ISSN 0965-5441, Petroleum Chemistry, 2006, Vol. 46, No. 6, pp. 439–441. © Pleiades Publishing, Inc., 2006. Original Russian Text © P.P. Samatov, U.M. Dzhemilev, A.Kh. Sharipov, 2006, published in Neftekhimiya, 2006, Vol. 46, No. 6, pp. 468–470.
Oxidation of Sulfides in Petroleum Diesel Fraction with Hydrogen Peroxide Catalyzed by Molybdenum Compounds P. P. Samatova, U. M. Dzhemilevb, and A. Kh. Sharipovb a
b
ZAO Opytnyi zavod Neftekhim, Ufa, Russia Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences, Ufa, Russia e-mail:
[email protected] Received April 30, 2006
Abstract—The catalytic properties of molybdenum compounds in the oxidation of sulfides from the diesel fraction of sour crude oil with hydrogen peroxide were studied. Comparative data on the performance of molybdenum complexes in the oxidation of diesel sulfides are reported. The activity of the catalysts was compared in terms of the degree and selectivity of conversion of sulfides into sulfoxides. The highest catalytic activity was shown by molybdenum bis-sulfoxide peroxo complexes. DOI: 10.1134/S0965544106060107
The selection of an effective catalyst is of great importance to the development of an economically viable industrial process for the production of a sulfoxide concentrate from petroleum feedstock. Aqueous solutions of perchloric, sulfuric, and acetic acids are, of course, effective catalysts for the oxidation of sulfides to sulfoxides [1, 2]. However, their use on the industrial scale is complicated by the corrosion of equipment and the formation of hardly utilizable acid waste. It is found that main-group metal compounds do not exhibit catalytic activity, whereas compounds of certain transition metals accelerate the oxidation of sulfides to sulfoxides [3]. The reaction of sulfide oxidation with peroxides catalyzed by Mo(V) complexes is very interesting and holds much promise [4, 5]. Comparative data on the performance of various molybdenum compounds in the oxidation of petroleum sulfides are lacking in the literature. To design complex catalysts that could be implemented in the industry, we studied in this work the oxidation of sulfides from the diesel fraction of sour crude oil in the presence of various molybdenum compounds. EXPERIMENTAL The oxidation of diesel sulfides was studied under isothermal conditions in the absence of the effect of diffusion factors. As a measure of the catalyst activity, the degree and selectivity of sulfide conversion to sulfoxides in an idealized well-stirred batch reactor was taken. In order to obtain comparable results on the activity of catalysts, all experiments were conducted at a tem-
perature of 60°ë optimal for the formation of sulfoxides. Peroxide consumption in all runs was 1.2 moles per mole of sulfide sulfur. The procedures of oxidation and analysis of the reactants and products were described in [6]. As a feedstock, the diesel cut of Arlan oil was used; this fraction boils in the range IBP 190–FBP 360°ë and contains 0.9 wt % sulfide sulfur and 2.2 wt % total sulfur. The sulfide composition of the diesel fraction was determined on a Finnigan 4021 GC/MS spectrometer [7]. The sulfides are represented mainly by thiamonocycloalkanes and thiabicycloalkanes (85–90%). A 30% hydrogen peroxide aqueous solution (GOST (State Standard) 177-88) and commercially available organic and inorganic molybdenum compounds were used in the work. Molybdenum peroxo bis(sulfoxide) complexes were prepared according to the following procedure: 5 g of a molybdenum compound and 25 ml of a hydrogen peroxide solution were placed in a flask and heated at 40°ë for 25 min with intense stirring. The resulting yellow suspension was cooled to 10°ë, and 8.2 g of sulfoxide was added dropwise to the reaction mixture. The reaction is exothermic. In the case of necessity for a sudden reduction of temperature, a supply of cold water to the reaction zone was provided. The product was cooled and filtered in vacuum. Under these conditions, 9–10 g of the product forms, which was recrystallized from methanol and analyzed spectrophotometrically. The IR spectrum of the molybdenum complex obtained has intense absorption bands at 810, 1090, and 2350 cm–1 characteristic of sulfoxides [8], as well as the bands of molybdenum peroxo complexes.
439
440
SAMATOV et al. 540 m. ν ( Mo 580 s. ν ( Mo
O O O O
) S, ) S,
940–956 ν (Mo=O)s and 860 br.s. (0–0) [9]
RESULTS AND DISCUSSION On the basis of the experimental data obtained in this work and published data, we propose the following structure of the isolated molybdenum peroxo complex containing two sulfoxide molecules in the coordination sphere: O O
O Mo
O O
R S O
O S R
R'
R'
,
where R and R' are the same or different ë-ë8 alkyl radicals with the normal or iso-branched chain. As ligands, cyclic sulfoxides can also be successfully used: R
R SO
SO
The experimental results are given in Table 1. As is seen, independently of the nature of the initial molybdenum compound, the yields of sulfoxides vary within the range ~62–75%. The best results were obtained when petroleum sulfides were oxidized in the presence of molybdenum compounds soluble in the reaction mixture (molybdenum acetylacetonate, ammonium molybdate, or molybdenum naphthenate). The maximal sulfoxide sulfur content was 0.68–0.7%. A disad-
vantage of oxidation in the presence of these compounds is the irreversible loss of a catalyst because of its dissolution in the organic phase; moreover, the presence of molybdenum compounds in the oxidate is extremely undesirable in some cases [10, 11]. Therefore, the task of further investigation was reduced to the search for catalysts based on molybdenum derivatives that have a high water solubility and do not contaminate the diesel fraction. From the literature [9], it is known that molybdenum compounds dissolve in a hydrogen peroxide solution to form molybdenum peroxo complexes. These complexes are soluble in water and highly reactive. We found that the reaction of molybdenum peroxo complexes with sulfoxides give molybdenum peroxo complexes, which contain sulfoxide molecules as ligands in the inner coordination sphere. Occurring in the inner sphere, sulfoxides increase the catalytic activity of molybdenum in the oxidation reactions of diesel sulfides (Table 2). As is seen from the data presented in Table 2, the catalytic activity of molybdenum bis-sulfoxide peroxo complexes prepared from various molybdenum compounds and sulfoxides levels out to slightly differ from one complex to another. At the same time, when the process is catalyzed by the molybdenum bis-sulfoxide peroxo complexes, the sulfide conversion to sulfoxides is 7–9% higher, the oxidation time is 4–8 times shorter, and the catalyst consumption is more than an order of magnitude lower than for the oxidation in the presence of molybdenum compounds (Table 1). The reaction selectivity significantly increases (the formation of acid products and sulfones decreases). In washed specimens of the oxidized diesel fraction that was prepared with the aid of molybdenum bis-sulfoxide peroxo complexes, molybdenum was determined by spectrophotometry and ESR methods. It is known that molybdenum compounds are easy to determine spectrophotometrically by the characteristic absorption maximum at 331 nm over a broad tempera-
Table 1. Oxidation of diesel sulfides in the presence of molybdenum compounds Amount of Amount of sulAmount of molybdenum Oxidation foxide sulfur Oxidate acidi- Sulfide conversion Molybdenum compound sulfones in oxcompound, wt time, min content in oxity, g of KOH/l to sulfoxide, % idate, wt % % of feedstock date, wt % Catalyst-free Molybdenum acetylacetonate Ammonium molybdate Molybdic acid Molybdenum naphthenate Molybdenum oxide Molybdenum stearate
– 0.05
90 60
0.18 0.68
– 0.8
0.1 0.8
20.0 75.5
0.05 0.02 0.02 0.03 0.04
45 70 60 90 60
0.68 0.67 0.70 0.57 0.56
1.0 1.1 1.1 0.6 0.8
1.2 0.8 1.2 1.0 1.0
75.5 74.4 77.7 63.3 62.2
* Hereinafter in Tables 1 and 2, the temperature is 60°C and the hydrogen peroxide consumption is 1.2 moles per mole of sulfide sulfur. PETROLEUM CHEMISTRY
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OXIDATION OF SULFIDES IN PETROLEUM DIESEL FRACTION
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Table 2. Oxidation of diesel sulfides in the presence of molybdenum bis-sulfoxide peroxo complexes Molybdenum peroxo complexes as prepared by dissolution in hydrogen peroxide of Molybdenum acetylacetonate Ammonium molybdate Molybdic acid Molybdenum naphthenate Molybdenum oxide Molybdenum stearate
Ligand
Amount of molybdenum bis-sulfoxide peroxo complex, wt % of feedstock
Oxidation time, min
Amount of sulfoxide sulfur in oxidate, wt %
Amount of sulfones in oxidate, wt %
0.001
15
0.25
None
0.2
83.3
0.001
10
0.77
0.05
0.1
85.5
0.0008
15
0.73
None
0.1
81.1
0.0007
7
0.77
None
0.1
85.5
0.0008
10
0.73
0.05
0.1
81.1
0.001
7
0.74
0.05
0.2
82.2
Thiophane sulfoxide Dimethyl sulfoxide Dibutyl sulfoxide Petroleum sulfoxides Diethyl sulfoxide Petroleum sulfoxides
ture range [12]. No molybdenum compounds were detected in the test samples. Thus, the molybdenum peroxo complexes that contain sulfoxide ligands in the coordination sphere are the most effective catalysts for the conversion of petroleum sulfides into sulfoxides, a prerequisite that makes the industrial application of these catalysts realistic. REFERENCES 1. E. N. Karaulova, Chemistry of Petroleum Sulfides (Khimiya, Moscow, 1970) [in Russian]. 2. G. D. Gal’pern, Usp. Khim. 45 (8), 1395 (1976). 3. T. P. Burmistrova, V. G. Ivanov, A. A. Emekeev, et al., Abstracts of Papers XVI Conference on Chemistry and Technology of Organic Sulfur Compounds and Sour Crudes (Zinatne, Riga, 1984) [in Russian]. 4. G. A. Tolstikov, Hydroperoxide Oxidation Reactions (Nauka, Moscow, 1976) [in Russian].
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Oxidate Sulfide acidity, conversion g of KOH/l to sulfoxide, %
5. U. M. Dzhemilev, N. S. Vostrikov, G. A. Tolstikov, and S. R. Rafikov, Dokl. Akad. Nauk SSSR 244 (2), 369 (1979). 6. A. Kh. Sharipov, R. M. Masagutov, Z. A. Suleimanova, et al., Neftekhimiya 29, 551 (1989). 7. R. M. Masagutov, E. A. Kruglov, J. N. Popov, et al., in Proc. of Tenth International Symposium on the Organic Chemistry of Sulphur, Bangor, University College of North Wales, 1982, p. 129. 8. S. Oae, Chemistry of Organic Sulfur Compounds (Kagaku Dozin, Tokyo, 1968; (Khimiya, Moscow, 1975). 9. I. I. Vol’nov, Chromium, Molybdenum, ang Tungsten Peroxo Complexes (Nauka, Moscow, 1989) [in Russian]. 10. T. V. Garipov, D. K. Chervyakov, and V. A. Antipov, Veterinariya, No. 1, 83 (1975). 11. G. A. Kashafutdinov, F. N. Mazitova, and N. A. Iglamova, Abstracts of Papers, XVI Conference on Chemistry and Technology of Organic Sulfur Compounds and Sour Crudes (Zinatne, Riga, 1976) [in Russian]. 12. V. A. Gavrilenko, E. I. Evzerikhin, V. A. Kolosov, et al., Izv. Akad. Nauk SSSR, Ser. Khim., No. 10, 1954 (1974).
