DD295878A5 - Method for producing a Söderberg electrode - Google Patents

Abstract

The invention relates to a process for producing a Soederberg electrode in which a feed composition of resin-coated carbonaceous particles is passed through three zones for the formation of the Soederberg electrode, one zone being a firing zone and one zone being an electrode forming and consuming zone. According to the invention, the feed composition used is a mixture of resin-coated carbonaceous aggregate, plasticizer having a boiling point of at least 200C and a proportion of 0-5% and hexamethylenetetramine, the resin-coated carbonaceous aggregate including a novolak phenolic resin coated on carbonaceous particle aggregate particles. The residual coking value of the feed composition used is at least as high as the preferred minimum coking value of traditional coal tar pitch based Soederberg compositions. manufacture; Soderberg electrode; Feed composition; resin-coated carbonaceous particles; carbonaceous aggregate; plasticizers; hexamethylenetetramine; novolak}

Description

Characteristic of the known state of the art

At the beginning of the 19th century, Soderberg developed a process for producing a continuous carbon electrode. The Söderberg process, named after that, produces a self-burning or permanent electrode formed continuously from a soft coal mixture which is fired in the same furnace in which it is used.

The Söderberg process is a continuous process that involves the addition of a mass to the top of the electrode fabrication facility. This mass is a mixture of a carbonaceous aggregate and a pitch binder. The mass is mobile enough to go through the temperature gradient. The temperature increases as the mass approaches the region of the electrolytic cell. During this migration, the hardening of the mass normally results in some sort of gel or jelly with loss of volatiles, the mass retaining thermoplasticity while the flowability is not high enough to cause excessive overflow of the mass. The agitated mass then approaches the consumption zone, where it becomes hard by compaction and graphitization of the binder under the action of the operating temperatures of the electrolytic cell and assumes the complete shape of the electrode. The electrode is not only used in the cell, but constantly consumed (consumed).

The device for producing a Söderberg electrode consists of a ribbed cylinder made of thin sheet into which the electrode mass is filled. In this way, the top of the device is filled with raw material. The formed electrode projecting from the lower end of the Söderberg device is continuously consumed in the furnace. The device is operated from time to time so that the electrode formed in the device can drip down to replace the amount of electrode consumed. This can cause the mass in the upper end of the device to drip down. During this process, the mass drips through a zone of increasing temperature and is burned by the heat of the furnace. The material in the Söderberg device thus consists of an upper section in the form of a moving mass, a lower section in the form of a fired hard electrode and an intermediate section in which the mass gradually changes from a moving mass to a hard fired electrode. For the sake of simplicity, this three-part structure in the present application is referred to as an electrode, although, strictly speaking, only the fired lower portion functions like an electrode.

The cylindrical container part of the Söderberg device corresponds generally to the water-cooled type of intake. It is designed so that the electrode can gradually move at a predetermined rate and slide down from time to time so that unfired portions of the mass are brought to ever higher temperatures as they approach the zone of hot electrolytic cell. The slippage is effected by loosening the tension of the holding or receiving device until the electrode slips down by its own weight. This manipulation of the electrode can be done from a location that is some distance from the oven. The slide of the electrode usually happens under full load. The operation of the electrode is maintained throughout the process so that further current flows through the electrode. The electrical contact is maintained by means of a sliding or sliding contact between the holding device and the electrode housing.

In this technique, the term "anode" is used when the fired carbon or graphite electrode is used as an anode in a real electrolysis, for example, in aluminum production, or in brine electrolysis, and the term "electrode" refers to one in general similar article for an application in which the function consists mainly of the passage of electricity.

The speed at which a Soderberg electrode is consumed depends on the particular application for which it is used. In ovens for the production of calcium carbide and ferroalloys, the feed rate z. In the range of about 4 inches to about 20 inches per day. The materials used in the manufacture of a Söderberg electrode generally consist of calcined anthracite, alone or with calcined petroleum coke, and a medium hard pitch (middle pitch).

Söderberg electrodes are used in several different applications. In the electrolytic production of aluminum, the anodes are predominantly produced by the pre-firing process. However, the Söderberg process is still widely used throughout the world in aluminum production. The anode mass is usually prepared based on petroleum coke.

The Söderberg process can also be used for the production of electrodes for use in electric furnaces. These are generally artificial graphite electrodes. The mass for such electrodes is made of low ash coal or petroleum coke. These substances are crushed and calcined to remove volatiles and then mixed with tar or pitch as a binder. The resulting mass can then be used in the Söderberg process for the preparation of the desired electrode or, alternatively, molded or extruded or pressed to produce a raw electrode which is fired, then cleaned and so used or to a desired shape for a specific use is processed. In comparison with the prefired electrodes, the electrodes thus produced generally have a lower performance in terms of their densities, plasticity, electrical properties and the like. Söderberg electrodes are generally used in aluminum reduction, calcium carbide production, the production of electric iron, the processing of poor copper and other iron alloys and in smelting processes. They are also used in phosphor production.

The content of volatile raw materials from which Söderberg electrodes are made may range from 5% to 15%. For petroleum coke, 10% is typical. In the calcination, hydrocarbons are removed and the coke undergoes volumetric shrinkage, resulting in a density increase. The mass loss can be 25% or more. If the raw material is not calcined, the release of volatiles and shrinkage occur during electrode formation and can lead to cracked structures.

In a Söderberg process which is currently in use, the electrode composition is prepared from electrically calcined anthracite with coal tar pitch and anthracene oil as a binder. In the composition of the composition, the calcined anthracite normally amounts to about 65 to about 70% by mass of the electrode composition, with the remainder being coal tar pitch and anthracene oil.

In binders in the Söderberg process, coal tar pitches of 30% to 35%, based on the mass of the electrode mass, are generally used. Such high pitch levels lead to excessive smoke and loss of volatiles, which in turn results in low intensity electrodes. In addition, coal tar pitch is under severe environmental pressure and is subject to a close examination for carcinogenic properties which may cause volatiles, e.g. The development of these components plays a dominant role in the Söderberg process, which is mainly due to the strong impact of such vapors in the Söderberg process on the workforce.

Companies applying the Söderberg process are therefore under great pressure to introduce costly and prohibitive environmental protection measures, alternative / methods such as. resorting to the "prebaked electrode process" which requires additional capital investment, costly new equipment and refitting, or resorting to environmentally safe binder systems while not sacrificing the carbon utilization rate of the binder electrode, These disadvantages have led to the Söderberg process However, even with pre-fired electrodes, there are disadvantages, such as porosity, which is a major problem requiring strict controls to avoid oxidation and to maximize coal (us) utilization.

To avoid these disadvantages, furfuryl alcohol and / or furfural resins are proposed for use in pitch binders in the manufacture of Söderberg electrodes. A resin would generally not function like pitch in a mass, ie as a sacrificial binder, but a properly selected resin (binder), while retaining the plasticity properties of coal tar pitch, would also contribute to similar residual carbon values and structure upon curing and pyrolysis. Furfuryl alcohol and Furturalharze have in the range of 93 ° C (200 ⁰ F) to 260 ° C (500 ⁰ F) thermosetting structures and a lack of fluidity and / or plasticity beyond this temperature result. In addition, furfural and furfuryl alcohols are volatile monomers and the vapors are both harmful and toxic. Consequently, the successful use of said binders in large scale applications is very limited.

The mass used in the conventional production of Söderberg electrodes can be poured directly into the electrode device. Alternatively, it can be poured into blocks or other forms for shipping and use. Such blocks are hard at room temperature and easy to handle. If such blocks (250 ° F) are heated to about 121 ⁰ C, the pasty consistency is restored so that the Ma can easily flow as required by the Soderberg equipment.

In summary, it can be stated that the Söderberg method for anode production is an old method and is generally considered uneconomical today. However, aluminum manufacturers around the world still produce aluminum in several companies using the Söderberg process. In Söderberg anodes, pitch is used in a binder content of about 25 to 30%, and they are affected by environmental problems. The problems are mainly in the area of toxic vapors produced in the zone of the electrolytic cell. Steam control and adequate protection are issues that need to be addressed. Industry has two alternatives: installing costly environmental protection, which involves substantial capital investment, or testing alternative environmentally safe and efficient binders.

Figures 1, 2 and 3 relate to the testing of a composition for its suitability as a feed composition for a Soderberg electrode. The test involves molding and pressing part of a composition into an ASTM standard dumbbell mold, placing the dumbbell sample on a flat surface, heating the dumbbell under Söderberg temperature conditions, and observing the heat treated trade.

Fig. 1 is a graph of an ASTM commercial sample in the pressed initial state resting on a shallow dish. Two surfaces of the dumbbell, which is made of a suitable composition, rest on the shell. The maximum vertical height under the dumbbell and between the two surfaces lying on the shell is called the gap height h. Fig. 2 is a diagram showing a dumbbell of a composition after a heat treatment which would not be a proper composition (composition). The dumbbell was exposed to the furnace heat; after heating to Söderberg electrode temperature, a measurable gap height h is still present. This means that the dumbbell did not show adequate flow and the mass became hard. Therefore, the composition used would have no suitable flow properties and should not be used for the production of a Söderberg electrode.

Fig. 3a is a graph showing a heat-treated dumbbell of a composition that would presumably be a suitable composition (i.e., a successful composition). The dumbbell was exposed to the furnace heat and sank or collapsed completely. A gap is no longer present (h = 0). Therefore, the composition used would have suitable flow properties for the production of a Söderberg electrode. FIG. 3 b shows the untreated dumbbell sample in real size, FIG. 3 c shows the sample after treatment (h = 0).

Object of the invention

The aim of the invention is to avoid the shortcomings of the known methods.

Explanation of the essence of the invention

The invention is based on the use of a mass in the Söderberg process, which includes as a sacrificial binder a high melting point novolak phenolic resin. The useful in the practice of the present invention resins are novolac resins with melting points of 100 ⁰ C or higher and, preferably, in the range of 110 ° C to 14O ⁰ C. Although resins with lower melting point may have sufficient plasticity, they are as such resins not desirable and generally contribute to lower residual carbon levels after pyrolysis. Also, lower melting point resins are volatile (especially the monomer, dimer, and trimeric components) and can become air pollutants that cause environmental problems.

The use of some pitch, rather than a portion of the novolak resin in the binder, is contemplated, although not preferred. Although novolak resins in conventional phenol resin practice (novolak resins are thermoplastic) are commonly used in conjunction with hexamethylenetetramine (hexa) and / or thermosetting phenolic resins in the Α-state as curing agents to make them thermosetting, such compositions tend to have a direct effect upon exposure to temperatures from 100 ⁰ C and above to a very hard mass to cure, and have no mobility.

It has surprisingly been found that suitable compositions can be made for use in Söderberg applications when such novolak resins are used alone and are properly selected in terms of molecular weight (melting point). Such compositions provide comparable and sometimes even better carbon content compared to coal tar pitch. It has also been found that some novolak resins with limited hexamethylenetetramine can be used and still retain the necessary thermoplastic properties. With suitable novolak resins having a melting point of about 100 ⁰ C z. B. Residual carbon values of at least 50% achieved when these resins are pyrolyzed under inert conditions to 800 ° C (1472 ° F). Such values can be compared to the retained carbon value of pyrolyzed coal tar pitch. In addition, it has been found that said resins have significant high temperature mobility and plasticity in the presence of small amounts of a curing agent, e.g. Hexamethylenetetramine, in proportions of 5% or less and, preferably, of 1.5% or less (based on the mass of the novolak phenolic resin). Such compositions also contribute to better carbon retention after pyrolysis. Suitable curing agents are formaldehyde donors, such as. Paraformaldehyde, and trisaminohydroxymethane, as well as hexamethylenetetramine. Hexamethylenetetramine is the preferred curing agent. Prior art coal tar pitch and binders are affected by the development of noxious fumes and pungent odor. The novolak resins used in this invention are thus prepared and characterized in that the content of the resins of free phenol (monomer) is less than 4 mass% and preferably less than 2 mass% based on the resin solids. In this way, the problem of the development of harmful vapors in the known technical solutions can be substantially reduced.

Although the novolak resins can be used by themselves, in practice it is preferable and advantageous for the use of a modest plasticizer, such as e.g. As the high-boiling glycols, glycol ethers, esters, dibasic esters, pyrollidones, aromatic alcohols, such as cyclohexanols, anthracene oil and the like. Decide. One could also use polymeric glycols, such as. As polyethylene oxides, and their derivatives use. Union Carbide Corporation sells a suitable polymeric glycol composition under the trade name Carbowax. These plasticizers help to keep the paste mixture in the different temperature zones of the Söderberg anode feed system plastic and flowable. Preferred plasticizers have a boiling point of about 200 ⁰ C (392 ° F) or higher, and the proportion of plasticizer is held on the total binder composition, preferably for 50% or less. Preferably, the plasticizer content is maintained at 20 to 40%. In selecting the amount of plasticizer, the degree of volatiles development, the carbon content, and the desired flowability must be considered as key factors. Examples of suitable high-boiling glycols are ethylene glycol, diethylene glycol and triethylene glycol. The preferred glycols are diethylene glycol and triethylene glycol.

While the use of coal tar pitch as a sacrificial binder in the Söderberg process poses a high risk of fouling, the carcinogenic and environmental problems associated with the use of coal tar pitch are minimized when the novolac resins selected in accordance with the present invention are used in the required proportions as sacrificial binders become.

The compositions prepared may be used in the form of resin-coated free-flowing granules which, as required, may be poured directly into the device for the production of the Söderberg electrode. In this case, the resin is preferably previously applied to the carbonaceous aggregate particles. Alternatively, as is often done for shipping reasons, the resin coated granules may alternatively be preformed by extrusion, compression or molding techniques to form solid preformed blocks or profiles which are easy to handle, store, transport and use, the resin in such a case serves as a binder and provides the green strength. The profiles or blocks are usually inserted directly into the device for the production of Söderberg electrodes; As the blocks approach the heat source, they become soft and flowable to fill the interior of the device. The invention, in summary, the object of a method for producing a Söderberg electrode, which includes the following steps:

(1) passing a feed composition of resin-coated carbonaceous particles through the three zones to form the Soderberg electrode, the feed composition descending in a first zone in the form of discrete free-flowing particles to a firing zone;

(2) passing the feed composition in the firing zone through a temperature gradient and converting it from discrete free flowing particles to a layer or bed of viscous mass moving down to the electrode forming and consumable zones, and

(3) curing the mass in the electrode forming and use zone to a permanent electrode shape and then consuming the mold as a continuously formed Söderberg electrode.

According to the invention the method is characterized in that the feed composition comprises a mixture of resin-coated carbonaceous aggregate, plasticizer having a boiling point of at least 200 ⁰ C and in a proportion of 0 to 50 parts by mass in%, based on the total weight of resin solids and plasticizer, and 0 hexamethylenetetramine based on resin solids, wherein the resin-coated carbonaceous aggregate includes a novolak phenolic resin coated on particles of a carbonaceous particle aggregate.

Suitably, the feed composition includes pitch in a mass fraction equal to or less than the mass fraction of the novolak resin.

The plasticizer preferably has a boiling point of at least 250 "C.

According to a further feature of the invention is characterized in that the plasticizer has a boiling point of at least about 200 ⁰ C and is selected from the group consisting of a glycol, Glykolester, other esters, aromatic alcohol, anthracene oil, pyrol and mixtures thereof.

The glycol is preferably diethylene glycol or triethylene glycol, but may also be a polyethylene glycol.

The plasticizer is suitably a dibasic ester selected from the group consisting of adipine dimethyl ester, glutarine dimethyl ester, succinimethyl ester and their mixtures. However, the plasticizer may also be an aromatic alcohol, a heterocyclic compound such as 2-pyrrolidone or an anthracene compound such. As anthracene oil, or a naphthalene compound. Preferably, the resin has a free phenol content of at most 4 mass parts in%, which is measured by gas chromatographic analysis. It is further characterized by a minimum melting point of 100 ⁰ C.

It is also expedient if the total content of volatile organic compounds in the resin does not exceed 5% by weight of its solids content.

In preparing a composition for use in the Soderberg process, care must be taken to achieve the required balance of properties. Thus, the properties required above the firing zone differ significantly from those required below the firing zone. In the upper part of the electrode, above the firing zone, the composition must have good plasticity and flowability. It is therefore important that the composition becomes fluid during heating to properly fill the Söderberg housing. It is also important that it does not break down into its constituent parts while flowing, but remains homogeneous. The flowability over the firing zone can generally be controlled by suitable settings in the design, especially in terms of resin to plasticizer ratio. If one chooses to use only resin, the resins should be chosen carefully to obtain a good flowable mass. The binder content (i.e., resin, plasticizer, and other additives used in bulk) should generally be kept as low as possible. Below the firing zone, the downwardly hanging part of the electrode is its working part, d. H. the part that carries the electric current. The physical properties of the carbon solid at the bottom of the electrode are critical to achieving proper electrode function.

In the fired lower end of the electrode several properties are important for proper operation. These include low resistivity, high mechanical strength, low Ε modulus, low thermal expansion, high thermal conductivity and excellent oxidation resistance. All of these properties can be controlled by adjusting the composition from which the electrode is made.

The electrical resistivity and the thermal conductivity of the electrode are important in terms of the generation and distribution of heat in the electrode. They are also important factors related to the temperature profile on any horizontal plane through the electrode in operation.

A suitable hot coating process consists of the following steps. A carbonaceous aggregate, preferably calcined anthracite in finely divided form, is heated to a temperature in the range of about 175 ⁰ C to about 200 ° C transferred to a mix muller with heating means to maintain the high temperature. A selected flocked novolak resin is then distributed as evenly as possible over the aggregate during mixing to ensure uniform melting of the flakes and coating of the aggregate with molten resin. Of course, it is possible to add to the hot or cold aggregate a selected molten novolak phenolic resin suitable for use in the practice of the invention. The use of a novolak resin in the form of a solution in low boiling solvent or a dispersion / emulsion in water for the coating of the aggregate is also possible. In such cases, however, care should be taken that the low boiling solvents are completely removed before use in the Söderberg process. Alternatively, using a preferred embodiment of the invention, a solution of the novolak resin in a high boiling plasticizer / solvent can be used. When using such a solution, the coating of the aggregate can be achieved by using hot or cold aggregate particles. After all of the resin has been added to the mixture, mixing is continued to promote uniform coating of the aggregate particles.

If hexamethylenetetramine is desired, it should be added to the Mischkollergang as a water solution. Alternatively, hexamethylenetetramine, if added in this manner, may be added as solid but powdered granules. It is preferably added to the drying unit and uniformly dispersed prior to mixing with the resin. In order to control the density, a softening agent selected from among alcohols, glycols and the like can be used.

The free-flowing granules from the Mischkollergang can be poured in granulated form into the housing of the Söderberg facility. Alternatively, it can be brought into the desired shape for the Söderberg facility by isostatic or compression molding, by vibration or extrusion molding. Such molds or blocks become fluid during passage through the Söderberg device when heated to conform to the interior surface of the Söderberg device.

In order to describe the invention in more detail, it will be demonstrated below with reference to several examples. Unless otherwise indicated, the percentages quoted in these examples and elsewhere in this application are percentages by mass, while temperatures are given in centigrade degrees, unless expressly stated otherwise.

In all the following examples, the aggregate was essentially a calcined petroleum coke mixture of fine particles of different sizes consisting of fine, coarse and intermediate particles. Fines are defined as an aggregate that passes through a No. 100 sieve but is retained on a No. 200 sieve. Intermediate material is defined as an aggregate that passes through No. 14 sieve but is retained on No. 100 sieve. G robgut is defined as an aggregate that passes through a No. 4 sieve and is retained on No. 14 sieve. The specified mesh sizes are in accordance with the U.S. Standard Sieve Series.

In all later described examples, a cold coating method was used. In the cold coating process, the carbonaceous aggregate was mixed in a Hobert mixer with novolak resin plasticizer and, in some cases, hexamethylenetetramine. Mixing continued until uniform coating was achieved and a mass was formed.

All masses were then used for the production of dumbbell specimens according to ASTM standard. In each case, 100 grams of mass were placed in a mold cavity (mold cavity) and pressed into a dumbbell mold in a Wabash press. The pressure was 12t (5-inch piston) and the press cycle 60s.

After the dumbbells described above, they were removed from the mold, placed on a flat surface and exposed to high temperatures in a muffle furnace. During the exposure, a nitrogen atmosphere was maintained in the furnace. The shape of the standard dumbbells is illustrated in FIG. Each standard dumbbell had two contact surfaces with the flat surface on which it was placed before being exposed to high temperature. The gap created under each dumbbell after being placed on the surface had a maximum standard dimension (height) of 8mm.

Unless otherwise stated, the carbonaceous aggregate used in all experiments consisted of about 33% fine particles, 47% intermediate particles and 20% coarse particles. In all examples, a plasticizer was used in conjunction with a novolak resin in a ratio of 60 parts novalak resin to 40 parts plasticizer on a mass basis. If hexamethylenetetramine is used in the examples, the percentage is based on the mass of phenolic resin solids. The percentage of free phenol in a novolak resin is based on the novolak resin in the present form. The percentage is measured by gas chromatography.

embodiments

example 1

This example demonstrates the utility of refractory novolak phenolic resins as binders for coke aggregates for use as a feed composition in the Soderberg process.

In the Söderberg process, the flux of the binder in the feed composition is crucial. This example is intended to demonstrate the flow properties of several different compositions using various novolak resins, various plasticizers, and various hexamethylenetetramine moieties.

In each experiment, a mass was prepared and pressed into dumbbells. Then the dumbbells were removed from the press and placed in the muffle furnace. In all experiments, the dumbbells were exposed to the oven temperature environment to about 500 ° C for about 30 minutes and observed for flow properties during this time. The lowering of the dumbbell during or after exposure to the heat of the furnace was considered desirable. Missing flow was registered as a failure.

When it was visually confirmed that a dumbbell had become solid and no longer deformed, the temperature at which this event occurred was recorded as a failure temperature. Complete lowering, d. H. Zero gap, was taken as an indication of the suitability of the mass in a Söderberg electrode.

The results of the experiments of this example are shown in Table 1. Each novolak resin used is identified by a letter. A detailed description of each resin is given in the footnote. After each dumbbell was removed from the oven, it was observed and the observations were recorded as shown.

Table 1

Novolak Resin (1) Approximate% Free% Novolak-% Hexa Used Failure Notes

Resin Melting Phenolic Resin * Plasticizer (2) Temperature Point Door ⁰ C (3)

A 9O ⁰ C 6-10 10 0 EC

15 0 ditto

20 0 ditto

A 90 ⁰ C 6-10 10 2 dito

15 2 ditto

20 2 ditto

A 90 ° C 6-10 10 5 dito

20 5 ditto

B 90 ° C 6-10 10 0 ditto

10 2 ditto

15 0 ditto

15 2 ditto

C 110-115 ⁰ C 3 10 9 ditto

10 9 T.E.G.

15 9 ditto

15 9 M.P.

20 9 T.E.G.

D 80-90 ° C 0.1 10 0 E.G.

10 2 ditto

10 0 T.E.G.

20 0 E.G.

2 T.E.:G.

E 115-120T 2 10 0 E.G.

10 2 E.G.

10 0 T.E.G.

10 2 ditto

15 0 ditto

150 1.2 200 1.2 400 1.2 150 1.2 200 1.2 400 1.2 150 1 150 1,2,3 150 1 150 1 150 1 150 200 200 4 300 4 500 4 400 4 200 5 200 5 300 6 200 6 300 6 300 7 300 7 500 7 500 7 500 7

approximate % Free % novolak % Hexa used -7 - 295 878 Novolac resin (i) resin melt phenol resin* Plasticizer (2) failure Bemerkun Point tempera gene 15 0 dito tur ⁰ C (3) 20 0 dito 500 7 20 2 dito 500 7 20 2 M.P. 500 · 7 20 0 D.B.E.-4 500 7 140-150 ⁰ C 0.5 * · 15 2 M.P. 500 7 F 15 2 T.E.G. 500 7 15 2 E.G. 500 7 500 7

* based on resin solids, expressed as% of the sum of resin solids plus aggregate * · metacresol

1. Resins A, B, C, D and E were commercial resins, Resin F was a trial resin. Below are descriptions of each resin:

A. A novolac resin with a melting point of about 90 ° C, which as a 65% solids solution in ethylene glycol having a viscosity of 4500-6500cps at 25 ⁰ C and a free phenol content of 6 to 10% is sold.

B. A novolak resin having a similar polymer structure as above except that it is sold as a 70-75% solids solution in ethylene glycol having a viscosity of 20000-40000 cps (about 20% glycol content).

C. A novolac resin with a melting point of 110 ⁰ C to 115 ° C and a free phenol content of at most 3.0%, which is mixed with 9% hexamethylenetetramine and ground to a powder to 98% through a #. 200 goes.

D. A novolak resin with 0.1% phenol and a melting point of 85-9O ⁰ C in flake form, which is ground to the extent that 98% go through a sieve no.200.

E. A commercially available novolak resin with 2.0% phenol and a melting point of 115-120 ° C sold in powder form, wherein the powder passes 98% through No. 200 sieve.

F. A meta-cresol-formaldehyde novolak resin in experiments with 0.5% free meta-cresol and a melt point range of 140-150 ⁰ C, which is ground to a powder, which is 98% through a sieve No. 200.

2. The following plasticizers were used: EG = Ethyienglykol (boiling point 198 ⁰ C) TEG = triethylene (Siedepunkt287 ° C)

MP = m-pyroKd.hN-methyl-pyrrolinone, b.p. 202 ⁰ C)

DBE-4 = einezweibasige Esterzusammensetzung manufactured by Du Pont: dimethyl auccinat boiling point 196 ⁰ C).

3. Comments:

1. Strong phenol smell

2. Slight deformation

3. Very slight deformation

4. More dimensional stability / slight expansion

5. Dry fluffy appearance / possible resin evaporation

6. More dimensional stability

7. Uniform lowering (no gap).

If a dumbbell remains plastic during heating to temperatures of about 500 ^° C., the resin used in the dumbbell would be judged to be particularly suitable for use in the starting material of a Söderberg electrode. In the experiments with the resins A, B or D (melting points below 100X), regardless of the Hexamethylenentetraminanteilen used, unsuitable failure temperatures (temperatures well below 500 ⁰ C) were registered. In the tests with the resins C, E and F (melting points above 100 ^° C.) unsuitable failure temperatures were found when using 9% hexamethylenetetramine. However, suitable plasticity at 500 ^° C. was possible when using 2% or less of hexamethylenetetramine, in some cases in conjunction with a higher-boiling plasticizer. Formulated short, the data of this example show that novolac resins appear to give higher molecular weight, high boiling solvents and little or no hexamethylenetetramine the paste mix upon exposure to temperatures of about 500 ⁰ C plasticity and fluidity, these temperatures in the operating environments of the Soederberg More general procedure. These novolak resins with high-boiling solvents and little or no hexamethylenetetramine would therefore be suitable for the production of the binder for Söderberg electrodes.

Example 2

The experiments of this example attempt to more clearly quantify the flowability and plasticity aspects of the paste blends under high temperature exposure. The coke unit mixture was essentially the same as in Example 1. The methods of blending, mixing and pressing were similar to those described in Example 1. In all cases of this example, the flow properties of the dumbbell samples were tested for 30 minutes at about 500 ⁰ C. After removal from the oven, the dumbbell specimens were cooled in each case, remained standing on a flat surface, and the gap in the middle was measured quantitatively. The lower the result of the gap measurement, the better the plasticity and fluidity of the composition.

A maximum gap dimension of 8 mm indicates lack of flow (i.e., no change in the dimensions of the dumbbell as compared to its cold pressed condition). Such a mass would be unsuitable for use in the Söderberg process. A gap dimension of zero would indicate a useful composition. Table 2 shows the results of the experiments of this example.

Table 2

Harzd) approximate % Free %Resin % Hexa slit spacing melting point phenol (2) Measurement, mm commercial Novolakpulver'G ' 105-110 <3.5 15 <2 5.3 commercial Novolac powder Έ ' 115-120 <2.0 15 0 0 15 4 3 experimental Novolakpulver'F ' 140-150 <0.05 15 0 0 15 4 0

(1) The following is the description of each resin:

G: novolak powder having a melting point in the range of 105-110 ° C and a free phenol content of <3.5%. Pulverized to go 98% through a # 200 sieve

 Resins E and F are as described in Example 1.

(2) Based on the resin solids expressed as% of the sum of resin solids plus aggregate.

Note: In the experiments of this example, the plasticizer triethylene glycol was used. The ratio of resin to plasticizer was the same as in the first example: (i.e., 60:40).

In Example 2, three resins were tested with melting points above 100 ⁰ C. Resin F, the resin with the highest melting point range (140 ° C-150 ° C), was suitable for use in the Söderberg process, regardless of whether it was used with 4% hexa or without hexa. Resin E with the next highest melting point range (115 ° C-120 ° C) was suitable for the Söderberg process if no hexa was used, but not so suitable when using 4% hexa. Resin F having the lowest melting point range (105 ^° C-HO ⁰ C) was less suitable when used with measurable hexamethylenetetramine moieties.

From these examples, it is apparent that novolak resins having a melting point of <100 ° C, when used in conjunction with triethylene glycol and hexamethylenetetramine contents of 2% or less, serve as good binders for Söderberg compositions because the compositions made from these binders provide excellent flow properties Temperatures of 500 ⁰ C have.

Example 3

In this example, the aggregate composition consisted of 10% coarse particles, 58% intermediate particles and 32% fine particles. The phenolic resin content was 15% based on aggregate plus resin solids. A ratio of phenolic resin to triethylene glycol of 60:40 was used. Blending, mixing and pressing were similar to those described in Example 1. In all cases of this example the dumbbell samples were tested at about 500 ⁰ C for 30 minutes on their flow properties. After removal from the oven, the dumbbell samples were cooled in each case and remained standing on a flat surface, with the middle gap measured quantitatively. The smaller the gap size, the better the plasticity and fluidity of the mass

 The results of the experiments of this example are shown in Table 3.

Table 3 resin type Approximate melting point % Free phenol % hexa Gap dimension, mm A A E 90 ° C 9O ⁰ C 115-120 ° C 6-10 6-10 <2.0 0 9 9 1 3 3

In Example 3, resin A, was a low melting resin (90 ⁰ C) and resin E, a high-melting resin (115-120 ⁰ C), treated and again showed that the low melting resin for use in the Soderberg process is unsuitable independently whether a high hexamethylenetetramine portion or no hexamethylenetetramine is used; Again, it has been demonstrated that higher melting resins are not suitable when the hexamethylenetetramine content is 9%. The experiments of Example 2 with Resin E can be compared with the experiments of Example 3 with Resin E (although slightly different percentages were used in the aggregate composition). Example 2 showed that Resin E without hexa is satisfactorily suitable for the Söderberg process, while Example 3 showed that resin does not satisfy at a 9% hexamethylene tetramine content.

Example 4

This example provides a relationship between coking value, relative polymer molecular mass (melting point) and degree of cure (influence of hexamethylenetetramine content). In the production of Söderberg masses, coal tar pitches with residual coking values of 45% or higher are preferred

 The results of the experiments of this example are shown in Table 4:

90 ⁰ C 40 110-115 ⁰ C 45 85-90X 35 115-12O ⁰ C 50 140-150 ° C 58 loinarzieststone 115-12O ⁰ C 53 15-120 ° C 58 110-115 ⁰ C 50

Table 4

Resin Type Approximate coking value (%) *

Melting point _

Нѳха on the basis of

E + 2% hexa

E + 9% hexa

C + 4% hexa

* Carbon (coking) values based on thermogravimetric analysis.

The Verkokungswerte of the novolak resins of this Example with a melting point of about 100 ⁰ C corresponding to the coking value of coal tar pitch or were higher. When hexamethylenetetamine was used, the coking value increased. This example shows that the use of novolac resins with a melting point of about 100 ⁰ C instead of coal tar pitch in the Soderberg mass is beneficial and provides better Verkokungswerte for the electrode.

Conclusions from the examples

A satisfactory Söderberg mass can be prepared using novolak resin as a binder for the mass, when the novolak resin has a melting point of 100 ⁰ C or higher, preferably a melting point in the range of 110-140 ⁰ C. The novolak resin may be used in conjunction with a small amount of hexamethylenetetramine (5% by mass of resin solids or less). It is estimated that the hexamethylenetetramine content should be 3% or less, preferably 1.5% -2.5%.

Example 1 demonstrated that the preparation of a satisfactory Söderberg mass with novolak resin as binder requires a phenolic content of the novolak resin of less than 6%. It is estimated that the content of the novolak resin of free phenol should preferably be at most 4%.

The invention offers a number of important advantages to industrial companies using Söderberg electrodes. The density of an electrode correlates with such properties, e.g. Strength, erosion resistance, electrical resistivity and coal consumption. The electrodes made in accordance with this invention will have better properties compared to coal tar pitch.

The data in the examples demonstrate that satisfactory and even higher performance Söderberg compositions can be made with the high-carbon novolac phenolic resins of this invention.

Although calcined powdered anthracite is a preferred carbonaceous aggregate for use in the present invention, these and similar aggregates suitable for use may be blended with powdered anthracite, powdered carbon, powdered graphite or the like to improve the physical and electrical properties of the product in the Söderberg facility is to be fine-tuned.

The application of the invention generally offers advantages in terms of the amount of binder required, the purity of the binder, a substantial reduction in the level of unwanted chemicals, a better structure in the product, the ready availability of raw materials, and better environmental safety compared to coal tar pitch

 Thus, when used in proportions of 10-15% binder solids based on the carbonaceous aggregate, a phenolic resin binder chosen in accordance with the present invention will provide a binder performance in the Söderberg mass as well as in the coked product with performance is comparable, which is achieved when using pitch in an amount of 30% to 35%, based on the aggregate mass.

Ash content and purity of the binder are extremely important for anode and electrode performance. The use of a resin binder in accordance with the present invention allows for better control of these parameters

 In contrast, the industry notes that the control of these parameters is increasingly difficult when using coal tar pitch. Similarly, the use of a resin binder in accordance with the invention allows for better control of such variables, e.g. B. insoluble quinolone (quinoline) substances, benzene substances and the like., Which are often considered problematic when using a pitchbinder. As a result, the general mixing of different coal tar pitches for optimum performance is rendered unnecessary. The uniformity of the product from batch to batch and the possibility of consistent production, which meet high specifications for optimum performance, are increased

 The reduction in the amount of binder required in accordance with the present invention provides the opportunity for better control of anode porosity, which is critical to controlling electrical properties. Generally, better structural integrity is achieved. Similarly, better erosion resistance can be observed in many cases.

As far as environmental safety is concerned, pollution and gas production are significantly reduced, which is a key benefit for domestic industry. The risk of cancer associated with the release of coal tar pitch air into the atmosphere is reduced.

Although the invention is described in this patent application with reference to the details of preferred embodiments of the invention, this description is to be understood in an illustrative and non-limiting sense; Likewise, changes by the skilled person daily without departing from the spirit of the invention and the scope of the appended claims.

Claims (12)

1. A method of making a Söderberg electrode, comprising the steps of: (1) passing a feed composition of resin-coated carbonaceous particles through three zones to form the Soderberg electrode, the feed composition descending in a first zone in the form of discrete free-flowing particles to a firing zone; (2) passing the feed composition in the firing zone through a temperature gradient and converting it from discrete free flowing particles to a layer or bed of viscous mass moving down to the electrode forming and consumable zones, and (3) hardening the mass in the electrode forming and use zone to a permanent electrode shape and then consuming the mold as a continuously formed Söderberg electrode; characterized in that as feed composition a mixture of resin coated carbonaceous aggregate, plasticizer having a boiling point of at least 200 ⁰ C and in a proportion of 0 to 5 parts by mass in%, based on the total weight of resin solids and plasticizer, and from 0 to a maximum of 5% % By weight of hexamethylenetetramine, based on resin solids, wherein the resin-coated carbonaceous aggregate includes a novolak phenolic resin coated on particles of a carbonaceous particle aggregate. A method according to claim 1, characterized in that the feed composition includes pitch in a mass fraction equal to or less than the mass fraction of the novolac phenolic resin. 3. The method according to claim 1, characterized in that the plasticizer has a boiling point of at least 250 ° C. 4. The method of claim 1, characterized in that the plasticizer has a boiling point of at least about 200 ⁰ C and is selected from the group consisting of a glycol, glycol esters, other esters, aromatic alcohol, anthracene oil, pyrol and their mixtures. 5. The method according to claim 4, characterized in that the glycol consists of diethylene glycol or triethylene glycol. 6. The method according to claim 4, characterized in that the glycol is a polyethylene glycol! is. 7. The method according to claim 4, characterized in that the plasticizer is a dibasic ester selected from the group consisting of adipine dimethyl ester, glutarine dimethyl ester, Succindimethylester and their mixtures. 8. The method according to claim 1, characterized in that the plasticizer is an aromatic alcohol. 9. The method according to claim 1, characterized in that the plasticizer is a heterocyclic compound, such as. B. 2-pyrrolidone. 10. The method according to claim 1, characterized in that the plasticizer is an anthracene compound, such as. As anthracene oil, or a naphthalene compound. 11. The method according to claim 1, characterized in that the resin has a free phenol content of at most 4 parts by mass in%, as measured by gas chromatographic analysis, and is characterized by a minimum melting point of 100 ° C. 12. The method according to claim 11, characterized in that the content of the resin in volatile substances is a total of at most 5 parts by mass in% of its solids content. For this 1 page drawings Field of application of the invention The invention relates to a method for producing a Söderberg electrode.