阅读说明：本技术 低硅铝比型分子筛及其制备方法 (Low-silica-alumina ratio type molecular sieve and preparation method thereof ) 是由 吴再坤 穆新伟 孔剑 王存文 汪铁林 覃远航 马家玉 李雁博 吕仁亮 冯魏良 王 于 2021-09-26 设计创作，主要内容包括：本发明涉及一种低硅铝比型分子筛及其制备方法,首先分别配制碱铝溶液和硅溶液,然后按照SiO-(2)：Al-(2)O-(3)＝1.00-1.05的硅铝比将硅溶液与碱铝溶液混合,快速搅拌所得凝胶并密封加热静置陈化,接着继续升温晶化,自然冷却后过滤、洗涤、干燥、研磨,得到低硅铝比型分子筛。该低硅铝比型分子筛产品某些方面的性能(如吸附性、再生性)优于中高硅铝比分子筛,并且制造和使用成本低、可反复再生循环利用,与活性炭吸附剂相比安全性大幅度提高。(The invention relates to a low silicon-aluminum ratio molecular sieve and a preparation method thereof, which comprises the steps of firstly preparing an alkali aluminum solution and a silicon solution respectively, and then preparing the alkali aluminum solution and the silicon solution according to SiO 2 ：Al 2 O 3 Mixing the silicon solution and the alkali aluminum solution according to the silicon-aluminum ratio of 1.00-1.05, quickly stirring the obtained gel, sealing, heating, standing and aging, continuously heating for crystallization, naturally cooling, filtering, washing, drying and grinding to obtain the low-silicon-aluminum-ratio molecular sieve. The low-Si-Al ratio molecular sieve has the advantages of better performance (such as adsorptivity and regenerability) than the medium-high Si-Al ratio molecular sieve, low manufacturing and using cost, repeated regeneration and cyclic utilization and greatly improved safety compared with an activated carbon adsorbent.)

1. A preparation method of a low-silicon-aluminum ratio type molecular sieve is characterized by comprising the following steps: (a) dissolving an aluminum source in water, adding an alkali source to obtain an alkali-aluminum solution, and dissolving a silicon source in water to obtain a silicon solution; (b) according to SiO₂：Al₂O₃Mixing the silicon solution with the alkali aluminum solution according to the silicon-aluminum ratio of 1.00-1.05, and quickly stirring to obtain gel; (c) and sealing and heating the gel, standing for aging, heating for crystallization, naturally cooling to room temperature, filtering, washing, drying and grinding to obtain the low-silica-alumina ratio molecular sieve.

2. The method of claim 1, wherein: the aluminum source is specifically sodium aluminate, the alkali source is specifically a mixture of sodium hydroxide and potassium hydroxide, and the silicon source is specifically sodium silicate.

3. The method of claim 1, wherein: the alkali source is added at least 3 times, and is stirred to be completely dissolved after each addition is finished, and then the addition is continued.

4. The method of claim 1, wherein: the mass fraction of the aluminum source in the alkali aluminum solution is 7-13%, the mass fraction of the alkali source is 17-30.5%, and the mass fraction of the silicon source in the silicon solution is 39-47.5%.

5. The method of claim 1, wherein: and during mixing, slowly adding the silicon solution into the alkali-aluminum solution, and rapidly stirring the mixture during and after the addition for 4 hours to ensure that the mixture is fully gelatinized.

6. The method of claim 1, wherein: the heating temperature of the gel sealing is 35-80 ℃, and the aging time is controlled within 24 h.

7. The method of claim 1, wherein: after aging, the mixture is continuously heated to 80-90 ℃ to complete crystallization, and the crystallization time is controlled within 12 h.

8. The method of claim 1, wherein: and repeatedly washing the filter residue with water until the pH value is less than 8, then placing the filter residue at 80-90 ℃ for drying, and then grinding the filter residue into powder.

9. The method of claim 1, wherein: the specific surface area of the low-silicon-aluminum ratio type molecular sieve is 570-650m²Per g, the pore diameter is 0.67-0.75nm, and the micropore volume is 0.23-0.34cm³Per gram, the particle diameter is 90-130nm, and the crystallinity is 85-94%.

10. A low silica-alumina ratio molecular sieve, characterized in that: the molecular sieve is prepared according to any one of claims 1 to 8.

Technical Field

The invention relates to the technical field of molecular sieves and environmental protection, in particular to a low-silica-alumina ratio type molecular sieve and a preparation method thereof.

Background

As an inevitable industrial waste gas, carbonyl sulfide (COS) gas is often difficult to remove due to low concentration, and residual COS can cause poisoning of downstream catalysts and damage to pipeline instruments and equipment, so the treatment of COS is always a difficult problem to solve.

The carbonyl sulfide in the mixed gas can be removed by adsorption by using the adsorbent, and the common COS adsorbent has a plurality of defects. For example, although activated carbon has the advantages of wide source, relatively low price, large specific surface area, abundant microporous structure and the like, and is a common adsorbent material in industrial waste gas treatment at present, activated carbon is difficult to regenerate after being used and has high carbon loss rate. In addition, the high-temperature inflammability of the activated carbon greatly reduces the use safety of the activated carbon.

Molecular sieves are also common adsorbent materials with varying pore sizes, specific surface areas and cavities. The molecular sieves are various in types, the high-efficiency selective adsorption of COS is hopeful to be realized by selecting proper molecular sieves, and the high-temperature regenerability and the safety of the molecular sieves are superior to those of activated carbon. With the stricter environmental protection policy, the molecular sieve replaces more and more active carbon in the aspect of treating low-concentration and large-gas-volume industrial COS pollution. We have developed a NaY type molecular sieve product and used it to adsorb and separate COS in a gas with certain success. On the basis, the inventor further studies deeply, the microstructure of the molecular sieve is regulated and controlled by strictly controlling the silica-alumina ratio, the hydrophobicity of the molecular sieve is enhanced, the COS adsorption capacity of the molecular sieve is improved, and the low silica-alumina ratio type molecular sieve still maintains the original adsorption performance after being regenerated for many times at high temperature.

Disclosure of Invention

The invention aims to provide a preparation method of a low-silica-alumina ratio type molecular sieve, which comprises the following steps: (a) dissolving an aluminum source in water, adding an alkali source to obtain an alkali-aluminum solution, and dissolving a silicon source in water to obtain a silicon solution; (b) according to SiO₂:Al₂O₃Mixing the silicon solution with the alkali aluminum solution according to the silicon-aluminum ratio of 1.00-1.05, and quickly stirring to obtain gel; (c) and sealing and heating the gel, standing for aging, heating for crystallization, naturally cooling to room temperature, filtering, washing, drying and grinding to obtain the low-silica-alumina ratio molecular sieve.

Further, the aluminum source is specifically sodium aluminate, the alkali source is specifically a mixture of sodium hydroxide and potassium hydroxide, and the silicon source is specifically sodium silicate.

Further, the alkali source is added in at least 3 times, and after each addition, the alkali source is stirred to be completely dissolved and then added continuously.

Further, the mass fraction of the aluminum source in the alkali-aluminum solution is 7% -13%, the mass fraction of the alkali source is 17% -30.5%, and the mass fraction of the silicon source in the silicon solution is 39% -47.5%.

Further, the silicon solution is slowly added into the alkali aluminum solution during mixing, and the mixture is rapidly stirred during and within 4 hours after the addition, so that the mixture is fully gelatinized.

Furthermore, the heating temperature of the gel sealing is 35-80 ℃, and the aging time is controlled within 24 h.

Further, after aging, the mixture is continuously heated to 80-90 ℃ to complete crystallization, and the crystallization time is controlled within 12 hours.

Further, repeatedly washing the filter residue obtained by filtering with water until the pH value is less than 8, then placing the filter residue at 80-90 ℃ for drying, and then grinding the filter residue into powder.

Further, the low silicon-aluminum ratio typeThe specific surface area of the sub-sieve is 570-650m²Per g, the pore diameter is 0.67-0.75nm, and the micropore volume is 0.23-0.34cm³Per gram, the particle diameter is 90-130nm, and the crystallinity is 85-94%.

It is another object of the present invention to provide a low silica to alumina ratio molecular sieve having the above structural and performance parameters. The molecular sieve can be used for separating and removing COS in gas, and the performance of the molecular sieve with saturated adsorption is basically unchanged after high-temperature regeneration, and the molecular sieve can be repeatedly used.

Compared with the prior art, the beneficial effects of the invention are embodied in the following aspects: (1) on the basis of the existing series of molecular sieve products of the inventor, a low-silica-alumina ratio molecular sieve is continuously developed, the types of the molecular sieve products are enriched, and the requirements of different users are met; (2) the adsorptivity and the regeneration performance of the developed low-silicon-aluminum ratio molecular sieve product are obviously superior to those of the medium-high-silicon-aluminum ratio molecular sieve; and (3) the production and use cost is low, the material can be repeatedly regenerated and recycled, and the safety is greatly improved.

Drawings

FIG. 1 is a flow chart of a process for preparing a low silica-alumina ratio molecular sieve;

FIG. 2 is a COS adsorption test reactor fixed bed test unit;

FIG. 3 is an XRD pattern of the low silica to alumina ratio molecular sieve prepared in example 1;

FIG. 4 is an SEM image of a low silica to alumina ratio molecular sieve prepared in example 1;

FIG. 5 is a graph of the adsorption capacity of the low silica-alumina ratio molecular sieve prepared in example 1;

FIG. 6 is a graph of the stability of the low silica alumina ratio molecular sieve prepared in example 1 after 10 regenerations.

Detailed Description

In order to make those skilled in the art fully understand the technical solutions and advantages of the present invention, the following description is further provided with reference to the specific embodiments and the accompanying drawings.

Example 1

4.474g NaAlO₂Dissolving in 45g deionized water, adding 6.218g NaOH and 4.306g KOH into the solution for three times, and stirring for 4h to obtain the final productAn alkaline aluminum solution. About 9.2g of sodium silicate was weighed out and dissolved in 10.36g of deionized water, and the resulting mixture was added to the above-mentioned alkali aluminum solution and stirred rapidly for 2 hours to obtain a homogeneous gel. And sealing and heating the gel to 40 ℃, standing and aging for 10h, transferring the mixture into a self-pressing kettle with a polytetrafluoroethylene lining, and placing the self-pressing kettle in a forced air oven at 80 ℃ for crystallization for 8 h. Naturally cooling to room temperature after crystallization, filtering, and repeatedly washing the filter residue with water until the pH value is reached<And 8, transferring the mixture to an oven to be dried for 6 hours at the temperature of 80 ℃, and then grinding the mixture to obtain the low-silica-alumina ratio type molecular sieve.

The microscopic detection results of FIGS. 3-4 show that the specific surface area of the low-silica-alumina-ratio molecular sieve is 607m²Per g, the pore diameter is 0.7139nm, and the micropore volume is 0.3207cm³The silicon-aluminum ratio was 1.02, the particle size was about 130nm, and the relative crystallinity was 92%.

In order to fully understand the capability and the regeneration performance of the low-silica-alumina ratio molecular sieve for removing COS by adsorption, adsorption and regeneration experiments are carried out. FIG. 2 shows the connection relationship between the apparatus used in the adsorption experiment and the respective components.

Experimental raw materials: the low silica alumina ratio molecular sieve prepared in example 1, the mixed gas with COS content of 200-1000ppm (wherein nitrogen is used as carrier gas), and the flow rate of the gas to be treated during adsorption is 10-100 mL/min. The fixed bed catalytic evaluation device is purchased from Suzhou Huaxiangshidao environmental protection science and technology, and the gas chromatograph is purchased from Fuli GC9790 Plus.

The adsorption experiment process comprises the following steps: accurately weighing 1g of low-silica-alumina ratio molecular sieve, and filling the low-silica-alumina ratio molecular sieve into a fixed bed, wherein the COS concentration of the mixed gas is set to be 200ppm, the gas flow is 10mL/min, and the experimental temperature is 25 ℃. Sampling is carried out at regular time in the experimental process, and the content of COS in the tail gas is detected by using a gas chromatograph and is compared with the initial content.

The result shows that the adsorption efficiency of the low-silica-alumina ratio molecular sieve on COS is 100% in 48h (the COS characteristic peak is considered to be all adsorbed if no COS characteristic peak is detected by gas chromatography, and the COS penetrating adsorption amount is judged to be lower than 1ppm by the invention), a slight COS characteristic peak appears on a spectrogram after 48h, and the adsorption saturation is reached after 72h (as shown in FIG. 5). The amount of adsorbed COS (mmol/g) can be calculated using the following formula:

in the formula, m: mass of adsorbent (g); v_m: molar volume of COS; q: mixed gas flow rate (ml/L); t: adsorption time; x₀、X_tThe initial and t-time values are indicated by the volume concentration (%) of COS in the mixed gas, respectively.

The regeneration experiment process comprises the following steps: and taking out the low-silica-alumina ratio molecular sieve with saturated adsorption, heating the molecular sieve to 300 ℃ in a muffle furnace, and carrying out constant-temperature treatment for 2 hours, thereby completing regeneration. The regenerated low silica-alumina ratio molecular sieve is used as an adsorbent, and the adsorption experiment is carried out again under the same condition. After ten regenerations, the COS adsorption capacity still reached 96.71% of that of fresh low silica-alumina ratio molecular sieve (as shown in fig. 6).

Example 2

22.37g NaAlO₂Dissolving in 100g of deionized water, adding 31.09g of NaOH and 21.53g of KOH into the solution for three times, and continuously stirring for 3 hours to fully and uniformly mix the solution to obtain the alkali aluminum solution. 46.0g of sodium silicate is weighed and dissolved in 71.8g of deionized water, the obtained mixed solution is added into the above-mentioned alkali-aluminum solution, and the mixture is rapidly stirred for 3 hours to obtain a uniform gel. And sealing and heating the gel mixture to 70 ℃, standing and aging for 2 hours, transferring the mixture into a polytetrafluoroethylene-lined self-pressing kettle, and placing the self-pressing kettle in a 85 ℃ blast oven for crystallization for 9 hours. Naturally cooling to room temperature after crystallization, filtering the mixture in the self-pressing kettle, and repeatedly washing the filter residue with water until the pH value is reached<And 8, placing the washed solid in an oven, drying at 80 ℃ for 12h, and grinding to obtain the low-silica-alumina-ratio molecular sieve.

The detection result shows that the specific surface area of the low-silicon-aluminum ratio type molecular sieve prepared in the embodiment is 650m²Per g, the pore diameter is 0.7089nm, and the micropore volume is 0.3142cm³The silicon-aluminum ratio is 1.01, the particle size is about 100nm, and the relative crystallinity is 92%.

The ability of the low silica alumina ratio type molecular sieve prepared in example 2 to adsorb and remove COS and the regeneration performance were tested according to the method in example 1.

The adsorption experiment process comprises the following steps: accurately weighing 1g of low-silica-alumina ratio molecular sieve, putting the low-silica-alumina ratio molecular sieve into a fixed bed, setting the concentration of COS in mixed gas to be 200ppm, the gas flow to be 10mL/min and the experimental temperature to be 26 ℃. The result shows that the adsorption efficiency of the low-silicon-aluminum ratio molecular sieve on COS is 100% within 72h of the experiment, a slight COS characteristic peak appears on a spectrogram after 72h, and the adsorption saturation is reached within 96 h.

The regeneration experiment process comprises the following steps: and taking out the low-silica-alumina ratio molecular sieve with saturated adsorption, heating to 400 ℃ in a muffle furnace, and carrying out constant-temperature treatment for 1h, thereby completing regeneration. The regenerated low silica alumina ratio molecular sieve is used as an adsorbent, and an adsorption experiment is carried out again under the same condition, and the result shows that after ten times of regeneration, the COS adsorption capacity of the regenerated low silica alumina ratio molecular sieve can still reach 97.24 percent of that of a fresh low silica alumina ratio molecular sieve.

For further analysis and comparison, the molecular sieves with the Si/Al ratio of 1.74 and 2.24 and the molecular sieves with the Si/Al ratio same as that of the examples 1-2 were respectively prepared under different conditions according to the examples 1-2 (see the Chinese patent of the same applicant entitled "NaY type molecular sieve and its preparation method and application in carbonyl sulfide adsorption"). The comparison shows that the regeneration temperature and the regeneration adsorption capacity are not as good as those of the low-silica-alumina-ratio molecular sieve. This is because the low silica alumina ratio type molecular sieve has an increased aluminum content and becomes an active site for adsorbing COS as compared with the medium-high type molecular sieve, contributing to enhancement of the physical adsorption capacity of the molecular sieve.