Method For Producing a Homogenized Mixture Of Carbon, Sulfur, and PTFE

Abstract

A method for producing a homogenized mixture of carbon, sulfur, and PTFE, wherein the sulfur is liquefied, and the liquid sulfur is then ground for the first time together with the carbon, so that the liquid sulfur is absorbed by the pores of the carbon particles and forms a preferably powdery composite with the carbon particles, whereupon PTFE is added and the mixture of the composite and the PTFE is then ground a second time and is thus homogenized.

Claims

1. A method for producing a homogenized mixture of carbon, sulfur, and PTFE, wherein the sulfur is liquefied, and the liquid sulfur is then ground for the first time together with the carbon, so that the liquid sulfur is absorbed by the pores of the carbon particles and forms a preferably powdery composite with the carbon particles, whereupon PTFE is added and the mixture of the composite and the PTFE is then ground a second time and is thus homogenized.

2. The method according to claim 1, wherein carbon particles in the form of soot are used.

3. The method according to claim 1, wherein the liquid sulfur is fed to an injector, which injects it into a mill.

4. The method according to claim 1, wherein until it is ground with the carbon particles, the liquid sulfur is controlled in a temperature range of between 119° C. and 220° C., preferably only 200° C., and ideally only 190° C.

5. The method according to claim 1, wherein the injector (7) is operated with injection gas, which is under overpressure, in particular in the form of nitrogen

6. The method according to claim 3 wherein the injection gas is heated up such that the sulfur remains liquid during the transport in the nitrogen, does not crystallize, and ideally reaches the grinding region, in which it is ground with the carbon particles, with a temperature, which lies in the temperature range.

7. The method according to claim 5, wherein following the grinding of the carbon particles with the sulfur, the injection gas is separated from the carbon-sulfur composite and is discharged.

8. The method according to claim 1, wherein the temperature of the carbon-sulfur bond sinks after the common grinding.

9. The method according to claim 1, wherein the first grinding takes place in an impact mill and in particular in a pin mill.

10. The method according to claim 1, wherein the second grinding takes place in an impact mill and in particular in a pin mill.

11. The method according to claim 1, wherein three separate dosages for sulfur, carbon particles, and PTFE are used, which are preferably set such that the homogenized mixture contains 50 m % to 70 m % of sulfur, 25 m % to 40 m % of carbon particles and in particular soot, and 1 m % to 10 m % of PTFE.

12. The method according to claim 1, wherein the homogenized mixture is created continuously while passing through the mills, and not batchwise, by means of several consecutive mill fillings.

13. The method according to claim 1, wherein the first grinding is a hot gas grinding.

14. The method according to claim 1, wherein the second grinding serves to cool the end product.

15. A device for carrying out a method for producing a homogenized mixture of carbon, sulfur, and PTFE, wherein the sulfur is liquefied, and the liquid sulfur is then ground for the first time together with the carbon, so that the liquid sulfur is absorbed by the pores of the carbon particles and forms a preferably powdery composite with the carbon particles, whereupon PTFE is added and the mixture of the composite and the PTFE is then ground a second time and is thus homogenized, wherein said device includes two impact mills arranged one behind the other in the mixture transport direction, one of which is preferably operated in the hot gas operation.

16. A use of a pin mill for the hot gas grinding of liquid sulfur and soot.

17. A use of a pin mill for cooling down and homogenizing a mixture of a soot/sulfur bond and PTFE.

18. The use of a first pin mill according to claim 16 and this subsequent use of a second pin mill, preferably as part of a continuous process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 shows the plant-related design, which a preferred exemplary embodiment of the method according to the invention requires.

[0030] FIG. 2 illustrates the pin plates of a pin mill, which is preferably used here for the grinding.

DETAILED DESCRIPTION

[0031] FIG. 1 shows a plant for carrying out the method according to the invention, which, according to the invention, uses a 2-step grinding process. A 2-step grinding process has the large advantage that a formation of small clumps of the sulfur/soot composite, which cools down, is prevented. At the same time, the 2-step grinding process results in that the end product is cooled in the second mill or when passing through the mill a second time, respectively, should only a single mill be used. In this way, a fine homogenization with the PTFE powder can be ensured with the use of a 2-step grinding process. The plant is characterized in that it operates the process according to the invention as continuous process. Unlike in the past, it is not provided to work in a batchwise manner, for instance with batches, which are specified by the volume of a mill filling. This increases the quality. The otherwise typical quality fluctuations, which occur from batch to batch, no longer apply.

[0032] The homogenized mixture, which is produced by means of the method according to the invention, is a mixture of carbon, sulfur, and PTFE, whereby the latter is also known as polytetrafluoroethylene. The carbon is mostly used in the form of soot.

[0033] The carbon bunker or soot bunker 1, respectively, can be seen well in FIG. 1. From it, soot is gravimetrically dosed in via the dosing device or the dosing screw 2, respectively. The dosing is preferably set such that the soot share in the finished homogenized mixture is approximately 25 m % to 40 m %, i.e. mass percent. Via the cellular wheel sluice 3, the soot reaches all the way to the mill feed line 4, which will be described in more detail below, preferably under the influence of the force of gravity.

[0034] The soot bunker 5 can likewise be seen well in FIG. 1. Powdery sulfur reaches from the sulfur bunker, again preferably under the influence of the force of gravity, into the dosing device or the dosing screw 6, respectively. The dosing is preferably set such that the sulfur share in the finished homogenized mixture is approximately 50 m % to 70 m %. The dosing device or the dosing screw 6, respectively, is heated. For this purpose, the dosing screw is usually equipped with one or several, preferably temperature-controlled or temperature-regulated heating elements at the dosing tube. The heating elements are set to a certain temperature, so that the sulfur changes its state from powdery to liquid during the dosing process due to the temperature influence. The sulfur thus leaves the dosing device in completely liquid state.

[0035] A precise dosing is important for a stable product quality of the later battery cell. In particular the temperature control or temperature regulation of the dosing tube thus has to be exact. This is so because the sulfur displays a particular melting-viscosity behavior. Sulfur has a melting point of around 119° C. When melting sulfur, a low-viscous liquid forms initially. In response to further heating, the viscosity increases until it reaches the maximum at 187° C. In response to further heating, the viscosity sinks again. To attain an exact dosing, the temperature of the sulfur thus has to be controlled carefully.

[0036] The sulfur reaches into an injector 7, preferably under the influence of the force of gravity.

[0037] The injector 7 is fed with heated-up, pressurized injector gas from a gas supply 8. For the most part, the injector gas is fed in in a preheated manner, with a temperature of 100° C. to 200° C.

[0038] Nitrogen is preferably used as injector gas. Nitrogen has the advantage that even under heat, it does not tend to undergo reactions with the sulfur to a noteworthy extent. However, a different inert gas could also be used instead. However, for reasons of process efficiency, nitrogen is clearly preferred.

[0039] As suggested in FIG. 1, a heating element 9, which controls the temperature of the injector gas accordingly, is provided upstream of the injector 7 for this purpose. The injector gas leaves the injector 7 via the mill feed line 4 and flows in the direction of the first mill. The temperature of the injector gas is thereby controlled such that the sulfur remains liquid in the injector gas during the transport, and does not crystallize out. The pressure of the injector gas is selected such that the sulfur is transported from the injector into the first mill 10. Before the injector gas, which is fraught with the sulfur, reaches the first mill, the soot is fed into the mill feed line 4 at the tube intersection 4a. Supported by the injector gas, the liquid sulfur and the soot now reach the first mill 10 or the grinding chamber thereof, respectively. The first mill 10 is typically an impact mill. Ideally, a so-called pin mill is used.

[0040] In the case of a pin mill, grinding disks are used as grinding tools, which are equipped with pins, which are positioned at a distance from one another, as it is illustrated by FIG. 2 as preferred embodiment. As a rule, at least one stationary pin disk 23 and at least one rotating pin disk 24 are used, wherein pin disks, which rotate in opposite directions, are also conceivable, however. The material to be ground is fed mostly in the center Z, which is not pin-fitted, of the pin disks 23, 24 or preferably of the stationary pin disk, respectively. From there, it is flung to the outside by means of the centrifugal force and is then mostly also discharged to the outside. The grinding process thereby takes place due to the impact with the pins 25 and the mutual particle impact.

[0041] As a rule, the rotating pin disk is speed-controlled or speed-regulated. As a rules, the faster the pin disk rotates, the finer the grinding result.

[0042] The sulfur and the soot are finely distributed and mixed well by means of the grinding. Due to the fact that the grinding takes place in hot gas operation in the first mill 10, the liquid sulfur is absorbed by the pores of the soot. It forms a composite therewith in the above-described sense.

[0043] After the end of the first grinding, the composite of soot and sulfur falls into the bunker 11 below the mill.

[0044] As can be seen well on the basis of FIG. 1, the injector gas or the nitrogen, as a rule, respectively, is moved in a circle. The injector gas, of which there is a surplus after the first grinding, is purified by means of a filter 12 and is guided out of the grinding plant through an injector 13. It is then preferably added to the injector gas supply 8 or to the nitrogen supply again, respectively, which is not illustrated figuratively here. It should also be noted that the discharge of the injector gas can also be realized by means of a fan, which is not illustrated figuratively here.

[0045] The sulfur/soot composite falls out of the bunker 11 into a cellular wheel sluice 14, which is speed-regulated or speed-controlled, as a rule. From there, it is ejected into a storage container 15. Free-flowing PTFE from the PTFE bunker 17 is added in this storage container 15 via a dosing device or a dosing screw 16, respectively. The PTFE powder falls into the dosing device or the dosing screw 16, respectively, under the influence of the force of gravity. From there, it is conveyed into the storage container 15.

[0046] The soot/sulfur/PTFE mixture is guided continuously from the storage container 15 into a second impact mill 19 via a further speed-regulated or speed-controlled cellular wheel sluice 18. It also applies here that the impact mill 19 is preferably designed as pin mill. What has been described above applies analogously here.

[0047] However, no hot gas grinding takes place in this second impact mill. Instead, the soot/sulfur mixture with the PTFE is not only homogenized, but is also cooled down for the further processing by means of the grinding process. Due to the fact that the cool-down takes place during this second grinding step, which leads to an immediate splitting of sulfur clumps, which may possibly form during the cool-down, no coarse, hard sulfur clumps cam be created during the cool-down process. In addition, the PTFE powder is present in an even and finally distributed manner.

[0048] The end product in the form of the homogenized mixture of carbon, sulfur, and PTFE is discharged via a further cellular wheel sluice 20. The excess process gas is filtered by the filter 21 and is discharged from the grinding plant by means of a further injector 22. In the alternative, a vacuum fan can also be used for the discharge.