Process for the (co-)polymerisation of olefins

Abstract

Process for the polymerization or copolymerization of olefins by bringing the olefins into contact with a catalyst under polymerization or copolymerization conditions in a reactor containing a charge powder. The process includes, prior to introducing the catalyst into the reactor, introducing a scavenger into the reactor which reacts with catalyst poison present. The scavenger is added to the reactor until the charge powder contains a remaining amount of scavenger of between 0.1 and 2.5 moles per ton of charge powder.

Claims

1. Process for the polymerisation or copolymerisation of olefins by bringing the said olefins into contact with a catalyst under polymerisation or copolymerisation conditions in a reactor comprising a charge powder, which process comprises, prior to the introduction of the catalyst into the reactor, the introduction of a scavenger into the reactor which reacts with catalyst poison present, wherein the scavenger is added to the reactor until the charge powder comprises a remaining amount of scavenger comprised between 0.1 and 2.5 moles per ton of charge powder.

2. Process for the polymerisation or copolymerisation of olefins by bringing the said olefins into contact with a catalyst under polymerisation or copolymerisation conditions in a reactor, which process comprises, prior to the introduction of the catalyst into the reactor, the introduction of a scavenger into the reactor which reacts with catalyst poison present, wherein the scavenger is added such that the level in the reactor of the product of decomposition of said scavenger and catalyst poison is controlled.

3. Process for the polymerisation or copolymerisation of olefins by bringing the said olefins into contact with a catalyst under polymerisation or copolymerisation conditions in a reactor, which process comprises, prior to the introduction of the catalyst into the reactor, the introduction of a scavenger into the reactor which reacts with catalyst poison present, wherein the addition of the scavenger is performed as a series of sequential injections of scavenger, and said injections are continued until the increase in level in the reactor of the product of decomposition of said scavenger and catalyst poison during an individual addition of the scavenger is less than the expected amount of the product of decomposition corresponding to a complete reaction of all the scavenger added with poison.

4. Process for the polymerisation or copolymerisation of olefins by bringing the said olefins into contact, under polymerisation or copolymerisation conditions in a reactor system, which process comprises, prior to the introduction of the catalytic system in the reactor system: i) the introduction of a scavenger into the reactor system which reacts with the catalyst poison present, and ii) subsequently introducing a catalyst poison into the reactor system'wherein the catalyst poison is water, and the scavenger addition is performed after the introduction of the charge powder into the reactor.

5. Process according to claim 1 wherein the catalyst poison is water.

6. Process according to claim 1 wherein the scavenger is selected from the group consisting of trialkylaluminium compounds, hydrides, chlorides or alcoholates of alkylaluminium, other trialkyl metal compounds, aluminoxanes and mixtures thereof.

7. Process according to claim 1 wherein the reactor is a gas phase reactor.

8. Process according to claim 1 wherein a cocatalyst is used in combination with the catalyst, the cocatalyst being an organometallic compound.

9. Process according to claim 1 wherein the principal olefin is ethylene and/or propylene.

10. Process according to claim 2 wherein the catalyst poison is water.

11. Process according to claim 2 wherein the scavenger addition is performed after the introduction of the charge powder into the reactor.

12. Process according to claim 2 wherein the remaining amount of scavenger (unreacted) is comprised between 0.1 and 2.5 moles per ton of charge powder.

13. Process according to claim 2 wherein the scavenger is selected from the group consisting of trialkylaluminium componds, hydrides, chlorides or alcoholates of alkylaluminium, other trialkyl metal compounds, aluminoxanes and mixtures thereof.

14. Process according to claim 2 wherein the reactor is a gas phase reactor.

15. Process according to claim 2 wherein a cocatalyst is used in combination with the catalyst, the cocatalyst being an organometallic compound.

16. Process according to claim 2 wherein the principal olefin is ethylene and/or propylene.

17. Process according to claim 3 wherein the catalyst poison is water.

18. Process according to claim 3 wherein the scavenger addition is performed after the introduction of the charge powder into the reactor.

19. Process according to claim 3 wherein the remaining amount of scavenger (unreacted) is comprised between 0.1 and 2.5 moles per ton of charge powder.

20. Process according to claim 3 wherein the scavenger is selected from the group consisting of trialkylaluminium compounds, hydrides, chlorides or alcoholates of alkylaluminium, other trialkyl metal compounds, aluminoxanes and mixtures thereof.

21. Process according to claim 3 wherein the reactor is a gas phase reactor.

22. Process according to claim 3 wherein a cocatalyst is used in combination with the catalyst, the cocatalyst being an organometallic compound.

23. Process according to claim 3 wherein the principal olefin is ethylene and/or propylene.

24. Process according to claim 4 wherein the remaining amount of scavenger (unreacted) is comprised between 0.1 and 2.5 moles per ton of charge powder.

25. Process according to claim 4 wherein the scavenger is selected from the group consisting of trialkylaluminium compounds, hydrides, chlorides or alcoholates of alkylaluminium, other trialkyl metal compounds, aluminoxanes and mixtures thereof.

26. Process according to claim 4 wherein the reactor is a gas phase reactor.

27. Process according to claim 4 wherein a cocatalyst is used in combination with the catalyst, the cocatalyst being an organometallic compound.

28. Process according to claim 4 wherein the principal olefin is ethylene and/or propylene.

29. Process according to claim 1 wherein the scavenger is added to the reactor until the charge powder comprises a remaining amount of scavenger comprised between 0.3 and 2 moles per ton of charge powder.

30. Process according to claim 7 wherein the reactor is a fluidised bed gas phase reactor.

31. Process according to claim 12 wherein the remaining amount of scavenger (unreacted) is comprised between 0.3 and 2 moles per ton of charge powder.

32. Process according to claim 14 wherein the reactor is a fluidised bed gas phase reactor.

33. Process according to claim 19 wherein the remaining amount of scavenger (unreacted) is comprised between 0.3 and 2 moles per ton of charge powder.

34. Process according to claim 21 wherein the reactor is a fluidised bed gas phase reactor.

35. Process according to claim 24 wherein the remaining amount of scavenger (unreacted) is comprised between 0.3 and 2 moles per ton of charge powder.

36. Process according to claim 26 wherein the reactor is a fluidised bed gas phase reactor.

Description

EXAMPLE 1

(1) The example illustrates the possibility to scavenge water poison with triethylaluminium (TEA), the gas product decomposition resulting from the reaction to follow is the Ethane and one solid co-product is also generated, i.e. alumina dioxide.

(2) In the following, we illustrate how from the Gas Chromatography (GC) measurements (i.e. ppm ethane) and knowing the reactor conditions (pressure P and temperature T) we can determine the ethane pressure (P.sub.ETHANE) in the reactor and to conclude on the amount of triethylaluminium which has not reacted (EXCESS_TEA).

(3) For a commercial unit these two parameters, P.sub.ETHANE and EXCESS_TEA, are online monitored.

(4) In this present example, some precise values and order of magnitude are given for a pilot plant reactor.

(5) Relationship between Pressure Ethane calculation and moles of Ethane generated via the GC measurements

(6) GC Measurements

(7) Ethane detection in ppm under Standard Pressure and Temperature

(8) $\text{Equivalent:}\mathrm{ppm}=\frac{V_{\mathrm{ETHANE}}*{10}^6}{V_{\mathrm{GAS}}}=\frac{n_{\mathrm{ETHANE}}*{10}^6}{n_{\mathrm{GAS}}}$ wherein is the amount of gas in moles
Reactor Conditions Pressure range: P=10-20 bars Temperature range: T=75-110 C. Reactor gas loop volume: V.sub.loop=10 m.sup.3 Calculation: Gas molar volume,

(9) $V_m=\frac{R*T}{P}$ wherein R is the universal gas constant
Chemistry 1 moles of TEA reacts with 3 moles of water and generates 3 moles of ethane Relationship moles of Ethane generated (measured by GC) and Partial Ethane pressure (value calculated)

(10) $P_{\mathrm{ETHANE}}=\frac{R*T}{V_{\mathrm{loop}}}*n_{\mathrm{ETHANE}}=\frac{R*T}{V_{\mathrm{loop}}}*n_{\mathrm{GAS}}*\mathrm{ppm}*{10}^{-6}=\frac{R*T}{V_{\mathrm{loop}}}*\frac{V_{\mathrm{loop}}}{V_m}*\mathrm{ppm}*{10}^{-6}=\frac{R*T}{V_{\mathrm{loop}}}*\frac{V_{\mathrm{loop}}}{\frac{R*T}{P}}*\mathrm{ppm}*{10}^{-6}\text{Thus:}$$P_{\mathrm{ETHANE}}=P*\mathrm{ppm}*{10}^{-6}\mathrm{and}{P}_{\mathrm{ETHANE}}=\frac{R*T}{V_{\mathrm{loop}}}*n_{\mathrm{ETHANE}}$
TEA Excess Volume TEA introduced, V Concentration TEA, C=0.5 mol/L Theoretical pressure if all the TEA introduced is consumed:

(11) $P_{\mathrm{theoretical}}=\frac{R*T}{V_{\mathrm{loop}}}*3*V*C$

(12) 3 represents the stoechiometric coefficient of Ethane production for the TEA/Water reaction

(13) We can conclude on the molar TEA excess, Excess_TEA in the loop as described below:

(14) $\mathrm{Excess\_TEA}=\frac{1}{3}*\frac{V_{\mathrm{loop}}}{R*T}*\left(P_{\mathrm{theoretical}}-P_{\mathrm{ETHANE}}\right)=V*C-\frac{1}{3}\frac{V_{\mathrm{loop}}}{R*T}*P_{\mathrm{ETHANE}}$
Some Values 1 mole of TEA which reacts completely with 3 moles of water will generate 3 moles of Ethane: P=10 bar T=70 C..fwdarw.P.sub.ETHANE=8.67 mbar P=10 bar T=110 C..fwdarw.P.sub.ETHANE=9.55 mbar

EXAMPLE 2

(15) Pilot Scale Process Operation

(16) A fluidised bed reactor 74 cm in diameter was used for the gas phase co-polymerisations of olefins. In the illustrated example, the catalyst is a Metallocene silica supported, oxygen and water sensitive.

(17) The purification of the pilot plant loop and the polyethylene polymer bed, used as the charge bed, is a crucial step (in particular with Metallocene or chromium oxide type catalysts).

(18) After the pressure swing in the empty reactor to remove oxygen content below 1 ppm, firstly 2.3 moles of TEA are injected on the empty reactor and was consumed as proven by the measured GC values of ethane corresponding to the expected value for the complete stoichiometric reaction between TEA and water (clear indication that all of the TEA reacted with the poison). Secondly two TEA injections are performed after the start-up bed loading (as detailed hereafter); the powder bed has a weight of 0.75 ton. GC measurements were performed intermittently after each injection of scavenger in order to detect and calculate the content of gaseous product of decomposition (e.g. ethane when ethyl Al compounds are used as scavenger).

(19) Thus, two consecutive additions of 1 mole of TEA were added to the reactor bed. Said additions were performed under fluidised conditions (circulation loop) at a temperature of 70 C. and a pressure of 10 bar.

(20) A purge was also performed after each injection (and ethane measurement) in order to remove the ethane formed.

(21) The first injection lead to a measured GC value of ethane corresponding to the expected value for the complete stoichiometric reaction between TEA and water giving a clear indication that all of the TEA reacted with the poison. The second injection lead to a measured GC value of ethane which was less than the previously measured amount; its value was 55% of the previously measured GC value.

(22) At this point, the treatment was stoppedthe calculation of the remaining amount of TEA per ton of charge powder gave a value of 0.6 mole per ton of charge powderand the polymerisation proceeded by composing the reacting gas phase and the catalyst injections (in this instance a Metallocene silica supported catalyst).

(23) The start-up could be made without upsets and the polymerisation could proceed successfully without formation of agglomerates or any sign other of fouling.

(24) Similar procedures (with different number of injections and/or with different quantities of TEA added per injection) were repeated successfully several times during similar cleaning/start-up process with the same pilot plant catalyst system.

(25) In the absence of this procedure, unreliable start-ups were encountered, leading to longer durations of the start-up phases, fouling of the reactor, and even including occasional reactor shutdowns.

EXAMPLE 3

(26) Pilot Scale Process Operation

(27) A fluidised bed reactor 74 cm in diameter was used for the gas phase co-polymerisations of olefins. In the illustrated example, the catalyst is a Metallocene silica supported, oxygen and water sensitive.

(28) The purification of the pilot plant loop and the polyethylene polymer bed, used as the charge bed, is a crucial step (in particular with Metallocene or chromium oxide type catalysts).

(29) After the pressure swing in the empty reactor to remove oxygen content below 1 ppm, firstly 2.3 moles of TEA are injected on the empty reactor and was consumed as proven by the measured GC values of ethane (clear indication that all of the TEA reacted with the poison). Secondly several TEA injection are performed after the start-up bed loading,

(30) GC measurements were performed intermittently after each injection of scavenger in order to detect and calculate the content of gaseous product of decomposition (e.g. ethane when ethyl Al compounds are used as scavenger).

(31) Three consecutive additions of TEA were added to the reactor bed; the first two injections were each of 1 mole of TEA and the third injection was of 2.25 moles of TEA (as detailed hereafter); the powder bed has a weight of 0.75 ton. Said additions were performed under fluidised conditions (circulation loop) at a temperature of 70 C. and a pressure of 10 bar.

(32) A purge was also performed after each injection in order to remove the ethane formed.

(33) The first two injections lead to similar measured GC values of ethane corresponding to the expected value for the complete stoichiometric reaction between TEA and water giving a clear indication that all of the TEA reacted with the poison. The third injection lead to a measured GC value of ethane which was less than the previously measured amount; its value was 13.4% of the previously measured GC value.

(34) At this point, the TEA treatment was stoppedthe calculation of the remaining amount of TEA per ton of charge powder gave a value of 2.6 mole per ton of charge powder. Consequently, an amount of 2.25 moles of water was injected directly in the bed through the fluidisation grid supporting the bedthe calculation of the remaining amount of TEA per ton of charge powder gave a value of 1.6 mole per ton of charge powder. Then, the polymerisation proceeded by composing the reacting gas phase and the catalyst injections (in this instance a Metallocene silica supported catalyst).

(35) The start-up could be made without upsets and the polymerisation could proceed successfully without formation of agglomerates or any sign other of fouling.