CC BY
1УДК 541.48-143:542.97
Mustafaeva R.E.
ORCID 0000-0001-9558-8246
PhD in Chemistry, Associate professor Department of «Petrochemical Technology and Industrial Ecology» Azerbaijan State University of Oil and Industry (Baku, Azerbaijan)
THE STUDY OF THE RELATIVE ADSORPTION AND REACTIVITY OLEFINS
Аннотация: the objective of this study is to determine the possibility of oxidation of the fraction of oil refining gases containing not only isobutene but also n-butene and propene on the proposed catalyst without separating C4 - hydrocarbons. According to the data obtained, isobutene has the highest adsorption capacity among the olefins under study. It significantly suppresses their reactivity duringjoint oxidation. Oxidation of isobutene itself is practically not inhibited by the olefins mentioned.
Ключевые слова: isobutene, olefins, adsorption, C4-hydrocarbons, methacrolein, tin-antimony catalyst.
Of the known methods for synthesizing acrylic monomers, preference is given to the process of gas-phase catalytic oxidation of olefins. For the gas-phase oxidation of isobutene to methacrolein, we use an oxide tin-antimony catalyst modified with additives of alkali metals - Li and Na [1-2].
The objective of this study is to determine the possibility of oxidation on the proposed catalyst of a fraction of oil refining gases containing not only isobutene, but also n-butene and propene, without separating C4 hydrocarbons .Since oxidative dehydrogenation of n-butenes to divinyl and oxidation of propane to acrolein [3-4] also occur on tin-antimony oxide catalysts, it is first necessary to clarify the nature of the mutual influence of C3 -C4 olefins on their reactivity. The studies were carried out
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using the competing reactions method on a pulsed micro catalytic setup. The relative adsorption and reactivity of olefins was studied on a tin-antimony catalyst with an atomic ratio of Sn / Sb =1.
The prepared mixtures contained 5 vol.% olefin and 5 vol.% oxygen, the next mixture consisted of 10 vol.% olefin and 5 vol.% oxygen. Binary mixtures of 5 vol.% of each olefin and 5 vol.% oxygen were also prepared. The diluent was helium containing no more than 5 . 10 -4 oxygen. % vol. A sample of the mixture was fed into the reactor with the catalyst in the form of a pulse.
Table 1. Oxidation of C3 -C4 - olefins on a tin-antimony catalyst.
Temperature, Contact Olefin content in the Olefin conversion, % Selectivity ,
0 C time, feed mixture %
second olefin vol.% General Products soft oxidation
300 2.6 C3H6 5.1 14.5 13.0 8.7
9.9 11.5 10.7 93.0
i-C4H8 5.3 52.3 42.0 80.3
10.6 17.5 12.3 74.9
C4H8-1 5.6 2,2 1.4 63.6
12.0 1.4 0.9 64.3
C4H8-2 5.7 2.3 1.6 69.6
9.6 1.5 0.9 60.0
350 4.8 C3H6 5.1 40.0 32.5 81.3
9.9 28.3 22.5 79.5
i-C4H8 5.3 100.0 77.0 77.0
10.6 60.5 49.0 81.0
C4H8-1 5.6 6.8 4.0 58.8
12.0 3.0 1.5 50.0
C4H8-2 5.7 4.0 1.7 42.5
9.6 3.2 1.5 46.9
C3H6 5.1 47.5 37.2 78.3
9.9 - - -
i-C4H8 5.3 100 74.5 74.5
10.6 - - -
5.6 9.6 5.4 56.3
C4H8-1 12.0 5.7 - - -
C4H8-2 9.6
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The degrof oxidative conversion of olefins was calculated based on the data of the thermographic analysis and their adsorption and reactivity was judged on this basis. As the number of pulses of the standard mixture fed increased, the activity of the catalyst in propene oxidation decreased to a certain constant value, which was established by the seventh pulse and was 5 times lower than the initial activity.The oxidation products are carbon dioxide, acetaldehyde, acrolein, methacrolein, methyl vinyl ketone. With increasing temperature and contact time, the selectivity of the catalyst for incomplete oxidation products decreases. This indicates their additional oxidation under these conditions (Table 1).
On the tin-antimony catalyst, simultaneously with oxidation, oxidative dehydrogenation of n-butenes into butadiene-1,3 and isomerization of butene-1 occurs.Table 2 shows that butene-1 is hydrogenated better than butene-2. During isomerization of butene-1, the yield of cis-butene-2 is 2-3 times higher than the yield of trans-butene-2. The obtained data allow us to conclude that the reactivity of olefins decreases in the series:
i-C4H8 > C3H6 > C4H8-1 > C4H8-2
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Table 2. Oxidation of individual olefins and their mixtures on Sn - Sb - About the catalyst. The content of each olefin in the initial mixture is 5 vol.% , t = 380 0 C , t = 4.8 s.
olefin Olefin oxidation state (%) when the following olefins are present in the mixture
C3H6 i-C4H8 C4H8-1 C4H8-2 C3H6+ i- C4H8 C3H6+ C4H8-1 C3H6+ C4H8-2 i-C4H8+ C4H8-2
C3H6 21 14 22 14
i-C4H8 37 37 29
C4H8-1 14 0
C4H8-2 13 0 0
This series is maintained at different temperatures and contact times in the studied range and with a change in the olefin concentration in the reaction mixture. Only the olefin conversion decreases due to the inhibitory effect of the reaction products. In order to draw a conclusion about the relative adsorption capacity of olefins, a comparison was made of their degrees of description in an individual state and in combination with each other.
From the data given in Table 3 it is evident that there is a difference in the oxidation of individual hydrocarbons and in various combinations with each other. Basically, the presence of the second component reduces the oxidation degrof the first component.
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Table 3. Oxidative dehydrogenation and isomerization of n- benzenes on tin-antimony catalyst t = 350 0 C , т = 4.8 s.
Olefin Olefin content in pulse, vol.% Degrof oxidative dehydrogenation,% Degree isomerization,%
C4H8-1 5.5 57.5 20.9
12.0 43.6 24.8
C4H8-2 5.7 26.8 -
9.6 22.7 -
Isobutene is adsorbed better than C3H6. This is indicated by the fact that the oxidation state of C3H6 in the presence of i - C4 H8 decreases by 3 times, and the conversion i - C4 H8 remains high, i.e. its oxidation is suppressed slightly. Isobutene completely suppresses the oxidation of butene-2, and the latter, in turn, slows down the transformation of i - C4 H8, reducing the conversion from 100% to 87%. C3 H6 is adsorbed better than n-butenes, completely suppressing their oxidation. The n-butenes themselves also affect the transformation of propene and reduce its conversion from 40% to 35% in the case of butene-1 and up to 30% in the case of butene-2. The stronger effect of butene-2 on propene oxidation indicates a somewhat greater oxidative adsorption capacity of butene compared to butene-1.
Thus, the series of relative adsorption capacity on the tin-antimony oxide catalyst has the form:
i-C4H8 > C3H6 > C4H8-2 > C4H8-1
When comparing the data in Tables 2 and 3, it is found that with a twofold increase in the concentration of n-butenes in the initial mixture, their conversion decreases less than with joint oxidation with isobutene and propene, which indicates a strong inhibitory effect from i - C4 H8 and C3 H6 due to the high adsorption capacity of the latter. On the contrary, in the case of isobutane and propene, their conversion
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decreases more strongly with individual oxidation than with oxidation in mixtures. This is explained by the fact that there is a greater difference in the adsorption capacity of hydrocarbons. The component with greater adsorption capacity (isobutene, propene) prevents adsorption, and as a result, oxidation of the second component.As a result, the total amount of reaction products is less when oxidizing a double amount of one of the indicated olefins (i- C4H8 and C3H6 ), and their inhibition of the reaction rate is weakened.
CONCLUSIONS. For gas-phase oxidation of olefins C3-C4, an oxide tin-antimony catalyst modified with alkali metals - Li and Na - was used. The studies were carried out using the method of competing reactions on a pulse microcatalytic unit. It was found that isobutene has the highest adsorption capacity among the olefins studied, making it possible to use not pure isobutene, but an industrial fraction of oil refining gases as a raw material. This makes it possible to use it in the process of obtaining methacrolein gas-phase catalytic oxidation of isobutene on a tin-antimony catalyst as a raw material, instead of pure isobutene, the production of which is quite expensive, an industrial fraction of oil refining gases.
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2. Lembransky R.A. et al. Izvestiya Vuzov, "Chemistry and Chemical Technology", 1997, No. 1, p. 42;
3. Faysal M. A. , Yousef A. A. , Charles B. M. Impact of pretreatment and thiol modifiers on the partial oxidation of glutaraldehyde using Pd/Al2O3 Applied Catalysis A: General Volume 661, 5 July 2023, p.119 -129;
4. Baghirova, N.N., Mustafayeva, R.E. The conversion of ethanol to acetone on a ZnO-CaO catalyst in presence of water vapor Nafta - Gaz., 2023, 79(10), с. 684-689
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