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C as catalyst under ambient conditions in water
Accepted Manuscript Ultrasound assisted selective catalytic transfer hydrogenation of soybean oil using 5% Pd/C as catalyst under ambient conditions in water Sonam V. Sancheti, Parag R. Gogate PII: DOI: Reference:
S1350-4177(17)30096-2 http://dx.doi.org/10.1016/j.ultsonch.2017.03.004 ULTSON 3581
To appear in:
Ultrasonics Sonochemistry
Received Date: Revised Date: Accepted Date:
31 December 2016 5 March 2017 5 March 2017
Please cite this article as: S.V. Sancheti, P.R. Gogate, Ultrasound assisted selective catalytic transfer hydrogenation of soybean oil using 5% Pd/C as catalyst under ambient conditions in water, Ultrasonics Sonochemistry (2017), doi: http://dx.doi.org/10.1016/j.ultsonch.2017.03.004
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1 1
Ultrasound assisted selective catalytic transfer hydrogenation of soybean oil using 5%
2
Pd/C as catalyst under ambient conditions in water
3 4 5 6 7
Sonam V. Sancheti, Parag R. Gogate*
8 9 10 11 12
Chemical Engineering Department,
13
Institute of Chemical Technology,
14
Matunga, Mumbai – 400 019, India
15 16 17 18 19 20 21
*
22
E-mail address: [email protected]
23
Tel.: +91 22 3361 2024
24 25
Corresponding author
Fax: +91 22 3361 1020
2 26
Abstract
27
Catalytic transfer hydrogenation (CTH) is an alternative approach that does not require the
28
use of potentially dangerous hydrogen gas. Pd/C is the most favoured catalyst for the
29
selective hydrogenation of soybean oil yielding lower extent of formation of stearic acid and
30
trans-isomer, which have adverse health effects. The present work deals with intensification
31
of catalytic transfer hydrogenation of soybean oil in the presence of 5 wt. % Pd/C using
32
ultrasound under ambient reaction conditions. The effect of important operating parameters
33
such as ultrasound power, temperature, type of hydrogen donor, type of formic acid salts,
34
catalyst loading and donor concentration on the progress of reaction has been investigated. It
35
was established that the maximum extent of hydrogenation as indicated by reduction in
36
iodine value from 135 to 95 was observed under optimized conditions of irradiation power as
37
100 W, 22 kHz frequency, 90% duty cycle, ammonium formate concentration of 0.32 mol /
38
50 ml water and 2% (w/w) Pd/C loading at ambient temperature and pressure in the presence
39
of solvent. The approach also offered excellent selectivity with controlled trans-isomer
40
formation as compared to the conventional approach of high pressure hydrogenation. Overall,
41
the work has successfully demonstrated process intensification benefits based on ultrasound
42
for the Pd/C catalysed transfer hydrogenation of soybean oil.
43 44
Keywords: Ultrasound; Physical effects; Catalytic transfer hydrogenation (CTH); Soybean
45
oil; heterogeneous catalyst
46 47 48 49
3 50
1. Introduction
51
Soybean oil consists of mainly triglycerides of saturated and unsaturated fatty acids,
52
particularly with chain length over the range of C16–C18. Hydrogenation of soybean oil is
53
important process in oleochemical industry because of the wide range of applications of the
54
obtained derivatives for the production of margarine, frying oils, etc. Hydrogenation of oil
55
leads to increased melting point, improved color and oxidation properties of soybean oil. The
56
selective reduction of linolenic acid (C18:3) in the soybean oil has a prime importance as it
57
alters the flavour reversion of oil. The quality and physical properties of the final product
58
obtained after hydrogenation are affected by the number of double bonds present in the oil
59
represented by the iodine value (IV) and also cis–trans-isomer content in the fatty acid. The
60
trans-isomer has been reported to be undesirable for human diet due to the adverse health
61
effects.
62
The catalytic transfer hydrogenation (CTH) is a safe, simple and eco-friendly method
63
compared to the conventional hydrogenation where hydrogen gas is used offering handling
64
problems due to the explosive nature of hydrogen gas. In the CTH approach, hydrogen gas is
65
replaced by hydrogen donors such as cyclohexadiene, hydrazine, formic acid, sodium
66
formate, ammonium formate, phosphinic acid or sodium hypophosphite in the presence of
67
suitable catalyst. Initial studies related to CTH were based on the use of homogeneous
68
catalyst. Fedeli et al. [1] investigated the use of homogeneous catalyst in the form of chelates
69
derived from the Schiff bases of the 2,2-dialkyl propylene-1,3-diamine with salicylaldehyde
70
for transfer hydrogenation of soybean oil. Typically, homogeneous catalyst offer
71
disadvantages due to separation and recycling issues and hence the focus shifted to the use of
72
heterogeneous catalyst offer advantage of comparatively easy recovery and recycle. Banerjee
73
et al. [2] investigated the transfer hydrogenation of 4-Nitrodiphenylamine in the presence of
74
two types of catalyst and reported that palladium is more active catalyst than Raney nickel.
4 75
Similarly, Zhang et al. [3] reported that Pd supported on activated carbon exhibits higher
76
activity for the catalytic transfer hydrogenation of phenol as compared to Pd nanoparticles
77
supported over other supports such as TiO2, Al2O3, TiO2-carbon composites. Tike et al. [4]
78
also studied the effect of using different catalysts such as Pd/Al2O3, Pd/C and Ru/C for
79
transfer hydrogenation of soybean oil and reported that 5 wt. % Pd/C has higher catalytic
80
activity as compared to other types investigated in the work. It was also reported that Pd/C as
81
catalyst resulted in the desired control over the formation of stearic acid as well as trans
82
isomer effectively enabling selective hydrogenation of edible oils as compared to the
83
conventional high pressure hydrogenation approach. It is also important to understand that
84
some of the hydrogen transfer agents require high temperatures for appreciable conversion
85
making the overall costs much higher. For example, Šmidovnik et al. [5] reported that
86
catalytic transfer hydrogenation of soybean oil in water using 10 wt. % Pd/C catalyst and
87
sodium formate as hydrogen donor was more effective at higher temperatures (investigations
88
over the range of 50-80°C). Tike et al. [4] also reported that as temperature increases the
89
extent of hydrogenation increases. Apart from temperature and catalyst, the type of hydrogen
90
donor and solvent also plays a major role in deciding the progress of the reaction. Šmidovnik
91
et al. [6] studied selective transfer hydrogenation of soybean oil over Pd/C catalyst in various
92
solvents using different hydrogen donors and reported that best results were obtained in
93
aqueous solution with sodium formate as hydrogen donor. Šmidovnik et al. [7] investigated
94
the kinetics of selective transfer hydrogenation using sodium formate as hydrogen donor at
95
different concentrations and also studied the effect of addition of emulsifier. The main focus
96
was on understanding the effect of donor concentration and the role of diffusion effects. It has
97
been observed that CTH processing typically requires higher temperature and also much
98
higher reaction times. Thus, the use of process intensification approaches with possible
99
benefits of reduced reaction times and temperatures can make the process efficient and
5 100
economical. Considering these aspects, the present work has focused on the use of ultrasound
101
as a process intensification approach for CTH based on the use of Pd/C as the catalyst, which
102
forms the main novelty of the present work.
103
Use of ultrasound offers immense potential as process intensification approach based
104
on the physical and chemical effects generated due to cavitation induced by the passage of
105
ultrasound. Typically, ultrasound is propagated via a series of compression and rarefaction
106
cycles induced in the molecules of the liquid medium. At sufficiently high power, the
107
negative pressure in the rarefaction cycle exceeds the attractive forces of the molecules of the
108
liquid required to hold them intact and cavities are formed. These cavities grow over a few
109
cycles taking in some vapour from the medium (rectified diffusion) and reach an equilibrium
110
size where the frequency of bubble resonance matches the applied sound frequency. The
111
acoustic field experienced by the bubble is not stable because of the interference of other
112
bubbles, which are continuously forming, growing or resonating. As a result, some bubbles
113
after expansion to an unstable size collapse violently generating intense local heating and
114
high pressures for very short lifetimes [8]. In addition to the generation of extreme conditions
115
within the bubble, there are also dominant physical effects produced as a result of the rapid
116
collapse of the cavitating bubble. The physical effects such as liquid streaming and
117
turbulence can break the agglomerates of solid and also remove the passive layers of
118
materials to give a larger and active surface area for the reaction to progress at faster rate [9-
119
10]. Due to these reasons, application of ultrasound can give intensified processing (lower
120
reaction times) under mild reaction conditions and with no/minimum side reactions leading to
121
higher selectivity and yields for the desired product. Many catalytic, non-catalytic organic
122
reactions have been reported to be intensified successfully using ultrasound [8, 10]. For
123
example, Xun et al. [11] investigated the ultrasound assisted hydrogenation of nitroarenes to
124
corresponding N-arylhydroxylamines using zinc as catalyst and ammonium formate as
6 125
hydrogen donor in acetonitrile under ambient conditions. An analysis of the literature also
126
revealed that there is not much literature available on ultrasound assisted catalytic transfer
127
hydrogenation of vegetable oils based on the use of Pd/C catalyst (which has been reported to
128
be most effective catalyst for conventional processing as discussed earlier). Also there has not
129
been much study dealing with understanding the effect of operating parameters or the
130
processing strategy to control the amount of stearic acid and trans-isomer formation.
131
Considering this analysis, the present work deals with an in depth study into understanding
132
the effect of operating parameters such as ultrasound power, temperature, type of donors,
133
donor concentration and catalyst loading on the progress of reaction including the analysis of
134
the trans-isomer formation.
135 136
2. Materials and methods
137
2.1 Materials
138
The refined soybean oil, obtained from Sahkari Bhandar, Matunga, Mumbai, India was used
139
for hydrogenation. The catalyst Pd/C (5 wt. % loading) with matrix activated carbon support
140
was obtained from Sigma Aldrich, India. The hydrogen donors (ammonium formate,
141
potassium formate, sodium formate and formic acid), Wij’s solution (1N), carbon
142
tetrachloride (AR), potassium iodide, sodium thiosulphate were obtained from S.D. fine
143
chemicals, Mumbai All chemicals and solvents used for product analysis were of high purity,
144
and used as received without any further processing.
145 146
2.2 Experimental procedure
147
0.012 mol (10.8-11 gm) of soybean oil and 0.32 mol of donor dissolved in 50 ml water (20 g
148
of ammonium formate in 50 ml water) were taken in a glass round bottom flask. The flask
149
was immersed in a thermostatically controlled bath. 0.22 g of Pd/C catalyst (2% w/w of oil)
7 150
was added after the desired temperature was obtained. Reaction was carried out for 1h in the
151
presence of mechanical stirring using teflon impeller at constant speed of rotation as 400 rpm.
152
The progress of the hydrogenation reaction was monitored by determining the iodine value
153
(IV) and fatty acid composition of samples removed periodically during the process. The
154
iodine value is calculated using equation 1. Besides iodine value, gas chromatography (GC)
155
analysis of some samples at optimum conditions was also performed to determine the fatty
156
acid composition after hydrogenation. Iodine Value =
( B - S ) × N of Na2S2O3 × 0.127g/meq × 100
(1)
Weight of Sample (g)
157 158 159 160 161
Where, B: V ml of Na2S2O3 volume for blank S: V ml of Na2S2O3 volume for sample
162
Ultrasonic bath (Model 6.5l200 H, Dakshin, India, 4.5 L capacity) with the internal
163
dimensions of 300 mm × 150 mm × 150 mm and four transducers placed at the bottom was
164
used as a source of ultrasonic irradiations in the present study for the ultrasound assisted
165
approach. The reaction was performed in 50 mL round bottom flask equipped with teflon
166
impeller connected to glass rod. The whole assembly of the glass reactor was kept in the
167
ultrasonic bath having different operating frequency of 22 kHz and 40 kHz with maximum
168
rated power of 200 W. The position of the reactor in the ultrasonic bath was fixed at the
169
centre of the vessel as per the earlier results demonstrating maximum cavitational activity at
170
this position [12]. The effect of operating parameters was investigated by performing number
171
of experiments at different temperatures ranging between 30 to 70 °C and power dissipation
172
levels over the range of 40 W to 120 W using different hydrogen donors such as formic acid,
173
sodium formate, ammonium formate etc. The effect of different catalyst loading ranging from
8 174
1 % (w/w) to 2.5 % (w/w), donor concentration over the range of 0.16 mol/ 50 ml H2O to
175
0.40 mol/ 50 ml H2O as well as water content in reaction also been investigated.
176
During the catalytic transfer hydrogenation, following transformations are possible
177
though it is always desirable to have less amount of stearic acid as well as linolenic acid and
178
higher concentration of linoleic and oleic acid.
179
C(18:3)
C(18:2) + C(18:1) + C(18:0)
180
C(18:2)
C(18:1) + C(18:0)
181
C(18:1)
C(18:0)
C(18:3) C(18:2) C(18:1) C(18:0)
Linolenic acid Linoleic aid Oleic acid Stearic acid
182 183
2.3 Analysis
184
Samples were withdrawn at different time intervals during hydrogenation. The withdrawn
185
samples, which contain oil, were extracted with n-hexane and separated from the aqueous
186
phase. After filtration of the catalyst Pd/C, n-hexane was evaporated and the reaction
187
products were analyzed by Wijj’s method to find the iodine value (IV), which determines the
188
degree of unsaturation [13]. As hydrogenation occurs, IV typically decreases. For quantitative
189
analysis of the fatty acids, methyl esters were prepared from hydrogenated soybean oil using
190
BF3-Methanol and gas chromatographically analyzed using BPX-70 (70% cyanopropyl
191
polysilphenylene–siloxane)
192
chromatograph (model Chemito 1000, Chemito Technologies Pvt. ltd., Mumbai, India) with a
193
flame ionization detector (FID). The column was operated over the range of 120–230°C at
194
3°C/min rate with hydrogen as carrier gas. Injector ports and detector were held at 250 and
195
260°C, respectively. This analysis allowed establishing the data of all kinds of fatty acid
196
methyl esters and geometrical cis–trans isomers quantitatively. It is important to know the
197
concentration of cis and trans isomers separately as the formation of the trans isomer needs to
198
be avoided as it is hazardous to human health.
199
The changes in the morphology of the commercial catalyst used in the work before and after
capillary
column
(30m×0.32mm.)
mounted
on
gas
9 200
the application in the ultrasound assisted selective catalytic transfer hydrogenation reaction
201
were established using scanning electron microscopy (SEM) analysis. SEM was performed
202
using JSM 6360 model obtained from JEOL, Japan
203 204
3. Results and Discussion
205
3.1 Fatty acid composition and properties of refined soybean oil
206
The composition of the refined oil has been analyzed using GC before the actual
207
hydrogenation so as to compare with the composition after hydrogenation and establish the
208
formation of different products (Table 1). As per the data represented in the table, the oil
209
contains 22.4 % of oleic acid, 54.2 % of linoleic acid and 6% of linolenic acid. The iodine
210
value of refined oil before hydrogenation was established as 134.
211
3.2 Effect of ultrasonic power
212
In order to achieve efficient cavitation for the maximum intensification of catalytic transfer
213
hydrogenation reaction using optimized operating power, experiments were performed in
214
ultrasonic bath at different power dissipation levels over the range of 60 W to 120 W at fixed
215
frequency of 22 kHz, 90% duty cycle and temperature of 30°C. The progress of the
216
hydrogenation reaction was monitored by the reduction in iodine value (IV). Iodine value
217
typically decreases with an increase in the extent of hydrogenation. An increase in the
218
ultrasonic power typically enhances the number of active cavitation bubbles, which would
219
result in higher cavitational intensity and hence there should be an increase in the rate of
220
reactions. The obtained results for the effect of power dissipation have been shown in Fig. 1.
221
As the irradiation power increased from 60 W to 100 W, it was observed that the iodine value
222
decreased from 112.82 to 95.2. Further increase in power to 120 W resulted in a higher final
223
iodine value as 98.86. Considering this analysis, 100 W is considered as optimum power and
224
used for the further experiments. The existence of optimum can be attributed to the fact that
10 225
at significantly higher power dissipation levels, there is formation of large number of
226
cavitation bubbles in the liquid, which creates cushioning effect leading to less intensity of
227
collapse and also presents barrier to the acoustic energy transmission into the reaction
228
mixture leading to lower energy availability for the cavitational effects. Similar results of
229
reduced cavitational activity beyond the optimum power can also be observed in the literature
230
[10,14-15]. Ammar et al. [14] studied ultrasound assisted Knoevenagel condensation of
231
benzaldehyde with ethyl cyanoacetate and reported that an increase in power intensity till an
232
optimum level of 30% led to relatively higher yield and also helped in reducing reaction time.
233
The product yield was also reported to decrease slightly with a further increase in ultrasound
234
power intensity beyond 30%. Dange et al. [15] also investigated the effect of power
235
dissipation for the ultrasound assisted synthesis of methyl butyrate using amberlyst-15 as a
236
catalyst over the power range of 50 to 145 W at constant frequency of 22 kHz. It was
237
reported that the conversion increased drastically over the range of 50 to 100 W and beyond
238
100 W, lower conversion was observed attributed to poor propagation of ultrasound waves
239
through the reaction mixture.
240
3.3 Effect of hydrogen donor type
241
Effect of type of donor on CTH of soybean oil was studied using different hydrogen donors.
242
Experiments were conducted in ultrasonic bath with constant irradiation power of 100 W,
243
frequency of 22 kHz, temperature of 30°C and constant donor loading of 0.32 mol (20 g in 50
244
ml water). Typically formic acid and its salts or secondary alcohols have been reported to be
245
efficient hydrogen donors in the presence of palladium catalyst [16-17], mostly attributed to
246
the ease of availability and handling. Also, these salts are true hydrogen transfer agents (no
247
hydrogen gas is released in the course of the reactions, and thus stoichiometric amounts of
248
donor and acceptor can be used and no special safety precautions are necessary even in large-
249
scale applications). Fig. 2 depicts the observed results for the iodine value reduction using
11 250
different donors. It can be established from the figure that ammonium formate gives
251
minimum possible iodine value at the end of reaction amongst all the donors and hence can
252
be established as the best donor type. In the case of sodium and potassium formate, reaction
253
proceeds slowly as compared to ammonium formate which might be attributed to formation
254
of alkali salts in the reaction mixture (Na2CO3, K2CO3, NaHCO3, KHCO3), which might
255
affect adsorption of reactant and palladium hydride formation on the active catalyst [18].
256
Ammonium formate is also preferred over other salts of formic acid as it decomposes into H2,
257
CO2 and ammonia after reaction which can be easily washed out with water. Gaseous
258
ammonia evolved can be absorbed again in formic acid and recycled back for the reaction
259
[18]. An additional advantage of using ammonium formate would be that due to the higher
260
solubility in water, water can be used as solvent and can give a “greener” approach for
261
hydrogenation. Considering the best performance obtained with ammonium formate, it was
262
used as hydrogen donor for further experiments related to effect of donor loading on the
263
progress of reaction.
264
3.4 Effect of hydrogen donor loading
265
The donor loading is an important factor in deciding the progress of reaction, especially
266
considering the solubility in water which decides the availability of water taking part in the
267
reaction. Effect of donor loading was studied over the range of 0.16 mol/ 50 ml H2O to 0.40
268
mol/50 ml H2O at constant ultrasonic power of 100W, frequency of 22kHz, 90 % duty cycle,
269
temperature of 30°C with Pd/C loading as 2% (w/w) of soybean oil. Fig. 4 depicts the
270
reduction in iodine value with different initial concentrations of ammonium formate. It was
271
observed that as the quantum of donor increases the final iodine value decreases. Use of 0.16
272
mol/50 ml H2O and 0.24mol/ 50 ml H2O of ammonium formate resulted in much slower rate
273
of reaction. An increase in the donor concentration to 0.32 mol/ 50 ml water resulted in best
274
results but a further increase to 0.40 mol/ 50 ml water showed only marginal difference in the
12 275
final iodine values obtained at the end of reaction. At 0.40 mol/50 ml H2O concentration of
276
ammonium formate, the final iodine value was the minimum as 93.15. But from Table 2 it
277
can be also observed that an increase in the donor concentration from 0.32 mol/ 50 ml water
278
to 0.40 mol/ 50 ml resulted in slight increase in the stearic acid concentration. Considering
279
this analysis, 0.32 mol/ 50 ml water is considered as optimum donor loading for further sets
280
of experiments (higher stearic acid formation needs to be avoided).
281
3.5 Effect of temperature
282
Increase in temperature generally increases the kinetic rate constant in the conventional
283
reaction systems. On the other hand, the cavitational intensity is negatively affected by an
284
increase in the temperature and hence it is possible that an optimum temperature exists [10,
285
19]. The effect of temperature on ultrasound assisted CTH of soybean oil was studied by
286
conducting reactions at different temperatures as 30°C, 45°C, 60°C and 75°C (Fig. 4). Other
287
reaction conditions used for the study were ultrasonic power of 100W, frequency of 22 kHz,
288
duty cycle of 90%, ammonium formate loading of 0.32 mol/50 ml H2O and Pd/C loading of
289
2% (w/w) of soybean oil. It was observed that as temperature increased from 30°C to 60°C,
290
iodine value obtained after 1h decreased from 95.20 to 88.82. It was also observed from
291
results given in table 2 that minimum iodine value was obtained at high temperature but this
292
was also accompanied with higher amount of trans-isomer being formed, which is
293
undesirable. Also beyond 60°C, further increase in temperature to 75°C increased the final
294
iodine value to 90.00. The decrease in reaction rate above the temperature of 60°C can be
295
attributed to the fact that an increase in the temperature increases the vapour pressure of the
296
liquid medium leading to a less violent collapse [20]. Existence of optimum temperature has
297
also been reported for the conventional approach (without using ultrasound). Šmidovnik et al.
298
[6] investigated CTH at different temperatures and reported that under ambient conditions,
299
time required for achieving IV 90 was about 9 h, which decreased significantly with an
13 300
increase in the temperature till an optimum level. It was also reported that the minimum
301
formation of the trans-isomer dominated the selection of the optimum temperature.
302
3.6 Effect of catalyst loading
303
Pd/C is the most beneficial catalyst for the catalytic transfer hydrogenation [4]. The amount
304
of catalyst plays a very important role in deciding the progress of reaction and hence the
305
profitability of the process. In order to establish optimum amount of catalyst for maximum
306
benefits, experiments were performed at different catalyst loading ranging from 1 % (w/w) to
307
2.5 % (w/w) keeping all the other parameters constant. The obtained results are represented in
308
Fig. 5. It can be seen that as the catalyst loading increases, the final iodine value decreases
309
and the extent of decrease was significant till 2 % (w/w) catalyst loading. Iodine value after 1
310
h using 1% (w/w) catalyst loading was 109.96 and that obtained for 2 % (w/w) catalyst
311
loading was 95.20. Further increase in catalyst amount to 2.5 % (w/w) did not affect the
312
reaction rate significantly. At high solid loading there is a reduced transfer of ultrasound
313
energy due to attenuation and possible scattering of the incident waves which reduces the
314
cavitational intensity giving lower intensification effects and hence reduced conversion [15,
315
21]. Also there is a possibility of aggregation of catalyst particles decreasing the available
316
surface area [21]. Considering the results obtained in the study, catalyst loading of 2 % (w/w)
317
was established as the optimum.
318
3.7 Effect of water quantity
319
When transfer hydrogenation at an acceptor (A) is performed in an aqueous solution, water is
320
involved in the reaction mechanism to abstract CO2 as HCO3 as represented in the equations:
321 322
Effect of quantity of water was studied over the range of 20 to 80 ml and the obtained results
323
have been given in Fig. 6. It can be seen from the figure that increasing dilution of formate
14 324
solution using higher water resulted in higher reduction in the iodine value (IV) confirming
325
higher extent of hydrogenation. With 20 ml water, the IV after 1 h was 100.61 whereas for
326
the case of 80 ml water, the iodine value was 91.92. The reason of enhanced reaction is that
327
water serves as a medium for contact of the hydrogen donor with the metal and the substrate
328
by forming a thin film of formate solution on the surface of the catalyst [22]. It is also
329
important to understand that optimum water is required (though not observed in the present
330
study) as beyond the optimum loading, any excess water will compete with the donor for the
331
active sites on the catalyst surface leading to lower availability of donors and hence lower
332
rates [23].
333
3.8 Fatty acid composition analysis after the reaction
334
The quantitative analysis for the fatty acids after the reaction has been shown in Table 2.
335
Comparison of catalytical transfer hydrogenation experiments at different conditions was
336
performed in terms of the desired specification of the hydrogenated product. It was observed
337
that ultrasound assisted CTH process with 100 W, 30°C, 0.32 mol/ 50 ml water and 2%
338
(w/w) catalyst loading as the operating conditions resulted in the minimum quantum of trans-
339
isomer. It is well known that formation of trans-isomer increases with an increase in
340
temperature [4]. Consequently, the ultrasound assisted CTH process was found to be quite
341
good as it offered selective hydrogenation with lower trans-isomer compared to high pressure
342
catalytic hydrogenation, which is the conventional approach (Table 3).
343
3.9 Comparison of the ultrasound assisted CTH with the conventional approach
344
The obtained best conditions in the present work for the approach of ultrasound assisted CTH
345
were operating temperature of 30 °C, ammonium formate as the donor at loading of 0.32 mol/
346
50 ml water and catalyst loading of 2% (w/w). Under these operating conditions, the
347
maximum decrease in the iodine yield was observed to be from 135 to 95 in 60 min as the
348
reaction time. Under the conventional approach, as per the reports of Tike and Mahajani [4],
15 349
for obtaining similar reduction in the iodine value, the required time was 90 min and the
350
temperature was 90 °C. Considering this comparison, the clear process intensification
351
benefits from the use of ultrasound can be established as the reduction in the reaction time by
352
33% and significant reduction in the temperature (90 °C to 30 °C) which can direct toward an
353
economical process synthesis route. The use of ultrasound results in cavitating conditions and
354
mainly the physical effects as intense turbulence and liquid circulation are beneficial for
355
enhancing the rate of heterogeneously catalyzed CTH. The turbulence promotes the rate of
356
mass transfer of the reactants toward the catalytic surface and also helps in maintaining the
357
surface of the catalyst clean thereby giving enhanced reaction rates.
358
3.10 Effect of ultrasound on catalyst morphology
359
The changes in morphology of the commercial catalyst before and after the use in ultrasound
360
assisted selective catalytic transfer hydrogenation reaction were established using the SEM
361
analysis and obtained images have been represented in Fig. 7 (a & b). The comparison of the
362
two catalysts revealed that the particle size of spent catalyst was lower attributed to the
363
cavitation effects. A reduction in the particle size means that higher surface area of catalyst is
364
available leading to higher reaction rates. It can be also seen that the roughness of the catalyst
365
is increased which can lead to better adsorption characteristics and higher catalytic activity.
366
Besides these effects, no other significant differences in surface morphology of both the
367
catalysts were observed.
368
4. Conclusions
369
Ultrasound assisted CTH of soybean oil was successfully performed using Pd/C (5 wt.
370
% loading) with matrix activated carbon support as a catalyst and water as solvent.
371
Ammonium formate was found to be an effective hydrogen donor for the ultrasound assisted
372
CTH of soybean oil. Excellent progress of hydrogenation was observed even at 30°C which
373
is much lower compared to the conventional approach which requires 90° C for the reaction
16 374
to progress at sustainable rate. The best conditions for maximum benefits were irradiation
375
power of 100W, duty cycle of 90% with ammonium formate loading as 0.32 mol / 50 ml
376
water and 2% (w/w) Pd/C loading. It was also established that the optimum conditions should
377
not only give higher reduction in the iodine value but also minimum formation of the stearic
378
acid as well as trans – isomer. Effect of temperature clearly established that the desired
379
optimum to maintain minimum trans-isomer formation might lead to lower iodine value
380
reduction. It has been also demonstrated that ultrasound assisted approach offered good
381
selectivity giving complete reduction of linolenic acid with a slight formation of stearic acid
382
(within the acceptable limits). Also the formation of trans-isomers was lower during
383
ultrasound assisted CTH of soybean oil at ambient temperature as compared to the
384
hydrogenation using hydrogen which is typically performed under conditions of high
385
pressure and temperature. Overall, the work demonstrated effective approach of
386
intensification of CTH based on the use of ultrasound with excellent benefits in terms of
387
lower reaction time and temperature as well as more importantly the desired product
388
characteristics.
389 390
5. References
391
1.
392
Fette, Seifen, Anstrichm., 78 (1976) 30-34
393
2.
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Reactions of 4-Nitrodiphenylamine, Appl. Catal. 59 (1990) l-12.
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3.
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phenol on supported Pd catalysts using formic acid as an alternative hydrogen source, Catal.
397
Today 234 (2014) 133–138.
E. Fedeli, G. Jacini, Homogeneous Selective Catalytic Hydrogenation of Soybean Oil,
A. A. Banerjee, D. Mukesh, Heterogeneous Catalytic Transfer Hydrogenation
D. Zhang, F. Ye, T. Xue, Y.Guan, Y. Meng, Y. Shanghai, Transfer hydrogenation of
17 398
4.
M. A. Tike, V. V. Mahajani Studies in catalytic transfer hydrogenation of soybean oil
399
using ammonium formate as donor over 5% Pd/C catalyst, Chem. Eng. J. 123 (2006) 31–41.
400
5.
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soybean oil, Chem. Eng. J. 51(1993) B51–B56.
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6.
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Am. Oil Chem. Soc. 69 (1992) 405–409.
404
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hydrogenation of soybean oil, J. Am. Oil Chem. Soc. 71 (1994) 507–511.
406
8.
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443-451.
408
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water or biphasic aqueous systems under sonochemical conditions : A review on catalytic
410
effects, Catal. Commun. 63 (2015) 2-9.
411
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chemical synthesis using ultrasound, Ultrason. sonochem. 36 (2017) 527-543.
413
11.
414
highly efficient reduction of nitroarenes to corresponding N-Arylhydroxylamines, Chem.
415
Res. Chinese Universities 25(2009), 183—188.
416
12.
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extraction of mangiferin from Mangifera indica leaves, Ultrason. Sonochem. 21 (2014) 606–
418
611.
419
13.
420
Press, Oxford, (1979) pp. 42–48
A. Šmidovnik, I. Plazl, T. Koloini, Kinetics of catalytic transfer hydrogenation of
A. Šmidovnik, A. Stimac, J. Kobe, Catalytic transfer hydrogenation of soybean oil, J.
A. Šmidovnik, J. Kobe, S. Leskovsek, T. Koloini, Kinetics of catalytic transfer
T. J. Mason, Ultrasound in synthetic organic chemistry, Chem. Soc. Rev. 26 (1997)
G. Cravotto, E. Borretto, M. Oliverio, A. Procopio, A. Penoni, Organic reactions in
S. V. Sancheti and P. R. Gogate, A review of engineering aspects of intensification of
S. Q. Xun, L. Rong-wen, H. Xin-yu, L. Lian-hai and Z. Shu-fen, Ultrasound-assisted
V.M. Kulkarni, V.K. Rathod, Mapping of an ultrasonic bath for ultrasound assisted
C. Paquat, Standard Methods for the Analysis of Oils, Fats and Derivatives, Pergamon
18 421
14.
H. B. Ammar, M. Chtourou, M.H. Frikha, M. Trabelsi, Green condensation reaction
422
of aromatic aldehydes with active methylene compounds catalyzed by anion-exchange resin
423
under ultrasound irradiation, Ultrason. Sonochem. 22 (2015) 559–564.
424
15.
425
Butyrate using Heterogeneous Catalyst, Ultrason. Sonochem. 26 (2015) 257–264
426
16.
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with alcohols, J. Am. Oil Chem. Soc., 43 (1966) 119-121.
428
17.
429
transfer from lithium formate in the presence of ruthenium and rhodium complexes,Croat.
430
Chem. Acta, 63 (1990) 203-206.
431
18.
432
solid sodium formate in the presence of palladium on carbon, J. Mol. Catal. 26 (1984) 321 –
433
326
434
19.
435
Eng. Chem. Res. 38 (1999)1215–1249.
436
20.
437
sonochemical reactors. Ultrason. Sonochem., 10 (2003) 325–330.
438
21.
439
synthesis from non-edible Schleichera triguga oil using heterogeneous catalyst : Kinetics and
440
thermodynamic analysis, Ultrason. Sonochem. 29 (2016) 288–298
441
22.
442
solvents in liquid-phase heterogeneous catalytic transfer reduction, Tetrahedron 48 (1992)
443
7735–7746
P. N. Dange, A. V. Kulkarni, V.K. Rathod, Ultrasound Assisted Synthesis of Methyl
H. N. Basu, M. M. Chakrabarty, Studies on conjugated hydrogenation: Nickel catalyst
R. Marčec, Catalytic hydro-dehalogenation of some organic halides by hydrogen
A. Zoran, Y. Sasson, Catalytic transfer hydrogenation of unsaturated compounds by
L. H. Thompson, L. K. Doraiswamy, Sonochemistry : Science and Engineering, Ind.
P. R.Gogate, A. M. Wilhelm, A.B. Pandit, Some aspects of the design of
A.N. Sarve, M.N. Varma, S.S. Sonawane, Ultrasound assisted two-stage biodiesel
A.F. Brigas, R.A.W. Johnstone, Metal- assisted reactions. Part 24. The importance of
19 444
23.
445
compounds by solid sodium formate in the presence of palladium on carbon. J. Mol. Cat. 26
446
(1984) 321-26
447
A. Zoran, Y. Sasson, J. Blum, Catalytic transfer hydrogenation of unsaturated
20 448
List of figures
449
Figure 1. Effect of ultrasound power on reduction in iodine value during ultrasound assisted
450
CTH of soybean oil. Frequency of 22 kHz, 90% duty cycle, temperature of 30°C, ammonium
451
formate concentration of 0.32 mol (20 g in 50 ml water), catalyst loading of 2% w/w of
452
soybean oil (0.22 g), soybean oil as 0.012 mol (10.8-11 ml).
453
Figure 2. Effect of type of donors on reduction in iodine value during CTH of soybean oil.
454
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
455
ammonium formate concentration of 0.32 mol/50 ml H2O, catalyst loading of 2% w/w of
456
soybean oil (0.22g), soybean oil as 0.012 mol (10.8-11 ml).
457
Figure 3. Effect of donor concentration on reduction in iodine value during CTH of soybean
458
oil. Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
459
ammonium formate as donor, catalyst loading of 2% w/w of soybean oil (0.22g), soybean oil
460
as 0.012 mol (10.8-11 ml).
461
Figure 4. Effect of temperature on reduction in iodine value during CTH of soybean oil.
462
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, ammonium formate
463
concentration of 0.32 mol/ 50 ml water, catalyst loading of 2% w/w of soybean oil (0.22g),
464
soybean oil as 0.012 mol (10.8-11 ml).
465
Figure 5. Effect of catalyst loading on reduction in iodine value during CTH of soybean oil.
466
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
467
ammonium formate concentration of 0.32 mol/ 50 ml water, Pd/C catalyst, oil (0.22g),
468
soybean oil as 0.012 mol (10.8-11 ml).
469
Figure 6. Effect of amount of water on reduction in iodine value during CTH of soybean oil.
470
Ultrasound power of 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
471
ammonium formate concentration of 0.32 mol, Pd/C catalyst, oil (0.22g), soybean oil as
472
0.012 mol (10.8-11 ml).
21 473
Figure 7. SEM images of Pd/C (5 wt% loading) with matrix activated carbon support. (a)
474
fresh catalyst (b) Spent catalyst after first cycle
475 476
List of tables
477
Table 1. Fatty acid composition and properties of refined soybean oil
478
Table 2. Effect of operating parameters and hydrogenation on the fatty acid composition as
479
well as formation of trans-isomers (geometrical) during soybean oil hydrogenation
480
Table 3. Fatty acid composition of soybean oil after hydrogenation using gaseous high
481
pressure hydrogen [4]
482
22
140
60 W 80 W
130
100 W
120 W Iodine value
120 110 100 90 80 0
483
15
30 Time (min)
45
60
484
Figure 1. Effect of ultrasound power on reduction in iodine value during ultrasound assisted
485
CTH of soybean oil. Frequency of 22 kHz, 90% duty cycle, temperature of 30°C, ammonium
486
formate concentration of 0.32 mol (20 g in 50 ml water), catalyst loading of 2% w/w of
487
soybean oil (0.22 g), soybean oil as 0.012 mol (10.8-11 ml).
488
23 140
Potassium formate Sodium Formate
130
Ammonium Formate 120 Iodine value
Formic Acid
110
100
90
80 0
15
30
45
60
Time (min)
489 490
Figure 2. Effect of type of donors on reduction in iodine value during CTH of soybean oil.
491
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
492
ammonium formate concentration of 0.32 mol/50 ml H2O, catalyst loading of 2% w/w of
493
soybean oil (0.22g), soybean oil as 0.012 mol (10.8-11 ml).
494 495 496 497 498 499 500 501 502 503 504 505
24
140
0.16 moles 0.24 moles
130
0.32 moles 0.40 moles
Iodine Value
120
110
100
90
80 0
15
30
45
60
506 507
Figure 3. Effect of donor concentration on reduction in iodine value during CTH of soybean
508
oil. Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
509
ammonium formate as donor, catalyst loading of 2% w/w of soybean oil (0.22g), soybean oil
510
as 0.012 mol (10.8-11 ml).
511
25 512 140
30°C 45°C
130
60°C 75°C
Iodine Value
120
110
100
90
80 0
513
15
30 Time (min.)
45
60
514
Figure 4. Effect of temperature on reduction in iodine value during CTH of soybean oil.
515
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, ammonium formate
516
concentration of 0.32 mol/ 50 ml water, catalyst loading of 2% w/w of soybean oil (0.22g),
517
soybean oil as 0.012 mol (10.8-11 ml).
518 519
26 140
1 % (w/w) 130
1.5 % (w/w)
2 % (w/w) Iodine Value
120
2.5 % (w/w)
110 100 90 80 0
15
30
45
60
520 521
Figure 5. Effect of catalyst loading on reduction in iodine value during CTH of soybean oil.
522
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
523
ammonium formate concentration of 0.32 mol/ 50 ml water, Pd/C catalyst, oil (0.22g),
524
soybean oil as 0.012 mol (10.8-11 ml).
525
27 526 527 140 130
Iodine Value
120
20 ml 110
50 ml 80 ml
100 90 80 0
15
30
45
60
528 529 530
Figure 6. Effect of amount of water on reduction in iodine value during CTH of soybean oil.
531
Ultrasound power of 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
532
ammonium formate concentration of 0.32 mol, Pd/C catalyst, oil (0.22g), soybean oil as
533
0.012 mol (10.8-11 ml).
534 535 536 537 538 539
28
540 541 542 543 544
545
(a)
(b)
Figure 7. SEM images of Pd/C (5 wt% loading) with matrix activated carbon support. (a) fresh catalyst (b) Spent catalyst after first cycle
29
546
Table 1. Fatty acid composition and properties of refined soybean oil
547 %
C12:0
C14:0
C16:0
C18:0
C18:1
C18:2
C18:3
C20:0
C22:0
C24:0
0.2
0.4
11.6
4.3
22.4
54.2
6
0.4
0.3
0.2
Fatty acid composition
548
Iodine value (Wijj’s) = 134
549
Table 2. Effect of operating parameters and hydrogenation processes on the fatty acid
550
composition as well as formation of trans-isomers (geometrical) during soybean oil
551
hydrogenation Sample
US
Catalyst
Donar
Temp. after
Power
Loading
552
(W)
Std.
NA
1
C18:1
C18:3
(%)
(%)
Cis
Trans
(%)
Conc.
(° C) 1h
C18:2 (%)
C18:0
IV
%(w/w)
(moles)
NA
NA
NA
4.3
22.4
55.5
0
6
135
100
30°
2
0.32
6
32.3
46.5
0.5
1.6
95.50
2
100
30°
2
0.4
6.8
37.3
42.3
0.7
1.2
93.15
3
100
30°
2.5
0.32
7.5
37.5
41.9
0.6
0.8
92.00
4
100
60°
2
0.32
12.0
34.4
40
1.1
0.6
88.82
30
553
Table 3. Fatty acid composition of soybean oil after hydrogenation using gaseous high
554
pressure hydrogen [4] Sr. No. Conditions
C18:0
C18:1
C18:2 (%)
C18:3
(min)
(%)
(%)
Cis
Trans
(%)
IV
1
High-pressure (Ni; 150 ◦C)
20
7.5
37.6
37.3
2
1.9
110.7
2
High-pressure (5% Pd/C; 150
5
7.2
37.4
37.6
3.6
0.52
110.3
◦C)
555 556 557
Time
31 558
HIGHLIGHTS:
559
First report of intensification of heterogeneously catalyzed transfer hydrogenation using
560
ultrasound
561
562
Significant reduction in the temperature and reaction as the key benefits
563
Selecting best set of operating conditions also helps in minimizing the formation of hazardous
564 565 566 567 568
Understanding the engineering aspects in terms of effect of operating parameters
trans-isomer
S1350-4177(17)30096-2 http://dx.doi.org/10.1016/j.ultsonch.2017.03.004 ULTSON 3581
To appear in:
Ultrasonics Sonochemistry
Received Date: Revised Date: Accepted Date:
31 December 2016 5 March 2017 5 March 2017
Please cite this article as: S.V. Sancheti, P.R. Gogate, Ultrasound assisted selective catalytic transfer hydrogenation of soybean oil using 5% Pd/C as catalyst under ambient conditions in water, Ultrasonics Sonochemistry (2017), doi: http://dx.doi.org/10.1016/j.ultsonch.2017.03.004
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1 1
Ultrasound assisted selective catalytic transfer hydrogenation of soybean oil using 5%
2
Pd/C as catalyst under ambient conditions in water
3 4 5 6 7
Sonam V. Sancheti, Parag R. Gogate*
8 9 10 11 12
Chemical Engineering Department,
13
Institute of Chemical Technology,
14
Matunga, Mumbai – 400 019, India
15 16 17 18 19 20 21
*
22
E-mail address: [email protected]
23
Tel.: +91 22 3361 2024
24 25
Corresponding author
Fax: +91 22 3361 1020
2 26
Abstract
27
Catalytic transfer hydrogenation (CTH) is an alternative approach that does not require the
28
use of potentially dangerous hydrogen gas. Pd/C is the most favoured catalyst for the
29
selective hydrogenation of soybean oil yielding lower extent of formation of stearic acid and
30
trans-isomer, which have adverse health effects. The present work deals with intensification
31
of catalytic transfer hydrogenation of soybean oil in the presence of 5 wt. % Pd/C using
32
ultrasound under ambient reaction conditions. The effect of important operating parameters
33
such as ultrasound power, temperature, type of hydrogen donor, type of formic acid salts,
34
catalyst loading and donor concentration on the progress of reaction has been investigated. It
35
was established that the maximum extent of hydrogenation as indicated by reduction in
36
iodine value from 135 to 95 was observed under optimized conditions of irradiation power as
37
100 W, 22 kHz frequency, 90% duty cycle, ammonium formate concentration of 0.32 mol /
38
50 ml water and 2% (w/w) Pd/C loading at ambient temperature and pressure in the presence
39
of solvent. The approach also offered excellent selectivity with controlled trans-isomer
40
formation as compared to the conventional approach of high pressure hydrogenation. Overall,
41
the work has successfully demonstrated process intensification benefits based on ultrasound
42
for the Pd/C catalysed transfer hydrogenation of soybean oil.
43 44
Keywords: Ultrasound; Physical effects; Catalytic transfer hydrogenation (CTH); Soybean
45
oil; heterogeneous catalyst
46 47 48 49
3 50
1. Introduction
51
Soybean oil consists of mainly triglycerides of saturated and unsaturated fatty acids,
52
particularly with chain length over the range of C16–C18. Hydrogenation of soybean oil is
53
important process in oleochemical industry because of the wide range of applications of the
54
obtained derivatives for the production of margarine, frying oils, etc. Hydrogenation of oil
55
leads to increased melting point, improved color and oxidation properties of soybean oil. The
56
selective reduction of linolenic acid (C18:3) in the soybean oil has a prime importance as it
57
alters the flavour reversion of oil. The quality and physical properties of the final product
58
obtained after hydrogenation are affected by the number of double bonds present in the oil
59
represented by the iodine value (IV) and also cis–trans-isomer content in the fatty acid. The
60
trans-isomer has been reported to be undesirable for human diet due to the adverse health
61
effects.
62
The catalytic transfer hydrogenation (CTH) is a safe, simple and eco-friendly method
63
compared to the conventional hydrogenation where hydrogen gas is used offering handling
64
problems due to the explosive nature of hydrogen gas. In the CTH approach, hydrogen gas is
65
replaced by hydrogen donors such as cyclohexadiene, hydrazine, formic acid, sodium
66
formate, ammonium formate, phosphinic acid or sodium hypophosphite in the presence of
67
suitable catalyst. Initial studies related to CTH were based on the use of homogeneous
68
catalyst. Fedeli et al. [1] investigated the use of homogeneous catalyst in the form of chelates
69
derived from the Schiff bases of the 2,2-dialkyl propylene-1,3-diamine with salicylaldehyde
70
for transfer hydrogenation of soybean oil. Typically, homogeneous catalyst offer
71
disadvantages due to separation and recycling issues and hence the focus shifted to the use of
72
heterogeneous catalyst offer advantage of comparatively easy recovery and recycle. Banerjee
73
et al. [2] investigated the transfer hydrogenation of 4-Nitrodiphenylamine in the presence of
74
two types of catalyst and reported that palladium is more active catalyst than Raney nickel.
4 75
Similarly, Zhang et al. [3] reported that Pd supported on activated carbon exhibits higher
76
activity for the catalytic transfer hydrogenation of phenol as compared to Pd nanoparticles
77
supported over other supports such as TiO2, Al2O3, TiO2-carbon composites. Tike et al. [4]
78
also studied the effect of using different catalysts such as Pd/Al2O3, Pd/C and Ru/C for
79
transfer hydrogenation of soybean oil and reported that 5 wt. % Pd/C has higher catalytic
80
activity as compared to other types investigated in the work. It was also reported that Pd/C as
81
catalyst resulted in the desired control over the formation of stearic acid as well as trans
82
isomer effectively enabling selective hydrogenation of edible oils as compared to the
83
conventional high pressure hydrogenation approach. It is also important to understand that
84
some of the hydrogen transfer agents require high temperatures for appreciable conversion
85
making the overall costs much higher. For example, Šmidovnik et al. [5] reported that
86
catalytic transfer hydrogenation of soybean oil in water using 10 wt. % Pd/C catalyst and
87
sodium formate as hydrogen donor was more effective at higher temperatures (investigations
88
over the range of 50-80°C). Tike et al. [4] also reported that as temperature increases the
89
extent of hydrogenation increases. Apart from temperature and catalyst, the type of hydrogen
90
donor and solvent also plays a major role in deciding the progress of the reaction. Šmidovnik
91
et al. [6] studied selective transfer hydrogenation of soybean oil over Pd/C catalyst in various
92
solvents using different hydrogen donors and reported that best results were obtained in
93
aqueous solution with sodium formate as hydrogen donor. Šmidovnik et al. [7] investigated
94
the kinetics of selective transfer hydrogenation using sodium formate as hydrogen donor at
95
different concentrations and also studied the effect of addition of emulsifier. The main focus
96
was on understanding the effect of donor concentration and the role of diffusion effects. It has
97
been observed that CTH processing typically requires higher temperature and also much
98
higher reaction times. Thus, the use of process intensification approaches with possible
99
benefits of reduced reaction times and temperatures can make the process efficient and
5 100
economical. Considering these aspects, the present work has focused on the use of ultrasound
101
as a process intensification approach for CTH based on the use of Pd/C as the catalyst, which
102
forms the main novelty of the present work.
103
Use of ultrasound offers immense potential as process intensification approach based
104
on the physical and chemical effects generated due to cavitation induced by the passage of
105
ultrasound. Typically, ultrasound is propagated via a series of compression and rarefaction
106
cycles induced in the molecules of the liquid medium. At sufficiently high power, the
107
negative pressure in the rarefaction cycle exceeds the attractive forces of the molecules of the
108
liquid required to hold them intact and cavities are formed. These cavities grow over a few
109
cycles taking in some vapour from the medium (rectified diffusion) and reach an equilibrium
110
size where the frequency of bubble resonance matches the applied sound frequency. The
111
acoustic field experienced by the bubble is not stable because of the interference of other
112
bubbles, which are continuously forming, growing or resonating. As a result, some bubbles
113
after expansion to an unstable size collapse violently generating intense local heating and
114
high pressures for very short lifetimes [8]. In addition to the generation of extreme conditions
115
within the bubble, there are also dominant physical effects produced as a result of the rapid
116
collapse of the cavitating bubble. The physical effects such as liquid streaming and
117
turbulence can break the agglomerates of solid and also remove the passive layers of
118
materials to give a larger and active surface area for the reaction to progress at faster rate [9-
119
10]. Due to these reasons, application of ultrasound can give intensified processing (lower
120
reaction times) under mild reaction conditions and with no/minimum side reactions leading to
121
higher selectivity and yields for the desired product. Many catalytic, non-catalytic organic
122
reactions have been reported to be intensified successfully using ultrasound [8, 10]. For
123
example, Xun et al. [11] investigated the ultrasound assisted hydrogenation of nitroarenes to
124
corresponding N-arylhydroxylamines using zinc as catalyst and ammonium formate as
6 125
hydrogen donor in acetonitrile under ambient conditions. An analysis of the literature also
126
revealed that there is not much literature available on ultrasound assisted catalytic transfer
127
hydrogenation of vegetable oils based on the use of Pd/C catalyst (which has been reported to
128
be most effective catalyst for conventional processing as discussed earlier). Also there has not
129
been much study dealing with understanding the effect of operating parameters or the
130
processing strategy to control the amount of stearic acid and trans-isomer formation.
131
Considering this analysis, the present work deals with an in depth study into understanding
132
the effect of operating parameters such as ultrasound power, temperature, type of donors,
133
donor concentration and catalyst loading on the progress of reaction including the analysis of
134
the trans-isomer formation.
135 136
2. Materials and methods
137
2.1 Materials
138
The refined soybean oil, obtained from Sahkari Bhandar, Matunga, Mumbai, India was used
139
for hydrogenation. The catalyst Pd/C (5 wt. % loading) with matrix activated carbon support
140
was obtained from Sigma Aldrich, India. The hydrogen donors (ammonium formate,
141
potassium formate, sodium formate and formic acid), Wij’s solution (1N), carbon
142
tetrachloride (AR), potassium iodide, sodium thiosulphate were obtained from S.D. fine
143
chemicals, Mumbai All chemicals and solvents used for product analysis were of high purity,
144
and used as received without any further processing.
145 146
2.2 Experimental procedure
147
0.012 mol (10.8-11 gm) of soybean oil and 0.32 mol of donor dissolved in 50 ml water (20 g
148
of ammonium formate in 50 ml water) were taken in a glass round bottom flask. The flask
149
was immersed in a thermostatically controlled bath. 0.22 g of Pd/C catalyst (2% w/w of oil)
7 150
was added after the desired temperature was obtained. Reaction was carried out for 1h in the
151
presence of mechanical stirring using teflon impeller at constant speed of rotation as 400 rpm.
152
The progress of the hydrogenation reaction was monitored by determining the iodine value
153
(IV) and fatty acid composition of samples removed periodically during the process. The
154
iodine value is calculated using equation 1. Besides iodine value, gas chromatography (GC)
155
analysis of some samples at optimum conditions was also performed to determine the fatty
156
acid composition after hydrogenation. Iodine Value =
( B - S ) × N of Na2S2O3 × 0.127g/meq × 100
(1)
Weight of Sample (g)
157 158 159 160 161
Where, B: V ml of Na2S2O3 volume for blank S: V ml of Na2S2O3 volume for sample
162
Ultrasonic bath (Model 6.5l200 H, Dakshin, India, 4.5 L capacity) with the internal
163
dimensions of 300 mm × 150 mm × 150 mm and four transducers placed at the bottom was
164
used as a source of ultrasonic irradiations in the present study for the ultrasound assisted
165
approach. The reaction was performed in 50 mL round bottom flask equipped with teflon
166
impeller connected to glass rod. The whole assembly of the glass reactor was kept in the
167
ultrasonic bath having different operating frequency of 22 kHz and 40 kHz with maximum
168
rated power of 200 W. The position of the reactor in the ultrasonic bath was fixed at the
169
centre of the vessel as per the earlier results demonstrating maximum cavitational activity at
170
this position [12]. The effect of operating parameters was investigated by performing number
171
of experiments at different temperatures ranging between 30 to 70 °C and power dissipation
172
levels over the range of 40 W to 120 W using different hydrogen donors such as formic acid,
173
sodium formate, ammonium formate etc. The effect of different catalyst loading ranging from
8 174
1 % (w/w) to 2.5 % (w/w), donor concentration over the range of 0.16 mol/ 50 ml H2O to
175
0.40 mol/ 50 ml H2O as well as water content in reaction also been investigated.
176
During the catalytic transfer hydrogenation, following transformations are possible
177
though it is always desirable to have less amount of stearic acid as well as linolenic acid and
178
higher concentration of linoleic and oleic acid.
179
C(18:3)
C(18:2) + C(18:1) + C(18:0)
180
C(18:2)
C(18:1) + C(18:0)
181
C(18:1)
C(18:0)
C(18:3) C(18:2) C(18:1) C(18:0)
Linolenic acid Linoleic aid Oleic acid Stearic acid
182 183
2.3 Analysis
184
Samples were withdrawn at different time intervals during hydrogenation. The withdrawn
185
samples, which contain oil, were extracted with n-hexane and separated from the aqueous
186
phase. After filtration of the catalyst Pd/C, n-hexane was evaporated and the reaction
187
products were analyzed by Wijj’s method to find the iodine value (IV), which determines the
188
degree of unsaturation [13]. As hydrogenation occurs, IV typically decreases. For quantitative
189
analysis of the fatty acids, methyl esters were prepared from hydrogenated soybean oil using
190
BF3-Methanol and gas chromatographically analyzed using BPX-70 (70% cyanopropyl
191
polysilphenylene–siloxane)
192
chromatograph (model Chemito 1000, Chemito Technologies Pvt. ltd., Mumbai, India) with a
193
flame ionization detector (FID). The column was operated over the range of 120–230°C at
194
3°C/min rate with hydrogen as carrier gas. Injector ports and detector were held at 250 and
195
260°C, respectively. This analysis allowed establishing the data of all kinds of fatty acid
196
methyl esters and geometrical cis–trans isomers quantitatively. It is important to know the
197
concentration of cis and trans isomers separately as the formation of the trans isomer needs to
198
be avoided as it is hazardous to human health.
199
The changes in the morphology of the commercial catalyst used in the work before and after
capillary
column
(30m×0.32mm.)
mounted
on
gas
9 200
the application in the ultrasound assisted selective catalytic transfer hydrogenation reaction
201
were established using scanning electron microscopy (SEM) analysis. SEM was performed
202
using JSM 6360 model obtained from JEOL, Japan
203 204
3. Results and Discussion
205
3.1 Fatty acid composition and properties of refined soybean oil
206
The composition of the refined oil has been analyzed using GC before the actual
207
hydrogenation so as to compare with the composition after hydrogenation and establish the
208
formation of different products (Table 1). As per the data represented in the table, the oil
209
contains 22.4 % of oleic acid, 54.2 % of linoleic acid and 6% of linolenic acid. The iodine
210
value of refined oil before hydrogenation was established as 134.
211
3.2 Effect of ultrasonic power
212
In order to achieve efficient cavitation for the maximum intensification of catalytic transfer
213
hydrogenation reaction using optimized operating power, experiments were performed in
214
ultrasonic bath at different power dissipation levels over the range of 60 W to 120 W at fixed
215
frequency of 22 kHz, 90% duty cycle and temperature of 30°C. The progress of the
216
hydrogenation reaction was monitored by the reduction in iodine value (IV). Iodine value
217
typically decreases with an increase in the extent of hydrogenation. An increase in the
218
ultrasonic power typically enhances the number of active cavitation bubbles, which would
219
result in higher cavitational intensity and hence there should be an increase in the rate of
220
reactions. The obtained results for the effect of power dissipation have been shown in Fig. 1.
221
As the irradiation power increased from 60 W to 100 W, it was observed that the iodine value
222
decreased from 112.82 to 95.2. Further increase in power to 120 W resulted in a higher final
223
iodine value as 98.86. Considering this analysis, 100 W is considered as optimum power and
224
used for the further experiments. The existence of optimum can be attributed to the fact that
10 225
at significantly higher power dissipation levels, there is formation of large number of
226
cavitation bubbles in the liquid, which creates cushioning effect leading to less intensity of
227
collapse and also presents barrier to the acoustic energy transmission into the reaction
228
mixture leading to lower energy availability for the cavitational effects. Similar results of
229
reduced cavitational activity beyond the optimum power can also be observed in the literature
230
[10,14-15]. Ammar et al. [14] studied ultrasound assisted Knoevenagel condensation of
231
benzaldehyde with ethyl cyanoacetate and reported that an increase in power intensity till an
232
optimum level of 30% led to relatively higher yield and also helped in reducing reaction time.
233
The product yield was also reported to decrease slightly with a further increase in ultrasound
234
power intensity beyond 30%. Dange et al. [15] also investigated the effect of power
235
dissipation for the ultrasound assisted synthesis of methyl butyrate using amberlyst-15 as a
236
catalyst over the power range of 50 to 145 W at constant frequency of 22 kHz. It was
237
reported that the conversion increased drastically over the range of 50 to 100 W and beyond
238
100 W, lower conversion was observed attributed to poor propagation of ultrasound waves
239
through the reaction mixture.
240
3.3 Effect of hydrogen donor type
241
Effect of type of donor on CTH of soybean oil was studied using different hydrogen donors.
242
Experiments were conducted in ultrasonic bath with constant irradiation power of 100 W,
243
frequency of 22 kHz, temperature of 30°C and constant donor loading of 0.32 mol (20 g in 50
244
ml water). Typically formic acid and its salts or secondary alcohols have been reported to be
245
efficient hydrogen donors in the presence of palladium catalyst [16-17], mostly attributed to
246
the ease of availability and handling. Also, these salts are true hydrogen transfer agents (no
247
hydrogen gas is released in the course of the reactions, and thus stoichiometric amounts of
248
donor and acceptor can be used and no special safety precautions are necessary even in large-
249
scale applications). Fig. 2 depicts the observed results for the iodine value reduction using
11 250
different donors. It can be established from the figure that ammonium formate gives
251
minimum possible iodine value at the end of reaction amongst all the donors and hence can
252
be established as the best donor type. In the case of sodium and potassium formate, reaction
253
proceeds slowly as compared to ammonium formate which might be attributed to formation
254
of alkali salts in the reaction mixture (Na2CO3, K2CO3, NaHCO3, KHCO3), which might
255
affect adsorption of reactant and palladium hydride formation on the active catalyst [18].
256
Ammonium formate is also preferred over other salts of formic acid as it decomposes into H2,
257
CO2 and ammonia after reaction which can be easily washed out with water. Gaseous
258
ammonia evolved can be absorbed again in formic acid and recycled back for the reaction
259
[18]. An additional advantage of using ammonium formate would be that due to the higher
260
solubility in water, water can be used as solvent and can give a “greener” approach for
261
hydrogenation. Considering the best performance obtained with ammonium formate, it was
262
used as hydrogen donor for further experiments related to effect of donor loading on the
263
progress of reaction.
264
3.4 Effect of hydrogen donor loading
265
The donor loading is an important factor in deciding the progress of reaction, especially
266
considering the solubility in water which decides the availability of water taking part in the
267
reaction. Effect of donor loading was studied over the range of 0.16 mol/ 50 ml H2O to 0.40
268
mol/50 ml H2O at constant ultrasonic power of 100W, frequency of 22kHz, 90 % duty cycle,
269
temperature of 30°C with Pd/C loading as 2% (w/w) of soybean oil. Fig. 4 depicts the
270
reduction in iodine value with different initial concentrations of ammonium formate. It was
271
observed that as the quantum of donor increases the final iodine value decreases. Use of 0.16
272
mol/50 ml H2O and 0.24mol/ 50 ml H2O of ammonium formate resulted in much slower rate
273
of reaction. An increase in the donor concentration to 0.32 mol/ 50 ml water resulted in best
274
results but a further increase to 0.40 mol/ 50 ml water showed only marginal difference in the
12 275
final iodine values obtained at the end of reaction. At 0.40 mol/50 ml H2O concentration of
276
ammonium formate, the final iodine value was the minimum as 93.15. But from Table 2 it
277
can be also observed that an increase in the donor concentration from 0.32 mol/ 50 ml water
278
to 0.40 mol/ 50 ml resulted in slight increase in the stearic acid concentration. Considering
279
this analysis, 0.32 mol/ 50 ml water is considered as optimum donor loading for further sets
280
of experiments (higher stearic acid formation needs to be avoided).
281
3.5 Effect of temperature
282
Increase in temperature generally increases the kinetic rate constant in the conventional
283
reaction systems. On the other hand, the cavitational intensity is negatively affected by an
284
increase in the temperature and hence it is possible that an optimum temperature exists [10,
285
19]. The effect of temperature on ultrasound assisted CTH of soybean oil was studied by
286
conducting reactions at different temperatures as 30°C, 45°C, 60°C and 75°C (Fig. 4). Other
287
reaction conditions used for the study were ultrasonic power of 100W, frequency of 22 kHz,
288
duty cycle of 90%, ammonium formate loading of 0.32 mol/50 ml H2O and Pd/C loading of
289
2% (w/w) of soybean oil. It was observed that as temperature increased from 30°C to 60°C,
290
iodine value obtained after 1h decreased from 95.20 to 88.82. It was also observed from
291
results given in table 2 that minimum iodine value was obtained at high temperature but this
292
was also accompanied with higher amount of trans-isomer being formed, which is
293
undesirable. Also beyond 60°C, further increase in temperature to 75°C increased the final
294
iodine value to 90.00. The decrease in reaction rate above the temperature of 60°C can be
295
attributed to the fact that an increase in the temperature increases the vapour pressure of the
296
liquid medium leading to a less violent collapse [20]. Existence of optimum temperature has
297
also been reported for the conventional approach (without using ultrasound). Šmidovnik et al.
298
[6] investigated CTH at different temperatures and reported that under ambient conditions,
299
time required for achieving IV 90 was about 9 h, which decreased significantly with an
13 300
increase in the temperature till an optimum level. It was also reported that the minimum
301
formation of the trans-isomer dominated the selection of the optimum temperature.
302
3.6 Effect of catalyst loading
303
Pd/C is the most beneficial catalyst for the catalytic transfer hydrogenation [4]. The amount
304
of catalyst plays a very important role in deciding the progress of reaction and hence the
305
profitability of the process. In order to establish optimum amount of catalyst for maximum
306
benefits, experiments were performed at different catalyst loading ranging from 1 % (w/w) to
307
2.5 % (w/w) keeping all the other parameters constant. The obtained results are represented in
308
Fig. 5. It can be seen that as the catalyst loading increases, the final iodine value decreases
309
and the extent of decrease was significant till 2 % (w/w) catalyst loading. Iodine value after 1
310
h using 1% (w/w) catalyst loading was 109.96 and that obtained for 2 % (w/w) catalyst
311
loading was 95.20. Further increase in catalyst amount to 2.5 % (w/w) did not affect the
312
reaction rate significantly. At high solid loading there is a reduced transfer of ultrasound
313
energy due to attenuation and possible scattering of the incident waves which reduces the
314
cavitational intensity giving lower intensification effects and hence reduced conversion [15,
315
21]. Also there is a possibility of aggregation of catalyst particles decreasing the available
316
surface area [21]. Considering the results obtained in the study, catalyst loading of 2 % (w/w)
317
was established as the optimum.
318
3.7 Effect of water quantity
319
When transfer hydrogenation at an acceptor (A) is performed in an aqueous solution, water is
320
involved in the reaction mechanism to abstract CO2 as HCO3 as represented in the equations:
321 322
Effect of quantity of water was studied over the range of 20 to 80 ml and the obtained results
323
have been given in Fig. 6. It can be seen from the figure that increasing dilution of formate
14 324
solution using higher water resulted in higher reduction in the iodine value (IV) confirming
325
higher extent of hydrogenation. With 20 ml water, the IV after 1 h was 100.61 whereas for
326
the case of 80 ml water, the iodine value was 91.92. The reason of enhanced reaction is that
327
water serves as a medium for contact of the hydrogen donor with the metal and the substrate
328
by forming a thin film of formate solution on the surface of the catalyst [22]. It is also
329
important to understand that optimum water is required (though not observed in the present
330
study) as beyond the optimum loading, any excess water will compete with the donor for the
331
active sites on the catalyst surface leading to lower availability of donors and hence lower
332
rates [23].
333
3.8 Fatty acid composition analysis after the reaction
334
The quantitative analysis for the fatty acids after the reaction has been shown in Table 2.
335
Comparison of catalytical transfer hydrogenation experiments at different conditions was
336
performed in terms of the desired specification of the hydrogenated product. It was observed
337
that ultrasound assisted CTH process with 100 W, 30°C, 0.32 mol/ 50 ml water and 2%
338
(w/w) catalyst loading as the operating conditions resulted in the minimum quantum of trans-
339
isomer. It is well known that formation of trans-isomer increases with an increase in
340
temperature [4]. Consequently, the ultrasound assisted CTH process was found to be quite
341
good as it offered selective hydrogenation with lower trans-isomer compared to high pressure
342
catalytic hydrogenation, which is the conventional approach (Table 3).
343
3.9 Comparison of the ultrasound assisted CTH with the conventional approach
344
The obtained best conditions in the present work for the approach of ultrasound assisted CTH
345
were operating temperature of 30 °C, ammonium formate as the donor at loading of 0.32 mol/
346
50 ml water and catalyst loading of 2% (w/w). Under these operating conditions, the
347
maximum decrease in the iodine yield was observed to be from 135 to 95 in 60 min as the
348
reaction time. Under the conventional approach, as per the reports of Tike and Mahajani [4],
15 349
for obtaining similar reduction in the iodine value, the required time was 90 min and the
350
temperature was 90 °C. Considering this comparison, the clear process intensification
351
benefits from the use of ultrasound can be established as the reduction in the reaction time by
352
33% and significant reduction in the temperature (90 °C to 30 °C) which can direct toward an
353
economical process synthesis route. The use of ultrasound results in cavitating conditions and
354
mainly the physical effects as intense turbulence and liquid circulation are beneficial for
355
enhancing the rate of heterogeneously catalyzed CTH. The turbulence promotes the rate of
356
mass transfer of the reactants toward the catalytic surface and also helps in maintaining the
357
surface of the catalyst clean thereby giving enhanced reaction rates.
358
3.10 Effect of ultrasound on catalyst morphology
359
The changes in morphology of the commercial catalyst before and after the use in ultrasound
360
assisted selective catalytic transfer hydrogenation reaction were established using the SEM
361
analysis and obtained images have been represented in Fig. 7 (a & b). The comparison of the
362
two catalysts revealed that the particle size of spent catalyst was lower attributed to the
363
cavitation effects. A reduction in the particle size means that higher surface area of catalyst is
364
available leading to higher reaction rates. It can be also seen that the roughness of the catalyst
365
is increased which can lead to better adsorption characteristics and higher catalytic activity.
366
Besides these effects, no other significant differences in surface morphology of both the
367
catalysts were observed.
368
4. Conclusions
369
Ultrasound assisted CTH of soybean oil was successfully performed using Pd/C (5 wt.
370
% loading) with matrix activated carbon support as a catalyst and water as solvent.
371
Ammonium formate was found to be an effective hydrogen donor for the ultrasound assisted
372
CTH of soybean oil. Excellent progress of hydrogenation was observed even at 30°C which
373
is much lower compared to the conventional approach which requires 90° C for the reaction
16 374
to progress at sustainable rate. The best conditions for maximum benefits were irradiation
375
power of 100W, duty cycle of 90% with ammonium formate loading as 0.32 mol / 50 ml
376
water and 2% (w/w) Pd/C loading. It was also established that the optimum conditions should
377
not only give higher reduction in the iodine value but also minimum formation of the stearic
378
acid as well as trans – isomer. Effect of temperature clearly established that the desired
379
optimum to maintain minimum trans-isomer formation might lead to lower iodine value
380
reduction. It has been also demonstrated that ultrasound assisted approach offered good
381
selectivity giving complete reduction of linolenic acid with a slight formation of stearic acid
382
(within the acceptable limits). Also the formation of trans-isomers was lower during
383
ultrasound assisted CTH of soybean oil at ambient temperature as compared to the
384
hydrogenation using hydrogen which is typically performed under conditions of high
385
pressure and temperature. Overall, the work demonstrated effective approach of
386
intensification of CTH based on the use of ultrasound with excellent benefits in terms of
387
lower reaction time and temperature as well as more importantly the desired product
388
characteristics.
389 390
5. References
391
1.
392
Fette, Seifen, Anstrichm., 78 (1976) 30-34
393
2.
394
Reactions of 4-Nitrodiphenylamine, Appl. Catal. 59 (1990) l-12.
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phenol on supported Pd catalysts using formic acid as an alternative hydrogen source, Catal.
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Today 234 (2014) 133–138.
E. Fedeli, G. Jacini, Homogeneous Selective Catalytic Hydrogenation of Soybean Oil,
A. A. Banerjee, D. Mukesh, Heterogeneous Catalytic Transfer Hydrogenation
D. Zhang, F. Ye, T. Xue, Y.Guan, Y. Meng, Y. Shanghai, Transfer hydrogenation of
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M. A. Tike, V. V. Mahajani Studies in catalytic transfer hydrogenation of soybean oil
399
using ammonium formate as donor over 5% Pd/C catalyst, Chem. Eng. J. 123 (2006) 31–41.
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soybean oil, Chem. Eng. J. 51(1993) B51–B56.
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Am. Oil Chem. Soc. 69 (1992) 405–409.
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hydrogenation of soybean oil, J. Am. Oil Chem. Soc. 71 (1994) 507–511.
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443-451.
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water or biphasic aqueous systems under sonochemical conditions : A review on catalytic
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effects, Catal. Commun. 63 (2015) 2-9.
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chemical synthesis using ultrasound, Ultrason. sonochem. 36 (2017) 527-543.
413
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highly efficient reduction of nitroarenes to corresponding N-Arylhydroxylamines, Chem.
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Res. Chinese Universities 25(2009), 183—188.
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extraction of mangiferin from Mangifera indica leaves, Ultrason. Sonochem. 21 (2014) 606–
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A. Šmidovnik, I. Plazl, T. Koloini, Kinetics of catalytic transfer hydrogenation of
A. Šmidovnik, A. Stimac, J. Kobe, Catalytic transfer hydrogenation of soybean oil, J.
A. Šmidovnik, J. Kobe, S. Leskovsek, T. Koloini, Kinetics of catalytic transfer
T. J. Mason, Ultrasound in synthetic organic chemistry, Chem. Soc. Rev. 26 (1997)
G. Cravotto, E. Borretto, M. Oliverio, A. Procopio, A. Penoni, Organic reactions in
S. V. Sancheti and P. R. Gogate, A review of engineering aspects of intensification of
S. Q. Xun, L. Rong-wen, H. Xin-yu, L. Lian-hai and Z. Shu-fen, Ultrasound-assisted
V.M. Kulkarni, V.K. Rathod, Mapping of an ultrasonic bath for ultrasound assisted
C. Paquat, Standard Methods for the Analysis of Oils, Fats and Derivatives, Pergamon
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14.
H. B. Ammar, M. Chtourou, M.H. Frikha, M. Trabelsi, Green condensation reaction
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of aromatic aldehydes with active methylene compounds catalyzed by anion-exchange resin
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under ultrasound irradiation, Ultrason. Sonochem. 22 (2015) 559–564.
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15.
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Butyrate using Heterogeneous Catalyst, Ultrason. Sonochem. 26 (2015) 257–264
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16.
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with alcohols, J. Am. Oil Chem. Soc., 43 (1966) 119-121.
428
17.
429
transfer from lithium formate in the presence of ruthenium and rhodium complexes,Croat.
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Chem. Acta, 63 (1990) 203-206.
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18.
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solid sodium formate in the presence of palladium on carbon, J. Mol. Catal. 26 (1984) 321 –
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Eng. Chem. Res. 38 (1999)1215–1249.
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sonochemical reactors. Ultrason. Sonochem., 10 (2003) 325–330.
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synthesis from non-edible Schleichera triguga oil using heterogeneous catalyst : Kinetics and
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thermodynamic analysis, Ultrason. Sonochem. 29 (2016) 288–298
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22.
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solvents in liquid-phase heterogeneous catalytic transfer reduction, Tetrahedron 48 (1992)
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7735–7746
P. N. Dange, A. V. Kulkarni, V.K. Rathod, Ultrasound Assisted Synthesis of Methyl
H. N. Basu, M. M. Chakrabarty, Studies on conjugated hydrogenation: Nickel catalyst
R. Marčec, Catalytic hydro-dehalogenation of some organic halides by hydrogen
A. Zoran, Y. Sasson, Catalytic transfer hydrogenation of unsaturated compounds by
L. H. Thompson, L. K. Doraiswamy, Sonochemistry : Science and Engineering, Ind.
P. R.Gogate, A. M. Wilhelm, A.B. Pandit, Some aspects of the design of
A.N. Sarve, M.N. Varma, S.S. Sonawane, Ultrasound assisted two-stage biodiesel
A.F. Brigas, R.A.W. Johnstone, Metal- assisted reactions. Part 24. The importance of
19 444
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compounds by solid sodium formate in the presence of palladium on carbon. J. Mol. Cat. 26
446
(1984) 321-26
447
A. Zoran, Y. Sasson, J. Blum, Catalytic transfer hydrogenation of unsaturated
20 448
List of figures
449
Figure 1. Effect of ultrasound power on reduction in iodine value during ultrasound assisted
450
CTH of soybean oil. Frequency of 22 kHz, 90% duty cycle, temperature of 30°C, ammonium
451
formate concentration of 0.32 mol (20 g in 50 ml water), catalyst loading of 2% w/w of
452
soybean oil (0.22 g), soybean oil as 0.012 mol (10.8-11 ml).
453
Figure 2. Effect of type of donors on reduction in iodine value during CTH of soybean oil.
454
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
455
ammonium formate concentration of 0.32 mol/50 ml H2O, catalyst loading of 2% w/w of
456
soybean oil (0.22g), soybean oil as 0.012 mol (10.8-11 ml).
457
Figure 3. Effect of donor concentration on reduction in iodine value during CTH of soybean
458
oil. Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
459
ammonium formate as donor, catalyst loading of 2% w/w of soybean oil (0.22g), soybean oil
460
as 0.012 mol (10.8-11 ml).
461
Figure 4. Effect of temperature on reduction in iodine value during CTH of soybean oil.
462
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, ammonium formate
463
concentration of 0.32 mol/ 50 ml water, catalyst loading of 2% w/w of soybean oil (0.22g),
464
soybean oil as 0.012 mol (10.8-11 ml).
465
Figure 5. Effect of catalyst loading on reduction in iodine value during CTH of soybean oil.
466
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
467
ammonium formate concentration of 0.32 mol/ 50 ml water, Pd/C catalyst, oil (0.22g),
468
soybean oil as 0.012 mol (10.8-11 ml).
469
Figure 6. Effect of amount of water on reduction in iodine value during CTH of soybean oil.
470
Ultrasound power of 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
471
ammonium formate concentration of 0.32 mol, Pd/C catalyst, oil (0.22g), soybean oil as
472
0.012 mol (10.8-11 ml).
21 473
Figure 7. SEM images of Pd/C (5 wt% loading) with matrix activated carbon support. (a)
474
fresh catalyst (b) Spent catalyst after first cycle
475 476
List of tables
477
Table 1. Fatty acid composition and properties of refined soybean oil
478
Table 2. Effect of operating parameters and hydrogenation on the fatty acid composition as
479
well as formation of trans-isomers (geometrical) during soybean oil hydrogenation
480
Table 3. Fatty acid composition of soybean oil after hydrogenation using gaseous high
481
pressure hydrogen [4]
482
22
140
60 W 80 W
130
100 W
120 W Iodine value
120 110 100 90 80 0
483
15
30 Time (min)
45
60
484
Figure 1. Effect of ultrasound power on reduction in iodine value during ultrasound assisted
485
CTH of soybean oil. Frequency of 22 kHz, 90% duty cycle, temperature of 30°C, ammonium
486
formate concentration of 0.32 mol (20 g in 50 ml water), catalyst loading of 2% w/w of
487
soybean oil (0.22 g), soybean oil as 0.012 mol (10.8-11 ml).
488
23 140
Potassium formate Sodium Formate
130
Ammonium Formate 120 Iodine value
Formic Acid
110
100
90
80 0
15
30
45
60
Time (min)
489 490
Figure 2. Effect of type of donors on reduction in iodine value during CTH of soybean oil.
491
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
492
ammonium formate concentration of 0.32 mol/50 ml H2O, catalyst loading of 2% w/w of
493
soybean oil (0.22g), soybean oil as 0.012 mol (10.8-11 ml).
494 495 496 497 498 499 500 501 502 503 504 505
24
140
0.16 moles 0.24 moles
130
0.32 moles 0.40 moles
Iodine Value
120
110
100
90
80 0
15
30
45
60
506 507
Figure 3. Effect of donor concentration on reduction in iodine value during CTH of soybean
508
oil. Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
509
ammonium formate as donor, catalyst loading of 2% w/w of soybean oil (0.22g), soybean oil
510
as 0.012 mol (10.8-11 ml).
511
25 512 140
30°C 45°C
130
60°C 75°C
Iodine Value
120
110
100
90
80 0
513
15
30 Time (min.)
45
60
514
Figure 4. Effect of temperature on reduction in iodine value during CTH of soybean oil.
515
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, ammonium formate
516
concentration of 0.32 mol/ 50 ml water, catalyst loading of 2% w/w of soybean oil (0.22g),
517
soybean oil as 0.012 mol (10.8-11 ml).
518 519
26 140
1 % (w/w) 130
1.5 % (w/w)
2 % (w/w) Iodine Value
120
2.5 % (w/w)
110 100 90 80 0
15
30
45
60
520 521
Figure 5. Effect of catalyst loading on reduction in iodine value during CTH of soybean oil.
522
Ultrasound power 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
523
ammonium formate concentration of 0.32 mol/ 50 ml water, Pd/C catalyst, oil (0.22g),
524
soybean oil as 0.012 mol (10.8-11 ml).
525
27 526 527 140 130
Iodine Value
120
20 ml 110
50 ml 80 ml
100 90 80 0
15
30
45
60
528 529 530
Figure 6. Effect of amount of water on reduction in iodine value during CTH of soybean oil.
531
Ultrasound power of 100W, frequency of 22 kHz, 90% duty cycle, temperature of 30°C,
532
ammonium formate concentration of 0.32 mol, Pd/C catalyst, oil (0.22g), soybean oil as
533
0.012 mol (10.8-11 ml).
534 535 536 537 538 539
28
540 541 542 543 544
545
(a)
(b)
Figure 7. SEM images of Pd/C (5 wt% loading) with matrix activated carbon support. (a) fresh catalyst (b) Spent catalyst after first cycle
29
546
Table 1. Fatty acid composition and properties of refined soybean oil
547 %
C12:0
C14:0
C16:0
C18:0
C18:1
C18:2
C18:3
C20:0
C22:0
C24:0
0.2
0.4
11.6
4.3
22.4
54.2
6
0.4
0.3
0.2
Fatty acid composition
548
Iodine value (Wijj’s) = 134
549
Table 2. Effect of operating parameters and hydrogenation processes on the fatty acid
550
composition as well as formation of trans-isomers (geometrical) during soybean oil
551
hydrogenation Sample
US
Catalyst
Donar
Temp. after
Power
Loading
552
(W)
Std.
NA
1
C18:1
C18:3
(%)
(%)
Cis
Trans
(%)
Conc.
(° C) 1h
C18:2 (%)
C18:0
IV
%(w/w)
(moles)
NA
NA
NA
4.3
22.4
55.5
0
6
135
100
30°
2
0.32
6
32.3
46.5
0.5
1.6
95.50
2
100
30°
2
0.4
6.8
37.3
42.3
0.7
1.2
93.15
3
100
30°
2.5
0.32
7.5
37.5
41.9
0.6
0.8
92.00
4
100
60°
2
0.32
12.0
34.4
40
1.1
0.6
88.82
30
553
Table 3. Fatty acid composition of soybean oil after hydrogenation using gaseous high
554
pressure hydrogen [4] Sr. No. Conditions
C18:0
C18:1
C18:2 (%)
C18:3
(min)
(%)
(%)
Cis
Trans
(%)
IV
1
High-pressure (Ni; 150 ◦C)
20
7.5
37.6
37.3
2
1.9
110.7
2
High-pressure (5% Pd/C; 150
5
7.2
37.4
37.6
3.6
0.52
110.3
◦C)
555 556 557
Time
31 558
HIGHLIGHTS:
559
First report of intensification of heterogeneously catalyzed transfer hydrogenation using
560
ultrasound
561
562
Significant reduction in the temperature and reaction as the key benefits
563
Selecting best set of operating conditions also helps in minimizing the formation of hazardous
564 565 566 567 568
Understanding the engineering aspects in terms of effect of operating parameters
trans-isomer