Kinetic investigation on liquid-liquid-solid phase transfer catalyzed synthesis of dibenzyl disulfide with H2S-laden monoethanolamine

Article abstract of DOI:10.1016/j.molcata.2015.10.013

An investigation has been done on the utilization of H₂S for the synthesis of dibenzyl disulfide (DBDS) using Amberlite IR-400 as a phase transfer catalyst. This involves absorption of H₂S in aqueous monoethanolamine (MEA) followed by reaction of this H₂S-laden MEA with organic reactant benzyl chloride (BC) to yield DBDS under liquid-liquid-solid (L-L-S) phase transfer catalysis condition. The effect of various parameters on the conversion of BC was studied and the selectivity of desired product was 100% at some level of process parameters. A suitable reaction mechanism has been proposed and a mathematical model has been developed to explain the kinetics of the reaction. Waste minimization was therefore affected with the utilization of _H2S-laden gas for production of a value-added fine chemical.

Full text of DOI:10.1016/j.molcata.2015.10.013

Accepted Manuscript
Title: Kinetic investigation on Liquid-Liquid-Solid Phase
Transfer Catalyzed Synthesis of Dibenzyl Disulfide with
H2S-laden Methyldiethanolamine
Author: Gaurav Singh Priya G. Nakade Pratik Mishra Preeti
Jha Sujit Sen Ujjal Mondal
PII:
S1381-1169(15)30116-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.10.013
MOLCAA 9656
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
6-9-2015
11-10-2015
12-10-2015
Please cite this article as: Gaurav Singh, Priya G.Nakade, Pratik Mishra,
Preeti Jha, Sujit Sen, Ujjal Mondal, Kinetic investigation on Liquid-Liquid-
Solid Phase Transfer Catalyzed Synthesis of Dibenzyl Disulfide with H2S-
laden Methyldiethanolamine, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2015.10.013
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Kinetic investigation on Liquid-Liquid-Solid Phase Transfer Catalyzed
Synthesis of Dibenzyl Disulfide with H2S-laden Methyldiethanolamine
Gaurav Singh, Priya G. Nakade, Pratik Mishra, Preeti Jha, Sujit Sen*, Ujjal Mondal
Catalysis Research Laboratory, Department of Chemical Engineering, National Institute of
Technology, Rourkela – 769008, India
*Corresponding author: Tel: +91-9938246590; Fax: +91-661-2462999; Email: sensujit@nitrkl.ac.in
Graphical abstract
1

Highlights
 In all experimental run, selectivity of the product DBDS was 100%.
 Reaction was kinetically controlled with activation energy 56.03 kJ/mol.
 Anion Exchange resin Amberlite IR-400 showed good reusability.
 Developed kinetic model predicts the results quite well at all temperatures.
 The proposed mechanism can successfully explain the course of the reaction.
2

ABSTRACT
An investigation has been done on the utilization of H2S for the synthesis of dibenzyl disulfide (DBDS)
using amberlite-400 as a phase transfer catalyst. This involves absorption of H2S in aqueous
monoethanolamine (MEA) followed by reaction of this H2S laden MEA with organic reactant benzyl
chloride (BC) to yield DBDS under liquid-liquid-solid (L-L-S) phase transfer catalysis condition. The
effect of various parameters on the conversion of BC was studied and the selectivity of desired product
was 100% at some level of process parameters. A suitable reaction mechanism has been proposed and a
mathematical model has been developed to explain the kinetics of the reaction. Waste minimization
therefore affected with the utilization of HꢀS-laden gas for production of a value-added fine chemical.
Keywords: dibenzyl disulfide, Liquid-liquid-solid phase transfer catalyst, Hydrogen sulphide, Kinetics
NOMENCLATURE
MEA
BC
monoethanolamine
benzyl chloride
PTC
H2S
phase transfer catalyst
hydrogen sulfide
dibenzyl sulfide
dibenzyl disulfide
sulfide anion
DBS
DBDS
Sꢀꢁ
3

Sꢀꢀꢁ
disulfide anion
QSQ
Q2S2
catalyst active intermediate
catalyst active intermediate
ꢂ
ꢀꢁꢃ
Sꢀ
concentration of disulfide anion (kmol/m3)
concentration of chloride anion (kmol/m3)
initial concentration of organic substrate in organic phase (kmol/m3)
[Clꢁꢃ
ꢂ
ꢂ
ꢂ
ꢃ
RCl
ꢄꢅꢆ,ꢇ
ꢄꢅꢆ
concentration of organic substrate in organic phase at any time t (kmol/m3)
total concentration of catalyst per total system volume (kmol/m3)
apparent reaction rate constant [min-1]
ꢃ
RCl
ꢈꢃꢉꢊꢉ
Q
ꢋꢌꢍꢍ
`
ꢋꢄꢅꢆ
overall reaction rate constant [m3/(kmol of catalyst .min)]
ꢎꢏꢐ
ꢎꢒ
equilibrium attachment/detachment constant for ꢑꢀꢀꢁ ions [m3/(kmol of catalyst .min)]
equilibrium attachment/detachment constant for ꢓꢔꢁ ions [m3/(kmol of catalyst .min)]
fraction of total number of catalyst cation attached to ꢑꢀꢀꢁ
fraction of total number of catalyst cation attached to ꢓꢔꢁ
fraction of total number of catalyst cation attached to both ꢑꢀꢀꢁ and ꢓꢔꢁ
fractional conversion of reactant
θꢕ
θꢖꢗ
θꢖꢗꢕ
XRCl
t
time (min)
4

1. INTRODUCTION
Due to decline in light-to-process crude, refineries around the world are forced to process heavy crude
that contains substantial amount of organo-sulfur and organo-nitrogen compounds. Typically hydro-
desulfurization process converts those organosulfur compounds to form hydrogen sulfide (H2S) and
ammonia (NH3). H2S is a toxic gas, poisonous even in a very small concentration, corrosive in presence
of water and classified as a hazardous industrial waste [1, 2]. Lots of work has already been done on
removal and recovery of hydrogen sulfide so far. Vilmain removed hydrogen sulfide using aqueous
chlorine solution by reactive absorption in a mechanically agitated gas-liquid reactor [3]. Copper-zinc
oxide supported on mesoporous silica reported good absorption capacity for hydrogen sulfide [4]. Ferrous
and alum water were also used for the removal of hydrogen sulfide [5].
The removal of H2S from various gas streams using aqueous solution of alkanolamines is a
commercialized industrial process since early thirties [6]. In refineries and natural gas processing gas
industries removal of NH3 and H2S are done by scrubbing with water and amine treating unit respectively.
Once H2S is absorbed, it is converted into element sulfur using Claus process, which is conventional
method to produce elemental sulfur from H2S but it is very energy expensive. Another disadvantage of
this method is high production rate of elemental sulfur in comparison to the rate of consumption, so the
disposal of elemental sulfur is a severe problem for refineries. Thus, an alternative process to Claus
process has been in high demand for better utilization of hydrogen sulfide. The present work was
undertaken to develop substitute of Claus process. This work dealt with the synthesis of dibenzyl
disulfide from hydrogen sulfide under the presence Amberlyte IR-400 as phase transfer catalyst.
Dibenzyl disulfide is very important compound and having very diversified applications in the field of
organic synthesis. Several methods have been described for the preparation of organic disulfides using
different reagents and catalysts. Dhar synthesized disulfide by alkylation of alkyl halides with
5

tetrathiotungstate and tetrathiomolybdates [7]. Benzyltriethylammonium tetracosathioheptamolybdate
[(C6H5CH2N(Et)3)6Mo7S24] was found to be a good reagent for the synthesis of disulfide from alkyl
halides [8]. Disulfides were synthesized by oxidative coupling of thiols in presence of air using Fe
(III)/NaI as a catalyst [9]. Thiols were oxidized into their corresponding disulfides through oxidative
coupling in presence of potassium phosphate as a catalyst [10]. Disulfide were also synthesized by
oxidative cleavage of aryl or alkyl tert-butyl sulfide [11]. Landini and Rolla synthesized primary and
secondary dialkyl and aryl alkyl sulfides by using sodium sulfide in presence of Phase transfer catalyst
(PTC) [12]. In the same way Wang and Tsang prepared symmetrical thioethers using sodium sulphide
(Na2S) and n-bromobutane [13]. Sen reported synthesis of dibenzyl sulfide from benzyl chloride using
H2S-rich aqueous monoethanolamine [14]. A few literatures are available on the preparation of
symmetrical thioethers from H2S-laden alkanolamine in presence of PTC. Na2S was also used for
preparation of aliphatic polysulfides in presence of quaternary onium salt and for reduction of nitroarens
to anilines under PTC condition [15, 16]. Bandgar reported synthesis of variety of symmetrical disulfides
from aryl alkyl halides by reduction of sulfur with borohydride exchange resin in methanol [17].
Phase transfer catalysis is a technique to lead a reaction from the reactants present in two mutually
insoluble phases under mild operating conditions. It is now commercially mature discipline having wide
range of industrial applications such as intermediates, perfumes, agrochemicals, pharmaceuticals and
polymers [18, 19]. Many organic compounds have been synthesized under the presence of different PTC
[20-24]. Sonavane also developed a one-pot method for synthesis of disulfides from the reaction of sulfur
with sodium sulfide in the presence of didecyldimethylamonium bromide (DDAB) as a PTC [25, 26].
Disulfides were also synthesized from alkyl halides using thiourea and elemental sulfur in presence of
polyethylene glycol (PEG 200) [27]. The conventional soluble PTCs are having one disadvantage of
separation. Distillation or extraction can be used for the separation of the catalyst but it may increase
complexity of the process and may affect purity and cost of the product. These drawbacks can be
overcome with the use of solid PTC such as polymeric resins and the phenomena is known as Liquid-
6

Liquid-Solid (L-L-S) PTC. Tri-phase PTC has several other advantages over soluble PTC in terms of
recovery and reusability of the catalyst. Amberlite IR-400 resin has been used for sometimes as a
heterogeneous catalyst for the synthesis of organic compounds [28]. The aim of the work is to utilize H2S
to synthesis fine chemical dibenzyl disulfide selectively. This work has a great industrial relevance as it
could replace the conventional Claus method followed in most refineries.
2. EXPERIMENTAL SECTION
2.1 Chemicals. Toluene (≥ 99%), Monoethanolamine (MEA) (≥99%) and Benzyl Chloride of analytical
grade were procured from Rankem (India), New Delhi, India. Amberlite IR-400 (Cl- form) was obtained
from Merck (India) Ltd., Mumbai, India.
2.2 Experimental Setup. All the reactions were carried out in a 6.5 cm internal diameter, fully baffled
mechanically agitated batch reactor of capacity 250 cm3. 2 cm diameter six-bladed glass disk turbine
impeller with digital speed regulation system, kept at a height of 1.5 cm from the bottom of the reactor,
was used for stirring the reaction mixture. The reactor was kept in an isothermal water bath (±1oC) having
PID controller.
2.3 Preparation of H2S-laden Aqueous MEA. 30-35 wt. % aqueous MEA solution was prepared by
adding adequate quantity of raw MEA in measured amount of distilled water. Then HꢀS gas was bubbled
through the aqueous MEA solution in gas bubbler, placed in ice bath. This gas bubbling process was
continued till desired sulfide concentration was attained. Sulfide concentration was estimated using
iodometric titration
2.4 Experimental Procedure. In each experimental run, 50 cm3 of aqueous alkanolamine solution
containing a known concentration of sulfide was taken into the 250 cm3 reactor and kept well agitated by
7

stirrer until the steady state temperature was reached. Then 50 cm3 of the organic phase containing
measured quantity of organic reactant (benzyl chloride) dissolved in solvent (toluene) and the catalyst
(Amberlite IR-400) was added into the reactor. The reaction mixture was then agitated at a constant speed
of stirring. Minimal amount of sample from the organic phase was withdrawn by micropipette at regular
time intervals after stopping the agitation and allowing the phases to separate.
2.5 Organic Phase Analysis. In present work, analysis of organic phase were performed on GC (Agilent
GC 7890B) by using a capillary column DB-5MS, 2 m x 3 mm, coupled with flame ionization detector.
The product was further confirmed by GC-MS (Agilent 5977A).
3. RESULT AND DISCUSSION
3.1 Parametric Study.
3.1.1 Effect of Stirring Speed. The speed of agitation was varied from 1000 to 2500 rpm in both the
conditions, with and without catalyst to determine effect of mass transfer resistance of reactants on the
reaction rate. Fig. 1 shows that rate of reaction is practically same in all stirring speeds. Therefore, it can
be assumed that beyond 1500 rpm, increase in stirring speed has no influence on reaction rate, so reaction
can be safely considered as a kinetically controlled reaction. Thus, the further synthesis was carried out at
1500 rpm to remove mass transfer resistance. In absence of catalyst the rate of reaction is very low,
therefore, further experiments have been performed in presence of catalyst only.
3.1.2 Effect of Sulfur Loading. Disulfide and polysulfide anions can easily be obtained by dissolving
elemental sulfur powder in S2- anion rich aqueous phase [25]. The effect of this elemental sulfur loading
on synthesis of DBDS was investigated by adding different concentration of sulfur powder in H2S-laden
8

MEA. The colour of aqueous MEA changed from greenish to reddish brown indicating formation of
polysulfide anions ꢑꢘꢀꢁ (where x = 1, 2, 3, 4) depending on sulfur loading.
At low sulfur loading, hydrosulfide (HS-) and sulfide (S2-) ions are the dominating sulfur species giving
BM and DBS respectively as the product [29]. So the selectivity of DBDS at 0.25 and 0.49 of sulfur to
sulfide mole ratio was found to be low and it was almost negligible in absence of sulfur loading (Fig. 2).
ꢀꢁ
Whereas at high sulfur loading, polysulfide anions ꢑ
are the dominating sulfur species, giving
ꢙ,ꢚ,ꢛ
unwanted products like trisulfidse and polysulfides, which consequently gives again low DBDS
selectivity. 100% selectivity of DBDS was observed at 1.875 kmol/m3 of sulfur due to presence of only
disulfide anions ꢑꢀꢀꢁ. So 1.875 kmol/m3 of sulfur was considered as an optimum reaction parameter and
further experiments were performed at this condition.
3.1.3 Effect of Catalyst Concentration. The influence of catalyst loading on BC conversion was
determined both in presence and absence of catalyst keeping other reaction condition constant (Fig. 3). It
was noticed that BC conversion was only 61% in absence of catalyst even after 480 min of reaction. A
drastic increase in BC conversion was observed with catalyst loading and conversion was observed to
increase with increase in catalyst loading.
In the presence of catalyst, Sulfide (S2-) and disulfide ꢜꢑꢀꢀꢁꢝ anions of aqueous phase react with
quaternary ammonium halide (Q+) to give catalyst active intermediates QSQ and Q2S2 respectively.
These catalyst intermediates then migrate from aqueous to organic phase to react with BC to give DBS
and DBDS respectively. With increase in catalyst concentration, more catalyst intermediates are formed
and travel to organic phase giving increased conversion of BC.
In present work, 100% selectivity of DBDS was observed due to adequate quantity of sulfur powder in
aqueous phase giving only disulfide ꢑꢀꢀꢁ anions.
9

Table 1 shows enhancement of initial reaction rate at different catalyst loading as compared to that in
absence of Amberlite catalyst. Enhancement factor indicates the importance of Amberlite IR-400 as a
PTC in DBDS synthesis.
In order to calculate order of reaction with respect to Amberlite IR-400 catalyst, natural logarithm of
initial reaction rate of different catalyst concentration was plotted against natural logarithm of Amberlite
concentration (Fig. 4). The order of reaction, obtained from slope of plot, was 0.55 which is considered as
1st order with respect to catalyst concentration.
3.1.4 Effect of Temperature. The effect of temperature on conversion of BC was studied under
otherwise similar conditions. The temperature was varied from 303 to 333K keeping other experimental
conditions constant. The effect of temperature on conversion of BC is shown in Fig. 5. The expected
nature of increased BC conversion with increase in temperature was noticed according to transition
theory.
Initial reaction rate was calculated at different temperature for Arrhenius plot. Natural logarithm of initial
reaction rate was plotted against 1/T (K-1) and apparent activation energy was calculated from slope of the
plot (Fig. 6). The apparent activation energy of kinetically controlled reaction was obtained as 56.03
kJ/mol.
3.1.5 Effect of Benzyl Chloride Concentration. The effect of reactant concentration was investigated by
varying organic reactant concentration (BC) keeping constant sulfide concentration in aqueous phase i.e.
different initial BC/ Sulfide mole ratio. Decrease in BC conversion was noticed with increase in ratio due
to limitation of sulfide anions present in aqueous phase (Fig. 7). At 1.04 BC/sulfide mole ratio, optimum
10

conversion was obtained but reduced to 94% for 1.39. So it is concluded that low initial BC/ sulfide mole
ratio is preferable for present work to get maximum conversion.
From the plot of ln(initial rate) vs. ln(concentration of BC) (Fig. 8), the order of reaction with respect to
BC concentration was obtained as 2.44, which is close to 2. Hence the order of reaction is second order
with respect to the concentration of reactant.
3.1.6 Effect of Sulfide Concentration. Sulfide concentration of aqueous phase was varied from 1.75 to
2.5 kmol/m3 keeping constant MEA concentration (35 wt %). There was slight decrease in conversion
noticed with decreasing sulfide concentration but almost 98% conversion was achieved at 2.50 kmol/m3
sulfide range at 480 min of reaction time (Fig. 9).
From the plot of ln (initial rate) against ln(initial sulfide concentration) (Fig. 10), the slope of linear fit
line was found out to be to be 2.14. Since this value is closer to 2, the reaction was considered second
order with respect to the sulfide concentration.
3.2 Catalyst recovery and reuse. After completion of synthesis process, agitation was stopped and
aqueous and organic phases were allowed to settle down in a separating funnel. Organic phase, present on
top of aqueous phase, containing product was removed and Amberlite catalyst was allowed to settle down
in aqueous phase. The catalyst present in aqueous phase was first recovered using filter paper then it was
washed with acetone first to remove organic traces, then with water and 50% aqueous sodium chloride
(NaCl) solution. After washing, catalyst was dried at 500C in oven to remove any adsorbed substance
present on it. For each run, recovered catalyst was reused in kinetic run four times and data were obtained
shown in Fig. 11.
From the Fig. 11, it is seen that reusability of Amberlite is excellent up to four uses. But in every run,
decrease in conversion was observed due to loss of catalyst in aqueous and organic phase and during
catalyst washing process.
11

3.3 Proposed mechanism of synthesis of Dibenzyl Disulfide under L-L-S PTC. The mechanism of
reaction between BC with H2S- laden MEA and sulfur powder in aqueous phase using Amberlite IR-400
as a PTC is shown in Scheme 2. Generally aqueous phase reactions are faster as compare to organic phase
reactions, so an ionic equilibrium exists in aqueous phase between RNH2 (MEA)-H2O-H2S which results
in formation of three active inorganic nucleophiles namely hydroxide (OH)-, sulfide (S2-) and disulfide
(Sꢀꢀꢁ) as represented in aqueous phase. In the present system, hydrosulfide anion (HS-) is not expected to
stay due to presence of sulfur powder in aqueous phase. Sulfur shifts ionic equilibrium to right giving
only sulfide (S2-) and disulfide (ꢑꢀꢀꢁ) anions in aqueous phase. The product was obtained from both
catalytic and non-catalytic contribution.
3.3.1 Non- catalytic Contribution. Ethanolamine sulfide ((RNH3)2S) and ethanolamine disulfide
((RNH3)2S2), formed in aqueous phase via reaction (2) and (3) respectively in Scheme 2, are insoluble in
organic phase. So they are expected to react with BC in aqueous-organic interface to give DBS and
DBDS respectively as shown in reaction (7)-(9). Due to 2nd order reaction rate of nucleophilic reaction,
DBS is expected to form via formation of intermediate product C6H5CH2SNH3R which again reacts with
BC to give desired DBS. The formed product travels from interface to organic phase from where selective
separation of products takes place.
3.3.2 Catalytic Contribution. Mass transfer and surface reaction are two important steps in presence of
solid catalyst in L-L-S PTC [30]. Synthesis steps involves:
Step 1: Diffusion of aqueous anions S2-and Sꢀꢀꢁ from bulk aqueous phase to PTC.
Step 2: Ion exchange reaction of these nucleophiles with catalyst cation (Q+) to form catalyst active
intermediate QSQ and Q2S2 as shown in reaction (4)-(6) and leaving Cl- anion.
12

Step 3: Diffusion of organic reactant BC from bulk organic phase to PTC.
Step 4: Synthesis reaction of BC at catalyst active site present at aqueous organic interphase to give
desired products (reaction 10-12).
Step 5: Diffusion of anion Cl- and product from interface to aqueous and organic phase respectively as
shown in scheme 2.
3.4 Kinetic modeling. The GC analysis shows that the formation of DBS is very less as compared to
DBDS. This observation can be attributed to less diffusion of aqueous sulfide (S2-) anion in comparison to
disulfide (Sꢀꢀꢁꢝ anion in the aqueous phase and the corresponding insignificant formation of catalyst
active intermediate QSQ as compare to Q2S2 in the ion exchange step. The overall rate of reaction
between the organic substrate RCl and a di-ionic inorganic nucleophile Sꢀꢀꢁ to form organic product RSꢀR
in the presence of PTC, QꢈClꢁ then can be expressed as a function of the concentrations of RCl
and QꢈSꢀꢀꢁQꢈ, i.e.
2 RCl ꢞ QꢈSꢀꢀꢁQꢈ → RSꢀR ꢞ 2 QꢈClꢁ
(13)
(14)
ꢂ
ꢃ
ꢤꢥꢦ
Rate, ꢟꢠ ꢡ ꢟ ꢢ ꢣꢏꢐ
ꢀꢁ
ꢈ
ꢂ
ꢃꢀ
ꢡ kꢊꢨꢩ RCl
ꢂ
Q Sꢀ
ꢊꢨꢩ
ꢈꢃꢪ
Q
ꢄꢅꢆ
ꢢꢧ
In the present work, a rigorous model based on the modification of the Langmuir-Hinshelwood/Eley-
Rideal mechanism will be developed and experimental data from the reaction between benzyl chloride in
the organic phase and disulfide in the aqueous phase to yield dibenzyl disulfide will be used to verify it.
This reaction system belongs to a general class of esterification reactions where the nucleophile is
extracted from the aqueous phase using a phase transfer catalyst. The reaction is mediated by polymer-
supported quaternary ammonium chloride and conducted in the batch slurry mode.
13

The whole reaction can be compared to the Eley- Rideal reaction mechanism [30], which includes
reaction between an adsorbed reactant with an un-adsorbed reactant from the bulk phase. Here, ion-
exchange step can be considered as the adsorption of first reactant to convert inactive sites into active
sites, and in organic phase reaction step, second reactant reacts with adsorbed reactant to yield desired
product RSꢀR.
We assume that the reaction mechanism consist of an ion-exchange reaction step between Sꢀꢀꢁ and Qꢈꢫꢁ
to form an active site,QꢈSꢀꢀꢁQꢈ followed by reaction of RCl at this site to form a final product, RSꢀR, and
an inactive site, QꢈClꢁ. These steps may be described as follows:
Ion Exchange step:
2 ꢜQꢈClꢁꢝꢪ ꢞ ꢜSꢀꢀꢁꢝꢬꢭ ↔ ꢜQꢈSꢀꢀꢁQꢈꢝꢪ ꢞ 2 ꢜClꢁꢝꢬꢭ
(15)
Organic phase reaction step:
ꢜQꢈSꢀꢀꢁQꢈꢝꢪ ꢞ 2 ꢜRClꢝꢊꢨꢩ ↔ 2 ꢜQꢈClꢁꢝꢪ ꢞ ꢜRSꢀRꢝꢊꢨꢩ
(16)
The reversible ion-exchange step may be compared to the Langmuir-Hinshelwood adsorption/desorption
mechanism. We can express the Equation (15) using traditional notations of heterogeneous catalysis as,
ꢜSꢀꢀꢁꢝ ꢞ 2 ꢜQꢈClꢁꢝ ↔ 2 ꢜClꢁꢝ ꢞ ꢜQꢈSꢀꢀꢁQꢈꢝ
(17)
Where Qꢈ is catalyst’s cation.
Assuming the formation of transitional site ClꢁQꢈSꢀꢀꢁQꢈClꢁ between the forward and backword reaction
steps, the whole reaction can be written as,
14

ꢜSꢀꢀꢁꢝ ꢞ 2 ꢜQꢈClꢁꢝ ↔ ClꢁQꢈSꢀꢀꢁQꢈClꢁ ↔ 2 ꢜClꢁꢝ ꢞ ꢜQꢈSꢀꢀꢁQꢈꢝ
(18)
We can split the ion exchange step as two separate equilibrium attachment/detachment steps. The
attachment/detachment of Sꢀꢀꢁ anion on the inactive site of QꢈClꢁ can be seen in the forward reaction step
as,
2 ꢜQꢈClꢁꢝꢪ ꢞ ꢜSꢀꢀꢁꢝꢬꢭ ↔ ClꢁQꢈSꢀꢀꢁQꢈClꢁ
(19)
Similarly, attachment/detachment of Clꢁ anion on an active site of QꢈSꢀꢀꢁQꢈ can be seen in the backward
reaction step as,
ꢜQꢈSꢀꢀꢁQꢈꢝꢪ ꢞ 2 ꢜClꢁꢝꢬꢭ ↔ ClꢁQꢈSꢀꢀꢁQꢈClꢁ
(20)
Assuming the rates of attachment/detachment are in equilibrium, Equation (21) and Equation (22) can be
obtained from Equation (19) and (20), respectively as,
ꢂ
ꢀꢁꢃ
θꢖꢗꢕ ꢡ Kꢕ Sꢀ ꢬꢭꢜ1 ꢟ θꢕ ꢟ θꢖꢗꢕ
ꢝ
(21)
(22)
ꢂ
ꢁꢃꢀ
θꢖꢗꢕ ꢡ Kꢖꢗ Cl ꢬꢭꢜ1 ꢟ θꢖꢗ ꢟ θꢖꢗꢕ
ꢝ
Where, Kꢕ and Kꢖꢗ are the equilibrium attachment/detachment constants for Sꢀꢀꢁ and Clꢁ anions,
respectively; [Sꢀꢀꢁ] and [Clꢁ] are the concentrations of Sꢀꢀꢁ and Clꢁ anions in the aqueous phase,
respectively; and θꢕ, θꢖꢗ, θꢖꢗꢕ are the fractions of total number of triphase catalyst cations attached to
Sꢀꢀꢁ, Clꢁ and both Sꢀꢀꢁ and Clꢁ anions, respectively.
15

Mathematically, this can be written as: θꢖꢗ ꢞ θꢖꢗꢕ ꢞ θꢕ ꢡ 1, which signifies that the sum total of all the
fractions of active and inactive sites of the catalyst equals to unity. It is assumed that once, transition sites
ClꢁQꢈSꢀꢀꢁQꢈClꢁ are formed, they are instantaneously transformed either into active sites QꢈSꢀꢀꢁQꢈ or
inactive sites QꢈClꢁ. At any instant of time there is very less fraction of transition site (θꢖꢗꢕꢝ present in
ꢜ
ꢝ
the reaction mixture as compare to active and inactive sites θꢖꢗ and θꢕ but can’t be neglected so, θꢖꢗ
ꢞ
θꢕ ꢮ 1. Equation (21) and (22) can be re-written as
ꢂ
ꢀꢁꢃ
θꢕ ꢡ Kꢕ Sꢀ ꢬꢭꢜ1 ꢟ θꢕ ꢟ θꢖꢗꢝ
(23)
(24)
ꢂ
ꢁꢃꢀ
θꢖꢗ ꢡ Kꢖꢗ Cl ꢬꢭꢜ1 ꢟ θꢕ ꢟ θꢖꢗꢝ
We have obtained a hyperbolic equation for the fraction of active PTC sites by combining the expressions
for θꢕ and θꢖꢗ as
ꢲꢳ
ꢯ ꢱꢕ
ꢰ
ꢴ
ꢵꢶ
ꢲ
θꢕ ꢡ ꢷꢈꢯ ꢖꢗ
(25)
ꢲ
ꢲꢳ
ꢳ
ꢂ
ꢃ
ꢵꢶ
ꢈꢯ ꢱꢕ
ꢴ
ꢵꢶ
ꢸꢹ
ꢰ
ꢲ
We can also write above equation in terms of catalyst concentration,
ꢲꢳ
ꢯ ꢱꢕ
ꢰ
ꢴ
ꢵꢶ
ꢲ
ꢀꢁ
ꢈ
ꢂ
ꢈꢃ
ꢂ
ꢈꢃꢉꢊꢉ
ꢡ Q
Q Sꢀ
Q
(26)
ꢲ
ꢲꢳ
ꢳ
ꢂ
ꢃ
ꢵꢶ
ꢷꢈꢯ ꢖꢗ
ꢈꢯ ꢱꢕ
ꢴ
ꢲ
ꢵꢶ
ꢸꢹ
ꢰ
ꢀꢁ
ꢈ
ꢂ
ꢈꢃꢉꢊꢉ
ꢂ
ꢈꢃ
are the total concentrations of catalyst and the concentration of catalyst
Where, Q
and Q Sꢀ
Q
attached to Sꢀꢀꢁ anions, respectively.
16

We obtain Equation (27) for the rate of the organic reactions by combining Equation (14) and Equation
(26) as,
ꢲꢳ
ꢯ ꢱꢕ
ꢴ
ꢵꢶ
ꢂ
ꢃ
ꢰ
ꢲ
ꢟꢠ ꢡ ꢟ ꢢ ꢣꢏꢐ
(27)
(28)
ꢤꢥꢦ
ꢂ
ꢃꢀ
ꢡ kꢊꢨꢩ RCl
ꢂ
Q
ꢊꢨꢩ
ꢈꢃꢉꢊꢉ
ꢄꢅꢆ
ꢲ
ꢲꢳ
ꢳ
ꢂ
ꢃ
ꢵꢶ
ꢢꢧ
ꢷꢈꢯ ꢖꢗ
ꢈꢯ ꢱꢕ
ꢴ
ꢲ
ꢵꢶ
ꢸꢹ
ꢰ
ꢲꢳ
ꢯ ꢱꢕ
ꢴ
ꢵꢶ
ꢂ
ꢃ
ꢰ
ꢲ
ꢟ ꢢ ꢣꢏꢐ
ꢤꢥꢦ
ꢂ
ꢃꢀ ꢈꢃꢉꢊꢉ
ꢂ
ꢡ kꢊꢨꢩ RCl Q
ꢊꢨꢩ
ꢷꢈꢯ ꢖꢗ
ꢲ
ꢲꢳ
ꢳ
ꢂ
ꢃ
ꢵꢶ
ꢢꢧ
ꢈꢯ ꢱꢕ
ꢴ
ꢲ
ꢵꢶ
ꢸꢹ
ꢰ
Let us introduce fractional conversion of reactant ( Xꢺꢖꢗ), which can be calculated as
ꢃ
ꢂ
ꢃ
ꢁ ꢣꢏꢐ
ꢤꢥꢦ
ꢫꢣꢏꢐ ꢡ ꢂ
(29)
ꢣꢏꢐ
ꢤꢥꢦ,ꢻ
ꢂ
ꢃ
ꢤꢥꢦ,ꢻ
ꢣꢏꢐ
ꢂ
ꢃ
ꢂ
ꢃ
Where, ꢼꢓꢔ ꢄꢅꢆ,ꢇ and ꢼꢓꢔ
ꢄꢅꢆ
represents initial concentration of benzyl chloride and concentration at
any time respectively. Now we can write Equation (28) in the form of fractional conversion as
ꢲꢳ
ꢲ
ꢯ ꢱꢕ
ꢴ
ꢜꢷꢁꢽ
ꢝ
ꢰ
ꢾꢿꣀ
ꢲ
ꢟꢠ ꢡ ꢢꢽ ꢡ kꢊꢨꢩ ꢼꢓꢔ
(30)
ꢵꢶ
ꢲ
ꢾꢿꣀ
ꢂ
ꢃ
ꢂ
ꢈꢃꢉꢊꢉ
Q
ꢄꢅꢆ,ꢇ
ꢷꢈꢯ ꢖꢗ
ꢄꢅꢆ
ꢲꢳ
ꢲ
ꢳ
ꢂ
ꢃ
ꢵꢶ
ꢢꢧ
ꢈꢯ ꢱꢕ
ꢰ
ꢴ
ꢵꢶ
ꢸꢹ
ꢲꢳ
ꢯ ꢱꢕ
ꢴ
ꢰ
ꢲ
ꣁꣂ
ꢵꢶ
ꣃꢸꢹ
ꢂ
ꢃ
ꢂ
ꢈꢃꢉꢊꢉ
Q
ꢄꢅꢆ,ꢇ
ꢷꢈꢯ ꢖꢗ
ꢸꢹ
ꢡ ꢜꢷꢁꣂ
ꢡ kꢊꢨꢩ ꢼꢓꢔ
꣄ꣅ
(31)
(32)
ꢲ
ꢲꢳ
ꢲ
ꢳ
ꢂ
ꢃ
ꢵꢶ
ꢝ
ꢈꢯ ꢱꢕ
ꢴ
ꢲ
ꢵꢶ
ꢾꢿꣀ
ꢰ
ꣁꣂ
ꣃꢸꢹ
ꢡ
ꢡ ꢋꢌꢍꢍ ꣄ꣅ
ꢝ
ꢲ
ꢜꢷꢁꢽ
ꢾꢿꣀ
ꢲꢳ
ꢯ ꢱꢕ
ꢰ
ꢴ
ꢵꢶ
ꢲ
ꢂ
ꢃ
ꢂ
ꢈꢃꢉꢊꢉ
Q
ꢄꢅꢆ,ꢇ
ꢷꢈꢯ ꢖꢗ
Where ꢋꢌꢍꢍ ꢡ kꢊꢨꢩ ꢼꢓꢔ
.The terms in the kꢬ꣆꣆ can be calculated
ꢲ
ꢲꢳ
ꢳ
ꢂ
ꢃ
ꢵꢶ
ꢈꢯ ꢱꢕ
ꢴ
ꢲ
ꢵꢶ
ꢸꢹ
ꢰ
experimentally. Thus, after integration of Equation (32) we get,
17

ꢽ
ꢾꢿ꣇
ꢡ ꢋꢌꢍꢍ
ꣅ
(33)
ꢷꢁꢽ
ꢾꢿ꣇
From the Equation (33) it is clear that the reaction follows second order kinetics.
3.5 Validation of kinetic model. The kinetic model was validated by considering Equation (33) was
valid at different temperatures by plotting of XRCl/(1-XRCl) against time (Fig. 12). The slope of each line
gives apparent rate constant kapp at different temperatures as shown in Table 2. Fig. 13 shows comparison
of calculated conversions of BC based on app. rate constants and experimentally obtained conversions of
BC. Good agreement has been observed between calculated and experimental conversions.
4. CONCLUSION
A detailed study has been carried out on the synthesis of DBDS from BC using Amberlite IR-400 as a
solid phase transfer catalyst. It is seen that at different speed of agitation there was no significant change
on the rate of reaction so the reaction was found to be kinetically controlled and all experiments were
done at a speed of 1500 rpm. The reaction was found to be approximately first order with respect the
concentration of the catalyst, second order with respect to the reactant concentration and second order
with respect to the sulfide concentration. 100% selectivity of DBDS was observed at 1.875 kmol/m3 of
sulfur loading. The obtained activation energy, for DBDS synthesis, from Arrhinius plot was 56.03
kJ/mol. Catalyst was recovered and reused four times with successive decrease in the conversion of BC.
A mathematical model was developed, based on kinetic study and proposed mechanism, to account for
the calculation of the rate constant and it was validated using experimental data.
18

ACKNOWLEDGMENT
We appreciate the technical support provided by Department of Chemical Engineering of the institute in
identifying the product using NMR.
ASSOCIATED CONTENT
Supporting information
Gas Chromatographs, NMR and MS spectra.
19

REFERENCES
[1] L. J. Keras. US Patent NO. US2011/0155646 (2011).
[2] H. Huang, Y. Yu, K. H. Chung, Energ. Fuel. 23 (2009) 4420.
[3] J. B Vilmain, V. Couroussea, P. F. Biarda, M. Azizia, A. Couvert, Chem. Eng. Res. and Des. 92
(2014) 191.
[4] B. Elyassi, Y. A. Wahedi, N. Rajabbeigi, P. Kumar, J. S. Jeong, X. Zhang, P. Kumar, V. V.
Balasubramanian, M. S. Katsiotis, K. A. Mkhoyan, N. Boukos, S. A. Hashimi, M. Tsapatsis, Microporous
and Mesoporous Mater. 190 (2014) 152.
[5] C. Wang, Y. Pei, Chemosphere. 88 (2012) 1178.
[6] A.L.Kohl, R.B. Nielsen, Gulf Publishing Company, Houston, TX. 5 (1997).
[7] P. Dhar, S. Chandrasekaran, J. Org. Chem. 54 (13), (1989) 2998.
[8] V. Polshettivar, M. Nivsarkar, J. Acharya, M.P. Kaushik, Tetrahedron Lett. 44 (2003) 887.
[9] N. Iranpoor, B. Zeynizadeh, Synthesis. (1999) 49.
[10] A.V. Joshi, S. Bhusare, M. Baidossi, N. Qafisheh, Y. Sesson, Tetrahedron Lett. 46 (2005) 3583.
[11] D. A. Dickman, S. Chemburkar, D. B. Konopacki, E. M. Elisseou, Synthesis. 6 (1993) 573.
[12] D. Landini, F. Rolla, Synthesis. (1974) 565.
[13] M. L. Wang, Y. H. Tseng, J. Mol. Cat. A: Chem. 203 (2003) 79.
[14] S. Sen, N. C. Pradhan, A. V. Patwardhan, Asia-Pac. J. Chem. Eng. 6 (2011) 257.
[15] M. Ueda, Y. Oishi, N. Sakai, Y. Imai, Macromolecules, 15 (1982) 248.
[16] N.C. Pradhan, M.M. Sharma, Ind. Eng. Chem. Res. 31 (1992) 1606.
20

[17] B. P. Bandgar, L. S. Uppala, V. S. Sadavarte, Tetrahedron Lett. 42 (2001) 6741.
[18] C. M. Starks, C. L. Liotta, M. Halpern, Chapman and Hall. (1994) 23.
[19] Y. Sasson, R. Neumann, (Eds.), Handbook of Phase transfer Catalysis, Blackie Academic and
Professional, London (1997).
[20] G. D. Yadav, N. M. Desai, Catal. Commun. 7 (2006) 325.
[21] G. D. Yadav, B. G. Motirale, Chem. Eng. J. 156 (2010) 328.
[22] G. D. Yadav, S. V. Lande, J. Mol. Catal. A: Chem. 244 (2006) 271.
[23] G. D. Yadav, P. R. Sowbna, Chem. Eng. J. 179 (2012) 221.
[24] G. D. Yadav, P. R. Sowbna, Chem. Eng. Res. Des. 90 (2012) 1281.
[25] S. U. Sonavane, M. Chidambaram, J. Among, Y. Sasson, Tetrahedron Lett. 48 (2007) 6048.
[26] S. U. Sonavane, M. Chidambaram, S. Khalil, J. Among, Y. Sasson, Tetrahedron Lett. 49 (2008) 520.
[27] M. Abbasi, M. R. Mohammadizadeh, Z. K. Taghavi, J. Iran Chem. Soc. 10 (2013) 201.
[28] H. Gurusamy, P. Parkunan, K. Madasamy, S. Ponnusamy, Tetrahedron Lett. 56 (2015) 150.
[29] S. Sen, S. K. Maity, N. C. Pradhan, A. V. Patwardhan, Int. J. Chem. Sci. 5 (2007) 1569.
[30] J. A. B. Satrio, H. J. Glatzer, L. K. Doraiswamy, Chem. Eng. Sci. 55 (2000) 5013.
21

Fig. 1. Effect of stirring speed on the rate of reaction. Operating conditions: Volume of aqueous and
organic phase = 5.0꣈ 10ꢁꢛm3each; concentration of BC = 2.6 kmol/m3 in org. phase; concentration of
toluene = 6.6 kmol/m3 in org. phase; concentration of catalyst = 0.29 kmol/m3 in org. phase; concentration
of sulfide = 2.53 kmol/m3, MEA/H2S mole ratio = 2.28; Temperature = 323 K; Sulfur loading= 1.875
kmol/m3.
22

Fig. 2. Effect of Sulfur Powder Loading on DBDS Selectivity. Operating conditions: Volume of aqueous
and organic phase = 5.0꣈ 10ꢁꢛm3 each; concentration of BC = 2.6 kmol/m3 in org. phase; concentration
of toluene = 6.6 kmol/m3 in org. phase; concentration of Catalyst = 0.29 kmol/m3 in org phase;
concentration of Sulfide = 2.53 kmol/m3; MEA/H2S mole ratio = 2.28; Temperature = 323 K; Agitation
Speed= 1500 rpm.
23

Fig. 3. Effect of catalyst loading on BC conversion. Operating conditions: Volume of aqueous and
organic phase = 5.0꣈ 10ꢁꢛm3each; concentration of BC = 2.6 kmol/m3 in org. phase; concentration of
toluene = 6.6 kmol/m3 in org. phase; concentration of Sulfide = 2.53 kmol/m3; MEA/H2S mole ratio =
2.28; Temperature = 323 K; Sulfur loading = 1.875 kmol/m3; Agitation Speed= 1500 rpm.
24

Fig. 4. ln (Initial Reaction Rate) Vs ln (Catalyst Concentration). All other conditions are same as Fig. 3.
25

Fig. 5. Effect of Temperature on BC conversion. Operating conditions: Volume of aqueous and organic
phase = 5.0꣈ 10ꢁꢛm3 each; concentration of BC = 2.6 kmol/m3 in org. phase; concentration of toluene =
6.6 kmol/m3 in org. phase; concentration of Catalyst = 0.29 kmol/m3 in org phase; concentration of
Sulfide = 2.53 kmol/m3; MEA/H2S mole ratio = 2.28; Sulfur loading = 1.875 kmol/m3; Agitation Speed=
1500 rpm.
26

Fig. 6. Arrhenius plot of ln (Initial Reaction Rate) vs 1/T. All other conditions are same as Fig. 5.
27

Fig. 7. Effect of BC concentration on reactant conversion. Operating conditions: Volume of aqueous and
organic phase = 5.0꣈ 10ꢁꢛm3 each; concentration of Catalyst = 0.29 kmol/m3 in org phase; concentration
of Sulfide = 2.53 kmol/m3; MEA/H2S mole ratio = 2.28; Sulfur loading= 1.875 kmol/m3; Agitation
Speed= 1500 rpm.
28

Fig. 8. Plot of ln(initial rate) vs. ln(reactant concentration). All other conditions are same as Fig. 7.
29