTBGs and TTBG) yield was 2.69 × 10−3 mmol/L when the
catalyst loading was 7.5 wt.% and was 2.64 × 10−3 mmol/L and
2.67 × 10−3 mmol/L when loading was 5.0 wt.% and 10.0 wt.%,
respectively. In conclusion, the catalyst loading was found
to exert a relatively modest influence on the etherification
reaction.
Amberlyst 35, providing a larger number of surface active
sites. As shown in Figure 2, the conversion of glycerol in
the presence of both dry and wet Amberlyst 35 was much
lower than that of the Amberlyst 15 catalyst. Based on these
results, Amberlyst 15 was selected as the catalyst for use in the
subsequent experiments.
e effects of the catalyst amount were next assessed
by varying the Amberlyst 15 loading in terms of the weight
percentage of the glycerol weight. Figures 3 and 4 show the
effects of the catalyst loading on the glycerol conversion and
ether concentration, respectively; both the glycerol conver-
sion and product yield were low at the lowest and highest
catalyst loading levels tested, respectively. e best results
were obtained at a 7.5 wt.% loading of glycerol. is pattern
3.2. Effect of the Reaction Time. In this study, an etherification
experiment was conducted for up to 60 hours to establish
the reaction profile as a function of time and select the
optimal reaction time. Figure 5 shows the conversion of
glycerol and the concentrations of MTBGs and DTBGs.

Journal of Chemistry
5
×10−3
3.0
100
90
80
70
60
50
40
30
20
10
0
2.5
2.0
1.5
1.0
0.5
0.0
50
60
70
80
2
4
6
8
10
Temperature (∘C)
Molar ratio
Glycerol conversion
Selectivity (DTBGs + TTBG)/(MTBGs + DTBGs + TTBG)
MTBGs + DTBGs + TTBG
Figure 6: Influence of the molar ratio on the product yield. Reaction
conditions: 70∘C, Amberlyst 15 catalyst = 7.5 wt.% to glycerol, and 8
hours.
Figure 7: Influence of temperature on glycerol conversion. Reaction
conditions: Amberlyst 15 catalyst = 7.5 wt.% to glycerol, molar
ratio = 4 : 1, and 8 hours.
e reaction was quite fast in the first reaction hour and
reached the highest conversion at approximately 6 hours; it
then began to decrease thereafer. e highest conversion of
glycerol was approximately 96.0% to 97.0% at 5 to 6 hours
and approximately 80% at 60 hours; the products yields
were highest at approximately 5 to 8 hours. Afer 6 hours,
both the conversion and MTBGs concentration decreased.
e concentration of DTBGs also decreased to 6 hours but
remained constant until 60 hours. ese results show that the
reverse reaction and a third-side reaction shown in Figure 1
play a role in the reaction, causing one mol glycerol and
one mol DTBG to be generated from two mole MTBGs
afer approximately 6 hours of reaction. is phenomenon
led to a decrease in glycerol conversion afer 6 hours of the
reaction. Based on the results of this experiment, to obtain
the maximum yield of the glycerol ethers, the reaction should
be set between 5 and 8 hours. Systematic optimization studies
will be conducted further to locate the optimal reaction time.
to the higher viscosity of the reaction mixture. When the
TBA/glycerol ratio was low, the higher viscosity led to less
mass transfer between the phases. As the ratio was increased,
mass transfer became easier and the highest concentrations
were obtained when the molar ratio was 8. When the molar
ratio was 10, more than two times the quantity of TBA was
present. e surplus TBA enhanced the side reaction, having
a negative influence on the ether concentration. In summary,
the molar ratio affects the reaction in a positive way; it is
essential to use large excesses of TBA to maximize total ether
concentration. erefore, the desired level of molar ratio
should be set from 4 to 8, while more accurate assessments
will be done with the design of the experiment approach.
3.4. Effect of Temperature. Glycerol conversion increased
with increasing reaction temperature. At high temperatures,
glycerol was not totally converted due to the occurrence
of deetherification reactions, which became increasingly
important as the reaction temperature was increased [10]. A
higher temperature also enhanced the secondary reactions,
such as the disproportionation of glycerol ethers [12], which
can be observed from the decreased glycerol conversion and
product yields. is also means that the activation energies in
the side reactions are higher than those in the etherification
reactions. In addition, in this study, one of the reactants,
TBA, has a comparatively low boiling point of 82.4∘C under
a standard atmosphere. e evaporation near 80∘C would
become so serious that the reflux condenser would be unable
to prevent a portion of the reaction mixture vapor from
leaving the condenser, resulting in a large loss of TBA. is
in turn would reduce the extent of glycerol conversion. On
the other hand, the temperature also affected the reaction by
its effect on the viscosity of the reaction mixture similar to the
molar ratio. A higher viscosity can impede mass transfer and
3.3. Effect of Molar Ratio. From the reaction mechanism,
the formation of an ether molecule consumes 1 to 3 TBA
molecules depending on the extent of the reaction, and the
hydrolysis side reaction consumes 1 TBA molecule. erefore,
to enhance the yield of the desired higher ethers of glycerol,
TBA should be present in excess compared to glycerol. Dif-
ferent TBA to glycerol molar ratios were tested to determine
their effects on total concentration of ethers. As shown in
Figure 6, an increase in the molar ratio leads to an increase in
total concentration of ethers when the molar ratio is less than
8. Concentration of ethers was almost zero at the lowest molar
ratio tested (TBA/glycerol = 2). e viscosity of the reaction
mixture can explain the influence of the molar ratio on this
reaction [11]. Given that these experiments were conducted
under the same reaction conditions and the stirring speed
was the same, the very low concentration was likely due

6
Journal of Chemistry
lower the selectivity. Figure 7 shows the effect of temperature
on glycerol conversion and selectivity of DTBG and TTBG.
e tert-butylation of glycerol was studied using Amberlyst
15 over the temperature range, 50 to 80∘C. e conversion
of glycerol increased with increasing temperature. On the
other hand, as the temperature increased, the side reaction
of the disproportionation of glycerol ethers would also occur,
as shown in the mechanism section. e highest glycerol
conversion was observed at 70∘C (97.0%); the selectivities
of DTBGs and TTBG were also highest at 70∘C (30.3%).
is pattern of temperature influence agrees with previous
results [16]. In summary, temperature affected the reaction
in the following aspects: enhancement of the side reactions;
TBA evaporation; and changes in the viscosity of the reaction
mixture. As mentioned previously, viscosity is also a function
of the molar ratio. erefore, further research will be needed
to study the relationships between temperature and other
factors.
and new trends in combustion,” Renewable and Sustainable
Energy Reviews, vol. 27, pp. 475–493, 2013.
[3] S. Nitayavardhana and S. K. Khanal, “Biodiesel-derived crude
glycerol bioconversion to animal feed: a sustainable option for
a biodiesel refinery,” Bioresource Technology, vol. 102, no. 10, pp.
5808–5814, 2011.
[4] E. A. Barsa and B. M. Steinmetz, “Preparation of glycerol tert-
butyl ethers,” US Patent 0240086 A1, 2009.
[5] A. Behr, J. Eilting, K. Irawadi, J. Leschinski, and F. Lindner,
“Improved utilisation of renewable resources: new important
derivatives of glycerol,” Green Chemistry, vol. 10, no. 1, pp. 13–30,
2008.
[6] A. Jaecker-Voirol, I. Durand, G. Hillion, B. Delfort, and X.
Montagne, “Glycerin for new biodiesel formulation,” Oil & Gas
Science and Technology, vol. 63, no. 4, pp. 395–404, 2008.
[7] H. Noureddini, W. R. Dailey, and B. A. Hunt, “Production
of ethers of glycerol from crude glycerol-the by-product of
biodiesel production,” Papers in Biomaterials 18, 1998.
[8] A. Behr and L. Obendorf, “Development of a process for the
acid-catalyzed etherification of glycerine and isobutene forming
glycerine tertiary butyl ethers,” Engineering in Life Sciences, vol.
2, pp. 185–189, 2003.
4. Conclusions
e etherification reaction of glycerol and tert-butyl alcohol
to GTBEs using Amberlyst as a catalyst was investigated
to produce as much DTBGs and TTBG as possible while
minimizing the production of MTBGs. Gas analysis by GC
was performed. e influence of the catalyst type and loading,
reaction time, molar ratio, and temperature on the ether-
ification reaction was investigated in detail by calculating
the conversion of glycerol and the selectivity of GTBEs. e
experimental results showed that Amberlyst 15, which has
large surface area and pore volume, was the best catalyst.
e catalyst loading was found to have some influence on
the etherification reaction. Based on the reaction time, the
reaction should be set between 5 and 8 hours to obtain the
maximum concentration of glycerol ethers. is might be
caused by the reverse reaction of glycerol ethers. e molar
ratio affected the reaction in a positive way. erefore, it
is essential to use large excesses of TBA to maximize the
product yield. e highest glycerol conversion and the highest
selectivity of DTBGs and TTBG were observed at 70∘C.
[9] V. Mangourilos, D. Bombos, T. Juganaru, I. Bolocan, M. Bom-
bos, and D. Ciuparu, “Etherification of glycerol with isobutene
on Amberlyst 35 ion exchange resin catalyst in presence of a
cationic emulsifier,” Revista de Chimie, vol. 60, no. 12, pp. 1338–
1342, 2009.
[10] F. Frusteri, F. Arena, G. Bonura, C. Cannilla, L. Spadaro, and
O. Di Blasi, “Catalytic etherification of glycerol by tert-butyl
alcohol to produce oxygenated additives for diesel fuel,” Applied
Catalysis A: General, vol. 367, no. 1-2, pp. 77–83, 2009.
[11] R. S. Karinen and A. O. I. Krause, “New biocomponents from
glycerol,” Applied Catalysis A: General, vol. 306, pp. 128–133,
2006.
[12] K. Klepa´cˇova´, D. Mravec, A. Kaszonyi, and M. Bajus, “Etheri-
fication of glycerol and ethylene glycol by isobutylene,” Applied
Catalysis A: General, vol. 328, no. 1, pp. 1–13, 2007.
[13] J. F. Izquierdo, P. R. Outo´n, M. Gala´n et al., “Ethers of
glycerol and isoamylenes as biodiesel additives: synthesis and
characterization,” Chemical Engineering Transactions, vol. 32,
pp. 877–882, 2013.
[14] N. Ozbay, N. Oktar, G. Dogu, and T. Dogu, “Conversion
of biodiesel by-product glycerol to fuel ethers over different
solid acid catalysts,” International Journal of Chemical Reactor
Engineering, vol. 8, article A18, 2010.
Conflict of Interests
e authors declare that there is no conflict of interests
regarding the publication of this paper.
[15] K. Klepa´cˇova´, D. Mravec, and M. Bajus, “tert-Butylation of
glycerol catalysed by ion-exchange resins,” Applied Catalysis A:
General, vol. 294, no. 2, pp. 141–147, 2005.
[16] K. D. M. Klepa´cova´, D. D. Mravec, E. Ha´jekova´, and M. Bajus,
“Etherification of glycerol,” Petroleum and Coal, vol. 45, pp. 54–
57, 2003.
Acknowledgment
is work was supported by the 2012 Research Fund of the
University of Seoul.
References
[1] F. Yang, M. A. Hanna, and R. Sun, “Value-added uses for crude
glycerol—a byproduct of biodiesel production,” Biotechnology
for Biofuels, vol. 5, article 13, 2012.
[2] C. A. G. Quispe, C. J. R. Coronado, and J. A. Carvalho Jr.,
“Glycerol: production, consumption, prices, characterization

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http://www.hindawi.com
Hindawi Publishing Corporation
http://www.hindawi.com
Hindawi Publishing Corporation
http://www.hindawi.com
Hindawi Publishing Corporation
http://www.hindawi.com
Hindawi Publishing Corporation
http://www.hindawi.com
Volume 2014
Volume 2014
Volume 2014
Volume 2014
Volume 2014