PROCESS FOR DECOMPOSING SIC OR SIC-CONTAINING MATERIALS

Abstract

Disclosed is a method for the decomposition of SiC or SiC-containing materials in which the reaction is guided exclusively via gaseous products for achieving a conversion which is as complete as possible. A preferred application is a recycling process for catalyst materials containing platinum metals on a carrier material made of silicon carbide (SiC). In the thermal process, the catalyst materials are freed from the carrier material, and then they can further be refined. (FIG. 1)

Claims

1. A method for decomposing SiC or SiC-containing materials, comprising: feeding the SiC or SiC-containing material and an additive into a reactor under reduced pressure, wherein the additive is one or more oxygen-containing compounds excluding molecular oxygen; adjusting a temperature and a pressure in the reactor such that an equilibrium partial pressure of oxygen in the reactor is: lower than a partial pressure of oxygen in the oxygen-containing compound so that an equilibrium reaction of the oxygen-containing compound to the oxygen-containing compound in a lower oxidation state and oxygen is shifted towards a formation of the oxygen-containing compound in a lower oxidation state and oxygen, and lower than a partial pressure of oxygen in the SiO.sub.2 which is formed from the SiC by oxidation with the oxygen of the additive so that a formation of condensed SiO.sub.2 on a surface of the SiC is avoided; wherein molecular oxygen is excluded from the reactor.

2. The method according to claim 1, wherein the partial pressure of oxygen in the reactor is lower than 10.sup.13 hPa.

3. The method according to claim 1, wherein the pressure in the reactor is 0.001 hPa to 900 hPa.

4. The method according to claim 1, wherein the oxygen-containing compound is selected from the group consisting of CO.sub.2, H.sub.2O and a metal oxide or metalloid oxide.

5. The method according to claim 1, wherein the metal oxide or metalloid oxide between 1,300 C. and 1,700 C. has an equilibrium partial pressure of oxygen of 10.sup.11 hPa.

6. The method according to claim 1, wherein the metal oxide or metalloid oxide is selected from the group consisting of SiO.sub.2 and Al.sub.2O.sub.3.

7. The method according to claim 1, wherein the reaction is conducted in a continuously working reactor.

8. The method according to claim 1, wherein the reactor is a revolving cylindrical furnace, continuous furnace, fluidized bed reactor or a flatbed furnace.

9. The method according to claim 8, wherein a reaction time is between 0.25 hours and 10 hours.

10. The method according to claim 1, wherein the SiC or SiC-containing material and the additive are heated to temperatures of 1,000 C. to 1,650 C.

11. The method according to claim 1, wherein adjusting the temperature is realized by thermal radiation or microwave radiation.

12. The method according to claim 1, wherein the reactor is a plasma burner.

13. The method according to claim 12, wherein a reaction time is between 0.1 seconds and 5 seconds.

14. The method according to claim 12, wherein adjusting the temperature is realized in a plasma burner into which the SiC or SiC-containing material and the additive are fed, and the reaction takes place directly in a plasma flame.

15. The method according to one of claims 12, wherein the oxygen-containing compound is H.sub.2O and fed into the plasma burner together with a hydrocarbon.

16. The method according to claim 1, wherein the SiC or SiC-containing material is fed into the reactor in ground, crushed and/or not treated form.

17. The method according to claim 1, wherein a mass loss of the SiC or SiC-containing material is at least 65% based on the SiC portion.

18. The method according to claim 1, wherein the SiC-containing material comprises catalyst carrier materials.

19. The method according to claim 18, wherein the SiC-containing material further comprises platinum, and the method further comprises separating platinum group metals from the catalyst carrier materials.

20. The method according to claim 11, wherein adjusting the temperature is realized by thermal radiation of graphite heaters, SiC heaters or metallic heaters.

Description

SHORT DESCRIPTION OF THE FIGURE

[0055] FIG. 1 shows the partial pressure diagram of oxygen for different process conditions.

[0056] FIG. 2 shows the particle size distribution of the SiC-containing starting material of example 1.

[0057] FIG. 3 shows the particle size distribution of the SiC-containing starting material of example 2.

EXAMPLES

[0058] The particle size distributions of the ground materials were determined with a sieve analysis on the basis of the DIN 66165-2:2016-08 in a sieve stack of the company RETSCH, model AS200 control. The work was conducted without a separation of the fine fraction prior to the sieving and with an amplitude of 0.7 mm/g, a sieving time of 20 min and an interval time of 1 s.

1. Flatbed Furnace

[0059] The SiC-containing material for this example consisted of a catalyst material from a diesel particulate filter comprising an SiC-based carrier material and an active coating with the platinum metals platinum and palladium. It was comminuted in a screen ball mill to the particle size distribution shown in FIG. 2. Subsequently, it was mixed with DORSILIT sand (SiO.sub.2 content 99.1% by weight) in the mixing ratio based on the mass of 1:1 and added into an Al.sub.2O.sub.3 crucible. The SiC portion of the starting material was ca. 80% by weight (based on the catalyst material).

[0060] In a vacuum furnace consisting of a water-cooled steel chamber and a treatment zone equipped with graphite heaters, the mixture in the Al.sub.2O.sub.3 crucible was reacted at a treatment temperature of 1,540 C. and a treatment duration of 3.5 h. The starting mass (however based on the total mixture of catalyst material and sand) was reduced by 90%. During the process the mean pressure in the reactor was 0.9 hPa. A subsequently conducted chemical analysis showed an enrichment of the platinum by the factor of 10.3. For palladium, an enrichment by the factor of 9.8 was shown. The chemical analyses were consistent with the mass balance. For CO as a gaseous product occurring during the process an unambiguous identification by means of mass spectroscopy was possible. In a filter downstream in the plant an SiO-containing residue was identified.

2. Plasma Burner

[0061] A similar SiC-containing material of a catalyst material originating from a diesel particulate filter such as in example 1 was comminuted in a screen ball mill to the particle size distribution shown in FIG. 3. Subsequently, together with an Ar/CO.sub.2/H.sub.2 mixture (ca. 50% by volume of Ar, 45% by volume of CO.sub.2 and 5% by volume of H.sub.2) it was directly transported through and reacted by a plasma burner. The plasma burner worked with a chamber pressure of between 0.5-10 hPa. Based on analogous experiments, the reaction time of the raw material in the plasma zone was determined to be between 0.1 and 0.5 seconds. Direct measurements of the temperature in the plasma zone were not conducted, however, with the chosen configuration and the process parameters plasma temperatures which are considerably higher than 10,000 K can be expected. Prior to the experiment, a characteristic spectrum of the chemical composition of the raw material was recorded, and this one was compared with the spectrum of the product. This showed a reduction of the SiC by 70% (based on the original SiC content in the catalyst material). The chemical analysis of the product by means of mass spectrometry with inductively coupled plasma (ICP-MS) showed an enrichment by the factor 7.3 for platinum and 6.6 for palladium.