HYBRID SAPO-34/ZSM-5 CATALYST, ITS PREPARATION AND ITS USE

Abstract

Prepare a hybrid SAPO-34/ZSM-5 catalyst via sequential steps as follows: a) form a mixture consisting essentially of ZSM-5 as a sole source of silicon atoms, aluminum isopropoxide and a solution of orthophosphoric acid; b) combine the mixture with an aqueous solution of tetraethylammonium hydroxide to form a reaction mixture; and c) subject the reaction mixture to hydrothermal conditions for a period of time sufficient to convert the reaction mixture to a hybrid SAPO-34/ZSM-5 catalyst. Use the hybrid catalyst in converting an oxygenate (methanol and/or dimethyl ether) to an olefin.

Claims

1. A process for preparing a hybrid SAPO-34/ZSM-5 catalyst that comprises sequential steps as follows: a) forming a mixture consisting essentially of ZSM-5 as a sole source of silicon atoms, aluminum isopropoxide and a solution of orthophosphoric acid; b) combining the mixture with an aqueous solution of tetraethylammonium hydroxide to form a reaction mixture; and c) subjecting the reaction mixture to hydrothermal conditions for a period of time sufficient to convert the reaction mixture to a hybrid SAPO-34/ZSM-5 catalyst, the hydrothermal conditions comprising a temperature within a range of from 190 degrees centigrade ( C.) to 210 C. and autogenous pressure.

2. The process of claim 1, wherein ZSM-5 is present in a weight ratio of SAPO-34 to ZSM-5 within a range of from 96:4 to 85:15.

3. The process of claim 1, wherein ZSM-5 is present in a weight ratio of SAPO-34 to ZSM-5 within a range of from 94:6 to 90:10.

4. The process of claim 1, further comprising a sequential step d) that follows step c) wherein the hybrid SAPO-34/ZSM-5 catalyst undergoes calcination in an oxygen-containing atmosphere at a temperature within a range of from 550 C. to 650 C. for a period of time within a range of from one hour to 12 hours.

5. A process for converting an oxygenate feedstream that comprises methanol and dimethyl ether to at least one olefin comprising placing the oxygenate in operative contact with the catalyst prepared by the process of claim 1.

6. The process of claim 5, wherein the olefin is at least one of ethylene, propylene and butenes.

Description

COMPARATIVE EXAMPLE (CEX A)PHYSICAL MIXTURE

[0013] Physically mix 1.5 grams (g) fresh calcined SAPO-34 with 1.5 g calcined ZSM-5 (Si/Al2=280) in mortar and pestle. Subject the resulting catalyst to catalyst testing as provided below and summarize results in Table 1 below.

CEx BPhysical Mixture

[0014] Physically mix 1.5 grams (g) fresh calcined SAPO-34 with 0.17 g calcined ZSM-5 (Si/Al2=280) in mortar and pestle. Subject the resulting catalyst to catalyst testing as provided below and summarize results in Table 1 below.

CEx CPhysical Mixture

[0015] Physically mix 1.5 grams (g) fresh calcined SAPO-34 with 0.1 g calcined ZSM-5 (Si/Al2=280) in mortar and pestle. Subject the resulting catalyst to catalyst testing as provided below and summarize results in Table 1 below.

CEx DHybrid

[0016] With stirring, combine 8.2 g of aluminum isopropoxide (Al(OC.sub.3H.sub.7).sub.3) with a solution of 4.6 g of 85 wt. % orthophosphoric acid in 8.4 g of water to form a preliminary mixture. Add 3 g of unclacined ZSM-5 (NH4 form, SiO.sub.2/Al2O3=280) to the preliminary mixture and continue stirring for 30 minutes (min). With continued stirring, add 16.8 g of an aqueous solution of 35 wt % tetraethylammonium hydroxide (TEAOH) to form a reaction mixture. Place the reaction mixture in a stainless steel pressure vessel lined with polytetrafluoroethylene and place the vessel and its contents in an oven operating at a set point temperature of 200 C. at autogeneous pressure for 120 hours (hr). Recover a solid catalytic reaction product from the vessel contents by centrifugation. Wash the catalytic reaction product with water, then dry it in air at 100. C. Subject the catalytic reaction product to catalyst testing as provided below and summarize results in Table 1 below.

Example (Ex) 1Hybrid

[0017] Replicate CEx D, but change the amount of uncalcined ZSM-5 to 1 g. Summarize results in Table 1 below.

Ex 2Hybrid

[0018] Replicate CEx D, but change the amount of uncalcined ZSM-5 to 0.8 g. Summarize results in Table 1 below.

TABLE-US-00001 TABLE 1 Ex/CEx A B C D 1 2 SAPO-34:ZSM-5 ratio 50:50 90:10 94:6 50:50 90:10 94:6 (w/w) Cycle time (g of MeOH/g >48 5.9 9.0 >48 15.3 26.0 of catalyst Selectivity % Ethylene 14.9 36.6 29.9 13.6 38.1 34.9 @ 3.5 g Propylene 42.9 38.5 36.2 27.7 34.7 35.9 MeOH/g of Ethylene/ 0.3 0.9 0.8 0.5 1.1 1.0 catalyst Propylene ratio Butenes 19.1 16.9 16.1 11.6 19.0 20.0 Ethylene 76.9 92.0 82.2 52.9 91.8 90.8 through Butenes (%) Methane 9.7 0.9 2.1 17.1 1.2 1.5 through butane (%) Pentane 8.2 6.6 11.2 11.7 5.7 6.0 plus Hexane Aromatics 5.2 0.3 2.5 18.1 1.2 1.6

Catalyst Testing

[0019] Evaluate catalyst performance in a continuous flow micro reactor system (stainless steel tube ( inch by 6 inches (6.35 millimers (mm) by 15.24 centimeters (cm)) with 200 grams (g) of 20 mesh to 50 mesh (295 micrometers (um) to 853 um) catalyst sandwiched between two aliquots (2.5 inches (6.4 cm)) of 20 mesh to 50 mesh quartz chips at ambient pressure (nominally one atmosphere (101.32 kilopascals (KPa)). Before initiating feed of methanol, heat treat the catalyst at a temperature of 500 C. for two hours (hr) to remove adsorbed water and volatile organic materials from the catalyst in helium (20 ml/min flow rate). After the heat treatment, feed methanol into the reactor system at a rate of 6 microliters per minute (ul/min) using an ISCO pump (100 DM) together with a mixed gas of He and N.sub.2 (5 vol %) of 20 ml/min at standard temperature and pressure (STP) (nominally one atmosphere (101.32 kilopascals (KPa) and 25 C.)).

[0020] The data presented in Table 1 demonstrate that the hybrid catalyst of Ex 1 and Ex 2 shows an improved lifetime with higher C.sub.2/C.sub.3 olefin ratio while maintaining at least the same overall selectivity to C.sub.2 to C.sub.4 olefins compared to a physical mixture of SAPO-34 and ZSM-5 at the same ratio of SAPO-34 to ZSM-5 (CEx B and C).