POROUS IRON-SILICATE WITH RADIALLY DEVELOPED BRANCH, AND IRON-CARBIDE/SILICA COMPOSITE CATALYST PREPARED THEREFROM

Abstract

The present invention provides an iron-carbide/silica composite catalyst that is highly reactive to a Fischer-Tropsch synthesis by firstly forming an iron-silicate structure having large specific surface area and well-developed pores through a hydrothermal reaction of an iron salt with a silica particle having a nanostructure, and then activating the iron-silicate structure in a high temperature carbon monoxide atmosphere. When using the iron-carbide/silica composite catalyst according to the present invention in the Fischer-Tropsch synthesis reaction, it is possible to effectively prepare liquid hydrocarbon with a high CO conversion rate and selectivity.

Claims

1. A porous iron-silicate with radially developed branches formed by a hydrothermal reaction of an aqueous solution containing an iron salt hydrate and a silica particle whose a structure has a role as a transformation template.

2. The porous iron-silicate of claim 1, which is termed by a hydrothermal reaction of an aqueous solution containing a silica particle and an iron salt hydrate in basic conditions.

3. The porous iron-silicate of claim 1, wherein the silica particle has a regular-shaped nanostructure.

4. A method of preparing a porous iron-silicate with radially developed branches, comprising the steps of: (i) heating a silica solution wherein a silica particle is mixed with a basic reagent; (ii) introducing an aqueous solution containing an iron salt hydrate to said heated silica solution; and (iii) decomposing a mixed solution of the iron salt hydrate and silica through a high-temperature hydrothermal reaction to form the porous iron-silicate.

5. The method of claim 4, wherein the silica particle has a surface area of 501000 m.sup.2/g and a pore volume of 0.2cm.sup.3/g.

6. The method of claim 4, wherein the basic reagent is sodium hydroxide and the amount of solid sodium hydroxide used is 0.5 to 2 times with respect to the weight of silica.

7. The method of claim 4, wherein the silica particle is a silica nanobead, a silica sol, or a silica structure having mesopores.

8. The method of claim 4, wherein the iron hydrate used in said Step (ii) is selected from the group consisting of iron (III) chloride hexahydrate, iron (II) chloride tetrahydrate, iron (III) nitrate nonahydrate, iron (III) sulfate hydrate, iron (II) perchlorate hydrate, and iron (II) sulfate hydrate.

9. The method of claim 4, wherein the hydrothermal reaction in said Step (iii) is carried out in an oil bath of 100 C. or higher by refluxing the reactants for 124 hours.

10. The method of claim 4, wherein the porous iron-silicate obtained after said Step (iii) is centrifuged at a speed of 3,00010,000 rpm for 10100 minutes.

11. An iron-carbide/silica composite catalyst which is obtained by activating, through a high-temperature calcination, a porous iron-silicate of claim 1 with radially developed branches formed by a hydrothermal reaction of an aqueous solution containing an iron salt hydrate and a silica particle whose a structure has a role as a transformation template.

12. The composite catalyst of claim 11, wherein the iron-carbide/silica composite catalyst is obtained by activating the porous iron-silicate under a carbon monoxide-containing atmosphere.

13. (canceled)

14. The composite catalyst of claim 11, wherein the size of iron-carbide particle loaded on the silica shell is 10100 nm.

15. The composite catalyst of claim 11, wherein the activated iron-carbide/silica catalyst is immersed in an organic passivation solvent for preventing oxidation.

16. The composite catalyst of claim 15, wherein the organic passivation solvent is ethanol or mineral oil.

17. The composite catalyst of claim 11, wherein the calcination temperature is in the range of 350 C.400 C.

18. A method of preparing a liquid hydrocarbon from synthetic gas, which comprises a first step of applying to a reactor, (a) a porous iron-silicate with radially developed branches formed by ahydrothermal reaction of an a ueous solution containing an iron salt hydrate and a silica particle whose a structure has a role as a transformation template or (b) an iron-carbide/silica composite catalyst which is obtained by activating, through a high-temperature calcination, a porous iron-silicate with radially developed branches thrilled by a hydrothermal reaction of an aqueous solution containing an iron salt hydrate and a silica particle whose a structure has a role as a transformation template; a second step of optionally activating the porous iron-silicate or the composite catalyst to form an iron-carbide/silica composite catalyst under a carbon monoxide-containing gas atmosphere; and a third step of carrying out a Fischer-Tropsch synthesis reaction on the synthetic gas in the presence of the activated iron-carbide/silica composite catalyst.

19. The method of claim 18, wherein the synthetic gas is carbon monoxide and hydrogen, or carbon monoxide and hydrogen with which one or more impurities selected from the group consisting of inert gas, methane and carbon dioxide are mixed.

20. The method of claim 18, wherein the synthetic gas is injected to the reactor in a gas hourly space velocity (GHSV) of 3.042.0 NL/g(cat)/hr in the third step.

21. The method of claim 18, wherein the reaction temperature of the third step is 250350 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 is a schematic diagram for the preparation of iron-carbide/silica nano-catalyst which is used for the Fischer-Tropsch synthesis according to an example of the present invention.

[0073] FIG. 2 is a flow chart of the preparation of the iron-carbide/silica catalyst in which the highly active iron-carbide nanoparticle is loaded, according to an example of the present invention.

[0074] FIG. 3 shows SEM images (a, b) of the silica nanobead support which is prepared by the stober method, and TEM images (c-d) and XRD spectrum (e) of the porous iron-silicate obtained therefrom.

[0075] FIG. 4 shows TEM images at a low magnification (a) and at a high magnification (b) of the iron-silicate particle using 1.4 eq. of iron salt with respect to silica.

[0076] FIG. 5 shows TEM images at a low magnification (a) and at a high magnification (b) of the iron-silicate particle using 2.8 eq. of iron salt with respect to silica.

[0077] FIG. 6 shows TEM images of the porous silica MCF structure (a) and the iron-silicate particle (b) obtained from the same.

[0078] FIG. 7 shows TEM images at a low magnification (a) and at a high magnification (b) of the iron-silicate particle using the commercial LUDOX silica particle.

[0079] FIG. 8 shows TEM images at a low magnification (a) and at a high magnification (b) of the iron-silicate particle prepared by using silica nanobead support and iron nitrate hydrate.

[0080] FIG. 9 shows TEM images at a low magnification (a) and at a high magnification (b) of the iron-silicate particle prepared by using silica nanobead support and iron sulfate hydrate.

[0081] FIG. 10 shows TEM images (a, b) and XRD spectrum (c) of the iron-carbide/silica catalyst activated from the iron-silicate powder according to Example 1 of the present invention.

[0082] FIG. 11 shows a TEM image of the iron-carbide/silica catalyst activated from the iron-silicate powder according to Example 2 of the present invention.

[0083] FIG. 12 shows the CO conversion with the time lapse in the Fischer-Tropsch synthesis reaction using the iron-carbide/silica catalyst according to Example 6 of the present invention.

[0084] FIG. 13 shows the product selectivity with the time lapse of the iron-carbide/silica catalyst according to Example 6 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0085] Hereinafter, the present invention will be explained more in detail. However, these examples are provided only for illustration of the present invention, and should not be construed as limiting the present invention.

Example 1

Synthesis of Branch-Shaped Iron-Silicate Structure Using Silica Nanobead

[0086] The silica nanoparticle capable of being used as the silica support were prepared by the well known stober method.

[0087] In order to obtain the spherical silica particle first, to a solution containing 1 L of ethanol and 80 mL of distilled water were added 40 mL of ammonium hydroxide solution (28%) and 100 mL of tetraethyl orthosilicate (TEOS), which was then stiffed for 2 hours. The silica particle obtained after 2 hours was precipitated through centrifugation and then dispersed in ethanol. In order to minimize the amount of ammonia that can be remained even after washing, two or more washings were performed by repeating the dispersion-precipitation process using ethanol. Thus washed silica particle was sufficiently dried in a vacuum oven of which temperature was set to 50 C.

[0088] The scanning electron microscopy (SEM) images of thus obtained silica particles were shown in FIG. 3(a) and (b). From the analysis results, it was confirmed that silica particles having the size of 220 nm were produced.

[0089] Next, 70 mL of distilled water, 1.0 g of sodium hydroxide and 1.0 g (16.6 mmol) of thus obtained silica particles were added together to a 250 mL 2-neck round bottomed flask, and stirred under air atmosphere while raising the temperature to 100 C. Thereafter, a solution of 2.3 g (11.6 mmol) of iron chloride hydrate (FeCl.sub.2.4H.sub.2O) dissolved in 30 mL of distilled water, which had been prepared in advance, was injected to the silica solution heated to 100 C., and refluxed for 5 hours.

[0090] After 5 hours, the temperature was lowered to room temperature to stop the reaction. The cooled colloidal solution was precipitated by centrifugation at 10,000 rpm for 30 minutes and washed twice or more by repeating the dispersion-precipitation process using ethanol.

[0091] The transmission electron microscopy (TEM) images and XRD analysis results thus obtained were shown in FIG. 3(c), (d) and (e). From these analysis results, it was confirmed that silica and the iron salt were reacted during the hydrothermal reaction in the presence of a base to be converted to a branch-shaped iron-silicate structure.

Reference Example 1

Shape Change Depending on Increase of Iron Salt

[0092] The same procedure as Example 1 was carried out except that the amount of iron chloride hydrate (FeCl.sub.2.4H.sub.2O) used was changed to 4.6 g (23.1 mmol) and 9.3 g (46.8 mmol), respectively.

[0093] The result of experiment as depicted in FIG. 4(b) shows that the branch-shaped structure of the iron-silicate particle was maintained to a certain degree until 1.4 eq. of iron salt was used with respect to silica. However, as shown in FIG. 5, when the amount iron salt was significantly increased to 2.8 eq. with respect to silica, the branch-shaped structure was destroyed and some agglomeration of particles was observed.

Example 2

Synthesis of Branch-Shaped Iron-Silicate Structure Using Porous Silica MCF Structure

[0094] In order to obtain the porous silica MCF as the silica support, first, 8.0 g of pluronic P123(EO.sub.20PO.sub.70EO.sub.20, Aldrich) was well dissolved and dispersed in 300 g of distilled water. To this solution were added 12 g of 1,3,5-trimethylbenzene (TMB or mesitylene) and 300 g of 1.6 M HCl, which was then stirred for 1 hour at 50 C. Then, 17.7 g of TEOS was added and the mixture was further stirred for 20 hours at 50 C., which was then transferred to a polypropylene (P.P) container and sealed with a stopper. It was introduced into an oven of which temperature was set to 100 C. and aged for 24 hours. After aging, it was cooled to room temperature, washed with distilled water, ethanol and acetone in the order, and dried at room temperature. Finally, the white powder thus obtained was calcined for 8 hours under air atmosphere at 500 C. to synthesize MCF. The structure of MCF thus obtained could be analyzed through the TEM image as shown in FIG. 6(a) to confirm the degree of pore formation, and it was confirmed that pores in the level of 30 nm were well formed.

[0095] Next, in order to obtain the branch-shaped iron-silicate particle, 70 mL of distilled water, 1.0 g of sodium hydroxide and 1.0 g of thus obtained MCF powder were added together to a 250 mL 2-neck round bottomed flask, and stirred under air atmosphere while raising the temperature to 100 C. Thereafter, a solution of 2.3 g of iron chloride hydrate (FeCl.sub.2.4H.sub.2O) dissolved in 30 mL of distilled water, which had been prepared in advance, was injected to the silica solution heated to 100 C., and refluxed for 5 hours. After 5 hours, the temperature was lowered to room temperature to stop the reaction. The cooled colloidal solution was precipitated by centrifugation at 10,000 rpm for 30 minutes and washed twice or more by repeating the dispersion-precipitation process using ethanol. The TEM image of thus obtained iron-silicate particle was shown in FIG. 6(b).

[0096] From the analysis result, it was confirmed that MCF and the iron salt were reacted during the hydrothermal reaction in the presence of a base to be converted to a branch-shaped iron-silicate structure.

Example 3

Synthesis of Branch-Shaped Iron-Silicate Structure Using Commercial Silica Sol

[0097] 70 mL of distilled water, 1.0 g of sodium hydroxide and 2.5 mL (SiO.sub.2 1 g) of Ludox AS-40 (40 wt % suspension in H.sub.2O) solution commercially available from Sigma Aldrich Corporation were added together to a 250 mL 2-neck round bottomed flask, and stiffed under air atmosphere while raising the temperature to 100 C. Thereafter, a solution of 2.3 g of iron chloride hydrate (FeCl.sub.2.4H.sub.2O) dissolved in 30 mL of distilled water, which had been prepared in advance, was injected to the silica solution heated to 100 C., and refluxed for 5 hours. After 5 hours, the temperature was lowered to room temperature to stop the reaction. The cooled colloidal solution was precipitated by centrifugation at 10,000 rpm for 30 minutes and washed twice or more by repeating the dispersion-precipitation process using ethanol.

[0098] The TEM images of thus obtained iron-silicate particle were shown in FIG. 7(a) and (b). From the analysis results, it was confirmed that the silica sol and the iron salt were reacted during the hydrothermal reaction in the presence of a base to be converted to a branch-shaped iron-silicate structure.

Example 4

Synthesis of Branch-Shaped Iron-Silicate Structure Using Iron Nitrate Hydrate

[0099] 70 mL of distilled water, 1.0 g of sodium hydroxide and 1.0 g of the silica particle in the size level of 220 nm which had been prepared by the stober method of Example 1 were added together to a 250 mL 2-neck round bottomed flask, and stirred under air atmosphere while raising the temperature to 100 C. Thereafter, a solution of 2.9 g (7.2 mmol) of iron nitrate hydrate (Fe(NO.sub.3).sub.3.9H.sub.2O)instead of the iron chloride hydrate used in Examples 1 to 3dissolved in 30 mL of distilled water, which had been prepared in advance, was injected to the silica solution heated to 100 C., and refluxed for 5 hours. After 5 hours, the temperature was lowered to room temperature to stop the reaction. The cooled colloidal solution was precipitated by centrifugation at 10,000 rpm for 30 minutes and washed twice or more by repeating the dispersion-precipitation process using ethanol.

[0100] The TEM images of thus obtained iron-silicate particle were shown in FIG. 8. From the analysis results, it was confirmed that the silica particle and the iron salt were reacted during the hydrothermal reaction in the presence of a base to be converted to a branch-shaped iron-silicate structure.

Example 5

Synthesis of Branch-Shaped Iron-Silicate Structure Using Iron Sulfate Hydrate (FeSO.SUB.4..7H.SUB.2.O)

[0101] 70 mL of distilled water, 1.0 g of sodium hydroxide and 1.0 g of the silica particle in the size level of 220 nm which had been prepared by the stober method of Example 1 were added together to a 250 mL 2-neck round bottomed flask, and stirred under air atmosphere while raising the temperature to 100 C. Thereafter, a solution of 2.0 g (7.2 mmol) of iron sulfate hydrate (FeSO.sub.4.7H.sub.2O) dissolved in 30 mL of distilled water, which had been prepared in advance, was injected to the silica solution heated to 100 C., and refluxed for 5 hours. After 5 hours, the temperature was lowered to room temperature to stop the reaction. The cooled colloidal solution was precipitated by centrifugation at 10,000 rpm for 30 minutes and washed twice or more by repeating the dispersion-precipitation process using ethanol.

[0102] The TEM images of thus obtained iron-silicate particle were shown in FIG. 9. From the analysis results, it was confirmed that the silica particle and the iron salt were reacted during the hydrothermal reaction in the presence of a base to be converted to a branch-shaped iron-silicate structure.

Example 6

Preparation of Iron-Carbide/Silica Catalyst

[0103] The iron-silicate powder of Example 1 synthesized from the silica bead was thermally treated under carbon monoxide atmosphere at 400 C. for 4 hours (normal pressure, flow rate of 200 mL/min) in a tube type calcining oven to give an iron-carbide/silica composite catalyst.

[0104] As a result, as can be seen from the TEM images of FIG. 10(a) and (b), it was confirmed that small iron-carbide particles having the size of 2040 nm were loaded on silica when thermally treated at 400 C. In case of the catalyst sample finally obtained, the result of measurement by ICP (Inductively coupled plasma/optical emission spectrometry) for analyzing the content of iron ingredient showed that the content of Fe was about 21 wt %.

Example 7

Preparation of Iron-Carbide/Silica Catalyst

[0105] The iron-silicate powder of Example 2 synthesized from the silica MCF structure was thermally treated under carbon monoxide atmosphere at 350 C. for 4 hours (normal pressure, flow rate of 200 mL/min) in a tube type calcining oven to give an iron-carbide/silica composite catalyst.

[0106] As a result, as can be seen from the TEM image of FIG. 11, it was confirmed that very small iron-carbide particles having the level of 1020 nm were loaded on silica when thermally treated at 350 C.

Example 8

Fischer-Tropsch Synthesis Using Iron Carbide/Silica Catalyst

[0107] The Fischer-Tropsch synthesis reaction was carried out based on the iron-carbide/silica catalyst obtained in Example 6. The reactor was a fixed-bed reactor, and the reaction proceeded under an automated system that can be operated by PC (personal computer).

[0108] 0.3 g of the catalyst after dried was directly loaded in a reactor having the inner diameter of 5 mm. In order to prevent the production of hot spots due to the serious heat in the catalyst during the reaction, 3.4 g of glass bead was additionally introduced thereto.

[0109] Also, after the catalyst was loaded inside the reactor, it was further activated for 4 hours under carbon monoxide atmosphere (40 mL/min) of normal pressure to return some oxidized part on the surface of the catalyst to pure iron-carbide, prior to the main reaction.

[0110] Thereafter, the synthetic gas of which hydrogen to carbon monoxide ratio was maintained at 1:1 was injected to the reactor under the conditions of 15 atm of reaction pressure and 8.0 NL/G(cat)-h of gas hourly space velocity (GHSV) to carry out the Fischer-Tropsch synthesis reaction at 320 C.

[0111] The results of reaction for 90 hours thereafter were depicted in FIGS. 12 and 13. Very excellent results were obtained such that even though only a small amount of catalyst was used with respect to the reactant flow, the CO conversion was increased to the level of 70% as shown in FIG. 12, and the selectivity of liquid hydrocarbon (C.sub.5+) approached the level of 45% as shown in the product selectivity graph of FIG. 13.

[0112] It should be understood that the present invention is not intended to be unduly limited by the illustrative examples set forth herein, various modifications to this invention will become apparent to those skilled in the art without departing from the gist of the claimed invention, and such modifications are within the scope of the claims.