451
potassium- modified heteropoly tungstate catalyst. Ethyl levulinate yield was
increased to 69% with addition of toluene as co-solvent [92].
We reported the butyl levulinate synthesis from furfuryl alcohol over Zn-modified
heteropoly tungstate supported on niobia catalysts [93]. About 94% butyl levulinate
yield was achieved with 20%Zn 1 TPA/Nb 2 O 5 catalyst. The catalyst activities
explained based on the presence of new Lewis acidic sites in heteropoly tungstate generated with the introduction of Zn ions into their secondary structure.
Partially Zn-exchanged catalyst was more effective than completely exchanged
catalyst, since it has both Bronsted and Lewis acidity. The catalyst with both
Bronsted and Lewis acidic sites is responsible for high conversion and yield. Lewis
acidic sites are useful for the etherification of furfuryl alcohol, and Bronsted acidity
was involved in ring opening to get butyl levulinate. All the reaction conditions
were optimized over the active catalyst. The product butyl levulinate yield was
dependent on the amount of active component supported on Nb 2 O 5 . Figure 16 shows
the dependence of Zn 1 TPA loading on Nb 2 O 5 . Even though the lower loading catalysts (5–15% Zn 1 TPA/Nb 2 O 5 ) show 100% furfuryl alcohol conversion, the butyl
levulinate yield was low. The intermediate ether was not fully converted to butyl
levulinate for the catalysts with low amount of Zn 1 TPA. The product yield was also
low at higher loadings of active component on support. The dark brown colour solid
was observed in the reaction mixture when high loading catalysts (25 and 30%)
were used. The high acidity of the catalyst is the reason to produce furfuryl alcohol
polymers so the butyl levulinate yield was lower than the optimum 20% Zn 1 TPA/
Nb 2 O 5 catalyst.
We reported the direct conversion of carbohydrates and their derived chemicals
to ethyl levulinate over Ti-exchanged tungstophosphoric acid catalysts [94]. A
series of Ti-exchanged TPA catalysts were prepared, characterized and evaluated
for the synthesis of alkyl levulinates. Table 8 reveals the activity of Ti 0.75 TPA catalyst for the preparation of EL from various starting materials. Ti 0.75 TPA catalyst
showed 92–98% yield of ethyl levulinate from carbohydrate-derived chemicals
such as furfuryl alcohol, 5-hydroxymethyl furfural and levulinic acid. However,
moderate yields of 63 and 21% of ethyl levulinate were achieved from fructose and
glucose, respectively. Diverse alkyl levulinates were also synthesized from furfuryl
alcohol. High EL yield of 97 and 98% was reached within 30 min when furfuryl
alcohol and levulinic acid were used as feed, respectively. During 5-HMF alcoholysis, about 92% EL yield was obtained in 360 min, whereas 21 and 63% yield of EL
was observed with glucose and fructose used as starting materials. These results
validated that the Ti 0.75 TPA was an effective catalyst for the preparation of EL from
carbohydrates (glucose, fructose) and their derived chemicals (LA, 5-HMF, FAL).
The details about the use of modified heteropoly acid catalysts towards the preparation of alkyl levulinates from variety of starting materials are shown in Table 9.
Carbohydrates to Chemicals and Fuel Additives over ModifiedPolyoxometalate Catalysts
potassium- modified heteropoly tungstate catalyst. Ethyl levulinate yield was
increased to 69% with addition of toluene as co-solvent [92].
We reported the butyl levulinate synthesis from furfuryl alcohol over Zn-modified
heteropoly tungstate supported on niobia catalysts [93]. About 94% butyl levulinate
yield was achieved with 20%Zn 1 TPA/Nb 2 O 5 catalyst. The catalyst activities
explained based on the presence of new Lewis acidic sites in heteropoly tungstate generated with the introduction of Zn ions into their secondary structure.
Partially Zn-exchanged catalyst was more effective than completely exchanged
catalyst, since it has both Bronsted and Lewis acidity. The catalyst with both
Bronsted and Lewis acidic sites is responsible for high conversion and yield. Lewis
acidic sites are useful for the etherification of furfuryl alcohol, and Bronsted acidity
was involved in ring opening to get butyl levulinate. All the reaction conditions
were optimized over the active catalyst. The product butyl levulinate yield was
dependent on the amount of active component supported on Nb 2 O 5 . Figure 16 shows
the dependence of Zn 1 TPA loading on Nb 2 O 5 . Even though the lower loading catalysts (5–15% Zn 1 TPA/Nb 2 O 5 ) show 100% furfuryl alcohol conversion, the butyl
levulinate yield was low. The intermediate ether was not fully converted to butyl
levulinate for the catalysts with low amount of Zn 1 TPA. The product yield was also
low at higher loadings of active component on support. The dark brown colour solid
was observed in the reaction mixture when high loading catalysts (25 and 30%)
were used. The high acidity of the catalyst is the reason to produce furfuryl alcohol
polymers so the butyl levulinate yield was lower than the optimum 20% Zn 1 TPA/
Nb 2 O 5 catalyst.
We reported the direct conversion of carbohydrates and their derived chemicals
to ethyl levulinate over Ti-exchanged tungstophosphoric acid catalysts [94]. A
series of Ti-exchanged TPA catalysts were prepared, characterized and evaluated
for the synthesis of alkyl levulinates. Table 8 reveals the activity of Ti 0.75 TPA catalyst for the preparation of EL from various starting materials. Ti 0.75 TPA catalyst
showed 92–98% yield of ethyl levulinate from carbohydrate-derived chemicals
such as furfuryl alcohol, 5-hydroxymethyl furfural and levulinic acid. However,
moderate yields of 63 and 21% of ethyl levulinate were achieved from fructose and
glucose, respectively. Diverse alkyl levulinates were also synthesized from furfuryl
alcohol. High EL yield of 97 and 98% was reached within 30 min when furfuryl
alcohol and levulinic acid were used as feed, respectively. During 5-HMF alcoholysis, about 92% EL yield was obtained in 360 min, whereas 21 and 63% yield of EL
was observed with glucose and fructose used as starting materials. These results
validated that the Ti 0.75 TPA was an effective catalyst for the preparation of EL from
carbohydrates (glucose, fructose) and their derived chemicals (LA, 5-HMF, FAL).
The details about the use of modified heteropoly acid catalysts towards the preparation of alkyl levulinates from variety of starting materials are shown in Table 9.
Carbohydrates to Chemicals and Fuel Additives over ModifiedPolyoxometalate Catalysts