BIFUNCTIONAL CATALYST

Abstract

A bifunctional catalyst for conversion of oxygenates, said catalyst comprising zeolite, alumina binder and Zn, wherein the Zn is present at least partly as ZnAl.sub.2O.sub.4.

Claims

1. A bifunctional catalyst comprising zeolite, alumina binder and Zn, wherein the Zn is present at least partly as ZnAl.sub.2O.sub.4.

2. Bifunctional catalyst according to claim 1, where the bifunctional catalyst is a catalyst for conversion of oxygenates.

3. Bifunctional catalyst according to claim 1, wherein the zeolite is ZSM-5 or ZSM-11.

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 % zeolite, 5-40 wt % ZnAl.sub.2O.sub.4, 0-40 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.

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

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

9. Bifunctional catalyst according to claim 1, wherein the Zn concentration is 3-25 wt %, such as 7-15 wt % such as 8-12 wt % in the catalyst.

10. Bifunctional catalyst according to claim 1, wherein Zn is present in the binder as mainly ZnAl.sub.2O.sub.4.

11. Bifunctional catalyst according to claim 1, wherein the amount of Zn present in the binder phase as ZnAl.sub.2O.sub.4 corresponds to at least 50% ZnAl.sub.2O.sub.4 relative to the total amount of Zn in the binder phase.

12. Bifunctional catalyst according to claim 1, wherein the amount of Zn present in the binder phase as ZnAl.sub.2O.sub.4 corresponds to at least 95% ZnAl.sub.2O.sub.4 relative to the total amount of Zn present in the binder phase.

13. Bifunctional catalyst according to claim 1, wherein the amount of Zn present in the binder phase as ZnO corresponds to up to 10% ZnO.

14. Bifunctional catalyst according to claim 1, wherein Zn in the zeolite is present as at least one of ZnO, Zn(OH)+ and Zn++ in ion exchange positions.

15. Bifunctional catalyst according to claim 1, wherein the total Zn content in the catalyst is 3-25 wt % Zn.

16. Bifunctional catalyst according to claim 1, wherein said catalyst is partly or fully spinelized.

17. Bifunctional catalyst according to claim 1, wherein the Zn content is substantially the same in its partly spinelized and fully spinelized form.

18. Bifunctional catalyst according to claim 1, wherein a fully spinelized form is obtained by heating a partly spinelized form at 300-550 C. in an atmosphere comprising steam.

19. A bifunctional catalyst according to claim 1, used in an oxygenate conversion process comprising: a conversion step wherein a feed stream comprising oxygenates such as methanol and/or DME is converted into a hydrocarbon stream rich in aromatics in presence of said bifunctional catalyst.

20. A bifunctional catalyst according to claim 1, wherein the oxygenate conversion process comprises: 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.

21. Method for producing a bifunctional catalyst comprising an alumina binder, zeolite and Zn, said method comprising the steps of impregnating an alumina/zeolite catalyst with a Zn-containing aqueous solution at least partly spinelizing the Zn impregnated alumina/zeolite catalyst by heating the impregnated alumina/zeolite catalyst to 300-650 C. for 0.25-7 h.

22. Method for producing a bifunctional catalyst comprising an alumina binder, zeolite and Zn, said method comprising the steps of impregnating a Zn compound or a solution of a Zn compound onto a zeolite or alumina/zeolite by mixing shaping said mixture by extrusion or pelletization at least partly spinelizing the Zn impregnated alumina/zeolite catalyst by heating the impregnated alumina/zeolite catalyst to 300-650 C. for 0.25-7 h.

23. Method according to claim 21, wherein the zeolite is a ZSM preferably H-ZSM-5.

24. Method according to claim 21, wherein the Zn aqueous solution is a Zn nitrate solution or a Zn acetate solution.

25. Method according to claim 21, wherein Zn impregnation and calcination and/or spinelization results in a total Zn content of 3-25 wt %, 8-15 wt % or 9-13 wt %, such more than 7 wt % Zn, more than 10 wt % Zn or 12 or more wt % Zn.

26. Method according to claim 21, wherein the Zn concentration is higher in the binder phase than in the zeolite phase.

27. Method according to claim 21, wherein the catalyst is further or fully spinelized by heating a partly spinelized form at 300-550 C. in an atmosphere comprising steam

28. A catalyst and method according to claim 1, where the selectivity to aromatics is 30-80%, as determined at 420 C., 20 bar, 10 mol % methanol and a WHSV of 1.6.

29. A catalyst and method according to claim 1, where the selectivity to CO.sub.x is 0-10% as determined at 420 C., 20 bar, 10 mol % methanol and a WHSV of 1.6.

Description

EXAMPLE 1: PREPARATION OF CATALYST

[0044] 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

[0045] 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.

[0046] 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.

[0047] 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.

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. Percentage of aromatics Aromatics in total hydro- selectivity regained after Zn content (wt %) carbon product (wt %) regeneration 5 52 90 10 51 95

EXAMPLE 3: STABILITY TOWARDS STEAMING

[0048] 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.

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 hydrocarbon Aromatics (wt %) in product (wt %), fresh hydrocarbon product, Zn content (wt %) catalyst steamed catalyst 5 52 28 10 51 36

EXAMPLE 4: METHANOL CRACKING VS. ZN CONTENT

[0049] 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.

[0050] 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.

[0051] 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.

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

[0052] 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.

[0053] 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.

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 Condition selectivity (%) 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