Synthesis of biodiesel without formation of free glycerol

Article abstract of DOI:10.1134/S1070428015070039

A new approach to the synthesis of biodiesel has been developed on the basis of alcoholysis of a triglyceride in combination with acetalization of glycerol with lower carbonyl compounds or acetals derived therefrom. A model synthesis of biodiesel not involving free glycerol has been accomplished using rapeseed oil and acid catalysts, as well as without a catalyst under generation of ethanol supercritical fluid; in the latter case, monoalkyl glycerol ethers are formed in addition to the expected cyclic ketals.

Full text of DOI:10.1134/S1070428015070039

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2015, Vol. 51, No. 7, pp. 915–917. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © V.B. Vol’eva, I.S. Belostotskaya, N.L. Komissarova, E.V. Koverzanova, L.N. Kurkovskaya, R.A. Usmanov, F.M. Gumerov, 2015,
published in Zhurnal Organicheskoi Khimii, 2015, Vol. 51, No. 7, pp. 935–938.
Synthesis of Biodiesel without Formation of Free Glycerol
a
a
a
a
V. B. Vol’eva , I. S. Belostotskaya , N. L. Komissarova , E. V. Koverzanova ,
a
b
b
L. N. Kurkovskaya , R. A. Usmanov , and F. M. Gumerov
a
Emanuel’Institute of Biochemical Physics, Russian Academy of Sciences,
ul. Kosygina 4, Moscow, 119334 Russia
e-mail: komissarova@polymer.chph.ras.ru
b
Kazan National Research Technological University,
ul. K. Marksa 68, Kazan, 420015 Tatarstan, Russia
Received January 5, 2015
Abstract—A new approach to the synthesis of biodiesel has been developed on the basis of alcoholysis of
a triglyceride in combination with acetalization of glycerol with lower carbonyl compounds or acetals derived
therefrom. A model synthesis of biodiesel not involving free glycerol has been accomplished using rapeseed oil
and acid catalysts, as well as without a catalyst under generation of ethanol supercritical fluid; in the latter case,
monoalkyl glycerol ethers are formed in addition to the expected cyclic ketals.
DOI: 10.1134/S1070428015070039
Modern biodiesel production by alkaline alco-
holysis of vegetable triglycerides involves the problem
of utilization of glycerol formed as by-product. Its
subsequent use in organic synthesis to obtain dihy-
droxyacetone, acrylic acid derivatives, etc., requires
refinement which is associated with additional expen-
ditures, so that the efficiency of the main production is
reduced. Therefore, many biodiesel manufacturers
consider crude biodiesel glycerol as waste material.
Taking into account the above stated, it seems reason-
able to search for new approaches to the synthesis of
biodiesel without formation of free glycerol.
catalyst (commonly used in the synthesis of biodiesel)
by acid one. In this article we describe a model syn-
thesis in the presence of sulfuric acid, p-toluenesul-
fonic acid, and a polymeric sulfonic acid cation ex-
changer in the H form (Amberlyst 15). Lower carbonyl
compounds (acetone, acetaldehyde, and butyralde-
hyde) and the corresponding diethyl acetals were used
for the ketalization. The latter ensured the absence of
water and free fatty acids in the reaction mixture.
The conversion of triglyceride (rapeseed oil) in the
reaction with acetone diethyl acetal and ethanol at
a ratio of 1:2:10 was considerably faster than the alco-
holysis in the absence of ketal, which required several
times longer time (about 40 h). This suggests that the
cyclic ketal is formed directly from the triglyceride and
that the entering alkenyl fragment promotes elimina-
tion of the acyl group. The combined alcoholysis–
ketalization process is synchronous, and no free glyc-
erol is formed. This interpretation is consistent with
intermediate formation of 4-(acyloxymethyl)-2,2-di-
methyl-1,3-dioxolane (1) which is then transformed
into final 2,2-dimethyl-1,3-dioxolan-4-ylmethanol (2)
A probable version is a combined process including
alcoholysis of triglyceride and ketalization of glycerol.
Cyclic ketals resulting from condensation of glycerol
with lower carbonyl compounds (such as acetone,
ethyl methyl ketone, acetaldehyde, etc.) have recently
been found to possess a variety of properties which
make it possible to consider them a new liquid biofuel.
The addition of cyclic ketals to alcohol-containing
gasoline increases the octane number and enhances the
phase stability [1], reduces diesel exhaust opacity [2],
inhibits thermooxidative degradation [3], and pro-
motes defrosting effect [4]. Thus, a combined alcohol-
ysis–ketalization process should ensure complete utili-
zation of the intrinsic potential of triglyceride in the
synthesis of a binary fuel composition. Implementation
of this process requires only replacement of alkaline
(
Scheme 1).
The combined process with participation of alde-
hydes or acetals derived therefrom is characterized by
a different ratio of isomeric five- and six-membered
cyclic acetals 3 and 4 as compared to the acetalization
of free glycerol. For example, the ratio 3/4 changes
9
15

9
16
VOL’EVA et al.
Scheme 1.
Me
Me
O
O
O
EtO
OEt
O
R2
O
Me C(OEt) , H
+
O
R2
O
O
R2
O
2
2
R1
O
R3
R1
O
R3 –R COOEt, –H
1
+
Me
Me OEt
O
R3
O
O
OH
O
O
O
Me
Me
O
Me
H+
O
R3
OH
2
O
–
R COOEt
Me
O
O
1
2
1
2
3
R , R , R = long-chain alkyl.
from 83:17 (from glycerol) to 68:32 (from triglycer-
ide), which is naturally related to more facile removal
of the acyl groups from positions 1 and 3 of the tri-
glyceride (Scheme 2).
indicates a more complex transformation sequence,
including exchange redox interaction between ethanol
and acetone with generation of an isopropyl alcohol–
acetaldehyde couple which then participates in the
process.
Conditions ensuring generation of ethanol super-
critical fluid provide additional possibilities of the
combined process. Under these conditions, the reaction
time is shortened to a few minutes, the amount of
alcohol is reduced, and no catalyst is necessary. In the
system triglyceride–acetone–ethanol (1:2:4) at 350°C
and a pressure of ~300 bar, the conversion of triglyc-
eride attained 75% in 30 min. The reaction mixture
was homogeneous, and it contained the expected fatty
acid ethyl esters (biodiesel) and dioxolane 2, as well
as some glycerol derivatives which were detected by
GC/MS, in particular dioxolane 3, 3-ethoxypropane-
EXPERIMENTAL
1
The H NMR spectra were recorded on a Bruker
Avance 500 spectrometer from solutions in CDCl3
using tetramethylsilane as internal standard. GC/MS
analyses were obtained on a Trace-1310 gas chromato-
graph coupled with an ISQ mass-selective detector
(TR-5MS quartz capillary column, 15 m×0.32 mm,
stationary phase 5% phenyl polysilphenylene-siloxane,
film thickness 0.25 μm; oven temperature program-
ming from 40 to 290°C at a rate of 15 deg/min and
5 min at the final temperature; injector and interface
temperature 250°C; carrier gas helium; sample volume
1
,2-diol (5), 3-isopropoxypropane-1,2-diol (6), 2,3-ep-
oxypropan-1-ol, and bis(hydroxymethyl)dioxane
Scheme 3). The formation of this set of products
(
Scheme 2.
OH
OR2
O
O
EtOH
+
MeCHO
Me
+
1
OR3
R O
OH
O
Me
O
3
4
1
2
3
1
2
3
R = R = R = H or R , R , R = long-chain acyl.
Scheme 3.
O
O
Me
OH
HOCH CH(OH)CH OH
2
2
+
+
EtOH
+
OH
OH
HO
Me
OEt
OH
Me
Me
Me
Me
O
2
5
OH
O
O
HOCH CH(OH)CH OH
2
2
O
OEt
MeCHO
Me
+
Me
Me
3
6
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 7 2015

SYNTHESIS OF BIODIESEL WITHOUT FORMATION OF FREE GLYCEROL
917
1
μL, split ratio 1:40; electron impact, 70 eV); the
chromatograms were recorded by the total ion current
scan range 30–450 a.m.u.). The components were
4.16 d.d (1H, CH, J = 5.9, 12.0 Hz), 4.30 d.d (1H, CH,
J = 4.4, 12.0 Hz).
(
Acid-catalyzed alcoholysis of triglyceride. A mix-
ture of 9 g (0.01 mol) of rapeseed oil, 30 mL of
ethanol, and 0.1 g of concentrated sulfuric acid or 0.5 g
of Amberlyst 15 was heated for 38–40 h under reflux
with stirring until almost complete conversion of the
initial triglyceride (TLC). The mixture was neutralized
with calcium oxide or ion exchanger was filtered off.
Excess alcohol was removed on a rotary evaporator,
and the residue was analyzed by GC/MS. It contained
fatty acid (stearic, oleic, palmitic, linoleic, etc.) ethyl
esters. The product was then used as a reference
sample of biodiesel.
identified using NIST-2011 database taking into
account general rules of fragmentation of organic com-
pounds under electron impact. A 5-μL sample was
withdrawn and diluted with 200 μL of chloroform, the
mixture was shaken, and 1 μL was injected into the
chromatograph. The reaction mixtures were also ana-
lyzed by TLC on Silufol UV-254 plates using hexane–
diethyl ether (1:1) as eluent and by H NMR. A con-
tinuous flow setup [5] was used to perform alcoholysis
of rapeseed oil in ethanol supercritical fluid.
1
Commercially available rapeseed oil was used as
model triglyceride. Ethanol was distilled over calcium
hydride. Acetone, acetaldehyde, and butyraldehyde
diethyl acetals were prepared by heating the corre-
sponding carbonyl compounds in excess ethanol under
reflux in the presence of 0.1 wt % of concentrated
sulfuric acid and molecular sieves with a water
capacity of 16–18%.
Combined alcoholysis of rapeseed oil with acet-
aldehyde diethyl acetal. The procedure was the same
as above. The product isolated by vacuum distillation
1
(bp 78–79°C/5 mm) was analyzed by H NMR. Its
spectral parameters corresponded to reference mixture
3/4 (see above) with the difference that the fraction of
4 was 32% against 17% in the reference sample.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 13-03-12078OFI_M).
A reference sample of acetal formed by the reaction
of acetaldehyde with glycerol (a mixture of isomers 3
and 4) was synthesized according to the procedure de-
1
scribed in [6]; bp 78–79°C (5 mm). H NMR spectrum,
REFERENCES
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3
1
2
3
4
.32 d and 1.37 d (CH in 3, J = 4.7 Hz), (3H, CH ),
3
3
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2
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3
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A reference sample of dioxolane 1 was prepared by
transesterification of rapeseed oil with an equivalent
amount of dioxolane 2 in the presence of sodium hy-
droxide (1 wt %) under stirring at 80°C. The progress
of the reaction was monitored by TLC. The target
product was separated from glycerol, residual triglyc-
eride, and dioxolane 2 by preparative TLC and was
4
5
6
1
1
identified by H NMR. H NMR spectrum, δ, ppm:
.92 m [3H, CH (CH ) ], 1.32 m (CH ), 1.36 s (3H,
0
3
2 n
2
CH ), 1.42 s (3H, CH ), 1.63 m (2H, CH ), 2.02–
3
3
2
2
.07 m (4H, CH ), 2.33 t (2H, CH CO, J = 7.2 Hz),
2 2
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 7 2015