Solid acid-catalyzed conversion of furfuryl alcohol to alkyl tetrahydrofurfuryl ether

Article abstract of DOI:10.1016/j.catcom.2014.08.030

The acidic zeolite HZSM-5 (Si/Al = 25) achieved 58.9% selectivity of methyl furfuryl ether (MFE) and 44.8% selectivity of ethyl furfuryl ether (EFE) from etherification of furfuryl alcohol with methanol and ethanol. MFE and EFE were quantitatively hydrogenated into methyl tetrahydrofurfuryl ether (MTE) and ethyl tetrahydrofurfuryl ether (ETE) using a Raney Ni catalyst.

Full text of DOI:10.1016/j.catcom.2014.08.030

Catalysis Communications 58 (2015) 76–79
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Solid acid-catalyzed conversion of furfuryl alcohol to alkyl
tetrahydrofurfuryl ether
Quan Cao a,b, Jing Guan a, Gongming Peng a, Tonggang Hou a, Jianwei Zhou a, Xindong Mu a,
⁎
a
CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, Shandong, China
University of Chinese Academy of Sciences, Beijing 100049, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 June 2014
Received in revised form 19 August 2014
Accepted 21 August 2014
Available online 30 August 2014
The acidic zeolite HZSM-5 (Si/Al = 25) achieved 58.9% selectivity of methyl furfuryl ether (MFE) and 44.8%
selectivity of ethyl furfuryl ether (EFE) from etherification of furfuryl alcohol with methanol and ethanol.
MFE and EFE were quantitatively hydrogenated into methyl tetrahydrofurfuryl ether (MTE) and ethyl
tetrahydrofurfuryl ether (ETE) using a Raney Ni catalyst.
© 2014 Published by Elsevier B.V.
Keywords:
Methyl tetrahydrofurfuryl ether
Ethyl tetrahydrofurfuryl ether
Furfuryl alcohol
Solid acid
Diesel additive
1. Introduction
additive [6]. It is notable that 6 mol of hydrogen was consumed to syn-
thesize alkanes when furfural was adopted as the primary substrate and
With depleting reserves of fossil fuels, tremendous efforts have been
dedicated to seeking effective chemical conversion of renewable bio-
mass into fuels [1]. Furfural, an important platform chemical and often
obtained by hydrolysis and dehydration of hemicellulose, has been
commercialized for decades [2]. It can be further converted into furfuryl
alcohol (FA) and 2-methylfuran (MF) by hydrogenation. These com-
pounds are often used as intermediates to synthesize fuels and many
other high value-added products [2]. Extensive investigations have
been conducted on the conversion of furfural, FA and MF into fuels or
fuel additives [3–5].
Producing diesel-range compounds from furfural and its derivatives
FA and MF has been reported in recent studies. Alkanes and alkyl
tetrahydrofurfuryl ether (ATE), derived from MF and FA respectively,
are regarded as promising candidates for producing bio-diesel, as
shown in Scheme 1 [4,6]. MF was first catalyzed by acids and underwent
hydroxyalkylation with the carbonyl-containing compounds. The prod-
ucts generated were then hydrogenated. In this way, MF was converted
to an alkane [4,5]. The high cetane number enables those alkanes to be
used as diesel [3]. Ed de Jong and his co-workers investigated the com-
bustion of diesel–ethyl tetrahydrofurfuryl ether (ETE) mixture using a
PACCAR diesel engine [6] and concluded that the mixture substantially
mitigated the emission of particulate matters and smoke. With the ce-
tane number reported to be 80–90, ETE presents to be a potential diesel
went through the complete hydrodeoxygenation of furans. Besides, all
the oxygen atoms of the reactants are removed, against the atom
economy [4]. Converting FA to ATE is, thus, significant for just 3 mol of
hydrogen consumed with only one oxygen atom being removed. How-
ever, only few studies on its synthetic method have been conducted.
In the present study, a method to synthesize alkyl tetrahydrofurfuryl
ether (ATE) is reported. Furfuryl alcohol was first catalyzed by solid
acids and then reacted with methanol and ethanol via etherification to
produce corresponding alkyl furfuryl ether (AFE). AFE is further hydro-
genated to yield ATE. Solid acids such as supported protic acid, resin, ze-
olite and heteropoly acid are less corrosive and have been used in
various organic syntheses such as etherification, acetal and esterifica-
tion [7]. Methanol and ethanol are selected, for they present to be po-
tential feedstock for fuels and chemicals [8,9].
2. Experimental
2.1. Typical experimental procedures
4 g HZSM-5 (Si/Al = 25), 50 mL methanol and 5 g furfuryl alcohol
were charged into a 100 mL vessel one by one. It was then put in an
oil bath preset at 25 °C with magnetic stirring (600 rpm) for 24 h. The
reaction was repeated for two times with negligible errors.
The catalyst in Table 1 Entry 1 was filtered, washed with 100 mL
methanol for three times, dried at 100 °C for 3 h and then used for the
⁎
Corresponding author. Tel.: +86 532 8066 2723; fax: +86 532 8066 2724.
E-mail address: muxd@qibebt.ac.cn (X. Mu).
http://dx.doi.org/10.1016/j.catcom.2014.08.030
1566-7367/© 2014 Published by Elsevier B.V.

Q. Cao et al. / Catalysis Communications 58 (2015) 76–79
77
Scheme 1. Reaction pathways for the conversion of FA and MF into biodiesel candidate alkane (pathway 1) and alkyl tetrahydrofurfuryl ether (ATE, pathway 2).
second run. Then it was calcinated at 500 °C for 3 h and used for the
third run.
form a stable oxonium ion [11]. Alkyl furfuryl ether (AFE) was reported
as an intermediate product in synthesizing alkyllevulinate (AL) from FA
(Scheme 1) [12–17]. Such minor by-product as furfuralcohol resin
(FAR) formed by polymerization of FA molecules was also observed in
this process [18,19] (Scheme 1). It was found that the system turned
yellow during the reaction and some viscous yellow liquid remained
in the reactor after the volatile components such as methanol, MFE
and ML were evaporated. The liquid was believed to be FAR [18,19].
AL can be used as a flavor agent or gasoline additive [13,20,21] and
FAR is an indispensable polymer in paints [18], but it is preferable
to carry out the reaction without generating these undesirable by-
products in the synthesis of MFE.
After the catalyst was filtered, the sample in Table 4 Entry 3 and 1 g
humid Raney Ni after being washed by 100 mL ethanol were charged
into a 250 mL autoclave. The autoclave was filled with H2 of 4 MPa
after being purged three times. Zero time and mechanical stirring
started after the autoclave was heated to 100 °C. The reaction lasted
for 2 h. The liquid product of 0.1 mL was diluted with 80 mL ethanol
and analyzed by gas chromatography–mass spectrometry (GC–MS) to
confirm the formation of ETE.
The materials used, detailed experimental procedures and analytical
methods are described in Supplemental information.
The three solid acid catalysts of HZSM-5 (Si/Al = 25), HZSM-5
(Si/Al = 80), and Amberlyst-15 were compared in their ability to con-
vert furfuryl alcohol to MFE in methanol in the initial screening. Figs. 1
and S1 demonstrate the changes of the MTE yield as time goes by. It
was found that HZSM-5 (Si/Al = 25) achieved a higher MFE selectivity
than HZSM-5 (Si/Al = 80) and Amberlyst-15. Lange et al. used different
solid acids to investigate the synthesis of ethyl levulinate (EL) through
FA reacting with ethanol and found that over 80% EL yield was achieved
using Amberlyst-15 at a temperature as high as 125 °C [13]. However,
the present study revealed that the overall yield of MFE and methyl
levulinate (ML) in the presence of Amberlyst-15 was less than 45% at
25 °C. FA turned to produce FAR due to its self-polymerization at a
low temperature. The influence of Si/Al ratio on the MFE and ML yields
was further studied and it was found that the decreasing Si/Al ratio from
3. Results and discussion
3.1. Etherification of furfuryl alcohol with methanol
Methyl tetrahydrofurfuryl ether (MTE) can be theoretically synthe-
sized by direct etherification of tetrahydrofurfuryl alcohol (TFA) with
methanol. Although HZSM-5 (Si/Al = 25) was reported to synthesize
dimethyl ether from methanol via etherification at 150 °C [10], the
GC–MS analysis indicated that no MTE was produced except the expect-
ed dimethyl ether even after four-hour reaction at 160 °C. This can be
explained by the steric effect caused by the tetrahydrofuran ring. It
leads to the relatively low reactivity of the hydroxyl group in TFA. There-
fore, an alternative pathway was suggested in Scheme 1, where MTE
was generated through first making furfuryl alcohol (FA) react with
methanol to produce methyl furfuryl ether (MFE) and then conducting
hydrogenation. The route is believed to be feasible because the hydroxyl
group in FA shows higher reactivity than that in TFA and FA is able to
Table 1
Conversion of FA in methanol with HZSM-5.a
Entry
HZSM-5
(Si/Al)
FA conversion
(%)
MFE yield
(%)
ML yield
(%)
MFE selectivity
(%)
1
25
25
25
38
50
80
94.2
51.2
78.8
82.1
75.4
64.8
55.4
27.2
43.1
42.3
39.7
33.4
16.9
7.1
12.0
15.8
14.9
8.4
58.9
53.2
54.7
51.5
52.7
51.5
2b
3c
4
5
6
a
Reaction conditions: FA 5 g; methanol 50 mL; HZSM-5 4 g; 25 °C; 24 h reaction time.
HZSM-5 (Si/Al = 25) was recycled for the second run after Entry 1.
HZSM-5 (Si/Al = 25) was recycled for the third run after calcination.
b
c
Fig. 1. MFE yield, LM yield and FA conversion versus reaction time. Reaction conditions:
Amberlyst-15 1 g; FA 5 g; methanol 50 mL; 25 °C.

78
Q. Cao et al. / Catalysis Communications 58 (2015) 76–79
Table 2
Conversion of FA in methanol with Amberlyst-15 and HZSM-5.a
Entry
Catalyst
FA conversion (%)
MFE yield (%)
ML yield (%)
MFE selectivity (%)
1b
2c
3
4
5
Amberlyst-15
Amberlyst-15
HZSM-5 (Si/Al = 25)
HZSM-5 (Si/Al = 38)
HZSM-5 (Si/Al = 50)
HZSM-5 (Si/Al = 80)
100
100
96.1
95.7
93.0
82.1
25.2
24.9
41.3
38.9
45.6
36.6
12.4
12.6
27.4
29.1
30.2
18.7
25.2
24.9
43.0
40.6
49
6
44.6
a
Reaction conditions: FA 5 g; methanol 50 mL; HZSM-5 4 g; 40 °C; reaction time 24 h.
Amberlyst-15 1 g.
Amberlyst-15 1 g; reaction time 30 h.
b
c
80 to 25 led to the increase of the MFE yield, ML yield and FA conversion,
as indicated in Table 1. The Si/Al ratio of 25 showed the highest FA con-
version and MFE selectivity (Entries 1, 4, 5 and 6). However, after being
recycled for the second run, HZSM-5 (Si/Al = 25) in Table 1 Entry 1
could only achieve 51.2% FA conversion and 27.2% MFE yield (Table 1
Entry 2), indicating that the catalyst was deactivating. We observed
that the catalyst turned black after the first run. After being calcinated,
the catalyst turned white again, but only 78.8% FA conversion and
43.1% MFE yield were obtained (Table 1 Entry 3). The NH3-TPD analysis,
as shown in Fig. S5, indicated that the catalyst lost some acid sites.
Temperature appears to have a profound effect on the activity of
the catalyst. The potential of different solid acid catalysts (HZSM-5
and Amberlyst-15) to convert FA was further examined at 40 °C.
Amberlyst-15 was used in both Table 2 Entry 1 and Fig. 1. Raising the
temperature to 40 °C led to the decline of the MFE yield from 38.2% to
25.2%, but the ML yield increased from 3.6% to 12.4%. Our findings are
the same with Lange's results [13] that higher temperature enhanced
the formation of ML and FAR. The results in Table 2 Entries 1 and 2
showed that MFE is stable at 40 °C even when the time was prolonged,
which was consistent with the results in Fig. 1. For HZSM-5, higher reac-
tion temperature also resulted in growing production of ML and higher
FA conversion, but lower MFE selectivity. To sum up, both the lower
temperature and lower Si/Al ratio are favorable conditions for MFE
formation.
Since HZSM-5 (Si/Al = 25) exhibited the best catalytic selectivity
among the solid acids, the impact of FA concentration and catalyst load-
ing on the reaction was investigated with the results shown in Table 3.
At a fixed level of FA concentration, the catalyst loading was supposed
to reach its optimum amount to achieve a maximum selectivity
of MFE (Entries 1 to 6). More catalyst loading facilitates the formation
of FAR and LM. Increasing FA concentration from 1 g/mL(methanol) to
2 g/mL(methanol) and 2 g/mL(methanol) to 3 g/mL(methanol) led to the de-
crease of the MFE yield, FA conversion and MFE selectivity (Entries 2
and 4; 5 and 8). This may be because the zeolite catalyst pores were
plugged by oligomers [22]. The highest yield and selectivity of MFE
could reach 55.4% and 58.9% respectively (Table 3 Entry 2).
selectivity of MFE was only 58.9%. Nevertheless, other chemical
feedstock items such as FAR and LM, both are useful chemicals in
many fields, were generated as the main by-products in the system
[13,18,20]. Accordingly, this route could convert most of the FA mole-
cules into value-added products and was thus believed as a promising
way for utilizing FA.
3.2. Etherification of furfuryl alcohol with ethanol
HZSM-5 (Si/Al = 25) presents to be the most efficient catalyst
among the solid acids investigated for the synthesis of MFE. It was uti-
lized for the etherification of furfuryl alcohol with ethanol and the re-
sults were displayed in Table 4. Higher steric hindrance of ethyl than
methyl led to lower reactivity of ethanol than methanol. Hence, 40 °C
was selected as the initial temperature for the reaction (Table 4
Entry 1). It was found that only 24.3% ethyl furfuryl ether (EFE) yield
and 71.5% FA conversion were achieved. Raising the temperature to
55 °C made the EFE yield increase to 40.6% and FA conversion to 90.6%
(Table 4 Entry 4). The higher selectivity to FAR was another reason for
the low EFE and EL yields at 40 °C, because FAR may cause the pores
of HZSM-5 to deactivate [22]. Similar to the results found in the MFE
synthesis, higher temperature also increased the EL yield (Table 4 En-
tries 1 and 4). When the temperature was raised to 70 °C, both the
EFE yield and selectivity dropped significantly (Table 4 Entries 4
and 5). Optimal temperature is required for the catalyst to achieve
high EFE selectivity. The highest EFE selectivity could reach 44.8%
(Table 4 Entry 4) under the experimental conditions. Compared with
Table 3, the reactivity of ethanol was lower than that of methanol at
the same temperature. Therefore, higher temperature was needed to
activate the catalyst for ethanol.
3.3. Hydrogenation of MFE and EFE into MTE and ETE
Recent studies demonstrated that a high 2,5-tetrahydrofuran-
dimethanol (THFDM) yield of up to 99% was obtained by hydrogenating
5-hydroxymethylfurfural (HMF) with a Raney Ni catalyst at 100 °C [23,
24]. Since HMF, MFE and EFE are similar in structure, Raney Ni was thus
selected in the present study as the hydrogenating catalyst for MFE
and EFE. As shown in Fig. S3, EFE was almost quantitatively converted
into ETE with Raney Ni at 100 °C under solvent free conditions. The con-
version may still be realized if such conditions such as the temperature
It was noted that the HZSM-5 (Si/Al = 25) catalyst is not particularly
effective in the etherification of FA with methanol since the maximum
Table 3
Conversion of FA in methanol with HZSM-5 (Si/Al = 25).
Entry FA
Catalyst FA conversion MFE yield ML yield MFE selectivity
(g) (g)
(%)
(%)
(%)
(%)
Table 4
Conversion of FA in ethanol with HZSM-5 (Si/Al = 25).
1
2
3
4
5
6
7
8
9
5
5
5
10
10
10
15
15
15
3
4
5
4
6
8
4
6
8
90.1
94.2
94.7
73.6
91.0
95.8
61.2
71.3
76.6
46.5
55.4
48.2
41.7
49.1
46.4
24.0
33.2
39.6
16.4
16.9
19.5
7.8
12.0
12.8
6.8
51.6
58.9
50.9
56.7
54.0
48.4
39.2
46.6
51.7
Entry Catalyst Temperature FA conversion EFE yield EL yield EFE selectivity
(g)
(°C)
(%)
(%)
(%)
(%)
1
2
3
4
5
4
2
3
4
4
40
55
55
55
70
71.5
66.3
78.4
90.6
97.8
24.3
23.6
28.8
40.6
23.8
16.1
20.7
29.6
47.0
53.3
33.9
35.6
36.7
44.8
24.3
8.5
9.8
Reaction conditions: methanol 50 mL; 25 °C; 24 h reaction time.
Reaction conditions: FA 5 g; ethanol 50 mL; 18 h reaction time.

Q. Cao et al. / Catalysis Communications 58 (2015) 76–79
79
Table 5
Cetane number measurements.
Sample
Diesel
41.0
10 vol.% MFE + 90 vol.% diesel
39.2
17 vol.% MTE + 83 vol.% diesel
46.8
17 vol.% ETE + 83 vol.% diesel
47.8
Cetane number
and catalyst loading alter, but that was not the focus of this study. Fig. S4
indicated that EFE was in-situ hydrogenated to ETE using Raney Ni. MTE
was also synthesized by hydrogenating the commercial MFE product
under the same conditions as those for EFE in the present study.
Young Scholar, China (No. JQ201305) and the Natural Science Founda-
tion of Shandong Province, China (O92003110C).
Appendix A. Supplementary data
3.4. Cetane number measurement
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2014.08.030. This data include MOL file and
InChiKey of the most important compounds described in this article.
The ability of MTE and ETE (both hydrogenated products) and MFE
(etherification intermediate) to improve the diesel cetane number
was discussed with results shown in Table 5. It was found that MFE
failed to raise the cetane number, as evidenced from a decrease from
41.0 to 39.2 after the addition of 10 vol.% MFE. On the contrary,
17 vol.% MTE and 17 vol.% ETE increased the cetane number from 41.0
to 46.8 and 47.8 respectively. ETE was slightly superior to MTE. It further
indicated that ATE with a longer alkyl chain was more capable to im-
prove the cetane number [6]. However, the major disadvantage of
MTE and ETE lay in their low flash points (ETE at 42.5 °C and MTE slight-
ly lower than 42.5 °C) [6]. Because the commonly used diesel (No. −20
to No. 10) requires the flash point to reach at least 55 °C, the amount of
MTE and ETE added into diesel must be limited. However, the amount
can be further increased if they are added in mixtures with higher boil-
ing points. Besides, more MTE or ETE could be added into diesel in some
extremely cold areas, where No. −30 and No. −50 diesels are used, and
they only require the flash point to reach 45 °C.
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MFE selectivity of 58.9% and EFE selectivity of 44.8% were achieved
with HZSM-5 (Si/Al = 25). Using a Raney Ni catalyst, MFE and EFE
were almost quantitatively hydrogenated into MTE and ETE. The poten-
tial application of MTE and ETE as a cetane number improver was then
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methanol and ethanol into diesel additives.
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