ZSM-23 ZEOLITE AND PREPARATION PROCESS AND USE THEREOF

Abstract

A ZSM-23 zeolite and a preparation process thereof are provided. The pore volume of mesopores having a pore size of 3-8 nm of the zeolite is 45-90% of the total pore volume of the zeolite. The zeolite has a relative crystallinity of 95-120% and a relative crystallinity retention of 95-100% after a hydrothermal treatment with steam for 2 hours at 600 C. The process for preparing the zeolite includes the following steps: (1) preparing or selecting a silicon source for preparing the ZSM-23 zeolite, such as amorphous silica; (2) performing an alkali treatment on the silicon source for preparing the ZSM-23 zeolite such as amorphous silica mentioned in step (1); and (3) preparing the ZSM-23 zeolite by using the alkali-treated amorphous silica as the silicon source. The ZSM-23 zeolite has a rich mesoporous structure and a good hydrothermal stability.

Claims

1. A ZSM-23 zeolite, which is characterized in that the pore volume of mesopores having a pore size of 3-8 nm, preferably 3-6 nm of the zeolite is 45-90%, preferably 50-85%, further preferably 55-81% of the total pore volume of the zeolite.

2. The ZSM-23 zeolite according to claim 1, which is characterized in that the zeolite has a relative crystallinity of 95-120%, and the zeolite has a relative crystallinity retention of 95-100% after a hydrothermal treatment with steam for 2 hours at 600 C.

3. The ZSM-23 zeolite according to claim 1, which is characterized in that the zeolite has a specific surface area of 300-430 m.sup.2/g, and a pore volume of 0.31-0.5 cm.sup.3/g, the specific surface area of micropores is 50-170 m.sup.2/g, and the specific surface area of mesopores is 150-310 m.sup.2/g, for example, the zeolite has a specific surface area of 320-405 m.sup.2/g, and a pore volume of 0.34-0.45 cm.sup.3/g, the specific surface area of micropores is 80-140 m.sup.2/g, and the specific surface area of mesopores is 261-295 m.sup.2/g.

4. A process for preparing the ZSM-23 zeolite according to claim 1, wherein the process comprises the following steps: (1) preparing or selecting a silicon source for preparing the ZSM-23 zeolite, such as amorphous silica; (2) performing an alkali treatment on the silicon source for preparing the ZSM-23 zeolite mentioned in step (1); (3) preparing the ZSM-23 zeolite by using the alkali-treated amorphous silica as the silicon source.

5. Use of the alkali-treated amorphous silica obtained in step (2) of the process of claim 4 as the silicon source in the preparation of the ZSM-23 zeolite.

6. The process or use according to claim 4, which is characterized in that in step (1), said amorphous silica has a specific surface area of 600-1300 m.sup.2/g, preferably 700-1200 m.sup.2/g; a pore volume of 0.6-1.3 cm.sup.3/g, preferably 0.7-1.2 cm.sup.3/g; and a pore diameter of 1-13 nm, preferably 2-10 nm.

7. The process or use according to claim 4, which is characterized in that in step (1), the preparation process of the amorphous silica is as follows: adding a silicon source to deionized water to be uniformly dispersed, and then adding a surfactant and stirring; adjusting the pH of the resulting solution to 1-5, preferably 1.5-4, and then heating it in a water bath for a period of time; filtering, washing, drying, and calcining to produce the amorphous silica.

8. The process or use according to claim 7, which is characterized in that in step (1), the silicon source is an inorganic silicon source, preferably one or more of water glass, silica sol, or white carbon black.

9. The process or use according to claim 7, which is characterized in that in step (1), the surfactant is one or more of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octodecyltrimethylammonium chloride, octodecyltrimethylammonium bromide.

10. The process or use according to claim 7, which is characterized in that in step (1), the molar ratio of said silicon source as SiO.sub.2 to the surfactant is 1:(0.02-0.3), preferably 1:(0.05-0.2).

11. The process or use according to claim 7, which is characterized in that in step (1), the molar ratio of said silicon source as SiO.sub.2 to the deionized water is 1:(30-300), preferably 1:(50-220).

12. The process or use according to claim 7, which is characterized in that in step (1), the temperature for heating is 30-80 C., preferably, 40-70 C., the time for heating is 0.5-8 hours, preferably, 3-6 hours.

13. The process or use according to claim 7, which is characterized in that in step (1), the temperature for drying is 80-120 C., the time for drying is 4-12 hours, the temperature for calcining is 500-600 C., the time for calcining is 2-6 hours.

14. The process or use according to claim 4, which is characterized in that in step (2), the alkali treatment involves adding the amorphous silica prepared in step (1) to an alkaline solution, heating and stirring.

15. The process or use according to claim 14, which is characterized in that in step (2), the alkali treatment is performed by using an inorganic alkali, and the inorganic alkali is one or more of sodium hydroxide, potassium hydroxide, or ammonia water.

16. The process or use according to claim 14, which is characterized in that in step (2), in the alkali treatment, the time for heating and stirring is 0.5-12 hours, preferably 2-8 hours; and the temperature for heating is 25-60 C., preferably 30-50 C.

17. The process or use according to claim 4, which is characterized in that in step (2), the molar ratio of the inorganic alkali as OH.sup. to the amorphous silica as SiO.sub.2 is 0.05-0.24, preferably 0.06-0.22.

18. The process according to claim 4, which is characterized in that in step (3), an alkali-treated amorphous silica is used as the silicon source, the silicon source is mixed with an aluminum source, an alkali source (MOH), a template agent (R) and water to form a gel, which is crystallized, filtered, washed, dried and calcined to produce the ZSM-23 zeolite.

19. The process according to claim 18, which is characterized in that in the gel, the molar ratio of the silicon source (as SiO.sub.2):the aluminum source (as Al.sub.2O.sub.3):the alkali source (as hydroxide):the template agent:H.sub.2O is 1:(0.003-0.03):(0.03-0.3):(0.05-2):(10-90); further preferably, in the gel, the molar ratio of the silicon source (as SiO.sub.2):the aluminum source (as Al.sub.2O.sub.3):the alkali source (as hydroxide):the template agent:H.sub.2O is 1:(0.005-0.02):(0.03-0.16):(0.08-1.6):(20-70).

20. The process according to claim 18, which is characterized in that the gel is crystallized at 150-200 C., preferably 170-180 C. for 24-96 hours, preferably 36-72 hours, filtered, washed, dried, and calcined to produce the ZSM-23 zeolite.

21. The process according to claim 18, which is characterized in that in step (3), the temperature for drying is 80-120 C., the time for drying is 4-12 hours, the temperature for calcining is 500-600 C., the time for calcining is 2-6 hours.

22. An alkali-treated amorphous silica, which is characterized in that: the specific surface area is 600-1300 m.sup.2/g, preferably 700-1200 m.sup.2/g; the pore volume is 0.6-1.3 cm.sup.3/g, preferably 0.7-1.2 cm.sup.3/g; the pore diameter is 1-13 nm, preferably 2-10 nm.

23. An alkali-treated amorphous silica, which is characterized in that: the specific surface area is 600-1300 m.sup.2/g, preferably 700-1200 m.sup.2/g; the pore volume is 0.6-1.3 cm.sup.3/g, preferably 0.7-1.2 cm.sup.3/g; the pore diameter is 1-13 nm, preferably 2-10 nm; wherein the alkali treatment is carried out according to step (2) of the process as described in claim 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 shows the XRD spectrum of the synthesized product of Example 1 of the present invention.

[0060] FIG. 2 shows the nitrogen gas physical adsorption diagram of the synthesized product of Example 1 of the present invention.

DETAILED DESCRIPTION

[0061] Analysis methods according to the present invention:

[0062] The specific surface area and the pore volume of the zeolite are measured with the ASAP 2405 physical adsorption instrument from Micromeritics Corporation (USA), where the specific surface area refers to the sum of the specific surface area of micropores and the specific surface area of mesopores.

[0063] The XRD spectra of the samples are obtained by using the Dmax2500 X-ray diffractometer produced by Rigaku Corporation (Japan), and the relative crystallinity of the sample is obtained by calculation. The relative crystallinity of the zeolite is determined as follows: taking the sum of the heights of diffraction peaks by 2 degree of approximately 11.3 and 19.5-23 in the XRD spectrum of a conventional ZSM-23 zeolite as 100% crystallinity and comparing with that of other samples to obtain the relative crystallinity.

[0064] According to the present invention, the ZSM-23 zeolite has an XRD pattern comprising the following characteristic peaks expressed by 2 degree: about 11.3+/0.3 (for example +/0.2 or +/0.1).

[0065] According to the present invention, the ZSM-23 zeolite has an XRD pattern comprising the following characteristic peaks expressed by 2 degree: 11.2-11.5, 19.5-19.9, 20.7-21.0, and 22.8-23.1.

[0066] In order to better illustrate the present invention, the present invention is further described below in conjunction with Examples and Comparative Examples. But the scope of the present invention is not limited to the scope of these examples.

Example 1

[0067] (1) Preparation of Mesoporous Silicon Source

[0068] To 250 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 0.5 hours, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.08. The solution was adjusted with hydrochloric acid to the pH of 2, and heated in a 50 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried at 80 C. for 8 hours, and calcined at 550 C. for 3 hours to produce an amorphous silica.

[0069] (2) Preparation of Microporous-Mesoporous ZSM-23 Zeolite [0070] a) 0.35 g of NaOH was dissolved in 35 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.14) prepared in step (1) was added, and the mixture was stirred in a 45 C. water bath for 3 hours; [0071] b) aluminum sulfate and isopropylamine (IPA) were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:OH.sup.:IPA:H.sub.2O=1:0.01:0.08:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. Its XRD spectrum was shown in FIG. 1 (confirming that the obtained product is a ZSM-23 zeolite), and the nitrogen gas physical adsorption curve was shown in FIG. 2. The specific properties were shown in Table 1.

Example 2

[0072] (1) Preparation of Mesoporous Silicon Source

[0073] To 250 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 0.5 hours, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.08. The solution was adjusted with hydrochloric acid to the pH of 2, and heated in a 50 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried at 100 C. for 4 hours, and calcined at 550 C. for 3 hours to produce an amorphous silica.

[0074] (2) Preparation of Microporous-Mesoporous ZSM-23 Zeolite [0075] a) 0.42 g of NaOH was dissolved in 40 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.17) prepared in step (1) was added, and the mixture was stirred in a 35 C. water bath for 6 hours; [0076] b) aluminum sulfate and isopropylamine (IPA) were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:OH.sup.:IPA:H.sub.2O=1:0.005:0.10:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. Its XRD spectrum was similar to FIG. 1, and the nitrogen gas physical adsorption curve was similar to FIG. 2. The specific properties were shown in Table 1.

Example 3

[0077] (1) Preparation of Mesoporous Silicon Source

[0078] To 1200 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 2 hours, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.2. The solution was adjusted with hydrochloric acid to the pH of 3, and heated in a 50 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried at 80 C. for 4 hours, and calcined at 500 C. for 3 hours to produce an amorphous silica.

[0079] (2) Preparation of Microporous-Mesoporous ZSM-23 Zeolite [0080] a) 0.15 g of NaOH was dissolved in 35 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.06) prepared in step (1) was added, and the mixture was stirred in a 45 C. water bath for 3 hours; [0081] b) aluminum sulfate, isopropylamine (IPA) and NaOH were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:OH.sup.:IPA:H.sub.2O=1:0.01:0.08:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. Its XRD spectrum was similar to FIG. 1, and the nitrogen gas physical adsorption curve was similar to FIG. 2. The specific properties were shown in Table 1.

Example 4

[0082] (1) Preparation of Mesoporous Silicon Source

[0083] To 800 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 2 hours, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.15. The solution was adjusted with hydrochloric acid to the pH of 4, and heated in a 50 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried at 90 C. for 4 hours, and calcined at 550 C. for 3 hours to produce an amorphous silica.

[0084] (2) Preparation of Microporous-Mesoporous ZSM-23 Zeolite [0085] a) 0.42 g of NaOH was dissolved in 40 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.17) prepared in step (1) was added, and the mixture was stirred in a 40 C. water bath for 3 hours; [0086] b) aluminum sulfate and isopropylamine (IPA) were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:OH.sup.:IPA:H.sub.2O=1:0.005:0.10:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. Its XRD spectrum was similar to FIG. 1, and the nitrogen gas physical adsorption curve was similar to FIG. 2. The specific properties were shown in Table 1.

Example 5

[0087] (1) Preparation of Mesoporous Silicon Source

[0088] To 210 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 1 hour, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.05. The solution was adjusted with hydrochloric acid to the pH of 2, and heated in a 60 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried at 80 C. for 8 hours, and calcined at 550 C. for 3 hours to produce an amorphous silica.

[0089] (2) Preparation of Microporous-Mesoporous ZSM-23 Zeolite [0090] a) 0.35 g of NaOH was dissolved in 35 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.14) prepared in step (1) was added, and the mixture was stirred in a 50 C. water bath for 2 hours; [0091] b) aluminum sulfate and isopropylamine (IPA) were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:OH.sup.:IPA:H.sub.2O=1:0.01:0.08:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. Its XRD spectrum was similar to FIG. 1, and the nitrogen gas physical adsorption curve was similar to FIG. 2. The specific properties were shown in Table 1.

Example 6

[0092] (1) Preparation of Mesoporous Silicon Source

[0093] To 210 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 1 hour, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.06. The solution was adjusted with hydrochloric acid to the pH of 2, and heated in a 60 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried at 80 C. for 8 hours, and calcined at 550 C. for 3 hours to produce an amorphous silica.

[0094] (2) Preparation of Microporous-Mesoporous ZSM-23 Zeolite [0095] a) 0.10 g of NaOH and 1.36 g of concentrated ammonia water (having a mass fraction of about 27%) was dissolved in 35 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.22) prepared in step (1) was added, and the mixture was stirred in a 40 C. water bath for 6 hours; [0096] b) aluminum sulfate and isopropylamine (IPA) were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:OH.sup.:IPA:H.sub.2O=1:0.01:0.15:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. Its XRD spectrum was similar to FIG. 1, and the nitrogen gas physical adsorption curve was similar to FIG. 2. The specific properties were shown in Table 1.

Comparative Example 1 (According to CN105540607A)

[0097] 0.51 g of pseudo-boehmite and 0.3 g of sodium hydroxide were added to 26 mL of deionized water under stirring at 35 C. The resulting solution was homogenized, then 0.3 g of isopropylamine was added, then 21 g of white carbon black was added, and the resulting mixture was homogenized and mixed for 1 hour. 24.5 g of cereal starch was added, and the resulting mixture was heated to 90 C., stirred and aged for 6 hours. Finally, the resulting mixture was transferred to a hydrothermal reaction vessel lined with PTFE, statically crystallized at 160 C. for 144 hours, taken out, cooled, filtered, and dried at 80 C. to obtain the raw powder of zeolite. The raw powder was calcined at 500 C. for 12 hours under an air atmosphere to produce a micropore-mesopore composite ZSM-23 zeolite, which was measured for its relative crystallinity, its specific surface area, its pore volume and its pore size distribution, and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. The specific properties were shown in Table 1.

Comparative Example 2

[0098] (1) Preparation of Mesoporous Silicon Source

[0099] To 250 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 0.5 hours, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.08. The solution was adjusted with hydrochloric acid to the pH of 2, and heated in a 50 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried, and calcined at 550 C. to produce an amorphous silica.

[0100] (2) a) 3.7 g of the mesoporous silicon source prepared in step (1) was dispersed in 35 mL of deionized water, and the mixture was stirred in a 50 C. water bath for 2 hours;

[0101] b) aluminum sulfate, isopropylamine (IPA) and NaOH were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:NaOH:IPA:H.sub.2O=1:0.01:0.08:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. The specific properties were shown in Table 1.

Comparative Example 3

[0102] (1) Preparation of Mesoporous Silicon Source

[0103] To 1200 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 2 hours, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.2. The solution was adjusted with hydrochloric acid to the pH of 3, and heated in a 50 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried, and calcined at 550 C. to produce an amorphous silica.

[0104] (2) a) 0.70 g of NaOH was dissolved in 40 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.28) prepared in step (1) was added, and the mixture was stirred in a 45 C. water bath for 3 hours;

[0105] b) aluminum sulfate and isopropylamine (IPA) were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:NaOH:IPA:H.sub.2O=1:0.01:0.16:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C.

Comparative Example 4

[0106] (1) Preparation of Mesoporous Silicon Source

[0107] To 1200 g of deionized water was added 50 g of water glass (having a SiO.sub.2 mass fraction of 27%). The mixture was stirred and dispersed evenly. Then octodecyltrimethylammonium chloride (C18TMACl) was added and the resulting mixture was stirred for 2 hours, wherein the molar ratio of SiO.sub.2 to C18TMACl was 1:0.2. The solution was adjusted with hydrochloric acid to the pH of 3, and heated in a 50 C. water bath for 4 hours. Then, the reaction system was filtered, washed, dried, and calcined at 550 C. to produce an amorphous silica.

[0108] (2) a) 0.10 g of NaOH was dissolved in 40 mL of deionized water, 3.7 g of the mesoporous silicon source (OH.sup./SiO.sub.2 molar ratio=0.04) prepared in step (1) was added, and the mixture was stirred in a 45 C. water bath for 3 hours;

[0109] b) aluminum sulfate, isopropylamine (IPA) and sodium hydroxide were successively dissolved in the remaining water, and to the resulting mixture was added the silicon source dispersion obtained from step a) to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:NaOH:IPA:H.sub.2O=1:0.01:0.08:1.0:50. The resulting gel was crystallized at 180 C. for 48 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity, its specific surface area, its pore volume, and its pore size distribution; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C.

Comparative Example 5 (Preparation of the Conventional ZSM-23 Zeolite)

[0110] Water glass, aluminum sulfate, isopropylamine (IPA), sodium hydroxide and water were mixed to produce a gel with a total molar ratio of SiO.sub.2 in the silicon source:Al.sub.2O.sub.3 in the aluminum source:NaOH:IPA:H.sub.2O=1:0.01:0.08:1.0:50. The resulting gel was heated at 180 C. for 72 hours, filtered, washed, dried, and calcined. The resulting product was measured for its relative crystallinity; and measured for its hydrothermal stability after a hydrothermal treatment with steam for 2 hours at 600 C. The specific properties were shown in Table 1.

TABLE-US-00001 TABLE 1 Content of Relative Specific Microporous Microporous mesopores crystallinity Relative surface surface surface Pore with pore Relative after crystallinity area, area, area, volume, size of crystallinity, hydrothermal retention, m.sup.2/g m.sup.2/g m.sup.2/g cm.sup.3/g 3-8 nm % treatment, % %.sup.d Example 1 395 105 290 0.42 77 102 103 100 Example 2 387 99 288 0.41 56 104 102 98 Example 3 398 107 291 0.45 80 114 110 96 Example 4 378 101 277 0.38 60 100 99 99 Example 5 384 91 293 0.40 69 113 108 96 Example 6 401 114 287 0.45 84 105 106 100 Comparative 289 126 163 0.28 31 103 74 72 Example 1 Comparative 69 61 8 0.03 .sup.a .sup.a .sup.a .sup.a Example 2 Comparative 232 167 65 0.24 .sup.b .sup.b .sup.b .sup.b Example 3 Comparative 108 84 24 0.09 .sup.c .sup.c .sup.c .sup.c Example 4 Comparative 228 188 40 0.24 18 100 101 100 Example 5 .sup.aUnder this condition, the zeolite product was not produced through crystallization, so this property could not be analyzed. .sup.bUnder this condition, the obtained products are mainly other zeolites, so this property could not be analyzed. .sup.cUnder this condition, the crystallization was incompleted, so this property could not be analyzed. .sup.dRelative crystallinity retention = crystallinity after hydrothermal treatment/relative crystallinity. Due to measurement errors, results greater than 100% were recorded as 100%.

[0111] It can be seen from the data in Table 1 that the preparation processes in the examples of the present invention could prepare ZSM-23 zeolites with micropore-mesopore composite structures through a simple synthesis process with a relatively small amount of surfactant at a relatively low cost. The obtained product, a micropore-mesopore composite ZSM-23 zeolite, has high crystallinity, large specific surface area and pore volume, high mesopore content, relatively concentrated size distribution, good thermal stability and hydrothermal stability, and broad application prospects. The performance of ZSM-23 zeolite samples was evaluated on a fixed bed micro reactor. The reaction conditions and catalytic results of Comparative Example 1, Comparative Example 5, Example 4 and Example 6 in the linear C.sub.20-C.sub.30 hydroisomerization reaction were as follows: Reaction raw materials: 90 wt % decahydronaphthalene, 10 wt % C.sub.20-C.sub.30 straight chain alkanes; Reaction conditions: reaction temperature 280 C.; Liquid hourly space velocity 1.0 h.sup.1; Hydrogen to oil ratio 600; Reaction hydrogen pressure 4.0 MPa;

Comparative Example 1

[0112] Liquid yield (C.sub.5.sup.+): 93%; C.sub.20-C.sub.30 Isomerization degree: 100%; C.sub.20-C.sub.30 isomerization product yield: 46%; Ratio of multiple-branched chain components to single-branched chain components in C.sub.20-C.sub.30 isomerization product: 0.6.

Comparative Example 5

[0113] Liquid yield (C.sub.5.sup.+): 94%; C.sub.20-C.sub.30 Isomerization degree: 100%; C.sub.20-C.sub.30 isomerization product yield: 44%; Ratio of multiple-branched chain components to single-branched chain components in C.sub.20-C.sub.30 isomerization product: 0.5.

Example 4

[0114] Liquid yield (C.sub.5.sup.+): 95%; C.sub.20-C.sub.30 Isomerization degree: 100%; C.sub.20-C.sub.30 isomerization product yield: 53%; Ratio of multiple-branched chain components to single-branched chain components in C.sub.20-C.sub.30 isomerization product: 2.1.

Example 6

[0115] Liquid yield (C.sub.5.sup.+): 96%; C.sub.20-C.sub.30 Isomerization degree: 100%; C.sub.20-C.sub.30 isomerization product yield: 54%; Ratio of multiple-branched chain components to single-branched chain components in C.sub.20-C.sub.30 isomerization product: 2.3.