Separation of Anisole and Valuable Byproducts from Liquid Reaction Mixtures by Solvent Extraction and Multicomponent Distillation

Article abstract of DOI:10.1007/s10953-020-01049-0

Anisole (methoxybenzene) is a widely used organic intermediate that can be synthesized via vapor-phase alkylation of phenol by methanol in the presence of a commercial NaX zeolite as a catalyst (SiO₂:Al₂O₃ ratio of 2.6:3). The indigenously synthesized anisole is then separated from the multicomponent liquid reaction mixture, consisting of o-cresol, p-cresol and p-xylen, along with unreacted methanol and phenol. The separated anisole has substantial demand for applications in the chemical, pharmaceutical, plastics and pesticides industries. Separation of individual components from the reaction mixture requires identification of techniques that could be scaled up. Distillation is one of the most dependable techniques for the separation of multicomponent liquid mixtures. The novelty of the present study is the synthesis and separation of anisole along with individual components of methanol, phenol and o-cresol from its reaction mixture using a single distillation column under atmospheric and vacuum conditions, respectively. Through this process, the purity of the resulting methanol, anisole and phenol were found to be 99.99, 99.80 and 98.29% by simple distillation, whereas 91.0% pure o-cresol was separated by vacuum distillation due to its high boiling point. The experimental results were used to calculate the material, individual component and energy balances, whereas the PRO/II process simulation was performed to scale-up the process. On the other hand, anisole recovery from a synthetic multicomponent liquid mixture was also successfully conducted using solvent extraction. The overall observations found the integration of solvent extraction with distillation to be an effective, economical and dependable solution for the isolation of anisole and other important by-products.

Full text of DOI:10.1007/s10953-020-01049-0

Journal of Solution Chemistry (2021) 50:160–177
https://doi.org/10.1007/s10953-020-01049-0
Separation of Anisole and Valuable Byproducts
from Liquid Reaction Mixtures by Solvent Extraction
and Multicomponent Distillation
Bukke Vani1,2 · Manideep Pabba1 · Swayampakula Kalyani1 · Sundergopal Sridhar1,2
Received: 10 April 2020 / Accepted: 7 October 2020 / Published online: 18 January 2021
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
Anisole (methoxybenzene) is a widely used organic intermediate that can be synthesized
via vapor-phase alkylation of phenol by methanol in the presence of a commercial NaX
zeolite as a catalyst (SiO2:Al2O3 ratio of 2.6:3). The indigenously synthesized anisole is
then separated from the multicomponent liquid reaction mixture, consisting of o-cresol,
p-cresol and p-xylen, along with unreacted methanol and phenol. The separated anisole has
substantial demand for applications in the chemical, pharmaceutical, plastics and pesticides
industries. Separation of individual components from the reaction mixture requires iden-
tifcation of techniques that could be scaled up. Distillation is one of the most dependable
techniques for the separation of multicomponent liquid mixtures. The novelty of the pre-
sent study is the synthesis and separation of anisole along with individual components of
methanol, phenol and o-cresol from its reaction mixture using a single distillation column
under atmospheric and vacuum conditions, respectively. Through this process, the purity
of the resulting methanol, anisole and phenol were found to be 99.99, 99.80 and 98.29%
by simple distillation, whereas 91.0% pure o-cresol was separated by vacuum distillation
due to its high boiling point. The experimental results were used to calculate the material,
individual component and energy balances, whereas the PRO/II™ process simulation was
performed to scale-up the process. On the other hand, anisole recovery from a synthetic
multicomponent liquid mixture was also successfully conducted using solvent extraction.
The overall observations found the integration of solvent extraction with distillation to
be an efective, economical and dependable solution for the isolation of anisole and other
important by-products.
Keywords Vapor-phase alkylation · Anisole · Multi-component liquid mixtures ·
Distillation · Material and energy balance · Solvent extraction
*
Sundergopal Sridhar
sridhar11in@yahoo.com
1
2
Membrane Separations Laboratory, Process Engineering and Technology Transfer, CSIR-IICT,
Hyderabad 500007, India
Academy of Scientifc and Innovative Research (AcSIR), Ghaziabad 201002, India
Vol:.(1234567890)
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1 Introduction
Anisole, a colorless liquid also known as methoxybenzene with the chemical formula
CH3OC6H5, smells similar to anise seeds [1]. It exhibits good solubility in most organic
solvents including diethyl ether, ethanol, benzene, chloroform, toluene, etc. [2]. Anisole is
utilized mainly for the manufacturing of perfumes, dyes, drugs, fabric softeners, pesticides,
analytical reagents, water treatment and photographic chemicals [3], besides use in food
items [4]. Predominantly, anisole has been synthesized by various methods such as bromi-
nation, alkalization, and vapor phase alkalization using catalysts such as zirconium, tung-
sten, niobium phosphate and zeolites [5]. Several studies have been reported on separation
processes used for the recovery of anisole from diferent binary mixtures [6, 7]. The most
commonly employed methods for anisole recovery include solvent extraction, distillation
entrainment, stripping and crystallization.
Distillation is a well-known separation process wherein the mixtures can be separated
by diferences in the boiling points or volatility of the individual components [8–10]. It
deals with the separation of binary and multi-component mixtures to recover organic sol-
vents including alcohols of diferent purities [11]. The removal of hazardous waste and
organic solvents from liquid mixtures helps to protect the environment from the contam-
inants [12]. Distillation plays a crucial role in the separation of multi-component liquid
mixtures, which is much more complicated. The process is usually inexpensive if the boil-
ing points are wide apart, but if the relative volatility is less than 1.0, it becomes more
expensive than crystallization and extraction [13, 14]. Close boiling mixtures cannot be
separated economically through conventional methods [15]. Zhibo et al. isolated anisole
by continuous distillation using a dynamic-accumulative operation method [16]. Stripping
crystallization was used to separate close boiling components such as p-xylene from the
multi-component xylene system [17, 18]. The close boiling point 3-picoline/4-picoline,
p-cresol/m-cresol, guaiacol/alkylphenols mixtures were separated by a dissociation based
extractive crystallization process [19]. Ylinen et al. reported p-cresol/m-cresol separation
by azeotropic distillation [20]. Lie et al. and Novak et al. separated xylenes and benzene/
cyclohexane systems by stripping crystalization [21, 22]. The extraction of phenolic com-
pounds and water from coal liquids was carried out by solvent extraction in which metha-
nol was used as a mediator [23, 24]. Masashi et al. used a single distillation column to
recover phenols, water and methanol from three separate efuent streams [25]. Raghu et al.
studied close boiling mixtures of 4-methyl phenol and 3-methyl phenol by stirring crystal-
lization [26]. From the literature, stripping crystallization and distillation methods appear
to have been extensively used to separate multi-component liquid mixtures, with faster
processing time and high product purity, without employing additional solvents. Very few
studies are available in the literature on multi-component liquid mixture separation through
single column distillation, which provides a wide scope for isolation of individual compo-
nents and by-products.
The reaction mixture in the present study was obtained from the synthesis of anisole
:Al O ratio
by vapor phase alkylation of methanol and phenol using a NaX zeolite (SiO2
of 2.6:3) as a catalyst at an elevated temperature of 300 °C. The catalyst used in2th3e pro-
cess is thermally stable and environment friendly, efectively replacing the existing ani-
sole production method. A single distillation column was employed to recover the indi-
vidual components such as anisole as the main product, o-cresol, p-cresol, and p-xylene
as by-products, apart from the unreacted compounds allowing methanol and phenol to
be used for recycle. Experimental parameters have been optimized for achieving high
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Journal of Solution Chemistry (2021) 50:160–177
162
product purity and efciency by varying the column pressure, vapor temperature, refux
ratio, packing material and column diameter. Depending on the separation, distillation
plants can be extremely complex and experimentation is challenging as with the present
work which deals with a multi-component liquid mixture. The experiments were con-
ducted in a single packed atmospheric pressure column under infnite and fnite refux
conditions for isolation of indigenously synthesized anisole. Among all the components,
percentage recovery and purity of anisole are the major objectives of process design.
Based on the experimental results, process simulation was performed using the PRO/
II™ simulator to design the industrial separation columns. On the other hand, a case
study was also undertaken to separate anisole from the synthetic reaction mixture using
a solvent extraction technique.
2 Materials and Methods
2.1 Materials
Methanol and column packing material were purchased from SD Fine Chemicals, Mum-
bai, India. Anisole (methoxybenzene) was obtained from Finar Chemicals, Ahmedabad,
India. Phenol, o-cresol and p-cresol were purchased from MolyChem, Mumbai, India.
p-Xylene and NaX commercial zeolite were obtained from Sigma Aldrich Chemi-
cals, Milwaukee, WI, USA. Borosil glass columns, connectors, condenser, refux unit,
round bottom fask reboiler, collector and all other glass items required for the distilla-
tion setup, besides a separating funnel for density-based separation, were supplied by
Gujarat Borosil Ltd., Ahmedabad, India. Digital temperature indicators used to meas-
ure the boiling point in the reboiler and vapor temperature at the top of the column
were purchased from Noble Corporations, Hyderabad, India. A 300 W heating mantle
of 2000 mL capacity, used to boil the mixtures, was procured from Labpro, Ambala,
India. A digital timer to maintain the refux ratio frequency and submerged circulation
pump of 18 W to circulate chilled water to the condenser were purchased from Globus,
Hyderabad, India. Ice fakes used to condense the vapors at the double heat exchanger
type condenser were generated by an ice making unit at IICT, Hyderabad, India. NaOH,
hexane, FeCl3 and Na2CO3 used in the solvent extraction process, were procured from
SV Chemicals, Hyderabad, India. Type-II water was generated by a cascaded reverse
osmosis (RO) membrane with electro deionization (EDI) system at the membrane sepa-
ration laboratory of IICT, Hyderabad for conducting the experiments.
2.2 Synthesis of Anisole by Vapor Phase Alkylation
Anisole was synthesized using the vapor phase alkylation method by the reaction of metha-
nol and phenol in the presence of a NaX zeolite (SiO2 to Al2O3 ratio: 2.6–3.0) as a catalyst.
The reaction was conducted at 300 °C with continuous stirring over an operating time of
3–4 h. As shown in Scheme 1, phenol frst reacts with NaX to form sodium phenoxide as
an intermediate, which further reacts with methanol to produce anisole as the main prod-
uct, along with o-cresol, p-cresol and p-xylene as by-products through o-methylation and
c-methylation, respectively [5, 27].
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Scheme 1 Synthesis of anisole and by-products through vapor phase alkylation
2.3 Distillation Column Setup
A round bottom fask of 2 L capacity was used as a reboiler and placed in a heating mantle
to distill the individual components from the multicomponent liquid mixture. A detailed
description of physical properties of these components is provided in Table 1. The heat-
ing mantle of 300 W was used to heat the liquid mixture in the reboiler. A glass column of
106.68 cm height and 1.95 cm diameter was fxed at the neck of the reboiler and flled with
various packing materials such as 6 mm stainless steel rings, 6 mm rashing rings, 3 mm SS
mesh type rings and 6 mm glass type rings for the separation of methanol, anisole, phenol
and cresol (Fig. 1a, b). The process could be optimized by varying diferent lengths and
diameters of the columns and packing material [28]. The packing plays a vital role in pro-
viding a large surface area for the contact of vapors with liquid, for the total column height
of up to 83.82 cm, which was randomly packed with 6 mm rasching rings, to optimize the
process. The details of the column diameter and type of packing materials are provided in
Table 1 Properties of multicomponent liquid mixture subjected to distillation
Component
Formula
Boiling point (°C)
Melting point (°C)
Molar mass Density (g·cm–3
)
(g·mol–1
)
Methanol
Anisole
Phenol
o-Cresol
p-Cresol
p-Xylene
CH4O
64.7
154
181.7
191
201.8
211–212
−97.6
−37
40.5
31
35.5
22–23
32.04
108.14
94.11
108.14
108.13
122.16
0.79
0.9
1.07
1.05
1.03
1.01
C7H8O
C6H6O
C7H8O
C7H8O
C8H10O
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Journal of Solution Chemistry (2021) 50:160–177
164
Fig. 1 a Schematic diagram of batch distillation column, b snapshot of batch distillation experimental set-
up
Table 2. A timer-controlled refux unit with a magnetic coil was connected to the column,
which contained a provision for the fow of three streams. The frst stream was directly
connected to the 24/29 size helical coil condenser, wherein the vapor turning to liquid was
followed by the second stream that reached back to the column. The bottom of the refux
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Journal of Solution Chemistry (2021) 50:160–177
Table 2 Column details for optimization
Column height (cm) Column diameter (cm) Packing height (cm) Packing type
66.04
106.68
53.34
1.27
1.95
1.95
1.95
48.26
83.82
43.18
78.74
Structural packing (manually rolled)
3 mm SS mesh type rings
6 mm glass type rings
101.6
6 mm stainless steel and rasching
unit was coupled with a glass collector for sample collection. Grease was applied to the
joints and polytetrafuoroethylene (PTFE) gaskets were used to ensure an airtight and leak
proof arrangement. The glass column and condenser were surrounded by glass wool for
better insulation. Digital temperature indicators were provided at the reboiler for measur-
ing the boiling temperature and vapor temperature at the top of the column. On the other
hand, a 2 L capacity glass conical-shaped separating funnel was arranged and used in the
laboratory for solvent extraction of anisole from the reaction mixture.
2.4 Experimental Procedure for Separation of Methanol, Anisole, Phenol
and o‑Cresol
The measured amounts of multicomponent liquid mixtures containing organic compounds
such as methanol, anisole, phenol, and cresols were taken into the three-neck reboiler and
placed in the heating mantle. The reboiler temperature was gradually increased to vaporize
the more volatile component from the reaction mixture. Among these organic compounds,
methanol is the most volatile component and its vapors start rising to the condenser at the
vapor temperature (VT) of 60 °C. Further, the VT reached a steady state with refux ratio
maintained at 1.5 and condensate collection was begun without any variation in the VT.
The same procedure was followed for anisole and phenol recovery by raising the reboiler
temperature up to 142 °C for anisole and an average temperature of 160 °C was main-
tained for phenol recovery. The experiments were conducted at the desired vapor pressure
that was kept constant, as any fuctuation in vapor pressure alters the purity of the compo-
nent. Figure 1a, b represent the experimental laboratory and snapshot of the setup where
methanol, anisole and phenol were isolated from the multi-component liquid mixture under
atmospheric pressure. On the other hand, the obtained residue contains very high boil-
ing point components such as o-cresol, p-cresol and other by-products. The o-cresol was
separated by vacuum distillation, in which boiling temperature was reduced by applying
a vacuum. The p-cresol and p-xylene components were left in the residue as by-products.
Figure 2 represents the proposed scheme for processing a multicomponent liquid mixture
by a batch distillation process, and all experiments were replicated thrice to achieve reli-
able results.
2.5 Experimental Procedure for Separation of Anisole by Aqueous NaOH Based
Solvent Extraction
Experiments were carried out at room temperature on a bench-scale using various normali-
ties of solvents. Among those, NaOH solution was selected as a solvent, as it dissolves the
by-products present in the anisole reaction mixture. Experiments were conducted by trial and
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166
Fig. 2 Proposed scheme of the multi-component batch distillation unit
error method by varying the 2 mol·L–1 NaOH ratio from 1:1 to 1:10 of the reaction mixture
volume. The measured amounts of synthetic mixture and NaOH solution were added to a sep-
arating funnel and mixed thoroughly by vigorous shaking. Then the separating funnel was
kept aside to attain two layers without any disturbance. The bottom layer that contained phenol
and cresols was drained cautiously through the stopcock, whereas the top layer that had ani-
sole was collected for further analysis.
2.6 Mathematical Equations for Calculations
The mixture boiling point was calculated as follows:
n
ꢀ
Mixture boiling point =
XiTbi
(1)
i=1
where Xi =mole fraction of component i, Tbi =boiling point temperature of component i,
and n=total number of components in the mixture.
The material and mass balances of the individual components were calculated as:
Material balance ∶ F = D + W + losses
(2)
Component balance ∶ FXi = (DXd) + (WXw) + losses
(3)
Reflux ratio R = L∕D
(4)
where F, D and W denote the volumetric fows of feed, distillate and residue; Xf, Xd and Xw
are mole fractions of feed, distillate and residue, correspondingly. In refux ratio calcula-
tions, L and D are the quantities of liquid returned to the distillation column and withdrawn
as a product, respectively.
The energy balance of the reaction mixture is calculated as follows:
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Journal of Solution Chemistry (2021) 50:160–177
Condensation with subcooling: Q = mꢀ + (mCpΔT)
Reboiler ∶ Q = (mꢀ)1.05(considering 5% losses)
(5)
(6)
where Q is the energy supplied to the system, m denotes the mass of a substance, λ is the
enthalpy of vaporization, Cpc is the heat capacity per gram, and ∆T is the change in tem-
perature (for convenience, the reference temperature Tr is considered as 25 °C).
3 Results and Discussion
3.1 Separation of Methanol, Anisole, Phenol and o‑Cresol
The individual organic compounds such as anisole, phenol and o-cresol in the multi-com-
ponent reaction mixture were separated by distillation, based on the diferences in volatil-
ity. Separate distillation experiments were conducted for separation of each component at
the temperatures mentioned in Fig. 2. Initially, 502 g of feed was introduced to separate the
low volatile compound, i.e., methanol, at a vapor temperature (VT) maintained at 60 °C
without any disturbance. The methanol distillate was collected at a steady state of VT to
achieve high purity levels. From Fig. 3a, it can be seen that the VT increased up to 60 °C
over a time period of 150 min, whereas a total of 401 g of methanol distillate was collected,
Time vs Temp
Time vs Volume
500
Time vs Temp
Time vs Volume
160
140
120
100
80
60
40
20
0
120
100
80
60
40
20
0
70
60
50
40
30
20
10
0
b
a
400
300
200
100
0
0
100
Time (min)
200
300
0
100
Time (min)
200
300
Time vs Temp
Time vs Volume
Time vs Temp
Time vs Volume
120
140
200
160
120
80
120
100
80
60
40
20
0
d
120
100
80
60
40
20
0
c
100
80
60
40
20
0
40
0
0
100
200
Time (min)
300
400
0
100
200
Time(min)
300
Fig. 3 Graphical representation of variation in temperature and volume with time of a methanol, b anisole,
c phenol, and d o-cresol recovery
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168
and the residual mixture was about 98 g in the reboiler, which was insufcient for further
product separation. Therefore, several batch experiments were conducted to obtain bulk
methanol-free mixtures to carry out the separation of additional components such as ani-
sole, phenol and cresols. The purity and recovery of the resultant methanol were found to
be 99.99% and 99.40%, respectively, after analysis by GC. The detailed analytical results
for methanol are provided in Table 3a. Though the experiments were conducted at vari-
ous VT, ultrapure grade methanol was achieved at 60 °C wherein the bulk of pure vapors
reached the condenser. In contrast, at other low VT, vapors move towards the reboiler, for
which reason the more volatile methanol was separated efectively at 60 °C, and the purity
was not afected due to the high boiling temperatures of the other organic compounds.
After the distillation of methanol, the residue of the reaction mixture was insufcient
to conduct the further separation of compounds. Therefore, three batch distillations were
performed to obtain a sufcient quantity of methanol-free reaction mixture. The bulk
Table 3 Analytical report from gas chromatography: a methanol, b anisole, c phenol, and d o-cresol frac-
tions
(a) Compound
Feed (502 g)
wt%
Distillate (401 g)
Residue (98 g)
wt%
wt (g)
wt%
wt (g)
wt (g)
Methanol
Anisole
Phenol
o-Cresol
p-Cresol
p-Xylene
80.37
4.95
14.37
0.16
0.09
0.05
403.48
24.85
72.13
0.81
0.47
0.26
99.99
401
–
–
–
–
0.91
25.1
72.8
0.8
0.5
0.3
0.89
24.38
71.75
0.80
0.47
0.26
–
–
–
–
–
–
(b) Compound
Feed (539 g)
Distillate (98 g)
Residue (433 g)
wt%
wt.(g)
wt%
wt.(g)
wt%
wt.(g)
Anisole
Phenol
o-Cresol
p-Cresol
p-Xylene
25.37
71.61
1.84
0.64
0.73
136.77
385.98
9.93
3.46
3.94
95.95
3.40
0.005
0.001
0.64
94.03
3.33
0.005
0.001
0.63
2.40
88.17
2.29
0.78
0.62
10.41
381.77
9.910
3.36
2.67
(c) Compound
Feed (136 g)
Distillate (108 g)
Residue (27 g)
wt%
wt.(g)
wt%
wt.(g)
wt%
wt.(g)
Phenol
92.127
4.398
1.938
1.316
125.29
5.98
2.64
95.88
2.85
0.60
0.22
103.55
3.08
0.65
76.60
9.29
7.74
6.05
20.68
2.51
2.09
1.63
o-Cresol
p-Cresol
p-Xylene
1.79
0.24
(d) Compound
Feed (200 g)
Distillate (131 g)
(Residue 60 g)
wt%
wt (g)
wt%
wt (g)
wt%
wt (g)
o-Cresol
p-Cresol
p -Xylene
59.76
24.92
15.31
119.52
49.85
30.63
91
7.17
1.39
119.21
9.39
1.83
0.10
76.33
23.57
0.059
45.80
14.14
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Journal of Solution Chemistry (2021) 50:160–177
methanol-free mixtures obtained from multiple batch experiments were used to carry out
further separation of components like anisole, phenol and cresols. The desired amount of
539 g of feed mixture was charged into the reboiler and then heated up to 170 °C. The
vapors started reaching the condenser in the optimal VT range of 139–142 °C to produce
pure anisole as distillate (Fig. 3b). Upon increasing the VT, the purity of anisole distillate
was enhanced, as evident from Fig. 3b, with the detailed analysis provided in Table 3b.
From the overall observations, the purity and recovery of anisole was about 95.52% and
71.65%, respectively. To enhance the purity of anisole further, the collected distillates were
considered as feed to conduct a second stage distillation. The detailed description of exper-
iments carried out for obtaining ultrapure anisole is provided in Sect. 3.2 on enrichment
studies.
An anisole free residue of 136 g was used as a feed for further separation of phenol, o-
cresol and p-cresol. From Fig. 3c, the total volume of phenol found to be collected as distil-
late was about 108 g at a vapor temperature range of 157–160 °C at a refux ratio of 1.5.
The obtained distillate purity was found to be 95.88%, with a phenol recovery of 82.60%.
The fnal product purity not only depends on the VT but also depends on the refux ratio,
type of packing material and diameter of the column.
On the other hand, o-cresol was separated from p-cresol and p-xylene by vacuum distil-
lation at a vapor temperature of 104–105 °C (Fig. 3d) under 200 mm-Hg (26.7 kPa) pres-
sure. In this process, vacuum distillation was chosen to separate cresols because of their
high boiling temperatures. The total amount of distillate collected was around 131 g of
o-cresol, with a purity of 91.0%. The purity of o-cresol was not signifcant due to the close
boiling points of o-cresol and p-cresol. The p-cresol and p-xylene were left over as by-
products. The experimental results are graphically depicted in Fig. 3a–d, as well as the
analytical values provided in Table 3 (a, b, c, and d) for separation of methanol, anisole,
phenol and o-cresol, respectively. From the overall observations, it can be concluded that
sequential separation of methanol, anisole, phenol and cresols is a viable option and the
distillate should not be collected beyond the stipulated vapor temperature of each organic
compound.
3.1.1 Material and Mass Balance for Methanol, Anisole, Phenol and o‑Cresol
The overall material and mass balances of individual components are presented in Table 4a,
in which the loss of methanol is minimal compared to other compounds. Anisole loss was
a little bit higher than for methanol. There is a chance for accumulation of other compo-
nents if the conditions are unstable, and in order to reduce the condensate rate, redemption
circulation was provided. Since product loss is a big drawback in separation processes, the
column was wrapped with wool to control heat loss as well as promote a sufcient con-
densation rate to reduce vapor losses. Phenol loss was very high, compared to methanol
and anisole, whereas cresol and methanol losses were low. The reason might be the high
boiling point of phenol, which leads to a slow condensation rate. The energy balance was
calculated from Eqs. 5 and 6 for all components at constant pressure and reference tem-
perature (Tr) of 25 °C. The feed, distillate and residue enthalpies were calculated by con-
sidering vapor, liquid temperatures and also specifc heat values at 25 °C of the individual
components. The detailed energy balance values are provided in Table 4b [29–32]. From
the calculated values, 482.68 kJ represents the energy supplied to the column for achiev-
ing the purity of 99.99% methanol (401 g), whereas 141.83 kJ energy was used to attain
95.52% purity of anisole (98 g). The purities of phenol (108 g) and o-cresol (131 g) were
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Journal of Solution Chemistry (2021) 50:160–177
170
Table 4 Overall (a) material and component balances (MB and CB), and (b) energy balances (EB) during
individual component separation
(a) Contents Methanol
column
Anisole
column
Phenol col-
umn
o-Cresol
Anisole
Phenol
column
enrichment
column
enrichment
column
MB CB
MB CB
MB CB
MB CB
MB CB
MB CB
Input g
502 403.5 539 130.65 136 125.29 200 119.52 202 182.55 175 169.3
499 401.9 531 99.63 108 103.55 191 119.27 194 149.46 91 89.45
3.0 1.11 8.0 31.11 1.0 1.76 9.0 0.255 8.0 33.09 14.0 13.54
0.57 0.275 1.48 23.81 0.73 0.140 4.5 0.188 3.96 18.12 8.00 7.99
λ/ kJ·mol–1 Ref. for λ
Output g
Losses g
Loss %
(b) Compo- Qf =mCp(Tf Qv =mCp(Tv Ql =mCp(Tl Q/kJ
Q/kJ
nents
–Tr)
– Tr)
– Tr)
(condensa- (reboiler)
tion with
subcooling)
Methanol
0
35.56
6.57
482.68
1.027
35.2
[29]
(feed and
reference
tempera-
ture are
the same)
Anisole
Phenol
o-Cresol
Anisole
enrich-
ment
20.33
19.56
12.28
19.26
79.50
4.99
7.80
141.83
89.29
68.24
77.05
4.88
48.3
[30]
[31]
[32]
[29]
13.58
0.025
28.55
58.83
43.69
48.3
15.80
Phenol
enrich-
ment
16.73
13.64
86.28
43.52
58.83
[30]
calculated to be 95.88% and 91.0%, when the quantities of energy supplied were 89.29 kJ
and 68.24 kJ, respectively. The amount of energy provided to the column can be reduced
by scaling up the process.
3.2 Enrichment Studies
Anisole and phenol purities play a signifcant role in industrial applications due to the
enormous market demand for ultrapure chemicals. Therefore, to fulfll the need, further
experiments were carried out to increase the purity levels of the organic compounds. The
so formed distillates of anisole and phenol were used as feed into a second stage purif-
cation step to achieve>99% purity. The same column and procedures were employed to
enrich the purity levels of anisole and phenol. From Fig. 4a, b, it can be clearly seen that
by raising the VTs of 133 °C and 161 °C with respect to time, anisole and phenol purities
were enhanced from 95.52 to 99.80% and from 95.88 to 98.29%, respectively, correspond-
ingly after which equilibrium was attained. The detailed analytical results of enriched ani-
sole and phenol studies are provided in Table 5a, b. The precise calculation of mass, com-
ponent and energy balances are provided in Table 4a, b, wherein the anisole mass balance
loss is very low, as compared to phenol loss. The enrichment factors for anisole and phenol
1 3

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Journal of Solution Chemistry (2021) 50:160–177
Time vs Temp
Time vs Volume
Time vs Temp
Time vs Volume
200
160
120
80
120
150
100
50
100
80
60
40
20
0
a
b
80
40
0
40
0
0
0
100
200
300
400
0
100
200
300
400
Time (min)
Time (min)
Fig. 4 Graphical representation of variation in temperature and volume with time of a anisole, and b phenol
enrichment
Table 5 GC analysis data for (a) anisole enrichment and (b) phenol enrichment
(a) Compound
Feed
202 g
Distillate 81 g
Residue
wt%
113 g
wt (g)
Frst cut
wt%
20 g
Second cut
wt%
61 g
wt%
wt (g)
wt (g)
wt (g)
Anisole
Phenol
o-Cresol
p-Cresol
p-Xylene
91.902
7.379
0.048
0.015
0.018
186.49
14.91
0.10
0.03
0.04
93.01
5.42
0.09
0.005
–
18.6
1.08
0.02
0.001
–
99.79
0.053
–
–
–
60.87
0.032
–
–
–
65.42
20.27
2.90
5.23
2.32
73.93
22.90
3.28
5.91
2.63
(b) Compound
Feed
wt%
175 g
wt (g)
Distillate
wt%
91 g
wt (g)
Residue
wt%
70 g
wt (g)
Phenol
96.72
2.09
0.87
0.23
169.3
3.65
0.98
0.39
98.29
1.16
0.49
0.01
89.45
1.16
0.45
0.01
94.72
3.45
1.20
0.52
66.31
2.41
0.84
0.36
o-Cresol
p-Cresol
p-Cylene
were found to be 99.80% and 98.29%, with amounts of 61 g and 91 g obtained as products,
when quantities of energy supplied to the column were 77.05 kJ and 86.28 kJ, respectively.
The energy utilized for the reboiler is also represented in Table 4b. From the enrichment
studies, it can been observed that the key product anisole was separated with high purity
and maximum recovery, which is the most important consideration for industrial applica-
tions. The removal of contaminants from anisole can be maximized, which improves prod-
uct quality.
1 3

Journal of Solution Chemistry (2021) 50:160–177
172
800
700
600
500
400
300
200
100
0
Anisole B.P curve
Phenol B.P curve
O-Cresol B.P curve
P-Cresol B.P curve
Xylenol B.P curve
Methanol B.P curve
0
50
100
150
200
250
Temperature (°C)
Fig. 5 Graphical representation of boiling point curves
3.3 Experimental Parameters
3.3.1 Efect of Boiling Temperature at an Absolute Pressure
The efect of the boiling temperature of individual components in the reaction mixture was
studied at various degrees of vacuum. Figure 5 illustrates the efect of boiling temperature
under diferent operating pressures, with individual component boiling points as expected
were found to decrease at higher vacuum when compared to atmospheric pressure. The
boiling temperature infuences the VT of the components, which directly afects the recov-
ery and purity of methanol, anisole, phenol and cresols at various absolute pressures. The
boiling points of liquids will be lower than atmospheric pressure than under vacuum, where
the vapor pressure equals the applied pressure [33].
3.3.2 Variation of Individual Component Boiling Temperatures in a Multi‑component
Liquid Mixture
The actual boiling points of individual components are provided in Table 1. When these
components are present in the feed mixture, their boiling temperature may become
increased due to the intermolecular interactions between molecules of the same group.
Moreover, properties also depend on atmospheric pressure, applied vacuum, temperature,
and nature of the molecules. In our experimental study, the boiling points of individual
components such as methanol, anisole, and phenol increased from 64.7 °C, 154 °C, and
181.7 °C (Table 1) to 70 °C, 160 °C, and 166 °C, corresponding to what may occur due to
the multi-component nature of the liquid mixture (Fig. 2).
3.3.3 Efect of Refux Ratio
The product purity plays a major role in the separation, as it enhances the process feasibil-
ity, dependability and economy. Experiments were performed with column refux ratios in
the range of 0.25 to 1.5, and the purity of individual components in the distillate are shown
1 3

173
Journal of Solution Chemistry (2021) 50:160–177
Table 6 (a) Variation of anisole, methanol and phenol purity with refux ratio, and (b) overall % recovery
and purity of fnal products
(a) Refux ratio
Methanol purity %
Anisole purity %
Phenol purity %
0.25
0.50
0.75
1.00
1.25
1.50
90.92
98.90
99.10
99.60
99.73
99.99
91.66
91.79
95.52
98.71
99.78
99.80
92.85
95.81
96.18
97.79
98.08
98.29
(b) Separation techniques
Compounds
% Purity
% Recovery
Atmospheric distillation
Methanol
Anisole
Anisole enrichment
Phenol
Phenol enrichment
o-Cresol
99.99
95.52
99.80
95.88
98.29
91.00
99.4
71.65
43.5
82.6
52.6
89.10
Vacuum distillation
in Table 6a, b. Hence, during distillation, the purity of components mainly depends on the
refux ratio. This set of experiments were conducted to study the efect of the refux ratio
on product purity. From Table 6a, b, it can be observed that the purity of individual com-
ponents of the mixture became increased by increasing the column refux ratio, wherein the
maximum refux ratio of 1.5 was ideal in achieving methanol, anisole and phenol purities
of 99.99%, 99.80% and 98.29%, respectively.
3.4 Separation of Anisole from the Synthetic Reaction Mixture by Solvent
Extraction
A case study was conducted for anisole recovery from a synthetic mixture containing
8.8134 g anisole+15.50 g phenol+0.524 g o-cresol+0.236 g p-cresol by the solvent
extraction technique. This synthetic mixture was treated with NaOH, FeCl3, Na2CO3 with
Table 7 Selection of solvent on the basis of solubility of components for solvent extraction
Salts
Normality
Phenol
p-Cresol
o-Cresol
Anisole
Ratios
NaOH
NaOH
NaOH
FeCl3
FeCl3
FeCl3
FeCl3
Na2CO3
Na2CO3
1.66
0.10
0.06
2
2
2
2
2
2
Soluble
Soluble
Soluble
Insoluble
Insoluble
Insoluble
Soluble
Insoluble
Insoluble
Soluble
Soluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
1:09
1:09
1:09
1:01
1:02
1:03
1:04
1:01
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Insoluble
Up to 1:10
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Journal of Solution Chemistry (2021) 50:160–177
174
Fig. 6 Process fow diagram for the purifcation of 1000 kg·h–1 multicomponent liquid mixture by PRO/II™
simulator
Table 8 Simulation results for designing of 1000 kg·h–1 capacity of a multicomponent distillation unit
Column ID
Condenser
duty
Reboiler
duty
Packed col-
Packed col- Product fow Product purity
umn diameter umn height
rate (kg·h–1
)
(106 kJ·h–1)
(106 kJ·h–1) (m)
(m)
T1
− 2.417
− 0.225
− 0.180
2.473
0.225
0.179
2
1.91
804.5
0.9986
0.9904
0.9835
(methanol
separator)
T2
0.7
0.5
6.86
1.52
49.45
110
(anisole sepa-
rator)
T3
(phenol sepa-
rator)
varying ratios of 1:1 to 10:1 over a period of 30 min with detailed descriptions provided
in Table 7. The byproducts completely dissolved in the aqueous NaOH and were isolated
from anisole present in the reaction mixture, due to which aqueous NaOH was selected
as a fnal solvent for this study compared to FeCl3 and Na2CO3. Hence, experiments were
conducted by a trial and error method by varying the volumetric ratio of 2 mol·L–1 NaOH
solution with respect to the reaction mixture. A purity of 99.8% anisole of 8.184 g quantity
was recovered from 8.8134 g of anisole present in the initial synthetic mixture.
3.5 Simulation to Design the Column Separation Train
Based on the experimental results, process simulation was performed using the PRO/
II™ commercial simulator, developed by Simsci-Aveva (www.aveva.com), to design the
separation columns [34]. Figure 6 represents the designed process fow diagram for the
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Journal of Solution Chemistry (2021) 50:160–177
purifcation of 1000 kg·h–1 multicomponent liquid mixture with known compositions
taken from Table 3(a). The Soave–Redlich–Kwong (SRK) thermodynamic model was
used [35] to estimate the properties and the operating parameters, and it was similar to
the experimental conditions. Details of the Norton 6 mm rasching rings and the energy
requirements of condenser, reboiler were estimated (Table 8). As seen from the results,
the methanol and phenol separation is entirely comparable with the experimental fnd-
ings. After verifying the experimental results with the simulator, it was found that by
recirculating 100 kg·h–1 feed from stage 1 to stage 4 in the packed column, 99.0% pure
anisole could be achieved.
4 Conclusions
The present study provides data on atmospheric and vacuum distillation adopted to sepa-
rate a multi-component reaction mixture comprised of methanol, anisole, phenol, cresols
and p-xylene formed during the production of value-added anisole from methanol and phe-
nol reactants. Based on the experimental studies, it was observed that atmospheric distilla-
tion is more feasible for these separations due to the absence of bumping problems, which
were encountered during vacuum distillation. Diferent experimental trials were performed
to optimize the operating parameters such as column length, outer and inner diameters,
besides refux ratios with random packing. Atmospheric distillation achieved>98% purity
and recovery of>70%. The material, individual components and energy balances were cal-
culated to scale up the process. On the other hand, solvent extraction was used to isolate
ultrapure anisole from the synthetic reaction mixture. From the solvent extraction study,
the recovery of anisole from the synthetic mixture was found to be 99.80%. Anisole of this
purity fnds applications in water treatment, drugs, pesticides and photographic chemicals.
From the results, it can be concluded that the atmospheric distillation is still an efective,
economical and dependable alternative to other separation techniques for achieving maxi-
mum purity. Vacuum distillation was successful in recovery of the high boiling cresols.
Process simulation was performed by the PRO/II™ commercial simulator to design distil-
lation columns on an industrial scale for processing 1000 kg·h–1 capacity of the multi-com-
ponent liquid mixture, which established the commercial feasibility of the process.
Acknowledgements The frst author wishes to acknowledge CSIR-IICT-AcSIR for providing funding and
the opportunity to carry out PhD research. We thank the Director, CSIR-IICT, for supporting this research
work of communication no. IICT/Pubs./2020/059.
Funding This funding was supported by CSIR Grant No. [31/014(2764)/2018-EMR-1].
Compliance with Ethical Standards
Confict of interest All authors have seen and approved the manuscript being submitted. Hence, on behalf of
all authors, the corresponding author states that there is no confict of interest.
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