Due highly selective process with a highly isolated yield

Due
to long-term sustainability issues of fossil fuel resources it has been necessitates
for the application of renewable biomass source to the energy, chemicals and
alternative fuels.1,2  In
Indian context, as per TIFAC
(Technology Information
Forecasting & Assessment Council ) 2014 report of Government of India, almost
623.4 Million  Metric Ton per year
biomass waste is generated in which 70% contributions is from agricultural
waste such as Rice husk; Wheat and Rice straw; Sugarcane baggasse etc. In
general such type of biomass contained mainly C6 sugar and its contribution is
in the domain of 33-51% based on the biomass source.1 Thus,
converting this major compound of C6 sugar such as cellulose, glucose, fructose
to valuable chemicals is an industrially and academically attractive option.3
Cellulose and glucose can be easily converted to fructose by acid
hydrolysis and isomerization, respectively.4,5 Further efficient
conversion of fructose to desired chemicals using right choice of heterogeneous
catalyst is challenging and need more research and development activity to make
the catalytic process benign and industrially relevant. Among various reactions
of fructose conversion, efficient transformation of fructose to 5-hydroxymentyl
furfural (5-HMF) is an important reaction to explore to identify new, stable,
economical, reusable, easily available heterogeneous catalyst. This type of
catalyst offer several advantages over liquid acid catalyst like easy
separation of product, reusability of catalyst and no corrosion of equipment,
which makes them more suitable for an industrial application.6,7   As per the updated evaluation of the U.S.
Department of Energy (DOE) top 10 list of biobased chemicals, where furan
molecules such as 5-hydroxymethyl-furfural (HMF), furfural, and
2,5-furandicarboxylic acid are mentioned in the “Top 10 +4” as additions to the
original DOE list.  HMF stands out among
the platform chemicals for a number of reasons: a) It has retained all six
carbon atoms that were present in the hexoses, b) high selectivity have been
reported for its preparation, in particular from fructose, c) which compares favourably
with other platform chemicals, such as levulinic acid or bioethanol, d) number
of important C-6 compounds can be formed through HMF includes
Alkoxymethylfurfurals, 2,5 furandicarboxylic acid,5-hydroxymethylfuroic acid,
hydroxymethylfuran, 2,5-dimethylfuran, and e) the diether of HMF are furan
derivatives with a high potential in fuel or polymer applications. Some other
important non furanic compounds can also be produced from HMF, namely,
levulinic acid, adipic acid, 1,6-hexanediol, caprolactam and caprolactone etc.8
The di?culty
of achieving a highly selective process with a highly isolated yield has thus so
far resulted in a relatively high cost of HMF, restricting its potential as a
key platform chemical. The stability of 5-HMF can be improved in reaction by
using suitable extracting solvents like dimethyl sulfoxide (DMSO), methyl
isobutyl ketone (MIBK) and MIBK-water  biphasic
system. Amongst these solvents, MIBK-Water biphasic system was reported to be
the best solvent system which improves activity especially for fructose
dehydration to 5-HMF.6,7,9 Various acidic heterogeneous catalysts
such as Al, Al-Si, Zr phosphate10, niobic acid 11,
ion-exchange resins12,13 zeolites14 like Mordinite, H-?,
H-ZSM-5, H-Y are reported. Among these catalysts, zeolites seems to be the
potential option due to its thermal stability, porous structure, adjustable
acidity, commercially available and reusability associated with catalytic
performance. Based on the available reported literature, H-USY zeolite and its
modified versions having additional features of mesoporosity as a catalyst  is not explored for fructose dehydration to
5-HMF so far. H-USY zeolite is used
in petroleum processes and is a 
ultrastable form of Y zeolite and was prepared by steaming treatment of
Y zeolite.15,16   Activity performance of H-USY can be
tuned by altering  its acidity. To modify
the acidity of H-USY, it is necessary to modify the catalyst during synthesis
or by post treatment. A dealumination of zeolite, in which the Al atom is
expelled from the zeolite lattice, is one of the best post-synthesis treatments
to ulter the acidity. Dealumination by thermal or hydrothermal or chemical
treatments and acids leaching.17 The modifed H- USY zeolites, make
changes in the Si/Al ratio of framework, its structure, acidity and porosity
usually exhibit improved reactivity, selectivity and coking behaviour for a
catalytic reaction, which is of great interest to the petroleum and chemical
industry.18 It
has been suggested that the amount of extra-framework Al species  formed during the process of dealumination,
is one of the key factors that significantly influence  catalytic activity.19,20 The
acid treatment in H-USY helps in further dealumination by removing Al from
framework or extraframework and creating mesoporosity which is one of the
criteria for transformation of bulky molecules like fructose. Different acids
like oxalic and nitric acid are reported for this treatment.21  In this work H-USY was treated with
phosphoric (H3PO4) and sulfuric (H2SO4)
acid and application of these acid
treated H-USY for 5-HMF synthesis by fructose dehydration, which probably not reported so
far. 

In
the present study, H-USY zeolite was modified by treating with 10-30%
phosphoric (H3PO4) acid and sulphuric (H2SO4)
acid in aqueous medium. The prepared and well characterized catalysts were used
for its application in fructose dehydration to 5-hydroxymethyl furfural
reaction in biphasic (MIBK-Water) system. The optimization of process
parameters and catalyst reusability study was also done. 

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2.         Experimental

2.1.      Chemicals
& Reagents

H-USY
(CBV 760) was procured from Zeolyst International (USA), D-Fructose , Isobutyl
methyl ketone (99 % )  was obtained from
M/s Loba Chemie, Mumbai (India), 
Isopropyl alcohol and toluene were procured from Thomas Baker, Mumbai
(India), Ethanol (99%) was supplied by M/s E Merck, Mumbai (India),Phosphoric
acid (93%), Sulfuric acid (98%) were taken from Thomas Baker ,Mumbai (India).
HPLC grade Acetonitrile and formic acid were procured from M/s Loba Chemie,
Mumbai (India).  All analytical grade
reagents were used as such without any purification.

2.2.      Catalyst
Synthesis

 H-USY zeolite was modified by treating with
sulphuric and phosphoric acid as follows: 1g of H-USY was added to 50 ml aqueous
solution of 10 wt % phosphoric acid. Resultant mixture was aged at 100oC
with constant stirring for 2 h. After 100oC, 2h ageing, the mixture
was stirred for one more hour. Finally, mixture was filtered and then washed
with 1 L of distilled water, followed by drying (120°C) in air for 6 h and then
calcined at 500oC for 5h. The final sample was designated as 10P-Y.
Similarly, 20P-Y and 30P-Y samples were prepared using aqueous solution of 20
and 30 wt % phosphoric acid

 Similar procedure was followed to prepare
catalysts by acid treatment with different percent of sulphuric acid on H-USY
and was designated as 10, 20 and 30S-Y, respectively.

2.3       Catalyst characterization

XRD plots of synthesized catalysts were recorded on X-ray
diffractometer P Analytical PXRD system, Model X-Pert PRO-1712 using Cu K?
(?=1.5404 Å) radiation for the phase identification at a scanning rate of
0.0671°/s in the 2? range from 5 to 50°. Relative crystallinity was calculated
by considering the peak intensities of 10-30P-Y and 10-30S-Y zeolite samples as
compared to parent H-USY sample. The crystallinity of H- USY is considered as
100%. The total integrated intensities of five peaks at 2q =6.33o, 10.36o,
12.14o, 15.97o, 24.03o were considered for the
comparison.

The
% relative crystallinity = ( Ai/AR)*100                                        (1)

Where Ai : Total integrated
intensities of the five peaks of 10-30P-Y and 10-30S-Y

AR: Total integrated
intensities of the five peaks of H-USY.

 The total acidity and
acid strength associated with sites were measured by NH3 TPD using a
Micromeritics AutoChem (2910, USA) equipped with thermal conductivity detector.
For each experiment, prior to the measurements, 100 (± 2) mg
sample was dehydrated at 400 ?C in He (30 cm? min?1)
for 1 h. The temperature was then decreased to 50 ?C
and then NH3 was allowed to adsorb by exposing sample to a gas
stream containing 10% NH3 in He for 1 h. It was then flushed with He
for another 1 h. The NH3 desorption was carried out in He flow (30
cm? min?1) by increasing the temperature up to 600 ?C
with a heating rate of 10 ?C min?1.

FTIR spectra & Pyridine-IR of the samples
were scanned on a Perkin Elmer spectrum in the domain of 450-4000 cm-1.
Energy dispersive analysis X-ray (EDAX) was done for
micro structural and compositional analysis. The samples were recorded on
AMETEK (EDAX) of detector type Octane Elite Plus and detector is SIN-C2. For
analysis, the powder samples were stick on the copper grids, that grids were
subjected to analysis. The solid state 31P and 27Al MAS NMR
spectra were generated on a JEOL- 400 MHz spectrometer, operated at 9.39 tesla.
A fine powder of sample was placed in 4 mm zirconia rotor and spun at 8 KHz for
31P and 27Al.

2.4 
           Catalytic evaluation

Fructose transformation to 5-HMF over H-USY and acid modified
H-USY zeolite was evaluated in a 150 ml SS316 pressure autoclave. The
temperature was monitored with an accuracy of ± 0.5 K with PID controller. In a
standard run, fructose (1g),  catalyst
(1g)  and 50 cc of  MIBK & water mixture (MIBK:Water volume
ratio of  10:1 i.e. 45.5 cc of MIBK &
4.5 cc of water) was placed in the autoclave. The reaction was conducted in the
temperature of 100-140oC for 5h at 600 rpm. As per the open literature 11,33,34
the external diffusion does not interfere the overall rate of reaction unless
stirrer speed is very low (

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