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TECHNOLOGICAL FEATURES OF THE SULFATION PROCESS OF
ALKYLBENZOLS WITH SULFATE ANGIDRIDE
T.N. Turdikulov,
Yu.Sh. Usmonova,
Kh.I. Kadirov
Tashkent Institute of Chemical Technology, Tashkent
https://doi.org/10.5281/zenodo.15526124
Abstract.
During the research, sulfonation process forms sulfons. Their
content in sulfonic acid is very little dependent on the technological regime
parameters and constitutes about 1% of the total mass, but at a CO3/AB molar
ratio greater than 1.08, their formation rate increases sharply.
Keywords:
sulfonation process, sulfons, hydrocarbons, alkylbenzenes, side
chain, electrophilic substitution mechanism
The production of sulfonic acids, which are currently used in various fields
of science, in the processes of sulfonation of hydrocarbons is discussed in various
sources. [1] The research results examine methods for sulfonating toluene and
ethylbenzene with sulfuric anhydride, sulfuric acid, and sulfuric anhydride in the
presence of methanesulfonic acid. [2] describe methods for sulfonating olefins,
including using photocatalysts, as well as methods for obtaining sulfonic acids,
which are essential amino acids, using a stable SO
3
·DMF complex as a sulfonating
agent. [3] The works present the results of studies on the processes of sulfonation
of alcohols, amines, and phenols with sulfonyl chloride to obtain sulfo compounds
used in pharmacology. [4] The literature is devoted to the optimization of the
sulfonation process of alkylbenzenes with a side chain length of C
9
-C
13
carbon
atoms (molecular mass 230-245 g/mol), including using mathematical methods
Organic raw materials - alkylbenzenes with the formula R-C
6
H
5
, where R is
the radical of the n-paraffin molecule with a carbon atom number from 10 to 13,
react with sulfur anhydride in the reactor, resulting in the formation of sulfonic
acid according to the following reaction:
R-С
6
Н
5
+ SO
3
→ R – С
6
Н
4
- SO
3
H
In addition to the above, side reactions can also occur, in which other types
of sulfonic acids, such as sulfonic anhydride or PSA, are formed.
2R–С
6
Н
4
-SO
3
Н + 3SO
3
→ R-С
6
Н
4
-SO
2
-О-SO
2
–С
6
Н
4
-R + H
2
SO
4
S-С
6
Н
5
+ 2SO
3
→ R-C
6
H
4
-SO
2
-O-SO
3
H
Additionally, sulfonation process produces sulfons. Their quantity in
sulfuric acid depends very little on the parameters of the technological regime and
is about 1% of the total mass, however, their formation rate increases sharply
when the molar ratio of SO
3
/AB exceeds 1.08. Sulfones have the following
structural formula:
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R - C
6
H
4
- SO
2
- C
6
H
4
- R'
When forming sulfonic acid, the indicated compounds, except for sulfons,
decompose or react directly with the AB residue or, upon mixing, are hydrolyzed
with water according to the following reactions:
R-C
6
H
4
-SO
2
-O-SO
3
H+ R-С
6
Н
5
→ 2R - С
6
Н
4
– SO
3
H
R - С
6
Н
4
- SO
2
- О - SO
2
– С
6
Н
4
- R + Н
2
О → 2R - С
6
Н
4
- SO
3
Н
High concentrations of SO
3
and high molar ratios of SO
3
:AB also lead to the
dealkylation of alkylbenzene with the formation of unsaturated hydrocarbons
(olefins), which polymerize to form resinous compounds, thereby deteriorating
the color of sulfonic acid.
Regarding the mechanism of sulfonation reactions, there are currently
several hypotheses:
1. Electrophilic substitution mechanism. This assumption is based on the
fact that at the first stage of the aromatic compound sulfonation mechanism,
intermediate p- and s-complexes are formed due to the electrophilic attack of the
carbon atom by the sulfuric anhydride molecule.
This reaction proceeds very quickly and is a first-order reaction, the rate of
which depends on the diffusion factors, as well as the intensity of mixing and the
removal of the released heat.
2.
Another assumption is that the sulfonation reaction of aromatic compounds
begins with the interaction of a mixture of sulfur trioxide and alkylbenzenes,
leading to the formation of intermediate compounds ABSA and PSA.
.
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The mechanism of the primary reaction of a mixture of linear alkylbenzenes
with SO
3
is presented below.
Further, the alkylbenzene mixture reacts with PSC to form two moles of
ABSC. In this case, one mole-equivalent is considered as a product of the first
stage, and the second as a contribution to increasing conversion.
.
In this basic reaction, pyrosulfonic acid acts as a sulfonating agent.
The intermediate product - sulfonic acid anhydride and PSA - are then
reacted with a mixture of alkylbenzenes or water to obtain the target product -
sulfonic acid.
The technological scheme of the plant for sulfonation of alkylbenzenes with
sulfur anhydride is presented in Figure 1. ABSA production is carried out on two
parallel technological lines, each of which consists of three main technological
units.
In the gas mixture preparation section, liquid sulfur is burned in a furnace
with excess dried air, resulting in sulfur dioxide (SO
2
). Further, SO
2
is converted
into SO
3
in a special apparatus - a converter, in the flow of dried air above the
catalyst layer (V
2
O
5
). Dried air participates in the process, as humid air forms
sulfuric acid with SO
3
, which leads to the breakdown of the technology and
increases equipment corrosion.
The sulfonation unit is designed to obtain alkylbenzenesulfonic acids -
ABSK by the interaction of a gas-air mixture of SO
3
and alkylbenzenes in the
reactor in film mode. The resulting alkylbenzenesulfonic acids, after stabilization
and hydrolysis, are transported to the raw material department.
Raw materials (alkylbenzenes) are fed into buffer tanks at a constant level.
The temperature of alkylbenzenes is maintained constant.
To remove a constant level of alkylbenzenes from the tank, they are pumped into
cartridge filters, where the pressure before and after the filters is measured, and
a temperature sensor is installed on the line. Alkylbenzenes enter the upper part
of the 120-tube multi-tube film reactor through distribution devices, the design
of which ensures the uniform distribution of alkylbenzenes through the tubes and
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the optimal ratio of raw materials and sulfonate gas in each reaction tube.
Figure 1. Technological scheme of the sulfuric anhydride sulfonation plant for
alkylbenzenes:
1 - air drying column; 2 - furnace, 3 - converter for converting SO
2
to SO
3
; 4 -
heat exchanger; 5 - pipette; 6 - separator; 7 - ABSA capacity; 8 - multi-tube film
sulfonation reactor; 9, 18 - refrigerator; 10 - cyclone for separating gas and
liquid phases; 11 - Cyclone for complete purification of waste reaction gases
from ABSA droplets; 12 - reservoir for storing ABSA; 13-16 - stabilization
columns; 17 - ABSA mixer
The reaction gas flow, containing 5-5.5% SO
3
by volume, is evenly
distributed over the pipes from top to bottom into the reactor.
The gas mixture pressure is measured before the reactor.
Pneumatic SO
3
-air mixture absorbers are installed in the reactor and the
supply pipe to the absorber, and the gas mixture is automatically pumped into the
absorber.
The heat is removed due to the circulation of the coolant through the
reactor jacket. Water is supplied to a heat exchanger, where it is cooled by water
with a temperature of 14-18°C coming from the chiller. The temperature of the
heat carrier is regulated by the reactor jacket.
The pressure in the upper and lower parts of the reactor is monitored, and
the flow of alkylbenzenes into the reactor is measured and controlled.
The mixture of the sulfonation product and the outgoing gas from the
reactor enters the cyclone, where the separation of the gas and liquid phases
occurs. A cyclone measures and maintains a constant level. The reaction gas
pressure at the cyclone outlet is measured.
To compensate for water losses, a tank with level measurement and control
is provided in the cooling circuit of the reactor jacket.
To further retain the unreacted SO
3
at the cyclone outlet, a nozzle is
installed on the vertical section of the pipe. In nozzles, alkylbenzenes are sprayed
with compressed air. Alkylbenzenes and technical air are preheated in heat
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exchangers. The pressure and flow rate of alkylbenzenes in the alkylbenzene
supply line are measured and regulated, and the air pressure in the heat
exchanger is maintained by a pressure regulator that directly affects the air. The
air and alkylbenzenes in heat exchangers are heated by water vapor, and the
pressure in the steam pipe is measured.
The purification of exhaust gases from the ABSA drip feed reaction is carried
out in a cyclone. Then the exhaust gases are sent to the purification stage, to the
absorption and exhaust gas processing unit.
The liquid phase (LFA), if the product quality is suitable, is pumped into the
LFA storage tank. The pump line is equipped with a mass flow meter with a
maximum and minimum signal, a manometer, a temperature sensor, and a
density analyzer with a maximum and minimum signal.
Non-standard acid is collected in a prefabricated container. The set
provides level control. The dosing pump in the static mixer mixes substandard
ABSA from the collection point with incoming raw materials and returns it to the
reactor.
In case of violation of the technological regime, in the event of an emergency
situation (disconnection of electricity, lack of raw materials, etc.), an emergency
tank is installed over the reactor, which allows washing the reactor AB and
preventing the products from igniting. The following parameters are monitored
in the reservoir: pressure, temperature, and there is also a level drop signal.
The device for absorption and purification of exhaust gases is designed to
purify exhaust gases after the sulfonation process, as well as when starting and
stopping the sulfur dioxide absorption unit before releasing exhaust gases into
the atmosphere.
A mixture of air with SO
3
is supplied for absorption during the start-up or
shutdown of the production line. In the absorber, a reaction occurs between SO
3
and H
2
O, resulting in the formation of H
2
SO
4
according to the following reaction:
SO
3
+ Н
2
O → H
2
SO
4
The sulfuric acid concentration is maintained at 97-98% by mass by
supplying demineralized water to the absorber. The reaction is exothermic,
therefore heat is removed in a water cooler. The resulting sulfuric acid is
discharged into the reservoir.
After sulfonation, the exhaust gases contain a small amount of sulfonic acid
and unreacted SO
2
and SO
3
.
Then, a wet filter is used to remove organic residues and SO
3
from exhaust
gases.
Further, the gaseous SO
2
and SO
3
in the gas purifier columns are neutralized
with sodium hydroxide (NaOH).
The neutralization reaction of these gases is as follows:
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SO
2
+ 2NaOH → Na
2
SO
3
+ H
2
O;
SO
3
+ Н
2
O → Н
2
SO
4
+ NaOH → Na
2
SO
4
+ H
2
O
Sodium sulfite is an unstable compound that reacts with oxygen to form
sodium sulfate:
2Na
2
SO
3
+ O
2
→ 2Na
2
SO
4
The small amounts of sulfonic and sulfuric acids remaining in the exhaust
gases react in the NaOH columns as follows:
R – С
6
Н
4
- SO
3
H + NaOH → R – С
6
Н
4
- SO
3
Na + 2Н
2
О
H
2
SO
4
+ 2NaOH → Na
2
SO
4
+ 2Н
2
О
The purified exhaust gas is discharged into the atmosphere, and the utilized
alkaline solution is discharged into the "KINEF" LLC sewer well. Wastewater can
be pumped into the preaerator.
Table 1 presents the main technological parameters, raw material characteristics,
and design features of the reactor for the sulfonation process of alkylbenzenes
with sulfur anhydride.
Table 1
Parameters of the sulfonation process of alkylbenzenes
Process Options
Meaning
Properties of raw materials
Alkylbenzenes
Density at 15°C, kg/m3
858-862
Mass fraction of sulfonated substances, %, not less than
98,0
Average molecular weight, kg/kmol
238,0 – 245,0
Mass fraction of linear isomers, %:
C
9
-benzene, not more
1,0
C
10
-benzene, not more
15,0
C
10
-C
11
-benzene
30,0 - 55,0
C
13
-C
14
-benzene, not more
30,0
C
14
-benzene, not more
1,0
Mass fraction of 2-phenylalkanes, %, not more than
20,0
Mass fraction of paraffins, %, not more than
0,3
Alkylbenzenesulfonic acids (grade A)
Mass fraction of ABSA, %, not less than
96,0
Mass fraction of sulfuric acid, %, not more than
2,0
Mass fraction of unsulfonated compounds, %, not more
than
2,0
Density at 50°C, kg/m3
1010-1050
Molecular weight, kg/kmol
318,0-326,0
Sulfonating gas
Sulfur dioxide content, % vol., not more than
5,5
Process Options
AB consumption at the reactor inlet, kg/h
2700-4500
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Molar ratio SO
3
:AB, not more than
1,08
Mass fraction of sulfuric acid, %, not more than
2,0
Gas mixture pressure at the reactor inlet, kPa, not more
than
90
High reactor pressure, kPa, not more than
90
Lower reactor pressure, kPa, not more than
10
Reaction gas temperature at reactor inlet, °C
45-50
AB temperature at reactor inlet, °C
20-45
Reactor design
Number of pipes, units.
120
Reactor tube diameter, m
0,025
Reactor tube length, m
6
The higher the concentration of SO
3
, the higher the rate of the sulfonation
reaction, the more heat is released per unit time. Therefore, the concentration of
SO
3
should not exceed 5.5% by volume.
Thus, in addition to the previously described reactions in the sulfonation
reactor of alkylbenzenes with sulfur anhydride, the thermodynamic parameters
of the reaction for the formation of by-products, including sulfons, included in the
high-viscosity component, have been calculated. It has been shown that the Gibbs
energy of sulfonation reactions is ΔG ≈ 0 kJ/mol. These reactions are included in
the hydrocarbon transformation scheme and are taken into account when
constructing the mathematical model of the sulfonation reactor.
Foydalanilgan rahbariy hujjatlar ro’yxati:
1. E.R. van Kouwen, W. Winkenwerder, Z. Brentzel, B. Joyce, T. Pagano, S. Jovic, G.
Bargeman, J. van der Schaaf, The mixing sensitivity of toluene and ethylbenzene
sulfonation using fuming sulfuric acid studied in a rotor-stator spinning disc
reactor,
Chem. Eng.
Process.
-
Process
Intensif. 160
(2021).
https://doi.org/10.1016/j.cep.2021.108303.
2. Y. Muramoto, H. Asakura, H. Suzuki, Reinvestigation of the Sulfonation Products
of Ethylbenzene by Means of HPLC, Nippon Kagaku Kaishi. 1991 (1991) 312–315.
https://doi.org/10.1246/nikkashi.1991.312.
3. Y. Muramoto, H. Asakura, Sulfonation of Ethylbenzene, 4-Nitro- and
4Aminoethylbenzene, and Analyses of the Products by NMR Spectra, Nippon
KAGAKU
KAISHI.
1975
(1975)
1953–1957.
https://doi.org/10.1246/nikkashi.1975.1953.
4. H. Cerfontain, A. Telder, L. Vollbracht, Aromatic sulfonation XI: Sulfonation of
benzene and toluene with sulfur trioxide; sulfone formation and sulfonic acid
isomer distribution., Recl. Des Trav. Chim. Des Pays‐Bas. 83 (1964).
https://doi.org/10.1002/recl.19640831102.
