ZSM-23 ZEOLITE AND PREPARATION PROCESS AND USE THEREOF

Abstract

A ZSM-23 zeolite and a process for preparing the same and use thereof are provided. The total acid amount of the ZSM-23 zeolite is 0.05-0.25 mmol/g, preferably 0.06-0.22 mmol/g, more preferably 0.06-0.20 mmol/g. The strong acid content of the ZSM-23 zeolite is 5-33%, preferably 7-33%, more preferably 9-33%, or further preferably 7-31%, further more preferably 10-28% of the total acid amount. The strong acid refers to an acid having a desorption temperature of 350 C. or higher in an NH3 temperature programmed desorption (NH3-TPD). The ZSM-23 zeolite has a low strong acid content.

Claims

1. A ZSM-23 zeolite, which is characterized in that the total acid amount of said ZSM-23 zeolite is 0.05-0.25 mmol/g, preferably, 0.06-0.22 mmol/g, more preferably, 0.06-0.20 mmol/g; the strong acid content of said ZSM-23 zeolite is 5-33%, preferably, 7-33%, more preferably, 9-33%, or further preferably, 7-31%, further more preferably, 10-28% of the total acid amount; wherein the strong acid refers to an acid having a desorption temperature of 350 C. or higher in an NH3 temperature programmed desorption (NH3-TPD), wherein optionally said ZSM-23 zeolite is a dried and calcined zeolite.

2. The zeolite according to claim 1, which is characterized in that the ZSM-23 zeolite has a grain size of 100-700 nm, preferably 200-600 nm, and further preferably 300-500 nm.

3. The zeolite according to claim 1, which is characterized in that said ZSM-23 zeolite has a SiO.sub.2/Al.sub.2O.sub.3 molar ratio of 35-300, a specific surface area of 200-400 m.sup.2/g, and a pore volume of 0.25-0.50 cm.sup.3/g; preferably, said ZSM-23 zeolite has a SiO.sub.2/Al.sub.2O.sub.3 molar ratio of 38-200, a specific surface area of 280-370 m.sup.2/g, and a pore volume of 0.28-0.40 cm.sup.3/g.

4. The zeolite according to claim 1, which is characterized in that said ZSM-23 zeolite has a relative crystallinity of 95-130% after calcination, and a relative crystallinity of 93-120% after a hydrothermal treatment with steam for 2 hours at 600 C.; preferably a relative crystallinity of 98-120% after calcination, and a relative crystallinity of 95-115% after a hydrothermal treatment with steam for 2 hours at 600 C.

5. A process for preparing said ZSM-23 zeolite according to claim 1, which is characterized in that the process comprises the following steps: (1) A mixed solution containing a template agent, and an amorphous silica-alumina and/or amorphous silica-alumina precursor is prepared, preferably, the amorphous silica-alumina and/or amorphous silica-alumina precursor is derived from an alkaline aluminum source (for example, an aluminate or a meta-aluminate, such as sodium aluminate, potassium aluminate, sodium meta-aluminate, and potassium meta-aluminate); (2) An alkali source and a silicon source are added to the mixed solution of step (1); (3) The material obtained in step (2) is crystallized, optionally filtered and washed, dried, and optionally calcined to produce the ZSM-23 zeolite.

6. The process according to claim 5, which is characterized in that in step (1), said template agent is one or more of isopropylamine, pyrrolidine, N,N-dimethyl formamide, and dimethylamine.

7. The process according to claim 5, which is characterized in that in step (1), in said mixed solution the molar ratio of silicon (as silica):aluminum (as alumina) is 1:(0.10-0.85), preferably 1:(0.20-0.79), further preferably 1:(0.24-0.78); the molar ratio of said aluminum (as alumina):the template agent is 1:(10-100), preferably 1:(15-85), further preferably 1:(20-65).

8. The process according to claim 5, which is characterized in that in step (1), an amorphous silica-alumina precursor is prepared by carbonization method, and then a template agent is added to the amorphous silica-alumina precursor to produce the mixed solution.

9. The process according to claim 5, which is characterized in that the preparation process of the amorphous silica-alumina precursor in step (1) is as follows: preparing a solution of an aluminum source (such as aluminate, preferably sodium aluminate) and a solution of a silicon-containing compound respectively; mixing the solution of the aluminum source with a part of the solution of the silicon-containing compound, introducing a CO.sub.2 gas for gelatination, when the volume of the introduced CO.sub.2 gas is 50-100%, preferably 70-90% of the total volume of the introduced CO.sub.2 gas, adding the remaining part of the solution of the silicon-containing compound, and optionally aging to produce the amorphous silica-alumina precursor.

10. The process according to claim 9, which is characterized in that the remaining part of the solution of the silicon-containing compound as silica comprises 5-85 wt %, preferably 30-70 wt % of the total addition amount of the solution of the silicon-containing compound as silica.

11. The process according to claim 9, which is characterized in that the reaction temperature of said gelatination is 10-40 C., preferably 15-35 C., the pH after the gelatination is controlled to 9-12.

12. The process according to claim 9, which is characterized in that said solution of the silicon-containing compound is water glass and/or a sodium silicate solution.

13. The process according to claim 9, which is characterized in that based on the mass of Al.sub.2O.sub.3, the concentration of the solution of the aluminum source is 15-60 gAl.sub.2O.sub.3/L, based on the mass of SiO.sub.2, the concentration of said solution of the silicon-containing compound is 40-260 gSiO.sub.2/L, the concentration of said CO.sub.2 gas is 30-60 v %.

14. The process according to claim 9, which is characterized in that the time of said ageing is 5-60 minutes, preferably 10-30 minutes; the temperature of said aging is 10-40 C., preferably 15-35 C.

15. The process according to claim 5, which is characterized in that in step (1), said mixed solution is stirred at 10-35 C. for 0.2-1.5 hours, preferably stirred at 10-25 C. for 0.5-1 hours.

16. The process according to claim 5, which is characterized in that in step (2), based on the aluminum (as alumina) in the mixed solution of step (1), based on the total charging molar ratios of SiO.sub.2:Al.sub.2O.sub.3:R.sub.2O(an alkali source, wherein R is an alkali metal, such as sodium and potassium):H.sub.2O=1:(0.0025-0.025):(0.015-0.08):(30-80) and template agent (SDA)/SiO.sub.2=0.10-1.8, preferably SiO.sub.2/Al.sub.2O.sub.3 is 50-200, H.sub.2O/SiO.sub.2 is 30-60, and R.sub.2O/SiO.sub.2 is 0.025-0.06, the alkali source and the silicon source are added to step (1).

17. The process according to claim 5, which is characterized in that in step (2), said silicon source is one or more of fumed silica, silica sol and water glass, said alkali source is one or more of sodium hydroxide, potassium hydroxide, and ammonia water.

18. The process according to claim 5, which is characterized in that in step (3), the crystallization is performed at 150-200 C. for 8-72 hours, preferably at 160-180 C. for 10-48 hours; the drying is performed at 60-130 C. for 2-12 hours, preferably at 80-120 C. for 4-8 hours; the calcining is performed at 500-600 C. for 2-8 hours, preferably at 530-570 C. for 3-6 hours or 4-6 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 shows the XRD spectrum of the synthesized product of the present invention.

[0056] FIG. 2 is a scanning electron microscope image of the synthesized product of the present invention.

DETAILED DESCRIPTION

[0057] Analysis methods according to the present invention:

[0058] The specific surface area and the pore volume are measured with the low-temperature liquid nitrogen physical adsorption method by using the ASAP 2405 physical adsorption instrument from Micromeritics Corporation (USA).

[0059] The silica-alumina molar ratio is determined by chemical analysis.

[0060] The XRD spectra of the samples are obtained by using the Dmax2500 X-ray diffractometer produced by Rigaku Corporation (Japan). The relative crystallinity of the zeolite is determined by X-ray powder diffraction (XRD), specifically by taking the sum of the heights of diffraction peaks expressed 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.

[0061] 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).

[0062] 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.

[0063] The grain size was obtained with JSM-7500F field emission scanning electron microscopy from JEOL Company (Japan).

[0064] The acid distribution (including total acid amount and strong acid content) was measured with NH3 temperature-programmed desorption (NH3-TPD), where the amount of the acid having a desorption temperature of 350 C. or higher was taken as the strong acid amount.

[0065] In the present invention, the acid amount is calculated as H.sup.+.

[0066] In the present invention, wt % is the mass fraction and v % is the volume fraction.

[0067] 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

[0068] A sodium aluminate working solution (40 g Al.sub.2O.sub.3/L) was prepared. A sodium silicate solution having a SiO.sub.2 concentration of 28 wt % was diluted to a sodium silicate working solution (100 g SiO.sub.2/L). 150 mL of the sodium aluminate working solution was placed in a gel-forming tank. Then 50 mL of the sodium silicate working solution was added. The reaction temperature was controlled to 20 C., and a CO.sub.2 gas with a concentration of 50 v % was introduced. When the pH value reached 10.0, the introduction of CO.sub.2 was terminated. Then 90 mL of the sodium silicate working solution was added, and then the remaining CO.sub.2 gas was introduced for stabilization. The system was aged at 25 C. for 30 minutes to produce an amorphous silica-alumina precursor. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.02:0.04:45, and IPA/SiO.sub.2=0.7 (IPA: isopropylamine as the template agent), to the above resulting amorphous silica-alumina precursor was added isopropylamine. The resulting mixture was stirred at 15 C. for 0.8 hours to produce a mixed solution containing the amorphous silica-alumina precursor and the template agent. Then to the mixed solution was added a mixture composed of sodium hydroxide, silica sol, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel.

[0069] The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 160 C. for 20 hours. After the completion of crystallization, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite product named ZSM-23-1; the obtained ZSM-23-1 was calcined in air at 550 C. for 3 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1. FIG. 1 showed the XRD spectrum of the zeolite, and FIG. 2 showed the scanning electron microscopy image of the zeolite, confirming that the obtained zeolite was a ZSM-23 zeolite.

Example 2

[0070] A sodium aluminate working solution (40 g Al.sub.2O.sub.3/L) was prepared. A sodium silicate solution having a SiO.sub.2 concentration of 28 wt % was diluted to a sodium silicate working solution (150 g SiO.sub.2/L). 200 mL of the sodium aluminate working solution was placed in a gel-forming tank. Then 40 mL of the sodium silicate working solution was added. The reaction temperature was controlled to 25 C., and a CO.sub.2 gas with a concentration of 50 v % was introduced. When the pH value reached 10.5, the introduction of CO.sub.2 was terminated. Then 40 mL of the sodium silicate working solution was added, and then the remaining CO.sub.2 gas was introduced for stabilization. The system was aged at 20 C. for 20 minutes to produce an amorphous silica-alumina precursor. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.005:0.04:60, and IPA/SiO.sub.2=0.15, to the above resulting amorphous silica-alumina precursor was added isopropylamine. The resulting mixture was stirred at 20 C. for 1 hour to produce a mixed solution containing the amorphous silica-alumina precursor and the template agent. Then to the mixed solution was added a mixture composed of sodium hydroxide, silica sol, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel. The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 180 C. for 18 hours. After the completion of crystallization, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite product named ZSM-23-2; the obtained ZSM-23-2 was calcined in air at 550 C. for 3 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1. Its XRD spectrum was similar to FIG. 1, and its scanning electron microscope image was similar to FIG. 2.

Example 3

[0071] A sodium aluminate working solution (50 g Al.sub.2O.sub.3/L) was prepared. A sodium silicate solution having a SiO.sub.2 concentration of 28 wt % was diluted to a sodium silicate working solution (100 g SiO.sub.2/L). 200 mL of the sodium aluminate working solution was placed in a gel-forming tank. Then 60 mL of the sodium silicate working solution was added. The reaction temperature was controlled to 30 C., and a CO.sub.2 gas with a concentration of 50 v % was introduced. When the pH value reached 10.0, the introduction of CO.sub.2 was terminated. Then 40 mL of the sodium silicate working solution was added, and then the remaining CO.sub.2 gas was introduced for stabilization. The system was aged at 35 C. for 15 minutes to produce an amorphous silica-alumina precursor. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.01:0.04:30, and IPA/SiO.sub.2=0.4, to the above resulting amorphous silica-alumina precursor was added isopropylamine. The resulting mixture was stirred at 25 C. for 0.5 hours to produce a mixed solution containing the amorphous silica-alumina precursor and the template agent. Then to the mixed solution was added a mixture composed of sodium hydroxide, silica sol, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel.

[0072] The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 160 C. for 24 hours. After the completion of crystallization, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite product named ZSM-23-3; the obtained ZSM-23-3 was calcined in air at 550 C. for 6 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1. Its XRD spectrum was similar to FIG. 1, and its scanning electron microscope image was similar to FIG. 2.

Example 4

[0073] A sodium aluminate working solution (20 g Al.sub.2O.sub.3/L) was prepared. A sodium silicate solution having a SiO.sub.2 concentration of 28 wt % was diluted to a sodium silicate working solution (150 g SiO.sub.2/L). 300 mL of the sodium aluminate working solution was placed in a gel-forming tank. Then 20 mL of the sodium silicate working solution was added. The reaction temperature was controlled to 30 C., and a CO.sub.2 gas with a concentration of 50 v % was introduced. When the pH value reached 11.0, the introduction of CO.sub.2 was terminated. Then 20 mL of the sodium silicate working solution was added, and then the remaining CO.sub.2 gas was introduced for stabilization. The system was aged at 20 C. for 30 minutes to produce an amorphous silica-alumina precursor. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.01:0.04:45, and IPA/SiO.sub.2=0.3, to the above resulting amorphous silica-alumina precursor was added isopropylamine. The resulting mixture was stirred at 15 C. for 1 hour to produce a mixed solution containing the amorphous silica-alumina precursor and the template agent. Then to the mixed solution was added a mixture composed of sodium hydroxide, silica sol, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel. The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 180 C. for 24 hours. After the completion of crystallization, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite product named ZSM-23-4; the obtained ZSM-23-4 was calcined in air at 550 C. for 4 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1. Its XRD spectrum was similar to FIG. 1, and its scanning electron microscope image was similar to FIG. 2.

Example 5

[0074] A sodium aluminate working solution (40 g Al.sub.2O.sub.3/L) was prepared. A sodium silicate solution having a SiO.sub.2 concentration of 28 wt % was diluted to a sodium silicate working solution (50 g SiO.sub.2/L). 150 mL of the sodium aluminate working solution was placed in a gel-forming tank. Then 140 mL of the sodium silicate working solution was added. The reaction temperature was controlled to 25 C., and a CO.sub.2 gas with a concentration of 50 v % was introduced. When the pH value reached 10.0, the introduction of CO.sub.2 was terminated. Then 140 mL of the sodium silicate working solution was added, and then the remaining CO.sub.2 gas was introduced for stabilization. The system was aged at 25 C. for 20 minutes to produce an amorphous silica-alumina precursor. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.01:0.04:45, and IPA/SiO.sub.2=0.4, to the above resulting amorphous silica-alumina precursor was added isopropylamine. The resulting mixture was stirred at 15 C. for 1 hour to produce a mixed solution containing the amorphous silica-alumina precursor and the template agent. Then to the mixed solution was added a mixture composed of sodium hydroxide, fumed silica, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel.

[0075] The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 180 C. for 12 hours. After the completion of crystallization, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite product named ZSM-23-5; the obtained ZSM-23-5 was calcined in air at 550 C. for 3 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1. Its XRD spectrum was similar to FIG. 1, and its scanning electron microscope image was similar to FIG. 2.

Example 6

[0076] A sodium aluminate working solution (40 g Al.sub.2O.sub.3/L) was prepared. A sodium silicate solution having a SiO.sub.2 concentration of 28 wt % was diluted to a sodium silicate working solution (50 g SiO.sub.2/L). 150 mL of the sodium aluminate working solution was placed in a gel-forming tank. Then 140 mL of the sodium silicate working solution was added. The reaction temperature was controlled to 25 C., and a CO.sub.2 gas with a concentration of 50 v % was introduced. When the pH value reached 10.0, the introduction of CO.sub.2 was terminated. Then 140 mL of the sodium silicate working solution was added, and then the remaining CO.sub.2 gas was introduced for stabilization. The system was aged at 25 C. for 20 minutes to produce an amorphous silica-alumina precursor. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.01:0.04:45, and SDA(structure-directing agent)/SiO.sub.2=0.1, to the above resulting amorphous silica-alumina precursor was added pyrrolidine (SDA). The resulting mixture was stirred at 15 C. for 1 hour to produce a mixed solution containing the amorphous silica-alumina precursor and the template agent. Then to the mixed solution was added a mixture composed of sodium hydroxide, fumed silica, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel.

[0077] The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 180 C. for 12 hours. After the completion of crystallization, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite product named ZSM-23-6; the obtained ZSM-23-6 was calcined in air at 550 C. for 4 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1. Its XRD spectrum was similar to FIG. 1, and its scanning electron microscope image was similar to FIG. 2.

Comparative Example 1 (According to CN101214971A)

[0078] An aluminum source, a silicon source, an alkali source, isopropylamine and H.sub.2O were prepared and mixed based on the molar ratio of Al.sub.2O.sub.3 in the aluminum source:SiO.sub.2 in the silicon source:NaOH in the alkali source:isopropylamine:H.sub.2O=0.006:1:0.06:0.8:12, wherein the aluminum source was sodium aluminate, the silicon source was silica sol, and the alkali source was sodium hydroxide, to produce a reaction mixture. Firstly, the aluminum source was added to an aqueous solution of sodium hydroxide and the resulting mixture was uniformly stirred; the silicon source was added and the resulting mixture was uniformly stirred; and then isopropylamine was added and the resulting mixture was uniformly stirred to produce a reaction mixture. The obtained reaction mixture was transferred to a high-pressure reaction vessel for a hydrothermal crystallization at 170 C. for 3 days. Then the resulting mixture was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite product named CNZSM-23-1; the obtained CNZSM-23-1 was calcined in air at 550 C. for 3 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1.

Comparative Example 2 (According to CN102992346A)

[0079] 8.12 g of H.sub.2O and 0.092 g of aluminum sulfate were uniformly mixed. To the resulting mixture was added 0.38 g of NaOH. Then to the resulting mixture was added 3.32 g of silica sol with a silica content of 30.5% under stirring. The stirring was continued until the solution becomes uniform. Then 10% ZSM-23 zeolite was added as crystal seed (the amount of crystal seed was calculated based on the mass percentage of the added SiO.sub.2). The reaction raw materials were added to the PTFE stainless steel reactor, and dynamically crystallized at 160 C. for 10 hours. The resulting product were filtered by suction and dried to obtain the product. The ratio of reaction raw materials was SiO.sub.2:0.008319A1203:0.27Na.sub.2O:35H.sub.2O. The product was named CNZSM-23-2, which was calcined in air at 550 C. for 3 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1.

Comparative Example 3

[0080] A sodium aluminate working solution (50 g Al.sub.2O.sub.3/L) was prepared. A sodium silicate solution having a SiO.sub.2 concentration of 28 wt % was diluted to a sodium silicate working solution (100 g SiO.sub.2/L). 200 mL of the sodium aluminate working solution was placed in a gel-forming tank. Then 60 mL of the sodium silicate working solution was added. The reaction temperature was controlled to 30 C., and a CO.sub.2 gas with a concentration of 50 v % was introduced. When the pH value reached 10.0, the introduction of CO.sub.2 was terminated. Then 40 mL of the sodium silicate working solution was added, and then the remaining CO.sub.2 gas was introduced for stabilization. The system was aged at 25 C. for 30 minutes to produce an amorphous silica-alumina precursor. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.01:0.04:30, and IPA/SiO.sub.2=0.4, to the above resulting amorphous silica-alumina precursor was added a mixture composed of sodium hydroxide, silica sol, isopropylamine, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel.

[0081] The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 160 C. for 24 hours. After the completion of crystallization, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite raw powder named CZSM-23-3, which was measured for its relative crystallinity; the obtained CZSM-23-3 was calcined in air at 550 C. for 3 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1.

Comparative Example 4

[0082] Solid aluminum sulfate was diluted to 60 mL of an aluminum sulfate working solution (a) with a concentration of 100 g Al.sub.2O.sub.3/L. Concentrated ammonia water was added to an appropriate amount of distilled water and diluted to a diluted ammonia water (b) with a concentration of about 10 wt %. A sodium silicate solution containing 28 wt % of SiO.sub.2 was diluted to 140 mL of a sodium silicate working solution (c) having a concentration of 100 g SiO.sub.2/L. To a 5-liter steel reaction tank was added 0.5 liters of distilled water, stirred and heated to 70 C. The valves of the containers containing (a), (b), and (c) were opened respectively, the flow rate of (a) was controlled so as to maintain a neutralization reaction time of 40 minutes, and then the flow rate of (b) was quickly adjusted to maintain the pH value of the system at 7-8, and the temperature of the system was controlled at around 60 C. After the reaction of aluminum sulfate was completed, the addition of (b) was terminated, and the formed silica-alumina sol was aged at 25 C. for 40 minutes. Based on the total charging molar ratio of SiO.sub.2:Al.sub.2O.sub.3:Na.sub.2O:H.sub.2O=1:0.02:0.04:45, IPA/SiO.sub.2=0.7, to the above resulting amorphous silica-alumina precursor was added isopropylamine. The resulting mixture was stirred at 15 C. for 0.8 hours to produce a mixed solution containing the amorphous silica-alumina precursor and the template agent. Then to the mixed solution was added a mixture composed of sodium hydroxide, silica sol, and water. The resulting mixture was stirred to be uniform to produce a silica-alumina gel.

[0083] The above-obtained gel was poured into a stainless steel reaction vessel, and statically crystallized at 180 C. for 36 hours. Then, the crystallization system was filtered, washed to neutral, and dried at 120 C. to obtain a zeolite named CZSM-23-4, which was measured for its relative crystallinity; the obtained CZSM-23-4 was calcined in air at 550 C. for 3 hours to measure its relative crystallinity after calcination, and hydrothermally treated with steam for 2 hours at 600 C. to measure its hydrothermal stability. The specific properties were shown in Table 1.

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

[0084] 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.

TABLE-US-00001 TABLE 1 Relative Relative crystallinity Specific crystallinity after Total Strong SiO.sub.2/Al.sub.2O.sub.3 surface Pore Grain Actual Relative after hydrothermal acid acid charging area, volume, size, SiO.sub.2/Al.sub.2O.sub.3 crystallinity, calcination, treatment, amount, content, molar ratio m.sup.2/g cm.sup.3/g nm molar ratio % % % mmol/g % Example 1 50 355 0.35 about 42 98 101 103 0.187 33.0 360 Example 2 200 344 0.32 about 196 104 102 105 0.058 10.6 420 Example 3 100 334 0.30 about 89 112 115 108 0.111 24.2 490 Example 4 100 348 0.32 about 91 100 105 104 0.106 21.7 450 Example 5 100 363 0.37 about 87 109 108 102 0.109 18.9 320 Example 6 100 352 0.36 about 89 105 104 101 0.107 20.5 470 Comparative 167 323 0.31 about 145 100 106 104 0.069 63.3 Example 1 1300 Comparative 120 288 0.28 about 117 104 102 104 0.083 68.2 Example 2 1000 Comparative 100 216 0.22 about 92 101 103 101 0.104 52.4 Example 3 610 Comparative 50 51 0.04 .sup.a .sup.a .sup.a .sup.a .sup.a .sup.a .sup.a Example 4 Comparative 228 0.24 100 101 Example 5 .sup.aUnder this condition, the zeolite product was not produced through crystallization, so this property could not be analyzed.

[0085] It can be seen from the data in Table 1 that the preparation processes in the examples of the present invention could synthesize ZSM-23 zeolites having high crystallinity, wider silica-alumina ratio range, relatively small crystal grains, relatively high content of weak acid and mid-strong acid, and good thermal stability and hydrothermal stability.

[0086] 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 and Example 3 in the linear C.sub.20-C.sub.30 hydroisomerization reaction were as follows: [0087] Reaction raw materials: 90 wt % decahydronaphthalene, 10 wt % C.sub.20-C.sub.30 straight chain alkanes; [0088] 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;

[0089] Comparative Example 3: liquid yield (C.sub.5.sup.+): 93%; C.sub.20-C.sub.30Isomerization degree: 100%; C.sub.20-C.sub.30isomerization product yield: 42%; Ratio of multiple-branched chain components to single-branched chain components in C.sub.20-C.sub.30 isomerization product:0.4.

[0090] Example 3: liquid yield (C.sub.5.sup.+): 96%; C.sub.20-C.sub.30Isomerization degree: 100%; C.sub.20-C.sub.30isomerization product yield: 58%; Ratio of multiple-branched chain components to single-branched chain components in C.sub.20-C.sub.30 isomerization product: 2.8.