Microwave-assisted catalytic upgrading of bio-based furfuryl alcohol to alkyl levulinate over commercial non-metal activated carbon

Article abstract of DOI:10.1016/j.mcat.2019.110630

A cheap and commercially available non-metal activated carbon (AC) as an efficient catalyst for the alcoholysis of furfuryl alcohol (FA) to alkyl levulinate (AL) under microwave assistance was firstly investigated. The catalyst gave an impressive methyl levulinate (ML) yield of 78% in only 5 min at 170 °C in the presence of FA (0.2 M, 3 mL) and AC (100 mg). Various reaction parameters in dependence of time such as temperature, catalyst and feedstock loadings as well as solvent types have been optimized. The re-utilization experiments of the catalyst showed that the activity related to the acidic groups of the catalysts, and the deactivation was due to the leaching of acidic specie, which was easily extracted by the solvent. Note that extremely low concentration of the active species extracted from AC (less than 1 wt %) could also give 62% ML yield. The present study provided a promising way for AL synthesis over cheap, commercially available and environmentally benign catalyst.

Full text of DOI:10.1016/j.mcat.2019.110630

MolecularCatalysis480(2020)110630
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Microwave-assisted catalytic upgrading of bio-based furfuryl alcohol to alkyl
levulinate over commercial non-metal activated carbon
Yantao Wanga,b,c, Deyang Zhaob,c, Konstantinos S. Triantafyllidisd,e, Weiyi Ouyangf,
⁎
Rafael Luquef,g, Christophe Lenb,c,
a School of Ressources Environmental & Chemical Engineering, Nanchang University, Nanchang 330031, China
b Sorbonne Universités, Université de Technologie de Compiègne, Centre de Recherche Royallieu, CS 60 319, F-60203 Compiègne cedex, France
c Chimie ParisTech, PSL Research University, CNRS, Institute of Chemistry for Life and Health Sciences, 11 rue Pierre et Marie Curie, F-75005 Paris, France
d Department of Chemistry, Aristotle University of Thessaloniki, University Campus, P.O. Box 116, GR-54124 Thessaloniki, Greece
e Chemical Process & Energy Resources Institute, CERTH, Thermi Rd., P.O. Box 60361, GR-57001 Thessaloniki, Greece
f Departamento de Quimica Organica, Universidad de Cordoba, Campus de Rabanales, Ed. Marie Curie (C3), Ctra Nnal IV-A, Km 396, E-14014 Cordoba, Spain
g Peoples Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya Str., Moscow, 117198, Russia
A R T I C L E I N F O
A B S T R A C T
Keywords:
A cheap and commercially available non-metal activated carbon (AC) as an efficient catalyst for the alcoholysis
of furfuryl alcohol (FA) to alkyl levulinate (AL) under microwave assistance was firstly investigated. The catalyst
gave an impressive methyl levulinate (ML) yield of 78% in only 5 min at 170 °C in the presence of FA (0.2 M, 3
mL) and AC (100 mg). Various reaction parameters in dependence of time such as temperature, catalyst and
feedstock loadings as well as solvent types have been optimized. The re-utilization experiments of the catalyst
showed that the activity related to the acidic groups of the catalysts, and the deactivation was due to the leaching
of acidic specie, which was easily extracted by the solvent. Note that extremely low concentration of the active
species extracted from AC (less than 1 wt %) could also give 62% ML yield. The present study provided a
promising way for AL synthesis over cheap, commercially available and environmentally benign catalyst.
Furfuryl alcohol
Alkyl levulinates
Activated carbon
Microwave
Metal-free
1. Introduction
furfural was used for FA production, however, it’s not fully utilized and
is oversupplied in the chemical market [6,29]. Thus, the development
Regarding the dwindling resources of fossil fuels, the exploitation of
alternative fuels and chemicals from abundant and renewable biomass
is attracting more and more attentions [1]. Alkyl levulinates (ALs),
which have been identified as one of top ten biorefinery candidates, are
a kind of promising renewable fuel additives and platform chemicals for
the synthesis of angelica lactone, GVL, valerates, as well as good
building blocks [2,3]. Generally, ALs were produced by direct ester-
ification of levulinic acid (LA) over acidic catalysts or enzymatic
methods [4,5], however, in the production of LA, its separation and
purification are costly, which made it unsuitable for as the raw material
for this purpose [6]. Recently, great efforts were devoted to develop
new methods to produce ALs from various feedstocks, such as raw
biomass [7], carbohydrates [8–16], 5-hydroxymethyl furfural or fur-
fural [17–20], and furfuryl alcohol (FA) [3,21–28]. Among them, FA is
a promising starting material due to its easy accessibility from furfural
by reduction of its aldehyde function. Besides, each year around 62% of
of a feasible and competitive pathway for FA upgrading is strongly
demanded.
It has been reported that acidic catalysts are crucial to the alcoho-
lysis of FA to ALs. Based on this point of view, various homogeneous
catalysts such as mineral acids [7,23], salts [21,22,30], ionic liquids
[6,8,11], and also heterogeneous catalysts, such as ion-exchanged re-
sins [23,31], oxides [32,33] and zeolites [23,32,34,35], have been
concretely investigated. Due to the advantages of less corrosion, easy
handle and separation, the exploration of heterogeneous catalysts is
progressing satisfactorily in recent years. For example, Song et al. have
synthesised a series of arylsulfonic acid functionalized hollow meso-
porous carbon spheres catalysts, and successfully applied them into the
ethanolysis of FA, which gave the best EL yield of ca.80% at 120 °C for
2 h [36]. Furthermore, they fabricated some ethane-bridged organosi-
lica nanotubes functionalized catalysts (labelled as ArSO3H-Si(Et)Si-Ph-
NTs), which furnished a good EL yield of 84% and reusability [37]. Rao
⁎ Corresponding author at: Sorbonne Universités, Université de Technologie de Compiègne, Centre de Recherche Royallieu, CS 60 319, F-60203 Compiègne cedex,
France.
E-mail address: christophe.len@chimieparistech.psl.eu (C. Len).
https://doi.org/10.1016/j.mcat.2019.110630
Received 26 June 2019; Received in revised form 9 September 2019; Accepted 12 September 2019
2468-8231/©2019ElsevierB.V.Allrightsreserved.

Y. Wang, et al.
MolecularCatalysis480(2020)110630
et al. developed a series of zinc exchanged tungstophosphoric acid
supported on niobia catalysts. It was found that the acidity of the cat-
alysts depended on the amount of Zn ions exchanged, which played a
key role on the activity of the catalysts [26]. More recently, Kong et al.
reported Fe modified zeolite USY as an efficient catalyst for the etha-
nolysis of FA to EL (ca. 91% yield). Different from Zn exchanged cat-
alysts, the strong acidic sites of USY were sharply reduced after Fe
modification, but concomitant large amount of weak acidic sites gen-
erated [38]. They suggested that the decrease of strong acidic sites
suppressed side reactions, and the enhanced weak acidic sites guaran-
teed the activity of the catalyst. However, despite of these promising
results, several defects of these above-mentioned catalysts, such as the
complex preparation process, the cost, environmental concerns, limited
their applications to some extent. Additionally, microwave-irradiations
have been recognized as an efficient and green method to facilitate
chemical reactions to achieve higher yield and selectivity in shorter
reaction times [39–43]. Recent study has shown that microwave
heating could improve the reaction rate of FA methanolysis to methyl
levulinate (ML) 6 times when compared to conventional heating
method [30]. Combining these two aspects, it’s appealing to explore
some cheaper, greener, more efficient and accessible catalysts for up-
grading FA to ALs under microwave irradiations.
for 10 min at 120 °C. The ionization mode was FID (70 eV, 300 μA,
250 °C). The identification of the compounds was performed by com-
parison of the retention times with pure standards and by GC/MS
analysis.
First, calibration curves for FA and ML were determined in the
0–100 mg mL−1 range, using n-decane (5.0 mg mL−1) as the internal
standard (see ESI Fig. S1).
The yield and conversion in continuous flow were calculated ac-
cording to Eqs. (1) and (2):
CPProduct
CMLFeed
Yield (%) =
× 100
(1)
(2)
[CMLInitial − CMLFinal
]
Conversion (%) =
× 100
CMLInitial
3. Results and discussion
3.1. Catalyst activity screening experiments
In the present paper, we report an efficient catalytic approach for
the conversion of FA to AL over commercial available activated carbon
under the assistance of microwave irradiation. The catalyst loading and
reaction temperature have great influence on ML yield and the forma-
tion rate. Control experiments and different spectroscopic techniques
were also conducted to better understand the catalyst performance.
Firstly, the effect of different kinds of acidic catalysts on the alco-
holysis of FA was studied at 150 °C for 5 min in methanol while keeping
the same amount of catalyst (50 mg) under microwave irradiation.
Conversion of FA without catalyst was very low (18%), and no desired
product ML was formed, however, FA achieved fully conversion with
other catalysts, even with commercial AC (Fig. 1). Surprisingly, AC
gave a comparable ML yield (36%) with zeolite catalysts HY5.2 (41%)
and HY60 (30%). More interestingly, lots of methoxymethyl furan
(MmF), which was considered as the intermediate from FA to ALs, has
been produced (Scheme 1). This means a higher ML yield could be
reached with AC as the catalyst by optimizing the reaction conditions
appropriately. Pleasingly, 55% of ML was obtained with AC (100 mg),
while MmF yield relatively decreased to 22% from 39%. In this case,
ML yield is even higher than HZSM-5-30 (50 mg) and slightly lower
than HZSM-5-50 (50 mg) which gave 54% and 60% ML yield respec-
tively. It should be noted that HZSM catalysts gave quite amount of α-
angelica lactone as the major side-product, which has been identified
by GC–MS. In spite of the home-made sulfonated carbon (SC) presented
the best catalytic performance on ML production (77% yield), the re-
sults with commercial AC seems more attractive as its commercial ac-
cessible. Therefore, these results highlight that commercial ACs could
replace common acid catalysts for AL production, which convinced us
to further optimize reaction parameters.
2. Materials and methods
2.1. Materials
Furfuryl alchohol (≥ 98%), methanol (≥ 99.9%), ethanol (≥
99.5%), n-propanol (≥ 99.5%), iso-propanol (≥ 99.5%), n-butanol (≥
99.5%), methyl levulinate (99%), n-decane (≥ 99%) were purchased
from Sigma-Aldrich and further used without purification. The catalysts
HY5.2, HY60, HZSM-5-30 and HZSM-5-50 were purchased from
Zeolytes International (USA). The zeolite materials were calcined at
600 °C during 24 h prior to use. Activated carbon (Charcoal activated
power, technical grade) was purchased from Panreac (Spain), and sul-
fonated carbon was prepared according to literature [44].
2.2. General procedure for the microwave-assisted synthesis of alkyl
levulinate
FA (0.2 M, 3 mL) feedstock solution and activated carbon (100 mg)
were introduced in a 10 mL vial closed with a septum. 2 min ramping
time was settled to reach desired reaction temperature. All of the ex-
periments were performed in a microwave reactor (CEM discover) and
stirred under magnetic stirring (600 rpm) for the desired time. The re-
action temperature was measured by means of IR sensor. At the end of
the reaction, the solution was filtered prior to analysis through a syr-
inge filter (PTFE, 0.22 μm, VWR).
2.3. Product analysis
GC-FID analysis was performed on a gas chromatograph (HP, 14009
Arcade, New York, United States) coupled with a FID detector equipped
with a Supelco 2-8047-U capillary column (15 m x0.25 mm i.d. and
0.25 μm film thickness, Alltech Part No.31163-01). H2 was used as
carrier gas at 1 mL min−1 flow rate. The samples were injected directly
onto the column using septum-equipped programmable injector (SPI)
system. The temperature of the injector was set 250 °C and the oven
started at 80 °C, held for 5 min, raised to 100 °C at a rate of 10 °C min-1,
held for 5 min and then raised to 120 °C at a rate of 10 °C min-1 and held
Fig. 1. Effect of catalysts on FA conversion, ML yield and MmF yield. Reaction
conditions: FA (0.2 M, 3 mL), catalyst (50 mg), methanol, 150 °C, 5 min a cat-
alyst (100 mg).
2

Y. Wang, et al.
MolecularCatalysis480(2020)110630
Scheme 1. Methanolysis of FA to ML via the intermediate MmF.
Table 1
Effect of AC catalyst and reaction time on FA conversion, ML and MmF yields.a.
Entry AC loading
(mg)
Time
(min)
FA conversion
(%)
ML yield
(%)
MmF yield
(%)
1
2
3
4
5
6
7
8
25
25
25
25
25
50
50
50
50
50
50
50
100
100
100
100
100
0
2.5
5
10
20
0
2.5
5
66
98
99
99
99
80
99
99
98
98
99
99
95
99
99
99
99
5
52
70
62
53
47
74
54
39
52
55
27
26
77
61
22
13
7
13
15
19
19
7
24
36
30
24
42
42
13
28
55
67
72
Fig. 2. Influence of temperature and reaction time on FA conversion, ML yield
and MmF yield. Reaction conditions: FA (0.2 M, 3 mL), catalyst (100 mg), me-
thanol, MW.
9b
10c
11
12
13
14
15
16
17
5
5
the effect of microwave irradiations that significantly accelerate the
reaction rate [30]. When compared the results obtained at 150 °C
(Table 1), we can conclude that higher reaction temperature benefits to
higher ML yield, and simultaneously shortened reaction time. For ex-
ample, a relative stable ML yield of 78% was achieved in 5 min at
170 °C, which is higher than that of 67% at 150 °C for 10 min (Table 1,
entry 16) and 36% at 130 °C for 30 min (Fig. 2). Moreover, lower re-
action temperature would limit the consumption rate of MmF to ML.
Therefore, in order to diminish the reaction time the temperature was
fixed at 170 °C for further investigation.
10
20
0
2.5
5
10
20
a
Reaction conditions: FA (0.2 M, 3 mL), methanol, AC (25–100 mg), MW,
150 °C.
b
Reaction conditions: FA (0.2 M, 3 mL), methanol, H2O (1 eq), AC (50 mg),
MW, 150 °C.
c
Reaction conditions: FA (0.2 M, 3 mL), methanol, H2O (2 eq), AC (50 mg),
3.4. Influence of FA loading variation
MW, 150 °C.
The concentration of the starting material, FA, is a key factor with
great influence on most of chemical reactions. Actually, FA poly-
merization or polycondensation could be easily occurred in acidic en-
vironment [46,47]. Thus, the effect of FA concentration at 0.1 M and
0.4 M were investigated within various reaction time periods
(0–10 min) (Fig. 3). With a lower concentration of FA (0.1 M), the yield
of ML increased to 83% in 7.5 min. It’s notable that better ML yield was
obtained is a short reaction time when a higher concentration of FA was
used (0.4 M vs 0.1 M at t = 0 min and 2.5 min). MmF yield was higher
in lower concentration of FA whatever the reaction time used. It seems
that higher FA loading did a favour to convert MmF to ML more rapidly,
but gave lower ML yield when prolonged reaction time to 10 min.
3.2. Influence of catalyst loading variation
The influence of catalyst dosage on the alcoholysis of FA in de-
pendence of time was also investigated (Table 1). In all cases, FA
reached more than 98% conversion in 2.5 min. In the meantime, MmF
was the major product, which is in line with literature, which reported
that the formation rate of alkoxymethylfuran was much higher than
that of alkyl levulinate [3]. The increase of reaction time and catalyst
loading facilitate the conversion of methoxymethylfuran (MmF) to ML,
and the best 72% ML was yielded with AC (100 mg) for 20 min (Table 1,
line 17). Experiments were also carried out at 150 °C for 5 min to study
the effect of water addition on ML formation. The results showed that
ML yield gradually decreased from 36% to 24% with the water loading
increasing to 2 eq (Table 1, lines 8–10). This effect was out of accord
with the results from Zhang et al. [3], who proved that the addition of
water has a positive effect on furfuryl alcohol and 2-butoxymethylfuran
conversions to butyl levulinate. Our results seem more agree with the
findings from Maldonado et al. [45], who demonstrated that water does
not participate in the mechanism for conversion of FA to ethyl EL, as EL
yield decreased with the addition of water.
3.3. Influence of the temperature
The influence of temperature on the alcoholysis of furfuryl alcohol
was studied in a range from 130 to 170 °C under batch microwave ir-
radiations with AC (100 mg) and FA (0.2 M, 3 mL) feedstock loading
(Fig. 2). Almost complete conversion was achieved as the temperature
increased from 130 °C to 170 °C at time 0, which means FA was fully
consumed when heating process finished. This could be attributed to
Fig. 3. Influence of FA loading and reaction time on ML and MmF yields.
Reaction conditions: FA (0.1-0.4 M, 3 mL), catalyst (100 mg), methanol, MW,
170 °C.
3

Y. Wang, et al.
MolecularCatalysis480(2020)110630
Fig. 5. Reusability of AC as catalyst on FA conversion, EL and EmF yields.
Reaction conditions: FA (0.2 M, 3 mL), catalyst (100 mg), ethanol, MW, 170 °C,
5 min. (a) Control test 1: AC (100 mg), ethanol (3 mL), MW, 170 °C, 5 min then
after centrifugation and filtration, the liquid solution was recharged with fresh
FA. The FA (0.2 M, 3 mL) was heated under MW at 170 °C for 5 min. (b) Control
test 2: AC (100 mg), ethanol (3 mL), MW, 170 °C, 5 min then after centrifuga-
tion and filtration, the solid was washed with ethanol for free times, dried and
then reused.
Fig. 4. Influence of the nature of the alcohol on FA conversion, AL and AmF
yields. Reaction conditions: FA (0.2 M, 3 mL), catalyst (100 mg), methanol,
MW, 170 °C, 5 min.
Generally, the polymerization of FA to oligomeric compounds at a high
concentration should response to the decrease of ML yield [48].
3.5. Scope of the reaction
catalyst.
Under optimized conditions (FA (0.2 M, 3 mL), AC (100 mg), MW,
170 °C, 5 min), the alcoholysis of FA using different alkyl alcohols was
studied. With the increase of the alcohol chain length, the yield of ALs
slightly decreased from 78% to 64% with methanol and n-butanol, re-
spectively (Fig. 4). With branch alcohol iso-propanol, 39% of iso-propyl
levulinate yield was relatively lower than that with linear alcohol n-
propanol (66%). One can notice that more intermediate was left with
iso-propanol. In our hands, conversion to iso-propyl levulinate is more
difficult, which was probably caused by steric effects and the nature of
the hydroxyl group(OHII) [22]. The tendency is consistent with the
literatures [22,25,49], and these results suggest that AC has a universal
catalytic ability for the alcoholysis of FA, and the high activity is
comparable with Al2(SO4)3 which gave 65% butyl levulinate yield in
40 min when heated to 150 °C by microwave [30].
To better understand the catalytic activity of this kind of commer-
cial activated carbon, BET, EDS, ICP-MS and acid-base properties of the
AC and spent ACs were measured (Table 2). No big changes in the
porosity and surface area of the carbons were observed by BET. How-
ever, EDS gave us a clear clue that species containing ‘sulphur’ possibly
attribute to the activity, and ca. 42% of average atomic was leached
after first run. This phenomenon consisted with the study of Zhu et al.
who identified the surface SO3H groups on graphene oxide were the
primary active sites, and the surface carboxyl groups worked sy-
nergistically during the alcoholysis of furfuryl alcohol [50]. More
concretely, these kinds of carbon materials contain a variety of oxygen-
containing functionalities, such as −OH, −COOH, and −SO3H etc.
Among them, hydroxyl groups were considered no contribution to the
catalyst activity, but carboxyl groups could help the absorption of FA on
the catalyst surface via hydrogen bonding, which will do a favour for
the conversion of FA to ALs. Similarly, Antunes et al. also proved that
oxygen-containing groups on carbon materials played a role in the
catalytic conversion of HMF to 5-ethoxymethylfurfural, 5-(ethox-
ymethyl)furfural diethylacetal and ethyl levulinate [17]. Rigorously,
EDS analysis couldn’t give a very accurate result, therefore, we also
titrated the acidic and basic groups on these samples following the
literature [51]. The results are in line well with EDS analysis as ˜
0.7 mmol/g acidic groups were lost after first run. Besides, no appar-
ently basic groups leaching were observed. Further treating AC with
ethanol and water in presence of 0.2 M furfuryl alcohol at 170 °C for 1 h
without MW offered 0.6 mmol g−1 and 0.9 mmol g−1 acidic groups
leaching respectively, which agreed with our results with microwave.
Simultaneously, when treating AC (1.5 g) with water (20 mL) at 170 °C
for 1 h, ICP-MS analysis of the filtrate showed that no significant
amounts of metals leached to water, only Ni content is at about
300 ppm. Thus, we speculate that the ‘active species’ is possibly the
acidic organosulfates on the activated carbon, and the deactivation of
the catalyst was due to the poor thermal stability of these organo-
sulfates groups.
3.6. Catalyst reusability
Recycling of the catalyst is an important step for a sustainable and
economically feasible catalytic system. Therefore, the recycle experi-
ments for AC catalyst were also carried out at 170 °C for 5 min in
ethanol. After each reaction the catalyst was separated by centrifuga-
tion, washed thoroughly with ethanol for three times and dried at
100 °C for the next catalytic reaction. Evidently, the catalyst activity
severely decreased at the second run, as FA conversion decreased from
99% to 62% and EL yield dropped to 12% from 74% (Fig. 5). To un-
derstand the deactivation of the catalyst, two control experiments were
performed (control test 1 and control test 2). One experiment was
conducted without FA as starting material under optimized conditions.
After 5 min under microwave irradiation and then centrifugation and
filtration furnished two separated phases: a liquid solution and a solid.
The liquid solution was recharged with FA (0.6 mmol) and decane
(0.015 g), and then the mixture was heated under MW at 170 °C for
5 min (control test 1). The control test 2 was performed using the op-
timized conditions with the recovered solid (after 3 times washing and
dry) instead of the pure AC. Control test 1 indicated that some active
species of AC were extracted into ethanol phase since EL was obtained
in 61% yield. Consequently, the recovered solid (control test 2) gave
poor EL and EmF yields due to leaching. Furthermore, the comparison
between control test 2 and run 2 probably implied that some other
factors may attribute to the catalyst decay, for example, oligomeric
compounds formed by FA polymerization covered some acidic groups
etc. From this point of view, the AC seems more like homogeneous
3.7. Reaction pathway and plausible mechanism
According to literatures, multiple pathways have been proposed for
the formation of AL from FA, including some key intermediates, such as
MmF and 4,5,5-trimethoxypentan-2-one (TMP). Besides, one possible
mechanism was regarding to aldehydration of FA to α-angelica lactone,
which was in turn readily attacked by alcohols to form AL [52].
4

Y. Wang, et al.
MolecularCatalysis480(2020)110630
Table 2
BET, EDS and acid-base properties of the AC catalyst and its spent AC catalyst.
Sample
BET total SSA
Micropore /External area
[(m2 −1) / (m2 −1)]
Total pore volume
EDSaverage atomic ‘S’
Acidic groups
Basic groups
Total content of surface
b
c
(m2 g−1
)
g
g
(cc g−1
)
(%)d
(mmol g−1
)
(mmol g−1
)
oxides [mmol g−1
]
ACa
702
412/289
392/318
0.546
0.579
43.58
25.34
2.585
1.877
1.100
1.079
3.685
2.296
Spent ACa 710
a
Spent AC is the sample recycled from run 1 in Fig. 5.
SSA: specific surface area from N2 sorption at −196 °C (multi-point BET method).
Total pore volume at P/Po = 0.99.
b
c
d
Si, P, S, K, and Ca were measured, total atomic Si + P+S + K+Ca = 100%.
Scheme 2. Plausible mechanism pathway for FA alcoholysis to ML via the intermediate MmF.
However, in our case, we proposed a plausible mechanism concerning
MmF as the key intermediate (Scheme 2). Because one can obviously
notice that MmF is the major intermediate (identified by GC–MS, see
ESI Figure S1), which token 77% yield at 0 min with AC (100 mg)
(Table 1, line 13), and this routes seems more reasonable as lower
energy was needed for the formation of alkoxymethylfuran [53]. After
elimination in acidic conditions, intermediate A could form compound
B0 using two different pathways: way 1 in the presence of aqueous
methanol and way 2 in methanol without water. These two ways are in
accordance with the mechanism reported by Maldonado et al. [45]. The
5

Y. Wang, et al.
MolecularCatalysis480(2020)110630
reaction barrier with water (from A to B0) was higher than that without
water (from A to B). This could explain why the yield of ML decreased
and MmF yield increased when additional water was introduced
(Table 1). Then, B0 was formed from B by releasing a molecule meth-
oxymethane, and after the addition with 3 eq. methanol in one or two
steps, the most important intermediate TMP could be produced. How-
ever, no peak of TMP was found in GC or GC–MS in the present work,
but some species (C and D) with similar structure to TMP were iden-
tified by GC–MS (see ESI Fig. S1 × 2 and X3). However, the species X1
and X4 (see ESI Fig. S1) may suggest that complex multiple pathways of
FA alcoholysis are possible.
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4. Conclusion
Commercial non-metal activated carbon was proved as an efficient
catalyst for the production of ALs by alcoholysis of FA under microwave
irradiations. Upon the optimization, 78% of ML yield was obtained in
5 min, which is comparable to the results of most literatures. The study
of catalyst reusability indicated that acidic groups containing ‘sulphur’
on AC could be easily extracted. Regardless of its poor stability, this
method is environmentally benign and economical for the conversion of
biomass-based derivatives into fine chemicals, because the catalyst is
quite cheap and commercially available.
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Acknowledgement
D.Z. and Y.W. would like to thank the China Scholarship Council
(CSC) for the financial support.
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