Optimum dehydration at reaction parameters: Fructose 1g, Temperature= 120?

 Optimum catalyst 10P-Y
was further investigated for its activity correlation in presence of polar and non
polar organic solvent. Fig. 7, represented the 5-HMF and furfural yield with
respect to polar and organic solvent in biphasic system with water in a ratio
of 10:1 v/v, keeping other operating conditions identical. 

Figure 7: Effect of
different solvents on fructose dehydration at reaction
conditions:Temperature:120?C,
Time: 5h,  Fructose:Catalyst ratio in g
1:1,  MIBK: Water (10:1 v/v)

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In this work, polar (n-ethanol and iso-propanol) and non
polar (toulene and MIBK) organic solvents were evaluated for its activity
performance in biphasic system with water at constant solvent:water (v/v) ratio
of 10:1. As expected, polar solvents are having less extracting capacity of
5-HMF from aqueous phase than organic solvent. Amongst polar solvent, iso-propanol
helps to extract more HMF than ethanol. It is reported that, fructose is less soluble in ethanol
than in C3-4 alcohols, which will decreases the fructose conversion
as well as 5-HMF productivity in case of ethanol than iso-propanol. It is also
supported by the observed fact that distribution coefficient (K=HMFsolvent
/ HMFwater) of HMF in ethanol is 10 whereas in iso-propanol is 14
.40,41

 Whereas, in case of non polar organic solvent the extracting
capacity is higher due to its less solubility with water than polar solvent.
Amongst non polar solvent, MIBK stands best compared to toulene, which gave
5-HMF yield of 65% and furfural yield of 1, it is not practically viable to make the
process economical and relevance to industry and academia. The 5-HMF slelectivity was found
to be 92% at catalyst loading of 0.7g as against 87% with 1g. Since, per batch
5-HMF productivity is higher in case of 1g catalyst loading, which is
industrially relevance and 5-HMF (B.P. 114-116oC) +furfural (B.P.
161oC) mixture can be easily separable by just simple distillation.
Hence, further experimentation was carried out using 1g catalyst loading.  Yet another important parameter for any
chemical reaction is to optimize reaction temperature.

3.2.2.3  Effect of temperature

The optimization of process parameter was further extended to
find out the optimum reaction temperature for 10P-Y to get maximum 5-HMF from
fructose dehydration in MIBK-Water biphasic system. The activity values are
plotted as Fig. 9

Figure 9: Reaction temperature effect on fructose
transformation at reaction parameters: Fructose
to Catalyst ratio 1, Time: 5h, MIBK: Water (10:1v/v)

 

HMF yield has increased with variation in reaction
temperature from 100 to 120oC. At 100oC, the 5-HMF yield
is very low (4%) and it has increased exponentially at 120oC to 65%.
This is because at 100oC, fructose to MIBK solubility is low, which is higher at 120oC and makes L-L
homogeneous phase, which increases the reaction rate as well as 5-HMF
extraction by MIBK in organic phase. Acid sites of zeolites strongly interact
with ketone group of adsorbed MIBK by formation of hydrogen bond. Molecules of
MIBK inside the pores of catalyst reduces oligomerization of 5-HMF by
displacement of 5-HMF from the acid sites into the reaction medium and with
dilution of fructose and HMF inside of pores by organic solvent molecules.
Absorption of HMF by MIBK prevents the return of HMF molecules in the pores of
zeolite. Effective interaction between ketone group of MIBK and acid site of
zeolites and extraction of 5-HMF from pores of zeolite happened at reaction
temperature (120oC and above).6

Above 120oC; the 5-HMF was observed to be
decreased as there is further decomposition of 5-HMF to humins and conversion
to furfural by loss of formaldehyde. In view of this, 120oC, was
observed to be the optimum reaction temperature for this reaction using 10P-Y
catalyst. The optimum reaction time is another important parameter to study for
attending maximum 5-HMF at lower reaction time.

3.2.2.4  Impact of Reaction Time

Fig.10 represents the effect of reaction time on 10P-Y
catalytic performance. As can be seen, as the reaction time (h) increases the
5-HMF and furfural formation increases. After 5h reaction time, the 5-HMF yield
is almost identical at 65%, where as furfural is still increasing. This gives
an impression that, after 5h of reaction time the 5-HMF formation may be
increases but its extraction in MIBK phase is saturated which limits its
further stability. Therefore this excess formation of 5-HMF after 5h reaction
time losses its formaldehyde due to acidic catalyst and converted into
furfural, which has reflected in increase of furfural formation at constant 5-HMF

Figure
10: Variation of reaction time on 5-HMF and Furfural formation at identical conditions:
Fructose: Catalyst ratio in g 1:1, Time:
5h, MIBK: Water (10:1v/v)

 

3.2.2.5
Catalyst reusability

The
reusability of 10P-Y
as shown in fig. 10 was reused for three cycles at optimized reaction
parameters: 120? C , fructose / catalyst ratio of 1,
volume ratio of MIBK: Water (10:1) at 5h reaction time.  After 5h, the catalyst was filtered and used
as such. The yield of 5-HMF was evaluated to be stable for three cycles. After
3 cycles yield of 5- HMF decreases from 65 to 55% and yield of furfural was
increases from 8 to 10 % as shown in Fig. 11. After four cycles, the used catalyst (brownish colour)
was further regenerated by re-calcination at 500oC for 5h. The
regenerated catalyst (looks like fresh white colour) was again re-evaluated for
the reaction at optimized reaction conditions. The regenerated catalyst regain
it activity as that of Fresh. Thus it can be concluded that the 10P-Y catalyst can be use
again without any activity
loss by regeneration after three reaction cycles.

Figure
11: Catalyst reusability study at optimal reaction conditions
Fructose:Catalyst ratio 1:1,Time:
5h, volume ratio of MIBK: Water (10:1),Temperature: 120?C

4. CONCLUSION

Fructose
dehydration to 5-HMF is a renewable reaction to synthesized important platform
chemical, having wide applications in petroleum and chemical sectors. H-USY a
thermally stable and commercially available zeolite was further modified by
post treatment modification by acid treatment. In the present study, H3PO4
and H2SO4 was used for treatment of parent USY. The
application of this acid treated H-USY probably is not reported so far. This
modified acid treated H-USY was thoroughly characterized by various
characterization techniques such as XRD; FTIR; Pyridine-FTIR; NH3-TPD; EDAX;
NMR etc to establish the physico-chemical properties of these newly prepared
catalysts. 10% H3PO4 treated H-USY (10P-Y) catalyst was
emerged as the best catalyst with 5-HMF yield and selectivity of 65% and 89%
selectivity at milder operating parameters of 120oC; 5h in MIBK:
water biphasic system.  Optimum combination of moderate acidity (both weak as
well as strong- 0.27mmol/g), moderate dealumination (58%) of Al from
extraframework as well as from framework of H-USY; formation of new Al-O-P bond
between framework Al, existence of elemental monomeric phosphorous (0.0075%),
availability of Bronsted and Lewis acidity and creation of mesopores are
responsible for 10P-Y catalyst to show best activity amongst other studied
catalysts.

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