EFFECT OF ORE AND FLUX ADDITIVES ON THE YIELD AND COMPOSITION OF PEAT SEMICOKING TAR

K. K. STRAMKOVSKAYA, V. D. IVANOVA, G. G. VOLKOV

(Presented by the Scientific-Methodological Seminar of KhTF)

Thermal decomposition of peat substance is a complex physicochemical process in which a number of consecutive and parallel reactions take place. The course of these reactions, which determine the yield and composition of the decomposition products, is influenced by both physical and chemical factors. The influence of physical factors—such as the process temperature, heating rate, particle size of the fuel, and pressure—has been well studied and described in the relevant literature.

Less attention has been devoted to studying the influence of chemical factors on the process of thermal decomposition of peat. The main attention has been directed toward elucidating the influence of the nature of the fuel, while the influence of mineral additives on the yield and composition of fuel pyrolysis products has been studied quite inadequately.

However, chemical compounds that form part of the mineral fraction of the fuel, or additives specially introduced into the fuel, cannot remain inert during the thermal processing of peat and other fuels. V. E. Rakovskii [1] believes that chemical action on the thermal decomposition of peat occurs in the form of processes of oxidation, reduction, saponification, and catalysis. The catalytic action of mineral additives either changes the rate of the reactions or causes new processes that are practically absent in processes without catalysts. The objects of chemical action may be both the initial fuel and the products of its primary decomposition.

Studies carried out [2] with Baltic shales, which are high-ash fuels and contain limestone and clay as the principal components of the mineral fraction, gave contradictory results. Pure calcium carbonate, limestone, sand, and other substances were used as additives. In this case, the authors explained the varying decrease or increase in tar yield in different ways. A. Küll [2] used shale ash as an additive in an amount two to three times that of the shale. The shale with the additive was subjected to semicoking at a temperature of 480°. As a result, the tar yield decreased, the gas yield also decreased, while the semicoke yield increased; this was explained by the adsorption properties of the ash, which contained free calcium oxide and therefore absorbed primarily the acidic components of the tar and gas. In the tar, the content of acidic components decreased from 24.9 to 8% and lower.

A. N. Khidosheli and M. B. Ravich [3, 4] showed that the introduction of NaOH and Na₂CO₃ promotes deeper cracking of liquid

and gaseous products of semicoking. The consequence of this is a decrease in the yield of primary tar, an increase in the yield of gas and gas gasoline, and also an increase in the yields of low-boiling fractions during distillation of the primary tar, whereas V. E. Rakovskii [1] gives data showing an increase in the yield of tar from peat when NaOH and KOH are added.

Iron oxides have a very great effect on the process of thermal decomposition of fuels. According to V. E. Rakovskii, the decomposition of peats containing different amounts of iron proceeds with the formation of unequal amounts of low-boiling and high-boiling phenols in the tars. Unfortunately, we have not found data on the influence of iron oxides on the yield of the chemical products of peat pyrolysis. S. M. Bruk [5] showed that the addition of 5% freshly reduced iron during the pyrolysis of gas coals increased gas evolution by 6%, the yield of crude benzene by 42%, and the yield of coke by 7%, while the yield of tar decreased by 4.7%. With the addition of iron oxides, a certain increase in the yield of all coking products was observed, which is quite improbable.

At present, in connection with the study of the question of using fuel-smelting materials in metallurgy—materials consisting of briquettes or shapes made from ore and fuel, or from fuel, ore, and fluxes—there has arisen a need for a detailed study of the influence of the mineral portion on the yield and composition of the tar from the thermal decomposition of these materials.

Of particular interest is the study of the influence of additions of ore and fluxes on the yield and composition of the products obtained in the semicoking of peat, in connection with the development of the problem of using fuel-smelting materials based on peat in the gas-blast process. In this process, alongside the smelting of pig iron, the production of gas and tar as raw materials for organic synthesis is envisaged. The semicoking process will constitute one of the stages of the gas-blast process.

In the present work, the influence of additions of ore and fluxes on the yield and composition of the tar from peat semicoking was investigated. Peat and fuel-smelting materials prepared on the basis of peat (a mixture with ore and fluxes) were subjected to semicoking at a temperature of 550°. For the preparation of fuel-smelting materials (TPM₁), lowland peat from the Tagan bog in Tomsk Oblast, with an average degree of decomposition, was used. Fuel-smelting materials TPM₂ were prepared on the basis of peat from the Vasyugan bog of transitional type, also with an average degree of decomposition.

Table 1

Characteristics of the peats

The characteristics of the peats are given in Table 1. Ore from the Bakchar deposit was used, and limestone was used as the flux. The chemical characteristics of these materials are given in Table 2.

Table 2

Composition of the ore and fluxes

The composition of the fuel–flux materials is presented in Table 3.

Table 3

Composition of the fuel–flux materials, % on a dry basis

The yields of semicoking products in a standard aluminum retort at a final temperature of 550° (average values from six determinations) are given in Table 4.

Table 4

Yields of semicoking products

The data obtained show that the tar yield during semicoking of fuel–flux materials decreases, while the yields of gas and semicoke increase somewhat. The decrease in tar yield during semicoking of fuel–flux materials, with a simultaneous increase in gas yield, indicates an acceleration of cracking reactions under the action of additions of iron ore and fluxes during peat semicoking.

Peat from the Taganskoe bog and the fuel–flux materials FFM₁ prepared on its basis were subjected to semicoking in a large laboratory installation at a temperature of 550°. The tar obtained was carefully dehydrated and subjected to group analysis according to the following scheme.

A 20 g sample was exhaustively dissolved in petroleum ether, and the undissolved portion of the tar was dissolved in benzene. The residue insoluble in benzene was taken as carbides and “free” carbon-

gen. From the benzene and petroleum-ether extracts, bases, carboxylic acids, and phenols were extracted by the usual methods [6]. The benzene solution remaining after extraction of the phenols was washed with water, dehydrated by standing over calcined sodium sulfate, and, after filtration, removal of the solvent, and drying, the known yield of asphaltenes was obtained.

The residue after removal of petroleum ether and the drying operations was dissolved in acetone, and paraffin was crystallized at a temperature of \(-4^\circ\). Neutral oils were determined by difference.

The group composition of the tars, given in Table 5, showed practically little difference in their composition. However, a more detailed study

Table 5

Group composition of the tar

indicates that the tar obtained from the fuel-flux materials differs somewhat from that obtained from pure peat. This is evidenced by the results of the distillation of phenols (Table 6).

Table 6

Results of distillation of crude phenols

These data show that the amount of low-boiling phenols (boiling in the temperature range 190–220°C) in the tar from the fuel-flux materials is considerably greater than in the tar obtained from peat: 51.9% versus 44.0%. This, apparently, is a very important quality of the crude tar phenols obtained during semicoking of TPM, making them a more valuable raw material for chemical syntheses.

Peat from the Vasyugan bog and fuel-flux materials TPM\(_{11}\), prepared on its basis, were subjected to semicoking in an aluminum retort (100-gram) at a final temperature of 550°. The primary tar, by treatment with petroleum ether and methanol in a separatory funnel, was divided into petroleum-ether and methanol extracts. After removal of the solvent, the extracts were each separately subjected to chromatographic separa-

…on neutral aluminum oxide with activity II–III according to Brockmann [7], at an adsorbate-to-adsorbent ratio of 1:50. The extract was introduced into the column, respectively, as a solution in petroleum ether and in benzene. Elution was carried out with petroleum ether, benzene, acetone, and methanol. The yields of the corresponding products are given in Table 7.

Table 7

Yields of the products of chromatographic separation of peat and fuel-flux-material tars

The separation of the fractions proceeded quite distinctly. Collection of a given fraction was stopped after pure solvent began to flow from the column (test for \(n_D^{20}\)). The experimental data indicate a change in the sorption properties of the substances comprising the tar of the fuel-flux materials. Thus, the yield of the ether and benzene eluates increased considerably, while that of the acetone eluate decreased sharply.

For all products of the chromatographic separation of the tars, the following were determined: specific gravity, refractive index, molecular weight, iodine and hydroxyl numbers, and also elemental composition.

Table 8

Characteristics of the products of chromatographic separation of the petroleum-ether extract of peat and fuel-flux-material tars

The results of these determinations, given in Tables 8 and 9, show that almost all these products obtained from peat tar and from the tar of the fuel-flux materials differ from one another. The eluates extracted from the tar of the fuel-flux materials with benzene and acetone, espe-

are especially strongly characterized by reduced molecular and specific weights, increased hydroxyl and iodine numbers, and also an increased oxygen content in the elemental composition.

These data show that additions of ore and fluxes exert a substantial influence on the process of thermal decomposition of peat. Evidently, oxides of iron and of other elements included in the additives accelerate the cracking reactions of high-molecular-weight products of the primary decomposition of peat, which leads to the formation of active carbon already at considerably low temperatures and to the production of lighter hydrocarbons and phenols.

Table 9

Characteristics of the products of chromatographic separation of the methanol extract of peat and fuel-flux tar

In the presence of activated carbon, the reduction of polyatomic phenols may occur and, apparently, did occur according to the scheme

\[ \mathrm{C_6H_4} \begin{matrix} \mathrm{OH}\\[-0.2em] \diagup\\[-0.2em] \diagdown\\[-0.2em] \mathrm{OH} \end{matrix} = \mathrm{CO} + \mathrm{C_6H_5OH}. \]

As a result of the indicated processes, a larger amount of light phenols and neutral substances eluted by petroleum ether was obtained in the tar of the fuel-flux materials.

Conclusions

1. The effect of the mineral components of fuel-flux materials on the yield of products during the semicoking of peat has been studied.

2. It has been shown that the tar yield decreases in the presence of ore and fluxes.

3. The amount of light phenols in the tar obtained from fuel-flux materials is significantly increased and amounts, relative to crude phenols, to 51.9% versus 44.01% found for peat tar, although in terms of group composition the indicated tars differ little.

4. Chromatographic analysis of the tar shows that the products eluted from the tar of fuel-flux materials by benzene and

with acetone, have lower specific and molecular weights, higher hydroxyl and iodine numbers, and also contain a larger amount of oxygen; this indicates that ore and flux additives exert a substantial influence on the process of thermal decomposition of peat.

REFERENCES

1. V. S. Rakovskii. General Chemical Technology of Peat. Gosenergoizdat, 1949.

2. A. Ya. Arna. On the influence of the mineral mass in the thermal decomposition of kukersite oil shale. Proceedings of TPI, No. 48, 1953.

3. A. N. Khidasheli. Study of the influence of catalysts on the yield of primary tar during the dry distillation of peat. Proceedings of the Grozny Polytechnic Institute, No. 5, 81–84, 1957.

4. M. B. Ravich. Study of the influence of additives of sodium compounds on the process of semicoking of bituminous coals. ZhPKh, Vol. XXIV, No. 9, 970–975, 1951.

5. A. S. Bruk, Z. A. Volkova et al. On the catalytic action of various substances in the pyrolysis of complex organic substances (bituminous coals). Eighth Mendeleev Congress on General and Applied Chemistry. Section of Chemistry and Chemical Technology of Fuel. Publishing House of the Academy of Sciences of the USSR, 1959.

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

7. M. S. Tsvet. Chromatographic Adsorption Analysis. Publishing House of the Academy of Sciences of the USSR, 1946.