On the Contact Effect of Refractory Materials on Benzene Yields in the Process of Coal Coking

E. T. Labykina

(Presented by Prof., Doctor of Technical Sciences I. V. Gebler).

One of the more important chemical products of coal coking is benzene [1]. It is therefore natural that the development of methods for increasing its yields is of definite interest. In the “secondary” transformations of coal-tar resin, it is advantageous to direct the process so that the products are enriched with aromatic compounds. The most important acting factors affecting the yields of “secondary” products are temperature, pressure, coking time, and also the catalytic action of incandescent coke and the chamber walls [2]. The effect of temperature and time has been studied sufficiently well; as for the catalytic influence of the chamber walls on the yields of the chemical products of coking, although this question is mentioned in the literature, no special investigations have been carried out in this area [3, 4, 2].

Since refractory material, in particular dinas, is used for the lining of coke-oven chamber walls, we were interested in the question of whether the composition of refractories can catalytically affect the yields of the chemical products of coking. For this purpose, experiments were carried out with fireclay, dinas, and so-called black dinas, which has an increased content of iron oxides. In the experiments to determine the yields of the chemical products of coal coking, we used the method of the Ukrainian Coal-Chemical Institute [5], considering it simpler and more convenient [6, 7, 8, 9, 10]. According to the procedure, we took a porcelain tube 25 mm in diameter, sealed at one end. Into the sealed end 20 g of coal, screened through a sieve with 500 openings per cm², was poured. The coal was separated from the refractory charge by an asbestos plug; then a column of refractory material 12 cm high, with grain sizes of 3–5 mm, was charged.

The porcelain tube was placed in a two-section tubular furnace with individual electric heating.

In the furnace, where the end of the tube with the refractory charge was placed, the temperature at the beginning of the experiment was set at 760° and maintained so until the end of the experiment. In the section where the coal was located, the temperature was raised from 150° to 1000° over the course of three hours. The experiment lasted about 3 h 30 min. Absorption apparatus was connected to the porcelain tube. Benzene was absorbed by activated carbon in two U-shaped tubes.

Kiselevsk coal from the Serov mine was subjected to investigation.

Technical analysis of the coal

Analytical moisture — 1.45%. Ash on dry substance — 15.37%. Volatile matter 37.60%.

The yield of the chemical products of coal coking is given in Table 1. In this case the experiments were carried out with a fireclay catalyst.

Table 1

The refractories used were chamotte, dinas, and those manufactured in the refractory shop of the Kuznetsk Metallurgical Combine.

The chemical composition of the refractories is given in Table 2.

Table 2

Results of the experiments

Experiments conducted with the refractory materials—chamotte, dinas, and black dinas—showed that these materials exert a catalytic influence on the yields of crude benzol.

Table 3 gives the benzol yields, as percentages of the weight of coal, for various materials.

Table 3

Weight of the coal charge in all experiments: 20 g.

Discussion of results

The experimental data obtained on benzol yields indicate the catalytic influence of refractory materials in the process of pyrolysis of coal-tar pitch; moreover, the increase in benzol yield in the series dinas—chamotte—black dinas is most likely connected with an increase in the content of iron compounds in the glassy part of the refractory shard.

As early as 1933, G. L. Stadnikov, referring to the work of F. Fischer, G. Schrader, and W. Meyer, pointed out that iron causes strong decomposition of phenols and aromatic hydrocarbons with the formation of finely divided coal, which may act as a reducing agent for phenols. It is understood that the matter concerns not iron as such, but iron compounds that are constituents of the coal ash.

In our experiments the refractory packing did not come into direct contact with the coal, but, in exactly the same way, finely divided carbon was deposited on the surface of the refractory grains in the form of the finest soot, separated as a result of mutual oxidation–reduction reactions between the products of coal distillation and the iron compounds included in the refractory...

material. This activated carbon, deposited on the surface of the refractory grains, grows through the adsorption of phenols and thus restores their dehydrogenating ability. In addition, in the presence of catalysts, reactions of dehydrogenation of unsaturated hydrocarbons or hydrocarbons are intensified. But this process evidently is of lesser importance, since the temperature of 760° by itself affects this process.

Under such conditions, the Berthelot synthesis is also probably possible, i.e., the reverse formation of a benzene molecule from three acetylene molecules.

Conclusions

1. Refractory material, depending on its chemical composition, exerts a catalytic influence on the secondary transformations of coal-tar pitch during coking.

2. The catalytic effect of refractories on the yields of crude benzene increases in the series dinas — red dinas — chamotte.

3. The increase in the catalytic action of refractories is associated with an increase in the content of iron compounds in the refractory material.

LITERATURE

1. Zhukov D. D. Coke and Chemistry, 8, 57, 1956.

2. Rinovskii E. V., Makarov G. N. ZhPKh, 22, 400, 1949.

3. Kuznetsov M. I. Coke and Chemistry II, 69, 1937.

4. Coke and Chemistry, 1, 29, 1935.

5. Gruzman L. D., Edelman I. I. Control of Coke-Chemical Production. Metallurgizdat, Moscow, 89, 1946.

6. Novikov V. N. Factory Laboratory, 2, 197, 1946.

7. Novikov V. N., Gruzdeva N. A. Factory Laboratory, 3, 307, 1950.

8. Stadnikov G. L. Analysis and Study of Coals, published by “Coke and Chemistry,” ONTI, Kharkov, 77, 1932.

9. Taits E. M., Titov N. G., Shinshakov P. V. Methods for Evaluating Uncaking Coals as Raw Material for Industrial Use. Ugletekhizdat, Moscow, 110, 1949.

10. Stadnikov G. L. Coal Chemistry. Goskhimizdat, Moscow–Leningrad, 223, 1933.

CORRECTIONS AND NOTED MISPRINTS

Izv. TPI, vol. 102.