Particle extrusion

1. A method of making helically formed extrudate particles for use in catalysis, comprising the steps:

providing an extruder with a die, the die comprising a plurality of channels extending from an inlet to an outlet, wherein from the inlet to the outlet each channel comprises a first section with a helical bore with a non-circular cross-section, and a second section with a cylindrical bore which has a diameter equal or greater than that of the first section, wherein the second section is at least twice as long as a diameter of the first section;

preparing a starting mixture for extrusion;

feeding the starting mixture through the die of the extruder; and

separating extruded material from the die of the extruder to provide the helically formed extrudate particles.

2. The method as claimed in claim 1 , wherein the first section of the die has a helical trilobal form.

3. The method as claimed in claim 1 , wherein the length of the first section of the die is at least equal to a pitch of the helical bore.

4. The method as claimed in claim 1 , wherein the second section of the die is substantially circular in cross-section.

5. The method as claimed in claim 1 wherein each channel of the die further comprises between the inlet and the first section a tapered inlet section wider at the inlet than at the first section, wherein an angle of taper for the tapered inlet section is between 30 degrees and 60 degrees.

6. The method as claimed in claim 1 , wherein each channel in the die is separated from each adjacent channel by a land at both the inlet and the outlet.

7. The method as claimed in claim 1 , wherein the diameter of the second sections of the channels is 10 to 50% greater than the diameter of the first section of the channels.

8. The method as claimed in claim 1 , wherein the inlet in the die forms an inlet plane, and the outlet forms an outlet plane, and wherein the inlet plane and the outlet plane are not parallel.

9. The method as claimed in claim 1 , wherein the die is provided in two or more modules which may engaged with or detached from each other, such that the first section of each channel is provided in one module and the second section of each channel is provided in another module.

10. The method as claimed in claim 1 further comprising a step of calcination and/or drying at a temperature between 350° C. to 750° C.

11. The method as claimed in claim 1 further comprising the step of partially evaporating a liquid accompanying the extruded material and formed extrudate particles at a temperature between 40° C. to 70° C.

12. A method of synthesizing hydrocarbons from syngas by contacting the syngas under reaction conditions with a Fischer-Tropsch catalyst, wherein the catalyst is prepared according to the method of claim 1 .