Humins with Efficient Electromagnetic Wave Absorption: A By-Product of Furfural Conversion to Isopropyl Levulinate via a Tandem Catalytic Reaction in One-Pot

Article abstract of DOI:10.1002/chem.202101928

Both one-pot catalytic conversion of furfural (FAL) to isopropyl levulinate (PL) and carbonization of by-product (humins) for electromagnetic wave absorption are discussed, which provides inspiration that humins can be applied to electromagnetic wave absorption. In the former, phosphotungstic acid (PW) is employed as a homogeneous catalyst to convert FAL to PL via a tandem reaction in one pot, with the formation of a vast amount of humins. With FAL and various intermediates as substrates, it was found that humins was a polymerization product of FAL, furfuryl alcohol (FOL) and furfuryl ester (FE) with furan rings. In addition, the in situ attenuated total reflection infrared (ATR-IR) spectra also provided a basis for the proposed reaction route. In the latter, with the humins as raw material, P species and WO₃ doped nano-porous carbon (Humins-700) platform formed after high-temperature annealing is used for electromagnetic wave absorption and manifests desirable absorption performance. The minimum reflection loss (RL_min) value is ?47.3 dB at 13.0 GHz with a thickness of 2.0 mm and the effective absorption bandwidth reaches 4.5 GHz (11.2–5.7 GHz).

Full text of DOI:10.1002/chem.202101928

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Accepted Article
Accepted Article
Title: Humins with Efficient Electromagnetic Wave Absorption: a By-
Product of Furfural Conversion to Isopropyl Levulinate via a
Tandem Catalytic Reaction in One-Pot
Authors: Mingwei Ma, Na Liang, Pan Hou, Peng Zhang, Jingjie Cao,
Hui Liu, Xingliang Xu, Huijuan Yue, Ge Tian, and Shouhua
Feng
This manuscript has been accepted after peer review and appears as an
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202101928
Link to VoR: https://doi.org/10.1002/chem.202101928
01/2020

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10.1002/chem.202101928
Chemistry - A European Journal
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Humins with Efficient Electromagnetic Wave Absorption: a By-
Product of Furfural Conversion to Isopropyl Levulinate via a
Tandem Catalytic Reaction in One-Pot
Mingwei Ma,a, † Na Liang,a, † Pan Hou,a Peng Zhang,a Jingjie Cao,a Hui Liu,a Xingliang Xu,b Huijuan
Yue,a Ge Tian *, a and Shouhua Feng a
Abstract: Both one-pot catalytic conversion of furfural (FAL) to
isopropyl levulinate (PL) and carbonization of by-product (humins) for
electromagnetic wave absorption are discussed, which provides
inspiration that humins can be applied to electromagnetic wave
absorption. In the former, phosphotungstic acid (PW) is employed as
a homogeneous catalyst to convert FAL to PL via a tandem reaction
in one pot, with the formation of a vast amount of humins. With FAL
and various intermediates as substrates, it was found that humins was
a polymerization product of FAL, furfuryl alcohol (FOL) and furfuryl
ester (FE) with furan rings. In addition, the in-situ attenuated total
reflection infrared (ATR-IR) spectra also provided a basis for the
proposed reaction route. In the latter, with the humins as raw material,
P species and WO3 doped nano-porous carbon (Humins-700)
platform formed after high-temperature annealing is used for
electromagnetic wave absorption and manifests desirable absorption
performance. The minimum reflection loss (RLmin) value is -47.3 dB at
13.0 GHz with a thickness of 2.0 mm and the effective absorption
bandwidth reaches 4.5 GHz (11.2 – 5.7 GHz).
its ester by catalytic hydrolysis or alcoholysis with Bronsted acid
(B).[5] And the FOL can be obtained by hydrogenation reduction
of FAL with the assistance of Lewis acid (L) or metal catalyst
under H2 atmosphere or alcohol solution.[6] Therefore,
a
bifunctional catalyst comprising L and B acid was designed to
carry out a one-pot conversion of FAL to LA or its ester (Scheme
1).[7] Recently, Zhang et al. used ZrO2@SBA-15 catalyst to
efficiently and selectively convert FAL to FOL or levulinate ester
and conducted a kinetic study.[7d] Galletti et al. used CuFe2O4 and
a commercial solid acid catalyst for a stepwise reaction to convert
furfural to isopropyl levulinate step by step.[7e]
However, the conversion from C5-C6 sugar, FAL, 5-
hydroxymethylfurfural (HMF) and other biomass or biomass
compounds into high value-added chemicals under the action of
acid catalysts inevitably leads to the formation of solid by-product,
called humins (Figure S1). It is a heterogeneous, polydisperse
material with rich organic functional groups.[8] The formation of
humins is undesirable because it reduces the yield of the target
product and incurs operational problems such as contamination
and blockage of valves and pipes during the process.[9]Since it is
unavoidable, we might as well utilize it while preventing its
generation, which is the focus of this work.
Introduction
The efforts to exploit humins have been ongoing for several
years, including combustion, carbonization, resin, catalytic
gasification, pyrolysis, and hydrotreatment.[10] Guigo et al. used
the humin based resin derived by sugar (C6) to modify the wood
to make it have better hydrophobicity and fire resistance.[11]
Among them, carbonization is one of the simpler and appropriate
methods, which could be widely applied in the synthesis of carbon
materials in the fields of catalysis, adsorption, electrochemical
energy storage, etc. Hedin et al. found that porous carbon-rich
humins with high specific surface area can be prepared from HMF
and sugars in concentrated sulfuric acid.[12] Luque et al. adopted
a solvent-free method (ball milling and thermal degradation) to
prepare nano-humins-based iron oxide composites, which could
oxidize isoeugenol to vanillin as catalyst under electromagnetic
wave heating.[13]
Today, the search for a greener and more sustainable path has
become a problem that must be addressed by humanity. Based
on this premise, the conversion of biomass to platform
compounds is a promising process that can replace traditional
fossil-based products.[1] At present, many important chemicals,
such as tetrahydrofuran, lactic acid, furfural (FAL), levulinic acid
(LA), furfuryl alcohol (FOL), etc. have been produced by catalytic
conversion of biomass-derived carbohydrates.[2] LA, a chemical
extracted from biomass, has been identified by the US
Department of Energy as one of the ten most valuable platform
chemicals,[3] and it is developed as intermediates in the
production of coatings, resins, anticancer agents, pesticides, and
as a condiment and spice in the fine chemical industry.[4] Recently,
FOL has been applied as a precursor for the production of LA or
Electromagnetic wave absorbing materials have attracted
widespread attention in civil and military applications. Carbon-
based materials are a fine electromagnetic wave absorbing
material with the advantages of light weight, large specific surface
area, good thermal conductivity, and tunable dielectric
properties.[14] And many researches were explored by adjusting
the microstructure and macroscopic morphology of carbon-based
materials.[15] Recently, carbon-rich biomass (spinach, waxberry,
loofah sponge, etc.) has also exhibited preferable
electromagnetic wave absorption performance after further
processing.[16]
[a]
M. Ma, † N. Liang, † P. Hou, P.Zhang, J. Cao, H. Liu, Prof. H. Yue,
Prof. G. Tian and Prof. S. Feng
State Key Laboratory of Inorganic Synthesis and Preparative
Chemistry
College of Chemistry, Jilin University
2699 Qian†jin Road, Changchun 130012 (P.R. China)
E-mail: tiange@jlu.edu.cn
[b]
X. Xu
College of Chemistry and Material Science, Shandong Agricultural
University
Shandong 271018, Taian (P. R. China)
Email: xingliangxu@163.com
[†]
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of
the document.
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Scheme 1. Routes to the production of PL from biomass-derived carbohydrates and upgrading of PL to other biomass-derived platform molecules.
From the above, an idea can be drawn that humins, a by-
product of biomass conversion, can be used for electromagnetic
wave absorption due to its rich carbon content. In this work, we
mainly discuss from the following two aspects: one-pot catalytic
conversion of FAL to isopropyl levulinate (PL) and carbonization
of humins, a by-product for electromagnetic wave absorption. In
the former, phosphotungstic acid (PW) as a homogeneous
catalyst enables the conversion of FAL to PL via a tandem
reaction in one pot, with the formation of a vast amount of humins
by-products. And by examining each step in the reaction, the
reason of the formation of humins as a by-product was
demonstrated. In addition, the in-situ ATR-IR was applied to
monitor the change of the C=O functional group of the reactant in
real time, which provided a basis for the proposed reaction route.
In the latter, nano-carbon particles with high specific surface area
formed by carbonization of the humins at high temperature, are
employed for electromagnetic wave absorption, and display good
absorption performance.
AL and LA) appearing in the reaction system as substrate were
completed (Table 1, entry 3 and 10-13). Compared with FAL, FOL
and FE as substrates, the yield (> 98 %) and selectivity (> 98 %)
of PL were higher, and no humins was formed with AL and LA as
substrates. And the colour of the solution after the reaction, the
filtered solution after the reaction and the filter residue was
compared (Figure 2). The results displayed that under the same
reaction conditions FAL produced the most humins, followed by
FOL/FE, and AL/LA did not produce humins. Therefore, it was
concluded that humins were polymerized from a compound with
Table 1. One-pot catalytic conversion of FAL (or the reaction
intermediates) to PL.[ a]
Sel.(%)
yield (%)
Con.
(%)
Entry
Substrate
Catalyst
PL
0
PL
0
Others[b]
1
FAL
FAL
FAL
FAL
FAL
FAL
FAL
FAL
FAL
FOL
FE
None
PW
PW
PW
PW
PW
SiW
PMo
PW
PW
PW
PW
PW
PW
PW
<1
0
2[c]
3
54
31
34
31
31
30
32
36
0
17
34
31
22
30
26
16
0
37
65
69
48
70
57
27
5
Results and Discussion
99
The conversion of FAL to PL via a tandem reaction in one pot.
4[d]
5[e]
6[f]
7
100
70
Polyoxometalates (POMs) was operated as a homogeneous
catalyst to convert FAL to isopropyl levulinate (PL) in one pot,
which is listed in Table 1. No reaction happened in the absence
of any catalyst (Table 1, entry 1). Based on the comprehensive
reaction temperature (Table 1, entry 2-4), time (Figure 1a), the
amount of PW catalyst (Table 1, entry 3 and 5-6) and the type of
polyoxometalates (Table 1, entry 3 and 7-8), the preferred
conditions for the reaction were determined to be 0.1 g PW at
160 °C for 7 hours, and a FAL conversion of 99 % and PL yield of
33 % were acquired. The high conversion and low selectivity
indicate that a large amount of by-products (humins) was
generated after the tandem reaction in one pot. So which
intermediate or substrate polymerizes to produce the humins?
It is generally acknowledged that humins are generated by
random polymerization during the acid-catalyzed hydrolysis or
alcoholysis of biomass and its platform compounds.[17] In the
catalytic system, the overall reaction route from FAL to PL is
displayed in Scheme 2.[8d, 18] In order to determine the source of
the humins, experiments using five compounds (FAL, FOL, FE,
100
83
8
43
9[g]
10
11
12
13
14[h]
15
5
100
100
100
100
96
67
59
99
99
32
11
67
59
99
99
31
11
33
41
1
AL
LA
1
FAL
D-xylose
65
------
100
[a] Reaction conditions: 1 mmol substrate, 0.1 g catalyst, 20 mL 2-PrOH,
160 °C and 7h. [b] Other yields are mainly of humins and trace amounts of
AL. [c][d] The catalyst amounts of entry 2 and 4 were 0.01 and 0.2 g,
respectively. [e][f] The reaction temperatures of entry 5 and 6 were 140
and 180 °C, respectively. [g] 5 mmol of pyridine was added additionally.
[h] See the cyclic reaction section in the Catalytic tests.
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Figure 1. Effect of different reaction temperatures on the one-pot catalytic conversion of FAL to PL. Reaction condition: 1 mmol FAL, 0.1 g catalyst, 20 mL
2-PrOH and 160 °C (a). In situ ATR-IR spectra during the one-pot catalytic conversion of FAL to PL over the PW catalyst at 160 °C. Reaction condition: 60
mmol FAL, 1 g catalyst, 150 mL 2-PrOH and 160 °C (b).
Figure 2. The colour of the solution after the reaction, the filtrate and the filter residue after the one-pot catalytic conversion of FAL to PL. Reaction
conditions: 1 mmol substrate, 0.1 g catalyst, 20 mL 2-PrOH, 160 °C and 7h.
a furan ring (FAL, FOL and FE), which could also be confirmed
from the discussion of the FT-IR spectrum in Figure S2. From it,
the absorption peaks of C = C stretching vibration on furan
(1377,1459 and 1615 cm-1), C-H stretching vibration (2968 cm-1)
and C = O stretching vibration (1719 cm-1) appear in the IR
spectrum.
As the reaction route was further explored (Scheme 2), under
the catalysis of Lewis (L) acid FAL is initially reduced to FOL with
alcohols as the hydrogen source, and then L acid or Bronsted (B)
acid catalyzed the etherification of FOL to furfuryl ester (FE). Next,
FOL and FE are converted to LA via angelica lactone (AL)
intermediate under the catalysis of B acid. Finally, LA is esterified
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