ENVIRONMENTAL REQUIREMENTS TO THE PETROLEUM PITCHES

 

O.I. Doshlov(professor), K.A.Trezubov(student of bachelor), I.O. Doshlov(master)

Scientific adviser: O.I. Doshlov

Irkutsk State Technical University

664074 Irkutsk, Lermontov St. 83

 

Today aluminium production is one of the most hazardous and environmentally unsafe industries in the Eastern Siberia. However, aluminium production volumes are constantly growing because of the increasing demand for aluminium. Thus, the problem of finding less toxic raw materials for aluminium production comes to the forefront.

Coal-tar pitches which carcinogetic activity is caused by a rather high content of benzopyrene (1,2 – 4%) are widely used for manufacturing graphitized electrodes, anode paste, burnt anodes, structural materials and other electrode items.

Benzpyrene belongs to the first class of hazard and is dangerous for people even at low concentrations because of its bioaccumulation property.

A pilot batch of the petroleum pitch PLP with refined environmental and technological characteristics compared to the coal-tar one was received on the basis of the Angarsk Petrochemical Company in accordance with the Irkutsk State Technical University (STB «Technolog»).

Although the petroleum pitches notably differ from the coal-tar pitches (with the same amount of the softening point) in a group chemical composition, density and a volatile-matter content they don’t degrade the quality of the obtained carbon materials.

Chart 1

Physico - chemical properties of coal and petroleum pitches

Indicator name

Coal-tar pitch

Petroleum pitch

1.   Form

Molten pitch or solid granular pitch

2.   Softening point,

70-80

95-120

3.    – fraction, %

18-21

18-25

4.    – fraction, %

7-8

6-8

5.   Volatile-matter content, %

53-63

50-58

6.   Ash content, % no more than

0,3

0,08

7.   Benzpyrene content, %

1,2-4

absent

8.   Density

1,285-1,330

1,250-1,320

9.   Water mass fraction in a solid pitch, % no more than

4,0

absent

 

Petroleum peck is a bituminous material in black with brilliant conchoidal fracture. Under normal conditions, a petroleum peck  –solid substance passing under heating viscous – fluid state.

Depending on the purpose of petroleum peck can be used as a bonding or impregnating material in the manufacture of graphite electrodes, anode paste, baked anodes, structural materials based on graphite, electric carbonic products, coal and coke briquettes. Regardless of the type of products in the preparation of these carbon materials, there are two components: a binder – peck; peck solid filler – coke, graphite, carbon black, coal.

The role of the binder is reduced to a thin film enveloping filler particles impregnated into its pores and the formation of coke – peck pasty mass, which after pressing acquires a predetermined shape. Compressed raw («green») blanks pass through firing stage. In some cases besides firing the material requires additional peck impregnation and subsequent firing. Usually all of these operations end graphitization of temperatures up to 2500.

On the one hand, the existing ownership of the carboniferous peck as binders and impregnating carbon materials, as well as the limited scale of the test petroleum peck put prerequisite – the proximity of physical- chemical and rheological properties of petroleum and carboniferous peck. On the other hand a significant difference in the nature of raw materials, processed in these carbon materials, does not allow to consider such an approach is quite justified.

On – apparently the only reliable criterion for assessing the suitability of petroleum pecks may be their technological test directly in the manufacture of the electrode, construction materials and anode paste. Only such tests are able to give an objective and comprehensive assessment of the quality of petroleum pecks.

The hygienic assessment of petroleum pitches proved that replacing a coal-tar pitch by a petroleum one the mean of the benzpyrene concentration in the air where electrolysers with anode mass work is decreasing in1,3-8,8 times, in swept dust â 7-24.3 times, and the amount of benzpyrene, which is being dislodged with a gas suction, 5-8 times.

Thus, the replacement of a coal-tar pitch by a petroleum one gives some environmental benefits for the industry of construction materials, graphitized electrodes, aluminium production, coal-produced materials and other consumers of coke-pitch compositions.

Reference:

1. Doshlov O.I. Adgezija i Adgezivy III tom. Irkutsk. IrGTU, 2008 g.

2. Mannweiler, U.Reduction of  polycyclic aromatic hydrocarbons (RAN) by using petroleum pitch as binder material: a comparison of anode properties and anode behavior of petroleum pitch and coal tar pitch anodes// Fuel and Energy Abstracts Volume: 38, Issue: 6, November, 1997.

3. Terent'ev V.G., Sysoev A.V., Grinberg I.S. i dr. Proizvodstvo aljuminija – M.Metallurgija, 1997.-350 s.