US2848424A - Process of preparing carbon electrodes and a paste therefor - Google Patents

Process of preparing carbon electrodes and a paste therefor Download PDF

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Publication number
US2848424A
US2848424A US545378A US54537855A US2848424A US 2848424 A US2848424 A US 2848424A US 545378 A US545378 A US 545378A US 54537855 A US54537855 A US 54537855A US 2848424 A US2848424 A US 2848424A
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United States
Prior art keywords
pitch
resins
paste
weight
anodes
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Expired - Lifetime
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US545378A
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English (en)
Inventor
Stanko Stefan
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Pechiney SA
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Pechiney SA
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06—Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08—Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/12—Anodes
    • C25C3/125—Anodes based on carbon
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/042—Electrodes formed of a single material
    • C25B11/043—Carbon, e.g. diamond or graphene
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/042—Electrodes formed of a single material
    • C25B11/043—Carbon, e.g. diamond or graphene
    • C25B11/044—Impregnation of carbon

Definitions

  • the present invention which results from applicants researches, makes it possible to improve considerably the quality of anodes and to cut down their consumption per ton of aluminum produced.
  • the invention consists in using as binder a pitch that possesses Well defined characteristics, and in adopting for the powdered carbon a continuous granulometry (particle distribution) comprising a minimum percentage .of coarse grains having dimensions exceeding 5.5 mm., as well as a minimum percentage of fine grains smaller than 0.16 mm.; these percentages are not the same for .prebaked anodes as for continuous anodes of the Soderberg type.
  • the invention comprises the adoption of a series of precautions and controls which will -be defined hereafter.
  • the softening temperature of the pitch should exceed 70 C. and it should preferably range between 70 and 85 C'.
  • Pitch is a complex mixture of hydrocarbons, the composition of which is not well defined.
  • the above mentioned softening temperature is measured by the Kramer-SHI OW method; it is the temperature at which a given weight of mercury (5 grams) passes, through a column of pitch five cm. high which adheres perfectly to the lower endof a tube 61mm. in diameter, the tube being vertically disposed within a vessel heated in such a manner that the temperature rises by 1 C, per minute.
  • the pitch itself serves as binder for the raw (unbaked) anode. but in the course of the baking it loses its volatile matters and it is its residual coke that binds the grains of carbon dust in the baked anode. Accordingly, this residue of the carbonization (coking) of the pitch has a vital efiect on the quality of the bakedanode.
  • a pitch is chosen which gives a residue on carbonizationtcoking) in excess of 50%.
  • the cokingresidue is determined as follows: a sample of pitch is placed in a small. crucible and slowly heated so as to attain a temperature of 460 to 470 C. Within about twenty minutes. The small crucible is then covered with an adjusted cover and is introduced into another larger crucible, the Space between the walls of the two crucibles being filled with grains of wood charcoal, so as tojavoid entry of air.v The assembly is heated in a mufiie-furnaee at 800C; for'five hours. Following cooling, out of contact with air, the coke residue is weighed;
  • T determine the proportion of benzene soluble resins in the pitch, pure crystallizable benzene is employed (95% illing between 7.9..5. .C. and 8.0.5 0)-
  • the anthracene oils, extracted from coal tar, are complex mixtures; to con l h ua y th pitc th re-u d o l having th follow ng chara t ristics:
  • distillationcurve of theanthracene oils used should fall between the two curves shown on the figure attached to the presentspecification.
  • a pitch of good quality, conforming to the present invention can be employed indifferently for producing either anodes pressed and baked before their use, or for producing carbon paste for feeding continuous anodes of the Soderberg type.
  • the granulometry (particle distribution) that should be adopted for the carbon dust is somewhat diiierent for these two types of anodes, as will be studied successively below:
  • Very pure cokes are used for manufacturing these anodes: pitch coke or petroleum coke, deprived of their voltatile matters by calcination in the absence of air and ground to dust.
  • the real specific gravity of the dust should range between 2 and 2.05, preferably between 2.02 and 2.05, for petroleum coke, and between 1.94 and 1.97 for pitch coke.
  • the dust should have a continuous granulometry, that is to say, it should include grains of all dimensions from mm. up to impalpable powder. Moreover, it should possess the following characteristics:
  • At least 45% of the total dust should be arrested by a sieve having openings of 0.83 mm. and 15% of the total dust should have dimensions ranging between 5.5 and 15 mm.
  • 33 to 35% of the total dust should consist of particles passing through a sieve having openings of 0.16 mm., while 25% should pass through a sieve with openings of 0.089 mm.
  • a powder (dust) of such granulometric composition is about 15%.
  • Mixing of the powder with the pitch is carried out according to the process described in French Patent No. 992,508. That is, the oversize on a sieve with openings of 0.16 mm. is first charged into a mixer and mixed until the temperature reaches 140 C. Thereupon, the pitch is introduced and the mixing is renewed until all grains of coke are well wetted. It is only then that the grains passing through the sieve having 0.16 mm. openings are introduced and the mixing is completed.
  • the green (raw) anode is then formed by compressing the paste at a pressure of 400 to 700 kg. per square centimeter, and thereafter, it is so baked that the real specific gravity of the baked anode is greater than that of the coke employed for making the paste.
  • experience shows that in this way anodes are obtained in which the binding coke derived from the pitch is burned by the oxygen of the alumina simultaneously with the grains of coke forming the mass of the anode, thereby avoiding loosening of these grains and formation of carbondust in the electrolyte.
  • Carbon paste for continuous anode of the Soderberg type Since the continuous anode is baked at the temperature of the electrolysis bath, that is at about 950 0., there should be used pitch coke or petroleum coke, the real specific gravity of whichfollowing calcination in the absence of 'airranges between 1.94 and 2, if it be desired to avoid formation of carbon dust due to the loosening of grains in the electrolysis bath.
  • the granulometric composition of the particles should be characterized by the following features:
  • Atleast 15 of the total particles should have sizes ranging between 5.5 mm. and 15 mm.;
  • the mixing of the powder with the pitch binder is carried out according to the process described in French Patent No. 992,508, as stated above in connection with the paste for the prebaked anodes.
  • the proportion of pitch relative to the total weight of paste is about 30%; it should enable the paste to be sufliciently fluid so that the paste spreads completely on the upper surface of the continuous anode. This fluidity is particularly important when electric current is led to the anode by means of vertically disposed metallic studs.
  • the anode the baked lower part of which is consumed as the electrolysis proceeds, slides within its fixed casing so as to compensate for the consumption.
  • the upper part of the anode does not slide on the walls of the casing during this downward motion; there always remains a layer of raw paste, more or less thick, which stays stuck to the walls of the casing.
  • separation occurs along the casing, between the part of the anode already hardened and the raw paste.
  • the paste, added at the top of the anode be sufficiently fluid so as to be able to fill in the voids created by such separation. If this kind of feeding does not take place, the voids remain within the mass of the anode, and 'it has been established that air enters therein and the anode burns inside the casing, which interferes considerably with the proper operation of the electrolysis.
  • the spreading test is carried out in the following manner: Samples of paste taken from the mixer are molded by compression to obtain cylinders 50 mm. in length and 25 mm. in diameter. They are placed on a metal sheet (sheet iron) 120 mm. long which is slightly inclined and provided with recesses for receiving the samples, the upper end of which is 15 to 20 mm. from the upper end of The lower ends of the samples can move downwards freely.
  • the sheet with the samples is disposed, with an inclination of 6.5 within a stove heated to 220 C.; it remains therein for two hours. After cooling, the elongation of each sample is measured.
  • elongation X 100 should range between 60 and .apasnge
  • continuous anodes:of theisoderberg type made of paste as above described,.it has been possible to obtain during a period of six months a consumption of 514 kg. carbon paste per-ton of produced aluminum, which corresponds to 440 kg. of baked anodeper ton aluminum.
  • the present invention represents a very important advance inthe manufacture'o'f anodes-intended for use in the production of aluminum. i
  • a binder suitable in the preparation of carbon paste for use in the production of electrodes consisting essentially of a pitch having the following characteristics:
  • Residue upon coking of said resins not less than 89% by weight of said resins.
  • Carbon paste suitable in the production of compressed and prebaked anodes for aluminum manufacture comprising a binder and particles of petroleum coke, said binder consisting essentially of a pitch having the following characteristics:
  • Residue upon coking of said resins not less than 89% by weight of said resins
  • At least 45% of the total particles are arrested by a screen having openings of 0.83 mm.;
  • Carbon paste suitable in the production of compressed and prebaked anodes for aluminum manufacture comprising a binder and particles of pitch coke, said binder consisting essentially of a pitch having the following characteristics Softening point, Kramer-Sarnow, between 70-85 C.;
  • Residue upon coking of said resins not less than 89% by weight of said resins
  • At least 45% of the :total particles are arrested by a screen having openings of 0.83 mm.;
  • the proportion of the binderrelativeto-the-tota1weight ofthe paste being about 15%.
  • Carbon paste suitable in the production of continuous anodes of the Soderberg type comprising a binder and coke particles, said binder consisting essentially :of
  • Residue upon coking of said resins not less than 89% by weight of said resins
  • the amount of binder added to the particles is such as to produce, following mixing, a fluid paste giving on a spreading test of a sample thereof, an elongation ranging between 60 and of the length of a cylindrical sample 50 mm. in length and 25mm. in diameter, disposed on a plane with an inclination of 6.5 and heated to 220 C. for two hours.
  • Process of preparing carbon electrodes comprising the steps of: intimately mixing into a paste powdered coke, approximately 15 of which has dimensions ranging between 5.5 mm. and 15 mm., with a pitch binder having the following characteristics:
  • Residue upon coking of said resins not less than 89% by weight of said resins
  • Process of preparing carbon electrodes of the Soderberg type comprising-the steps of: intimately mixing into a paste coke particles with a pitch binder having the following characteristics:
  • Proportion of benzene insoluble resins and resins soluble in anthracene oils not less than 20% by weight of the Residue upon coking of said resins, not less than 89% by weight of said resins;

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Working-Up Tar And Pitch (AREA)
US545378A 1954-11-16 1955-11-07 Process of preparing carbon electrodes and a paste therefor Expired - Lifetime US2848424A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR336986X 1954-11-16

Publications (1)

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US2848424A true US2848424A (en) 1958-08-19

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Country Status (5)

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US (1) US2848424A (fr)
CH (1) CH336986A (fr)
DE (1) DE1100973B (fr)
GB (1) GB803085A (fr)
SE (1) SE189413C1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3025229A (en) * 1959-06-03 1962-03-13 Kaiser Aluminium Chem Corp Improvements in the method of making carbon anodes
US3053748A (en) * 1957-06-18 1962-09-11 Pechiney Prod Chimiques Sa Novel type electrode for electrolytic cells
US4086156A (en) * 1974-12-13 1978-04-25 Exxon Research & Engineering Co. Pitch bonded carbon electrode
US4959139A (en) * 1989-01-09 1990-09-25 Conoco Inc. Binder pitch and method of preparation

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB659261A (en) * 1949-07-28 1951-10-17 Cie De Prod Chim Et Electro Me Method of preparing carbon-base pastes

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB659261A (en) * 1949-07-28 1951-10-17 Cie De Prod Chim Et Electro Me Method of preparing carbon-base pastes

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3053748A (en) * 1957-06-18 1962-09-11 Pechiney Prod Chimiques Sa Novel type electrode for electrolytic cells
US3025229A (en) * 1959-06-03 1962-03-13 Kaiser Aluminium Chem Corp Improvements in the method of making carbon anodes
US4086156A (en) * 1974-12-13 1978-04-25 Exxon Research & Engineering Co. Pitch bonded carbon electrode
US4959139A (en) * 1989-01-09 1990-09-25 Conoco Inc. Binder pitch and method of preparation

Also Published As

Publication number Publication date
DE1100973B (de) 1961-03-02
SE189413C1 (fr) 1964-05-12
CH336986A (fr) 1959-03-15
GB803085A (en) 1958-10-15

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