Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Utilizing fused bath
Reexamination Certificate
1998-07-28
2001-05-22
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Utilizing fused bath
C204S294000, C252S510000, C373S097000
Reexamination Certificate
active
06235184
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to a new material for the manufacture of anodes used in the processes for the electrolytic production of primary aluminum.
More specifically, the present invention refers to a new type of anode which composition comprises sugar cane molasses as binding agent.
Therefore, the present invention refers to the replacement of electrolytic pitch usually employed in conventional anode manufacturing processes for the primary aluminum industry. The electrolytic pitch is replaced by sugar cane molasses either pure or provided with additives.
BACKGROUND OF THE INVENTION
The aluminum industry techniques have been known for more than a century in all the aluminum plants all over the world such as, for example, the Hall-Heroult process. Such premises usually incorporate attached thereto what we know as anode plants which are essential elements in this kind of industry.
The process for manufacturing anodes presently in use comprises the production of a mixture of petroleum coke with residual reduction anodes known as butts, and electrolytic pitch which is obtained from the tar. The first two ingredients, that is, petroleum coke and residual reduction anodes are submitted to crushing, sieving and classifying operations in specific granulometric fractions in such a way that after they are mixed, they may produce the highest “packing” degree that can be attained for the purpose of using as little binding agent and obtaining the best mechanical properties for the anode.
All the above mentioned fractions are heated and subsequently mixed to the electrolytic pitch. This operation is carried out in continuous or batch mixers by using temperature range from 80° C. to 350° C. depending on the process used.
The result of the mixing step described above is a slurry which may be directly used in the electrolytic reduction vats when the aluminum is produced through Soderberg process, for producing the required anode for the reduction process. Said anode is produced by baking said slurry in the heat of the reduction vats which operate at temperature from 900° C. to 1,000° C.
Alternatively, said slurry may also be pressed or compacted or vibrocompacted in suitable presses or compactors, with or without vacuum, in order to produce green anodes which are usually designed to be used in the process known as pre-baked process.
However, before being used in the pre-baked reduction process, said green anodes should be submitted to baking in special furnaces which may be open or closed. In such furnaces, the green anodes are baked within a temperature range from 900° C. to 1,200° C. in order to attain the required physical and chemical properties to be used in furnaces for reducing alumna to primary aluminum.
It is also known by those skilled in the art that during the process for the preparation of the above-mentioned anodic slurry for the Soderberg process, as well as during the process for baking the green anodes for the pre-baked process, aromatic components are released from the electrolytic pitch and despite the fact that they are below the limits set out by the regulations of a number of countries they are deleterious either by inhalation or contact and the result is a noxious environment.
Another typical inconvenience from the use of electrolytic pitch is that since it is in the solid form dust is generated and often the plant operators get burned by exposing the skin in contact with the dust under the sun. Said burns are deemed as quite severe.
Another inconvenience in the use of solid electrolytic pitch is related to the dirty caused in the plant area and the frequent problems at navigation ports when handling the electrolytic pitch which is usually transported by ships.
Trying to minimize the above-mentioned inconveniences, systems based on the gas treatment in association or not with efficient dust removing systems have been used. Also to minimize said inconveniences it has been tried to replace solid electrolytic pitch by liquid electrolytic pitch. However, such resources are not fully efficient and demand very high investment costs.
OBJECTS OF THE INVENTION
Therefore, an object of the present invention is to provide a new anode material to be used in processes for the electrolytic production of primary aluminum which material shall not bring about an insalubrious environment during the process for the preparation of the anodic slurry and/or during the baking process.
Another object of the present invention is to provide a new anode material to be used in processes for the electrolytic production of primary aluminum which production process should not produce dirt in the plant area as well as overcome the frequent problems of handling the raw material for manufacturing said anodes found in navigation ports.
Another object of the present invention is to provide a new anode material to be used in processes for the electrolytic production of primary aluminum which material should not cause any damage to the health of operators.
Another object of the present invention is to provide a new anode material to be used in processes for the electrolytic production of primary aluminum which process should not be aggressive to the environment close to the producing process area.
Still another object of the present invention is to provide a process for the electrolytic production of primary aluminum which does not require sophisticated gas treatment systems and/or dust removing systems in the anode plants, so that the accomplishment of the process as a whole may be cost-effective.
DETAILED DESCRIPTION OF THE INVENTION
These and other objects and advantages of the present invention are accomplished by using sugar cane molasses, either pure or provided with additives, as the binding agent in the manufacture of anodes used in processes for the electrolytic production of primary aluminum.
Said sugar cane molasses, either pure or provided with additives, is used instead of the traditional solid or liquid electrolytic pitch.
Within the scope of the present invention, “sugar cane molasses” should mean the main honey (syrup) for producing molasses or the sugar production waste.
As additives in the present invention, mention could be made to substances based on lithium, fluorine, alumina, boron, sulfur and the mixtures thereof, provided that such additives do not have properties and performance similar or close to those shown by anodes produced from electrolytic pitch
The technique for using sugar cane molasses as binding agent for making the slurry and the green anode according to the present invention is similar to that of traditional processes for producing electrolytic pitch-based anodes which is widely known in the aluminum industry. However, the coke, the butt and the sugar cane molasses content is variable in addition to other conditions of the process such as the mixture temperature, the baking temperature and the tine which vary according to the type of coke, molasses itself, additives and/or the required properties for the anode to be produced.
Thus, the composition of the anode according to the present invention comprises about 50 to 70% by weight of petroleum coke, from 15 to 30% by weight of butt and 15 to 25% by weight of sugar cane molasses.
Preferably, the percentage of sugar cane molasses used in the anode composition according to the present invention is about 18% by weight based on the total composition weight.
Alternatively, according to the present invention the additives, the substances based on lithium, fluorine, aluminum, alumina, boron, sulfur and the mixtures thereof may be included in percentages varying from about 0 to 10% by weight.
According to the present invention, the process for manufacturing anode comprises the preparation of a mixture containing petroleum coke, residual reduction anodes and sugar cane molasses. The petroleum coke and the residual anodes are crushed, sieved and classified in specific granulometric fractions. The granulometric fractions thus obtained are heated and mixed with the sugar cane molasses in continuous or batch
De Carvalho José Ricardo Duarte
Dognini Deusa Maria Braga
Sarcinelli Eduardo Baptista
Albras Aluminio Brasileiro S.A.
Helfgott & Karas, P O.
Valentine Donald R.
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