CN1724363A - A kind of high-silicon ultra-stable natural stilbite and its preparation method - Google Patents

Abstract

A natural high-Si desmine with super thermal stability (more than 1000 deg. C) and open artery structure is prepared from natural STI zeolite through acid exchange, ammonium exchange, calcining, ammonium fluorosilicate exchange and calcining.

Description

A kind of high-silicon ultra-stable natural stilbite and its preparation method

technical field

The invention belongs to the technical field of modification of natural zeolite materials, and in particular relates to a high-silicon super-stable natural stilbite and a preparation method thereof. Using natural STI zeolite as raw material, through dealumination and silicon supplementation modification methods, such as acid exchange, ammonium exchange and then roasting, ammonium fluorosilicate exchange and then roasting, etc., to obtain high-silicon natural STI zeolite (Si/Al>7.0), its pore The structure is open and perfect, and the thermal stability of the structure reaches above 1000°C.

Background technique

Zeolite molecular sieve is an inorganic aluminosilicate or phosphate crystal, the skeleton contains regular and orderly arranged pores or cages of molecular size (ca. It is widely used in industrial catalysis, adsorption separation and ion exchange.

It is a kind of natural stilbite found in Beijing area of my country. It has high grade, large reserves and low mining cost. It is a new natural mineral resource with wide application prospects. The natural zeolite belongs to the STI (Stilbite) zeolite structure type, with ten-membered ring channels (along the [100] direction, 0.49×0.62nm) and intersecting eight-membered ring channels (along the [101] direction, 0.27×0.56nm). Its single crystal structure was first determined by Galli. The ideal unit cell composition is Na ₄ Ca ₈ [Al ₂₀ Si ₅₂ O ₁₄₄ ]·56H ₂ O, which belongs to the calcium-rich STI zeolite [Galli, E.Acta Cryst.1971, B27, 833]. At present, there are few detailed studies on this zeolite in China, and its application is only in the primary industry with very low added value.

The thermal stability of the original Ca-STI zeolite structure is poor, and the skeleton is completely destroyed after roasting at 350°C for 2 hours, which greatly limits its application in the fields of catalysis and adsorption [Qiu Jin et al., Acta Chem. Sinica, 1999, 57(4), 377]. Mortier et al. found that the structural stability of STI zeolites is related to the position and type of exchangeable cations in the dehydration process [Mortier, W.J.etc.Am.Meneral.1981, 66, 309], among which Ca-STI zeolite has the worst stability, while H-STI zeolite structure is the most stable [Jacobs, P.A. etc. Faraday. Trans. 1979, I 75, 883]. Our research group has systematically studied the stability of STI zeolite modified by ammonium exchange, and found that the modified Na-STI zeolite still maintains a perfect structure after 700°C calcination. Modified STI zeolites (Na-STI and H-STI) have selective adsorption to olefins and alcohols with different chain lengths, and their surfaces have hydrophobic and solid acid properties [Li Jun et al., Acta Chem. Sinica, 2000, 58 (8), 988]. Compared with H-FER zeolite (ferrierite), H-STI zeolite has lower conversion rate of n-butene isomerization to isobutene catalytic reaction, but higher selectivity [Li, J. etc. Microporous Mesoporous Mater. 2000, 37(3), 365. Hong, S. B. etc. J. Am. Chem. Soc. 2004, 126(18), 5817]. H-STI zeolite can also be used as a host material to assemble functional substances to prepare structurally stabilized functional materials. The LiCl/H-STI host-guest material prepared by our research group has good moisture-sensitive properties [Zou Jing, Long Yingcai, ZL 01 1 12692.2. Zou Jing et al., Acta Chemical Sinica, 2001, 59(6), 862. Zou, J. etc. J. Mater. Chem. 2004, 14, 2405]. The acid resistance of H-STI zeolite has also been successfully developed for acid-resistant ion exchangers and adsorbents [Long Yingcai et al., ZL 03 141 604.7. Long, Y.-C. etc. Chin. J. Chem. 2004, 22(7), 668]. In order to further develop the application of this high-quality natural resource in the fields of catalysis, adsorption and functional materials, and further improve the thermal and hydrothermal stability of the zeolite, it is very necessary to realize the ultra-stabilization of its skeleton structure.

Generally, there are two ways to prepare H-type zeolite, that is, acid exchange and ammonium exchange followed by roasting. The former requires zeolite itself to have good acid resistance, while the latter has higher requirements for its thermal stability. Usually the HY zeolite used in petroleum catalytic cracking is prepared through the latter. Obviously, both methods are suitable for preparing H-STI zeolite from natural STI zeolite. At the same time, these two methods will cause partial dealumination of the skeleton, so that the silicon-aluminum ratio of the skeleton will be significantly increased, but at the same time, the defects of the skeleton will also increase. Generally speaking, the increase of silicon-aluminum ratio is beneficial to improve the thermal stability of zeolite framework, but the increase of framework defects will decrease its stability, which is a competitive process. For natural STI zeolites, acid exchange and calcination are easy to dealuminate the framework, and the presence of a large amount of non-framework aluminum will significantly reduce its exchange capacity and adsorption performance. Hong et al. used 1,4-lutidine butane as a template for the first time to synthesize STI zeolite with a high silicon-aluminum ratio (Si/Al=7.1), and its thermal stability was as high as 1100°C [Hong, S.B.etc.J.Am.Chem .Soc.2004, 126(18), 5817]. However, the templates used in the literature are difficult to prepare and the cost is high, and the composition ratio range of the synthetic reactants is very narrow, and the silicon-aluminum ratio of the product is difficult to continue to increase. We have chemically processed natural STI zeolite to obtain Na-STI zeolite with a silicon-aluminum atomic ratio of 6.81, and its thermal stability has been proved to have reached above 800 °C. This suggests that it is possible to further increase the framework silicon-aluminum ratio of natural STI zeolite through chemical treatment to achieve super-stabilization of the structure. Through the method of chemical modification, we have obtained H-STI zeolite with a framework silicon-aluminum ratio of 4.5-7.3. The framework structure and the thermal stability of the cationic product can reach 1000°C, and the structure is basically ultra-stable [Zhong Ying et al., Chem. Journal of the Chinese Academy of Sciences, 2005, 63(8), 720-724. Cheng, X. W. etc. Microporous Mesoporous Mater. 2005, 83, 233-243].

The invention adopts the modification method of dealumination and silicon supplementation, uses natural STI zeolite as raw material, roasts in air after acid exchange and ammonium exchange, and then roasts in air after exchange with ammonium fluorosilicate to prepare high-silicon ultra-stable STI Zeolite. The natural mineral resources used are of high grade, abundant reserves, low mining cost, simple preparation method, low investment in industrialization, and low production cost. As an adsorbent, catalyst and functional material, it has broad market prospects.

Contents of the invention

The purpose of the present invention is to propose a high-silicon ultra-stable natural stilbite (STI) and its preparation method, which can significantly increase the silicon-aluminum ratio of the product skeleton, keep the pore structure perfectly open, and achieve ultra-stable thermal stability.

The high-silicon stabilized natural stilbene (ST1) proposed by the present invention is to use natural STI zeolite as raw material, roast in air after acid exchange and ammonium exchange, and roast in air after exchange with ammonium fluorosilicate, etc. process to obtain high-silicon ultra-stable STI zeolite.

The high-silicon ultra-stabilized STI zeolite obtained by the invention has a skeleton silicon-aluminum ratio of 7.1-11.4, a specific surface area of 200-510m ² /g, a micropore volume of 0.06-0.19m ³ /g, and a thermal stability of 1000°C.

The preparation method of high silicon ultra-stable STI zeolite of the present invention is as follows:

The natural stilbene (ST1) is heat-exchanged with acid, washed and dried with water; then heat-exchanged with ammonium, washed and dried with water; then roasted in an air atmosphere in a tube furnace with both ends open; and then exchanged with ammonium fluorosilicate solution , washed with water and dried; finally roasted to obtain high-silicon ultra-stabilized STI zeolite.

In the above method, the original natural STI sample (Ca-STI zeolite) used was provided by the geological department of China, and its unit cell composition was Na _0.2 Mg _0.1 Ca _8.4 [Al _17.2 Si _54.8 O ₁₄₄ ]·65H ₂ O, and the chemical composition was m (SiO ₂ ):m(Al ₂ O ₃ ):m(MgO):m(CaO):m(Na ₂ O)=56.86:14.83:0.11:8.13:8.85×10 ^-2 , the atomic ratio of silicon to aluminum is 3.08, The grain size is 5-10 μm.

In the above method, the acid used is hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ) or acetic acid (HAc), etc., the concentration is 0.1-1mol/L, and the solid-liquid ratio is 1:10-1: 20. The exchange temperature is 80-100°C, 1-3 hours each time, and the exchange times are 1-4 times.

In the above method, the ammonium used is ammonium chloride (NH ₄ Cl), ammonium nitrate (NH ₄ NO ₃ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) or ammonium acetate (NH ₄ Ac), etc., with a concentration of 0.1- 1mol/L, the solid-liquid ratio is 1:10-1:20, the exchange temperature is 80-100°C, each time is 1-3h, and the number of exchanges is 1-4 times.

In the above method, the concentration of ammonium fluorosilicate ((NH ₄ ) ₂ SiF ₆ ) is 0.1-1mol/L, the solid-liquid ratio is 1:10-1:20, the exchange temperature is 20-50°C, and each time is 40-50h , the number of exchanges is 1-4 times.

In the above method, the calcination temperature is 400-600°C, the calcination time is 0.5-2h, and the air flow rate is 1-10mL/min.

The characteristics of the high silicon ultra-stable STI zeolite provided by the present invention can be characterized by the following methods:

1. Powder X-ray Diffraction (XRD). In powder X-ray diffraction, refer to the standard STI pattern to confirm that the product structure has not been destroyed after treatment.

2. Segmented temperature programmed roasting (TPH). The zeolite sample used to measure the thermal stability is programmed to heat up to 600°C in the muffle furnace for 2 hours, and then cooled to room temperature after constant temperature for 1 hour. The relative crystallinity data of the samples treated at 700, 800, 900, and 1000°C were sequentially obtained by calcination at a higher temperature.

3. Low temperature nitrogen adsorption. The product specific surface area and pore volume were calculated by the BJH method.

4. X-ray fluorescence scattering analysis (XRF). Calculate the product chemical silicon to aluminum ratio.

5. ²⁷ Al high-resolution magic-angle solid-state nuclear magnetic resonance spectrum ( ²⁷ Al MAS NMR). Calculate the non-skeletal aluminum content of the product.

Description of drawings

Fig. 1 is the XRD spectra of Ca-STI zeolite after acid exchange and then ammonium exchange roasting (H-STI) and ammonium fluorosilicate exchange roasting product (H-STI'). It can be seen that the structure of the product remains perfect after treatment. XRF results show that its chemical silicon-aluminum ratio is 4.63, and after deducting non-framework aluminum (34.6% content, calculated by ²⁷ Al MAS NMR), its skeleton silicon-aluminum atomic ratio is 7.1; The silicon-aluminum ratio is 9.09, and the skeleton silicon-aluminum atomic ratio reaches 11.4 after deducting the non-framework aluminum (the content is 20.2%, calculated by ²⁷ Al MAS NMR).

Figure 2 is the low-temperature nitrogen adsorption spectra of H-STI(a) and H-STI'(b) zeolites respectively. Both present typical type I adsorption curves, but the specific surface area and micropore volume of the former are 509m ² /g and 0.190cm ³ /g, which indicates that its structure is perfect and the pores are open, while the specific surface area and micropore volume of the latter are 199m ² /g and 0.061cm ³ /g, indicating that the pores are partially blocked.

Fig. 3 is the TPH spectrum of products H-STI zeolite (1) and H-STI' (2) zeolite. It can be seen that the relative crystallinity remains above 75% after calcination at 1000°C, indicating that the modified zeolite structure basically achieves ultra-stabilization, especially for H-STI', the relative crystallinity after calcination at different temperatures is significantly higher than that of The corresponding H-STI shows that its thermal stability increases significantly with the increase of the silicon-aluminum ratio.

Detailed ways

Further describe the present invention by embodiment below:

Example Acid exchange Ammonium exchange Roasting     Ammonium Fluosilicate Exchange acid type Concentration/Temperature Solid-to-liquid ratio/times Ammonium type Concentration/Temperature Solid-to-liquid ratio/times temperature traffic time Concentration/Temperature Solid-to-liquid ratio/times one HCl 0.1/80 1:10/4 NH ₄ Cl 0.1/80 1:10/4 400 1 2 0.1/20 1:10/4 two HCl 0.5/90 1:15/2 NH ₄ Cl 0.5/90 1:15/2 500 5 1 0.5/30 1:15/2 three _{H2SO4 _} 0.2/100 1:10/4 (NH ₄ ) ₂ SO ₄ 0.5/100 1:10/4 550 10 0.5 0.8/40 1:20/1 Four _{H2SO4 _} 1.0/90 1:20/1 (NH ₄ ) ₂ SO ₄ 1.0/100 1:20/1 600 8 0.5 1.0/50 1:18/1 five HNO ₃ 1.0/100 1:20/3 NH ₄ NO ₃ 0.8/95 1:18/3 450 9 1 0.9/45 1:15/3 six HNO ₃ 0.8/95 1:10/4 NH ₄ NO ₃ 0.3/95 1:20/4 500 4 1.5 0.3/50 1:20/4 seven HAc 0.5/85 1:15/2 _NH4Ac 0.9/85 1:15/3 550 6 0.8 0.6/35 1:16/3 eight HAc 1.0/100 1:20/1 _NH4Ac 0.5/80 1:10/4 600 3 2 1.0/50 1:20/2 Nine HCl 1.0/80 1:20/4 NH ₄ NO ₃ 1.0/100 1:10/4 450 10 1 0.7/40 1:10/4 ten HAc 0.5/100 1:10/3 NH ₄ Cl 1.0/90 1:20/2 550 8 1.5 0.5/45 1:20/2

Note: The units in the table are as follows:

Concentration——mol/L;

Solid to liquid ratio - mass ratio;

Temperature——℃;

Flow rate——mL/min;

Time - h.

Claims (5)

1, a kind of high silicon super stabilizing modified natural stilbite is characterized in that its framework si-al ratio is 7.1-11.4, specific surface area 200-510m ²/ g, micropore volume are 0.06-0.19m ³/ g, thermostability reaches 1000 ℃.

2, a kind of preparation method of high according to claim 1 silicon super stabilizing modified natural stilbite is characterized in that concrete steps are as follows:

Natural stilbite (ST1) with the acid heat exchange, is washed oven dry; Use the ammonium heat exchange again, the washing oven dry; Roasting in air atmosphere in the tube furnace of both ends open then; With the ammonium fluosilicate solution exchange, washing is dried again; After roasting obtains high silicon super stabilizing STI zeolite; Wherein, maturing temperature is 400-600 ℃, and roasting time is 0.5-2h, and air flow quantity is 1-10mL/min.

3, preparation method according to claim 2 is characterized in that used acid is hydrochloric acid, sulfuric acid, nitric acid or acetic acid, and used ammonium is ammonium chloride, ammonium nitrate, ammonium sulfate or ammonium acetate.

4, preparation method according to claim 2, the concentration that it is characterized in that acid or ammonium is 0.1-1mol/L, solid-to-liquid ratio is 1: 10-1: 20, the exchange temperature is 80-100 ℃, each 1-3h, exchange number of times 1-4 time.

5, preparation method according to claim 2 is characterized in that ammonium silicofluoride concentration is 0.1-1mol/L, and solid-to-liquid ratio is 1: 10-1: 20, and the exchange temperature is 20-50 ℃, each 40-50h, exchange number of times 1-4 time.

Images