Study of Phenols in Medium-Temperature Tar
Abstract Generated abstract
This paper examines the composition and yield of phenols in tar obtained from medium-temperature coking of Kuznetsk gas coal, with particular attention to lower phenols of industrial value. Phenols were extracted from the tar distillate boiling up to 340 degrees using water, alkali treatment, acid decomposition, and bicarbonate purification, then separated by distillation and rectification, with fractions characterized by refractive index and hydroxyl number. The study found that most phenols were concentrated in the distillate, crude phenols amounted to about 17.7 percent of anhydrous tar, and lower phenols boiling below 230 degrees reached 8.76 percent. The results suggest that medium-temperature pyrolysis can substantially increase yields of phenol, cresols, and xylenols compared with other coal-processing regimes.
Full Text
STUDY OF PHENOLS IN MEDIUM-TEMPERATURE TAR
N. M. SMOLYANINOVA, E. I. GRYAKOV, V. S. SHVED
(Presented by Prof. I. V. Gebler, Doctor of Technical Sciences)
Along with petroleum and natural gas, coal and brown-coal tars are a source of raw material, especially cyclic raw material, necessary for the broad development of the organic-synthesis industry.
One of the most valuable products of the processing of various tars should be considered the low-boiling, or so-called lower, phenols, the demand for which increases with each year. At present, according to data from Giprokoks, demand for lower phenols in the USSR considerably exceeds their production.
The main sources for obtaining phenols are coke chemistry and the developing production of synthetic phenol based on benzene, with the first source predominating. High-temperature coking of coals is far from the best method of obtaining phenols, owing to the excessively low yields, amounting to hundredths of a percent of the coal.
A considerably higher yield of phenols is observed in low-temperature pyrolysis of coals. However, the phenols of primary tars are represented mainly by higher homologues, the nature of which has been poorly elucidated; effective methods for converting them into lower phenols have not yet been developed, and practical application is very limited.
Of greatest interest is medium-temperature tar, obtained by pyrolysis of coals at a temperature on the order of 700°. From a few, very limited investigations [1—4] it is known that precisely the medium-temperature regime of thermal processing of hard coals should provide the best conditions for the formation of lower phenols.
We carried out a study of the phenols of tar from medium-temperature coking of Kuznetsk gas coal. The tar in the quantity required for the investigation was obtained in an enlarged laboratory installation.
After dehydration by the salting-out method with heating to 70°, the tar contained 4.43% water (by Dean and Stark) and had a specific gravity \(d^{20}_{4}=1.06\). Its group composition, determined by the method of G. L. Stadnikov [5], is given in Table 1.
As is evident from these data, the characteristics of the tar indicate its medium-temperature character.
For better and more convenient extraction of phenols from the tar, the pitch was first separated by distilling off its broad fraction boiling up to 340°.
Table 1
| No. | Composition of the tar | Content, % of anhydrous tar |
|---|---|---|
| 1 | “Free carbon” | 7,82 |
| 2 | Carboxylic acids | 0,60 |
| 3 | Organic bases | 2,07 |
| 4 | Phenols: | |
| a) soluble in petroleum ether, | 5,26 | |
| b) insoluble in petroleum ether. | 14,54 | |
| 5 | Paraffins | 1,01 |
| 6 | Asphaltenes | 2,72 |
| 7 | Neutral oils | 49,60 |
| 8 | Losses | 16,35 |
| Total | 100 |
The fraction obtained had a specific gravity \(d^{20}_{4}=0.986\) and contained 19.8% phenols, calculated on an anhydrous tar basis. The latter indicates that the overwhelming quantity of phenols is concentrated in the distillate up to 340°.
The phenols were separated from the fraction by the procedure adopted at the Institute of Fossil Fuels of the Academy of Sciences of the USSR [6]. In order to avoid losses, the water-soluble phenols were first extracted by treating the fraction with hot distilled water containing 40 g/l \(Na_2SO_3\) (to prevent oxidation). The remaining phenols were separated with a 13% aqueous alkali solution. The phenolates were decomposed with a 10% solution of sulfuric acid, and the phenols were separated from the solution in a separatory funnel. Together with the phenols, carboxylic acids were also extracted; these were separated from the mixture by treating it at 60° with a 10% solution of \(NaHCO_3\).
The results of the separation of phenols are given in Table 2.
Table 2
| Tar | Weight of initial fraction, g | Weight of water-soluble phenols, g | Weight of phenols separated by alkali, g | Yield of crude phenols, g | Yield of phenols, % of initial fraction | Yield of phenols, % of anhydrous tar |
|---|---|---|---|---|---|---|
| Broad fraction (up to 340°) | 248,60 | 1,30 | 73,58 | 74,88 | 30,10 | 17,70 |
It is evident from Table 2 that the losses of phenols in the indicated extraction procedure are small and amount to no more than 10% of their resources in the fraction.
The phenols obtained were distilled from a Wurtz flask at atmospheric pressure into three fractions: phenol–cresol, xylenol, and a fraction of higher phenols. The distillation (Table 3) showed that the yield of lower phenols (boiling point below 230°) from medium-temperature coking tar is 8.76%, that is, several times higher than in ordinary coking.
In order to determine the content of the most valuable representatives—phenol and cresols—the phenol-cresol fraction was subjected to rectification on a laboratory column with a number of theoretical plates equal to 16. Before rectification, the fraction was additionally purified from residues of nitrogenous and readily resinifying substances by the method of V. A. Lanina and N. D. Edemskaya [6]. This operation consists in heating the fraction being purified with 0.5% by weight of crystalline potassium permanganate and then distilling it from the products formed by interaction with the indicated reagent.
The narrow fractions obtained after rectification were characterized by determining the refractive index and hydroxyl numbers (by the method of Verley and Bölsing [7]).
For rectification, 18.24 g of the phenol-cresol fraction under study was taken; the results are given in Table 4. From these data it follows that the first three phenolic fractions and the intermediate fraction consist predominantly of phenol (the refractive index of pure phenol
Table 3
| No. | Fractions | Yield of fractions, in grams | Yield of fractions, % of crude phenols | Yield of fractions, % of anhydrous tar |
|---|---|---|---|---|
| 1 | Phenol-cresol (up to 210°) | 18.79 | 25.40 | 4.42 |
| 2 | Xylenol (210—230°) | 18.42 | 24.90 | 4.34 |
| 3 | Higher phenols (230—260°) | 14.10 | 19.10 | 3.32 |
| 4 | Still residue plus losses | 22.75 | 30.70 | 6.52 |
| Total | 74.06 | 100.00 | 17.60 |
Table 4
| No. | Fractions | Yields, in grams | Yields, % of initial fraction | Yields, % of crude phenols | Yields, % of tar | $n_D^{20}$ | %, OH |
|---|---|---|---|---|---|---|---|
| 1 | Phenolic 180.0—181.5° | 1.81 | 9.93 | 2.52 | 1.83 | 1.5240 | 18.7 |
| 2 | Phenolic 181.5—182.0° | 2.57 | 14.10 | 3.58 | 1.83 | 1.5452 | 17.99 |
| 3 | Phenolic 182.0—184.0° | 3.15 | 17.28 | 4.39 | 1.83 | 1.5482 | 17.52 |
| 4 | Intermediate 184.0—187° | 2.52 | 13.82 | 3.51 | 0.61 | 1.5475 | 17.07 |
| 5 | Ortho-cresol 187.0—194.0° | 3.85 | 21.10 | 5.36 | 0.93 | 1.5428 | 15.52 |
| 6 | Still residue | 2.51 | 13.67 | 3.50 | 0.60 | — | — |
| 7 | Losses | 1.82 | 10.00 | 2.47 | 0.44 | — | — |
is, at 20°, 1.5400 and the hydroxyl number is 18.08%). The lower refractive index of the first fraction in comparison with the other fractions is explained by the presence in it of water occluded by the precip-
column. The ortho-cresol fraction, apparently, also consists almost entirely of ortho-cresol (for pure ortho-cresol the refractive index is 1.5453, and the hydroxyl number is 15.73%).
Thus, the yield of the most valuable phenolic fraction is more than 10% calculated on total phenols and more than 2% on tar. The yield of the ortho-cresol fraction is also significant, amounting to more than 5% of the total phenols and about 1% of the tar.
The study carried out showed that the implementation of the medium-temperature regime of coal pyrolysis will make it possible to increase the yield of lower phenols by 5–8 times or more in comparison with low-temperature pyrolysis.
The results obtained may be useful in finding the optimum regime for the pyrolysis of vapor-gas products obtained in new installations, including continuous coking installations.
REFERENCES
- Dirichs A., Kubichka R. Phenols and Bases from Coals. Gostekhizdat, 1958.
- Nikol’skii N. A., Stepanenko M. A. Processing of coal at medium temperatures. “Coke and Chemistry,” No. 19, 1938.
- Fitz W. — Brennstoff-Chemie, 12, 1931.
- Koppers H. — Brennstoff-Chemie, 11, 1934.
- Stadnikov G. L. Analysis and Study of Coals. Publishing House of the Academy of Sciences of the USSR, 1936.
- Lanin V. A., Edemskaya N. D., Mekhun L. M. Report on research work for 1955. Archives of the IGI, Academy of Sciences of the USSR.
- Weibel S. Identification of Organic Compounds. Foreign Literature Publishing House, Moscow, 1957.