Process for the activation of a supported chromium oxide based catalyst
View Patent ↗Process for the activation of a supported chromium oxide based catalyst in a fluidized bed activation reactor which has a catalyst bed being fluidized by a fluidization gas. The activation includes treatment at temperatures above 500° C., in which in an initial stage, where there is an initial temperature increase, the fluidization velocity (Vf1) of the fluidization gas is maintained below 6.5 centimeters per second (cm/sec) until the temperature inside the activation reactor reaches at least 200° C., and the fluidization gas is then brought to a value (Vf2) which is at least 1 cm/sec higher than Vf1.
1. Process for the activation of a supported chromium oxide based catalyst in a fluidised bed activation reactor which comprises a catalyst bed being fluidised by a fluidisation gas, said activation including treatment at temperatures above 500° C., wherein
(i) in an initial stage in which there is an initial temperature increase, the fluidisation velocity (Vf1) of the fluidisation gas is maintained below 6.5 centimeters per second (cm/sec) until the temperature inside the activation reactor reaches at least 200° C., and
(ii) said fluidisation gas is then brought to a value (Vf2) which is at least 1 cm/sec higher than Vf1.
2. Process according to claim 1 wherein the fluidisation gas velocity during the initial stage of the activation process is maintained below 5.5 cm/sec.
3. Process according to claim 1 wherein the control of the fluidisation gas velocity during the initial stage of the activation process is maintained until the temperature inside the activation reactor reaches 250° C.
4. Process according to claim 3 wherein the control of the fluidisation gas velocity during the initial stage of the activation process is maintained until the temperature inside the activation reactor reaches 400° C.
5. Process according to claim 1 wherein the fluidisation gas velocity during the initial stage of the activation process is maintained above 1.5 cm/s.
6. Process according to claim 1 wherein the fluidisation gas used during the initial stage of the activation process is selected from the group consisting of an inert gas, an oxidising gas and sequentially an inert gas followed by an oxidising gas.
7. Process according to claim 6 wherein an inert gas is used as fluidisation gas during the initial activation stage.
8. Process according to claim 1 wherein the fluidisation gas velocity Vf2 of the fluidisation gas used during the consecutive stage of the activation process is at least 1.5 cm/sec higher than Vf1.
9. Process according to claim 1 wherein the fluidisation gas used during the consecutive stage of the activation process is selected from the group consisting of an inert gas, an oxidising gas and sequentially an inert gas followed by an oxidising gas.
10. Process according to claim 1 wherein said consecutive stage includes thermal treatments with holding temperatures higher than 600° C.
11. Process according to claim 1 wherein the fluidisation gas velocity Vf2 is at least 6 cm/s.
12. Process according to claim 1 wherein the fluidisation gas velocity Vf2 is maintained below 12 cm/s.
13. Process according to claim 1 wherein the duration of the initial fluidisation stage lasts at least 10 minutes.
14. Process according to claim 1 wherein the duration of the consecutive fluidisation stage lasts at least 10 minutes.
15. Process according to claim 1 wherein the consecutive stage comprises at least two separate thermal treatment steps wherein
the first step consists in bringing the catalyst from the initial stage under an inert atmosphere to a temperature comprised between 600 and 900° C. and then keeping the catalyst during a holding time of less than or equal to 8 hours under an inert atmosphere at a temperature comprised between 600 and 900° C., and
the second step consists in the treatment of the catalyst coming from step 1 under an oxidizing atmosphere at a temperature comprised between 400 and 700° C. during a holding time comprised between 2 and 10 hours, and
wherein the maximum temperature of step 2 is always lower than the maximum temperature of step 1 and wherein the difference between the maximum temperature of step 1 and the maximum temperature of step 2 is comprised between 50 and 250° C.
16. Process according to claim 1 wherein the supported chromium oxide based catalyst is a titanium modified supported chromium oxide based catalyst.
17. Process according to claim 1 wherein the catalyst support is a refractory oxide support selected from the group consisting of silica, alumina, aluminophosphate, metal oxides, and combinations thereof.
18. Process according to claim 1 wherein the catalyst support is a spherical and/or spheroidal refractory oxide support.
19. Process according to claim 1 wherein the chromium oxide based catalyst contains 0.3 to 2% by weight of chromium (this weight being expressed with respect to the weight of final supported catalyst).
20. Process according to claim 1 wherein the chromium oxide based catalyst contains between 0.5 and 5% by weight of titanium (this weight being expressed with respect to the weight of final supported catalyst).
21. Process according to claim 1 wherein the supported chromium oxide based catalyst is not subjected to any other fluidisation gas treatment before the initial claimed stage and/or consecutive claimed stage(s).
22. Activated supported chromium oxide based catalyst obtained according to claim 1 .
23. Process according to claim 1 wherein the fluidisation gas velocity (Vf2) is at least 7 cm/sec.
24. Process according to claim 1 wherein the duration of the initial fluidisation stage lasts at least 1 hour.
25. Process according to claim 1 wherein the duration of the consecutive fluidisation stage lasts at least 1 hour.