PROCESS TO PREPARE PROPYLENE

Abstract

The invention is directed to a process to prepare propylene from a mixture of hydrocarbons having an olefin content of between 5 and 50 wt. % and boiling for more than 90 vol. % between 35 and 280 ?C or from a hydrocarbon feed comprising paraffins, naphthenics and/or aromatics and optionally up to 10 wt. % of olefins, by first contacting the feed with a low acidic density cracking catalyst in a reactor, separating propylene and subsequently contacting the residue with a high acidic density cracking catalyst in a reactor at a more elevated temperature, separating propylene and recycling the residue to first and second cracking reactors. Aromatics may be added to first and second cracking step to improve cycle length.

Claims

1. A process to prepare propylene from a mixture of hydrocarbons having an olefin content of between 5 and 50 wt. % and boiling for more than 90 vol. % between 35 and 280° C. or from a hydrocarbon feed comprising paraffins, naphthenics and/or aromatics, wherein the process comprises the following steps: (a) feeding the mixture of hydrocarbons, having a temperature between 450 and 750° C., to a reactor where the feed is contacted with a low acidic density cracking catalyst at a hydrocarbon partial pressure of below 3 bar and at a weight hourly space velocity of between 0.5 and 100 h.sup.−1; (b) isolating propylene the effluent of step (a) wherein a first high boiling fractions remains; (c) feeding all or part of the first high boiling fraction, having a temperature between 400 and 750° C., to a reactor where the first high boiling fraction is contacted with a high acidic density cracking catalyst at a hydrocarbon partial pressure of below 3 bar and at a weight hourly space velocity of between 0.5 and 100 h.sup.−1 and wherein the temperature of the mixture of hydrocarbons as fed to the reactor in step (a) is lower than the temperature of the first high boiling fraction as fed to the reactor in step (c); (d) isolating propylene from the effluent of step (c) wherein a second high boiling fractions remains; and (e) recycling all or part of the second high boiling fraction to step (a) and/or to step (c).

2. The process according to claim 1, wherein the weight hourly space velocity in step (a) is greater than the weight hourly space velocity in step (c).

3. The process according to claim 1, wherein part of the first high boiling fraction and/or all or part of the second high boiling fraction is contacted in a step (f) with hydrogen in the presence of an aromatic conversion catalyst as present in a reactor to obtain a fraction rich in aromatics and wherein all or part of the fraction rich in aromatics is recycled to step (c) and/or to step (f).

4. The process according to claim 3, wherein contacting in step (f) takes place at a temperature of between 400 and 700° C., at a weight hourly space velocity of between 0.1 and 50 h.sup.−1, a hydrocarbon partial pressure below 10 bar and a hydrogen partial pressure below 10 bars.

5. The process according to claim 3, wherein the aromatic conversion catalyst is a heterogenous catalyst comprising ZnO, a medium pore zeolite, and a binder.

6. The process according to claim 1, wherein the low acidic density catalyst is an amorphous catalyst.

7. The process according to claim 1, wherein the low acidic density catalyst in step (a) is a heterogenous catalyst comprising a medium or large pore zeolite having a silica to alumina ratio of between 2 and 1000.

8. The process according to claim 7, wherein the heterogenous catalyst comprises up to 70 wt. % ZSM-5, between 1-20 wt. % P.sub.2O.sub.5 and a binder.

9. The process according to claim 8, wherein the heterogenous catalyst comprises between 25 and 80 wt. % ZSM-5.

10. The process according to claim 1, wherein the weight hourly space velocity in step (a) is between 0.5 and 50 h.sup.−1.

11. The process according to claim 1, wherein the high acidic density catalyst in step (c) is a heterogenous catalyst comprising up to 80 wt. % ZSM-5 having a silica to alumina ratio of between 2 and 1000, between 1-20 wt. % P.sub.2O.sub.5 and a binder.

12. The process according to claim 7, wherein the silica to alumina ratio of the high acidic density catalyst is lower than the silica alumina ratio of the low acidic density catalyst.

13. The process according to claim 12, wherein the heterogenous catalyst comprises between 35 and 50 wt. % ZSM-5.

14. The process according to claim 1, wherein the weight hourly space velocity in step (c) is between 1 and 50 h.sup.−1.

15. The process according to claim 1, wherein the hydrocarbon partial pressure excluding aromatics in steps (a) and (c) is below 1 bar.

16. The process according to claim 1, wherein the mixture of hydrocarbons comprises a fraction as isolated from the effluent of a Fluid Catalytic Cracking process and/or isolated from the effluent of a steam cracker process.

17. The process according to claim 1, wherein the content of aromatic compounds in the hydrocarbon mixture as fed to the reactor in step (c) is between 10 and 80 wt. %.

18. The process according to claim 1, wherein part of the second high boiling fraction as obtained in step (d) is recycled to step (c) as a recycle stream.

19. The process according to 18, wherein in step (d) propylene and other low boiling compounds are isolated from the effluent of step (c) in a debutanizer distillation column which is operated under partial vacuum and wherein the second high boiling fraction is obtained as a bottom product of the debutanizer distillation column.

20. A process to prepare propylene from a hydrocarbon starting feed comprising paraffins, naphthenics and/or aromatics by adding aromatic compounds to the hydrocarbon starting feed resulting in an upgraded feed containing between 10 and 70 wt % and wherein the upgraded feed is catalytically cracked in the presence of an acidic cracking catalyst to propylene and other reaction products.

21. The process according to claim 20, wherein the upgraded feed contains between 20 and 50 wt % aromatic compounds.

22. A process to prepare propylene from a hydrocarbon feed comprising paraffins, naphthenics and/or aromatics wherein the process comprises the following steps: (aa) feeding the feed in admixture with a recycle stream and having a temperature of between 450 and 700° C. to a continuously operated reactor comprising a high acidic density cracking catalyst where the mixture is contacted with a high acidic density cracking catalyst at a hydrocarbon partial pressure, excluding aromatics, of below 3 bar and at a weight hourly space velocity of between 1 and 30 h.sup.−1, (bb) isolating propylene and optionally other low boiling compounds from the effluent of step (aa) wherein a high boiling fractions remains, (cc) recycling part of the high boiling fraction to the reactor of step (aa) wherein the total content of aromatics in the combined mixture as fed to the reactor in step (aa) is maintained at between 5 and 50 wt. %, optionally by additionally feeding an aromatic comprising further hydrocarbon mixture to the reactor.

23. The process according to 22, wherein in step (bb) propylene and other low boiling compounds are isolated from the effluent of step (aa) in a distillation column which is operated under partial vacuum and wherein the high boiling fraction is obtained as a bottom product of the distillation column.

24. The process according to claim 22, wherein the high acidic density catalyst in step (aa) is a heterogenous catalyst comprising up to 80 wt. % ZSM-5 having a silica to alumina ratio of between 2 and 1000, between 1-20 wt. % P.sub.2O.sub.5 and a binder.

25. The process according to claim 22, wherein part of the high boiling fraction is contacted in a step (dd) with hydrogen in the presence of an aromatic conversion catalyst as present in a reactor to obtain a fraction rich in aromatics and wherein all or part of the fraction rich in aromatics is recycled to step (aa) as the further hydrocarbon mixture.

26. The process according to claim 25, wherein contacting in step (dd) takes place at a temperature of between 400 and 550° C., at a weight hourly space velocity of between 0.5 and 5 h−1, a hydrocarbon partial pressure below 10 bar and a hydrogen partial pressure below 10 bars.

27. The process according to claim 25, wherein the aromatic conversion catalyst is a heterogenous catalyst comprising ZnO, a medium pore zeolite, and a binder.

28. A Process configuration suited to prepare propylene from an olefin comprising hydrocarbon mixture comprising: (i) one or more parallel operated first reactors comprising an amorphous heterogeneous cracking catalyst or a heterogeneous cracking catalyst comprising a medium or large pore zeolite having a silica to alumina ratio of between 1 and 1000; (ii) first distillation and/or flash separation units fluidly connected to an outlet of the one or more first reactors, and having at least an outlet for a propylene comprising fraction and an outlet for high boiling compounds; (iii) means to recycle the high boiling compounds from the outlet for high boiling compounds of the distillation and/or flash separation units to an inlet of the one or more parallel operated first reactors; (iv) one or more parallel operated second reactors comprising a heterogeneous cracking catalyst comprising up to 80 wt. % ZSM-5 having a silica to alumina ratio of between 2 and 1000, between 1-20 wt. % P.sub.2O.sub.5 and a binder, and wherein an inlet of the second reactors is fluidly connected to the outlet for high boiling compounds of the first distillation and/or flash separation unit; (v) second distillation and/or flash separation units fluidly connected to an outlet of the one or more second reactors of (iv), and having at least an outlet for a propylene comprising fraction and an outlet for high boiling compounds; and (vi) means to recycle the high boiling compounds from the outlet for high boiling compounds of the second distillation and/or flash separation units to the inlet of the one or more parallel operated first reactors and to the inlet of the one or more parallel operated second reactors.

29. The configuration according to claim 28, further comprising inlet means (vii) for a further hydrocarbon feed fluidly connected to the inlet of the one or more parallel second reactors.

30. The configuration according to claim 28, further comprising (viii) one or more parallel operated aromatic conversion reactors fluidly connected to the outlet for high boiling compounds of the second distillation and/or flash separation units and means to recycle part of the effluent of the aromatic conversion reactors to the inlet of the one or more first reactors, to the inlet of the one or more second reactors and to the inlet of the aromatics conversion reactors.

31. The configuration according to claim 30, wherein the aromatic conversion reactors have an inlet for hydrogen and have a bed of a heterogeneous catalyst comprising ZnO, a medium pore zeolite, and a binder.

Description

EXAMPLE 1

[0061] To a pilot plant fixed bed reactor containing 1.5 grams of a fixed bed catalyst at a WHSV of 30 h.sup.−1 a FCC naphtha boiling between 20 and 206° C. and having the composition as listed in Table 1 was fed. The temperature in the reactor was 600° C.

[0062] ZSM-5 crystal with SAR 30 (CBV 3024E, ex Zeolyst) was mulled in a 55/45 wt/wt. mixture with alumina (ex Sasol) and extruded to prepare a formed mass. The extruded mass was dried at 120° C. overnight and calcined for 3 hours in flowing air at 600° C. The calcined extrudates were impregnated to incipient wetness with phosphoric acid and then dried at 120° C. overnight and calcined for 3 hours at 600° C. in flowing air.

TABLE-US-00001 TABLE 1 Total Normal Paraffin 4.4 % wt Total Iso Paraffin 31.1 % wt Total Saturated Naphthene 6.9 % wt Total Unsaturated Naphthene 3.9 % wt Total Normal Olefin 12.3 % wt Total Iso Olefin 19.8 % wt Total Di Olefin 0.2 % wt Total Aromatic 21.4 % wt Total 100.0 % wt

[0063] The composition of the reaction products are listed in Table 2.

Example 2

[0064] Example 1 was repeated except that 20 wt % of the feed was replaced by toluene. This resulted in that the total conversion (defined as: (the mass production of H2,C1-C4 hydrocarbons and delta aromatics)/(mass feedstock)*100%) dropped from 22 wt % to 19 wt % and the conversion of the FCC naphtha itself increased from 22 wt % to 24 wt %. The addition of toluene illustrates the advantageous effect of a recycle containing aromatics to the cracking reactor. In Example 1 the conversion for the feed as is was 22%. In Example 2 the conversion was the absolute conversion on total feed basis was 19%, or 24% conversion on the FCC naphtha part of the feed. Product selectivities were not affected by the addition of the aromatics, as is shown by the results reported in table 2.

TABLE-US-00002 TABLE 2 Reaction products Example 1 Example 2 (wt % of the C1-C4 Feed fraction + delta FCC naphtha plus aromatics) FCC naphtha 20 wt % toluene CH4 1% 1% C2+ 1% 1% C2= 16%  16%  C3+ 4% 3% C3= 42%  43%  iC4+ 1% 1% nC4+ 1% 1% iC4= 9% 9% nC4= 15%  15%  aromatics 10%  10%  Total Coke yield 0.13 wt % 0.08 wt %

Example 3

[0065] Example 1 was repeated for about 3000 minutes (50 hours) except that the feed is now hexane and the WHSV was 60 h.sup.−1. The conversion of the feed in time is presented by the black circles (w/o aromatics) in FIG. 1.

Example 4

[0066] Example 3 was repeated except that 20 wt % of the feed was replaced by toluene. The conversion of the feed in time is presented by the open circles (w/aro) in FIG. 1. In FIG. 1 it is shown that the conversion of the crackable part of the feed (hexanes) was initially lower when toluene was added. Example 4 with toluene showed substantially improved stability and the catalyst deactivation with time on stream due to coking of the catalyst was significantly reduced. The addition of toluene did not negatively affect product selectivities of propylene (for both experiments around 35%) and butylenes (for both experiments around 20-24%).

Example 5

[0067] To a pilot plant fixed bed reactor containing 3 grams of a fixed bed catalyst described in example 1 at a WHSV of 10 h.sup.−1 a non-olefinic feed having the composition as listed in Table 3 and boiling between 20 and 220° C. was fed during about 1200 minutes. The temperature in the reactor was 600° C. The conversion in time is shown as the black circles (1st pass) in FIG. 2.

TABLE-US-00003 TABLE 3 compounds Wt % Total Normal Paraffins 23 Total Iso Paraffins 44 Total Naphthenes 23 Total Olefins 0 Total Aromatics 10 Xylenes 3.3 C9 aromatics 6.7 Total 100

Example 6

[0068] Example 5 was repeated wherein part of the reactor liquid effluent was recycled to the reactor thereby substituting part of the feed such that the feed now consisted of 80 wt % recycle and 20 wt % fresh feed. The recycle contained 2 wt % olefins. The conversion in time is shown as the open circles (recycle) in FIG. 2.

[0069] FIG. 2 shows that the total conversion (of total combined feed to the reactor) is higher when part of the liquid effluent is recycled to the reactor. The selectivities to the desired C3 and C4 olefins were not influenced in any significant manner when examples 5 and 6 were compared.