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Session Chairperson: Jaffar G. Ameeri, Aluminium Bahrain, P.O. Box 570, Manama, Baharain
TRACKING THE CARBONISATION PATHWAY OF DIFFERENT PITCHES AND PITCH COKE MIXTURES BY CRYSTALLITE HEIGHT (Lc) MEASUREMENT: N.R. Turner, Bitmac Limited, Scunthorpe Works, Dawes Lane, Scunthorpe, North Lincolnshire, DN15 6UR, UK
Pitches with a range of properties, e.g. Q.I. content, were carbonised to a final temperature of 1080°C. The same pitches were co-carbonised with finely divided petroleum coke. Lc has been measured at the end of the carbonisation cycles and at intermediate points to track the status of carbonisation for different pitches and pitch/filler coke combinations. The original pitch Q.I. content and pitch aromaticity appear to influence the carbonisation pathway of the pitch and the pitch-coke mixtures according to Lc data. The properties of the filler coke also appear to influence the ultimate size of the crystallites formed in the binder matrix at the end of the carbonisation cycle. It appears that there is a variable degree of interaction between the filler coke and the pitch, with extent of the interaction depending on the properties of the two components. The results so far reinforce the importance of consistency in raw materials preparation and in the baking process if uniform anodes are to be produced.
ABSORPTION OF OXYGEN FROM AIR INTO COAL TAR PITCH: Jaromir Cibulec, Daniel Kostal, DEZA Corporation, P.O. Box 28, 757 28 Valasske Mezirici, Czech Republic
Changes in the properties of coal tar pitch during contact with atmospheric oxygen were studied. There were found to be changes in the content of toluene insolubles and the melting point. These changes are dependent on the quantity of the absorbed oxygen and on the temperature of the pitch during absorption. As the reaction of the air with the pitch is very rapid, reaction speed is controlled by the speed of absorption of oxygen into the pitch. When surface of the pitch is motionless, the rate determining step of the reaction is controlled by the rate of absorption of the oxygen into the pitch which is dependent on the diffusion coefficient of molecular oxygen in air. When the surface of the pitch is agitated, the reaction rate is controlled by the rate of reaction of the oxygen with the pitch. The mechanism of the reaction is described and a practical application is discussed.
X-RAY AND MICROSCOPY INVESTIGATIONS ON THE CATALYST-CARBONIZED STRUCTURE OF COAL TAR PITCH--PETROLEUM COKE PILOT ANODES: Jilai Xue and Harald A. Oye, Institute of Inorganic Chemistry, the Norwegian University of Science and Technology, N-7034 Trondheim, Norway
The carbonization has important impacts on the energy consumption and the productivity in anode baking. It was found that the coke yield of the coal tar pitch binder in its mixtures with petroleum coke increased with addition of catalysts, such as S, AlF3, and FeCp2 (CO)4. Then the structures of the samples taken from the carbon pilot anodes with and without above additions were further investigated using X-ray diffraction and microscopic techniques. The remained S, Al and Fe in the carbons after heat treatments were also analysed. The coke yield, Lc value, and porosity will be presented against various heat treatment temperatures for different additions. The possibility of obtaining the carbon anodes by lower baking temperatures with the required structure will be discussed based on above results.
3:15 pm BREAK
COAL-TAR/PETRO INDUSTRIAL PITCHES: E.R. McHenry, Koppers Industries, 1005 Wm. Pitt Way, Pittsburgh, PA 15238
Throughout the 20th Century coal tar has been the dominant raw material for producing industrial pitches in North America. However, the coal tar supply in North America has been decreasing due to closure of metallurgical and foundry coke-oven batteries. Because of lower carbon yield, petroleum-based pitches have only limited usage. To increase the raw material base and provide more flexibility in characteristics, coal tar/petro pitches are being developed. The evaluation of the coal-tar/petro industrial pitches is reported.
PETROLEUM PITCH, A REAL ALTERNATIVE TO COAL TAR PITCH AS BINDER MATERIAL FOR ANODE PRODUCTION: Roger Marzin, Carola Acuna, Intevep S.A., Departamento de Refinacion, Apdo. 76343, Caracas 1070 A, Venezuela; Maria de Oteyza, Maraven, S.A., Nuevos Desarrollos, PO Box 829, Caracas 1010A, Venezuela; Raymond C. Perruchoud, R&D Center, Le Chable, P.O. Box 157, CH-3960 Sierre, Switzerland
A petroleum pitch, specially developed for aluminum anodes was produced, at commercial scale, as a real alternative to coal tar pitch. Using a highly aromatic refinery stream and well designed process conditions, it is possible to produce the right chemical composition needed for a high quality binder material for anodes. Through a Dynamic Process Optimization study, the paste formulation and parameters were adjusted to produce full size anodes with 100 % petroleum pitch. The performance of baked anodes were similar to coal tar pitch anodes, with the advantage of a much lower content of cancerogenic Polycyclic Aromatic Hydrocarbons (PAH). Comparative green and baked anode properties, PAH emissions and storage stability test for molten pitch are presented.
REDUCTION OF POLYCYCLIC AROMATIC HYDROCARBONS (PAH) IN ANODES BY USING PETROLEUM PITCH AS BINDER MATERIAL: A COMPARAISON OF ANODE PROPERTIES AND ANODE BEHAVIOR OF PETROLEUM AND COAL TAR PITCH ANODES: Dr. Ulrich Mannweiler R&D Carbon Ltd. Winterthurerstrasse 92, CH-8006 Zürich, Switzerland; Raymond C. Perruchoud, R & D Carbon Ltd., Le Chable, P.O. Box 157, CH-3960 Sierre, Switzerland; Roger Marzin, Intevep S.A., Departamento de Refinacion, Apdo. 76343, Caracas 1070 A, Venezuela
Petroleum pitch as binder material of anodes has the great advantage, that the content of cancerogenic Polycyclic Aromatic Hydrocarbons (PAH) compared to coal tar pitch is practically inexistent. In applying the correct content of pitch and through optimization of all process parameters during anode manufacturing, full size anodes with coal tar pitch (CTP) and petroleum pitch (PP) have been prepared in an anode plant. While baked anode properties for coal tar and petroleum pitch anodes are very similar, the PAH content can be reduced by 98 %. In this paper the behavior of representative lots of coal tar and petroleum pitch anodes in 100 kA electrolysis cells and the properties of the resulting anode butts will be described.
TESTS OF PITCH PRODUCED FROM THE MIXTURE OF COAL RESIN AND REMAINDERS AFTER OIL PYROLYSIS: M.L. Itskov, E.A. Yanko, Russian National Aluminium-Magnésium Institute (VAMI), 199026 St. Petersburg, Russia; V.V. Krukov, Central Investigations Laboratory, 101000, Moscow, Russia
Actually the main type of binding materials, used in the anode paste production is a coal tar pitch. This binder provides the necessary quality of anode, but its using is related to increased emissions of cancerogenous matters, especially, benzapyrene, into the anode paste and aluminium reduction plants. The cancerogenous danger could be considerably reduced if using, as a binding material in the anode paste production, pitch produced at the distillation of the mixture of coal resin and remainders after oil pyrolysis, called "modified pitch". This report gives the results of laboratory investigations and industrial tests of anode paste, produced with using above mentioned binder, in the aluminium reduction. The laboratory investigations and industrial tests on Soderberg pots have shown, that by using the modified pitch we succeeded to produce anode paste of satisfactory quality. In this case we achieve a considerable reducing of the emissions of cancerogenous matters, namely benzapyrene, from the surface of anode.
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