Preparation of potential biofuel 5-ethoxymethylfurfural and other 5-alkoxymethylfurfurals in the presence of oil shale ash

Article abstract of DOI:10.1039/c3ra46570e

5-Ethoxymethylfurfural (EMF) can be prepared from the corresponding halomethylfurfural and absolute ethanol in good yield. The use of significantly more affordable 96% ethanol results in formation of levulinic acid or its ester in considerable amount (up to 16%), which is difficult to separate from the desired EMF. In the present study we report that the addition of oil shale ash prevents the hydrolysis of the furan ring and enables the use of 96% ethanol with great success. The developed procedure is applicable to a wide range of aqueous alcohols, is operationally simple and utilizes an inexpensive basic ash, which is deposited in millions of tons per year. Notably, the basicity of the ash is decreased during the process, making its deposits less hazardous to the environment.

Full text of DOI:10.1039/c3ra46570e

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Preparation of potential biofuel 5-ethoxymethyl
furfural and other 5-alkoxymethylfurfurals in the
presence of oil shale ash†
Cite this: RSC Adv., 2014, 4, 5689
a
a
b
a
Indrek Viil, Aleksei Bredihhin, Uno Maeorg and Lauri Vares*
¨
5
-Ethoxymethylfurfural (EMF) can be prepared from the corresponding halomethylfurfural and absolute
ethanol in good yield. The use of significantly more affordable 96% ethanol results in formation of
levulinic acid or its ester in considerable amount (up to 16%), which is difficult to separate from the
desired EMF. In the present study we report that the addition of oil shale ash prevents the hydrolysis of
the furan ring and enables the use of 96% ethanol with great success. The developed procedure is
applicable to a wide range of aqueous alcohols, is operationally simple and utilizes an inexpensive basic
ash, which is deposited in millions of tons per year. Notably, the basicity of the ash is decreased during
the process, making its deposits less hazardous to the environment.
Received 11th November 2013
Accepted 17th December 2013
DOI: 10.1039/c3ra46570e
www.rsc.org/advances
The latter substances are both readily available from carbohy-
drates and lignocellulosic biomass (Scheme 1).
Introduction
5
Diminishing fossil resources and growing environmental
EMF can be achieved in high yield and purity if absolute
concerns have initiated an intense search for renewable sources ethanol is used; the use of more conventional 96% aqueous
5
for liquid fuels and chemicals. The use of degradable lignocel- ethanol leads to the formation of considerable amounts of EL
6
lulosic biomass, as an abundant, inexpensive and CO
source of carbon, has been considered one of the most prom-
ising ways to substitute the products from non-renewable fossil calcium carbonate decreases the amount of EL formed, down to
-neutral and formic acid (Scheme 2).
2
We have previously shown that addition of sodium or
1
6
sources. 5-Ethoxymethylfurfural (EMF) is a promising second- roughly 10 mole percent. However, herein we are pleased to
generation biofuel, which has been tested as a possible additive report that the use of oil shale ash as a basic additive reduces
or even substitute for diesel fuel. EMF is a liquid, with a boiling the formation of levulinate down to negligible amounts.
ꢀ
ꢁ1
point of 235 C and an energy density 8.7 kW h L . This is
Oil shale ash is a waste, which is formed as a by-product of
higher than that of ethanol (6.1 kW h L ) and comparable to burning oil shale in power plants. In Estonia, most of the
gasoline (8.8 kW h L ) and diesel fuel (9.7 kW h L ). EMF can electricity is produced by burning oil shale and as a conse-
ꢁ
1
ꢁ
1
ꢁ1
2
be synthesized from 5-hydroxymethylfurfural (HMF) in ethanol quence, 5–7 million tons of ash are deposited yearly in deposit
7
or from fructose, glucose or sugarcane through an HMF inter- plateaus next to the power plants. Currently, less than 5% of it
3,4
mediate. However, the furan ring of HMF is prone to hydro- is recycled and used in construction materials and agriculture.
lytic cleavage under acidic conditions and, besides the desired The content of kerogen (the organic part of oil shale) as well as
4a–e
EMF, a fair amount of ethyl levulinate (EL) is formed, as well.
the chemical composition of the mineral part can vary signi-
Unfortunately, due to similar polarity and only 10 Dalton differ- cantly depending on the country. Estonian oil shale (kukersite)
ence in molar mass, the EL is not easily separable from EMF by is highly calcareous. The ash remaining aer combustion is rich
8
simple distillation or chromatography and this hampers the use in free lime (CaO), anhydrite (CaSO
) and silicates.
4
of the current routes for large scale EMF production.
The ash collected from the various parts of the boiler system
EMF 4 and other alkoxymethylfurfurals (AMF) can also be contains typically 16–25% free calcium oxide and 8–15%
synthesized by combining an alcohol with 5-chlor- magnesium oxide, while ash from an electrostatic precipitator
5
omethylfurfural (CMF) 1 or 5-bromomethylfurfural (BMF) 2.
a
University of Tartu, Institute of Technology, Nooruse 1, Tartu 50411, Estonia. E-mail:
lauri.vares@ut.ee
b
Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c3ra46570e
1
Scheme 1 Synthesis of alkoxymethylfurfurals.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 5689–5693 | 5689

View Article Online
RSC Advances
Paper
Thermogravimetric analysis of ashes showed that there was
1
1% of calcium hydroxide and 2% of mineral carbon dioxide in
both ashes.
The basicity of the ashes was measured by titration in the
Scheme 2 Hydrolysis of halomethylfurfural.
following way: 35% hydrochloric and 48% hydrobromic acid
were used to titrate the basicity of ashes in the presence of
bromophenol blue. 0.5 g of ash was stirred in 10 mL of water.
Titration was stopped when the color of the aqueous suspen-
sion of ash turned from dark blue to yellow and the amount of
acid added was measured. It turned out that 1 gram of ash A
binds 8 millimoles of hydrogen ions whereas 1 gram of ash B
binds 10 millimoles of hydrogen ions. Oil-shale ash consists of
contains normally less free calcium oxide (6–14%) and
magnesium oxide (8–11%). Hydration of ash upon storage
9
under open atmosphere in plateaus initiates the formation of
compounds like Ca-hydroxide (portlandite) and Ca-sulphoalu-
minate (ettringite) whose dissolution in surface water causes
10
7
high alkalinity (pH 12–13) and environmental issues.
Our current discovery of using ash for the preparation of
EMF has double benets: (i) waste material can be used in an
important chemical transformation, which is difficult to
perform otherwise, and (ii) the pH of the ash decreases, making
its storage and recycling less problematic.
variety of compounds (Ca(OH)
2 3 3
, CaCO , CaO, MgO, CaSiO ,
SiO , CaSO , etc.) with different reactivity towards acidic
2
4
species. To ensure the presence of sufficient amount of reactive
base, an excess of oil-shale ash was used.
Preparation of EMF (4) and other 5-alkoxymethylfurfurals
Experimental
General
Optimization experiments were carried out as follows: 10 mL of
alcohol or its solution in water was added to the mixture of 0.3–
All reagents were obtained from commercial sources and used
without further purication. CMF and BMF were synthesized
according to literature procedures. Absolute ethanol was
2
obtained by distillation from CaH and stored under argon.
Alcohol–water solutions were prepared by mixing correspond-
ing volumes of absolute alcohol with a calculated volume of
water. Reactions were monitored by TLC using UV light and
4
KMnO for visualizing spots. NMR spectra were recorded using
Bruker AVANCE II 400 MHz spectrometer.
0
.6 g BMF or CMF and (if ash additive was used) 0.5 g oil shale
ash A or B. In one reaction the ash was substituted with 90 mg
Ca(OH) . The mixture was stirred under the conditions speci-
ed in Tables 1 and 2. Excess alcohol was then removed by
6
2

rotary evaporation under reduced pressure. 10 mL of water was
added to the viscous slurry followed by extraction with diethyl
ether (3 ꢂ 30 mL). The organic phases were combined, dried
over anhydrous sodium sulfate, ltered and concentrated to
afford the nal product as yellowish oil. The purity and
1
composition of the product were determined by H NMR spec-
Ashes used
troscopy. No unreacted BMF or CMF was detected in the
Oil shale ashes used in the current work were taken from product unless specically stated (Table 2, entries 3, 5 and 9).
pulverized-red boiler (ash A) and from electrostatic precipi- Large scale EMF synthesis: BMF (2, 10.018 g, 53 mmol) was
tator (ash B) from an Estonian thermal power plant. added to the suspension of oil shale ash A (15.0 g) in ethanol
Table 1 Synthesis of EMF (4)
Combined yield
(%, 4 + 8)
Product composition
(4 : 8)
a
ꢀ
Entry
Substrate
Additive
Time (h)
Temp. ( C)
1
2
3
4
5
6
7
8
9
BMF
BMF
BMF
CMF
CMF
CMF
CMF
CMF
CMF
BMF
BMF
BMF
—
0.5
0.5
0.5
1
2
2
70
70
70
70
70
70
70
r.t.
r.t.
r.t.
r.t.
r.t.
98
84
73
86
84
80
67
85
82
87
75
88
87 : 13
99 : 1
99 : 1
84 : 16
99 : 1
98 : 2
100 : 0
99 : 1
99 : 1
100 : 0
100 : 0
100 : 0
Ash A
Ash B
—
Ash A
Ash B
Ca(OH)
Ash A
Ash B
Ash A
Ash B
Ash A
2
1
72
72
16
16
17
1
1
1
0
1
2
b
a
b
Ash A is from pulverized-red boiler; ash B is from electrostatic precipitator. Reaction carried out on 10 g scale.
5690 | RSC Adv., 2014, 4, 5689–5693
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Table 2 Conditions, yields and compositions of final products of AMF syntheses starting from BMF
Product comp.
(AMF : AL : HMF)
ꢀ
Entry
Alcohol
MeOH
n-PrOH
i-PrOH
% (alcohol)
Additive
Time (h)
Temp. ( C)
Comb. yield
1
2
3
4
5
6
7
8
9
95
95
99
—
Ash B
—
Ash B
—
Ash B
Ash B
Ash B
—
2
2
2
2
2
2
5.5
3.5
2
r.t.
r.t.
65
65
65
65
65
65
65
65
65
95
68
12
91 : 9 : 0
100 : 0 : 0
18 : 1 : 0
100 : 0 : 0
78 : 2 : 0
98 : 2 : 0
91 : 0 : 9
71 : 0 : 29
66 : 5 : 0
100 : 0 : 0
80 : 4 : 16
a
99
61
71
b
100
100
99
90
97
97
75
72
c
n-BuOH
58
1
1
0
1
97
90
Ash B
Ash B
2
2
86
70
a
b
c
The product also contained 81% of unreacted BMF. The product also contained 20% of unreacted BMF. The product also contained 29% of
unreacted BMF.
(
96%, 300 mL) and stirred for 17 hours at r.t. Then ethanol was NMR (100 MHz, CDCl
removed on a rotary evaporator. The residue was diluted with 66.5, 64.7, 14.9 ppm.
water (300 mL) and extracted with diethyl ether (4 ꢂ 300 mL).
Aer drying with Na SO
3
): d ¼ 177.6, 158.7, 152.5, 121.8, 110.9,
1
5-Propoxymethylfurfural 5. H NMR (400 MHz, CDCl
3
): d ¼
2
4
, solvents were removed to afford EMF 9.58 (s, 1H), 7.19 (d, J ¼ 3.5 Hz, 1H), 6.49 (d, J ¼ 3.5 Hz, 1H), 4.50
4
(7.204 g, 88%) as yellowish oil. No further purication was (s, 2H), 3.45 (t, J ¼ 6.7 Hz, 2H), 1.60 (m, 2H), 0.90 (t, J ¼ 7.4 Hz,
1
3
needed.
3H) ppm. C NMR (100 MHz, CDCl ): d ¼ 177.6, 158.8, 152.5,
3
121.9, 110.8, 72.8, 64.9, 22.7, 10.3 ppm.
1
Kinetic NMR measurements of EMF synthesis
6 mg of BMF was dissolved in 0.7 mL of 5% D O solution in
5-Isopropoxymethylfurfural 6. H NMR (400 MHz, CDCl
3
):
d ¼ 9.56 (s, 1H), 7.17 (d, J ¼ 3.5 Hz, 1H), 6.48 (d, J ¼ 3.5 Hz, 1H),
2
2
4
.49 (s, 2H), 3.68 (spt, J ¼ 6.0 Hz, 1H), 1.17 (d, J ¼ 6.0 Hz, 6H)
deuterated ethanol C D OD. The solution was transferred to an
NMR tube and proton spectra was measured at specic time
intervals. When ash impact was investigated, 40 mg of BMF and
5
2
5
1
3
ppm. C NMR (100 MHz, CDCl
3
): d ¼ 177.5, 159.3, 152.4, 122.0,
110.6, 72.0, 62.4, 21.8 ppm.
5
-Butoxymethylfurfural 7. 1H NMR (400 MHz, CDCl ): d ¼
3
0 mg of ash B were vigorously shaken with 1 mL of 5% D
2
O
9
(
.58 (s, 1H), 7.19 (d, J ¼ 3.5 Hz, 1H), 6.49 (d, J ¼ 3.5 Hz, 1H), 4.49
solution in deuterated ethanol C OD. Before each NMR
2 5
D
s, 2H), 3.50 (t, J ¼ 6.6 Hz, 2H), 1.55 (m, 2H), 1.36 (m, 2H), 0.89 (t,
measurement, the reaction mixture was centrifuged to remove
ash particles and then the supernatant was transferred to the
NMR tube. Aer each NMR measurement, the solution was
quickly transferred from the NMR tube back to an ash pellet in
micro test tube and was vigorously shaken between NMR
measurements. Incubations and measurements of solutions
13
J ¼ 7.4 Hz, 3H) ppm. C NMR (100 MHz, CDCl
3
): d ¼ 177.6,
1
58.8, 152.5, 121.8, 110.8, 70.9, 64.9, 31.5, 19.1, 13.7 ppm.
Results and discussion
were carried out at room temperature. Mole fractions of mixture Preparation of EMF (4)
components were calculated from corresponding peak integrals
in proton spectra.
Our results and conditions explored for the synthesis of EMF
with 96% ethanol are summarized in Table 1. In general, when
ash was used as an additive, a signicantly lower ethyl levuli-
nate content was observed compared to conditions where ash
NMR spectral data
1
5
-Methoxymethylfurfural 3. H NMR (400 MHz, CDCl
3
): d ¼ was not used (entries 1 and 4). Starting from BMF (2), 99% pure
ꢀ
9
(
1
.62 (s, 1H), 7.21 (d, J ¼ 3.5 Hz, 1H), 6.53 (d, J ¼ 3.5 Hz, 1H), 4.49 EMF was obtained with both ashes aer half-an-hour at 70 C
1
3
s, 2H), 3.42 (s, 3H) ppm. C NMR (100 MHz, CDCl
3
): d ¼ 177.7, (entries 2 and 3), whereas from the less reactive CMF (1), two
ꢀ
58.3, 152.6, 121.7, 111.1, 66.5, 58.7 ppm.
hours at 70 C was needed (entries 5 and 6). Calcium hydroxide
1
5
-Ethoxymethylfurfural 4. H NMR (400 MHz, CDCl ): d ¼ was also a suitable base for this conversion, although the yield
3
9
(
.59 (s, 1H), 7.19 (d, J ¼ 3.5 Hz, 1H), 6.50 (d, J ¼ 3.5 Hz, 1H), 4.50 of EMF was lower (entry 7). We also tested the conversion at
1
3
s, 2H), 3.56 (q, J ¼ 7.1 Hz, 2H), 1.21 (t, J ¼ 7.1 Hz, 3H) ppm.
C
room temperature (entries 8–11). In the case of CMF, the
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 5689–5693 | 5691

View Article Online
RSC Advances
Paper
conversion was rather sluggish, requiring 3 days to reach full propoxymethylfurfural 5 was obtained cleanly. When the steri-
conversion. However, the yield of EMF was good and it con- cally more hindered propane-2-ol was used, the already low
tained 1% of EL (8). More reactive BMF, on the other hand, water content (1%) led to a signicant amount of HMF (5) (entry
reacted faster and no EL was observed, affording the EMF with 7) which increased to 29% with propane-2-ol containing 10%
up to 87% yield (entry 10). Both ashes behaved rather similarly water (entry 8). In the case of propane-2-ol the ash also had an
and EL contents are basically identical in all cases; some vari- impact on the reaction speed (entries 5 vs. 6), whereas the
ation in yields can be seen as ash A gives slightly higher yields in content of the corresponding levulinate (10) remained
all comparable cases. We also scaled up the reaction to 10 g unchanged.
scale (entry 12) and the results were pleasing: EMF was obtained
If aqueous BuOH was used as the alcohol, the reaction
cleanly in 88% yield. It is important to note that the procedure without the ash did not reach completion in 2 hours (entry 9)
described herein is especially suitable for large scale synthesis; and besides the desired product 7, also a fair amount of cor-
both ethanol and the extraction solvent, diethyl ether, can be responding levulinate 12 was formed. The addition of ash
reused, and no further purication of any kind is needed to under otherwise identical reaction conditions afforded butox-
obtain pure EMF.
ymethylfurfural 7 in good yield and high purity (entry 10). The
Spent ashes are easily separated by sedimentation and can increased water content to 10% resulted in signicant amounts
be stored in open air storages (ash hills) or put underground in of hydrolysis products (12 and 13) and a corresponding decrease
old mines. In addition, aqueous phase from extraction con- in yield (entry 11). In general, it can be said that for the aqueous
taining calcium chloride/bromide, can aer concentration be alcohols investigated, the use of ash increased the conversion
potentially used as counter-ice reagent on the roads or treated to the corresponding alkoxymethylfurfurals signicantly and
with sulfuric acid to obtain gypsum and HCl/HBr can be suppresses the formation of hydrolysis products.
recovered.
Kinetic measurement of EMF synthesis reaction
Preparation of other 5-alkoxymethylfurfurals
6
BMF reaction progress with 95% ethanol-d in the absence or
We also used other alcohols to synthesize corresponding presence of ash B was studied by NMR spectroscopy. The
alkoxymethylfurfurals in addition to EMF. Aqueous methanol, decrease of BMF and increase of the desired product, EMF, and
propan-1-ol, propan-2-ol and butan-1-ol were utilized to prepare byproducts, EL and acetal (2-(diethoxymethyl)-5-(ethoxymethyl)
methoxy-, propoxy-, isopropoxy- and butoxymethylfurfural, furan), are depicted in Fig. 1. It can be seen that the acetal
respectively, from BMF. The conditions and results from these formation is fast and its concentration does not change
syntheses are presented in Table 2. All these experiments were substantially over 6 hours. In addition, the amount of acetal is,
carried out using ash B.
at a rst approximation, independent of the presence of ash. It
In the case of 95% aqueous methanol the ash is crucial to is clearly seen that with the ash, levulinate content is lower and
keep levulinate content low (entries 1 vs. 2). Without the ash the yield of EMF is higher. If the usual extractive work-up is
there was 9% of methyl levulinate 9 present in the nal applied then the small amount of acetal formed is hydrolyzed to
product (entry 1). In case of propane-1-ol the reaction was slow the corresponding aldehyde and therefore not present in the
without the ash and a large amount of unreacted BMF was still nal product.
present aer 2 hours (entry 3). However, the addition of ash
The current work shows that the problem of furan ring acidic
speeded up the reaction considerably (entry 4) and the desired hydrolysis of the alkoxymethyfurfurals in the presence of water
Fig. 1 Mole fractions of reaction mixture components in the absence (left) and presence (right) of ash B.
5692 | RSC Adv., 2014, 4, 5689–5693
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
can be avoided or substantially diminished by the use of basic
oil shale ash that neutralizes the acid by-product. Even if levu-
linate esters are formed, oil shale ash probably catalyzes their
basic hydrolysis and thereby puries the desired product. In
addition to preventing the hydrolysis, ash also binds acid
species which otherwise must be separated in an additional
step. Compared to other bases, oil shale ash is inexpensive or
free. Furthermore, it is a waste product available in vast
amounts in regions where oil shale is used as a source of energy.
Thereby, the present method recycles environmentally
hazardous waste and offers a simple solution for the synthesis
of alkoxymethylfurfurals with aqueous alcohols at room
temperature.
2 G. J. M. Gruter and F. Dautzenberg, Eur. Pat. Appl.,
EP1834950A1, 2007.
3 (a) G. A. Kraus and T. Guney, Green Chem., 2012, 14, 1593–
1596; (b) C. M. Lew, N. Rajabbeigi and M. Tsapatsis, Ind.
Eng. Chem. Res., 2012, 51, 5364–5366; (c) S. Dutta, S. De,
M. Imteyaz Alam, M. M. Abu-Omar and B. Saha, J. Catal.,
2012, 288, 8–15; (d) J. T. Liu, Y. Tang, K. G. Wu, C. F. Bi
and Q. Cui, Carbohydr. Res., 2012, 350, 20–24; (e)
S. Saravanamurugan and A. Riisager, Catal. Commun.,
2012, 17, 71–75.
4 (a) H. Wang, T. Deng, Y. Wang, X. Cui, Y. Qi, X. Mu, X. Hou
and Y. Zhu, Green Chem., 2013, 15, 2379–2383; (b) B. Liu and
Z. Zhang, RSC Adv., 2013, 3, 12313–12319; (c)
M. Balakrishnan, E. R. Sacia and A. T. Bell, Green Chem.,
2
012, 14, 1626–1634; (d) P. Che, F. Lu, J. Zhang, Y. Huang,
Conclusions
X. Nie, J. Gao and J. Xu, Bioresour. Technol., 2012, 119, 433;
(e) P. Lanzafame, D. M. Temi, S. Perathoner, G. Centi,
A. Macario, A. Aloise and G. Giordano, Catal. Today, 2011,
175, 435–441; (f) A. A. Rosatella, S. P. Simeonov,
R. F. M. Fradea and C. A. M. Afonso, Green Chem., 2011,
13, 754–793.
5 (a) N. Kumari, J. K. Olesen, C. M. Pedersen and M. Bols, Eur.
J. Org. Chem., 2011, 1266–1270; (b) M. Mascal and
E. B. Nikitin, Green Chem., 2010, 12, 370–373; (c) M. Mascal
and E. B. Nikitin, ChemSusChem, 2009, 2, 859–861; (d)
M. Mascal and E. B. Nikitin, ChemSusChem, 2009, 2, 423–
426; (e) M. Mascal and E. B. Nikitin, Angew. Chem., Int. Ed.,
2008, 47, 7924–7926.
The current work provides a simple method for production of
alkoxymethylfurfurals in high yield and purity. This method
provides a useful application for oil shale ash, which is an
environmentally hazardous industrial waste. Furthermore, the
use of ordinary ethanol, low cost additives and no need for
chromatography, it has the potential to be applied to large-scale
biofuel synthesis.
Acknowledgements
We sincerely thank Andres Trikkel and Rein Kuusik, Tallinn
University of Technology, Estonia, for providing thermog-
ravimetry to the ashes and Dr John J. Kane (Immunexcite, Inc.,
Lexington, MA, USA) for critically reading the manuscript. The
authors would like to thank Archimedes Foundation (project
no. 3.2.0501.10-0004) and Estonian Ministry of Education and
Research (project no. SF0180073s08) for nancial support.
6 A. Bredihhin, U. M ¨a eorg and L. Vares, Carbohydr. Res., 2013,
375, 63–67.
7 M. Liira, Ph.D. Thesis, University of Tartu, 2012.
8 L. Bityukova, R. M ˜o tlep and K. Kirsim ¨a e, Oil Shale, 2010, 27,
339–353.
9
R. Kuusik, M. Uibu and K. Kirsim ¨a e, Oil Shale, 2005, 22, 407–
19.
0 (a) M. Liira, K. Kirsim ¨a e, R. Kuusik and R. M ˜o tlep, Fuel,
2009, 88, 712–718; (b) R. M ˜o tlep, T. Sild, E. Puura and
K. Kirsim ¨a e, J. Hazard. Mater., 2010, 184, 567–573.
4
References
1
1
J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew. Chem.,
Int. Ed., 2007, 46, 7164.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 5689–5693 | 5693