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THERMODYNAMIC ANALYSIS OF THE SULFONATION REACTION
OF ALKYLBENZENES
Turdikulov T.N.
Kodirov O.Sh.
Bakhramov H.K.
Kadirov H.I.
Tashkent Institute of Chemical Technology
https://doi.org/10.5281/zenodo.15347823
Abstract.
In this study, alkylbenzenes with a side chain length from 9 to 14
carbon atoms undergo sulfonation. In addition, the raw material may contain
unsaturated and isostructured side-chain alkylbenzenes. Using the Gauss
program, the thermodynamic parameters of the target and side reactions of
alkylbenzenes were calculated depending on the length of the hydrocarbon
chain and its structure.
Keywords:
pyrolysis, C
9
-C
14
hydrocarbons, naphthalene fraction,
dicylopentadiene, petroleum polymer resins, sulfonation processes.
Introduction
In many countries, deep processing of pyrolysis products has also been
established, in which various valuable reagents are obtained. For example, in
this article, the authors studied the yield of naphthalene by thermal processing
of heavy pyrolysis resin. In the work, by atmospheric-vacuum distillation,
distillate and cubic residue fractions were obtained by treating heavy pyrolysis
resin in a mixer reactor in the temperature range of 250-270°C for 6-8 hours.
The distillate was separated by re-distillation into fractions in a short
temperature range: main fraction (up to 200 °C), naphthalene fraction (200 -
230 °C), methylnaphthalene fraction (230 - 245 °C), residue (245 - 340 °C).
As a result of the thermal treatment carried out by the authors, an increase
in the naphthalene fraction and the amount of naphthalene in it was observed,
while a decrease in the content of mono- and bicyclic alkenes and dienes, vinyl
aromatic hydrocarbons, indene and its homologues, dihydronaphthalenes in the
product was observed [1].
Currently, certain methods for the utilization of liquid products of the
pyrolysis process are mainly aimed at extracting products of technical
hydrogenation of certain fractions, as well as individual products (benzene,
toluene, xylene, discyclopentadiene, naphthalene, etc.) for further use. In
addition, the liquid products of the pyrolysis process are also utilized in the
direction of production of low-molecular-weight "oil polymer resins," which
have a common name [2].
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Foreign companies currently produce 30-40 types of petroleum polymer
resins of various nature and applications [3-5], while in our country, the
products of the pyrolysis process are currently used as fuel.
Other important producers of sulfonic acids are Sasol, Fogla Group, ISU
Chemical, Solvay, Huntsman, Kao, Hansa Group, Miwon Chemical, NCSP, FUCC,
Ho Tung, Nanjing Gige.
The obtained results and their analysis.
Most producers of ABSA use the technology of sulfonation of alkylbenzenes
in a multi-tube film reactor. This design allows for a significant reduction in the
formation of a viscous component in the reaction medium with the correct
selection of raw material consumption.
Based on the analysis of literature sources and the composition of the raw
material, a list of reactions occurring during the sulfonation of alkylbenzene
with sulfur trioxide has been compiled:
1.
Targeted reaction for the formation of ABSA:
R – С
6
Н
5
+ SO
3
→ R – С
6
Н
4
– SO
3
H
2.
Formation of sulfons:
R – С
6
Н
5
+ R – С
6
Н
4
– SO
3
H → R – C
6
H
4
– SO
2
– C
6
H
4
– R' + H
2
O
3.
Formation of sulfonic anhydride:
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
4.
Formation of PSA:
R – С
6
Н
5
+ 2SO
3
→ R – C
6
H
4
– SO
2
-O-SO
3
H
5.
Interaction of PSA with residual blood pressure to form ABSA:
R – C
6
H
4
– SO
2
-O-SO
3
H+ R – С
6
Н
5
→ 2R – С
6
Н
4
– SO
3
H
6.
Hydrolysis of sulfonic acid anhydride to obtain ABSA:
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
7.
Sulfonation of AB with an unsaturated hydrocarbon radical into a
side chain.
R – С
6
Н
5
+ SO
3
→ R(SO
3
H) – С
6
Н
5
The sulfons formed as a result of side reactions are located in the
unsulfonated part, i.e., as a highly viscous component, on the walls of the reactor
tubes, disrupting the hydrodynamic flow regime of the organic liquid.
Prediction of various properties of molecules, as well as the properties of
reactions based on quantum chemistry and molecular dynamics methods, is
carried out in many software products, including the Gauss software package,
which uses modern theory of electronic structure.
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In this work, the thermodynamic characteristics of the transition state were
calculated using the Gauss software package using the DFT method.
Alkylbenzenes with a side chain length from 9 to 14 carbon atoms undergo
sulfonation. In addition, the raw material may contain unsaturated and
isostructured side-chain alkylbenzenes. Using the Gauss program, the
thermodynamic parameters of the target and side reactions of alkylbenzenes
were calculated depending on the length of the hydrocarbon chain and its
structure.
The electron-donating alkyl group is ortho- and para-oriented. At the same
time, steric factors also have a great influence on the sulfonation of
alkylbenzenes with a side chain length of 9-14 carbon atoms, and sulfonation
occurs mainly in a para state.
Targeted reaction for ABSA formation
Table 1
Calculated thermodynamic parameters of sulfonation reactions of
alkylbenzenes with a linear hydrocarbon chain
As can be seen from Table 1, the rate of chemical transformation does not
increase with increasing chain length of the substituent. This is due to the fact
that in this case, the transfer force from the electron-density substituent to the
benzene ring practically does not change with the growth of the side chain. The
average Gibbs energy of the reaction is DG=-225.9 kJ/mol.
To determine the structure of the hydrocarbon isochain, the Gibbs energy
of the methyl radical at different positions relative to the hydrocarbon chain was
calculated. The calculation results are presented in Figure 1.
Hydrocarbon
substituent length
ΔG, kJ/mol
ΔH, kJ/mol
ΔS, J/(mol∙K)
9
-223,6
-212,3
37,2
10
-235,5
-209,8
84,7
11
-224,8
-212,3
41,2
12
-224,3
-212,3
39,6
13
-224,3
-212,3
39,7
14
-223,0
-212,3
35,3
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Figure 1. Dependence of Gibbs energy on the position of the methyl radical
relative to the hydrocarbon chain
As can be seen from Figure 1, during the sulfonation process, the highest
value of the Gibbs energy up to the meta-position, equal to -234.66 kJ/mol,
corresponds to the time when the methyl radical is located at the sixth carbon
atom in the hydrocarbon chain. In this regard, we assume that the highest value
of Gibbs energy occurs when the methyl radical is located at the sixth carbon
atom, regardless of the length of the hydrocarbon chain.
where R is an isostructured hydrocarbon substituent with a chain length of
9-14 carbon atoms
Table 2
Calculated thermodynamic parameters of the sulfonation reaction of
alkylbenzenes with an isostructured hydrocarbon substituent.
Hydrocarbon
substituent
length
ΔG, kJ/mol
ΔH, kJ/mol
ΔS, J/(mol∙K)
9
-223,4
-212,3
36,7
10
-232,5
-209,8
74,9
11
-232,6
-209,8
75,1
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12
-233,3
-209,8
77,3
13
-223,4
-214,6
29,1
14
-224,7
-212,4
40,6
Thus, thermodynamic calculations confirm the formation of both iso- and
unsaturated structured ABSK, as well as the formation of by-products such as
PSK and sulfons.
Result
It was established that under the conditions of the industrial process of
sulfonation of alkylbenzenes with sulfur dioxide in the reactor (temperature 303
K, pressure 110 kPa), reversible sulfonation reactions (∆G≈0 kJ/mol) occur, and
the by-products included in the composition contain unsulfonated residues,
which is confirmed by the values of the Gibbs energy of the reactions, located in
the range from (-94.2) to 0 kJ/mol. Mathematical model of a sulfonation reactor,
filled with an activity parameter of the reaction medium, depending on the
concentration of the high-viscosity component and taking into account heat and
mass transfer, washing periods of the reactor operation depending on the
technological parameters of the inter-process and the composition of the raw
material.
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