Ultrasound assisted enzyme catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate

Article abstract of DOI:10.1016/j.ultsonch.2014.06.018

The present work illustrates the transesterification of glycerol to glycerol carbonate (GlyC) from dimethyl carbonate (DMC) using commercial immobilized lipase (Novozym 435) under ultrasonic irradiation. The experiments were performed in a batch reactor placed in an ultrasonic water bath using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound power on the conversion of glycerol to GlyC. It has been found that ultrasound-assisted lipase-catalyzed transesterification of glycerol would be a potential alternative to conventional alkali-catalyzed method, as high conversion (99.75%) was obtained at mild operating conditions: molar ratio of DMC to glycerol 3:1, catalyst amount of 13% (w/w), lower power input (100 W), duty cycle 50% and temperature (60 °C) in a relatively short reaction time (4 h) using Novozym 435 as catalyst. Ultrasound reduces the reaction time up to 4 h as compared to conventional stirring method (14 h) catalyzed by Novozym 435. The repeated use of the catalyst under the optimum experimental condition resulted in decay in both enzyme activity and product conversion.

Full text of DOI:10.1016/j.ultsonch.2014.06.018

Ultrasonics Sonochemistry 22 (2015) 311–316
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Ultrasound assisted enzyme catalyzed synthesis of glycerol carbonate
from glycerol and dimethyl carbonate
⇑
Govind V. Waghmare, Mangesh D. Vetal, Virendra K. Rathod
Chemical Engineering Department, Institute of Chemical Technology, Matunga, Mumbai 400019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 April 2014
Received in revised form 11 June 2014
Accepted 24 June 2014
Available online 30 June 2014
The present work illustrates the transesterification of glycerol to glycerol carbonate (GlyC) from dimethyl
carbonate (DMC) using commercial immobilized lipase (Novozym 435) under ultrasonic irradiation. The
experiments were performed in a batch reactor placed in an ultrasonic water bath using a sequence of
experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading,
duty cycle and ultrasound power on the conversion of glycerol to GlyC. It has been found that ultrasound-
assisted lipase-catalyzed transesterification of glycerol would be a potential alternative to conventional
alkali-catalyzed method, as high conversion (99.75%) was obtained at mild operating conditions: molar
ratio of DMC to glycerol 3:1, catalyst amount of 13% (w/w), lower power input (100 W), duty cycle
50% and temperature (60 °C) in a relatively short reaction time (4 h) using Novozym 435 as catalyst.
Ultrasound reduces the reaction time up to 4 h as compared to conventional stirring method (14 h) cat-
alyzed by Novozym 435. The repeated use of the catalyst under the optimum experimental condition
resulted in decay in both enzyme activity and product conversion.
Keywords:
Glycerol
Glycerol carbonate
Lipase
Enzyme activity
Ultrasound
Optimization
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
(190 °C) and low volatility (vapor pressure is 8 mbar at 177 °C),
low toxicity, and good biodegradability. Glycerol carbonate (GlyC)
In the fastest growing era of industrialization, dependence on
natural resources and its consumption has grown very rapidly.
Thus, there is requirement to take some protective steps towards
the use of such depleting resources by considering future perspec-
tive. One potential solution to these issues is to develop new tech-
nology for the utilization of easily available and cheap sources to
produce value added products. In recent years, there has been a
rapid increase in the production of glycerol as it is the main
byproduct in the manufacture of biodiesel by transesterification
of oils with methanol. Its bio-based origin and broad reactivity
range made glycerol as very useful component for chemical
industry.
Considering the recent developments in the utilization of glyc-
erol into value-added chemicals, there are many applications
which valorise glycerol in the field of oral care, cosmetics, phar-
macy and polymer industry [1]. Among these chemicals, glycerol
carbonate (glycerine carbonate or 4-hydroxymethyl-2-oxo-1,3-
dioxolane, CAS 931-40-8) a promising molecule containing both
a hydroxyl group and a 2-oxo-1,3-dioxolane group (ODO), have
high boiling point (110–115 °C at 0.1 mmHg), high flash point
is a valuable intermediate for the production of glycidol [2,3]. It is
also used as chemical intermediate, polar protic solvent, electro-
lytes liquid carrier in batteries, curing agent in cement and con-
crete, cosmetics, blowing agent, detergents and monomer for
polymerization. GlyC has gained much attention in the recent
years due its wide reactivity and as a way to valorize glycerol
[4]. Many synthetic routes have been proposed in the literature
for the production of GlyC by glycerol with carbonyl sources like
carbon monoxide (CO) and oxygen [5], carbon dioxide (CO2) [6],
phosgene [7], urea [8–10], dimethyl carbonate (DMC) or diethyl
carbonate (DEC) [11–15], carbon dioxide and oxirane [16] cata-
lyzed by different metals and enzymatic catalysts. In the midst of
this, synthesis of GlyC using glycerol and DMC is the largest
focused area of the researchers due to environmental friendly nat-
ure of DMC which can replace potentially hazardous chemicals like
phosgene [17]. Recently the synthesis of GlyC using glycerol and
DMC were reported using biocatalyst [18–21]. The biocatalytic
processes are safer than chemical processes due to the ambient
reaction conditions, simplicity in the purification of products and
also follows the SHE norms (safety, health and environment). Cur-
rently enzyme catalyzed processes are costlier than chemical pro-
cesses due to higher cost of enzyme. This problem can be solved by
the use of immobilized enzyme which can be recycled. Similarly,
⇑
Corresponding author. Tel.: +91 22 33612020; fax: +91 22 24145614.
E-mail address: vk.rathod@ictmumbai.edu.in (V.K. Rathod).
http://dx.doi.org/10.1016/j.ultsonch.2014.06.018
1350-4177/Ó 2014 Elsevier B.V. All rights reserved.

312
G.V. Waghmare et al. / Ultrasonics Sonochemistry 22 (2015) 311–316
the cost of enzyme has been reduced in recent years due to
increase in productivity. It has been reported that presence of free
glycerol forms the coat over enzyme surface which slowdown
reaction rate due to inhibition of mass transfer between enzymes
and substrate. To overcome this problem Lee et al. used silica gel
as glycerol reservoir for synthesis of glycerol carbonate using
Novozym 435 in the solvent free medium which reports 74% con-
version after 48 h [22]. Hence to accelerate the reaction rate there
is a need to select proper technique which reduces the effect of free
glycerol. Use of proper solvent which dissolves glycerol and also
act as a favorable medium for enzyme catalyzed reactions is one
of the ways to tackle this problem. Tert-butyl alcohol was reported
as favorable and non-toxic medium for biocatalytic reactions [23].
Among newly reported techniques ultrasonic irradiation has the
potential for process intensification based on the cavitation phe-
nomenon. The liquid medium under ultrasonic irradiations, form
small bubbles which grow during multiple cycles of compression
and rarefaction of sound waves which undergoes sudden expan-
sion and then collapse violently to produce tremendous amount
of local heat and pressure which are responsible for the higher
mass transfer and reaction rate [24]. Hence, to overcome the draw-
backs of the conventional stirring method, ultrasonic irradiation is
considered as green methodology due to its high efficiency, mild
reaction conditions and no side reactions. Although ultrasound
can be used for process intensification of enzyme catalyzed reac-
tion, limited papers are available for its application to enhance
enzyme catalyzed reaction [25–29].
according to the maximum efficiency of ultrasonic irradiation as
described by the previous literature [30].
In a 50 mL baffle glass reactor, glycerol (99%) (0.92 g, 10 mmol)
and DMC (0.91 g, 10 mmol) were dissolved in tert-butyl alcohol
and made the total volume up to 20 mL. Novozym 435 (0.5 g)
was then added as biocatalyst along with molecular sieves (2 g)
which acts as scavenger for methanol. By considering the addition
of enzyme as starting time of the reaction, samples (200 lL) were
taken periodically at 20 min time interval. The progress of reaction
was evaluated using GC analysis. Reactions were performed at var-
ious temperatures ranging from 40 °C to 70 °C for 5 h. The fre-
quency of ultrasonic bath was 25 kHz and the duty cycle selected
was 50% (10 min ON 10 min OFF).
2.3. Analytical method
2.3.1. Gas chromatography
The conversion of glycerol to GlyC was analyzed using gas chro-
matography (Chemito GC 8610) equipped with flame ionization
detector (FID), a packed column OV-17 (1/8’’ diameter, 3 m length)
and nitrogen as carrier gas at the rate of 30 mL/min, air and hydro-
gen was used at the flow rate of 300 mL/min and 30 mL/min
respectively. Sample was injected at 70 °C which was kept constant
for 1 min and it rises up to 300 °C at the rate of 17 °C/min. Both
injector and detector are kept at constant temperature of 320 °C.
200
centrifuged at 8000 rpm for 5 min using micro centrifuge and
L supernatant liquid was directly used for injection in the col-
umn for GC analysis. The progress of the reaction was monitored
using internal standard method with 500 L n-decane previously
lL samples were periodically taken from the reaction course,
This work describes the effect of ultrasound on the synthesis of
GlyC by transesterification of glycerol and DMC using lipase
(Novozym 435) as catalyst and tert-butyl alcohol as nontoxic
solvent in a batch reactor. To explore the effect of ultrasonic irradi-
ation on synthesis of GlyC using lipase as catalyst, various param-
eters such as effect of power, duty cycle, molar ratios of substrate,
temperature, catalyst loading etc. were studied and the analysis
was carried out using gas chromatography (GC).
2
l
l
added in the reaction mixture as the internal standard to calculate
the relative response of the detector towards the analyte and the
standard.
2.3.2. Esterification activity
The enzymatic activity of Novozym 435 was determined by the
procedure reported by Gharat et al. [31]. The activity was evalu-
ated using esterification reaction between oleic acid and n-butanol
at the molar ratio 1:3 in 3 mL iso-octane, 0.05 mL DI water, and
200 mg of enzyme was added in the reaction mixture, the flask
was shaken at 250 rpm for 30 min at 30 °C. The reaction was
stopped by adding 10 mL of methanol and immediately titrated
with 0.05 M NaOH using phenolphthalein as indicator [31]. The
esterification activity was determined by following equation:
2. Materials and methods
2.1. Materials
Novozym 435 (lipase B from Candida antarctica; immobilized on
macro-porous polyacrylic resin beads, bead size 0.3–0.9 mm, bulk
density 0.430 g/cm3) was received as a gift sample from Zytex
India Pvt. Ltd., Mumbai. Glycerol carbonate was received as a gift
sample from Huntsman India Pvt. Ltd., Mumbai. Glycerol AR grade,
tert-butyl alcohol and n-decane were purchased from S D Fine-
Chem. Ltd., Mumbai. All other chemicals such as dimethyl carbon-
ate 99%, acetone, were purchased from Himedia Laboratories Pvt.
Ltd., Mumbai. Molecular sieves 5 Å were purchased from Rarco
chemicals, Mumbai.
V ꢀ M ꢀ 100
Esterification activity ðEaÞ ¼
E ꢀ t
where V – difference between volumes of NaOH required to titrate
blank and samples, M – molarity of NaOH, E – amount of enzyme
(mg) and t – time of reaction (min).
The activity is the amount of product formed or substrate con-
sumed in the reaction mixture under specified conditions of tem-
perature, pH, substrate and enzyme concentrations. One unit of
2.2. Lipase-catalyzed synthesis of glycerol carbonate
enzyme activity is defined as 1 lmol of oleic acid consumed in
the esterification reaction per min per mg lipase.
The transesterification of glycerol and DMC using Novozym as
catalyst under ultrasonic irradiation was carried out in the ultra-
sonic bath (Model 6.5l200 H, Dakshin, India, 4.5 liter capacity) with
the internal dimensions 300 mm ꢀ 150 mm ꢀ 150 mm and four
transducers placed at the bottom of the batch. The reaction was
carried out in 50 mL flat bottom baffled glass reactor (id 4.5 cm)
with 3 blade turbine glass impeller equipped with stirring motor,
reflux condenser and thermometer. The whole assembly was kept
in ultrasonic bath with temperature control of 2 °C having operat-
ing frequency of 25 kHz and 40 kHz with maximum rated power of
200 W. The position of the reactor in the ultrasonic bath was fixed
2.4. Statistical analysis
Statistical analysis is very important to summarize and inter-
pret the obtained data. To analyze the obtained results single factor
ANOVA with Microsoft excel was used. All experimental results
were carried out in triplicate and data is represented as mean SD.
P-value less than 0.05 were considered to be statistically
significant.

G.V. Waghmare et al. / Ultrasonics Sonochemistry 22 (2015) 311–316
313
enzyme loading – 13%, duty cycle 50%, frequency of UI 25 kHz,
power of UI 150 W are kept constant. The results obtained are
depicted in Fig. 2. It was observed that at 60 °C the conversion of
glycerol increases up to 99%, further increase in temperature up
to 70 °C reaction rate increases initially but final conversion of
glycerol decreases slightly. The increase in reaction rate at elevated
temperature is probably due to lowering of viscosity at higher tem-
perature which leads to increase in diffusion of substrate. How-
ever, at higher temperature, cavitation effect reduces as well as
there is possibility of deactivation of enzyme. At 70 °C the reaction
progresses very fast in 1 h but the final conversion after 5 h is
decreases. Similarly, the enzyme used in the present study is active
in the range of 40–60 °C. Therefore, considering conversion and
efficiency of the catalyst, optimum temperature selected was 60 °C.
3. Results and discussion
3.1. Effect of DMC to glycerol molar ratio
Since the rate of reaction can be manipulated by varying the
amount of one of the reactant, the molar ratio of substrates is an
important parameter affecting the course of reaction. According
to the stoichiometric calculations, the synthesis of GlyC from glyc-
erol and DMC requires equimolar mixture of substrates. However it
was reported that type of catalyst and reaction conditions strongly
affect the mechanism of reaction. The excess of DMC is required
due to the reversible nature of transesterification reaction to shift
the equilibrium in the forward direction. Using 3-fold excess
DMC and basic inorganic catalyst, only GlyC was formed and the
secondary product such as (glycerol dicarbonate, diglyceride tri-
carbonate) were formed at 10-fold excess DMC at higher tempera-
ture (95 °C) [32]. In order to obtain the reaction profile, the
reaction was first carried out for 10 h. However, it is observed that
there was no considerable difference in the conversion of glycerol
after 5 h. Hence, all the subsequent reactions were carried out for
5 h. It was reported that in case of enzyme catalyzed synthesis of
GlyC, the ratio of DMC to glycerol was 2:1 with THF as solvent
and in solvent free medium it was 10:1 [22,33]. Here, the effect
of molar ratio on rate of reaction was studied using different com-
binations of molar ratios from 1:1 to 4:1 with lipase as catalyst
under ultrasonic irradiation and the results are represented in
Fig. 1. The glycerol carbonate conversion increased when the molar
ratio of DMC to glycerol increased to 3:1. However, further increase
of the molar ratio to 4:1 didn’t get any considerable increase in
conversion probably due dilution of glycerol with DMC which leads
to the lesser collision frequency with the enzyme. The conversion
rate at 1:1, 2:1, 3:1 and 4:1 M ratio of DMC to glycerol were found
to be 66.34%, 77.72%, 96% and 99.64% respectively after 5 h. Hence
3:1 was considered to be an optimum molar ratio.
3.3. Effect of enzyme loading
Amount of catalyst used plays very important role in the kinet-
ics of reaction and economic profitability of the process. In order to
obtain optimum amount of enzyme loading, experiments were
performed with the enzyme loading amount ranging from 8% to
16% (based on the w/w percent of the total weight of reactants).
The results obtained are represented in Fig. 3. It was found that
by increasing the enzyme loading from 8% to 13% the conversion
of glycerol increases and after 5 h the conversion obtained at 13%
loading was 99.64%. Again by increasing the loading up to 16%,
the initial rate slightly increases but finally gives the conversion
of 98.27% which is similar to enzyme loading of 13%. The increase
in reaction rate by increase in enzyme loading is due to the rapid
formation of enzyme-substrate complex at sufficient enzyme load-
ing. However excess enzyme loading leads to the problem of mix-
ing by increase in viscosity. By considering the economic
profitability and conversion of glycerol, the loading of 13% was
considered to be optimized for the proceeding reactions.
3.2. Effect of temperature
3.4. Effect of irradiation power
Temperature plays very vital role on the rate of enzyme cata-
lyzed reactions as the catalytic activity of enzymes depends on
reaction temperature. Hence, the effect of temperature on the con-
version of glycerol to GlyC was investigated at various tempera-
tures ranging from 40 °C to 70 °C. The other reaction parameters,
speed of agitation 200 rpm, DMC to glycerol molar ratio 3:1,
The amplitude of irradiation affects the formation of cavitation
which in turn decides the progress of reaction. The reactions were
carried out by changing the power of the irradiation ranging from
0 W to 150 W at duty cycle of 50% keeping other parameters con-
stant. The results obtained are depicted in Fig. 4 which shows that
at lower irradiation power of 50 W, the rate of reaction as well as
100
100
80
80
60
60
40
40
40 ˚C
1:1
50 ˚C
2:1
60 ˚C
70 ˚C
20
0
20
0
3:1
4:1
0
60
120
Time (Min)
180
240
300
0
60
120
Time (Min)
180
240
300
Fig. 1. Effect of DMC to glycerol molar ratio on conversion (%) at temperature 60 °C,
agitation speed 200 rpm, enzyme loading 13%, power of UI 150 W, frequency of UI
25 kHz, duty cycle 50%.
Fig. 2. Effect of temperature on conversion (%) at DMC to glycerol ratio 3:1,
agitation speed 200 rpm, enzyme loading 13%, power of UI 150 W, frequency of UI
25 kHz, duty cycle 50%.

314
G.V. Waghmare et al. / Ultrasonics Sonochemistry 22 (2015) 311–316
100
100
80
60
40
20
0
80
60
40%
50%
60%
75%
40
8%
10%
20
13%
16%
0
0
60
120
180
Time (Min)
240
300
0
60
120
Time (Min)
180
240
300
Fig. 5. Effect of Duty cycle on conversion (%) at DMC to glycerol ratio 3:1,
temperature 60 °C, agitation speed 200 rpm, enzyme loading 13%, power of UI
100 W, frequency of UI 25 kHz.
Fig. 3. Effect of enzyme loading on conversion (%) at DMC to glycerol ratio 3:1,
temperature 60 °C, agitation speed 200 rpm, power of UI 150 W, frequency of UI
25 kHz, duty cycle 50%.
ultrasonic waves. The percent duty cycle can be varied by changing
the ON/OFF time of ultrasound. In this work the range of duty cycle
from 40% to 75% was studied to evaluate the effect of ultrasonic
irradiation on the conversion of glycerol. The results obtained are
depicted in Fig. 5. As expected, it is observed that by increasing
the duty cycle from 40% to 50% the conversion increases signifi-
cantly after 5 h. On the other hand, an increase in duty cycle after
50%, leads to the lesser conversion of glycerol. The lower conver-
sion at higher duty cycle is may be due to the denaturation of
enzyme by increase in the exposure time under ultrasonic irradia-
tion. It was reported by Avhad et al. that the extensive cavitation at
higher duty cycle affects the proteins structure due to imparted
mechanical shear [35]. Hence the duty cycle of 50% is considered
as an optimum for the next set of experiments.
conversion of glycerol was less as compared to higher irradiation
power. This may be due to the formation of lower cavitation phe-
nomenon at lower irradiation power. By increasing the irradiation
power up to 100 W the rate of reaction and conversion increases
successively. Further increase in irradiation power doesn’t result
in significant increase in the conversion. Hence, the irradiation
power of 100 W was considered as optimized power for proceed-
ing experiments. To calculate the power dissipation at sample site
in ultrasonic bath calorimetric analysis was performed with differ-
ent irradiated power at 25 kHz frequency [34]. The power dissipa-
tion at 50 W, 100 W and 150 W was found to be 42 W, 46.2 W and
61.6 W respectively.
3.5. Effect of duty cycle
3.6. Reusability of enzyme
Duty cycle refers to the total exposure time of ultrasonic irradi-
ation on the reaction mass in one cycle. It is recommended to use
ultrasonic instruments with particular duty cycle to reduce the
possible deactivation of enzyme due to continuous exposure of
There is a need to reuse the catalyst after every cycle as enzyme
plays a very crucial role in the economic profitability of bio cata-
lyzed reactions. Thus, reusability study was critically essential for
the economic feasibility of reaction. Reusability study was per-
formed using optimized parameters. After each cycle, the immobi-
lized enzyme was filtered off, washed with acetone and dried in
oven for 30 min at 40 °C and then kept in desiccator at room tem-
perature (30 2 °C). The recycled enzyme was used for the next
cycle. The results obtained after six cycles are depicted in Fig. 6
which shows that the conversion of glycerol goes on decreasing
by increase in the number of cycles. Also it was observed that
the catalytic activity of enzyme also decreased after each cycle.
The reusability of Novozym 435 was compared with earlier work
reported by Lanjekar et al. where the activity of Novozym 435
was unaffected after six cycles under conventional stirring method
[23] and a sudden decrease in enzyme activity was observed after
repetitive use under ultrasonic irradiation. The loss in activity and
decrease in percent conversion was may be due to the breakage of
bonding between enzyme and supporting media using ultrasound
irradiation.
100
80
0 W
50 W
75 W
60
100 W
150 W
40
20
0
0
60
120
180
240
300
3.7. Comparative analysis of ultrasonic irradiation vs conventional
stirring method
Time (Min)
Fig. 4. Effect of ultrasound power on conversion (%) at DMC to glycerol ratio 3:1,
temperature 60 °C, agitation speed 200 rpm, enzyme loading 13%, frequency of UI
25 kHz, duty cycle 50%.
To compare the results obtained under ultrasound and conven-
tional stirring method, three experiments were carried out under

G.V. Waghmare et al. / Ultrasonics Sonochemistry 22 (2015) 311–316
315
100
80
60
40
20
0
4 h. Using ultrasound the time of reaction was significantly
reduced from 14 h (94.85%) to 4 h (99.75%). From this it can be
concluded that in case of ultrasonication coupled with stirring
gives higher conversion compared with ultrasonication alone and
conventional stirring method. The illustrative chromatogram of
glycerol carbonate synthesis was represented in Fig. 7 which
shows the complete conversion of glycerol and formation of glyc-
erol carbonate. The calorimetric study was performed to calculate
the power dissipation for conventional stirring method and ultra-
sound assisted reaction. From power calculations it was observed
that, ultrasonic irradiation requires nearly 20% extra power than
conventional stirring method. It sounds technically feasible in case
of process intensification and ambient operating conditions. In case
of scaling up the process, the most important point is the uniform
distribution of irradiation power and the formation of dead zone in
reactor. These hurdles could be overcome by employing multiple
transducers having uniform power distribution over wide area.
Gogate et al. reported the various factors for implementation of
large scale sonochemical reactors [36]. For successful employment
of ultrasonication in large scale operations there is need of com-
bine efforts of chemists, chemical engineers and physicists.
0
1
2
3
4
5
6
Number of cycles
Fig. 6. Reusability of the enzyme on conversion (%) at DMC to glycerol ratio 3:1,
temperature 60 °C, agitation speed 200 rpm, enzyme loading 13%, frequency of UI
25 kHz, duty cycle 50%, power of UI 100 W, reaction time 4 h.
4. Conclusion
The present work deals with the synthesis of GlyC by transeste-
rification of glycerol and DMC using lipase as catalyst in tert-butyl
alcohol as non-toxic solvent under ultrasonic irradiation. The key
advantage of the present work is to provide an ecofriendly route
for the transesterification of glycerol using DMC instead of metha-
nol and use of tert-butyl alcohol as a promising solvent. The
involvement of dimethyl carbonate as substrate is the type of
green methodology that aids an environmental-benign transesteri-
fication reaction. Ultrasound treatment resulted in significant
intensification in the process with reaction time reduced by 10 h
as compared to conventional stirring method. The optimum ultra-
sound parameters observed were 25 kHz frequency, 100 W rated
power with 50% duty cycle. It provides efficient route for the syn-
thesis as low enzyme (13% w/w) loading was required under
milder conditions (atmospheric pressure and 60 °C temperature).
Therefore, the transesterification of glycerol using Novozym 435
under ultrasonic irradiation described herein gives an interesting
alternative for synthesis of GlyC.
Table 1
Comparison of ultrasonic irradiation with conventional stirring method.
Time (h)
% Glycerol conversion
Ultrasonication with stirring
Ultrasonication without stirring
Conventional stirring method
4
4
14
99.75 0.8
63.38 1.24
94.85 1.54
Mean SD of three replicated samples. Results show P value < 0.05, it is statistically
significant.
optimized conditions for enzyme catalyzed transesterification i.e.
ultrasonication with and without stirring and conventional stirring
method. The results obtained are shown in Table 1. It was observed
that the conversion of glycerol when ultrasound coupled with stir-
ring gives the conversion of 99.75% and with conventional stirring
method the conversion was very less about 30% whereas, in case of
only ultrasound without stirring the conversion was 54.30% after
25.000
[mv]
19.800
14.600
9.400
4.200
-1.000
0.00
1.10
2.20
3.30
4.40
5.50
6.60
7.70
8.80
9.90
11.00
[min]
Fig. 7. The illustrative chromatogram of glycerol carbonates synthesis.

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G.V. Waghmare et al. / Ultrasonics Sonochemistry 22 (2015) 311–316
[19] P.-J. Seong, B.W. Jeon, M. Lee, D.H. Cho, D.-K. Kim, K.S. Jung, et al., Enzymatic
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