DE1209037B - Porous carbon molded body and process for its manufacture - Google Patents

Description

Porous carbon form body and process for its manufacture Manufacture of electrodes for the electrolytic extraction of metals, in particular Aluminum, is generally made up of small pieces of carbon, granulated to powdery, mixed with pitch as a binder, pressed into the required shape and then subjected to calcination, so that the finished electrode in the Elektrolyseöfeii can be introduced and there the high temperature required for electrolysis Withstands time. The starting material for carbon is either graphite, that is crystalline carbon, or pitch or petroleum coke are available.

The latter is a very pure carbon that either consists of the dry evaporation of tar pitch or petroleum residues. Petroleum coke, in particular, is being used more and more because it is used for electrodes The required level of conductivity is relatively easy to achieve with this component \ verden.

In order to produce shaped bodies of the required quality from this initially more or less fine-grained product, these materials have to be solidified, which is now generally done by mixing with pitch and suitably shaping the mixture by pressing. The resulting lyrrine moldings must then be subjected to a "baking" process carried out at high temperature (1000 to 1200 ° C) and mottled for a period of time, whereby all volatile2 constituents are removed , after which the finished electrode then consists practically of pure carbon.

A long time ago a process was developed by which binding asphalt bitumens were produced at relatively low temperatures. and can be converted into a high-carbon, infusible material within hours by means of a molecular transformation at temperatures below 300-C. This was made possible by the action of atmospheric oxygen within evenly distributed flea spaces in a compressed mixture. The non-linear conversion product resulting from the initially fusible and binding asphalt bitumen has the properties of so-called pyrobitumen, i. In other words, it is insoluble and infusible and easily turns into pure carbon on further heating, sometimes in an electrolysis furnace. Pyrobitumen has a carbon content of around 9211/1., And the resulting carbon is practically identical to petroleum coke.

The production of the above-mentioned pitch or petroleum coke on liquid tar pitch or petroleum products, residues or bitumen requires a high supply of heat, since these lighter hydrocarbons are very rich in light hydrogen-containing components and require more or less laborious and time-consuming manipulations, see above that the production and supply of pitch or petroleum coke, especially recently, has become costly. Petroleum residues, even fairly consistent ones, result in only 50 "/ or even less carbon in the form of petroleum coke. On the other hand, in nature in several areas there are laaer sites of different types of bitumen, which largely correspond to pyrobitumen and are even more or less pure pyrobitumen, such. as Impsonit well Albertit u. ä.

These products, which contain 90 "/" and more carbon, have so far not found any technical use, because they cannot be processed as binders like normal asphalt bitumens due to their infusibility and insolubility. They were only used marginally as fuel, as they usually contain small residues of volatile components that foam up in the furnace, prevent burning and lead to the build-up of smoke and soot.

Attempts have now been made here to isolate electrodeiiköiper natural pyrobitumen and this already very high carbon content Product by means of a relatively simple supply of heat its by nature only a small amount of hydrogen can still be withdrawn and practically entirely in carbon to transform.

In doing so, they gave rise to considerable problems, namely, on the one hand, the difficulty or even apparent impossibility to shape the infusible material and on the other hand subsequently to convert molecularly without the moldings disintegrating again in the process. These problems were resolved in the course of the investigation, which will be discussed further below will be discussed in more detail.

So there was the basic idea in the manufacture of electrodes instead of pitch or petroleum coke, which is more or less expensive Must be made detours, as early as possible during the preparation of the raw electrode start from a naturally occurring high-carbon raw material. In pursuit This idea was followed by experiments with natural pyrobitumen or related products undertaken.

Such materials can be found in nature in some cases as almost pure pyrobitumen. Above all , this includes - as already mentioned - the material known as impsonite, which is found, for example, in various regions of the North American continent. But there is a whole range of bituminous materials, the character of which ranges from solubility in welding and low-meltability to insolubility and infusibility. The natural formation of these products, which become more and more carbon-rich with increasing geological age, corresponds to the formation of coal from cellulose via peat and lignite, whereby the end product is anthracite. Such products, which are related to asphalt bitumen but can be described as natural pyrobitumen, are known under the names impsonite, albertite, wurtzite, elaterite, etc. Often there are also combinations of pyrobitumen with so-called asphaltites, i.e. left poorly soluble and difficult to melt intermediate products, such as B. grahamite, gloss pitch and the well-known gilsonite, which is still meltable and soluble, but already contains 85 to 86% carbon. To distinguish it from pure pyrobitumen, the various types of types found in nature mentioned above are referred to below as natural pyrobitumen, which means that the character varies and, in general, the insolubility and infusibility is not one hundred percent. As far as is known, the so-called impsonite represents the purest natural pyrobitumen and can already be described as practically insoluble and infusible.

As far as natural pyrobitum particles are spoken of in the following, are understood to mean particles that are made from the aforementioned high-carbon, Difficult or non-meltable natural pyrobitumina exist. These particles can be produced by appropriate comminution, but it should be noted that that in many cases the materials found in nature disintegrate very easily and frequently the crushing process is relatively simple.

The invention is based, inter alia, on the object of providing a shaped body and a method for forming this shaped body, for the production of which natural pyrobitumen is preferably used, which is currently due to its special properties, such as, for. B. crumbling when heated, cannot be processed. In preliminary tests with natural pyrobitumen (impsonite), this material was first crushed and later formed from these particles without the addition of a special binder, but these only had a relatively low strength. However, the dimensional stability increased with the pressing temperature, and a relatively favorable pressing temperature is 350.degree. A subsequent increase in the temperature does not in all cases lead to a noticeable increase in the strength of the molded body. At very high pressures and at the same time high temperatures, however, test specimen strengths could be achieved which are sufficient for practical use. Calcination of such specimens, e.g. B. in the "baking" process known in the manufacture of electrodes, but does not succeed because the specimens disintegrate again by themselves.

To carry out the actual tests, mixtures of the natural pyrobitum particles with normal bitumen as an additional binding agent with a penetration of 80 were produced, the individual natural pyrobitum particles being coated with a thin layer of bitumen. In these tests, about 1 to 5 percent by weight of bitumen 80 was added. The compression was carried out in such a way that a porous, shaped body resulted, its pore system. was essentially coherent and also in communication with the outside air.

In order to make such a shaped body a usable metallurgical electrode, e.g. B. for aluminum electrolysis furnaces, three things must be achieved, among other things; Firstly, volatile constituents must be removed as far as possible; secondly, the bitumen used as a binder must be in a heat-resistant form, i.e. H. be converted to infusibility, and thirdly, the electrical resistance must be adjusted by suitable thermal treatment so that it meets the requirements. This was achieved in that the shaped body was then treated at an elevated temperature of about 170 to 300 ° C under the action of oxygen until the bitumen 80 was largely or practically completely converted into infusible and insoluble pyrobitumen and also until the small residual components volatile substances present in the natural pyrobitum particles used were also converted or expelled. The electrical resistance can then be adjusted by briefly bringing the molded body, which has already been converted, to a temperature of about 500 ° C. or above. The shaped body now has the required strength and other properties and can be used accordingly.

A molded body produced in this way now exists to a large extent mostly made of natural pyrobitumen, the particles of which are also made by a originally fusible bitumen transformed into pyrobitumen are bound. Such Shaped bodies can, among other things, also be used as fuel briquettes for coal firing will.

The above-described conversion of the pressed molded body to the usable electrode was lengthy with various types of pyrobitum and only possible at temperatures below about 220'C , because the studies carried out have shown that pyrobitumen, such as. B. Impsonite, contrary to the information in the literature, oily vapors occur at higher temperatures, which condense as a thin, yellowish oil. Strong self-heating was also observed and it was found that the test specimens tend to disintegrate if their temperature increases significantly above 200.degree . C. during the treatment time.

To accelerate and simplify this process and also to avoid uncontrolled sales heating, it has proven to be advantageous in the case of various types of pyrobitur if the natural pyrobitum particles are pretreated by themselves before being mixed with biturns as a biadein and before pressing to remove their remaining stock to remove volatile or soluble bituminous substances or partly also in insoluble and insoluble bituminous pyrobitumen. uilizuwandeln. For this purpose, the natural pyrobitum particles are heated beforehand, preferably to a temperature between 170 and 300 ° C. It must be ensured that the heating level, due to self-heating, does not increase so much that self-c # - # tzUi.idiiii- occurs, ii.;,. d - if necessary, it is advantageous or also necessary to provide for the necessary cooling and / or to reduce the admission of oxygen, for example to reduce the oxygen level in the surrounding air.

The duration of the heat treatment depends to a large extent on the nature of the pyrobittline involved and can only be determined in individual cases according to the properties of the raw material. Basically Ailt but that the pretreatment uni faster C LI goes, the higher the temperature is chosen. But spontaneous inflammation must be avoided. In some cases a 5 hour heat treatment was enough, but for best Sortca this time should be accordingly olistäiid-1, -eit conversion a conversion time up to 20 hours may be required.

If the natural pyrobitunia particles have been made according to the above-described process, they can be used as additives for the production of electrode bodies, using previously known processes, e.g. for electrodes which are coated with pitch as a binding agent and which have to be subjected to the process for calcination, or for the manufacture of full electrode assemblies for so-called Söderberg-Flektroden-

Claims (2)

1. A Verfahron to Heistellung porous from - [ 'vlasseteilchen formed coal Fornikörper, d a d u rch - e k en ii z eic li ii et that the mass particles that are at least partly Naturpyrobitumenteilchen, with a small amount Asphalt Bitumen be mixed or coated as an additional binder in the order of 3 to 10 percent by weight, that the mixture is deformed into a shaped body with a coherent, externally accessible pore system of approximately 5 to 20 percent by volume of the body and that the shaped body is at elevated temperature is treated from about 170 to 300'C under the action of oxygen until the binder bitumen is largely or entirely converted into infusible or insoluble pyrobitumen and preferably up to the. Natural pyrobitum particles initially present residual constituents of refugees are expelled or partly also converted, the upper temperature limit being chosen so that spontaneous ignition does not occur, and - e, c - this limit is to be reduced to 220 ° C if necessary. 2. The method according to claim 2, characterized in that for at least partial carbonization or coking of the pyrobitumen or for the production of the desired electrical resistance of the molded body to a temperature of over 300 to, for example, 500-'C, substantially below wide-liendem Satierstol. Tab-.e close, is heated. 3. The method according to claim 2 or 3, characterized izei - nzeielinet that the natural pyrobit-ameiiteilcheii before mixing with the additional binderbituii-ieii by heating, preferably under the effect of oxygen, for Ausreibl-iii- or Umluna fully volatile and soluble bituminous Remainder parts are converted into insoluble and ineligible pyrobitumen. 4. Veriahren according to claim 4, characterized in that the natural pyrobitum particles are heated under re-uliertern, oxygen access to about 170 to 300 -'C without self-ignition occurring. 5. The method according to any one of claims 2 to 5, characterized in that the Naturpyrobitumente'Ichen. before mixing with binder bitumen. are at least partially freed from their ashes by methods known per se, for example flotation. 6. Process for the production of electrode material, for example in the form of aggregates in the production of electrodes according to the "bak-ine," or Söderber process, characterized in that natural pyrobitument parts are vorzuasweise under metered oxygen influence for expulsion or to convert still volatile and soluble bituminous residues into insoluble and infusible pyrobitumen by heating to 170 to 30WC.