Effects of Ultrasonic Waves on Enhancement of Relative Volatilities in Methanol–Water Mixtures

Abstract

Penggunaan gelombang ultrabunyi dalam pelbagai bidang termasuk proses pemisahan telah meningkat sejak akhir-akhir ini. Kajian ini melaporkan keberkesanan penggunaan gelombang ultrabunyi dalam meningkatkan pemisahan campuran binari dalam turus penyulingan. Campuran binari yang digunakan adalah metanol-air. Kesan keamatan gelombang bunyi yang berbeza iaitu 50, 100, 200 and 250 W/A.cm 2 pada frekuensi 40 kHz terhadap keseimbangan wap-cecair (KWC) dikaji bagi mendapatkan nilai keamatan yang sesuai. Eksperimen juga dijalankan bagi mengkaji kesan frekuensi (25 and 68 kHz) terhadap data KWC. Didapati, penggunaan gelombang ultrabunyi berjaya meningkatkan proses pemisahan dengan meningkatkan nilai kemeruapan relatif. Purata kemeruapan relatif yang tertinggi bagi metanol-air iaitu 29.413 diperoleh daripada uji kaji yang menggunakan keamatan 200 W/A.cm 2 dan frekuensi 25 kHz. Proses peronggaan dan kesan vakum yang wujud semasa perambatan gelombang ultrabunyi dalam cecair membawa kepada perubahan nilai kemeruapan relatif dan data KWC. Keputusan yang diperoleh menunjukkan keberkesanan penggunaan gelombang ultrabunyi bagi meningkatkan pemisahan campuran binari dalam turus penyulingan.
Kata kunci: Keseimbangan wap–cecair, metanol–air, gelombang ultrabunyi, kemeruapan relatif

The application of ultrasonic wave in various fields including separation process has increased predominantly. This paper reports the practicability of using ultrasonic wave to enhance separation of binary mixtures by distillation. The binary mixture utilized was methanol-water. The effect of different ultrasonic intensity at 50, 100, 200 and 250 W/A.cm 2 with frequency of 40 kHz to vapor-liquid equilibrium (VLE) of methanol-water was investigated to obtain the most suitable operating intensity. Experimental studies were also carried out to investigate the frequency effect (25 and 68 kHz) to VLE data. It was found that the use of ultrasonic wave enhanced the separation process by increasing the relative volatility of components. The highest average relative volatility of methanol-water at 29.413 was obtained from experimental study using intensity 200 W/A.cm 2 and frequency of 25 kHz. The changes in relative volatility and VLE were caused by cavitational activities and vacuum effect that occur during transmission of ultrasonic wave in liquid medium. The results from this study proved the practical feasibility of using ultrasonic wave to enhance separation of binary mixtures in distillation column.

Key words: Vapor–liquid equilibrium, methanol–water, ultrasonic waves, relative volatility

Full text

Jurnal Teknologi, 48(F) Jun 2008: 61-73
© Universiti Teknologi Malaysia
1 Chemical Engineering Department, Faculty of Chemical & Natural Resources Engineering,
Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
Tel: +60-7-5535569, Fax: +60-7-5581463, Email: adnan@fkkksa.utm.my
2&3 Chemical Engineering Department, Faculty of Chemical & Natural Resources Engineering,
Universiti Malaysia Pahang, Beg Berkunci 12, 25000 Gambang, Kuantan, Pahang, Malaysia
Tel: +6012-5662739/+6019-2401134, Fax: +609-5492399, Email: ctkhol@yahoo.com, rmy@
ump.edu.my
EFFECTS OF ULTRASONIC WAVES ON ENHANCEMENT OF
RELATIVE VOLATILITIES IN METHANOL-WATER MIXTURES
ADNAN RIPIN1, SITI KHOLIJAH ABDUL MUDALIP2 &
ROSLI MOHD YUNUS3
Abstract. Theapplicationof ultrasonicwaveinvariouseldsincludingseparationprocesshas
increased predominantly. This paper reports the practicability of using ultrasonic wave to enhance
separation of binary mixtures by distillation. The binary mixture utilized was methanol-water.
The effect of different ultrasonic intensity at 50, 100, 200 and 250 W/A.cm2 with frequency of
40 kHz to vapor-liquid equilibrium (VLE) of methanol-water was investigated to obtain the most
suitable operating intensity. Experimental studies were also carried out to investigate the frequency
effect (25 and 68 kHz) to VLE data. It was found that the use of ultrasonic wave enhanced the
separation process by increasing the relative volatility of components. The highest average relative
volatility of methanol-water at 29.413 was obtained from experimental study using intensity 200
W/A.cm2 and frequency of 25 kHz. The changes in relative volatility and VLE were caused by
cavitational activities and vacuum effect that occur during transmission of ultrasonic wave in
liquid medium. The results from this study proved the practical feasibility of using ultrasonic wave
to enhance separation of binary mixtures in distillation column.
Keywords: Vapor-liquid equilibrium, methanol-water, ultrasonic waves, relative volatility
Abstra�.Abstra�. Penggunaan gelombang ultrabunyi dalam pelbagai bidang termasuk proses
pemisahan telah meningkat sejak akhir-akhir ini. Kajian ini melaporkan keberkesanan
penggunaan gelombang ultrabunyi dalam meningkatkan pemisahan campuran binari dalam
turus penyulingan. Campuran binari yang digunakan adalah metanol-air. Kesan keamatan
gelombang bunyi yang berbeza iaitu 50, 100, 200 and 250 W/A.cm2 pada frekuensi 40 kHz
terhadap keseimbangan wap-cecair (KWC) dikaji bagi mendapatkan nilai keamatan yang sesuai.
Eksperimen juga dijalankan bagi mengkaji kesan frekuensi (25 and 68 kHz) terhadap data KWC.
Didapati, penggunaan gelombang ultrabunyi berjaya meningkatkan proses pemisahan dengan
meningkatkan nilai kemeruapan relatif. Purata kemeruapan relatif yang tertinggi bagi metanol-
air iaitu 29.413 diperoleh daripada uji kaji yang menggunakan keamatan 200 W/A.cm2 dan
frekuensi 25 kHz. Proses peronggaan dan kesan vakum yang wujud semasa perambatan gelombang
ultrabunyi dalam cecair membawa kepada perubahan nilai kemeruapan relatif dan data KWC.

ADNAN, SITI KHOLIJAH & ROSLI
62
Keputusan yang diperoleh menunjukkan keberkesanan penggunaan gelombang ultrabunyi bagi
meningkatkan pemisahan campuran binari dalam turus penyulingan.
Kata kunci: Keseimbangan wap-cecair, metanol-air, gelombang ultrabunyi, kemeruapan relatif
1.0 INTRODUCTION
Methanol can be produced from natural gases and coal. By a simple reaction
between coal and steam, a gas mixture called syn-gas (synthesis gas) is formed. The
components of this mixture are carbon monoxide and hydrogen, which through
an additional chemical reaction with water as a side product before converted
to methanol [1]. Separation of methanol-water in industry has been done using
distillation technique. Although methanol-water mixtures do not form an azeotrope
(normal binary), a number of distillation columns are required to obtain high purity
methanol.
Ultrasonic wave is a sound wave having frequency higher than human audibility
limits [2]. Sound wave with frequency above 20 kHz is usually considered as
ultrasonic [3]. The use of ultrasonic wave has gain consumers interest in various
elds,includingseparationprocess[4-6].Indistillationprocess,ultrasonicwaveis
believed to be capable of increasing separation of mixtures by altering the relative
volatility of components in the mixtures. As an exploratory study, this research has
primary aim to investigate the possibility of ultrasonic wave application in distillation
to enhance separation of binary mixtures.
Since the successful application of distillation is greatly dependent upon an
understanding of equilibrium existed between vapor and liquid phases of the
mixtures, the study on ultrasonic effect to VLE was rstly done using typical
binary mixture found in literature. The binary mixture was methanol-water [7-
8]. The effects produced by different ultrasonic intensities and different ultrasonic
frequencies to VLE data were investigated. The results show that ultrasonic wave
can favorably change the relative volatility of methanol-water mixtures, thereby
allowing an easier separation compared to an ordinary distillation process.
2.0 ULTRASONIC CAVITATION THEORY
Cavitation normally takes place in liquid medium once the media is subjected to
rapid, alternating high pressure, ultrasonic excitation or pulsed heating lasers [9].
Voids containing small micro bubbles are created when the differences between
amplitude pressure of ultrasonic waves and the hydrostatic pressure in the liquid
are large enough to exceed the local tensile strength of the liquid medium. These
bubbles expand during negative part of pressure cycle (rarefaction cycle), reach the
maximum radius and then collapse at the onset of positive pressure cycle (compression

EFFECTS OF ULTRASONIC WAVES ON ENHANCEMENT OF RELATIVE VOLATILITIES 63
cycle) [10]. This process repeats continuously according to pressure oscillation of
ultrasonicwaves.Dependingonsomecircumstances,thebubbleswillbelledeither
by gases or by vapor of the liquid itself [11]. The vacuum environments/spots
which created inside the liquid medium during negative pressure cycle or expansion
cycle of ultrasonic wave, also helps towards inducing the boiling process as well
asdrawntheuidsintocavitationmicrobubbles[12-13].Due tothissituation,at
high temperature (near boiling point), the vapors of volatile component enter the
cavitation bubbles and released during the bubbles collapse.
3.0 EXPERIMENTAL METHOD
3.1 Materials
Methanol used in this study was supplied by R&M Chemical Industries (M) Sdn
Bhd.Thepurityof thechemicalwas99.8%.Itwasusedwithoutfurtherpurication
sincenosignicantimpuritieswasdetectedbythegaschromatography.Waterused
in this study was distilled water. The refractive indices and boiling points of each
material used were measured, and the results with those reported in the literature
are listed in Table 1.
Table 1 Physical properties of materials
Material
Refractive indices,
h
DBoiling point, Tb (K)
Experimental Literature [8] Experimental Literature [8]
Methanol 1.3280 1.3290 337.97 337.80
Water 1.3330 1.33301 373.15 373.13
3.2 Apparatus and Procedure
The experimental studies were performed using an Ultrasonic-Distillation System.
Theapparatusconsistsof a distillationask,acondenser,awaterbath,ultrasonic
generating equipments, and thermocouples. The apparatus has a 250 cm3 capacity
andcanbeoperatedbetweenlowtomoderatepressurerange.Thedistillationask
was immersed in a water bath equipped with 40 kHz ultrasonic transducer and
heater. The ultrasonic transducer, supplied by Crest Ultrasonic (M) Sdn Bhd, was
connected to 500 Watt ultrasonic generator. The liquid and vapor temperatures were
measured using thermocouples, TC-08 with precision of 0.01oC and linked using
Pico data logger to a computer. Methanol-water mixtures at different compositions

ADNAN, SITI KHOLIJAH & ROSLI
64
werepreparedandfedintothedistillationask.Themixtureswerelettobeboiled
with the absence or the presence of ultrasonic wave until reached an equilibrium.
The vapor and liquid phases reach equilibrium once the vapor temperature
remained constant for a period of 10-20 minutes. When equilibrium was reached,
liquidsamplesfromthedistillationaskandcondensedvaporweretakenandtheir
compositions were measured using a refractometer at ambient condition. Distillation
was initially done at atmospheric pressure to obtain methanol-water VLE data in
the absence of ultrasonic waves. Then, distillation was repeated using ultrasonic
waves at intensities of 50, 100, 200 and 250 W/A.cm2 and frequency of 40 kHz to
determine the most suitable operating intensity. After that, the same procedure was
repeated at 25 kHz and 68 kHz frequency.
3.3 Analysis Procedure
In order to analyze the mixture of methanol-water, a calibration curve of the
refractive index versus mole fraction of the methanol is required. Samples in Table
2 were prepared and measured using a refractometer at ambient condition. The
composition of distillate and bottom products was determined by interpolation
from the plotted graph (Refer to Figure 1).
Table 2 Refractive indices with different compositions of methanol-water
Samples Mole fraction of
methanol,
%
Refractive
indices,
h
D (27oC)
Methanol (mL) Water (mL)
0 10 0 1.3330
1.0 9.0 5 1.3340
2.0 8.0 10 1.3356
3.0 7.0 16 1.3376
4.0 6.0 23 1.3389
5.0 5.0 31 1.3401
6.0 4.0 40 1.3410
7.0 3.0 51 1.3395
8.0 2.0 64 1.3372
9.0 1.0 80 1.3333
9.5 0.5 89 1.3312
10 0 100 1.3280

EFFECTS OF ULTRASONIC WAVES ON ENHANCEMENT OF RELATIVE VOLATILITIES 65
1.3272
1.3293
1.3314
1.3335
1.3356
1.3377
1.3398
1.3419
0 20 40 60 80 100
Methanol fraction (mole %)
Refractive indices, η
D
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
Without sonication I=50 W/A.cm
2
Reference line I=100 W/A.cm
2
I=200 W/A.cm
2
I=250 W/A.cm
2
Figure 1 Refractive index of methanol-water mixtures against mole fraction of
methanol
4.0 RESULTS AND DISCUSSION
4.1 Experimental Study without Sonication
VLE data for methanol-water was measured at atmospheric pressure without the
presence of ultrasonic wave. Figure 2 illustrates the VLE data of methanol-water
in comparison with Khalfaoui et al. [7], where the vapor phase composition was
plotted against the liquid phase composition. This was done to verify the reliability
of developed method and VLE apparatus that was used to obtain VLE data. As
illustratedinthegure,theVLEdataobtainedconcurredwiththosefoundinthe
literature [7]. The average deviations of experimental data with the literature values
are less than 10% and thus lay within an acceptable limit (Refer Table 3). This
proves the practical feasibility of using the developed method and VLE apparatus
to obtain VLE data.

ADNAN, SITI KHOLIJAH & ROSLI
66
1.3272
1.3293
1.3314
1.3335
1.3356
1.3377
1.3398
1.3419
0 20 40 60 80 100
Methanol fraction (mole %)
Refractive indices, η
D
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
Without sonication I=50 W/A.cm
2
Reference line I=100 W/A.cm
2
I=200 W/A.cm
2
I=250 W/A.cm
2
Figure 2 xy-diagram of methanol-water system at atmospheric pressure: (u)
Experimental data, (n) Literature value [7]
Table 3 Vapor and liquid composition of methanol-water
x1,% y1,% % deviation
Experimental data Literature value, [7]
10 38 43 -11.6
20 70 61 14.8
30 83 68 22.1
40 85 74 14.9
50 86 79 8.9
60 88 83 6.0
70 90.5 87 4.0
80 93 91 2.2
90 96 95 1.1
Average deviation 6.9

EFFECTS OF ULTRASONIC WAVES ON ENHANCEMENT OF RELATIVE VOLATILITIES 67
4.2 Experimental Study with Sonication
4.2.1 Effect of Ultrasonic Intensity on VLE
Figure 3 shows the equilibrium curve of methanol-water system with different
ultrasonic intensities in comparison to the unsonicated data. As can be seen in this
gure,theequilibriumcurvesof methanol-waterwereshiftedupwardandbecome
further from the reference line when the ultrasonic intensity increased up to 200
W/A.cm2. Geankoplis [14] stated that the further the equilibrium curve lies from
the 45º line, the easier the separation of components. However, the VLE curve was
shifted downward and become closer to the reference line when intensity of 250
W/A.cm2 was applied to the system. The changes on VLE data with ultrasonic
application were related to the changes of mixtures’ relative volatility (Refer Figure
4). The relative volatility of methanol-water was calculated using the following
equation:
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
(1)
1.3272
1.3293
1.3314
1.3335
1.3356
1.3377
1.3398
1.3419
0 20 40 60 80 100
Methanol fraction (mole %)
Refractive indices, η
D
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
Without sonication I=50 W/A.cm
2
Reference line I=100 W/A.cm
2
I=200 W/A.cm
2
I=250 W/A.cm
2
Figure 3 Equilibrium curve of methanol-water system with different ultrasonic
intensity at frequency of 40 kHz
The changes of relative volatility and VLE data of methanol-water were caused
by the cavitational activities and vacuum effects, which occur during transmission of
ultrasonic wave in the liquid medium. Detailed mechanism of cavitation activities
has been mentioned previously in Section 2.0. Vacuum conditions, which were
created at low-pressure phase of ultrasonic cycle, aid the vaporization of volatile

ADNAN, SITI KHOLIJAH & ROSLI
68
component in the liquid medium and draw it into the cavitation micro bubbles
[12-13]. According to Mason [13], the presence of volatile components in liquid
mixtureswouldcausethecavitation microbubbles tobe lled withthe vaporof 
the volatile component. Since methanol is more volatile than water, more vapor of
methanol was vaporized and trapped inside the micro bubbles. The trapped vapor
was released during the bubble collapses and increase its concentration in vapor
phases. Due to this situation, more methanol was vaporized during ultrasonic-
distillation process compared to ordinary distillation procedure.
As shown in Figure 4, the application of ultrasonic wave up to 200 W/A.cm2
increased the average relative volatility of methanol-water,
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
. The highest
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
value at 17.264 was obtained at intensity 200 W/A.cm2.Thisndingalignedwith
the statement given by Mason [13] who stated that an increase in ultrasonic intensity
would contribute to an increase in cavitation and vacuum effect. This is because, as
ultrasonic intensity increased, greater ultrasonic energy enters the liquid medium
and produce more cavitation micro bubbles and creates larger vacuum effects inside
the liquid medium. This helps in increasing the amount of methanol that is trapped
inside the cavitation micro bubbles and thus released during their collapse. This
phenomenon has consequently increased the relative volatility of methanol-water
mixtures. However, Mason [13] also stated that ultrasonic intensity could not be
increasedindenitely.
0.00
4.00
8.00
12.00
16.00
20.00
0 50 100 150 200 250 300
Ultrasonic intensity, W/A.cm
2
Average relative volatility
0.000
5.000
10.000
15.000
20.000
25.000
30.000
35.000
0 20 40 60 80
Ultrasonic frequencies, kHz
Average relative volatility
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
Ref line F=40 kHz
F=68 kHz F=25 kHz
Figure 4 Average relative volatility of methanol-water as a function of ultrasonic
intensity at frequency of 40 kHz
Figure 4 also shows that the average relative volatility of methanol-water decreased
with the application of ultrasonic wave above 200 W/A.cm2. The
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
value obtained

EFFECTS OF ULTRASONIC WAVES ON ENHANCEMENT OF RELATIVE VOLATILITIES 69
with sonication at 250 W/A.cm2 was 12.256. This is because, as ultrasonic intensity
increased beyond 200 W/A.cm2, too many cavitation micro bubbles were formed
and perturbed the normal cavitation processes. These bubbles collide with each
other and produce bigger bubbles. Some of the bubbles do not collapse and form a
bubble cushion at the radiating face of ultrasonic transducers that reduce the effect
of coupling sound energy into the liquid system [15]. Hence, less cavitational and
vacuum effects are produced. This consequently reduced vaporization of volatile
components in the liquid medium and decreased the average relative volatility of
methanol-water with the application of ultrasonic intensity beyond 200 W/A.cm2.
Therefore, the best operating intensity at frequency of 40 kHz was 200 W/A.cm2.
4.2.2 Effect of Ultrasonic Frequency on VLE
Ultrasonicfrequencyisanotherimportantparameterthatdenessoundeldand
signicantly inuences the cavitation formation. Therefore, upon examining the
effect of ultrasonic wave to VLE data, the selection of operated ultrasonic frequency
is very crucial.In thissection,theinuenceof  differentultrasonicfrequenciesto
VLE data at constant intensity (200 W/A.cm2) is discussed. Figure 5 illustrates the
VLE data of methanol-water with different ultrasonic frequency. The equilibrium
curves were shifted downward and closer to the reference line with the increased
of applied frequency. The changes in average relative volatility of binary mixture
with the presence of ultrasonic wave caused the shifting of VLE curves. Figure
6 illustrates the relation of average relative volatility of methanol-water,
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
with
different ultrasonic frequency.
0.00
4.00
8.00
12.00
16.00
20.00
0 50 100 150 200 250 300
Ultrasonic intensity, W/A.cm
2
Average relative volatility
0.000
5.000
10.000
15.000
20.000
25.000
30.000
35.000
0 20 40 60 80
Ultrasonic frequencies, kHz
Average relative volatility
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
Ref line F=40 kHz
F=68 kHz F=25 kHz
Figure 5 Equilibrium curve of methanol-water system with different ultrasonic
frequency at intensity 200 W/A.cm2

ADNAN, SITI KHOLIJAH & ROSLI
70
The results obtained demonstrate that an increase of ultrasonic frequency at
constant intensity decrease the average relative volatility of the mixture. The highest
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
at 29.413 for methanol-water was obtained at frequency of 25 kHz while the
lowest value was obtained at frequency of 68 kHz. According to Van Winkle, the
largest relative volatility indicates the easiest separation process [16]. As a result,
the separation of binary mixture by distillation becomes easier with the application
of ultrasonic wave at the frequency of 25 kHz. As discussed before, cavitation
phenomenon is responsible for the changes in relative volatility and VLE data of
methanol-water mixtures.
During cavitation processes, the liquid molecules are wrench apart and create
voids that contain small gas bubbles and vacuum spots [10]. At constant ultrasonic
power the cavitation formation is greatly dependent on the ultrasonic frequency.
According to Mason [15], more power is required at higher frequency to produce
the same cavitation and vacuum effects in a liquid medium. At higher frequency, the
rarefaction cycle is shortened. This result in production of smaller cavitation micro
bubbles and generation of smaller vacuum environment inside the liquid medium,
which in turn, reduced the vaporizations of volatile component in liquid mixtures.
This phenomenon explains why the increase of ultrasonic frequency decreases the
relative volatility of binary mixtures.
0.00
4.00
8.00
12.00
16.00
20.00
0 50 100 150 200 250 300
Ultrasonic intensity, W/A.cm
2
Average relative volatility
0.000
5.000
10.000
15.000
20.000
25.000
30.000
35.000
0 20 40 60 80
Ultrasonic frequencies, kHz
Average relative volatility
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Methanol in liquid (mole %)
Methanol in vapor (mole %)
Ref line F=40 kHz
F=68 kHz F=25 kHz
Figure 6 Relative volatility of methanol-water system with different ultrasonic
frequency at intensity 200 W/A.cm2

EFFECTS OF ULTRASONIC WAVES ON ENHANCEMENT OF RELATIVE VOLATILITIES 71
4.3 Changes in Chemical Properties
The literature review shows that the sonolyis of chemical compound that originated
from acoustic cavitation would cause chemical decomposition and change the
chemical properties [17-20]. In this research, sonication of liquid mixtures was
done at high operating temperature, which is at the mixture’s boiling point.
Therefore, the chemical changes with respect to ultrasonic wave application at
high temperature were negligible [13, 17]. According to Mason [13], it is not very
sensible to attempt sonochemical reaction in a liquid medium near its boiling point
since the sonication of liquid mixtures at their boiling point will cause boiling. This is
because, the vacuum effects that occurred at low-pressure phase of ultrasonic cycle,
induce boiling in liquid medium and drawn it into cavitation micro bubbles. Due to
this situation, the cavitation processes and vacuuming effects, which occur during
propagationof ultrasonicwavesindistillationask,aretechnicallyresponsibleon
the changes of average relative volatility and VLE data instead of the changes on
the chemical properties.
5.0 CONCLUSION
Ultrasonic waves has the potential to manipulate the relative volatility (α), and hence,
the VLE of a binary mixture. Results from experiments conducted at different
ultrasonic intensities and at frequency of 40 kHz show that 200 W/cm2 was the best
sonication intensity for methanol-water mixture within the range of investigated
intensities. Further increase in ultrasonic intensity beyond 200 W/A.cm2 decreased
the
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
methanol-water mixture. Results obtained from experimental study at
different ultrasonic frequencies and constant intensity of 200 W/A.cm2 show that
the
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
decreased with the increase in ultrasonic frequency. The highest
( )
( )
22
11
12
/
/
xy
xy
=α
12
α
obtained
at frequency of 25 kHz and intensity of 200 W/A.cm2 was 29.413. Results from this
study prove that ultrasonic waves can be employed to improve the relative volatility
of components in binary mixture and hence increase the separation of methanol-
water in distillation column.
ACKNOWLEDGEMENTS
This work was supported by Ministry of Higher Education under Fundamental
Research Grant Scheme. Special thanks are dedicated to Universiti Teknologi
Malaysia, Skudai for their sponsorship and graduate scholarship to Siti Kholijah
Abdul Mudalip.

ADNAN, SITI KHOLIJAH & ROSLI
72
List of Symbols and Gree� Letters
T temperature (oC)
xi liquid phase mole fraction
yi vapor phase mole fraction
α
ij relative volatility of component i and j
¯
α
12 average relative volatility of component 1 and 2
h
D
refractive indices
Tb boiling point (K)
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