STUDY OF PEAT TAR

K. K. STRAMKOVSKAYA, A. T. RUBANOV, Yu. LI

(Presented by the scientific seminar of the Faculty of Chemical Technology)

For the development of a rational technology for using tar from the chemical-metallurgical process on peat, searches were carried out for the characteristics of the tar and for pyrolysis conditions under which the most valuable raw material for organic synthesis can be obtained. Some parameters necessary for technological calculations of tar processing were also determined.

The tar for the study was obtained in a laboratory unit consisting of a reactor, which was a stainless-steel tube 600 mm in diameter and 900 mm long, and condensation equipment—a cooler and a receiver for tar and water. The reactor was heated by two tubular furnaces, one of which was located above the part of the chamber into which the fuel was placed, i.e., above the coking chamber, and the other was installed above the part of the tube serving as the pyrolysis chamber. Heating was controlled by laboratory voltage regulators. The tar was obtained at coking temperatures and pyrolysis of vapor–gas products of 600, 700, and 800°C, and also at a coking temperature of 600°C with pyrolysis of vapors and gases at a temperature of 400°C.

Peat from the Tagan bog and fuel-smelting materials (FSM) prepared on its basis were subjected to thermal decomposition. The characteristics of the peat are presented in Table 1.

Table 1

Technical and elemental composition of the fuel, %

The component composition of the fuel-smelting materials: combustible part of the peat—53.95%, mineral part (ore + peat ash)—46.05%.

The group composition of the tar samples, determined according to the method of G. L. Stadnikov [1], is given in Table 2. These data show that the total amount of phenols decreases from 15 to 9.6% when the pyrolysis temperature is changed from 600 to 800°C.

The decrease in the phenol content with increasing temperature by a factor of 1.5 is evidently explained primarily by deeply proceeding decomposition reactions. According to V. E. Rakovskii [2], at high

Table 2

Group composition of resins from the thermal decomposition of peat and fuel-smelting materials

temperatures (600°C) can decompose with the formation of carbon oxides, free carbon, hydrogen, and water vapor. In addition, at temperatures of 700–800°C condensation of polynuclear aromatic compounds may occur, in whose formation phenols evidently play a substantial role.

With a decrease in the total amount of phenols as the pyrolysis temperature rises, the content of light phenols in the resins should increase noticeably, owing to the reduction of polynuclear phenols in the presence of carbon, and also as a result of the cracking of high-molecular-weight alkyl-substituted phenols.

The amount of high-molecular-weight solid paraffins in the resins also decreases sharply with increasing pyrolysis temperature, because, as the pyrolysis temperature is increased from 600 to 800°C, thermal destruction of high-molecular-weight hydrogen-rich hydrocarbons occurs, with the formation of liquid low-molecular-weight hydrocarbons and gas.

With increasing pyrolysis temperature, the amount of asphaltenes, i.e., polynuclear compounds insoluble in benzene, increases noticeably.

The pyrolysis process of nitrogen-containing substances of basic character apparently proceeds chiefly in the direction of interaction with other substances possessing high reactivity, which leads to some decrease in the content of nitrogenous bases in the resin as the pyrolysis temperature increases.

Thermal decomposition of carboxylic acids hardly occurs at the given temperatures. Evidently, low-molecular-weight carboxylic acids are already obtained at a temperature of 600°C.

As for the effect of the presence of ore in the fuel on the group composition, the analyses showed that the content of individual groups of compounds in the tars of the 600-degree regime, obtained both from pure peat and from fuel–fluxing materials, differs by amounts lying within the limits of experimental error.

For further characterization, all tar samples were distilled at atmospheric pressure in an apparatus intended for the distillation of small quantities [3]. The suitability of this apparatus for determining the fractional composition of tars was based on the good agreement between the results of kerosene distillation in the indicated apparatus and according to GOST 2177—59.

The results of the tar distillation are given in Table 3.

Table 3

Fractional composition of tars from the thermal decomposition of peat and fuel–fluxing materials

These data show that, despite the large discrepancies in parallel experiments, one can note the general direction of the effect of pyrolysis temperature on the yield of fractions from the tars of peat and fuel–fluxing materials. All samples of the tars obtained have a high yield of oily fractions, amounting to 69—76.5% of the tar, and a low pitch yield—23—26%.

With an increase in the pyrolysis temperature from 600 to 800°C, the fractional composition of the tars also changes. Thus, for example, the yield of the light fraction boiling up to 200°C increases by 4%, while the yield of heavy fractions decreases somewhat. The data obtained also show that the presence of iron ore in the fuel does not exert a substantial influence on the fractional composition of the tar. However, the distillation of tars of the 600-degree regime with steam that we carried out (Table 4) showed that the phenols volatile with steam are contained in the tar from FFM in an amount 1.3% greater than in the tar from peat.

The fractional composition of the phenols volatile with steam also differs strongly. Thus, the content of phenols boiling up to 210°C in the crude phenols from FFM tar is 73.5%, whereas in phenols from peat tar it is only 53.2%, which, recalculated to the corresponding tar, amounts to 9.5% versus 6.7%. Thus, in the pyrolysis tar of FFM there are 1.3 times more light phenols than in the pyrolysis tar of peat.

The fractional composition of the neutral oils volatile with steam is also somewhat different. From the T.P.M. pyrolysis tar, 93.5% distilled over at a temperature of 290°C, whereas in the distillation of similar oils of peat tar, 93.5% distilled over at a temperature of 340°C.

Table 4

Characteristics of products volatile with steam obtained from tars of the thermal decomposition of peat and T.P.M. at 600°C

In view of the fact that in the chemical-metallurgical process the production of a large amount of low-temperature tar is expected, which in the upper parts of the blast furnace has undergone strong pyrolysis, tar was obtained from pure Tagan peat at a temperature of 600°C in the coking chamber and 400°C in the pyrolysis chamber.

To determine the technological characteristics of the tar with the aim of identifying ways of using it rationally, it was subjected to further investigation. For this purpose the tar was carefully dehydrated by repeated heating to 60°C in a water bath and then subsequent cooling to a state in which the tar was solid and the water liquid and was readily separated. Some physicochemical characteristics of this tar are given below:

Content in % of anhydrous tar:

As can be seen, the density of this tar is close to unity, and therefore it is difficult to separate it from water by simple settling. In addition, at room temperature the tar is in an immobile state, and the water contained within the mass of tar is poorly separated.

The dehydrated tar was distilled into fractions from a copper flask with a one-ball attachment. The results of the tar distillation and the characteristics of the fractions are given in Table 5.

This tar is also characterized by a high yield of oily fractions, 75–76%.

Sixty-six percent of the phenols and 55% of the bases pass into the distillate fractions, amounting to 10.4 and 2.3% of the tar. The maximum amount of phenols is in the fraction boiling at 230–270°C. As the boiling temperature of the fractions increases, the phenol content in them decreases.

The greatest content of bases and carboxylic acids is in the fraction boiling at 200–230°C. During distillation under atmospheric pressure, only about 50% of all the solid paraffins and waxes present in the tar pass into the fractions. The other half remains in the pitch.

Fig. 1. Distillation curves of peat tar. ITK—the curve of true boiling temperatures. M. V., \(d_4^{20}\)—curves of changes in molecular weights and density.

The curves of true boiling temperatures, molecular weights, and density are shown in the figure; they can be used in technological calculations for the distillation of tar.

Table 5

Characteristics of Distillate Fractions

Conclusions

1. It has been established that, when the temperature of thermal decomposition of fuel-smelting materials is raised from 600 to 800°C, the content of phenols in the tar decreases by a factor of 1.5, that of solid paraffin by a factor of 1.6, and that of bases by a factor of 1.2, while the amount of carboxylic acids remains almost unchanged.

2. It has been shown that at the decomposition temperature of the TPM, both at low temperatures—600°C—and at high temperatures—800°C—the tar is obtained with a high yield of oily fractions (up to 76%) and a low yield of pitch (21–23%).

3. With an increase in pyrolysis temperature from 600 to 800°C, the content in the tar of light fractions boiling up to 200°C increases by 4%.

4. The presence of a large amount of iron ore in the fuel during pyrolysis substantially affects the composition of the phenols. In tar obtained under identical temperature conditions from TPM, there are 1.3 times more light phenols boiling up to 210°C than in tar from pure peat.

5. A detailed characterization is given of the tar from the 600-degree regime and of the distillate fractions obtained from it.

Literature

1. G. L. Stadnikov. Analysis and Study of Coals. Publishing House of the Academy of Sciences of the USSR, 1936.

2. V. E. Rakovskii. General Chemical Technology of Peat. Gosenergoizdat, 1949.

3. G. Lib, V. Sheniger. Synthesis of Organic Preparations from Small Quantities. Goskhimizdat, 1957.