Process for preparing catalysts
A process for manufacturing a catalyst composition comprises the steps of (i) precipitating one or more metal compounds from solution using an alkaline precipitant, preferably comprising an alkaline carbonate, optionally in the presence of a thermostabilizing material, ii) ageing the precipitated composition, and (iii) recovering and drying the aged composition, wherein the ageing step is performed using a pulse-flow reactor.
1. A process for manufacturing a catalyst composition comprising the steps of
(i) precipitating one or more metal compounds from solution using an alkaline precipitant,
(ii) aging the precipitated composition in a pulse-flow reactor,
(iii) removing carbon dioxide from the pulse-flow reactor, and
(iv) recovering and drying the aged composition,
wherein the pulse-flow reactor is in the form of an elongate vessel having:
(i) one or more inlets for introducing a slurry of the precipitated composition located at one end of the reaction vessel,
(ii) a first outlet for removing the aged composition located at the opposite end of the vessel and a second outlet for removing carbon dioxide located at the opposite end of the vessel,
(iii) means for imposing on the slurry a pulsatile oscillatory motion in a direction substantially parallel to the direction of the fluid flow,
(iv) a plurality of stationary baffles mounted substantially transversely to the direction of fluid flow, and an un-baffled disengagement portion adjacent the first and second outlet.
2. A process according to claim 1 wherein the precipitated metal compounds comprise compounds of one or more metals selected from the group consisting of Ca, Mg, Ti, V, Cr, Mn, Fe, Cr, Co, Ni, Cu, Zn and Pb.
3. A process according to claim 1 wherein the precipitated metal compounds comprise compounds of one or more metals selected from the group consisting of Co, Ni, Cu and Fe.
4. A process according to claim 1 wherein the precipitated metal compounds comprise compounds of Cu, Zn and Mg.
5. A process according to claim 1 wherein a metal oxide thermostabilising material is present during the precipitation of the metal compounds.
6. A process according to claim 1 wherein an alumina sol is present during the precipitation of the metal compounds.
7. A process according to claim 1 wherein the alkaline precipitant comprises an alkaline carbonate.
8. A process according to claim 1 wherein the alkaline precipitant comprises an alkali metal carbonate.
9. A process according to claim 1 wherein the pulse-flow reactor comprises a single straight section or a plurality of straight sections joined by U-bends.
10. A process according to claim 1 wherein the pulse-flow reactor is in a horizontal orientation or a vertical orientation.
11. A process according to claim 1 wherein the internal cross-sectional area of the reactor taken up by each baffle is the same or different along the length of the reactor and is 20-80% of the total area.
12. A process according to claim 1 wherein when reactor is of circular cross-section, the baffles are discs having one central orifice through which the slurry may pass or comprise several orifices, or the discs are imperforate and have a smaller diameter than the internal diameter of the vessel thus leaving an annular space around their periphery.
13. A process according to claim 1 wherein ≧5 baffles are present in the reactor.
14. A process according to claim 1 wherein the pulsatile flow is provided by continuously pumping the slurry along the vessel using a centrifugal, diaphragm or gear pump and superimposing reciprocating oscillations by using suitable pumps, valves or other mechanisms such as a piston located so as to constitute an end wall of the reactor, or in hydraulic communication with an end of the reactor.
15. A process according to claim 1 wherein the oscillation frequency is in the range 0.1-10 Hz.
16. A process according to claim 1 wherein the amplitude of the oscillation is in the range 0.05-0.5 times the diameter of the reactor.
17. A process according to claim 1 , wherein the aging step is performed at a temperature in the range 0 to 100° C.
18. A process according to claim 1 further comprising a step of calcining the catalyst composition.
19. A process according to claim 3 further comprising a step of reducing the catalyst composition.
20. A process according to claim 1 wherein the precipitating step occurs in the presence of a thermostabilising material.
21. A process according to claim 8 wherein the alkali metal carbonate is sodium carbonate or potassium carbonate.
22. A process according to claim 1 , further comprising using the carbon dioxide removed from the pulse-flow reactor to prepare the alkaline prepare a metal carbonate precipitant.