A ZSM-48 molecular sieve and its preparation method

Abstract

The present invention relates to a ZSM-48 molecular sieve and a preparation method thereof, comprising the following steps: step 1) preparing a pre-crystallization liquid; step 2) crystallization; step 3) filtering, washing, drying and roasting the obtained crystallization product; in step 1), the alkali source is a molecular sieve crystallization mother liquor; in the pre-crystallization liquid, the silicon source is calculated by SiO2, the aluminum source is calculated by Al2O3, the alkali source is calculated by Na2O, and the molar ratio of silicon source: aluminum source: alkali source: deionized water is 20~120:1:0.5~40:200~6200. The present invention has the advantage that the molecular sieve crystallization mother liquor is used to replace the alkali source, the pre-crystallization liquid containing molecular sieve structural fragments is first prepared, and then a structure directing agent is added for crystallization. Under the condition of low structure directing agent dosage, highly crystalline pure phase ZSM-48 molecular sieve is crystallized in a relatively short time, and the product yield is ≥98%.

Description

Technical Field

[0001] The invention relates to the technical field of ZSM-48 molecular sieves, and in particular to a ZSM-48 molecular sieve and a preparation method thereof. Background Art

[0002] The hydroisomerization process of normal alkanes is an important method for producing high-quality diesel, aviation fuel oil and lubricating oil in the field of petrochemicals. ZSM-48 molecular sieve is a high-silicon zeolite molecular sieve first synthesized by Mobil Corporation in the United States in the 1980s. It has a unique one-dimensional ten-membered ring straight-through channel and an ideal pore size of 0.56nm×0.56nm, which is close to the kinetic diameter of normal alkanes. At the same time, it also has suitable acidity and can be used as a catalyst in the hydroisomerization process of normal alkanes.

[0003] At present, the ZSM-48 molecular sieve synthesized by conventional methods has problems such as low acid content, high synthesis cost, and long synthesis cycle. Therefore, it is very necessary to develop a low-cost and high-acid ZSM-48 molecular sieve synthesis method. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a ZSM-48 molecular sieve and a preparation method thereof. The molecular sieve crystallization mother liquor is used instead of the alkali source, a pre-crystallization liquid containing molecular sieve structural fragments is first prepared, and then a structure directing agent is added for crystallization. Under the condition of low template dosage, highly crystalline pure phase ZSM-48 molecular sieve is crystallized in a relatively short time, and the product yield is ≥98%.

[0005] The present invention is achieved through the following technical solutions: On the one hand, a method for preparing a ZSM-48 molecular sieve is provided, comprising the following steps:

[0006] Step 1) preparing a pre-crystallization solution;

[0007] The seed crystal, silicon source, aluminum source, alkali source and deionized water are mixed to obtain a suspension, and the suspension is heated and stirred to obtain a clear, translucent colloidal pre-crystallization liquid, that is, a pre-crystallization liquid containing molecular sieve structure fragments; wherein the pH value of the obtained pre-crystallization liquid is 8.0-11.0, and the solid obtained after evaporation does not contain any crystalline phase according to XRD detection;

[0008] Step 2) crystallization;

[0009] Adding a structure directing agent to the obtained pre-crystallization liquid, stirring evenly, static aging, then sealing, heating and crystallizing to obtain a crystallized product;

[0010] Step 3) filtering, washing, drying and calcining the obtained crystallized product;

[0011] In step 1), the alkali source is a molecular sieve crystallization mother liquor; in the pre-crystallization liquid, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the alkali source is calculated as Na2O, and the molar ratio of silicon source: aluminum source: alkali source: deionized water is 20~120:1:0.5~40:200~6200; preferably 60~110:1:2~22:1130~4500.

[0012] According to the technical scheme, in step 1), the seed crystal, silicon source, aluminum source, alkali source and deionized water are mixed to obtain a suspension, and after heating and stirring, a clear and translucent colloidal pre-crystallization liquid is obtained, and the pH value is 8.0-11.0. After evaporation, the obtained solid does not contain any crystalline phase according to XRD detection; in addition, the present invention uses molecular sieve crystallization mother liquor to replace the alkali source, so as to realize the reuse of production wastewater, reduce the amount of synthetic structure directing agent, and improve the economic efficiency of ZSM-48 molecular sieve industrial production; the obtained crystallization product has high yield, short crystallization time, high efficiency and high product crystallinity; the product does not have strong acid center, has high acid content, and exhibits good catalytic performance in the hydroisomerization reaction of linear alkanes.

[0013] The obtained clear and translucent colloidal pre-crystallization liquid has no precipitation and suspended matter visually observed; the solid residue obtained by evaporating the pre-crystallization liquid is subjected to XRD detection, and the detection result shows an amorphous phase.

[0014] Preferably, the silicon source is at least one of sodium silicate, white carbon black, silica sol, silica gel powder, and tetraethyl orthosilicate. The aluminum source is at least one of aluminum hydroxide, sodium aluminate, aluminum sulfate, aluminum sol, aluminum nitrate, aluminum trichloride, and aluminum isopropoxide.

[0015] Furthermore, in step 1), the molecular sieve crystallization mother liquor is selected from the crystallization mother liquor produced in the production of LTA molecular sieve and / or FAU molecular sieve; and the Na2O content in the molecular sieve crystallization mother liquor is 10-150 g / L, preferably 30-90 g / L.

[0016] Through the above technical scheme, LTA and FAU molecular sieve raw powders are the main raw materials for the production of industrial adsorbents, with large market demand, and are the main products of molecular sieve production companies. LTA and FAU molecular sieves will produce a large amount of crystallization mother liquor during the production process, which requires a special sewage treatment process to treat, resulting in increased production costs and greater environmental pressure. Considering that the crystallization mother liquor contains unreacted Na2O, SiO2 and other substances, the crystallization mother liquor wastewater produced by the production of LTA and FAU molecular sieves is used to replace the alkali source used to synthesize other high-value molecular sieves, which can achieve the reuse of molecular sieve production wastewater and reduce production and operation costs. The use of LTA and FAU crystallization mother liquors in the synthesis of ZSM-48 molecular sieves can obtain products with high acid content and good crystallization. At the same time, the amount of structure directing agent is low and the crystallization time is short, which has great practical significance.

[0017] Furthermore, in step 1), the seed crystals are selected from at least one of completely crystallized Na-ZSM-48 molecular sieve, NH4-ZSM-48 molecular sieve, and H-ZSM-48 molecular sieve; and the amount of the seed crystals added accounts for 0.05-10wt.%, preferably 0.5-5wt.% of the silicon source.

[0018] Preferably, the seed crystal is at least one of completely crystallized Na-ZSM-48 molecular sieve, NH4-ZSM-48 molecular sieve or H-ZSM-48 molecular sieve, and is in a calcined or uncalcined state.

[0019] Furthermore, in step 1), the heating temperature of the heating and stirring is 60-120°C, preferably 80-120°C, and more preferably 100-120°C; the stirring speed is 10-80rpm, preferably 30-50rpm; and the heating time is 1-12h, preferably 3-6h.

[0020] Furthermore, in step 2), the molar ratio of the structure directing agent to the alkali source in the obtained pre-crystallization solution is 0.5-10:3-30; preferably 1.0-5:5-20.

[0021] Further, in step 2), the structure directing agent is selected from at least one of 1,6-hexanediamine, triethylamine, hexamethonium bromide, hexamethonium hydroxide, hexamethonium chloride, ethylenediamine, tetramethylammonium, and allyltrimethylammonium chloride.

[0022] Furthermore, in step 2), the aging temperature is 60-120° C., preferably 80-100° C.; the aging time is 1-24 h, preferably 6-18 h.

[0023] Furthermore, in step 2), the heating crystallization process is preferably dynamic crystallization, the rotation speed is 30-90 rpm, preferably 30-50 rpm; the crystallization temperature is 140-210° C., preferably 160-190° C.; the crystallization time is 1-24 h, preferably 6-24 h.

[0024] Furthermore, in step 3), the drying temperature is 60-120°C, preferably 80-100°C; the drying time is 1-24h, preferably 6-12h; the calcination temperature is 500-650°C, preferably 550-630°C; and the calcination time is 1-16h, preferably 5-12h.

[0025] A ZSM-48 molecular sieve is also provided, which is prepared by the above-mentioned preparation method of the ZSM-48 molecular sieve.

[0026] Specifically, the Na-ZSM-48 molecular sieve prepared according to the above preparation method needs to be ammonium exchanged, filtered, washed, dried, and calcined to obtain the H-ZSM-48 molecular sieve before acidity characterization and Pt loading to prepare a hydroisomerization reaction catalyst.

[0027] Ammonium exchange, filtration, washing, drying and roasting are conventional operations for preparing H-type molecular sieves from Na-type molecular sieves. The ammonium salt used for ammonium exchange is at least one of ammonium sulfate, ammonium chloride and ammonium nitrate; the concentration of the ammonium exchange solution is 0.1~1.5mol / L, preferably 0.3~1.0mol / L; the liquid-solid ratio of the ammonium exchange solution to the Na-ZSM-48 molecular sieve is 10~100mL / g, preferably 15~50mL / g, and more preferably 30~50mL / g; the ammonium exchange temperature is 60~100℃, preferably 70~90℃; the ammonium exchange time is 1~12h, preferably 3~8h; the number of ammonium exchanges is 1~5 times, preferably 1~3 times. The amount of washing water is 0.2~2.5L / g, preferably 0.5~1.5L / g. The drying temperature is 60-120°C, preferably 80-100°C; the drying time is 1-24h, preferably 6-12h; the calcination temperature is 450-600°C, preferably 500-580°C; the calcination time is 1-12h, preferably 3-10h.

[0028] The acid properties of the H-ZSM-48 molecular sieve obtained by the method of the present invention are characterized (NH3-TPD). There is no strong acid center in the product, and the acid content of the product is high. The weak acid content is 0.10-0.35 mmol / g, and the medium-strong acid content is 0.05-0.30 mmol / g.

[0029] After obtaining the H-ZSM-48 molecular sieve according to the above method, the H-ZSM-48 molecular sieve is impregnated in a Pt solution to obtain a hydroisomerization reaction catalyst. The impregnation is preferably saturated impregnation; the Pt solution is preferably an aqueous solution of chloroplatinic acid; the amount of Pt impregnated is 0.1-1.0% of the mass of the H-ZSM-48 molecular sieve, preferably 0.1-0.5%. After impregnation, drying and calcination are required, and the drying and calcination conditions are the same as those of ammonium exchange.

[0030] After obtaining the hydroisomerization reaction catalyst, it needs to be reduced in situ before the hydroisomerization reaction is carried out. The reduction conditions of the hydroisomerization reaction catalyst are: temperature of 300-500°C, preferably 400°C; time of 2-5h, preferably 3h; heating rate of 0.5-5°C / min, preferably 2°C / min; H2 flow rate of 30-60mL / min, preferably 40mL / min.

[0031] The conditions for the hydroisomerization reaction are: normal pressure reaction, V(H2) / V(C 12 ) is 1000~5000, preferably 2500; C12 The flow rate is 0.2~0.8mL / h, preferably 0.5mL / h; the temperature is 200~330℃, preferably 250℃; the space velocity is 0.30~0.80h -1 , preferably 0.60h -1 .

[0032] Beneficial Effects

[0033] 1) Silicon source and aluminum source are crystallized into molecular sieves with specific topological structures under the guidance of structure-directing agents (or / and molecular sieve structure fragments and other substances with structure-directing effects), in which the alkali source provides pH (molecular sieve crystallization generally requires alkaline conditions) and balances the negative charge of the framework. In addition, the mother liquor of molecular sieve crystallization is used to replace the alkali source to achieve the reuse of production wastewater, the amount of synthetic structure-directing agent is low, and the economic efficiency of industrial production of ZSM-48 molecular sieve is improved;

[0034] 2) The crystallization product has high yield, short crystallization time, high efficiency and high product crystallinity;

[0035] 3) The product does not have a strong acid center, has a high acid content, and exhibits good catalytic performance in the hydroisomerization reaction of straight-chain alkanes. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a comparison diagram of the XRD diffraction spectra of samples Z1 to Z5, DZ-1, DZ-2, and DZ-3 according to the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods without specific conditions in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0039] Unless otherwise specified, the reagents and raw materials used in the examples and comparative examples of the present invention can be obtained through commercial channels.

[0040] Example 1

[0041] 155mL 4A molecular sieve crystallization mother liquor (40g / L), 1.14g sodium aluminate, 100g silica sol (30wt.%) and 0.9g calcined Na-ZSM-48 molecular sieve seed were added to 78g deionized water in sequence, and heated at 100°C with stirring (speed 30rpm) for 4h to obtain a pre-crystallization solution. 9.46g hexamethylammonium hydroxide aqueous solution (25wt.%) was added thereto, stirred evenly, statically aged at 80°C for 6h, sealed in a kettle, and dynamically crystallized at 190°C (speed 50rpm) for 16h. After the crystallization was completed, the ZSM-48 molecular sieve was obtained by filtration, washing, drying at 80°C for 12h, and calcining at 580°C for 10h, recorded as Z1.

[0042] Example 2

[0043] 186mL 13X molecular sieve crystallization mother solution (60g / L), 33.4g aluminum sulfate 18hydrate, 200g silica gel powder (90wt.%) and 1.8g calcined H-ZSM-48 molecular sieve seed were added to 885g deionized water, and heated at 90°C with stirring (speed 50rpm) for 6h to obtain a pre-crystallization solution. 26.34g hexamethylammonium bromide was added thereto, stirred evenly, statically aged at 100°C for 12h, sealed in a kettle, and dynamically crystallized at 175°C (speed 30rpm) for 24h. After the crystallization was completed, the ZSM-48 molecular sieve was obtained by filtration, washing, drying at 100°C for 8h, and calcining at 590°C for 8h, recorded as Z2.

[0044] Example 3

[0045] 13.6 mL NaY molecular sieve crystallization mother solution (82 g / L), 0.2 g aluminum hydroxide, 6 g white carbon black and 0.3 g uncalcined Na-ZSM-48 molecular sieve seed were added to 56 g deionized water, and heated at 120 ° C with stirring (speed 10 rpm) for 2 h to obtain a pre-crystallization solution. 10.25 g hexamethylammonium bromide was added thereto, stirred evenly, statically aged at 110 ° C for 4 h, sealed in a kettle, and dynamically crystallized at 180 ° C (speed 30 rpm) for 16 h. After the crystallization was completed, the ZSM-48 molecular sieve was obtained by filtration, washing, drying at 90 ° C for 12 h, and calcining at 590 ° C for 8 h, recorded as Z3.

[0046] Example 4

[0047] 68.9 mL 4A molecular sieve crystallization mother solution (45 g / L), 0.7 g aluminum isopropoxide, 41.66 g tetraethyl silicate and 0.1 g uncalcined H-ZSM-48 molecular sieve seed were added to 18.7 g deionized water, and heated at 75 ° C with stirring (speed 50 rpm) for 8 h to obtain a pre-crystallization solution. 2.84 g hexamethylammonium hydroxide (25 wt.%) and 0.03 g 1,6-hexanediamine were added thereto, stirred evenly, statically aged at 75 ° C for 18 h, sealed in a kettle, and dynamically crystallized at 185 ° C (speed 20 rpm) for 12 h. After the crystallization was completed, the ZSM-48 molecular sieve was obtained by filtration, washing, drying at 80 ° C for 12 h, and calcining at 600 ° C for 6 h, recorded as Z4.

[0048] Example 5

[0049] 8 mL 4A molecular sieve crystallization mother liquor (40 g / L), 5 mL 13X crystallization mother liquor, 0.19 g aluminum hydroxide, 1.8 g white carbon black and 0.15 g NH4-ZSM-48 molecular sieve seed were added to 11.9 g deionized water in sequence, and heated at 110 ° C with stirring (speed 50 rpm) for 12 h to obtain a pre-crystallization solution. 0.2 g allyl trimethyl ammonium chloride (98 wt.%) was added thereto, stirred evenly, statically aged at 90 ° C for 12 h, sealed in a kettle, and dynamically crystallized at 165 ° C (speed 50 rpm) for 24 h. After the crystallization was completed, the ZSM-48 molecular sieve was obtained by filtration, washing, drying at 80 ° C for 12 h, and calcining at 570 ° C for 10 h, recorded as Z5.

[0050] Comparative Example 1: According to the scheme of Example 4, without pre-crystallization, all raw materials were mixed, and then directly aged and crystallized. The obtained sample was recorded as DZ-1.

[0051] Comparative Example 2: According to the scheme of Example 4, the added 4A molecular sieve crystallization mother liquor was replaced with equal amounts of NaOH and H2O, and the obtained sample was recorded as DZ-2.

[0052] Comparative Example 3: Synthesized according to the method disclosed in patent CN110342536B, SiO2 / Al2O3=100, template / SiO2=2.5, Na2O / SiO2=0.1, H2O / SiO2=40, 160°C, dynamic crystallization for 60h, the obtained sample is recorded as DZ-3.

[0053] Examples 1-5 and Comparative Examples 1-3 were characterized, and the results are listed in Table 1.

[0054] Table 1 Yield, crystallinity and acid properties of samples

[0055]

[0056] From the results in Table 1, it can be seen that the Z1~Z5 samples synthesized by the method of the present invention have high product yield and crystallinity, high raw material utilization rate, and high weak acid and medium-strong acid content. The product yield and crystallinity of DZ-1 and DZ-2 are relatively low, and the weak acid and medium-strong acid content are relatively low, which respectively illustrates the necessity of pre-crystallization and the use of molecular sieve crystallization mother liquor. The weak acid and medium-strong acid content of DZ-3 are relatively low, indicating that the sample synthesized by the method of the present invention has a relatively high weak acid and medium-strong acid content. Figure 1 From the comparison of the XRD diffraction spectra, it can be seen that compared with Z1~Z5, the crystallinity of DZ-1 and DZ-2 is lower.

[0057] The Na-ZSM-48 molecular sieves prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were mixed with a 1.0 mol / L aqueous solution of ammonium chloride at a liquid-solid ratio of 50:1 mL / g, and ammonium exchanged at 80° C. for 5 h, followed by washing and suction filtration, which was recorded as one ammonium exchange, and the ammonium exchange was repeated once to obtain an exchange product; the exchange product was dried at 100° C. for 12 h, and then calcined at 500° C. for 6 h to obtain an H-ZSM-48 molecular sieve; the H-ZSM-48 molecular sieve was impregnated with 0.5% Pt by mass of the H-ZSM-48 molecular sieve by a saturated impregnation method, dried at 80° C. for 3 h, and then calcined at 500° C. for 4 h to obtain a catalyst;

[0058] The catalyst was used in the hydroisomerization reaction of n-dodecane. The catalyst reduction conditions were: 400°C for 3h, H2 flow rate of 40mL / min; the reaction conditions were: normal pressure, V(H2) / V(C 12 )=2500, C 12 The flow rate is 0.5 mL / h, the temperature is 250°C, and the space velocity is 0.60 h -1 ; The reaction results are shown in Table 2.

[0059] Table 2 Catalytic results of samples in the hydroisomerization reaction of n-dodecane

[0060]

[0061] From the results in Table 2, it can be seen that the hydroisomerization reaction is carried out using n-dodecane as a representative. According to the reaction results, it can be seen that the catalyst prepared using the ZSM-48 molecular sieve provided by the present invention has a higher n-alkane conversion rate and isoalkane yield, which is better than the comparative example ZSM-48 molecular sieve.

[0062] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a ZSM-48 molecular sieve, characterized in that: The following steps are involved: Step 1) preparing a pre-crystallization solution; The seed crystal, silicon source, aluminum source, alkali source and deionized water are mixed to obtain a suspension, and the suspension is heated and stirred to obtain a clear, translucent colloidal pre-crystallization liquid, that is, a pre-crystallization liquid containing molecular sieve structure fragments; wherein the pH value of the obtained pre-crystallization liquid is 8.0-11.0, and the solid obtained after evaporation does not contain any crystalline phase according to XRD detection; Step 2) crystallization; Adding a structure directing agent to the obtained pre-crystallization liquid, stirring evenly, static aging, then sealing, heating and crystallizing to obtain a crystallized product; Step 3) filtering, washing, drying and calcining the obtained crystallized product; In step 1), the alkali source is a molecular sieve crystallization mother solution; in the pre-crystallization solution, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the alkali source is calculated as Na2O, and the molar ratio of silicon source: aluminum source: alkali source: deionized water is 20-120:1:0.5-40:200-6200; In step 1), the heating temperature of the heating and stirring is 60-120° C., the heating time is 1-12 hours, and the stirring speed is 10-80 rpm.

2. The method for preparing the ZSM-48 molecular sieve according to claim 1, characterized in that: In step 1), the molecular sieve crystallization mother liquor is selected from the crystallization mother liquor produced in the production of LTA molecular sieve and / or FAU molecular sieve; and the Na2O content in the molecular sieve crystallization mother liquor is 10-150 g / L.

3. The method for preparing the ZSM-48 molecular sieve according to claim 1, characterized in that: In step 1), the seed crystals are selected from at least one of completely crystallized Na-ZSM-48 molecular sieve, NH4-ZSM-48 molecular sieve, and H-ZSM-48 molecular sieve; and the amount of the seed crystals added accounts for 0.05-10 wt.% of the silicon source.

4. The method for preparing the ZSM-48 molecular sieve according to claim 1, characterized in that: In step 2), the molar ratio of the structure directing agent to the alkali source in the obtained pre-crystallization solution is 0.5-10:3-30.

5. The method for preparing the ZSM-48 molecular sieve according to claim 4, characterized in that: In step 2), the structure directing agent is selected from at least one of 1,6-hexanediamine, triethylamine, hexamethonium bromide, hexamethonium hydroxide, hexamethonium chloride, ethylenediamine, tetramethylammonium, and allyltrimethylammonium chloride.

6. The method for preparing the ZSM-48 molecular sieve according to claim 1, characterized in that: In step 2), the aging temperature is 60-120° C., and the aging time is 1-24 hours.

7. The method for preparing the ZSM-48 molecular sieve according to claim 1, characterized in that: In step 2), the heating crystallization is dynamic crystallization, the rotation speed is 30-90 rpm, the crystallization temperature is 140-210° C., and the crystallization time is 1-24 h.

8. The method for preparing the ZSM-48 molecular sieve according to claim 1, characterized in that: In step 3), the drying temperature is 60-120° C., the drying time is 1-24 hours, the roasting temperature is 500-650° C., and the roasting time is 1-16 hours.

9. A ZSM-48 molecular sieve, characterized in that: The molecular sieve is prepared by the preparation method of the ZSM-48 molecular sieve described in any one of claims 1 to 8.

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