Catalyst system and process for preparing dimethyl ether

Abstract

The invention relates to a catalyst system and process for preparing dimethyl ether from synthesis gas as well as the use of the catalyst system in this process.

Claims

1. A catalyst system for a continuous synthesis gas-to-dimethyl ether process, comprising two spatially separated subsequent catalyst layers 1 and 2 in flow direction, the catalyst layers 1 and 2 having a volume ratio of from 9:1 to 1:9, catalyst layer 1 being formed of a packed bed of synthesis gas-to-methanol catalyst 1 particles or an admixture of catalyst 1 particles and inert 1 particles in a weight ratio of from 1:4 to 4:1, catalyst 1 particles comprising based on the total weight of catalyst 1 particles, which is 100 weight-%, 30 to 70 weight-% CuO, 10 to 30 weight-% ZnO, 10 to 30 weight-% Al.sub.2O.sub.3, the amount of ZrO.sub.2, if present, is in the range of from 0.5 to 5 weight-%, 0 to 7 weight-% of further additives, inert 1 particles comprising Al.sub.2O.sub.3, catalyst layer 2 being formed of a packed bed of an admixture of catalyst 1 particles and methanol-to-dimethyl ether catalyst 2 particles in a weight ratio of from 1:9 to 9:1, catalyst 2 particles being formed of an acidic aluminosilicate zeolite with a SiO2≥Al.sub.2O.sub.3 molar ratio of from 10 to 1500:1 of framework type MFI, comprising based on the total weight of catalyst 2 particles, which is 100 weight-%, 10 to 90 weight-% of at least one binder material, selected from Al.sub.2O.sub.3, SiO2, TiO2 and ZrO2, and 0.01 to 20 weight-% of copper, wherein the catalyst system is employed in one or more containments, which allow for the spatial separation of the subsequent catalyst layers 1 and 2, the containment having at least two sections in which the catalyst layers 1 and 2 are located, and the two sections being linked in a way that reactants can flow from catalyst layer 1 to catalyst layer 2.

2. The catalyst system according to claim 1, wherein catalyst layer 2 directly follows catalyst layer 1 or is separated from it by a layer of inert particles.

3. The catalyst system according to claim 1, wherein the catalyst 1 particles comprise, based on the total weight of catalyst 1 particles, which is 100 weight-%, 30 to 70 weight-% CuO, 10 to 30 weight-% ZnO, 10 to 30 weight-% Al.sub.2O.sub.3, 1 to 5 weight-% ZrO.sub.2, 0 to 7 weight-% of further additives.

4. The catalyst system according to claim 3, wherein the further additives comprise 1-7 weight-% of a lubricant.

5. The catalyst system according to claim 1, wherein the catalyst 2 particles comprise, based on the total weight of catalyst 2 particles, which is 100 weight-%, 30 to 80 weight-% of at least one acidic aluminosilicate of framework type MFI, 20 to 70 weight-% of at least one binder material selected from Al2O3, SiO2, TiO2 and ZrO2, and 0.01 to 20 weight-% copper.

6. The catalyst system according to claim 5, wherein the catalyst 2 particles comprise ZSM-5 aluminosilicate, Al.sub.2O.sub.3 as binder material and copper.

7. The catalyst system according to claim 1, wherein catalyst layer 2 is formed of a packed bed of an admixture of catalyst 1 particles and catalyst 2 particles in a weight ratio of from 3:2 to 7:3.

8. The catalyst system according to claim 1, wherein the catalyst 1 particles, catalyst 2 particles and inert 1 particles have each an average maximum particle diameter of from 0.5 to 5 mm.

9. The catalyst system according to claim 1, wherein the catalyst system is located in one or more tubular reactors.

10. The catalyst system according claim 1, wherein the catalyst layers 1 and 2 are present as packed beds and wherein the catalyst 1 particles, catalyst 2 particles and inert 1 particles are extrudates with an average maximum diameter of from 1 to 3.5 mm and a ratio of average length to average maximum diameter of from 0.5:1 to 10:1.

11. A process for producing dimethyl ether which comprises converting synthesis gas by contacting the synthesis gas with the catalyst system as claimed in claim 1.

12. A process for preparing dimethyl ether from synthesis gas, comprising administering synthesis gas to catalyst layer 1 in a catalyst system as defined in claim 1, and removing dimethyl ether-containing product gas from catalyst layer 2.

13. The process of claim 12, wherein temperature in catalyst layers 1 and 2 are maintained within a temperature range of from 200 to 400° C.

14. The process of claim 13, wherein catalyst layer 1 is maintained at a temperature within the range of from 260 to 280° C. and catalyst layer 2 is maintained at a temperature within the range of from 270 to 280° C.

Description

EXAMPLES

(1) The tubular reactor (inner diameter of 1″, total length of 2 meters) possesses two independent heating sections: heating section one from 0 to 0.8 meters, heating section two from 0.8 to 2 meters of the reactor length. Each section can be heated to a different temperature.

(2) The two catalyst layers are filled in such a way that the catalyst layer one is located within the heating section one and the catalyst layer two is located within the heating section two. The catalyst layer one has a weight of 270 g, a volume of 330 ml and a height of 0.6 m. The catalyst layer two has a weight of 430 g, a volume of 450 ml and a height of 0.95 m.

(3) Catalyst Layer 1

(4) The first catalyst layer comprises a 50:50 weight-% mixture of synthesis-gas-to-methanol catalyst and an inert material alpha alumina oxide. The synthesis-gas-to-methanol catalyst contains 58.3 weight-% CuO, 19.4 weight-% ZnO, 17.0 weight-% Al.sub.2O.sub.3, 2.4 weight-% ZrO.sub.2 and 2.9 weight-% graphite as lubricant for tableting to cylindrical shaped bodies with diameter and height of 3 mm.

(5) The synthesis-gas-to-methanol catalyst is prepared in the following way: A solution of copper, aluminium, zinc and zirconium salts, the atomic Cu:Al:Zn:Zr ratio being 1:0.5:0.3:0.03, is precipitated with a sodium hydroxide and carbonate solution at a pH of 9 and at from 25 to 50° C. The precipitate is filtered off the suspension and washed with deionized water until the washing water is free of nitrates. The precipitate is dried. The dried precipitate is calcined at from 250 to 800° C. to give a mixed oxide. The calcined material is mixed with 3 weight-% graphite powder. The mixture is formed to cylindrical tablets with a diameter and height of 3 mm.

(6) Catalyst Layer 2

(7) The second catalyst layer comprises an 70%:30% or 60%:40% weight-%-mixture of synthesis-gas-to-methanol catalyst just described and of methanol-to-dimethyl ether catalyst. The methanol-to-dimethyl ether catalyst contains 60 weight-% ZSM-5 zeolite as acidic component and 40 weight-% alumina oxide as binder for extrusion to cylindrical shaped bodies with diameter of 3.2 mm or 1.6 mm and a length of up to 3.2 mm. In addition, the cylindrical shaped bodies containing zeolite and alumina oxide can be impregnated with 0.5 weight-% copper.

(8) The methanol-to-dimethyl ether catalyst is prepared in the following way: Powder of ZSM-5 zeolite is mixed together with aluminium oxide hydroxide, the weight ratio being 1.5:1. Formic acid, carboxy methyl cellulose and water is added in necessary amount to obtain material that can be kneaded. After kneading the material is pressed through an extruder die. The extruded material is dried and afterwards calcined at from 400 to 700° C. In addition, the calcined material can be further impregnated with copper. Therefore, a copper salt solution is contacted with the extruded material in necessary amount to obtain extrudates with 0.5 weight-% copper. The copper loaded material is dried and then calcined at from 200 to 350° C.

(9) The described catalytic materials are used in the process for dimethyl ether synthesis from synthesis gas.

Comparative Example 1

(10) The reactor is filled with 947 ml of a 60%:40% weight-%-mixture of synthesis-gas-to-methanol catalyst and of methanol-to-dimethyl ether catalyst. The synthesis-gas-to-methanol catalyst contains 58.3 weight-% CuO, 19.4 weight-% ZnO, 17.0 weight-% Al.sub.2O.sub.3, 2.4 weight-% ZrO.sub.2 and 2.9 weight-% graphite as lubricant for tableting to cylindrical shaped bodies with diameter and height of 3 mm. The methanol-to-dimethyl ether catalyst contains 60 weight-% ZSM-5 zeolite as acidic component and 40 weight-% alumina oxide as binder for extrusion to cylindrical shaped bodies with diameter of 3.2 mm and a length of up to 3.2 mm.

(11) The catalyst bed is activated with hydrogen using commonly known activation procedures. Then, a flow of 4550 NL/h of synthesis gas which comprises 62 vol-% H.sub.2, 23 vol-% CO, 5 vol-% CO.sub.2 and 10 vol-% Ar is applied to the catalyst bed at 70 bar. Before entering the reactor with the catalyst bed the synthesis gas is preheated to 255° C. The heating section one of the reactor is heated to 255° C. and the heating section two of the reactor is heated to 270° C. The catalyst converts the synthesis gas to the main product dimethyl ether.

(12) The conversion of the synthesis gas to the products is monitored by gas chromatography by analysing the gas composition before and after the catalyst bed. The temperature inside the catalyst bed is measured with thermocouples located at different heights of the catalyst bed.

Example 2

(13) The reactor is filled with two catalyst layers. The catalyst layer one, which is located at the reactor inlet within the heating section one, comprises 330 ml of a 50%:50% weight-%-mixture of synthesis-gas-to-methanol catalyst and of an inert material alpha alumina oxide. The synthesis-gas-to-methanol catalyst contains 58.3% weight-% CuO, 19.4 weight-% ZnO, 17.0 weight-% Al.sub.2O.sub.3, 2.4 weight-% ZrO.sub.2 and 2.9 weight-% graphite as lubricant for tableting to cylindrical shaped bodies with diameter and height of 3 mm.

(14) The catalyst layer two, which is located directly behind the catalyst layer one within the heating section two, comprises 450 ml of an 70%:30% weight-%-mixture of synthesis-gas-to-methanol catalyst just described and of methanol-to-dimethyl ether catalyst. The methanol-to-dimethyl ether catalyst contains 60 weight-% ZSM-5 zeolite as acidic component and 40 weight-% alumina oxide as binder for extrusion to cylindrical shaped bodies with diameter of 1.6 mm and a length of up to 3.2 mm.

(15) The catalyst bed is activated with hydrogen using commonly known activation procedures. Then, a flow of 2205 NL/h of synthesis gas which comprises 62 vol-% H.sub.2, 23 vol-% CO.sub.3 5 vol-% CO.sub.2 and 10 vol-% Ar is applied to the catalyst bed at 50 bar. Before entering the reactor with the catalyst bed the synthesis gas is preheated to 255° C. Also the heating section one of the reactor with the catalyst layer one inside is heated to 255° C. The heating section two of the reactor with the catalyst layer two inside is heated to 257° C. The catalyst layer one partially converts the synthesis gas to methanol. The resulting gas, comprising methanol and unconverted synthesis gas, is subsequently directed to the catalyst layer two where the synthesis gas/methanol mixture is further converted to the main product dimethyl ether.

(16) The conversion of the synthesis gas to the products is monitored by gas chromatography by analysing the gas composition before and after the catalyst bed. The temperature inside the catalyst bed is measured with thermocouples located at different heights of the catalyst bed.

(17) It was found that the catalyst activity, demonstrated by conversion of synthesis gas, is less reduced over time if the catalyst bed in the reactor comprises a two layer composition (example 2) instead of one catalyst layer (comparative example 1).

Example 3

(18) The reactor is filled with two catalyst layers. The catalyst layer one, which is located at the reactor inlet within the heating section one, comprises 330 ml of a 50%:50% weight-%-mixture of synthesis-gas-to-methanol catalyst and of an inert material alpha alumina oxide. The synthesis-gas-to-methanol catalyst contains 58.3% weight-% CuO, 19.4 weight-% ZnO, 17.0 weight-% Al.sub.2O.sub.3, 2.4 weight-% ZrO.sub.2 and 2.9 weight-% graphite as lubricant for tableting to cylindrical shaped bodies with diameter and height of 3 mm.

(19) The catalyst layer two, which is located directly behind the catalyst layer one within the heating section two, comprises 450 ml of an 700%:3020% weight-%-mixture of synthesis-gas-to-methanol catalyst just described and of methanol-to-dimethyl ether catalyst. The methanol-to-dimethyl ether synthesis catalyst contains 60 weight-% ZSM-5 zeolite as acidic component and 40 weight-% alumina oxide as binder for extrusion to cylindrical shaped bodies with diameter of 1.6 mm and a length of up to 3.2 mm. In addition, the cylindrical shaped bodies containing zeolite and alumina oxide are impregnated with 0.5 weight-% copper.

(20) The catalyst bed is activated with hydrogen using commonly known activation procedures. Then, a flow of 2152 NL/h of synthesis gas which comprises 62 vol-% H.sub.2, 23 vol-% CO.sub.3 5 vol-% CO2 and 10 vol-% Ar is applied to the catalyst bed at 50 bar. Before entering the reactor with the catalyst bed the synthesis gas is preheated to 256° C. Also the heating section one of the reactor with the catalyst layer one inside is heated to 256° C. The heating section two of the reactor with the catalyst layer two inside is heated to 260° C. The catalyst layer one partially converts the synthesis gas to methanol. The resulting gas, comprising methanol and unconverted synthesis gas, is subsequently directed to the catalyst layer two where the synthesis gas/methanol mixture is further converted to the main product dimethyl ether.

(21) The conversion of the synthesis gas to the products is monitored by gas chromatography by analysing the gas composition before and after the catalyst bed. The temperature inside the catalyst bed is measured with thermocouples located at different heights of the catalyst bed.

(22) It was found that the catalyst activity, demonstrated by conversion of synthesis gas, is even less reduced over time if the dimethyl ether synthesis catalyst is impregnated with 0.5 weight-% copper (example 3) compared to the copper-free dimethyl ether synthesis catalyst (example 2).

(23) The catalyst deactivation in examples 1 to 3 was determined by measuring the relative catalyst activity in dependence on the time-on-stream in a range of from 25 to 400 hours. The relative catalyst activity was determined from the product gas composition. The following deactivation in %/h was obtained.

(24) Example 1: 0.04

(25) Example 2: 0.02

(26) Example 3: 0.001.

(27) The temperature in the catalyst bed in the heating section 2 was 265 to 282° C. in example 1, 270 to 278° C. in example 2 and 270 to 275° C. in example 3.