CN1052453C - Method for preparing vanadium-silicon molecular sieve (VS-1) - Google Patents

Abstract

A method for preparing a vanadium-silicon molecular sieve (VS-1) with an MEI structure, comprising dissolving a vanadium source in an aqueous solution of tetrapropylammonium hydroxide and mixing it with solid silica gel beads of 60 to 220 meshes to obtain a reaction mixture. The reaction mixture was crystallized at 120～180° C. for 2～8 days in an autoclave, then filtered, washed, dried and roasted according to conventional methods, wherein the molar composition of said reaction mixture is:

SiO ₂ /VO ₂ 15～600,

TPAOH/SiO ₂ 0.04～0.40

H ₂ O/SiO ₂ 1-30.

Description

A kind of preparation method of vanadium silicon molecular sieve (VS-1)

The invention relates to a preparation method of a vanadium-silicon molecular sieve, in particular to a preparation method of a vanadium-silicon molecular sieve (VS-1) with an MFI structure.

The introduction of transition element vanadium with coordination and valence characteristics into molecular sieves can combine the performance of molecular sieves with the catalytic performance of transition metals to produce unique catalytic effects. Experiments have shown that vanadium-silicon zeolites have good catalytic performance in many organic oxidation reactions, such as vanadium-containing ZSM-5 molecular sieve (VS-1) with MFI structure in toluene oxidation, phenol hydroxylation, xylene ammoxidation, alkane oxidation It shows good catalytic performance in many organic redox reactions, especially good reaction selectivity, and has a good application prospect.

Vanadium can be introduced into high silica molecular sieves by impregnation or ion exchange. For example, F.Cavani and F.Trifiro (Zeolites, 1988, Vol 8, January) reported that HZSM-5 and HZSM-11 were impregnated with NH ₄ VO ₃ to obtain Molecular sieve containing vanadium; B.IWhittington and JR Anderson (J.Phys.Chem, 1991,95,3306-3310) reported the ZSM-5 molecular sieve containing vanadium prepared by post-modification method; , Vol. 8, No. 3, p. 339, 1992) reported that molecular sieves containing vanadium were obtained by mixing and grinding V ₂ O ₅ and ZSM-5 and other molecular sieve samples uniformly and roasting them in a water-containing atmosphere. However, it is difficult to introduce vanadium into the framework structure of molecular sieves by these methods. So far, the truly effective vanadium-silicon molecular sieves are synthesized by hydrothermal crystallization.

There are not many reports on the synthesis of vanadium-silicon molecular sieve (VS-1) with MFI structure by hydrothermal crystallization method. In 1985, Japan's TomoynkiINUI et al. (Applied Catalysis, 18 (1985), 311-324) reported a method for hydrothermally synthesizing VS-1, which used VCl ₃ , Na ₂ SiO ₃ , TPABr (tetrapropane ammonium bromide), H ₂ SO ₄ , NaCl, etc. as raw materials, three solutions containing different components were mixed and centrifuged to separate the precipitate, and the other three solutions containing different components were mixed and centrifuged to separate the solution. After mixing the precipitate with the solution, hydrothermal crystallization, the operation steps of this method are very complicated.

People such as P.Fejes have reported a kind of method (Zeolite Chemistry and Catalysis, 1991, P173-180) of synthesizing VS-1, and this method is to use VO (COO) ₂ and sodium silicate as raw material, use TPABr as template agent, and ZSM-5 molecular sieve seeds were added to prepare a synthetic solution with the composition of SiO ₂ : 0.2VO ₂ : 39.2H ₂ O : 0.3 TPABr, and the synthetic solution was crystallized at 160° C. for 10 days.

MSRigutto and Van Bekkum reported a method for hydrothermally synthesizing VS-1 (Applied Catalysis, 68 (1991) L1～L7), the molar ratio of the synthetic liquid used in this method is: 100 SiO : ₁₁ TPAOH (tetrapropane ammonium hydroxide): 11NH ₃ : (100 x) VOSO ₄ : 1200 H ₂ O, where x = 0.010, 0.020, 0.040, the SiO ₂ raw material used is Ludox AS-40 (Dupont), that is, colloidal SiO ₂ solution , the crystallization condition was crystallization at 180 °C for 3 days under _N2 atmosphere.

In the prior art of the above three hydrothermal synthesis of VS-1, either the preparation process is more complicated, or a larger amount of template is required due to the larger H ₂ O/SO ₂ , which makes the product cost higher.

The purpose of the present invention is to provide a method for preparing VS-1, so that the prepared VS-1 molecular sieve has low cost and relatively simple preparation steps.

The feature of the method provided by the present invention is to adopt cheap solid silica gel pellets as a silicon source, soak the SiO _pellets with vanadium-dissolved tetrapropylammonium hydroxide (TPAOH) aqueous solution, and the crystallization reaction is formed on the surface of the silica gel pellets Carry out layer by layer from outside to inside until the crystallization is complete, so that as little water as possible can be added to the synthesis system, so that a small amount of organic base (TPAOH) can be added to meet the basicity and template dosage required for the synthesis of vanadium-silicon molecular sieves , thereby reducing costs and simplifying operations.

The method for preparing VS-1 molecular sieve provided by the present invention is to dissolve the vanadium source in tetrapropyl ammonium hydroxide aqueous solution, and mix with solid silica gel pellets to obtain a reaction mixture, and the reaction mixture is heated in an autoclave at 120- Crystallization at 180°C for 2 to 8 days, then filter, wash, dry and roast according to conventional methods, wherein the molar composition of the reaction mixture is:

Scope Scope Preferred

SiO ₂ /VO ₂ 15～600 40～300

TPAOH/SiO ₂ 0.04～0.40 0.05～0.30

H ₂ O/SiO ₂ 1～30 1～15

Said vanadium source in the method provided by the present invention can be vanadium pentoxide, metavanadate (MVO ₃ ), vanadium salt (for example VCl ₃ , V(C ₂ O ₄ ) ₂ ), vanadium oxycompound (for example VOSO ₄ , VOCl ₃ ) or organovanadium complexes (eg vanadium triacetylacetonate V(C ₅ H ₇ O ₂ ) ₃ ).

In the method provided by the present invention, when the vanadium source is dissolved in the tetrapropylammonium hydroxide aqueous solution, the auxiliary agent ethylenediamine can be added to promote the dissolution of the vanadium source. Wherein the molar ratio of ethylenediamine/ _VO2 is 0-20.

The particle size of the solid silica gel beads in the method provided by the invention is 60-220 mesh, and the preferred particle size is 80-180 mesh.

The crystallization conditions in the method provided by the present invention are that the temperature is 120-180°C and the time is 2-8 days; Crystallize at ℃ for 2-6 days.

Compared with the prior art, the method for preparing VS-1 molecular sieve provided by the present invention has cheap and easy-to-obtain raw materials, the low consumption of organic ammonium template makes the product cost low, and the condition control of the preparation process is not so strict and complicated. , the preparation process is relatively simple, and it is easy to be applied in industry, and because the water consumption in the reaction system is less, the single-pot output is increased.

The following examples will further illustrate the present invention. In the following examples, the solid silica gel beads used are products of Qingdao Silica Gel Factory, TPAOH is a product of Tokyo Chemical Industry, Japan, and the rest of the reagents are commercially available chemically pure reagents.

Instance 1

Weigh 0.116g V ₂ O ₅ and dissolve in 8.12g 40wt% TPAOH aqueous solution, stir and dissolve at 24°C for 40 minutes, then add 6.52g 80-120 mesh SiO ₂ pellets (92% on a dry basis), and then add 1.81g H ₂ O , after mixing evenly, the resulting reaction mixture was charged into a stainless steel reactor with a polytetrafluoroethylene liner, and crystallized at 136° C. for 5 days. The crystallized product was filtered, washed and dried, and then calcined at 520°C for 6 hours. Wherein the molar composition of reaction mixture is:

SiO ₂ : 0.013VO ₂ : 0.16TPAOH : 4H ₂ O, (SiO ₂ /VO ₂ =77)

The X-ray diffraction (XRD) data of the obtained samples showed that the synthesized VS-1 molecular sieve had a typical MFI structure. The relative crystallinity of the obtained sample was 89.7% (compared to Silicalite-1 with good crystallinity, synthesized according to the method described in Stud. Surf. Sci. Catal. 18 (1984) P159). Using Perkin-Elmer-580 double-beam infrared spectrometer to carry out infrared (IR) analysis on this sample, the data shows that the characteristic absorption peak of 970cm ^-1 that Silicalite-1 does not have appears on the IR spectrum of VS-1, This is caused by V(V) entering the zeolite framework and affecting the antisymmetric stretching vibration of the Si-O bond, which is considered to be the evidence that V enters the zeolite framework.

Instances 2~5

Prepare according to the method and steps of example 1, but change _V O _consumption , be mixed with the reaction mixture of following molar composition:

(2) SiO ₂ : 0.033VO ₂ : 0.16TPAOH : 4H ₂ O. (SiO ₂ /VO ₂ =30)

(3) SiO ₂ : 0.0071VO ₂ : 0.16TPAOH : 4H ₂ O. (SiO ₂ /VO ₂ =140)

(4) SiO ₂ : 0.0034VO ₂ : 0.16TPAOH : 4H ₂ O. (SiO ₂ /VO ₂ =294)

(5) SiO ₂ : 0.0021VO ₂ : 0.16TPAOH: 4H ₂ O. (SiO ₂ /VO ₂ =476)

The above four reaction mixtures were crystallized at 140°C for 6 days, and the crystallized products were filtered, washed, and dried, and then calcined at 510°C for 6 hours. The crystallinity of the samples were: (2) 82.9%, (3) 91.2%, (4) 93.7%, (5) 96.9%. The characteristic absorption peak of 970cm ^-1 appears in its IR spectrum.

Instances 6-8

Weigh 0.21g of NaVO ₃ 2H ₂ O and dissolve it in 625g of 52% TPAOH aqueous solution, stir and dissolve at room temperature for 50min, then add 6.52g of 80-120 mesh SiO ₂ pellets (92% on a dry basis), stir well, and then add (6 ) 0.0g water; (7) 9.08g water; (8) 28.88g water, mix homogeneously, obtain the reaction mixture of following proportioning:

(6) SiO ₂ : 0.013 VO ₂ : 0.16TPAOH : 1.95H ₂ O

(7) SiO ₂ : 0.013 VO ₂ : 0.16TPAOH: 7H ₂ O

(8) SiO ₂ : 0.013 VO ₂ : 0.16TPAOH: 18H ₂ O

The above three reaction mixtures were transferred into a stainless steel reactor, and crystallized at 139° C. for 6 days. The crystallized product was filtered, washed and dried, and then calcined at 520°C for 6 hours. The relative crystallinity of the obtained samples were: (6) 82.4%; (7) 90.5%; (8) 85.6%. The characteristic absorption peak of 970cm ^-1 appears in its IR spectrum.

Instances 9-11

Dissolve three parts of 0.44g V(C ₅ H ₇ O ₂ ) ₃ in (9) 4.06g, (10) 8.12g, (11) 14.21g 40% TPAOH aqueous solution respectively, stir and dissolve at 30°C for 40min, and then respectively Add 6.52g of 80-120 mesh SiO _pellets , mix evenly, add (9) 424g, (10) 3.61g, (11) 1.75g distilled water respectively, stir evenly, and the molar compositions of the three reaction mixtures obtained are respectively:

(9) SiO ₂ : 0.0125 VO ₂ : 0.08TPAOH: 4H ₂ O

(10) SiO ₂ : 0.0125 VO ₂ : 0.16TPAOH: 5H ₂ O

(11) SiO ₂ : 0.0125 VO ₂ : 0.28TPAOH: 6H ₂ O

The three reaction mixtures were crystallized at 136°C for 6 days. The crystallized product was calcined at 510° C. for 7 hours after filtering, washing and drying. The relative crystallinity of the obtained products are respectively (9) 83.3%, (10) 89.7% (11) 90.1%, and the characteristic absorption peak of 970cm ^-1 appears on the IR spectra.

Instance 12

Dissolve 0.27g VOSO ₄ 3H ₂ O and 0.6g ethylenediamine in 7.11g 40% TPAOH aqueous solution, stir and dissolve at 22°C for 30min, add 6.52g 80-120 mesh SiO ₂ pellets and 2.42g H ₂ O, mix well , the molar composition of the resulting reaction mixture is:

SiO ₂ : 0.0125VO ₂ : 0.14TPAOH: 4H ₂ O : 0.10 Ethylenediamine

The reaction mixture was crystallized at 150°C for 4 days, filtered, washed and dried, then calcined at 500°C for 8 hours. The relative crystallinity of the obtained sample was 89.6%. A characteristic absorption peak at 970cm ^-1 appeared on its IR spectrum.

Instance 13

Dissolve 0.20g of VOC ₂ O ₄ in 7.11g of 40% TPAOH aqueous solution, stir and dissolve at 16°C for 50 minutes, add 6.67g of 100-160 (90% on a dry basis) mesh SiO ₂ pellets and 2.26g of H ₂ O, mix well, and obtain The molar composition of the reaction mixture is:

SiO ₂ : 0.013VO ₂ : 0.14TPAOH : 4H ₂ O

The reaction mixture was crystallized at 140°C for 7 days, filtered, washed and dried, then calcined at 500°C for 9 hours. The relative crystallinity of the obtained sample was 84.8%. A characteristic absorption peak at 970cm ^-1 appeared on its IR spectrum.

Example 14

Dissolve 0.20 g of VCl ₃ in 9.14 g of 40% TPAOH aqueous solution, stir and dissolve at 26°C for 60 min, add 6.52 g of 80-120 mesh SiO ₂ pellets, then add 3.0 g of H ₂ O, and stir evenly. The molar ratio of the resulting reaction mixture is:

SiO ₂ : 0.013VO ₂ : 0.18TPAOH : 5H ₂ O

The reaction mixture was pre-crystallized at 110°C for 1 day, and then crystallized at 154°C for 4 days. The crystallized product was filtered, washed, and dried, and then calcined at 490°C for 10 hours. The relative crystallinity of the obtained product was 87.5 %. A characteristic absorption peak at 970cm ^-1 appeared on its IR spectrum.

Claims (9)

1. a kind of preparation method of the vanadium-silicon molecular sieve with MFI structure is that silicon source, vanadium source, tetrapropyl ammonium hydroxide templating agent and water are mixed into gel to make reaction mixture, and this reaction mixture is crystallized in autoclave complete, then filter, wash, dry and roast according to conventional methods; it is characterized in that wherein said silicon source is a solid silica gel pellet, said mixing into gel is that vanadium source is dissolved in tetrapropyl ammonium hydroxide aqueous solution, and Mix evenly with solid silica gel beads to obtain a reaction mixture, wherein the molar composition of said reaction mixture is: SiO ₂ /VO ₂ = 15-600, TPAOH/SiO ₂ ＝0.04～0.40 H ₂ O/SiO ₂ =1-30. 2. according to the preparation method of claim 1, it is characterized in that ethylenediamine auxiliary agent can be added when vanadium source is dissolved in the tetrapropyl ammonium hydroxide aqueous solution, and wherein ethylenediamine/ _VO The mol ratio is 0～20 . 3. The preparation method according to claim 2, wherein the molar ratio of ethylenediamine/ _VO2 is 1-10. 4. The preparation method according to claim 1, wherein said vanadium source is vanadium pentoxide, metavanadic acid, vanadium salt, vanadium oxy compound or organic vanadium complex. 5. The preparation method according to claim 1, wherein the particle size of said solid silica gel beads is 60-220 mesh. 6. The preparation method according to claim 5, wherein said particle size is 80-180 mesh. 7. The preparation method according to claim 1, wherein said crystallization conditions are a temperature of 120-180° C. and a time of 2-8 days. 8. The preparation method according to claim 1, wherein the crystallization condition is to pre-crystallize at 80-115° C. for 8-48 hours, and then crystallize at 120-180° C. for 2-6 days. 9. according to the preparation method of claim 1, wherein the molar composition of said reaction mixture is: SiO ₂ /VO ₂ = 40-300, TPAOH/SiO ₂ ＝0.05～0.30 H ₂ O/SiO ₂ =1-15.