EFFECT OF TEMPERATURE ON THE YIELD OF PYROBITUMENS FROM PEAT

S. I. SMOLYANINOV, S. G. MASLOV

(Presented by the Scientific-Methodological Seminar of the CTF)

When a number of solid fossil fuels are heated, their group composition changes significantly; in particular, the yield of the group of substances extracted by organic solvents varies noticeably. This group of substances has been given the name pyrobitumens [1—10].

The change in their yield during the heating of peat interested us in connection with elucidating the mechanism of thermal briquetting, since one of the reasons for the formation of the strong structure of thermal briquettes, apparently, is the formation of plastic products during the thermal decomposition of peat, while the yield of pyrobitumens is their characteristic external manifestation.

Since the literature lacks systematic data on the yield of pyrobitumens from various peats as a function of temperature, it was decided to carry out the work whose results are presented below.

The object of the study was a series of peats selected from bogs of Tomsk oblast. Their characteristics are given in Table 1. A sample of air-dry peat, ground to pass a 0.5 mm sieve, was placed in a quartz

Table 1

Characteristics of peat samples

test tube, heated at a rate of 5—6 degrees per minute, and rapidly cooled. Pyrobitumen was extracted from the sample thus prepared with an alcohol–benzene mixture. The results obtained are shown graphically in Fig. 1. It is evident from the figure that the yield of pyrobitumens as a function of temperature has a maximum, which is reached in the temperature interval 260—280°C. Such a dependence can be explained by the fact that pyrobitumens are intermediate products of thermal

decomposition of solid fuel. The reactions of formation and removal of pyrobitumens proceed simultaneously; on the ascending part of the curve the former predominate, and on the descending part—the latter.

As to the causes of pyrobitumen formation, there is no single opinion. G. L. Stadnikov and V. S. Krym [3, 4] see the cause of the increase in extract yield in the depolymerization of previously polymerized bitumens. Most researchers—N. M. Karavaev, G. E. Fridman, E. V. Kondrat’ev, and a number of others [1, 2, 5, 6, 8–10]—consider pyrobitumens to be products of destruction of the organic mass of the fuel. V. E. Rakovskii [6] speaks of the solubility in benzene of products of thermal dissociation of inert complexes of the type

Fig. 1. Dependence of the yield of pyrobitumens on the peat-heating temperature: 1—peat with a degree of decomposition of 5%; 2—20%; 3—50%; 4—35%.

\[ \left[ \begin{array}{c} \mathrm{R}\!-\!\mathrm{C_6H_2}(\mathrm{OH})_2\!-\!\mathrm{R} \end{array} \right]_x \left[ \begin{array}{c} \mathrm{R}\!-\!\mathrm{C_{10}H_6}\!-\!\mathrm{N} \end{array} \right]_y \]

which occurs as a result of heating them to 200–250°C. A. I. Khrisanfova [5] showed that condensation products of humic acids with glycerin dissolve in organic solvents. Thus, the formation of pyrobitumens apparently occurs not only as a consequence of destruction of the organic part of the fuel, but also as a result of synthesis from fragments formed during thermal destruction.

N. M. Karavaev and Yan Huang [8] found that, with increasing temperature, the amount of waxes remained almost unchanged, while the accumulation of pyrobitumens occurred through formation of the resinous fraction; at a temperature of 280°C its yield was four times greater than the yield from unheated coal. As is known, the resinous fraction of bitumens is prone to polymerization reactions. M. V. Goftman [10] indicates that heating to a temperature of 300°C leads to polymerization of the resinous fraction of bitumens. V. E. Rakovskii [6] came to the same conclusion. G. E. Fridman [2] believes that the pyrobitumen formed exists within a very small temperature interval and then again decomposes, with the formation mainly of liquid products, as well as solid residue and gases. The two views cited above on the removal of pyrobitumens do not exclude one another, but only complement each other.

In our previously published works it was reported [11, 12] that the optimum temperature for thermal briquetting of peat lies within the range 240–280°C, that is, taking into account the temperature correction for self-heating,

heating of peat (20–25°) [13], coincides with the temperature of the maximum yield of pyrobitumens. Apparently, the presence of an optimum temperature for thermobriquetting is associated with the temperature maximum in the yield of pyrobitumens.

Conclusions

1. The dependence of the yield of pyrobitumens on the heating temperature has been shown for a number of peats.

2. It has been found that the maximum yield of pyrobitumens depends on the type of peat and lies in the interval 260–280°C.

3. The optimum temperature of thermobriquetting coincides with the temperature of the maximum yield of pyrobitumens and, apparently, is determined by it.

References

1. E. V. Kondrat’ev, S. K. Kupichev. Change in the chemical composition of peat in the process of its self-heating. Kh. T. T., vol. VI, issue 5, 403, 1935.

2. G. E. Fridman. Initial stage of thermal decomposition of solid fuel in the presence of water vapor under pressure. DAN SSSR, vol. LXXVII, No. 5, 875, 1951.

3. G. L. Stadnikov. Origin of Coals and Oil. Publishing House of the Academy of Sciences of the USSR, 1937.

4. V. S. Krym. Chemistry of Solid Fuel. GONTI, Ukraine, 1963.

5. A. I. Khrisanfova. Transformation of humic acids into sintering products. Trudy IGI AN SSSR, vol. 2, 278, 1950.

6. V. E. Rakovskii, F. L. Kaganovich, E. A. Novichkova. Chemistry of Pyrogenic Processes. Publishing House of the Academy of Sciences of the BSSR, Minsk, 1959.

7. D. P. Zverev, Yu. V. Pushkarev. Production of thermobriquettes—a path toward improving the quality indicators of peat fuel. KhTT, 4, 55, 1967.

8. N. M. Karavaev, Yang Khuan. Action of water on coal at elevated temperatures and pressures. Publishing House of the Academy of Sciences of the USSR, Department of Technical Sciences, Metallurgy and Fuel, 4, 151, 1961.

9. S. G. Aronov, L. L. Nesterenko. Chemistry of Solid Combustible Minerals. Kharkov University Press, Kharkov, 1960.

10. M. V. Goftman. Applied Chemistry of Solid Fuel. Metallurgizdat, 1963.

11. S. I. Smol’yaninov, A. M. Denisov. Influence of the temperature and pressure of briquetting on the mechanical properties of peat thermobriquettes. Izv. TPI, 112, 82, 1963.

12. S. I. Smol’yaninov, G. G. Krinitsyn, S. G. Maslov. Prospective assessment of peat from a number of deposits in Tomsk Oblast as raw material for metallurgical processing of Bakchar iron ores. Izv. TPI (in press).

13. S. G. Maslov, S. I. Smol’yaninov. On the study of the mechanism of thermobriquetting. (Determination of the actual temperature of thermobriquetting.) Proceedings of the Conference of Young Chemical Scientists of Tomsk (in press).