LTFT CATALYST FINES REMOVAL

Abstract

The invention provides a method, stage and plant for removing LTFT catalyst fines and/or organometallic catalyst compounds from of LTFT wax, downstream from the LTFT reactor. The method includes at least one stage having the steps of causing a differential pressure across a filter element; causing high mechanical shearing and/or centrifugal forces along and/or away from the surface of the filter on the high pressure side of the filter to cause the particles to be continuously removed from the filter surface; and wherein the differential pressure is selected to be sufficient to force flow of the wax across the filter to cause filtration.

Claims

1. A method for removing LTFT catalyst fines and/or organometallic catalyst compounds from of LTFT wax, downstream from the LTFT reactor, which includes at least one stage having the steps of: causing a differential pressure across a filter element; causing high mechanical shearing and/or centrifugal forces along and/or away from the surface of the filter on the high pressure side of the filter to cause the particles to be continuously removed from the filter surface; and wherein the differential pressure is selected to be sufficient to force flow of the wax across the filter to cause filtration.

2. A method as claimed in claim 1 wherein the transmembrane pressure is between 1.5 and 6 bar.

3. A method as claimed in claim 2 wherein the transmembrane pressure is between 1.5-2 bar.

4. A method as claimed in any one of claims 1 to 3 wherein the shearing and/or centrifugal forces are formed by rotating the filter element in the wax mixture.

5. A method as claimed in any one of claims 1 to 4 wherein the filter element has pores smaller than the fine catalyst particles to be removed.

6. A method as claimed in any one of claims 1 to 5 wherein, for each stage, the wax mixture is fed under pressure into a filter vessel with one or more hollow filter elements extending into the vessel, with the filtrate moving through the filter element out of the vessel.

7. A method as claimed in claim 6, wherein each hollow filter element is rotated at a high rpm relative to a generally stationary wax mixture.

8. A method as claimed in claim 7, wherein the filter element includes a hollow cylinder with a porous filter surface or wall.

9. A method as claimed in claim 8, wherein and further includes a plurality of circular discs extending perpendicularly from the cylinder and being axially aligned with the cylinder with each disc being hollow with the hollow extending from the hollow of the cylinder.

10. A method as claimed in claim 9, wherein each stage or vessel includes two or more rotating filter elements arranged such that the discs of adjacent filter elements overlap and wherein the spinning direction of the shafts are preferably in the same direction such that overlapping regions of filter elements move in opposite direction relative to each other to maximise shearing forces and turbulent flow.

11. A method as claimed in any one of claims 1 to 10 wherein the filter element has a pore size of between 20 and 40 nm created by TiO.sub.2 coating on a ceramic base.

12. A method as claimed in any one of claims 1 to 11 which includes more than one stage and wherein the stages are arranged in series with the concentrated wax and catalyst mixture or retentate flowing downstream from one stage to another and finally from the last stage to a catalyst regeneration or processing unit.

13. A stage for removing LTFT catalyst fines and organometallic catalyst compounds from LTFT wax, downstream from the LTFT reactor, which includes: a filter vessel; a filter element; a differential pressure, in use, across a filter element; a means for causing high mechanical shearing and/or centrifugal forces along and/or away from the surface of the filter on the high pressure side of the filter to cause the particles to be continuously removed from the filter surface; and wherein the differential pressure is selected to be sufficient to force flow of the wax across the filter to cause filtration.

14. A Fischer-Tropsch wax cleaning plant, downstream of a LTFT reactor, which plant includes at least one stage as claimed in claim 13.

15. A method for removing LTFT catalyst fines and/or organometallic catalyst compounds from LTFT wax, substantially as described herein with reference to the accompanying drawings.

16. A stage for removing LTFT catalyst fines and/or organometallic catalyst compounds from LTFT wax, substantially as described herein with reference to the accompanying drawings.

17. A Fischer-Tropsch wax cleaning plant, substantially as described herein with reference to the accompanying drawings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0029] FIG. 1 shows a possible layout of a wax treatment unit which includes a stage unit in accordance with the invention. The wax treatment unit may also include a centrifuge and particle guard beds and other process equipment.

[0030] FIG. 2 shows a 3-stage unit, in accordance with the invention.

[0031] Experimental trial runs were done on a laboratory scale using one stage of a Dynamic Cross Flow unit. The disc of the unit was rotated at 1200 RPM. The FT wax flow rate was between 0.5 kg/h and 4 kg/h depending on the catalyst concentration in the retentate resulting in a flux range of 15-116 kg/m2.Math.h, with a 30 nm pore size membrane. The total membrane surface area was 0.034 m.sup.2. The filtration temperature was 150 C. with a pressure of 2 bar applied to the filtration vessel resulting in a transmembrane pressure of 1.8 bar. The test FT wax stream contained 600-750 wt-ppm catalyst. The retentate was concentrated up to 20% mass. A test with permeate recycle keeping the retentate concentration constant at 20% mass was maintained for 14 days. During this test the flux was kept constant at 15 kg/m.sup.2.Math.h. No solid particles or catalyst could be detected in the permeate using RFA analysis thereby maintaining a 100% filtration efficiency throughout the test with neither fouling nor abrasion observed.

[0032] It shall be understood that the example is provided for illustrating the invention further and to assist a person skilled in the art with understanding the invention and is not meant to be construed as unduly limiting the reasonable scope of the invention.