370
Maheria et al. demonstrated a study of the effect of different protozeolites of
varied catalytic characteristics on % LA conversion into n-butyl levulinate. This
butyl ester is one of the value-added chemicals as mentioned earlier in the text and
finds its wide applications as a reaction intermediate in bio-based chemical synthesis, a plasticizing agent, a solvent, and an odorous substance. One hundred percent
selectivity and higher % LA conversion was obtained in case of H-BEA zeolite
owing to its three-dimensional structure along with its moderate acidity and medium
pore
size.
The
order
of
catalytic
activity
was
found
as
H-BEA > H-Y > H-ZSM-5 > H-MOR [183].
Subsequent research was focused on generating hierarchical zeolites (meso-HZSM-5 and meso-H-BEA) and applying them as solid acid catalysts in levulinic
acid esterification reaction to synthesize n-butyl levulinate [179, 180, 182].
Morawala et al. synthesized mesozeolite BEA using controlled desilication by solgel method with the help of rice husk, CTAB, and microporous zeolite BEA precursor. Zeolite BEA derivatives have been synthesized with rice husk and CTAB
(designated as MCRK) and with only CTAB surfactant (designated as MCCK). The
bimodal porosity of mesozeolite BEA is confirmed by XRD, BET surface area,
solid-state NMR, and thermal (TGA) analysis. Both mesozeolites were found to
exhibit higher thermally stability as compared to the parent zeolite. MCRK was
found more thermally stable as compared to MCCK and parent H-BEA, which may
be due to thicker walls (due to introduction of zeolite building units into the mesopore walls) of MCRK and MCCK. They concluded that use of rice husk has contributed toward increasing the thermal stability of the compounds. Also, upon analysis
of spent catalysts, the authors have observed enhanced ability of mesozeolite to
retain acidity after converting microporous structure of zeolite H-BEA into hierarchical structure. Further, the surface area of both mesoporous materials was found
higher as compared to parent microporous H-BEA. Both hierarchical zeolites performed better than parent microporous zeolite BEA in LA esterification to generate
n-butyl levulinate. Higher % LA conversion (95.6%) and selectivity (91%) were
observed in the case of MCRK as compared to parent H-BEA and MCCK due to
higher acidity and lower Si/Al ratio of MCRK. The authors observed the preferential order of activity as MCRK > MCCK > parent H-BEA (18) > Al-MCM-41 [182].
Further, an attempt was made to synthesize mesoporous zeolite BEA using
TTAB surfactant as structure-directing agent via desilication approach. Further,
catalysis efficiency of synthesized mesozeolite BEA (MTCK) was studied toward
synthesis of n-butyl levulinate from LA esterification. An optimization study was
undertaken using the Box-Behnken method. The material was characterized by
using usual catalyst characterization techniques. MTCK was found to exhibit
improved surface area and acidity and possess bimodal porosity. XRD and BET
surface area analysis confirmed the creation of mesopores within microporous zeolite H-BEA. The authors obtained a 99.4% LA conversion, 91.51% yield, and 99%
selectivity of n-butyl levulinate, over micromeso-MTCK catalyst under reaction
condition of 120 °C reaction temperature and 13% catalyst concentration. At optimized process parameters (by BBD), an optimum of 99.44% LA conversion was
obtained. From response surface methodology analysis, reaction time parameter is
K. C. Maheria et al.
Maheria et al. demonstrated a study of the effect of different protozeolites of
varied catalytic characteristics on % LA conversion into n-butyl levulinate. This
butyl ester is one of the value-added chemicals as mentioned earlier in the text and
finds its wide applications as a reaction intermediate in bio-based chemical synthesis, a plasticizing agent, a solvent, and an odorous substance. One hundred percent
selectivity and higher % LA conversion was obtained in case of H-BEA zeolite
owing to its three-dimensional structure along with its moderate acidity and medium
pore
size.
The
order
of
catalytic
activity
was
found
as
H-BEA > H-Y > H-ZSM-5 > H-MOR [183].
Subsequent research was focused on generating hierarchical zeolites (meso-HZSM-5 and meso-H-BEA) and applying them as solid acid catalysts in levulinic
acid esterification reaction to synthesize n-butyl levulinate [179, 180, 182].
Morawala et al. synthesized mesozeolite BEA using controlled desilication by solgel method with the help of rice husk, CTAB, and microporous zeolite BEA precursor. Zeolite BEA derivatives have been synthesized with rice husk and CTAB
(designated as MCRK) and with only CTAB surfactant (designated as MCCK). The
bimodal porosity of mesozeolite BEA is confirmed by XRD, BET surface area,
solid-state NMR, and thermal (TGA) analysis. Both mesozeolites were found to
exhibit higher thermally stability as compared to the parent zeolite. MCRK was
found more thermally stable as compared to MCCK and parent H-BEA, which may
be due to thicker walls (due to introduction of zeolite building units into the mesopore walls) of MCRK and MCCK. They concluded that use of rice husk has contributed toward increasing the thermal stability of the compounds. Also, upon analysis
of spent catalysts, the authors have observed enhanced ability of mesozeolite to
retain acidity after converting microporous structure of zeolite H-BEA into hierarchical structure. Further, the surface area of both mesoporous materials was found
higher as compared to parent microporous H-BEA. Both hierarchical zeolites performed better than parent microporous zeolite BEA in LA esterification to generate
n-butyl levulinate. Higher % LA conversion (95.6%) and selectivity (91%) were
observed in the case of MCRK as compared to parent H-BEA and MCCK due to
higher acidity and lower Si/Al ratio of MCRK. The authors observed the preferential order of activity as MCRK > MCCK > parent H-BEA (18) > Al-MCM-41 [182].
Further, an attempt was made to synthesize mesoporous zeolite BEA using
TTAB surfactant as structure-directing agent via desilication approach. Further,
catalysis efficiency of synthesized mesozeolite BEA (MTCK) was studied toward
synthesis of n-butyl levulinate from LA esterification. An optimization study was
undertaken using the Box-Behnken method. The material was characterized by
using usual catalyst characterization techniques. MTCK was found to exhibit
improved surface area and acidity and possess bimodal porosity. XRD and BET
surface area analysis confirmed the creation of mesopores within microporous zeolite H-BEA. The authors obtained a 99.4% LA conversion, 91.51% yield, and 99%
selectivity of n-butyl levulinate, over micromeso-MTCK catalyst under reaction
condition of 120 °C reaction temperature and 13% catalyst concentration. At optimized process parameters (by BBD), an optimum of 99.44% LA conversion was
obtained. From response surface methodology analysis, reaction time parameter is
K. C. Maheria et al.