Study of the Material Composition of Sulfur Compounds in Crude Benzene from Coke Production at the Kuznetsk Metallurgical Plant
Abstract Generated abstract
This study examines the qualitative and quantitative composition of sulfur compounds in crude benzene from coke production at the Kuznetsk Metallurgical Plant and in benzene toluene fractions before and after sulfuric acid washing. Using a modified Faragher method, with adjusted combustion conditions for total sulfur determination, the authors measured hydrogen sulfide, mercaptans, carbon disulfide, disulfides, and thiophene sulfur. The results show that the crude product is comparatively low in sulfur, mainly containing carbon disulfide and thiophene sulfur, while acid purification removes active sulfur compounds but leaves notable carbon disulfide in processed fractions. The persistence of carbon disulfide is attributed to incomplete removal during rectification, suggesting that improved operation of the carbon disulfide column is important for producing low-sulfur benzene.
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STUDY OF THE MATERIAL COMPOSITION OF SULFUR COMPOUNDS IN CRUDE BENZOL FROM THE COKE-CHEMICAL PRODUCTION OF THE KUZNETSK METALLURGICAL COMBINE
N. M. SMOLYANINOVA, V. A. CHEMERKO
(Presented by the Scientific-Methodological Seminar of the CTF)
The new standard for coal benzol (GOST-61) limits the content of carbon disulfide and thiophene in benzol of the higher grades “especially pure” and “pure for synthesis, 1st grade” to no more than 0.0001% of each of these components. Benzol of such purity is necessary for the organic-synthesis industry, in particular for the production of cyclohexane and phenol, and the demand for such raw material has increased sharply.
However, the commercial product produced until recently by coke-chemical enterprises does not satisfy these requirements. Obtaining sulfur-free benzol with the existing technology is extremely difficult and is associated with large expenditures of raw material and reagents. Therefore, the question of obtaining low-sulfur grades of benzol at coke-chemical enterprises is very urgent and requires prompt resolution.
The correct choice of the direction of research and the development of methods for obtaining sulfur-free benzol must, above all, be based on exact knowledge of the qualitative and quantitative composition of the sulfur compounds entering into the composition of crude benzol and the products of its processing. This will also make it possible to correctly assess the possibilities of the existing technology.
We have carried out a study of the material composition and quantitative content of sulfur compounds in crude benzol from the KMK and in the products of its processing. The crude benzol and the unwashed and washed benzol–toluol (BT) fractions were subjected to investigation. The characteristics of the indicated products are given in Tables 1 and 2.
The determination of the individual varieties of sulfur compounds was carried out by the Faragher method as modified by the Institute of Petroleum of the Academy of Sciences of the USSR [1]. We made the following deviations from this method: 1) the determination of total sulfur was carried out by the method of combustion in a vertical tube in a current of air; 2) elemental sulfur was not determined separately, but was extracted together with the mercaptans, since the metallic mercury ordinarily used to remove elemental sulfur also extracts carbon disulfide.
In the course of the work it was noted that the method for determining total sulfur as set forth by L. D. Gluzman and I. I. Edelman [2] does not ensure complete combustion owing to the nonuniform feed of benzol. For
To eliminate this drawback, we placed an asbestos or nickel screen beneath the dropping funnel. The benzol drops fell onto this screen and evaporated uniformly in the air stream. If the product under study contained a nonvolatile residue, the screen was lowered into the hot zone, where it burned out. In addition, more accurate results were obtained by raising the temperature of the combustion furnace to 900°C.
Table 1
| Fractional composition of crude benzol | Index |
|---|---|
| Temperature at which the first drop falls, °C | 80.0 |
| Distillate up to 100°C (by volume) | 77.9 |
| Distillate up to 125°C | 86.4 |
| Distillate up to 150°C | 89.5 |
| Distillate up to 180°C | 92.4 |
| Specific gravity of crude benzol | 0.887 |
| Specific gravity of distillate up to 180°C | 0.878 |
Table 2
| Content of pure products, % by weight | Crude benzol | Unwashed BT fraction | Washed BT fraction |
|---|---|---|---|
| Light benzol | 0.69 | 0.97 | 0.62 |
| Pure benzene | 79.30 | 79.00 | 8.10 |
| Pure toluene | 10.85 | 10.61 | 12.50 |
| Pure xylene | 1.08 | 1.89 | 1.64 |
| Solvents | 1.31 | — | 0.23 |
| Still residues | 3.66 | 4.00 | 3.98 |
| Washing losses | 3.10 | 3.50 | — |
The quantitative content of sulfur compounds in the fractions subjected to study is given in Table 3.
Table 3
| Samples | Total sulfur, % | Hydrogen sulfide, % | Mercaptans and elemental sulfur, % | Carbon disulfide, % | Disulfides, % | Thiophene sulfur, % |
|---|---|---|---|---|---|---|
| Crude benzol | 0.183 | 0.011 | 0.017 | 0.049 | 0.008 | 0.098 |
| Unwashed fraction | 0.098 | none | 0.001 | 0.018 | 0.006 | 0.072 |
| Washed fraction | 0.098 | —"— | none | 0.024 | none | 0.072 |
The data obtained show that the crude benzol of KMK contains a small amount of sulfur compounds, mainly represent—
carbon-disulfide sulfur—0.049% and thiophene sulfur—0.098%; this is associated with the low sulfur content of the coals of the Kuznetsk Basin. The content of thiophene sulfur in crude benzol obtained from Donetsk coals is 10–11 times higher than in benzol from Kuznetsk coals. Undoubtedly, purification of the products of processing crude benzol from eastern plants will require lower costs for sulfur removal, which in turn will reduce the cost of low-sulfur benzol.
Analysis of the washed and unwashed fractions showed that, after sulfuric-acid purification, the products contain no active sulfur. However, the content of carbon disulfide is significant and varies within the range from 0.01% to 0.02%, which is apparently due to abnormal operation of the carbon-disulfide column in the rectification shop. This is confirmed by the data from the analysis of crude benzol, from which it is evident that the head fraction is removed from it very poorly: from 1/3 to 1/2 of the carbon disulfide remains in the BT fraction after preliminary rectification.
The identical content of total sulfur in the washed and unwashed fractions is explained by the removal, during sulfuric-acid purification (washing), of mercaptans and disulfides, which are readily soluble in concentrated sulfuric acid. Their loss is compensated by the increased content of carbon disulfide in the washed fraction.
The content of thiophene sulfur in crude benzol is considerably higher than in the BT fractions, while its content in the latter is the same. The former can apparently be explained by instability of the temperature regime of coking (the sulfur content in the KMK coal charge is practically constant), and the latter by the presence, although to an insignificant degree, of a process of sulfonation of thiophene, the products of which dissolve in sulfuric acid. Otherwise, the content of thiophene sulfur should have increased somewhat after purification, if one takes into account that the yield of the washed fraction is 96.5%. The bulk of the thiophene is removed by copolymerization with high-boiling unsaturated hydrocarbons in the presence of concentrated sulfuric acid.
The amount of disulfides in the unwashed fraction is less than in crude benzol, which may be connected with the presence in the latter of high-boiling representatives, such as ethyl disulfide and propyl disulfide, which remain during preliminary rectification in the heavy benzol. Instability of the coking temperature regime also affects the content of disulfides.
Elemental sulfur, formed during the oxidation of hydrogen sulfide and present in crude benzol, passes into the high-boiling fractions (solvent naphtha). Therefore, the unwashed fraction contains only mercaptans.
Conclusions
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The material composition of the sulfur compounds of KMK crude benzol and of the products of its processing has been determined. It has been established that this product is low-sulfur and contains predominantly carbon-disulfide and thiophene sulfur.
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The relatively high content of carbon disulfide in the washed and unwashed BT fractions is a consequence of its incomplete removal during rectification.
LITERATURE
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Methods for the Analysis of Organic Compounds of Petroleum, Their Mixtures, and Derivatives. Publishing House of the USSR Academy of Sciences, 1960.
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L. D. Gluzman, I. I. Edelman. Laboratory Control of Coke-Chemical Production. Metallurgizdat, 1957.
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L. Ya. Kolyandr. Processing of Crude Benzol. Metallurgizdat, Kharkov, 1960.
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S. S. Nametkin et al. Analysis of sulfur compounds of light petroleum distillates. Proceedings of the USSR Academy of Sciences, Department of Technical Sciences, No. 1–2, p. 10, 1943.