371
found as the most influential parameter in the esterification of LA with n-butanol
over MTCK catalyst. The catalyst reusability study was performed up to four catalytic runs, and the catalyst was found reusable without any significant loss of its
activity. The authors claimed that the green protocol developed for LA esterification
to synthesize n-butyl levulinate can also be further explored in green conversion of
other biomass-derived scaffolds into other value-added chemicals [180].
Many other researchers are working on esterification of levulinic acid with various alcohols to synthesize alkyl levulinates. Several reports exist on use of various
zeolite-based catalysts for alkyl levulinate synthesis. Some examples of use of hierarchical zeolites BEA with a secondary porosity were reported [159] and Nandiwale
et al. [157]-synthesized ZSM-5 mesozeolites through a post-synthetic extraction of
framework silicon with NaOH. Newly introduced mesoporosity was found to contribute in enhancing the catalytic activity of these materials in the esterification of
levulinic acid with ethanol. Hierarchical ZSM-5 zeolite obtained by desilication has
also been used as support to incorporate a second acid functionality, like dodecatungstophosphoric acid [184]. The study revealed that modified desilicated
H-ZSM-5 gives higher yield as compared to the parent H-ZSM-5 zeolite, due to the
increase of higher surface area after desilication. Modification through desilication
involves the extraction of silicon selectively, thus enhancing the surface area, generating mesoporosity, and increasing the mass transfer at the catalytic active sites
[154, 157, 184].
8 Concluding Remarks and Outlook
LA provides remarkable potential for the development of several linear as well as
heterocyclic systems and an economical alternative to the carbon-derived fossil
fuels for designing novel derivatives. Researches in the field promise a larger objective of conversion of biological residues and wastes into sophisticated synthesized
valuable chemicals. LA, however, having a potential for dozens of other molecules,
has had the authors inclined toward the class of molecules—levulinate esters—
which are being used in numerous industries in today’s time and promise of greater
utilization in several other undiscovered applications. The conversion is an esterification reaction with alcohol molecules, requiring the presence of an acid catalyst.
Catalyzing the above-said reaction has seen a groundbreaking research with scientists bringing out several moieties for undergoing the strenuous transformation
with an optimum yield. Research has yielded featured materials like MOFs, zirconia, heteropolyacids, zeolites, and even carbonaceous and supported catalytic entities for the aforementioned purpose [93, 180, 182, 183, 185, 186]. Special focus has
been on zeolites, which possess sized pores which can be engineered using processes like dealumination, desilication, as well as the merging of two or more zeolite molecules with a high yield and affinity toward the reactant molecules.
The monitoring of the reaction however becomes a bit difficult and hard to handle, requiring the confirmation of the same using several spectroscopic techniques,
Solid Acid-Catalyzed Esterification of Levulinic Acid for Production of Value-Added…
found as the most influential parameter in the esterification of LA with n-butanol
over MTCK catalyst. The catalyst reusability study was performed up to four catalytic runs, and the catalyst was found reusable without any significant loss of its
activity. The authors claimed that the green protocol developed for LA esterification
to synthesize n-butyl levulinate can also be further explored in green conversion of
other biomass-derived scaffolds into other value-added chemicals [180].
Many other researchers are working on esterification of levulinic acid with various alcohols to synthesize alkyl levulinates. Several reports exist on use of various
zeolite-based catalysts for alkyl levulinate synthesis. Some examples of use of hierarchical zeolites BEA with a secondary porosity were reported [159] and Nandiwale
et al. [157]-synthesized ZSM-5 mesozeolites through a post-synthetic extraction of
framework silicon with NaOH. Newly introduced mesoporosity was found to contribute in enhancing the catalytic activity of these materials in the esterification of
levulinic acid with ethanol. Hierarchical ZSM-5 zeolite obtained by desilication has
also been used as support to incorporate a second acid functionality, like dodecatungstophosphoric acid [184]. The study revealed that modified desilicated
H-ZSM-5 gives higher yield as compared to the parent H-ZSM-5 zeolite, due to the
increase of higher surface area after desilication. Modification through desilication
involves the extraction of silicon selectively, thus enhancing the surface area, generating mesoporosity, and increasing the mass transfer at the catalytic active sites
[154, 157, 184].
8 Concluding Remarks and Outlook
LA provides remarkable potential for the development of several linear as well as
heterocyclic systems and an economical alternative to the carbon-derived fossil
fuels for designing novel derivatives. Researches in the field promise a larger objective of conversion of biological residues and wastes into sophisticated synthesized
valuable chemicals. LA, however, having a potential for dozens of other molecules,
has had the authors inclined toward the class of molecules—levulinate esters—
which are being used in numerous industries in today’s time and promise of greater
utilization in several other undiscovered applications. The conversion is an esterification reaction with alcohol molecules, requiring the presence of an acid catalyst.
Catalyzing the above-said reaction has seen a groundbreaking research with scientists bringing out several moieties for undergoing the strenuous transformation
with an optimum yield. Research has yielded featured materials like MOFs, zirconia, heteropolyacids, zeolites, and even carbonaceous and supported catalytic entities for the aforementioned purpose [93, 180, 182, 183, 185, 186]. Special focus has
been on zeolites, which possess sized pores which can be engineered using processes like dealumination, desilication, as well as the merging of two or more zeolite molecules with a high yield and affinity toward the reactant molecules.
The monitoring of the reaction however becomes a bit difficult and hard to handle, requiring the confirmation of the same using several spectroscopic techniques,
Solid Acid-Catalyzed Esterification of Levulinic Acid for Production of Value-Added…