265
propylsulfonic acid-functionalized SBA-15 offered 96% yield of butyl levulinate
with 100% selectivity [5]. Hence, it is important to select a catalyst with appropriate
porosity, pore structure, and acidity to achieve maximum conversion and selectivity
of the desired product.
3.2 Deactivation and Reusability of the Catalyst
Deactivation of the catalyst is evaluated by subjecting it to the loss of activity with
increasing time on stream. Among the various reasons for deactivation, coking is a
major one for the deactivation of catalysts in biomass conversion reactions. The
other possible ways of catalyst deactivation are blockage of pore or active sites by
insoluble byproducts/intermediates, metal leaching, sintering, decrease in specific
surface area, loss of pore volume, etc. Sometimes, the basic metal oxides (MgO)
can form hydroxides, which are more soluble in water and tend to leach. Also, the
reaction byproducts can accumulate on the active catalytic site, thereby restricting
the accessibility resulting in a low conversion. In the case of zeolites, degradation
due to desilication or dealumination at harsh hydrothermal conditions is one of the
ways of catalyst deactivation [2]. In order to avoid pore blockage in microporous
zeolites, incorporation of larger size metal should be avoided. Many of the catalysts
presented in this chapter showed good catalytic activity up to five reaction cycles,
but their applicability at commercial scale and for real biomass feedstock needs to
be tested. Fouling of MOF catalysts by humin formation is common in biomass
conversion that can be prevented by using a proper solvent such as ethanol in case
of selective conversion of glucose to 5-HMF [61]. Temperature can also influence
deactivation as observed in catalytic cracking of fatty acid mixture; the order of
deactivation over the composite catalyst was almost constant at moderate rate,
whereas ZSM-5 deactivation order decreased with increasing temperature. The
same order of deactivation was also observed for used palm oil cracking [97].
3.3 Kinetic/Mechanistic Aspects
Kinetic data obtained by careful evaluation of reaction parameters helps in process
scale-up, technology transfer, and evaluation of economic feasibility. Due to the
large number of complex reactions taking place in biomass conversion, it is not easy
to explain kinetics at the molecular level. Few kinetic studies are discussed here. In
the case of catalytic cracking of vegetable oil, a simplified lumped kinetics is
presented by the grouping of components having similar chemical functions [34].
The complexity of the model varies according to the degree of lumping. Adding
more lumps will make the process of kinetic parameters more intrinsic; thus, more
kinetic parameters need to be estimated, and accordingly, more experimental
information is required. For vegetable oil cracking, three, four, and six lumped
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…
propylsulfonic acid-functionalized SBA-15 offered 96% yield of butyl levulinate
with 100% selectivity [5]. Hence, it is important to select a catalyst with appropriate
porosity, pore structure, and acidity to achieve maximum conversion and selectivity
of the desired product.
3.2 Deactivation and Reusability of the Catalyst
Deactivation of the catalyst is evaluated by subjecting it to the loss of activity with
increasing time on stream. Among the various reasons for deactivation, coking is a
major one for the deactivation of catalysts in biomass conversion reactions. The
other possible ways of catalyst deactivation are blockage of pore or active sites by
insoluble byproducts/intermediates, metal leaching, sintering, decrease in specific
surface area, loss of pore volume, etc. Sometimes, the basic metal oxides (MgO)
can form hydroxides, which are more soluble in water and tend to leach. Also, the
reaction byproducts can accumulate on the active catalytic site, thereby restricting
the accessibility resulting in a low conversion. In the case of zeolites, degradation
due to desilication or dealumination at harsh hydrothermal conditions is one of the
ways of catalyst deactivation [2]. In order to avoid pore blockage in microporous
zeolites, incorporation of larger size metal should be avoided. Many of the catalysts
presented in this chapter showed good catalytic activity up to five reaction cycles,
but their applicability at commercial scale and for real biomass feedstock needs to
be tested. Fouling of MOF catalysts by humin formation is common in biomass
conversion that can be prevented by using a proper solvent such as ethanol in case
of selective conversion of glucose to 5-HMF [61]. Temperature can also influence
deactivation as observed in catalytic cracking of fatty acid mixture; the order of
deactivation over the composite catalyst was almost constant at moderate rate,
whereas ZSM-5 deactivation order decreased with increasing temperature. The
same order of deactivation was also observed for used palm oil cracking [97].
3.3 Kinetic/Mechanistic Aspects
Kinetic data obtained by careful evaluation of reaction parameters helps in process
scale-up, technology transfer, and evaluation of economic feasibility. Due to the
large number of complex reactions taking place in biomass conversion, it is not easy
to explain kinetics at the molecular level. Few kinetic studies are discussed here. In
the case of catalytic cracking of vegetable oil, a simplified lumped kinetics is
presented by the grouping of components having similar chemical functions [34].
The complexity of the model varies according to the degree of lumping. Adding
more lumps will make the process of kinetic parameters more intrinsic; thus, more
kinetic parameters need to be estimated, and accordingly, more experimental
information is required. For vegetable oil cracking, three, four, and six lumped
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…