EFFECT OF THE TEMPERATURE OF THERMAL PROCESSING OF GAS COALS ON THE YIELD AND COMPOSITION OF LOWER PHENOLS

N. M. SMOLYANINOVA, V. S. SHVETS

(Presented by Professor Doctor I. V. Gebler)

In the thermal processing of solid fuels, the temperature conditions of the process have a decisive influence on the yield and composition of phenols. Taking into account the great demand of the chemical industry for low-boiling phenols, research aimed at finding the temperature conditions of the process that ensure the greatest yields and the optimum composition of phenols obtained in the pyrolysis of low-metamorphosed coals of the gas type, which possess great chemical potential, is of interest.

The present work is devoted to studying the influence of heating temperature on the yield and composition of phenols obtained in the thermal processing of gas coal from the Leninsk deposit of the Kuznetsk Basin.

In order to obtain the quantity of phenols necessary for the investigation, an enlarged laboratory installation was constructed, consisting of a pyrolysis furnace with a capacity of about 15 kg of coal and a tar-trapping system including a condenser and an electrofilter. The furnace design is shown in Fig. 1.

The experiments were carried out at chamber wall temperatures of 600, 700, and 800°, and the yields of coke, tar, pyrogenetic water, and gas were determined (Table 1).

Table 1

Yields of pyrolysis products, in % of dry coal

In Table 2 the characteristics of the tar and its group composition, determined by the method of Stadnikov [1], are presented.

From the tables given it follows that, with an increase in the temperature of thermal processing, the yield of tar decreases, and its composition changes—

Fig. 1. Laboratory furnace for coal pyrolysis:
1 — body of the coking chamber; 2 — pyrolysis chamber; 3 — upper cover; 4 — fitting; 5 — lower cover; 6 — lever; 7 — clamping screw; 8 — angle piece; 9 — stand; 10, 16 — thermocouples; 11 — Teflon plug; 12 — cap nut; 13 — insulating brick; 14 — iron plate; 15 — thermocouple sheath; 17 — gasket; 18 — thermal insulation; 20, 21 — electric heaters of the pyrolysis chamber; 22 — casing.

is toward a decrease in the content of neutral oils, organic bases, and phenols, and an increase in the content of “free carbon” and asphaltenes, which indicates the occurrence of processes of thermal destruction of the components of the low-temperature tar, accompanied, along with cracking reactions, also by condensation and polymerization reactions.

Table 2

Before the extraction of phenols, the tar samples were preliminarily subjected to distillation (a broad fraction up to 340° was taken off) in order to separate the pitch.

The phenols were isolated from the broad fraction with a 13% NaOH solution by the generally accepted method. Particular attention was paid to the fullest possible extraction of phenols by decomposing pyridine phenoxides with 30% sulfuric acid, and also to the extraction of water-soluble phenols from aqueous solutions with sulfuric ether.

The yield of phenols, calculated on an anhydrous tar basis, was 18.3% at 600°; 14.3% at 700°; and 2.60% at 800°, that is, with an increase—

Table 3

Table 4

with an increase in the pyrolysis temperature from 600 to 800°, the yield of phenols decreased almost sevenfold.

The obtained “crude” phenols were distilled (for the purpose of preliminary separation of the low-boiling phenols from the high-boiling ones) from a Wurtz flask into three fractions: phenol–cresol, xylenol, and higher phenols. The distillation results are given in Table 3.

The data of Table 3 show that the yield of lower phenols (distillate up to 230°) is greatest at a temperature of 600° and exceeds that in the ordinary coking process by more than 5 times. After purification from resinous and nitrogenous substances, carried out by the method of V. A. Lanina and N. D. Edemskaya [2], the phenol–cresol fraction was subjected to precise rectification on a laboratory column with eighteen theoretical plates. Rectification was carried out under vacuum, at a residual pressure of 20 mm Hg; narrow fractions were collected, for which the refractive indices were determined.

On the basis of the additivity property of the refractive index, the amount of the most important components in the mixtures (narrow fractions) was determined approximately by the formula [3].

\[ V_2 \simeq 100\,\frac{n_{1,2}-n_1}{n_2-n_1}. \]

The results obtained are given in Tables 4 and 5.

From the data of Table 4 it is evident that, with an increase in the pyrolysis temperature of the coal, the yield of the phenol fraction, both calculated on the initial fraction and calculated on the tar, increases regularly from 21.7% at 600° to 43.6% at 800°, while the yield of cresols decreases from 29.52 to 14.6%, respectively. However, as follows from Table 5, where the yields are given

Table 5

for the lower phenols recalculated to tar and to the initial fraction, the absolute yield of phenol at 600° is more than 5 times higher than under industrial conditions (meaning coking of an ordinary charge), and the yield of cresols is 4–7 times greater.

An increase in the process temperature from 600 to 800° under these conditions leads to a reduction in the yield of phenol by more than twofold, and of the cresol isomers by 6–9 times.

The investigation carried out showed that the optimum temperature for obtaining high yields of lower phenols and especially cresols is 600°.

The results obtained may be used in substantiating the technological regime of existing semicoking installations, and will also be useful in finding the optimal pyrolysis regime.

References

1. G. L. Stadnikov. Analysis and Study of Coals. Publishing House of the Academy of Sciences of the USSR, 1936.
2. V. A. Larin et al. Report for 1955. Archives of IGI, Gosplan Economic Council.
3. B. V. Ioffe. Refractometric Methods of Chemistry. Goskhimizdat, 1960.