CN1207196C - Nano grade titanium silicon molecular sieve and its synthesis technology - Google Patents

Abstract

The present invention relates to a nanometer titanium-silicon molecular sieve and a synthesizing technology thereof, particularly to a titanium-silicon molecular sieve and a preparing method thereof. The molar composition of the molecular sieve is Na<1(+/-)X>Ti<1.5(+/-)Y>Si<1(+/-)Z>O5, wherein the value of X is from 0.01 to 0.2, the value of Y is from 0.1 to 0.5, and the value of Z is from 0.1 to 0.2. XRD powder diffraction peak (2theta) data comprises 11.40(+/-)0.2, 27.8(+/-)0.2, 36.2(+/-)0.5 and 46.8(+/-)0.5, and crystal cell parameters are: a=b=8.000(+/-)0.500 A, c=12.000(+/-)0.500 A. Crystal particles are tetragonal in shape and are in the size of 10 to 20 nm. Tetrabutyl titanate or tetraisopropyl titanate, ethyl orthosilicate, sodium hydroxide and water are used as raw materials, and a sol-gel method and a hydrothermal synthesizing method are jointly adopted to prepare the nanometer titanium-silicon molecular sieve. With the advantages of fine crystal particles, high reaction activity, no need of expensive templates, low synthesis cost, high exchange capacity on radioactive elements and heavy metal elements, favorable thermal stability and favorable radiation resistant performance, the molecular sieve can be widely used for removing heavy metal pollutants and radioactive pollutants in environment, purifying nuclides, etc.

Description

A kind of nanoscale titanium silicon molecular sieve and its synthesis process

technical field

The invention relates to a titanium-silicon molecular sieve and a synthesis process thereof. The molecular sieve is mainly used for removing radioactive pollutants and heavy metal pollutants in the environment or performing nuclide purification, and belongs to the technical fields of environmental protection and applied chemistry.

Background technique

Molecular sieves have a wide range of industrial applications in the separation of gas and liquid molecules, ion exchange, and catalytic reactions due to their uniform microporous structure and the ability to select appropriate molecules to enter their framework. With the continuous increase of industrial demand, people are designing and synthesizing the skeleton structure of molecular sieves and the size and shape of pores. The research on titanium-silicon molecular sieves has developed rapidly in recent years. In the early 1980s, Taramasso (TaramassoM, PeregoG, NotariB, US4410501, 1983) of Enichem Company in Italy reported for the first time that a molecular sieve TS-1 (MFI type), is considered a milestone in the field of molecular sieve research due to its excellent catalytic performance in the selective oxidation of various organic compounds with the participation of dilute hydrogen peroxide (30 wt%). Subsequently, it was reported that Ti-β (BEA type), Ti-ZSM-12 (MTW type), Ti-M (MOR type), Ti-MCM-41 (hexagonal system), Ti-MCM-48 (cubic crystal system) were synthesized. Crystal system) and Ti-HMS (hexagonal system) and other titanium silicon molecular sieves.

There are currently two main methods for the synthesis of titanium silicate molecular sieves:

(1) Isomorphic substitution method

The isomorphic substitution method is a gas-phase method using TiCl ₄ as a titanium source and a liquid-phase method using (NH ₄ ) ₂ TiF ₆ as a titanium source, also known as a gas-solid isomorphic substitution method (Thangaraj A, Kumar R, et al. Appl. Catal., 1990, 57, 1-3). The raw materials used in this method are generally high-silicon or all-silica zeolite molecular sieves as the silicon source material, and TiCl ₄ as the titanium source material. The isomorphic substitution reaction is carried out in a quartz tube fixed-bed reactor, and TiCl ₄ is brought into the reactor with N ₂ gas, and the isomorphic substitution is carried out at 400-700°C for a certain period of time to obtain titanium-silicon molecular sieve (TS). The framework structure of the zeolite is not changed during the crystal substitution process, and the corresponding TS-1 and TS-2 can be obtained by using ZSM-5 and ZSM-11 high-silica zeolite molecular sieves with MFI and MEL structures as silicon sources for isomorphic substitution. The disadvantages of this synthesis method mainly include the following aspects: high operating temperature and high energy consumption; it is a gas-solid phase operation, the reaction is difficult to control, and the process is complicated; high requirements for equipment and low reliability; large sample grains; Realize industrialization.

(2) Hydrothermal synthesis method

The hydrothermal synthesis method, also known as the direct synthesis method, is currently the most commonly used synthesis method for titanium-silicon molecular sieves. Generally, it is synthesized by mixing titanium source and silicon source materials with a template agent in a certain proportion and performing hydrothermal interaction with each other. The process is usually to stir the above-mentioned mixed sol at 70-90°C, after hydrolyzing for a certain period of time, transfer it to an autoclave, age at 90°C for 1-2 days, and then crystallize at 170°C under autogenous pressure for 2-10 After washing, filtering, and drying the obtained crystals, they were calcined at 550°C for 5-10 hours to obtain the original titanium-silicon molecular sieve powder (Reddy J S, Kumar R. Zeolites, 1992, 12, 95-100).

The silicon source materials used in the synthetic raw materials are ethyl orthosilicate (TEOS) and butyl orthosilicate (TBOS); the titanium source materials include ethyl orthotitanate (TEOT) and butyl orthotitanate (TBOT); the templating agent Usually tetrapropylammonium hydroxide (TPAOH), tetrabutylammonium hydroxide (TBAOH) and the like are used. The difference of templating agent causes the difference of crystal structure (Esposito A, Taramasso M, et al. USP4396783,1983). When TPAOH is used as a template, the synthesized titanium-silicon molecular sieve has a ZSM-5 type MFI structure, that is, TS-1 (also known as Ti-ZSM-5); when TBAOH is used as a template, the synthesized titanium-silicon molecular sieve has a ZSM- 11 zeolite-type MEL structure, that is, TS-2 (also known as Ti-ZSM-11).

The shortcoming of this synthesis method mainly contains the following aspects at present:

(1) A large amount of expensive TPAOH template needs to be used in the synthesis process.

(2) The smaller the particle size of titanium silicon molecular sieve, the better the activity. Therefore, it is very important to control the grain size of titanium-silicon molecular sieves, which should generally be less than 0.2 μm, but the particle size of titanium-silicon molecular sieves currently synthesized is mostly above 1 μm.

(3) Low ion exchange capacity, poor thermal stability and radiation resistance.

Contents of the invention

The purpose and task of the present invention is to provide a nano-scale titanium-silicon molecular sieve and its synthesis process, so that it does not need to use expensive templates in the synthesis, the synthesized molecular sieve has fine grains, and has a high resistance to radioactive elements and heavy metal elements. High exchange capacity, good thermal stability and radiation resistance.

The nano-scale titanium-silicon molecular sieve of the present invention is characterized in that the nano-scale titanium-silicon molecular sieve exhibits the following physical and chemical properties:

(1) Its molar composition is Na _1±X Ti _1.5±Y Si _1±Z O ₅ , where the value of X is 0.01-0.2, the value of Y is 0.1-0.5, and the value of Z is 0.1-0.2;

(2) XRD powder diffraction peak (2θ) data: 11.40±0.2, 27.8±0.2, 36.2±0.5, 46.8±0.5;

(3) The unit cell parameters are a=b=8.000±0.500 Å, c=12.000±0.500 Å;

(4) The crystal grains are square and the size is 10-20 nanometers

(5) Appearance: white powder.

The synthesis process of the nano-scale silicon-titanium molecular sieve is as follows: Tetraisopropyl titanate ([(CH ₃ ) ₂ CHO] ₄ Ti), 5% to 15% ethyl orthosilicate ([C ₂ H ₅ ] ₄ SiO ₄ ), 1% to 10% sodium hydroxide, and 65% to 80% water are the synthetic raw materials (the above are weight percentages, and the raw materials are analytically pure), and the sol-gel method and the hydrothermal synthesis method are used to complete the synthesis. Its synthesis comprises the following steps in turn:

(1) 65%～80% water and 1%～10% sodium hydroxide are mixed with the aqueous solution of sodium hydroxide by weight percentage;

(2) under continuous stirring, 5% to 15% by weight of tetraisopropyl titanate is added dropwise to the aqueous solution of sodium hydroxide, and the pH value of the solution is controlled at 10 to 12;

(3) adding tetraethyl orthosilicate at a rate of 0.01 ml/sec to 0.1 ml/sec dropwise at a rate of 5% to 15% by weight to obtain a white colloid;

(4) Transfer the white colloid to a simple reaction autoclave, and perform a hydrothermal reaction at 140-250° C. for 3-10 days to obtain a solid product;

(5) The above solid product was washed with acetone and deionized water respectively, centrifuged and dried in an oven to obtain a white powder sample.

The invention synthesizes a nano-scale titanium-silicon molecular sieve by using raw materials with better hydrolysis performance, adjusting raw material ratio and adding sequence, solution pH value, controlling dropping speed and hydrothermal synthesis temperature and the like. The molecular sieve has small crystal grains between 10 and 20nm, which greatly improves the reactivity of the product; in addition, there is no need to use expensive templates in the synthesis, which greatly reduces the synthesis cost; the titanium-silicon molecular sieve is resistant to heavy metal Elements and radioactive elements have high exchange capacity, good thermal stability and radiation resistance, and can be widely used in the removal of heavy metal pollutants and radioactive pollutants in the environment and the purification of nuclides.

Description of drawings

Figure 1 is a SEM image of the present invention. It can be seen from the figure that the sample particles are very fine, and the size of the powder is nanoscale. Since nanocrystals have a large specific surface area and surface free energy, they are basically in an agglomerated state, so the specific morphology of the particles cannot be seen from the SEM photos.

Fig. 2 is a TEM image of the present invention. It can be seen from the figure that the visible particles are regular tetragonal crystal grains, and the particle size of the particles is about 10-20 nm.

Detailed ways

Example 1:

Add 6% sodium hydroxide to 76% water, under continuous stirring, first add 8% tetraisopropyl titanate dropwise to the aqueous solution of sodium hydroxide, then add 10% tetraethyl orthosilicate in 0.06ml /s speed dropwise into the mixture to obtain a white colloid. Then the colloid was transferred to a simple high-pressure reactor, and the hydrothermal reaction was carried out at a temperature of 190° C. for 4 days. The obtained solid product was washed with acetone and deionized water respectively, centrifuged and dried in an oven to obtain the desired sample.

The atomic absorption spectrometry (AAS) was used to measure the distribution coefficient of the sample to cesium in the aqueous solution of 0.1M HNO ₃ and 100ppm cesium up to 36500ml/g; in the aqueous solution of 0.1M NaOH and 100ppm strontium, the distribution coefficient to strontium could be Up to 9000ml/g; in an aqueous solution of 0.1M NaOH and 100ppm lithium, the distribution coefficient for lithium can reach 800ml/g.

Example 2:

Add 2% sodium hydroxide to 80% water, under continuous stirring, first add 5% tetraisopropyl titanate dropwise to the aqueous solution of sodium hydroxide, then add 13% tetraethyl orthosilicate in 0.02ml /s speed dropwise into the mixture to obtain a white colloid. Then the colloid was transferred to a simple reactor, and the hydrothermal reaction was carried out at a temperature of 140° C. for 10 days. The obtained solid product was washed with acetone and deionized water respectively, centrifuged and dried in an oven to obtain the desired sample.

The atomic absorption spectrometry (AAS) is used to measure that the distribution coefficient of the sample to cesium in an aqueous solution of 0.1M HNO ₃ and 100 ppm cesium can be as high as 10000ml/g. In the aqueous solution of 0.1M NaOH and 100ppm strontium, the distribution coefficient of strontium can be as high as 15000ml/g. In an aqueous solution of 0.1M NaOH and 100ppm lithium, the distribution coefficient for lithium can reach 600ml/g.

Example 3:

Add 10% sodium hydroxide to 70% water, under continuous stirring, first add 15% tetraisopropyl titanate dropwise to the aqueous solution of sodium hydroxide, then add 5% tetraethyl orthosilicate in 0.09ml /s speed dropwise into the mixture to obtain a white colloid. Then the colloid was transferred to a simple reactor, and the hydrothermal reaction was carried out at 250° C. for 4 days. The obtained solid product was washed with acetone and deionized water respectively, centrifuged and dried in an oven to obtain the desired sample.

The atomic absorption spectrometry (AAS) is used to measure that the distribution coefficient of the sample to cesium in an aqueous solution of 0.1M HNO ₃ and 100 ppm cesium can be as high as 11000ml/g. In the aqueous solution of 0.1M NaOH and 100ppm strontium, the distribution coefficient of strontium can be as high as 8000ml/g. In an aqueous solution of 0.1M NaOH and 100ppm lithium, the distribution coefficient for lithium can reach 1033ml/g.

Claims (2)

1. A nanoscale titanium-silicon molecular sieve, characterized in that the nanoscale titanium-silicon molecular sieve shows the following physical and chemical properties: (1) Its molar composition is Na _1±X Ti _1.5±Y Si _1±Z O ₅ , where the value of X is 0.01-0.2, the value of Y is 0.1-0.5, and the value of Z is 0.1-0.2; (2) XRD powder diffraction peak (2θ) data: 11.40±0.2, 27.8±0.2, 36.2±0.5, 46.8±0.5; (3) The unit cell parameters are a=b=8.000±0.500 Å, c=12.000±0.500 Å; (4) The crystal grains are square and the size is 10-20 nanometers; (5) Appearance: white powder. 2. a synthetic method of nanoscale titanium-silicon molecular sieve as claimed in claim 1, its method comprises the steps successively: (1) 65%～80% water and 1%～10% sodium hydroxide are mixed with the aqueous solution of sodium hydroxide by weight percentage; (2) under continuous stirring, 5% to 15% by weight of tetraisopropyl titanate is added dropwise to the aqueous solution of sodium hydroxide, and the pH value of the solution is controlled at 10 to 12; (3) adding tetraethyl orthosilicate at a rate of 0.01 ml/sec to 0.1 ml/sec dropwise at a rate of 5% to 15% by weight to obtain a white colloid; (4) Transfer the white colloid to a simple reaction autoclave, and perform a hydrothermal reaction at 140-250° C. for 3-10 days to obtain a solid product; (5) The above solid product was washed with acetone and deionized water respectively, centrifuged and dried in an oven to obtain a white powder sample.

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