Study of the Kinetics of the Sulfonation Reaction of Styrene-DVB Copolymers of Different Structures
Abstract Generated abstract
This study examines how the porous structure of styrene and divinylbenzene copolymers affects the kinetics of sulfonation with sulfuric acid. Experimental kinetic data for gel and porous copolymers prepared with different pore-forming agents were fitted to an exponential dependence, and rate constants, activation energies, and concentration effects were compared across temperatures and acid strengths. Increasing pore volume and pore size markedly increased the sulfonation rate and reduced diffusion limitations, with highly accessible copolymers prepared in n-butanol behaving as if the reaction were controlled mainly by chemical kinetics. The work also finds two kinetic regions at sulfuric acid concentrations below about 96%, attributed to different sulfonating species, while in more concentrated acids the monomeric sulfur trioxide species predominates.
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STUDY OF THE KINETICS OF THE SULFONATION REACTION OF STYRENE AND DVB COPOLYMERS OF DIFFERENT STRUCTURES
A. K. Svetlov, E. E. Sirotkina, M. F. Tavobilov, V. D. Lazarchenko
The process of sulfonation of gel styrene and DVB copolymers, as is known, is limited by intragranular diffusion /1/. An increase in the reaction rate is possible by increasing the porosity of the granules by varying the type and amount of pore-forming agent /2/. The greatest total pore volume and pore size, with a homogeneous globular structure, are possessed by copolymers synthesized in an n-butanol medium (Table I).
Table I
Porosity characteristics of styrene and DVB (8%) copolymers
(pore-forming agent 1.0 wt. h.)
| Characteristics | n-heptane | isooctane | iso-octyl alcohol | n-butyl alcohol | gel copolymer |
|---|---|---|---|---|---|
| Pore volume, cm³/g | 0,10 | 0,20 | 0,72 | 0,85 | 0,03 |
| Pore size, eff., Å | 1,4–2,3 | 1,4–3,1 | 1,9–3,2 | 4,2–5,5 | 1,5–2,2 |
| Specific surface area by nitrogen, m²/g | 54,94 | 56,82 | 12,45 | 6,58 | 0,38 |
| Swelling, ml/g | 3,8 | 3,2 | 0,9 | 0,1 | 2,9-- |
According to electron microscopy data, samples obtained in a medium of normal alcohols have a homogeneous globular structure with globule sizes of 800–1000 Å, while those obtained in isomeric alcohols also have small globules of 600–700 Å and 300–400 Å. The structure of samples obtained with saturated hydrocarbons is amorphous.
Processing of the experimental data on a computer showed that, up to 4 hours, the process is described most fully (with a correlation coefficient of 0,98) by an exponential dependence of the form:
\[ S_{\tau} = S_T \left(1 - e^{-K_{\mathrm{eff}}\sqrt{\tau}}\right), \]
where \(S_\tau\) is the sulfur content in the copolymer at time \(\tau\), %;
\(S_T\) is the theoretical sulfur content in the copolymer, %;
\(K_{\mathrm{eff}} = K \beta_{\mathrm{ad}}\) is the effective rate constant, sec\(^{-1}\);
\(\beta_{\mathrm{ad}}\) is the adsorption coefficient;
\(\tau\) is the reaction time, sec.
On the kinetic curves for the sulfonation of gel copolymers and porous copolymers having pore sizes in the range 30–1000 Å, for all the temperatures studied three regions are observed: kinetic, transition, and diffusion. The fraction of copolymer converted in each of the regions and the duration in time vary with increasing porosity of the sample and reaction temperature. Sulfonation of a previously unswollen gel copolymer practically does not occur during the first hour, since the structure is scarcely accessible to the reagent. The process proceeds with complete destruction of the granules to a few microns. The same is observed for copolymers with isooctane and n-heptane. With increasing porosity the reaction rate increases (Table 2), and the limiting effect of diffusion processes weakens.
Table 2
Values of the kinetic parameters of the sulfonation reaction of styrene and DVB copolymers
| Sample | Effective rate constant, \(K_{\mathrm{eff}}\cdot 10^{-3}\), sec\(^{-1}\), 100°C | Effective rate constant, \(K_{\mathrm{eff}}\cdot 10^{-3}\), sec\(^{-1}\), 110°C | Effective rate constant, \(K_{\mathrm{eff}}\cdot 10^{-3}\), sec\(^{-1}\), 120°C | Activation energy \(E_{\mathrm{sr}}\), kcal/mol | Pre-exponential factor |
|---|---|---|---|---|---|
| Gel copolymer | 1.2 | 3.6 | 10.0 | 30.1 | \(7.6 \cdot 10^{14}\) |
| Copolymer with n-heptane | 1.6 | 4.3 | 12.0 | 28.5 | \(9.2 \cdot 10^{13}\) |
| Copolymer with isooctane | 3.0 | 9.0 | 14.0 | 14.4 | \(3.0 \cdot 10^{6}\) |
| Copolymer with isooctyl alcohol | 17.0 | 22.0 | 29.0 | 7.5 | \(3.0 \cdot 10^{2}\) |
| Copolymer with n-butyl alcohol | 20.0 | 24.5 | 30.2 | 5.5 | \(0.9 \cdot 10^{2}\) |
And for the copolymer obtained with n-butanol, the reaction proceeds only in the kinetic region. The rate of the process is then maximal, and the activation energy is minimal. For all structures, with an increase in the reaction temperature the rate constant increases and the activation energy decreases. The Arrhenius dependence is obeyed. In the case of highly porous samples, the granule size has no effect on the rate of the process, which is the case for gel and low-porosity copolymers.
The sulfonation reaction of styrene copolymers with sulfuric acid has certain special features, since it is known that the sulfonating agents may be the monomer $SO_3$ and the bisulfoniuм ion $SO_3H^+$, formed upon dissociation of the acid /4/. In sulfonation of copolymers with n-butanol by sulfuric acid of 92–96% concentration, the kinetic curves show two regions corresponding to chemical kinetics. The rate constant of the reaction in the first kinetic region is an order of magnitude higher than in the second (Table 3).
Table 3
| Acid concentration, % | First kinetic region: rate constant, $K_{\mathrm{ef}} \cdot 10^{-3}$, sec$^{-1}$ at 100°C | First kinetic region: rate constant, $K_{\mathrm{ef}} \cdot 10^{-3}$, sec$^{-1}$ at 110°C | First kinetic region: rate constant, $K_{\mathrm{ef}} \cdot 10^{-3}$, sec$^{-1}$ at 120°C | First kinetic region: activation energy, kcal/mol | Second kinetic region: rate constant, $K_{\mathrm{ef}} \cdot 10^{-4}$, sec$^{-1}$ at 100°C | Second kinetic region: rate constant, $K_{\mathrm{ef}} \cdot 10^{-4}$, sec$^{-1}$ at 110°C | Second kinetic region: rate constant, $K_{\mathrm{ef}} \cdot 10^{-4}$, sec$^{-1}$ at 120°C | Second kinetic region: activation energy, kcal/mol |
|---|---|---|---|---|---|---|---|---|
| 92 | 2.0 | 2.8 | 3.4 | 6.8 | 1.8 | 2.7 | 3.9 | 10.9 |
| 94 | 2.3 | 3.0 | 3.8 | 6.5 | 2.0 | 2.9 | 4.1 | 9.5 |
| 96 | 3.7 | 4.7 | 5.6 | 5.8 | 2.5 | 3.3 | 4.4 | 8.5 |
| 98 | 20.0 | 24.7 | 30.2 | 5.4 | absent | absent | absent | absent |
| 100 | 30.2 | 40.5 | 52.1 | 5.2 | —"— | —"— | —"— | —"— |
| 104 | 49.1 | 60.0 | 70.1 | 5.0 | —"— | —"— | —"— | —"— |
| 106 | 58.3 | 72.1 | 83.2 | 4.8 | —"— | —"— | —"— | —"— |
| 108 | 67.5 | 80.5 | 91.4 | 4.5 | —"— | —"— | —"— | —"— |
The degree of conversion of the copolymer in the first kinetic region amounts to 60–70% of the total. With increasing concentration
acid, the reaction rate increases in both regions. The second kinetic region, starting at a concentration of 98%, is absent. In the concentration interval 96–100%, a stepwise change in the rate constant occurs (Table 3). In the first kinetic region the sulfonating agent is the monomer \(SO_3\), which has a higher reactivity /5/; in the second, it is the bisulfone ion. The stepwise change in the rate constant is due to a sharp increase in the concentration of unbound monomer in the acid /6/. In concentrated acids the sulfonating agent is the monomer.
Conclusions
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It has been established that, with an increase in the size and volume of the pores of the copolymers, the rate of sulfonation increases. With the maximally accessible structure, despite the heterogeneity of the system, the reaction proceeds as a homogeneous one and is controlled only by the parameters of chemical kinetics.
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It has been shown that, at an acid concentration below 96%, there are two kinetic regions on the conversion curve, corresponding to two sulfonating agents—the monomer \(SO_3\) and the bisulfone ion. In concentrated acids the sulfonating agent is the monomer.
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STUDY OF THE REACTION OF VINYL ACETATE WITH ACETIC ACID
V. D. Pirogov, E. E. Sirotkina
In the synthesis of oligomers of 9-vinylcarbazole /P-9-VK-O/ by the interaction of carbazole with vinyl acetate, during the reaction there is iso-