Conversion of glucose into platform chemicals using aluminophosphates (SAPO-5 and MeAPO-5) in [BMIM]Cl ionic liquid

Article abstract of DOI:10.4314/bcse.v28i1.6

The conversion of glucose into platform chemicals such as 5-hydroxymethylfurfural, levulinic acid and formic acid has been investigated using two aluminophosphate based zeotypes (SAPO-5 and MeAPO-5) catalysts in 1-butyl-3-methylimidazolium chloride [BMIM]Cl ionic liquid as a reaction medium. The silico aluminophosphates (SAPO-5) and metal aluminophosphates (MeAPO-5) were designed and chosen for their tunable amount and strength of acid sites. The dehydration of glucose using each catalyst gave more than 90% glucose conversion. Among all the catalysts tested, the most hydrophilic SAPO-5 (1.5T) results in a better 5-HMF yield of 8% at 100 deg;C and 6 h reaction time. Contrary to this, the more hydrophobic SAPO-5 gives higher yield of levulinic acid and formic acid and no 5-HMF yield at this particular reaction time. In general, despite the higher glucose conversion attained by these aluminophosphate based catalysts, the lower yield obtained by these materials can be attributed to the type of acidity and the incompatibility of the pore diameter of the AFI channels of the catalysts and the desired products.

Full text of DOI:10.4314/bcse.v28i1.6

Bull. Chem. Soc. Ethiop. 2014, 28(1), 45-52.
Printed in Ethiopia
DOI: http://dx.doi.org/10.4314/bcse.v28i1.6
ISSN 1011-3924
 2014 Chemical Society of Ethiopia
CONVERSION OF GLUCOSE INTO PLATFORM CHEMICALS USING
ALUMINOPHOSPHATES (SAPO-5 and MeAPO-5) IN [BMIM]Cl IONIC LIQUID
Lijalem Ayele1, Gemechu Dadi1, Wondimagenge Mamo1, Yonas Chebude1 and Isabel Diaz1,2*
1ChemistryDepartment, Addis Ababa University, P. O. Box 1176, Addis Ababa, Ethiopia
2Instituto de Catálisis y Petroleoquímica, CSIC, c/Marie Curie 2, 28049 Madrid, Spain
(Received June 12, 2013; revised September 25, 2013)
ABSTRACT. The conversion of glucose into platform chemicals such as 5-hydroxymethylfurfural, levulinic
acid and formic acid has been investigated using two aluminophosphate based zeotypes (SAPO-5 and MeAPO-5)
catalysts in 1-butyl-3-methylimidazolium chloride [BMIM]Cl ionic liquid as a reaction medium. The silico
aluminophosphates (SAPO-5) and metal aluminophosphates (MeAPO-5) were designed and chosen for their
tunable amount and strength of acid sites. The dehydration of glucose using each catalyst gave more than 90%
glucose conversion. Among all the catalysts tested, the most hydrophilic SAPO-5 (1.5T) results in a better 5-HMF
yield of 8% at 100 °C and 6 h reaction time. Contrary to this, the more hydrophobic SAPO-5 gives higher yield of
levulinic acid and formic acid and no 5-HMF yield at this particular reaction time. In general, despite the higher
glucose conversion attained by these aluminophosphate based catalysts, the lower yield obtained by these
materials can be attributed to the type of acidity and the incompatibility of the pore diameter of the AFI channels
of the catalysts and the desired products.
KEY WORDS: Biomass, 5-Hydroxymethylfurfural, Levulinic acid, Formic acid, Ionic liquids,
Aluminophosphate
INTRODUCTION
The world’s economic and geopolitical factors together with an increase in demand for
energy, fuels and materials by society lead scientists to investigate new and renewable
energy resources [1]. Renewable and vastly abundant biomass resources have the potential to
serve as a sustainable supply of fuels and chemical intermediates by developing cost effective
processing methods to transform highly functionalized carbohydrate moieties into value added
chemicals. Among other primary renewable building blocks, 5-hydroxymethylfurfural (5-HMF)
is considered an important intermediate due to its rich chemistry and potential availability from
carbohydrates such as fructose, glucose, sucrose, cellulose and inulin. 5-HMF is very useful not
only as intermediate for the production of the biofuel 2,5-dimethylfuran (DMF) and other
molecules, but also for important molecules such as levulinic acid, 2,5-furandicarboxylic acid
(FDA), 2,5-diformylfuran (DFF), dihydroxymethylfuran and 5-hydroxy-4-keto-2-pentenoic acid
[2, 3].
Recently, considerable improvement has been reported for the conversion of fructose to 5-
HMF, whereas the transformation of glucose, sucrose and cellulose remains difficult. More
efficient reaction conditions (lower temperature, and higher carbohydrate initial concentration),
higher conversions and 5-HMF selectivity are desirable, and these processes have to be
environmentally friendly [4-8]. Recent work on glucose dehydration to platform chemicals such
as 5-hydroxymethylfurfural over phosphate of aluminum, titanium, zirconium and niobium
catalysts showed the synergistic effect of Brønsted and Lewis acids, which result in 5-HMF
selectivity range of 30-60% [9]. In this direction, apart from several attempts in using zeolites
[10], no other microporous solids have been tested. Zeotypes are aluminophosphate based
crystalline microporous solids whose acidity can be controlled from the synthesis conditions.
Silicoaluminophosphates (SAPOs) and aluminophosphates (MeAPOs) can be designed by
__________
*Corresponding author. E-mail: idiaz@icp.csic.es

46
Lijalem Ayele et al.
different mechanisms of silicon and metal insertion to obtain tuned acidity including both Lewis
and Brønsted acid sites [11, 12]. Among the zeolitic materials reportred in the literature,
mordenite zeolites with moderate acidity have shown promising fructose conversion with
maximum selectivity to 5-HMF (90%) [13]. On the other hand, Chloride based IL like
[BMIM]Cl have an exceptionally high capacity for dissolving carbohydrate since the extensive
hydrogen bonding network that constituent the structure of the solid carbohydrate is disrupted. It
can also open up the possibility of ‘one-pot’ reactions directly from crude biomass [14, 15].
Therefore, the present study explores the catalytic activity of tuned SAPO-5 and MeAPO-5
molecular sieves with AlPO-5 (AFI) structure having similar pore size and channels structure as
mordenite, in the presence of ionic liquid [BMIM]Cl instead of conventional solvents like water
and DMSO because of its unique dissolving properties for crude biomass such as glucose.
EXPERIMENTAL
Preparation of ionic liquid ([BMIM]Cl)
The [BMIM]Cl ionic liquid used in this study was synthesized in our laboratory (Scheme 1) and
characterized using NMR spectroscopy. 1-Methylimidazole (61.29 mL) and excess 1-
chlorobutane (85.42 mL) were placed in a 250 mL round bottom flask, equipped with a
thermometer, magnetic stirrer bar, condenser and drying tube. The flask was placed in an oil
o
bath and its solution heated under reflux at 70 C for 48 h and the product was washed with
1,1,1-trichloromethane three times to purify the product from unreacted methyl imidazole.
Finally, the washing solvent was removed by evaporation under reduced pressure using rotary
evaporator.
1-Methylimidazole
1-Chlorobutane
1-Butyl-3-methylimidazolium chloride
Scheme 1. Synthesis of [BMIM]Cl from 1-methylimidazole and 1-chlorobutane.
Synthesis and activation of SAPO-5 and MeAPO-5 catalysts
SAPO-5 and MeAPO-5 samples were kindly donated by the authors [11, 12] from the Institute
of Catalysis and Petroleochemistry, CSIC (Madrid, Spain). Each microporous material contains
water molecules adsorbed on the surface, and is prepared in the presence of structure directing
agent (SDA). This structure directing agent has to be removed to provide the material with the
catalytic activity. The calcination of SAPO-5 and MeAPO-5 samples was carried out by putting
the samples in a time and temperature controlled furnace for six hours in the temperature range
o
of 550 to 600 C to remove the structure directing agents. Complete removal of the SDA was
confirmed by thermogravimetric analysis (TGA).
Experimental methods for conversion of glucose
In a typical run for the conversion of glucose into platform chemicals in the IL, a 250 mL two-
necked round bottom flask was equipped with water cooled condenser, and magnetic stirrer
under inert gas atmosphere. After an appropriate amount of glucose (5 g) was dissolved in
[BMIM]Cl (16 g) for 15 min in the reactor, 0.5 g of the catalyst was added, and the reaction was
Bull. Chem. Soc. Ethiop. 2014, 28(1)

Conversion of glucose into platform chemicals using aluminophosphates in [BMIM]Cl
47
o
continued by heating the flask at a constant temperature of 100 C. Samples were taken at 30
min, 1, 3, 6, and 12 h, and extracted three times with 5 mL ethyl acetate and diethyl ether. The
extracting solvent was removed using rotary evaporator and the product was collected, and then
dissolved in chloroform and kept in refrigerator for analysis.
Analysis of ionic liquid, glucose, products and its residues
The characterization of glucose, the synthesized ionic liquid ([BMIM]Cl), products and its
1
residues were performed with NMR (Bruker 400 MHz) spectroscopy. The H and 13C NMR
spectra of the synthesized [BMIM]Cl, and d-glucose were recorded in CDCl3 and D2O,
respectively.
1
The H and 13C NMR spectra of 5-HMF and its residues were also recorded in CDCl3 as
solvent. The amount (mol %) of 5-HMF obtained from the reaction mixture was determined
using mesitylene (1,3,5 trimethyl benzene) as an internal standard. Glucose conversion for each
reaction interval was determined using the 1H NMR of pure glucose as a reference. The yield of
5-HMF (mol %) and glucose conversion were calculated based on the mole of the glucose
loaded into the reaction mixture using the following formula.
Integralarea of 5 - HMF
Integralarea of std
Proton of std
(I) Mole of 5- HMF =
x
x molof std
Proton of 5 - HMF
Mole of 5- HMF obtained
Moleof glucose loaded
(II) 5- HMFyield=
x100 %
Mole of unreacted glucose
Mole of loaded glucose
(III) % Conversion= (1−
) x100 %
RESULTS AND DISCUSSION
5-Hydromethylfurfural (5-HMF), levulinic acid (LA), and formic acid (FA) have been produced
from carbohydrates like glucose and fructose under various conditions catalyzed by mineral
acids, organic acids, strong acidic resins and zeolite in different solvents, including water,
organic solvents, organic/water mixtures, and ionic liquids. In this work, we have used different
aluminophosphates (SAPO-5 and MeAPO-5) as catalysts in 1-butyl-3-methylimidazolium
chloride [BMIM]Cl ionic liquid as a reaction medium (Scheme 2).
OH
H
OH
COOH
H3C
H
O
HO
HO
O
O
OH
MeAPO-5, 100 0C
O
Levulinic acid (LA)
H
OH
+
(Me=Co, Sn, Mg, V)
[BMIM]Cl
H
H
HCOOH
Formic acid (FA)
Glucose
5-HMF
Scheme 2. Dehydration of glucose to 5-HMF, levulinic acid (LA) and, formic acid (FA) [3].
The catalysts with the structure directing agent employed are listed in Table 1. After
calcination of all the materials, they were dried overnight at 100 oC to remove water molecules.
Bull. Chem. Soc. Ethiop. 2014, 28(1)

48
Lijalem Ayele et al.
The reaction setup included an initial contact time (15 min) between the glucose and ionic
liquid in order to allow proper solution and any possible catalytic effect of the ionic liquid. Prior
studies in our laboratory have shown no conversion at all of the glucose in the presence of ionic
liquid at 100 oC (blank). After this initial contact time, the catalyst was added under continuous
stirring and under nitrogen flow. The evolution of the catalytic reaction was followed by taking
samples at 30 min, 1, 3, 6, and 12 h.
Table 1. Calcination data of SAPO-5, ALPO-5 and MeAPO-5 catalysts.
Sample
SDA
TEA
Time (h)
T (oC)
550
600
600
600
600
600
600
600
550
550
550
550
550
550
Weight loss TGA (%)
SAPO-5 1.5T
SAPO-5 1.5B
SAPO-5 0.5T,1B
SAPO-5 1T,0.5B
SAPO-5 0.75T,0.75B
SAPO-5 mFBP
SAPO-5 MCHA
ALPO-5
6
6
10
15.7
12
BP
TEA:BP
TEA:BP
TEA:BP
FBP
12
6
12
7
11.5
15.3
13.5
13.6
11
6
MCHA
MCHA
TPA
6
6
CoAPO-5*
18
6
CoAPO-5
MCHA
MCHA
MCHA
MCHA
MCHA
-
MgAPO-5
12
6
14
MnAPO-5
13
SnAPO-5
6
14
VAPO-5
6
25
C
H
3
N
CH3
N
N
N
C
H
3
C
H 3
F
Triethylamine
(TEA)
Benzylpyrro
lidine (BP)
Meta-fluoro-Benzyl
pyrrolidine (mFBP)
N-methyl-dicyclo
hexylamine (MCHA)
For initial comparison with previous experiments undertaken with commercial zeolites, the
sample taken at 3 h was first analyzed by NMR. Table 2 shows the results obtained at 3 h
reaction time for the SAPO-5 and MeAPO-5 catalyst prepared with TEA, BP and different
ratios of the mixtures of the two templates.
1
The 3 h reaction product of H NMR analysis results in Table 2 show that all catalysts
converted glucose more than 90% at this specific reaction time, but the corresponding yield is
rather low. Despite this low formation of 5-HMF, there are differences in the catalysts
depending on the synthesis method that are to be remarked. The highest yield, 0.63%, is
obtained for SAPO-5 catalyst with triethylamine (1.5T) as a template. The 1H NMR spectrum of
1.5T catalyzed reaction (Figure 1) shows the major peaks of the 5-HMF δ 9.87 (s, 1H), 7.106 (d,
1H), 6.79 (d, 1H), 4.93 (s, 2H) and 3.373 (br, 1H) although the peaks are very weak compared
to the peaks of the IL which could not be purified from our product.
This sample is reported to contain higher number of Brønsted acid sites but weaker and
more hydrophilic [11]. This mild acidity could be responsible for a better performance of this
catalyst. On the other hand, SAPO-5 1.5B sample with less but strong Brønsted acid site
brought very small 5-HMF yield at this reaction time. Although, SAPO-5 catalyst with equi-
molar composition of templates (0.75T, 0.75B) showed the maximum glucose conversion
(99.25%), its yield was the least compared to the others at this specific reaction time.
Bull. Chem. Soc. Ethiop. 2014, 28(1)

Conversion of glucose into platform chemicals using aluminophosphates in [BMIM]Cl
49
Table 2. Conversion of glucose into 5-HMF, levulinic (LA) and formic (FA) in [BMIM]Cl at 3 h.
Catalyst
Conversion (%)
5-HMF yield (%)
Other products
LA. FA
SAPO-5 1.5T
SAPO-5 1.5B
SAPO-5 1B, 0.5T
SAPO-5 1T, 0.5B
SAPO-5 0.75B, 0.75T
SAPO-5 mFBP
SAPO-5 MCHA
AlPO-5
95.8
94.9
98.0
96.9
99.2
99.4
93.2
-
0.63
0.15
0.15
0.16
0.13
1.99
1.03
-
LA, FA
LA, FA
LA, FA
LA, FA
CoAPO-5*
96
-
CoAPO-5
96
0.12
-
MgAPO-5
95
MnAPO-5
96
-
SnAPO-5
96
0.1
-
VAPO-5
-
Reaction conditions: 16 g ionic liquid, 5 g glucose, 0.5 g catalyst, 100 oC, 3 h.
Figure 1. 1H NMR spectra of 5-HMF produced by SAPO-5 1.5T at 3 h reaction time.
In the analysis of the 6h reaction product (Table 3) the maximum 5-HMF yield (7.96%) was
obtained by the SAPO-5 1.5T catalyst. On the other hand, SAPO-5 1.5B showed the maximum
glucose conversion (99.9 %), but gave no 5-HMF yield at this specific reaction time. Instead,
peaks of other products, levulinic and formic acid, showed dominance. This could be related to
the strong Brønsted acid sites of the catalyst as a result of its hydrophobicity that brings the
further conversion of glucose and 5-HMF to LA and FA.
Table 3. SAPO-5 and MeAPO-5 catalyzed dehydration of glucose in [BMIM]Cl.
Types of catalyst
SAPO 1.5T
SAPO 1.5B
CoAPO-5*
CoAPO-5
Glucose conversion (%)
5-HMF yield (%)
Other products
LA, FA
99.8
99.9
95
7.96
0
LA, FA
0
LA, FA
95
0.46
0.24
LA, FA
SnAPO-5
98
LA, FA
Reaction conditions: 16 g ionic liquid, 5 g glucose, 0.5 g catalyst, 100 oC, 6 h.
Bull. Chem. Soc. Ethiop. 2014, 28(1)

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Lijalem Ayele et al.
100
100
98
96
94
92
90
88
86
84
82
80
A
98
96
94
92
90
88
86
84
82
80
B
200
400
600
800
200
400
600
800
Temperature (ºC)
Temperature (ºC)
100
100
C
98
96
94
92
90
88
86
84
82
80
D
98
96
94
92
90
88
86
84
82
80
200
400
Temperature °C
600
800
200
400
Temperature °C
600
800
Figure 2. Thermogravimetric analysis of the recovered catalysts SAPO-5 1.5T (A), SAPO-5
1.5B (B), CoAPO-5 (C) and CoAPO-5*(D). Dotted lines correspond to calcined
samples, whereas solid lines are the recovered ones.
The table also indicated that, among the MeAPO-5 catalysts, CoAPO-5 catalyst (synthesized
with MCHA as SDA) gave better yield of 5-HMF compared to other MeAPO-5 catalysts. On the
contrary, CoAPO-5* (synthesized with TPA as SDA) gave no 5-HMF. The difference in their
catalytic activities might be attributed to the difference in their structure directing agent and
therefore, in the crystal size and mesoporosity generated therein. Moreover, SnAPO-5 gave
clearly observable 1H NMR spectra of the product at 6 h reaction time, even though the amount
of 5-HMF obtained remains very small. This indicates that SnAPO-5 is a promising catalyst for
the clean conversion of glucose to 5-HMF, in the same trend observed for Sn-Beta zeolite [10].
Although, among these platform chemicals high attention was given to the production of 5-
HMF which could serve as a sustainable source of liquid fuels and chemicals, none of the
explored catalysts improved the yield to 5-HMF neither by increasing the reaction temperature
or the reaction time. Thus the explanation to this low yields together with very high conversions
and short reactions times must be related to the microporous structure of the zeotypes as well as
the type of acidity. The unidimensional structure of the AFI type (SAPO-5 and MeAPO-5)
catalysts and their small pore size (7.3Å) [16] compared to the starting material glucose (8.6 Å)
and the product, 5-hydroxymethylfurfural (9.3 Å) [17] itself, seems to be hindering the
accessibility of glucose to the catalytic sites for its partial dehydration to 5-HMF and the rapid
diffusion of 5-HMF once formed inside the channels of the catalysts. Moreover, the ionic liquid
used here as a solvent ([BMIM]Cl) is polar, and might compete for substrate (glucose) with the
catalysts. This can reduce the free movement of glucose on the surface of the catalyst. The
solvent also interfered with the extraction of 5-HMF from the reaction mixture, due to the
polarity nature of 5-HMF. In an attempt to close the mass balance, we recovered the catalysts
Bull. Chem. Soc. Ethiop. 2014, 28(1)

Conversion of glucose into platform chemicals using aluminophosphates in [BMIM]Cl
51
after the first cycle of reaction and among the recycled catalysts, those showing some
tendencies, SAPO 1.5T, SAPO 1.5B, CoAPO-5 and CoAPO-5* were selected for
thermogravimetric analysis. Figure 2 shows the thermogravimetric curves for both the calcined
and recycled catalysts.
The TGA of the four calcined catalyst showed only one sharp weight loss below 100 oC that
is attributed to the removal of the physisorbed water molecules. Moreover, the TGA of the
o
calcined sample showed no weight loss above 100 C indicating that the calcination of the
catalyst was completed under the temperature employed, and there was no organic templates
remaining prior to the catalytic reaction. On the other hand, all the recovered catalysts showed
other important weight losses, besides to weight loss due to water molecules. The weight losses
o
observed in the recovered catalyst above 100 C might be due to the decomposition of some
organic molecules stacked in the pore of the catalysts. These organic molecules might be the
ionic liquids, or products of glucose dehydration such as 5-HMF, levulinic acid, or other
reaction intermediates and condensation products.
Table 4 summarizes the total weight losses of the recovered catalysts, which interestingly
are very similar to those of the initial as made samples, indicating that the entire micro pore
volume is filled by organic molecules. However, further studies will be needed to investigate the
reaction mechanism leading to 5-HMF, LA, FA and/or ionic liquids being stacked in the pores
of the catalyst.
Table 4. The recovered catalyst and the total weight losses.
The type of catalyst
SAPO 1.5T (A)
SAPO 1.5B (B)
CoAPO-5 (C)
Total weight loss (%)
14
17
19
17
CoAPO-5* (D)
The surface properties and type of acidity of the catalyst also limit the yield of 5-HMF
obtained compared to LA and FA. For example from Table 3 it is possible to see that 1.5B
resulted no 5-HMF at 6 h reaction time rather it gave LA and FA that can be remarked to the
strong Brønsted acid sites of the catalyst that brings the further conversion of glucose and 5-
HMF to LA and FA.
CONCLUSION
In this work, the efficiency of different zeotypes (SAPO-5 and MeAPO-5) catalysts in
converting glucose into 5-hydroxymethylfurfural and other bulk chemicals levulinic acid and
formic acid is investigated. The differences in efficiency of these materials are related to the
difference in their synthesis method which results in difference in the acidity and surface
properties of the catalysts. Glucose conversion of greater than 90% was obtained with all the
catalyst. The high glucose conversion with each catalyst indicates that, even the amount of 5-
HMF obtained is small, the catalysts interacts with glucose molecules and led to the formation
of certain reaction intermediates. The presence of organic molecules was observed from the
TGA of the recovered catalyst indicates that diffusion of product is limiting the yield and
selectivity values.
ACKNOWLEDGEMENTS
Dr. Luis Gomez-Hortigüela and Dr. Manuel Sanchez-Sanchez from the Instituto de Catalisis y
Petroleoquimica (CSIC) are deeply acknowledged for the donation of the catalysts. Isabel
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52
Lijalem Ayele et al.
Pacheco, from the same Institute is also acknowledged for running the TGA. The authors also
thank the Spanish Research Council (CSIC) for funds through the programme CSIC for
development, project number i-COOP014. The Chemistry Department, Addis Ababa University
is also acknowledged for financial support.
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