2
UMRIGAR ET AL.
selectivity.3 Zeolites have been also used to achieve good
yield of glucose acetalized products with alcohols of dif-
ferent chain lengths with the change of Si/Al ratio of zeo-
lites and shape selectivity varies the amount of oligomers
formed.3
Based on above studies, the reaction of LA with diols, such
as 1,2-PDOL ,1,2-ethane diol (EDOL), and TRIOL, using a
solid heterogeneous catalyst Hꢀ and desilicated Hꢀ (D-Hꢀ)
was studied to produce value-added chemicals or polymers
and biofuel additives using conventional and MW-irradiated
reactors. The main objective of this study is to valorize LA and
diols using optimum amount and enhancement of the selec-
tivity of intermediates, such as E (ester), K (ketal), and also
the final product, that is, KE, and to reduce the amount of
oligomerized or polycondensate products.
Levulinic acid (LA) or 4-oxopentanoic acid is a main
renewable, most promising alternative compound and can be
derived from lignocellulose by acid-catalyzed reactions of
cellulose-containing biomass.4 At DuPont Co., researchers
are actively pursued to make utilization of LA in syntheses
of solvents and surfactants such as pyrolidones, monomer
as ꢂ-methylene Ƴ-valerolactone, and fuel additives such as
LA esters.5 Also as per global LA consumption of around
2600 tons/year, it is going to be increased in the coming
years, especially due to the research enhancement in the
biofine process, which will lower the LA costs to 0.09–0.22
$/kg,4 and hence it can be used as a raw material to produce
different esters and KEs. Amarasekara et al.6 reported LA
oligomerization with glycerol using solid acidic catalysts such
as Sb2O3, p-toluenesulfonic acid, and 1-(1-propylsulfonic)-3-
methylimidazolium chloride for the production of keto (K),
glycerol-ketal (KE), and glycerol-ester (E). Freitas et al.7 also
performed the ketalization between ethyl levulinate (Elevu)
and ethylene glycol (EG) and 1,2-dodecanediol using acid
catalysts such as p-toluensolfonic acid, Amberlyst 70, zeolite
H-ZSM-5, and niobium phosphate. Mullen et al.8 mentioned
that low to moderate to strong protic acidity of catalyst can
improve the synthesis of cyclic ketals. It shows better selec-
tivity of ketal (>95%) and conversion (>95%) with ethyl lev-
ulinate.
2
EXPERIMENTAL
2.1 Catalyst preparation
2.1.1 Desilication
Pretreatment of Hꢀ (Si/Al ratio = 25) catalyst was carried out
using 0.2 M alkali (NaOH) solution (30 mL/g) at 340 K under
continuous stirring for 45 min. The samples were washed with
distilled water followed by ammonium exchange in 10 wt%
NH4NO3 solution (15 mL/g) under reflux for 4 h. The proce-
dure was repeated twice, and the sample was washed and dried
◦
overnight at 100 C. Finally, the dry sample was calcinated by
◦
◦
flowing air (50 mL/min) at 550 C at a rate of 10 C/min for 10
h in a conventional drier.
2.2 Materials and methods
LA, 1,2-PDOL, EDOL, TRIOL, and Hꢀ with a quoted purity
of 0.99 (each) were obtained from Merck (Mumbai, India).
Other analytical solvents such as diethylether, alcohol, sodium
bicarbonate for neutralization and separation in case of the
conventional process, and diethylether for a gas chromatog-
raphy mass spectrophotometer (GCMS) were also procured
from Merck. Product analysis was carried out using a gas
chromatograph mass spectrometer (7890A GC and MS of
ACCUTOF GCV (JMS-T100GCV) system) with oven tem-
1,2,3-Propane triol or glycerol (TRIOL) is available as
abundant by-product from soap- and biodiesel-making indus-
tries. It is a renewable resource with a three-carbon TRIOL
having many applications in food, pharmaceutical, and per-
sonnel care product industries. The new area of interest is
also the utilization of such feed stock by converting glycerol to
value-added products. It is used as a model compound for the
exploration of its conversion to H2 and CO2, and transforma-
tion to other alcohols, such as 1,2-propanediol (1,2-PDOL)
and 1,3-propanediol (1,3-PDOL), which can be utilized as
solvents for the organic synthesis.9 These diols and glycerol
have been utilized for the production of esters and KEs for the
present work.
◦
perature of 131.9–250 C, at a flow rate of 1 mL/min of helium
◦
gas with ion source temperature of 250 C. GC ramp program
used is 110–1 M-8-200-5 M-10-280 HP5.
2.3 Experimental procedure
To apply green energy concept, the thermal energy source
choice is the use of microwave (MW)-assisted chemistry for
the organic synthesis. Effects like much shorter reaction times,
improved selectivity of the most desired product, enhanced
product yields, cleaner reaction with easier workup, and
reduction in waste are mostly observed with MW activation in
organic reactions.10 Despite of abundant literatures on aspects
cited above, very few publications dealt with zeolite-catalyzed
conventional as well as microwave-irradiated (MWI) esterifi-
cations of bio-derived carboxylic acids.
Esterification and ketalization reactions were performed in
a continuous fixed bed reactor (using H2 as a carrier gas at
the flow rate of 10 mL/min) having length (L) and diameter
(D) as L × D = 1 × 2.5 (cm × cm). Catalyst particle size and
properties are shown in Table 1, and MWI reactions were
carried out in a thermostated batch reactor equipped with a
magnetic stirrer with a closed reflux. For each run, LA and
polyols (PDOL, EDOL, and TRIOL) were mixed at different
operating conditions, and a product mixture was withdrawn
at different intervals of time and analyzed by GCMS.