Bifunctional catalyst comprising evenly distributed phosphorous

Abstract

A bifunctional catalyst for conversion of oxygenates, said bifunctional catalyst comprising zeolite, alumina binder, Zn and P, wherein P is evenly distributed across the catalyst.

Claims

1. A bifunctional catalyst having a center, a core, an outer surface, and a shell, the core surrounding the center and having a diameter of about 300 m, the shell having a width of about 300 m, the catalyst comprising a ZSM-5 zeolite, an alumina binder, Zn and P with a zeolite phase and a binder phase, wherein the P is present and is evenly distributed throughout the catalyst, such that the concentration of the P at the center of the catalyst is substantially the same as the concentration of the P at the core of the catalyst, the P has a concentration of 0.1-3 wt % at the core of the catalyst, and the Zn has a concentration above 3 wt % at the core of the catalyst, and wherein the total Zn content in the catalyst is 3-25 wt %, the alumina binder is an alumina binder or an alumina-based binder comprising mixtures of aluminum oxide and aluminum hydroxide and/or silica alumina, and wherein a P/Zn atomic ratio in the catalyst is at least 0.2.

2. Bifunctional catalyst according to claim 1, wherein the P concentration at the catalyst shell is between 0.1 wt %-10 wt %.

3. Bifunctional catalyst according to claim 1, wherein Zn is present as ZnAl.sub.2O.sub.4.

4. Bifunctional catalyst according to claim 1, wherein the catalyst is an extruded or pelletized catalyst.

5. Bifunctional catalyst according to claim 1, comprising 30-80 wt % ZSM-5, 3-40 wt % ZnAl.sub.2O.sub.4, 0.2-40% AlPO.sub.4, up to 40 wt % Al.sub.2O.sub.3, 0-10 wt % ZnO.

6. Bifunctional catalyst according to claim 1, wherein Zn is present in both zeolite and alumina binder phases.

7. Bifunctional catalyst according to claim 1, wherein a molar ratio of P/Zn is 0.2-5.

8. Bifunctional catalyst according to claim 1, wherein a molar ratio of P/Zn is substantially the same at the catalyst shell and the catalyst core.

9. Bifunctional catalyst according to claim 1, wherein the alumina binder further comprises silica.

10. Bifunctional catalyst according to claim 1, wherein the catalyst, by X-ray diffraction, does not contain free ZnO in the binder.

11. Bifunctional catalyst according to claim 1, wherein the Zn concentration is 5-25 wt % in the catalyst.

12. Bifunctional catalyst according to claim 1, wherein the binder comprises ZnAl.sub.2O.sub.4.

13. Bifunctional catalyst according to claim 12, wherein the molar amount of Zn present in the binder as ZnAl.sub.2O.sub.4 constitutes at least 50% of the total amount of Zn present in the binder.

14. Bifunctional catalyst according to claim 12, wherein the molar amount of Zn present in the binder as ZnAl.sub.2O.sub.4 constitutes at least 96% of the total amount of Zn present in the binder.

15. Bifunctional catalyst according to claim 1, wherein the binder comprises ZnO, and the molar amount of Zn present in the binder as ZnO corresponds to up to 10% ZnO relative to the total amount of Zn present in the binder.

16. Bifunctional catalyst according to claim 1, wherein the zeolite comprises Zn, and the Zn in the zeolite is present as ZnO, Zn(OH)+ and/or Zn++ in ion exchange positions.

17. Bifunctional catalyst according to claim 1, with a total Zn content in the catalyst of 8-15 wt %.

18. Bifunctional catalyst according to claim 1, wherein the binder comprises zinc, and the zinc and alumina in the binder of said catalyst are partly or fully spinelized.

19. Bifunctional catalyst according to claim 18, wherein the Zn and alumina content in the binder is substantially the same in its partly spinelized and fully spinelized form.

20. Bifunctional catalyst according to claim 19, wherein a fully spinelized form of Zn and alumina in the binder is obtained by heating a partly spinelized form at 300-550 C. in an atmosphere comprising steam.

21. A methanol conversion process using the bifunctional catalyst of claim 1, comprising: a conversion step wherein a feed stream comprising oxygenates is converted into a hydrocarbon stream rich in aromatics in presence of said bifunctional catalyst, and a separation step wherein the hydrocarbon stream rich in aromatics is separated into at least an aromatics rich product stream, a stream comprising water and a recycle stream.

22. A process according to claim 21, where the catalyst used in the process has a selectivity to aromatics of 30-80%, as determined at 420 C., 20 bar, 10 mol % methanol and a WHSV of 1.6.

23. A process according to claim 21, where the catalyst used in the process has a selectivity to CO, of 0-10% as determined at 420 C., 20 bar, 10 mol % methanol and a WHSV of 1.6.

Description

EXAMPLE 1: PREPARATION OF CATALYST

(1) A base catalyst containing 65 wt % H-ZSM-5 and 35% Al.sub.2O.sub.3 was prepared by mixing followed by extrusion following well known procedures. Upon calcination, samples of the base catalyst were impregnated with an aqueous solution containing zinc nitrate at different Zn concentrations. The resulting pore-filled extrudates were heated to 470 C. in air and kept at 470 C. for 1 h to obtain catalysts with various amounts of Zn.

EXAMPLE 2: CATALYST ACTIVITY AND REGENERATION

(2) Catalysts prepared by the procedure described in example 1 were subjected to conversion of methanol at 420 C. in an isothermal fixed bed reactor. N.sub.2 was used as an inert co-feed to obtain a methanol concentration of 7 mol % in the reactor inlet. The total pressure was 20 bar, and the space velocity (WHSV) of methanol was 2 h.sup.1.

(3) Zn/H-ZSM-5 catalysts suffer from reversible as well as irreversible deactivation. Deposition of carbon (coke) on the catalyst is responsible for reversible deactivation. In the example shown in table 1, the deactivated (coked) catalyst is regenerated by removal of the deposited carbon by combustion in a flow of 2% O.sub.2 (in N.sub.2) at 500 C.

(4) Due to irreversible deactivation, the catalyst did not fully regain its activity after regeneration. The results in table 1 show, that a catalyst containing 10% Zn is able to regain significantly more of its original activity after regeneration than a catalyst containing 5% Zn.

(5) TABLE-US-00001 TABLE 1 Catalyst activity after regeneration. Wt % of aromatics in hydrocarbon product is defined as the mass of aromatics relative to the total mass of hydrocarbons in the effluent stream. Aromatics in total Percentage of aromatics Zn content hydrocarbon product selectivity regained (wt %) (wt %) after regeneration 5 52 90 10 51 95

EXAMPLE 3: STABILITY TOWARDS STEAMING

(6) To simulate catalyst activity after extended operation under industrial conditions, the catalysts were subjected to methanol conversion after steaming under severe conditions. Methanol conversion was performed under the same conditions as in example 2. The results in Table 2 show that the catalyst containing 10% Zn retains significantly more of its original activity than the catalyst containing 5 wt % Zn after severe steaming.

(7) TABLE-US-00002 TABLE 2 Loss of catalyst activity upon severe steaming (100% steam for 48 h at 500 C. and 1 bar). Wt % of aromatics in hydrocarbon product is defined as the mass of aromatics relative to the total mass of hydrocarbons in effluent stream. Aromatics in Aromatics (wt %) in Zn content hydrocarbon product hydrocarbon product, (wt %) (wt %), fresh catalyst steamed catalyst 5 52 28 10 51 36

EXAMPLE 4: METHANOL CRACKING VS. ZN CONTENT

(8) Cracking (decomposition) of methanol/DME can occur via several mechanisms. For example, the acidic sites in the catalyst may catalyze cracking of DME to CH.sub.4, CO, and H.sub.2, while certain Zn species catalyze cracking of methanol to CO and H.sub.2. CO.sub.2 can be formed as a primary cracking product or indirectly via the water gas shift reaction.

(9) When methanol is converted over a catalyst containing Zn, part of the methanol is converted to CO.sub.x due to cracking, which results in lower yield of hydrocarbon products. Methanol conversion has been performed at 420 C., 20 bar, 10 mol % methanol (N2 balance), and a space velocity (WHSV) of 1.6.

(10) The results in Table 3 were obtained using catalysts prepared according to example 1. The results show that the cracking activity is highly dependent on the amount of Zn, i.e. higher Zn content leads to higher cracking activity.

(11) TABLE-US-00003 TABLE 3 CO.sub.x selectivity at different contents of Zn Zn content (wt %) CO.sub.x selectivity (%) 0 <0.1 3 2 5 4 10 9

EXAMPLE 5: CO.SUB.x .SELECTIVITY AFTER CALCINATION AND STEAMING

(12) A base catalyst containing 65% ZSM-5 and 35% Al.sub.2O.sub.3 was impregnated with aqueous zinc nitrate solution. The resulting pore filled extrudates were calcined in air and steam, respectively. Furthermore, the catalyst calcined in air was subjected to steaming after calcination. Methanol conversion over these catalysts was performed using the same conditions as in example 4.

(13) The results in table 4 show that the presence of steam during calcination of the impregnated catalyst or heating the catalyst in the presence of steam after calcination leads to lower selectivity to CO.sub.x. This observation may be rationalized by the fact that the presence of steam leads to formation of ZnAl.sub.2O.sub.4 rather than free ZnO in the binder phase.

(14) TABLE-US-00004 TABLE 4 CO.sub.x selectivity for catalysts containing 10% Zn, calcined in the presence of different amounts of steam CO.sub.x selectivity Condition (%) Calcined in air 9 Calcined in steam (500 C., 2 h) 2 Calcined in air, steamed after calcination (500 C., 5 h) 4 Calcined in air, steamed after calcination (500 C., 48 h) <0.1

EXAMPLE 6: PREPARATION OF CATALYST COMPRISING P

(15) A base catalyst containing 65 wt % H-ZSM-5 and 35% Al.sub.2O.sub.3 was prepared by mixing followed by extrusion following well known procedures. Upon calcination, samples of the base catalyst were impregnated with an aqueous solution of zinc nitrate and phosphoric acid. The resulting pore-filled extrudates were heated to 470 C. and kept at 470 C. for 1 h to obtain catalysts with 10 wt % Zn and 0, 1 and 3 wt % P, respectively.

EXAMPLE 7: STABILITY TOWARDS STEAMING

(16) To simulate catalyst activity after extended operation under industrial conditions, the catalysts of example 6 were subjected to methanol conversion after steaming under severe conditions. Methanol conversion has been performed at 420 C., 20 bar, 10 mol % methanol (N2 balance), and a space velocity (WHSV) of 1.6. The results in Table 5 show that the catalysts containing P retains significantly more of the original activity than the catalyst without P, resulting in a higher yield of aromatics.

(17) TABLE-US-00005 TABLE 5 Loss of catalyst activity upon severe steaming (100% steam for 48 h at 500 C. and 1 bar). Wt % of aromatics in hydrocarbon product is defined as the mass of aromatics relative to the total mass of hydrocarbons in the effluent stream. All catalysts contain 10 wt % Zn. Atomic P/Zn Aromatics in Aromatics (wt %) in P content ratio in the hydrocarbon product hydrocarbon product, (wt %) catalyst (wt %), fresh catalyst steamed catalyst 0 0 51 36 0.8 0.2 51 41 2.3 0.5 55 42

EXAMPLE 8: METHANOL CRACKING VS. P CONTENT

(18) The results in Table 6 were obtained using catalysts prepared according to example 6, with 10% Zn and different amounts of P. Methanol conversion was performed under the same conditions as in example 7. The results show that the cracking activity is suppressed when P is present in the catalyst. Noticeably, the catalyst containing a low amount of P (0.8 wt %), thus having a low atomic P/Zn ratio (0.2), showed the same activity in methanol cracking as the catalyst without P. On the other hand, the catalyst containing a higher amount of P (2.3 wt %), thus having a higher atomic P/Zn ratio (0.5), shows significantly lower activity for methanol cracking, i.e. formation of CO and CO.sub.2, indicating that a certain minimum amount of P is needed in order to suppress methanol cracking. The desired amount of P may depend on the Zn concentration.

(19) TABLE-US-00006 TABLE 6 CO.sub.x selectivity for fresh catalysts containing 10% Zn and different amounts of P Atomic P/Zn P content (wt %) ratio in the catalyst CO.sub.x selectivity (%) 0 0 9 0.8 0.2 9 2.3 0.5 2.5

EXAMPLE 9: CATALYST ACTIVITY EVENLY VS HAMMOCK

(20) Impregnation; Hammock P Distribution

(21) A base catalyst containing 65 wt % H-ZSM-5 and 35% Al.sub.2O.sub.3 was prepared by mixing followed by extrusion following well known procedures. Upon calcination, samples of the base catalyst were impregnated with an aqueous solution of zinc nitrate and phosphoric acid. The resulting pore-filled extrudates were heated to 470 C. and kept at 470 C. for 1 h to obtain the final catalyst. Concentrations profiles of Zn and P measured by SEM-WDX across an extrudate for this catalyst is shown in FIG. 1. A distinct hammock profile for the concentration of phosphorus across the extrudate is observed, meaning that the concentration (wt %) of phosphorus is significantly higher at the edge of the extrudates than it is in the center. In fact, almost no phosphorus has reached the center of the extrudate.

(22) Adding Phosphorus Prior to Extrusion; Even P Distribution

(23) A base catalyst containing H-ZSM-5 and Al2O3 in a 65/35 ratio, where phosphoric acid was added prior to extrusion was prepared. Upon calcination, samples of the base catalyst were impregnated with an aqueous solution of zinc nitrate. The resulting pore-filled extrudates were heated to 470 C. and kept at 470 C. for 1 h to obtain the final catalyst. Concentrations profiles of Zn and P across an extrudate for this catalyst is shown in FIG. 2. An even distribution of phosphorus across the extrudate is observed in this case. Fluctuations in the concentration are observed, but the concentration of phosphorus is not systematically lower in the centre of the extrudate. Applicant has also shown that an even distribution of P may also be achieved by impregnation for example by ammoniumdihydrogenphosphate.

(24) Catalytic Activity

(25) Prior to measuring the catalytic activity, catalyst samples were subjected to accelerated aging by steaming at 500 C. in 100% steam at a total pressure of 1 bar for 48 h. Methanol conversion has been performed at 420 C., 20 bar, 10 mol % methanol (N2 balance), and a space velocity (WHSV) of 1.6. As shown in FIG. 3, the catalyst with an even distribution of phosphorus shows much higher wt % of aromatics in the hydrocarbon product upon steam treatment. This is ascribed to the fact that that phosphorus is present throughout the extrudate, resulting in a much more effective catalyst.

(26) FIG. 1: Concentration profiles of Zn, P, and Al across an extrudate measured by SEM-WDX. The sample is prepared by co-impregnation with an aqueous solution of Zn(NO3)2 and H3PO4.

(27) FIG. 2: Concentration profiles of Zn and P across an extrudate measured by SEM-WDX. The carrier is prepared by adding H3PO4 prior to extrusion (along with ZSM-5, alumina etc.). The carrier is impregnated with an aqueous solution of Zn(NO3)2.

(28) FIG. 3: Aromatics wt % for steamed catalysts (500 C., 48 h). All catalysts are impregnated with 10 wt % Zn.