Study of Tar from the Semi-Coking of Peat-Based Fuel-Smelting Materials
Abstract Generated abstract
This study examines tar produced during semi-coking of peat-based fuel-smelting materials containing peat, iron ore, and limestone flux, with the aim of assessing its composition for potential chemical utilization. The tar was dehydrated, dissolved in benzene, and fractionated by adsorption chromatography on neutral and alkaline alumina using petroleum ether, benzene, methanol, and mixed solvents, followed by measurements of physical properties, iodine numbers, elemental composition, and empirical formulas. Threefold chromatography isolated about 7.36% paraffin hydrocarbons, identified as a solid fraction melting at 52°C and corresponding to C20H42, while only about one quarter of the tar could be obtained as hydrocarbon fractions. Olefinic, naphthenic, aromatic, and oxygen-containing compounds remained difficult to separate on activated alumina, and repeated chromatography did not successfully isolate light phenols, apparently because reactive oxygen compounds underwent condensation.
Full Text
STUDY OF THE SEMI-COKING TAR OF PEAT-BASED FUEL-SMELTING MATERIALS
K. K. STRAMKOVSKAYA, M. S. POTAPOVA
(Presented by the scientific seminar of the Faculty of Chemical Technology)
The economics of the integrated chemical-metallurgical utilization of peat in the gas-smelting process will depend to a considerable degree on the quantity and quality of the chemical products obtained in this process. One of the products of the gas-smelting process is tar, a detailed analysis of which will indicate ways for its rational utilization.
In the present work, the tar from the semi-coking of fuel-smelting materials was studied by the method of adsorption chromatography.
The fuel-smelting materials were prepared on the basis of peat from the Tagan deposit and had the following composition: peat (absolutely dry) 53.5%, iron ore—40.0%, fluxes—6.5%. Limestone was used as the flux. Ore from the Bakchar deposit was used. The detailed composition of the fuel-smelting materials has been described previously [1].
Semi-coking was carried out in a large-scale laboratory unit at a temperature of 550°C with a heating rate of 3° per minute.
Active alumina was used as the adsorbent for chromatographic separation of the tar. In this case, neutral alumina of medium activity II—III (closer to III) was used for isolating oxygen-containing compounds.
The separation of hydrocarbons was carried out on alkaline alumina of activity I and II (closer to I).
Before analysis, the tar was dehydrated by settling at a temperature of 70°, and then dissolved in benzene and poured without residue into the chromatographic column. Petroleum ether, benzene, and methanol were used for elution. The isolation of the corresponding fraction was considered complete when pure solvent began to flow from the column (refractive-index test). The solvent was then distilled off, and the fraction was dried in a vacuum desiccator.
Primary chromatography of the tar was carried out on neutral alumina of activity II—III at a tar-to-sorbent ratio of 1:15.
The results are given in Table 1.
It is known that, in the chromatographic separation of a complex mixture of compounds on active alumina, petroleum ether extracts paraffinic, olefinic, and naphthenic hydrocarbons [2]. In order to check the purity of the separation of oxygen-containing compounds from hydro-
of the hydrocarbon portion; for the petroleum-ether eluate an infrared spectrum was recorded, which showed the presence of peaks corresponding to oxygen compounds of the ketone and aldehyde type. Therefore, for a clearer separation from oxygen-containing compounds, percolation was carried out on the same aluminum oxide, at an adsorbate:adsorbent ratio of 1:20. The hydrocarbon constituents of the fraction were washed out with petroleum ether with a boiling point below 80°, and the oxygen-containing ones with methanol. As a result, the following was obtained: petroleum-ether eluate 73.1%, methanol eluate 19.0%; the losses on aluminum oxide were 7.9%.
Table 1
Chromatographic separation of the semi-coking tar of fuel-smelting materials
| Petroleum-ether eluate, % | Benzene eluate, % | Methanol eluate, % | Residue on sorbent |
|---|---|---|---|
| 36,1 | 17,8 | 35,9 | 10,2 |
Final chromatography of the petroleum-ether eluate was carried out on aluminum oxide of activity I—II, closer to I, at an adsorbate:adsorbent ratio of 1:100. Petroleum ether (boiling point below 80°) and petroleum ether—benzene 85:15 were used as solvents.
For the products obtained, the melting point, molecular weight, refractive index, iodine number, and elemental composition were determined. From the elemental-analysis data, the empirical formula was calculated.
The experimental data given in Table 2 show that the hydrocarbon portion of the tar is very difficult to separate from oxygen-containing compounds.
Table 2
Characteristics of the hydrocarbon portion of the semi-coking tar of fuel-smelting materials
| Indicators | Solid paraffin | Olefins and naphthenes | Aromatic hydrocarbons | Residue on aluminum oxide |
|---|---|---|---|---|
| Solvent | Petroleum ether | Petroleum ether | Petroleum ether—benzene 85:15 | Residue on aluminum oxide |
| Yield per fraction | 27,07 | 34,80 | 31,60 | 7,60 |
| Yield per tar | 7,35 | 9,20 | 8,32 | |
| $n_D^{20}$ | 1,4249 | 1,5558 | 1,5774 | |
| Iodine number | 0 | 50,7 | 57,1 | |
| Melting point, °C | 52 | < 25 | < 25 | |
| Molecular weight | 2,82 | 245 | 268 | |
| Elemental composition, % C | 85,80 | 86,5 | 90,95 | |
| Elemental composition, % H | 14,20 | 9,32 | 6,14 | |
| Elemental composition, % O | — | 4,18 | 2,14 | |
| Empirical formula | $\mathrm{C}_{20}\mathrm{H}_{42}$ | $\mathrm{C}_{13,6}\mathrm{H}_{17,6}\mathrm{O}_{0,49}$ | $\mathrm{C}_{19,3}\mathrm{H}_{16,9}\mathrm{O}_{0,39}$ |
Only after threefold chromatography was it possible to isolate fairly pure paraffins from the tar in an amount of 7.35%.
Table 3
Characteristics of the products of chromatographic separation of benzene eluates of semi-coking tar of fuel-smelting materials
| Indicators | Petroleum ether–benzene 85:15 | Petroleum ether–benzene 50:50 | Benzene | Benzene–methanol 50:50 | Residue on aluminum oxide |
|---|---|---|---|---|---|
| Yield per fraction | 9,71 | 52,10 | 8,65 | 20,10 | 9,54 |
| Yield per tar | 1,75 | 9,26 | 1,58 | 3,58 | 1,54 |
| Iodine number | 1,537 | 1,552 | 1,568 | — | |
| Molecular weight | 127 | 83 | 69 | 55 | |
| Elemental composition, % C | 156 | 134 | 193 | 283 | |
| Elemental composition, % H | 78,03 | 77,59 | 77,91 | 75,18 | |
| Elemental composition, % O | 8,32 | 7,96 | 7,85 | 7,01 | |
| Empirical formula | $\mathrm{C}_{10}\mathrm{H}_{12,9}\mathrm{O}_{1,4}$ | $\mathrm{C}_{8,8}\mathrm{H}_{10,7}\mathrm{O}_{1,3}$ | $\mathrm{C}_{12,5}\mathrm{H}_{13,1}\mathrm{O}_{1,7}$ | $\mathrm{C}_{13,4}\mathrm{H}_{19,7}\mathrm{O}_{3,1}$ |
with a melting point of 52° and a composition corresponding to the empirical formula $\mathrm{C}_{20}\mathrm{H}_{42}$.
The olefin–naphthene part of the tar, eluted with petroleum ether and amounting to 9.2%, contained an admixture of oxygen-containing compounds even after threefold chromatography. The elevated refractive index of this fraction ($n_D^{20}$ 1.5558) is explained by strong resinification (rapid darkening) of the fraction during its drying. Although this part of the tar is mobile at room temperature, it has a high molecular weight (245) and corresponds to the empirical formula $\mathrm{C}_{13.6}\mathrm{H}_{17.6}\mathrm{O}_{0.49}$.
The aromatic hydrocarbons, eluted with a mixed solvent (petroleum ether–benzene 85:15) in an amount of 8.32% (Table 3), are high-molecular-weight ($M = 268$) and evidently have unsaturated bonds in the side chains. This fraction also contains a small admixture of oxygen-containing compounds.
Thus, by threefold chromatography it was possible to isolate from the tar only about 24% hydrocarbons. The entire remaining part of the tar contains oxygen compounds in large amounts. Thus, the benzene eluate from the primary chromatography of the tar was subjected to secondary separation on neutral aluminum oxide of activity I at an adsorbate:adsorbent ratio of 1:50. The results of the study (Table 3) showed the presence of a considerable amount of oxygen in each eluate. All these substances are apparently aromatic in character ($n_D^{20}$ 1.537—1.568), with a large number of unsaturated bonds, as indicated by the high iodine numbers.
An attempt at repeated chromatography of the methanol eluate in order to isolate light phenols from it did not give good results. Evidently, repeated contact of reactive oxygen-containing compounds with aluminum oxide leads to condensation reactions and to the formation of high-molecular-weight compounds with a high melting point. It was not possible to isolate light phenols in this way.
Conclusions
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From the semi-coking tar of fuel-smelting materials, 7.36% paraffin hydrocarbons were isolated, with a melting point of 52°C and a composition corresponding to the empirical formula $\mathrm{C}_{20}\mathrm{H}_{42}$.
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Olefinic, naphthenic, and aromatic hydrocarbons of the tar could not be separated from one another and from oxygen compounds on activated aluminum oxide even by threefold chromatography.
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Light phenols are not isolated from the complex mixture of oxygen-containing compounds of the tar by repeated chromatography on active aluminum oxide.
Literature
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K. K. Stramkovskaya, V. D. Ivanova, G. G. Volkov. Influence of additions of ore and fluxes on the yield and composition of peat semi-coking tar. Izv. TPI, vol. 136, 1965.
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M. S. Tsvet. Chromatographic Adsorption Analysis. Publishing House of the Academy of Sciences of the USSR, 1946.