MFI zeolite with microporous and mesoporous hierarchical structure, preparation method therefor, and catalytic use thereof

Abstract

The present invention relates to a method of preparing an MFI zeolite with a microporous and mesoporous hierarchical structure in which a non-benzene-based first structure-directing agent, which provides ordered microporous pore sizes and a framework of MFI zeolite seed crystals, and a second structure-directing agent containing one benzene ring and an ammonium ion, which functions as a mesopore-directing agent without interfering with the function of the first structure-directing agent, are simultaneously used; an MFI zeolite with a microporous and mesoporous hierarchical structure, which is prepared by the method, and a catalyst use thereof for a reaction of converting acetylene into an aromatic compound; and a method of preparing an aromatic compound from acetylene using the catalyst.

Claims

1. A method for preparing an MFI zeolite with a microporous and mesoporous hierarchical structure in which an ordered microporous MFI zeolite additionally has mesopores, the method comprising: a first step of preparing a first aqueous solution in which a non-benzene-based first structure-directing agent, providing ordered microporous pore sizes and a framework of MFI zeolite seed crystals, is dissolved in water; a second step of preparing a second(2) aqueous solution in which a cationic surfactant, as a second structure-directing agent, containing one benzene ring and an ammonium ion connected to a bivalent alkyl group or alkoxy group, is dissolved in water; a third step of mixing an aluminum precursor with the second aqueous solution to prepare a second′(2′) aqueous solution; a fourth step of sequentially adding a silica precursor and the second′ aqueous solution to the first aqueous solution to prepare a mixed solution; and a fifth step of hydrothermally crystallizing the mixed solution obtained in the fourth step to form the MFI zeolite.

2. The method of claim 1, wherein the non-benzene-based first structure-directing agent is tetraalkylammonium hydroxide having a C.sub.1-4 alkyl.

3. The method of claim 1, wherein the second structure-directing agent is a compound represented by Formula 1 below: ##STR00003## wherein, in Formula 1, X is Br, F, I, or Cl, L is —O— or a direct bond, and 1≤n≤6 is satisfied.

4. The method of claim 1, wherein the second structure-directing agent does not prevent the first structure-directing agent from providing a framework of MFI zeolite seed crystals of ordered microporous pore sizes, and serves as a mesopore-directing agent.

5. The method of claim 1, wherein the MFI zeolite with a microporous and mesoporous hierarchical structure is a cubic particle in which each side has a deviation of less than 10% in length.

6. The method of claim 1, wherein the MFI zeolite is a zeolite selected from the group consisting of ZSM-5, silicalite, TS-1, AZ-1, Bor-C, boracite C, encilite, FZ-1, LZ-105, monoclinic H-ZSM-5, mutenite, NU-4, NU-5, TSZ, TSZ-III, TZ-01, USC-4, USI-108, ZBH, and ZKQ-1B.

7. The method of claim 1, wherein the first structure-directing agent and the second structure-directing agent are used at a weight ratio of 1:(0.1 to 5).

8. The method of claim 1, wherein the silica precursor is tetraethyl orthosilicate (TEOS), glass water, fumed silica, or colloidal silica, and the aluminum precursor is sodium aluminate, aluminum isopropoxide, aluminum oxide, or aluminum hydroxide.

9. The method of claim 1, wherein the second structure-directing agent is benzyltrimethylammonium bromide (BTMAB).

10. The method of claim 9, wherein a molar ratio of tetraethyl orthosilicate as the silica precursor:sodium aluminate as the aluminum precursor:tetraalkylammonium hydroxide as the first structure-directing agent:benzyltrimethylammonium bromide as the second structure-directing agent:water is (30 to 35):(0.7 to 1.3):(5 to 10):(10 to 15):(1100 to 1200).

11. The method of claim 1, wherein the fifth step is performed at a temperature ranging from 150° C. to 250° C. for 12 hours to 48 hours.

12. An MFI zeolite with an ordered microporous and mesoporous hierarchical structure, in which an ordered microporous MFI zeolite additionally has mesopores, prepared by the method of claim 1.

13. The MFI zeolite of claim 12, wherein the non-benzene-based first structure-directing agent is tetraalkylammonium hydroxide having a C.sub.1-4 alkyl.

14. The MFI zeolite of claim 12, wherein the second structure-directing agent is a compound represented by Formula 1 below: ##STR00004## wherein, in Formula 1, X is Br, F, I, or Cl, L is —O— or a direct bond, and 1≤n≤6 is satisfied.

15. A method of converting acetylene, the method comprising: providing an acidic catalyst comprising the MFI zeolite of claim 12; and contacting acetylene with the acidic catalyst to produce aromatic compounds.

16. The method of claim 15, wherein the aromatic compounds are benzene, toluene, or xylenes.

17. The method of claim 15, further comprising a step of converting the aromatic compounds by transalkylation, hydrocracking, esterification, or a combination thereof to produce a product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features, and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 shows the results of observing the shape of the ZSM-5 zeolite (marked as HCZ-1) having a hierarchical structure according to the present invention by field emission scanning electron microscopy (FE-SEM), in which conventional ZSM-5 zeolite is used as a control group;

(3) FIG. 2 shows the XRD analysis results of the ZSM-5 zeolite (marked as HCZ-1) having a hierarchical structure according to the present invention, in which conventional ZSM-5 zeolite is used as a control group;

(4) FIG. 3 shows the adsorption amount of the ZSM-5 zeolite (marked as HCZ-1) having a hierarchical structure according to the present invention with respect to relative pressure, in which conventional ZSM-5 zeolite is used as a control group;

(5) FIG. 4 shows a conversion reaction of acetylene into an aromatic compound using the catalyst according to the present invention; and

(6) FIG. 5 schematically shows a crystal having an MFI structure into which a structure-directing agent is inserted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) Hereinafter, the present invention will be described in more detail with reference to Examples. However, these Examples are only illustrative of the present invention, and the scope of the present invention is not limited to these Examples.

Example 1: Preparation of ZSM-5 Zeolite with Hierarchical Structure

(8) 2.441 g of 41.7 wt % tetrapropylammonium hydroxide (TPAOH) was added to 8.388 g of water and stirred for 30 minutes to prepare a first solution. Additionally, 1.91 g of benzyltrimethylammonium bromide (BTMAB) was added to 3 g of water to prepare a second solution. Sodium aluminate (NaAlO2) was added to the second solution and mixed by stirring for 30 minutes. Tetraethyl orthosilicate (TEOS) and the second solution were sequentially added to the first solution to prepare a mixed solution. The mixed solution was stirred for about 3 hours until this solution became transparent. The mixed solution was hydrothermally synthesized at 190° C. for 24 hours by using an autoclave. The resultant was filtered and washed with distilled water and ethanol to obtain crystals. The obtained crystals were dried overnight at 110° C., and then sintered at 550° C. In this case, the reactants were used at a molar ratio of TEOS:NaAlO2:TPAOH:BTMAB:H2O of 32:1:8:13:1138. The shape of the synthesized ZSM-5 zeolite with a hierarchical structure was observed by field emission scanning electron microscopy (FE-SEM), and the results thereof are shown in FIG. 1. As shown in FIG. 1, the ZSM-5 zeolite with a hierarchical structure according to the present invention was formed in the shape of a regular cube, and thus this ZSM-5 zeolite was named HCZ-1 (hierarchical cubic zeolite-1).

Comparative Example 1: Preparation of Conventional ZSM-5 Zeolite

(9) A conventional ZSM-5 zeolite was prepared in the same manner as in Example 1, except that benzyltrimethylammonium bromide (BTMAB) was not used. The shape of the ZSM-5 zeolite prepared in this way was observed by FE-SEM, and the results thereof are shown in FIG. 1.

Example 2: Conversion of Synthesized Zeolite to Proton Form (H-Form)

(10) Since each of the zeolites synthesized according to Example 1 and Comparative Example 1 has a sodium-bonded form, the sodium-bonded form is required to be converted to a proton form in order to impart activity as a catalyst, and thus the two kinds of zeolites were treated as follows to be converted to a proton form.

(11) Specifically, the sodium-bonded zeolite prepared according to Example 1, Na-HCZ-1, was added to 30 mL of a 1 M aqueous ammonium sulfate solution, stirred at 70° C. for 24 hours, and then vacuum-filtered with distilled water to be converted into an ammonium form. The process was repeated twice. Then, the zeolite converted to an ammonium form was sintered at 500° C. for 3 hours or more to be converted to a proton form. The conventional zeolite prepared in a sodium form according to Comparative Example 1, conventional Na-ZSM-5, was also converted to a proton form in the same manner.

Experimental Example 1: Analysis of Characteristics of ZSM-5 Zeolite

(12) The zeolites prepared according to Example 1 and Comparative Example 1 and converted to a proton form according to Example 2 were analyzed by XRD, and the results thereof are shown in FIG. 2. As shown in FIG. 2, the ZSM-5 zeolite with a hierarchical structure according to the present invention, HCZ-1, includes an XRD peak inherent to ZSM-5 observed from conventional ZSM-5 zeolite, and this indicates that the microstructure of ZSM-5 is maintained.

(13) Moreover, the adsorbed quantities of the zeolites according to relative pressure were measured as shown in FIG. 3, and the BET surface areas and mesopore volumes of the zeolites were measured and given in Table 1 below. As shown in FIG. 3, the adsorbed quantity of the HCZ-1 having a hierarchical structure was greater than the adsorbed quantity of the conventional ZSM-5 zeolite, and the mesopore volume of the HCZ-1 having a hierarchical structure was remarkably increased as compared with the mesopore volume of the conventional ZSM-5 zeolite.

(14) TABLE-US-00001 TABLE 1 Conventional ZSM-5 HCZ-1 BET surface area (m.sup.2/g) 432 303 Mesopore volume (cm.sup.3/g) 0.089 0.425

Experimental Example 2: ZSM-5 Zeolite Catalytic Conversion of Acetylene

(15) The acetylene conversion reaction shown in FIG. 4 was performed using each of the zeolites prepared according to Example 1 and Comparative Example 1 and imparted with catalytic activity according to Example 2, and the results thereof were summarized in a series of tables below. The selectivity of a catalytic reaction, yield of each component, and yields of aromatic compounds and total products using the conventional ZSM-5 zeolite were given in order in FIGS. 2 to 4, and those for using the ZSM-5 zeolite (HCZ-1) having a hierarchical structure according to the present invention were given in FIGS. 5 to 7.

(16) Specifically, in the acetylene conversion reaction, acetylene (C.sub.2H.sub.2), hydrogen (H2), and nitrogen (N2) as an internal standard were reacted at 400° C. while being injected into a reactor filled with 0.3 g of each of the catalysts at flow rates of 10 sccm, 40 sccm, and 50 ccm, respectively.

(17) The values in the following tables are calculated as follows. For reference, TOS means time on stream.

(18) $C_2{H}_2\mathrm{input}=\frac{C_2{H}_2\mathrm{input}-C_2{H}_2\mathrm{output}}{C_2{H}_2\mathrm{input}}$$\mathrm{Selectivity}=\frac{X\mathrm{output}}{C_2{H}_2\mathrm{input}-C_2{H}_2\mathrm{output}}$

(19) In the equations, X indicates CH.sub.4, C.sub.2H.sub.6, C.sub.2H.sub.4, C.sub.8H.sub.5, C8H6, benzyl, toluene, or xylene as a product of the acetylene conversion reaction.
Yield of X=C.sub.2H.sub.2 conversion rate×selectivity of X

(20) TABLE-US-00002 TABLE 2 C.sub.2H.sub.2 TOS Conversion rate Selectivity (%) (min) (%) CH.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.4 C.sub.3H.sub.8 C.sub.3H.sub.6 benzene toluene xylene unknown 0 89.19 0.01 0.01 0.61 0 0.29 0.31 0.36 0.19 0.11

(21) TABLE-US-00003 TABLE 3 C.sub.2H.sub.2 TOS Conversion rate Yield (%) (min) (%) CH.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.4 C.sub.3H.sub.8 C.sub.3H.sub.6 benzene toluene xylene unknown 0 89.19 0.01 0.01 0.54 0 0.26 0.28 0.32 0.17 0.09

(22) TABLE-US-00004 TABLE 4 Temperature C2H2 Yield (%) and specimen TOS conversion rate Aromatic Total conditions (min) (%) compound products 400° C. ZSM-5 0 89.19 0.77 1.68 (Si/Al = 40)

(23) TABLE-US-00005 TABLE 5 C.sub.2H.sub.2 TOS Conversion rate Selectivity (%) (min) (%) CH.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.4 C.sub.3H.sub.8 C.sub.3H.sub.6 benzene toluene xylene unknown 0 84.01 0.01 0 0.67 0 0.21 0.16 0.28 1.33 0.17

(24) TABLE-US-00006 TABLE 6 C.sub.2H.sub.2 TOS Conversion rate Yield (%) (min) (%) CH.sub.4 C.sub.2H.sub.6 C.sub.2H.sub.4 C.sub.3H.sub.8 C.sub.3H.sub.6 benzene toluene xylene unknown 0 84.01 0 0 0.56 0 0.17 0.14 0.24 1.12 0.14

(25) TABLE-US-00007 TABLE 7 Temperature C2H2 Yield (%) and specimen TOS conversion rate Aromatic Total conditions (min) (%) compound products 400° C. HCZ-1 0 84.01 1.49 2.38 (Si/Al = 34)

(26) Comparing the results of Tables 2 to 4 with the results of Tables 5 to 7, when the ZSM-5 zeolite (HCZ-1) having a hierarchical structure according to the present invention was used, the yield of total products was increased, the yield of an aromatic compound was remarkably increased, and in particular, the selectivity and yield of xylene were increased seven-fold compared to when the conventional ZSM-5 was used.