282
decarboxylation to produce non-2-en-4-one which further upon hydrogenation
yielded 4-nonanone, a known food flavoring agent. 4-Nonanone was upgraded to
C15–C16 range diesel fuel by undergoing aldol condensation with 5-HMF in the
presence of MgO–CaO base catalyst followed by HDO [64] (Fig. 5d).
3 Solvent Effects
The catalytic conversion of lignocellulose biomass is generally carried out in aqueous solutions, and the kinetics and selectivity of such reactions can be tuned by
varying the temperature, pressure, and solvent composition [70, 71]. Some reactions
have shown improvement in performance by altering the solvent composition. For
example, the yield of acid-catalyzed conversion reaction showed an increase in the
presence of mixed solvent environment [72, 73]. However, solvent selection for a
new process requires either trial and error experiments or simulation methods that
are computationally expensive. Ab initio DFT simulations can probe mechanistic
details of reaction; however, the simulations are computationally expensive which
makes the screening of multiple solvent compositions infeasible. In contrast,
classical molecular dynamic (MD) simulations allow characterization of larger
molecules surrounded by complex solvent environment with reduced computational
burden [74]. With the use of classical molecular dynamic (MD) simulations in
combination with experiments, the rate of acid-catalyzed reactions in biomass
conversion in a mixture of solvents can be estimated [75]. Classical MD simulations
were used to explain the selectivity trends for Brønsted acid-catalyzed dehydration
of 1,2-propanediol which when carried out in pure water showed higher selectivity
toward propanal (~41%) than acetone (~5). Similar selectivity trends were observed
for aqueous mixtures of the aprotic solvents except for aqueous dimethyl sulfoxide
solution wherein acetone (selectivity ~48%) was formed as the major product.
Classical MD simulations were used to calculate the free energy difference (ΔΔG)
between the reactant and the product, and the value of ΔΔG was correlated to the
rate of formation of the product which indicated that the stabilization of the product
relative to the reactant in solvent-mediated environment enhanced the selectivity
[76]. Classical MD simulations were also used to explain the increase in yield of
5-HMF from glucose in the presence of aqueous mixture of dimethyl sulfoxide
(DMSO) and acetonitrile as the solvents [77]. Using MD simulation, it was observed
that acetonitrile increased the coordination between water and glucose which lead
to an increase in the isomerization of glucose to fructose [77]. The stability of
hydronium ions formed during acid-catalyzed biomass conversion reactions in
mixed solvent environment has been shown to affect the reaction kinetics [78].
Water-rich local solvent domains were formed near the hydronium ion which was
attributed to the increased stability of hydronium ion. Molecular dynamic simulations
were also used to unravel the interaction between lignin and cellulose in the two
solvent system (THF-water) [79]. THF in water was found to dissolve and
disaggregate the lower weight lignin molecules which allowed molecules to separate
S. Gupta
decarboxylation to produce non-2-en-4-one which further upon hydrogenation
yielded 4-nonanone, a known food flavoring agent. 4-Nonanone was upgraded to
C15–C16 range diesel fuel by undergoing aldol condensation with 5-HMF in the
presence of MgO–CaO base catalyst followed by HDO [64] (Fig. 5d).
3 Solvent Effects
The catalytic conversion of lignocellulose biomass is generally carried out in aqueous solutions, and the kinetics and selectivity of such reactions can be tuned by
varying the temperature, pressure, and solvent composition [70, 71]. Some reactions
have shown improvement in performance by altering the solvent composition. For
example, the yield of acid-catalyzed conversion reaction showed an increase in the
presence of mixed solvent environment [72, 73]. However, solvent selection for a
new process requires either trial and error experiments or simulation methods that
are computationally expensive. Ab initio DFT simulations can probe mechanistic
details of reaction; however, the simulations are computationally expensive which
makes the screening of multiple solvent compositions infeasible. In contrast,
classical molecular dynamic (MD) simulations allow characterization of larger
molecules surrounded by complex solvent environment with reduced computational
burden [74]. With the use of classical molecular dynamic (MD) simulations in
combination with experiments, the rate of acid-catalyzed reactions in biomass
conversion in a mixture of solvents can be estimated [75]. Classical MD simulations
were used to explain the selectivity trends for Brønsted acid-catalyzed dehydration
of 1,2-propanediol which when carried out in pure water showed higher selectivity
toward propanal (~41%) than acetone (~5). Similar selectivity trends were observed
for aqueous mixtures of the aprotic solvents except for aqueous dimethyl sulfoxide
solution wherein acetone (selectivity ~48%) was formed as the major product.
Classical MD simulations were used to calculate the free energy difference (ΔΔG)
between the reactant and the product, and the value of ΔΔG was correlated to the
rate of formation of the product which indicated that the stabilization of the product
relative to the reactant in solvent-mediated environment enhanced the selectivity
[76]. Classical MD simulations were also used to explain the increase in yield of
5-HMF from glucose in the presence of aqueous mixture of dimethyl sulfoxide
(DMSO) and acetonitrile as the solvents [77]. Using MD simulation, it was observed
that acetonitrile increased the coordination between water and glucose which lead
to an increase in the isomerization of glucose to fructose [77]. The stability of
hydronium ions formed during acid-catalyzed biomass conversion reactions in
mixed solvent environment has been shown to affect the reaction kinetics [78].
Water-rich local solvent domains were formed near the hydronium ion which was
attributed to the increased stability of hydronium ion. Molecular dynamic simulations
were also used to unravel the interaction between lignin and cellulose in the two
solvent system (THF-water) [79]. THF in water was found to dissolve and
disaggregate the lower weight lignin molecules which allowed molecules to separate
S. Gupta