WO2009094936A1

WO2009094936A1 - Catalyst for fischer-tropsch synthesis and its preparation method

Info

Publication number: WO2009094936A1
Application number: PCT/CN2009/070243
Authority: WO
Inventors: Guozhu Bian; Huaping Mao; Hui Han; Peijun Cong
Original assignee: Accelergy Shanghai R & D Center Co., Ltd.; Bp International Limited
Priority date: 2008-01-23
Filing date: 2009-01-21
Publication date: 2009-08-06
Also published as: CN101537359A; AU2009208263A1

Abstract

In a method of making an iron-based catalyst for Fischer-Tropsch Synthesis with elements Fe, Mn, K, and Cu, a Fe, Mn nitrates solution is mixed with an ammonium glycolate or ammonium citrate solution to obtain a slurry material. The slurry material is processed to obtain a dry material, which is then impregnated with K and Cu to obtain a material containing Fe, Mn, K and Cu, which is further processed to obtain an iron based catalyst. The catalyst prepared by the method when applied in Fischer-Tropsch-Synthesis reactions can help achieve a high CO conversion and low CO2 selectivity for the reactions.

Description

Catalyst for Fischer-Tropsch synthesis and its preparation method

FIELD OF THE INVENTION The present invention relates to a method of making iron based catalyst for

Fischer-Tropsch Synthesis.

BACKGROUND OF THE INVENTION

Fischer-Tropsch Synthesis is known as a reaction to convert synthesis gas ("syngas") to hydrocarbons. Catalysts are very important for Fischer-Tropsch Synthesis reactions in achieving high conversion of CO to hydrocarbons so that the reaction can be successfully commercialized. After years of development, iron based catalysts are widely used in Fischer-Tropsch Synthesis reactions because of their potent activity over wide temperature ranges.

Properties of iron-based catalysts are very sensitive to the process of making them. Therefore, continued efforts have been made to develop new processes for making iron-based catalysts with improve properties, such as selectivity to a certain product, activity or lifetime, etc.

SUMMARY OF THE INVENTION

In one aspect, embodiments of the present invention provide a method of making an iron-based catalyst including Fe, Mn, K, and Cu for Fischer-Tropsch

Synthesis. The method comprises mixing a solution including Fe and Mn nitrates with an ammonium glycolate or ammonium citrate solution at a neutral or weakly acidic pH to obtain a slurry material and processing the slurry material to obtain a dry material of substantially powder form. The dry material is subsequently calcined to obtain a calcined material, and potassium and copper are added to the calcined material by impregnation to obtain a catalyst precursor. The catalyst precursor is calcined to obtain the catalyst.

In another aspect, embodiments of the present invention provide a catalyst for Fischer-Tropsch Synthesis prepared by the above method. The catalyst comprises elements Fe, Mn, K, and Cu, wherein K and Cu loadings are about 1 wt% and 0.5 wt%, respectively. When applied in a Fischer-Tropsch Synthesis reaction under certain conditions, the catalyst is able to keep a high CO conversion and low CO₂ selectivity of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a method for making a catalyst in accordance with an embodiment of the invention;

FIG. 2 is a block diagram of a parallel reactor that can be used to test catalysts;

FIG. 3 is a chart illustrating activity data of catalysts prepared by using glycolic acid and reduced at a temperature of 27O⁰C;

FIG. 4 is a chart illustrating activity data of catalysts prepared by using glycolic acid and reduced at a temperature of 300⁰C; FIG. 5 is a chart illustrating activity data of catalysts prepared at different

H₂/CO conditions by using glycolic acid;

FIG. 6 is a chart illustrating activity data of catalysts prepared by using citric acid and reduced at a temperature of 27O⁰C;

FIG. 7 is a chart illustrating activity data of catalysts prepared by using citric acid and reduced at a temperature of 300°C;

FIG. 8 is a chart illustrating activity data of catalysts prepared at different H₂/CO conditions by using citric acid;

FIG. 9 is a chart illustrating activity data of catalysts prepared at a H₂/CO ratio of 1.0 by using citric acid; FIG. 10 is a chart illustrating activity data of catalyst prepared by using citric acid and applied in reactions at different reaction temperatures;

FIG. 11 is a chart illustrating activity data of catalysts prepared by using citric acid and reduced at different temperatures.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS In an embodiment, as shown in Figure 1, a method 100 of making a catalyst for Fischer-Tropsch Synthesis having elements Fe, Mn, K, and Cu comprises a Sol-Gel step 115, drying and decomposing step 120, first calcining step 125, K (potassium) element impregnating and drying step 130, Cu (copper) element impregnating and drying step 135, second calcining step 140, and pressing and crushing step 145. The Sol-Gel step 115 may further comprise solution preparation step 105 and solution mixing and aging step 110. Method 100 can be used to make catalysts with different Fe/Mn molar ratios and different K and Cu loadings. In one embodiment, catalysts with Fe/Mn molar ratios varying from 9:1 to 2:8 and K and Cu loadings respectively at about 1 wt% and 0.5 wt% are made using method 100.

In one embodiment, in the solution preparation step 105, an ammonium glycolate or ammonium citrate solution at a neutral or weakly acidic pH is employed. The ammonium glycolate or ammonium citrate solution may be prepared by mixing glycolic acid or citric acid with NH₄OH. For example, to make a catalyst with an Fe/Mn molar ratio of 9:1, a total 0.225 molar of iron and manganese nitrate, are dissolved in 100 ml deionized water to get a nitrate solution, and 34.9 g of 98% glycolic acid is added to about 40 ml of 25-28 wt% NH₄OH

(the molar ratio of the used glycolic acid to the used NH₃.H₂O is about 1 :1) to get an ammonium salt solution with a pH value of 6.5.

In the solutions mixing and aging step 110, the ammonium salt solution is added to the nitrate solution at a flux velocity of 100 ml/min, and during the process of adding, the solution is stirred under a stirring velocity of 100 rpm so as to obtain a mixture. Then the mixture is allowed to age for about 0.5-2 hours to obtain a slurry material.

In the drying and decomposing step 120, the slurry material can be dried in air at about 100⁰C to obtain a dried material, which is afterwards decomposed in air at 130~ 190 ° C to become a powder.

In the first calcining step 125, the decomposed powder can be calcined at 35O⁰C in flowing air for about 1 hour.

In the K element impregnating and drying step 130, a potassium carbonate deionized water solution with a predefined K concentration is prepared. The K concentration is determined by a desired value of K loading in the catalyst to be prepared. For example, for a desired value of K loading of 1 wt%, the amount of the deionized water can be 1.2 ml per each gram of the material from the first calcining step. For example, if there is lOOg of material obtained from the first calcining step 125, the amount of the deionized water used can be 120 ml. During impregnation, the calcined powder obtained from the step 125 is added into the potassium carbonate deionized water solution for about 1 hour, and then the mixture dried in air at HO⁰C for about 6 hours to get a dried material.

In the Cu element impregnating and drying step 135, a copper nitrate deionized water solution with a predetermined Cu concentration is prepared. The Cu concentration is determined by a desired value of Cu loading in the catalyst to be prepared. For example, for a desired value of Cu loading is 0.5 wt%, the amount of the deionized water is 1.2 ml per each gram of the material from the K element impregnating and drying step 130. During impregnation, the dried material obtained from the K element impregnating and drying step 130 is added into the copper nitrate solution for about 1 hour, and then the mixture is dried in air at 11O⁰C for about 16 hours to get a catalyst precursor.

In the second calcining step 140, the catalyst precursor can be re-calcined at 400⁰C in flowing air for about 4 hours. In the pressing and crushing step 145, the re-calcined material can be pressed under a pressure of 25 MPa, and then be crushed and sieved in order to obtain a catalyst with 20-40 mesh particle size.

Similarly, catalysts with different Fe/Mn molar ratios, such as Fe/Mn molar ratios of 7:3, 6:4, 5:5, 4:6, 3:7, and 2:8, can be prepared using method 100 by adjusting accordingly the iron and manganese nitrate concentration in the nitrate solution in the solution preparation step 105.

Alternatively, in another embodiment, in the solution preparation step 105, citric acid, instead of glycolic acid, is used. A molar ratio of the citric acid to the NH₃ 'H₂O can be about, for example, 1 : 1 , so as to get an ammonium salt solution at a neutral or weakly acidic pH.

In some embodiments, when a solution, such as the Fe, Mn nitrates solution or ammonium salt solution, is commercially available, the step to prepare such solution in method 100 can be omitted.

Parameters involved in the method can be adjusted according to actual situation. The term "at a neutral or weakly acidic pH" may mean that the value of pH can vary, for example, from 6 to 7. For calcining 1O g of catalyst, the flowing air can have a flow rate varying from 100 to 500 ml/min, such as 200 ml/min, 250 ml/min, 300 ml/min, 350 ml/min and 400 ml/min, etc. The time for K and Cu impregnation treatment can vary from 0.5-2 hours, such as 0.5 hour, 1 hour, 1.5 hours, and 2 hours, etc. The time for drying treatment can vary from 4 to 24 hours, such as 4 hours, 6 hours, 8 hours, 12 hours, 16 hours, 18 hours, and 20 hours, etc.

A series of catalysts (namely, "A"-series catalysts) with different Fe/Mn molar ratios (for example, Fe/Mn molar ratios of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, and 9:1) can be prepared using method 100 in which glycolic acid is used in preparing the nitrate solution. Another series of catalysts (namely, "B"-series catalysts) with different Fe/Mn molar ratios (for example, Fe/Mn molar ratios of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, and 9:1) can be prepared using method 100 in which citric acid is used in preparing the nitrate solution. In these catalysts with different Fe/Mn molar ratios, the K and Cu loadings are set at 1 wt% and 0.5 wt%, respectively. In one embodiment, the "A"-series catalysts include Al (Fe/Mn=2:8), A2 (Fe/Mn=3:7), A3 (Fe/Mn=4:6), A4 (Fe/Mn=5:5), A5 (Fe/Mn=6:4), A6 (Fe/Mn=7:3), and A7 (Fe/Mn=9:l), and the "B"-series catalysts include Bl (Fe/Mn=2:8), B2 (Fe/Mn=3:7), B3 (Fe/Mn=4:6), B4 (Fe/Mn=5:5), B5 (Fe/Mn=6:4), B6 (Fe/Mn=7:3), and B7 (Fe/Mn=9:l).

Fischer-Tropsch Synthesis experiments may be performed to test the properties of the prepared catalysts. The experiments can be performed in a parallel reactor. For example, as shown in Figure 2, a parallel reactor 200 developed by Accelergy Shanghai R&D Center Co., Ltd. can be used. The parallel reactor 200 comprises an input module 210, a reaction module 220, a real-time monitor module 230 and an analyzer module 240. The reaction module 220 comprises a plurality of reaction chambers or tubes 220-1, 220-2...220-n (where n is a positive integer). The reaction module 220 further comprises a device (not shown) for controlling reaction conditions in the reaction tubes. More information about the parallel reactor 200 can be obtained from Accelergy Shanghai R&D Center Co., Ltd., or from related publications. The catalysts may be reduced before they are tested in the reactors using conventional methods for catalysts reduction. During the experiments, different catalysts can be disposed in respective reaction tubes, and a predefined feed gas (e.g., H₂ + CO) is input into the reaction tubes by the input module 210, and the reaction conditions are controlled such that Fischer-Tropsch Synthesis reactions take place over the respective catalysts in the reaction tubes. The real-time monitor module 230 can be used to monitor processes of the Fischer- Tropsch Synthesis experiments, and the analyzer module 240 can be used to analyze products of the Fischer-Tropsch Synthesis experiments. .

Alternatively, a single tube reactor can be used instead of the parallel reactor.

In one set of experiments, the "A"-series catalysts are reduced in the parallel reactor under the conditions that: T=270°C, H₂/CO molar ratio (H₂/CO) =1.7, gas pressure in the reactor (P) is at atmospheric pressure, and gaseous hourly space velocity (GHSV) =2000h^"1. The catalysts after reduction are used in Fischer- Tropsch Synthesis experiments under the reaction conditions that: T=240°C, H₂/CO=1.7, P=2.0MPa, and GHSV=2000h-¹. Activity data of the different "A"-series catalysts, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 3 and listed in Table 1. As shown in Figure 3 and Table 1, CO conversions of the reactions using the catalysts Al, A5 and A6, respectively, reach a stable state in a short time (about 15-20 hours). Afterwards, the reactions using the catalysts A5 and A6 achieve higher CO conversions and lower CO₂ selectivity compared to the other A-series catalysts.

Table 1

In another set of experiments, the "A"-series catalysts are reduced in the parallel reactor under the conditions that: T=300°C, H₂/CO=1.7, P=atmospheric pressure, and GHSV=2000h^"1. The catalysts after reduction are used in Fischer- Tropsch Synthesis experiments under the reaction conditions that: T=240°C, H₂/CO=1.7, P=2.0MPa, and GHSV=2000h-¹. Activity data of the different "A"- series catalysts, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 4 and listed in Table 2. As shown in Figure 4 and Table 2, CO conversions of the reactions using the catalysts Al , A3, A4 and A6, respectively, reach a stable state in a short time (about 20-40 hours). Afterwards, the reaction using the catalyst A6 achieves higher CO conversion and lower CO₂ selectivity compared to the other A-series catalysts. Table 2

In yet another set of experiments, selected "A"-series catalysts: A4, A5 and A6 are reduced in the parallel reactor under the conditions that: T=270°C, H₂/CO=1.7, P=atmosρheric pressure, and GHSV=2000h^"1. The catalysts after reduction are used in Fischer-Tropsch Synthesis experiments under the reaction conditions that: T=240°C, H₂/CO=1.7 for the 1st 150 hours and H₂/CO =1.0 for the next 100 hours, P=2.0MPa, and GHSV=2000h^"1. Activity data of the catalysts, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 5. As shown in Figure 5, when the input of H₂/CO decrease from 1.7 to 1.0, the CO conversion of the reaction using the catalyst A6 remains stable, while the CO conversions of the reactions using the catalyst A4 and A5, respectively, significantly decrease.

In yet another set of experiments, the "B"-series catalysts are reduced in the parallel reactor under the conditions that: T=270°C, H₂/CO=1.7, P=atmospheric pressure, and GHSV=2000h^"1. The catalysts after reduction are used in Fischer- Tropsch Synthesis experiments under the reaction conditions that: T=240°C, H₂/CO=1.7, P=2.0MPa, and GHSV=2000h-¹. Activity data of the different "B"-series catalysts, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 6 and listed in Table 3. As shown in Figure 6 and Table 3, CO conversions of the reactions using the catalysts Bl, B2 and B5, respectively, reach a stable state in a short time (about 20-40 hours). The reaction using the catalyst B5 achieves higher CO conversion and lower CO₂ selectivity compared to the other B-series catalysts. Table 3

In yet another set of experiments, the "B"-series catalysts are reduced in the parallel reactor under the conditions that: T= 300⁰C, H₂/CO=1.7, P=atmospheric pressure, and GHSV=2000h^"1. The catalysts after reduction are used in Fischer- Tropsch Synthesis experiments under the reaction conditions that: T=240°C, H₂/CO=1.7, P=2.0MPa, and GHSV=2000h-¹. Activity data of the different "B"-series catalysts, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 7 and listed in Table 4. As shown in Figure 7 and Table 4, CO conversions of the reactions using the catalysts Bl, B2 and B3, respectively, reach a stable state in a short time (about 20-40 hours). The reaction using the catalyst B3 achieves higher CO conversion and lower CO₂ selectivity compared to the other B-series catalysts.

Table 4

In yet another set of experiments, selected "B"-series catalysts: B4, B5 and B6 are reduced in the parallel reactor under the conditions that: T=270°C, H₂/CO=1.7, atmospheric pressure, and GHSV=2000h^"1. The catalysts after reduction are used in Fischer-Tropsch Synthesis experiments under the reaction conditions that: T=240°C, H₂/CO=1.7 for the 1st 150 hours and H₂/CO=1.0 for the next 100 hours, P=2.0MPa, and GHSV=2000h^"1. Activity data of the different "B"-series catalysts, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 8. As shown in Figure 8, when the input of H₂/CO decrease from 1.7 to 1.0, the CO conversions of the reactions using the catalysts B4 and B5, respectively, remain stable, while the CO conversion of the reaction using the catalyst B6 significantly decreases.

In yet another set of experiments, selected "B"-series catalysts: Bl, B3, B6 and B7 are reduced in the parallel reactor under the conditions that: T=270°C, H₂/CO=1.0, atmospheric pressure, and GHSV=2000h^"1. The catalysts after reduction are used in Fischer-Tropsch Synthesis experiments under the reaction conditions that: T=240°C, H₂/CO=1.0, P=2.0MPa, and GHSV= 200Oh^"1. Activity data of the different "B"-series catalysts, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 9. As shown in Figure 9, CO conversion of the reaction using the catalyst B3 reaches a stable state in a short time (about 20-30 hours). In yet another set of experiments, selected catalyst B3 is reduced in the parallel reactor under the conditions that: T= 27O⁰C, H₂/CO=1.7, atmospheric pressure, and GHSV=2000h^"1. The catalyst after reduction is used in Fischer-Tropsch Synthesis experiments under different reaction temperatures of 21O⁰C, 225⁰C and 24O⁰C, while the other reaction conditions are same as that: H₂/CO=1.7, P=2.0MPa, and GHSV=2000h^"1. Activity data of the catalyst B3 with different reaction temperatures, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 10. As shown in Figure 10, the reaction with higher reaction temperature achieves higher CO conversion.

In yet another set of experiments, selected catalyst B3 is reduced in the parallel reactor under different reduction temperatures of 24O⁰C, 27O⁰C and 300°C, while the other reduction conditions are same as that H₂/CO=1.7, atmospheric pressure, and GHSV=2000h^"1. The catalysts after reduction are used in

Fischer-Tropsch Synthesis experiments under the reaction conditions that:

T=240°C, H₂/CO=1.0, P=2.0MPa, and GHSV= 200Oh^"1. Activity data of the catalysts with different reduction temperatures, regarding the relationship between the CO conversion and the reaction time, are plotted in Figure 11. As shown in Figure 11, the reaction using the catalyst with higher reduction temperature achieves higher CO conversion.

Crystalline-phase and BET- surface-area data of selected "A"-series catalysts: Al, A3, A5, A6 and A7 are listed in Table 5 and 6, respectively.

Table 5

Table 6

Crystalline-phase and BET-surface-area data of selected "B"-series catalysts: Bl, B3, B5, B6 and B7 are listed in Table 7 and 8, respectively. Table 7

Table 8

Claims

1. A method of making an iron-based catalyst including Fe, Mn, K, and Cu for Fischer-Tropsch Synthesis, comprising: mixing a solution including Fe and Mn nitrates with an ammonium glycolate or ammonium citrate solution at a neutral or weakly acidic pH to obtain a slurry material; processing the slurry material to obtain a dry material of substantially powder form; calcining the dry material to obtain a calcined material; adding potassium and copper to the calcined material by impregnation to obtain a catalyst precursor; and calcining the catalyst precursor.

2. The method according to claim 1, further comprising preparing the ammonium glycolate or ammonium citrate solution by dissolving glycolic acid or citric acid in an ammonia solution with a molar ratio of glycolic acid or citric acid to ammonia of about 1 :1.

3. The method according to claim 1, wherein the ammonium glycolate or ammonium citrate solution has a pH value of 6.5.

4. The method according to claim 1, wherein the step of mixing comprises aging for about 0.5 to about 2 hours.

5. The method according to claim 1, wherein processing the slurry material comprises centrifuging the slurry to obtain a precipitate, drying the precipitate to obtain a solid material and decomposing the solid material at 130 ⁰C-190 ⁰C.

6. The method according to claim 1, wherein processing the slurry material comprises calcining the slurry material in flowing air at 300~400°C.

7. The method according to claim 6, wherein the slurry material is calcined in flowing air at about 35O⁰C.

8. The method according to claim 1, wherein the catalyst precursor is calcined in flowing air at 350~450°C.

9. The method according to claim 8, wherein the catalyst precursor is calcined in flowing air at about 400°C.

10. The method according to claim 1, wherein the step of adding comprises: impregnating the calcined material by a potassium carbonate solution with a predefined concentration for a predefined time, and drying the solution to obtain a dried material; impregnating the dried material by a copper nitrate solution with a predefined concentration for predefined time, and then drying the solution to obtain the catalyst precursor.

11. The method according to claim 1, wherein the step of adding comprises: impregnating the calcined material by a copper nitrate solution with a predefined concentration for a predefined time, and drying the solution to obtain a dried material; and impregnating the dried material by a potassium carbonate solution with a predefined concentration for a predefined time, and then drying the solution to obtain the catalyst precursor.

12. A catalyst prepared by the method according to claim 1, with a K loading at about 1 wt%.

13. A catalyst prepared by the method according to claim 1, with a Cu loading at about 0.5 wt%.

14. A catalyst prepared by the method according to claim 1, comprising elements Fe, Mn, K, and Cu, wherein K and Cu loadings are about 1 wt% and 0.5 wt%, respectively.