Catalyst reprocessing
A process for re-processing of a Fischer-Tropsch catalyst is described comprising the steps of; (i) de-waxing the Fischer-Tropsch catalyst, (ii) subjecting the de-waxed catalyst to hydrometallurgical leaching or extraction to separate catalyst metal or metals from catalyst support material, and (iii) recovering the separated catalyst metal or metals, wherein the de-waxing step is performed using a pressurised near-critical or supercritical fluid under conditions that minimise catalyst metal spinel formation.
1. A process for re-processing of a Fischer-Tropsch catalyst comprising the steps of
(i) de-waxing the Fischer-Tropsch catalyst,
(ii) subjecting the de-waxed catalyst to hydrometallurgical leaching or extraction to separate catalyst metal or metals from a catalyst support material, and
(iii) recovering the separated catalyst metal or metals,
wherein the de-waxing step is performed using a pressurised near-critical or supercritical fluid selected from the group consisting of one or more of C3-C12 alkanes, one or more C2-C4 alcohols, or water under conditions that minimise catalyst metal-support spinel formation.
2. A process according to claim 1 wherein the catalyst is a cobalt-based Fisher-Tropsch catalyst.
3. A process according to claim 1 wherein the catalyst comprises cobalt and alumina and the spinel is cobalt aluminate.
4. A process according to claim 1 wherein the catalyst metals include a precious metal.
5. A process according to claim 4 wherein the precious metal is selected from the group consisting of platinum, rhenium or ruthenium.
6. A process according to claim 1 wherein the pressurised fluid is near-critical or supercritical iso-propanol.
7. A process according to claim 1 wherein the pressurised fluid is applied to the catalyst at a temperature below 600° C.
8. A process according to claim 1 wherein the hydrometallurgical leaching comprises selective dissolution using acidic, alkaline or neutral aqueous solutions at elevated temperature above 50° C. and pressures up to about 20 bar abs and/or extraction of the catalyst metal or metals using suitable extractant molecules that form complexes with the catalyst metal or metals.
9. A process according to claim 1 wherein the catalyst metal or metals are recovered by filtration, precipitation, separation or flocculation.
10. A process according to claim 1 wherein the Fischer Tropsch catalyst comprises a precious metal, cobalt and alumina and is subjected to steps comprising:
(i) de-waxing using the pressurised fluid at near-critical or supercritical conditions at a temperature below 600° C. to obtain de-waxed catalyst having a carbon content ≦1% wt,
(ii) subjecting the de-waxed catalyst to a step of alkaline leaching and filtration to separate the aluminium,
(iii) subjecting the remaining cobalt/precious metal residue to an acid leaching and filtration step that separates the cobalt, and
(iv) subjecting the precious metal in the insoluble residues to treatment with a strong acid or treatment with acid and peroxide, followed by ion exchange on a suitable ion-exchange material.
11. A process according to claim 10 , wherein the aluminium is separated as sodium aluminate.
12. A process according to claim 10 , wherein the cobalt is separated as a cobalt salt.
13. A process according to claim 1 wherein the Fischer Tropsch catalyst comprises rhenium, cobalt and alumina and is subjected to steps comprising;
(i) de-waxing using a pressurised fluid at near-critical or supercritical conditions at a temperature below 600° C. to obtain a de-waxed catalyst having a carbon content ≦1% wt,
(ii) subjecting the de-waxed catalyst to a step of acid leaching at elevated temperature to separate cobalt and rhenium from the bulk of the aluminium, and
(iii) precipitating the aluminium and cobalt with a base to leave a relatively pure [ReO 4 ] solution.