CN107416859A - A kind of preparation method and application of step hole Beta molecular sieves - Google Patents

Abstract

The invention discloses a preparation method and application of a stepped pore Beta molecular sieve, belonging to the field of molecular sieve preparation. In this method, kaolin or retort clay activated by sub-molten salt is used as the whole aluminum source and part of the silicon source, and without adding any organic template, the activated mineral, alkali source, supplementary silicon source, seed crystal and Deionized water is mixed evenly in a certain proportion, and a step-pore Beta molecular sieve with macropore-micropore composite is synthesized through one-step hydrothermal crystallization. The advantage of the method provided by the present invention is that natural minerals activated by sub-molten salts are used as all aluminum sources and part of silicon sources, and no organic template is used in the synthesis process, which not only greatly reduces the synthesis cost of Beta molecular sieves, but also significantly The greenness of the production process of the molecular sieve material is improved, and the synthesized Beta molecular sieve is a macropore-micropore composite stepped pore material with high relative crystallinity and BET specific surface area, so it has a good industrial application prospect.

Description

A kind of preparation method and application of step hole Beta molecular sieve

technical field

The invention belongs to the field of molecular sieve preparation, and in particular relates to a method for preparing a stepped pore Beta molecular sieve.

Background technique

Beta molecular sieve was first synthesized by Wadlinger of Mobil Company in 1967, and its successful synthesis marked the beginning of the era of high silica zeolite. Beta molecular sieve has a unique pore structure, suitable acidity, and good thermal and hydrothermal stability. It is an important catalytic and adsorption material and is widely used in the fields of petroleum refining, petrochemical and fine chemical synthesis. As we all know, tetraethylammonium hydroxide (TEAOH) is currently the most widely used template for the synthesis of Beta molecular sieves. However, the use of organic templates also brings many negative problems. First, organic species used as templates are generally expensive, and their own synthesis process is complicated and cumbersome; second, the synthesis process of molecular sieves produces a large amount of waste water, because it contains a large amount of organic templates that are harmful to the environment, so it must be treated effectively. Third, in the later stage of molecular sieve synthesis, the method of high-temperature roasting is generally used to remove the organic template agent, and this process not only needs to consume a lot of energy, but also the organic species will be oxidized and decomposed by heat, and a large amount of harmful gases will be released ( Such as greenhouse gases), in addition, the removal process of organic templates will also cause the collapse of the zeolite framework structure, thereby reducing the availability of molecular sieves.

US 3308069 reports that white carbon black is used as the silicon source, sodium aluminate is used as the aluminum source, and it is made into a slurry, and the crystallization reaction is carried out at 75~200°C for 3~60 days in a crystallization kettle, and the raw materials are calculated as oxides. The molar ratio is: SiO ₂ /Al ₂ O ₃ =10~200, TEAOH/SiO ₂ =0.1~1.0, Na ₂ O/TEAOH=0~0.1, H ₂ O/TEAOH=20~75. This patent discloses the synthesis method of Beta molecular sieve for the first time, but in this process, the consumption amount of organic template agent tetraethylammonium hydroxide is relatively large and the crystallization time is long, and the synthesis cost is high.

In order to reduce the synthesis cost of Beta molecular sieves, many researchers try to use cheap non-tetraethylammonium hydroxide templates. For example: using dimethylbenzylamine-benzyl halide (EP 159846), dibenzyldimethylamine (US 4642226), diethylenetriamine (US7704487B2) and relatively cheap tetraethylammonium halide (US 4847055) Or use a composite template system, such as TEAOH-diethanolamine (US 5139759) and the like.

Although the above method reduces the cost of molecular sieves, there are still problems of waste water and waste gas discharge during the synthesis process. Therefore, in recent years, the research work on reducing the synthesis cost of Beta molecular sieves has shifted from looking for relatively cheap alternative templates to synthesizing Beta molecular sieves without templates.

Patent CN 101249968A has invented a method for synthesizing Beta molecular sieve without template agent, using white carbon black as the silicon source and sodium aluminate as the aluminum source, by adding roasted Beta molecular sieve seed crystals to the initial gel, in the crystallization kettle Crystallization reaction at 100~180℃ for 12-24 hours, the molar ratio of raw materials in terms of oxides is: SiO ₂ /Al ₂ O ₃ =31.4~40.3, Na ₂ O/SiO ₂ =0.26~0.342, H ₂ O/SiO ₂ =13~50. The SiO ₂ /Al ₂ O ₃ molar ratio of the Beta molecular sieve seed crystal is 22-25, and the seed crystal addition amount is 5-20 wt% of the silicon source. The invention breaks through the restriction that an organic template must be used in the synthesis of Beta molecular sieves, and the crystallization time is short. However, this method has disadvantages such as narrow synthesis phase region and small selection range of seed crystals.

Patent CN200610115385.1 reports a method of preparing Beta molecular sieves from kaolin, using acid-treated kaolin as a source of silicon and aluminum, and then adding it to the aqueous solution of TEA ⁺ and Na ⁺ and stirring evenly, at 120~185°C Crystallize under hydrothermal conditions for 26-60 hours. The molar ratio of raw materials in terms of oxides is: SiO ₂ /Al ₂ O ₃ =60~100, Na ₂ O/SiO ₂ =0.019~0.095, TEAOH/SiO ₂ ≥0.03, H ₂ O/SiO ₂ =1.3~5.3 . In the method, the reaction is carried out in an ultra-concentrated system, the crystallization time is short, and the crystallinity of the Beta molecular sieve is high. However, this method still uses a large amount of organic templates, resulting in high synthesis costs.

The following publications also relate to the template-free synthesis of Beta molecular sieves.

Public literature (Chemistry of Materials 2008, 20(14), 4533-4535) reported for the first time that calcined Beta molecular sieves were introduced as seed crystals into the initial gel without organic templates to realize the template-free synthesis of Beta molecular sieves. They used white carbon black as silicon source, NaAlO ₂ as aluminum source, and calcined agglomerated nano Beta molecular sieve (SiO ₂ /Al ₂ O ₃ molar ratio is 20~25) as seed crystal, and the initial gel ratio of the synthesis system 40SiO ₂ : 1Al ₂ O ₃ : 10Na ₂ O: 570H ₂ O, the crystallization condition is crystallization at 140°C for 17~19 hours. Short, greatly reducing the production cost of molecular sieves.

Thereafter, open literature (Chemistry of Materials 2009, 21(18), 4184-4191) reported the synthesis of different raw materials in a template-free system (freeze-dried _SiO2 powder or silica sol as silicon source, aluminum isopropoxide as aluminum source) For Beta molecular sieve, the raw powder of nano-beta molecular sieve without roasting is mainly used as the seed crystal, the initial gel ratio is 25SiO ₂ :0.25~0.75Al ₂ O ₃ :7.5Na ₂ O:375H ₂ O, and the crystallization temperature range It is 100~125℃. The author believes that the synthesis can only be carried out at a lower crystallization temperature (≤125°C), and the Beta molecular sieve product has a low yield (25-30%) and is rich in aluminum (7.8<SiO ₂ /Al ₂ O ₃ <11), crystallization The particle size is larger than that of the seed crystal.

Open literature (Chemistry An Asian Journal, 2010, 5, 2182-2191) has reported a kind of synthetic method of Beta molecular sieve without template agent, they take white carbon black as silicon source, _NaAlO as aluminum source, the Beta molecular sieve after roasting is The ratio of seed crystal and gel is SiO ₂ /Al ₂ O ₃ =40~100, Na ₂ O/SiO ₂ =0.275~0.325, H ₂ O/SiO ₂ =25. The crystallization condition was crystallization at 140°C for 30-70 hours. This method successfully used Beta molecular sieve synthesized by the template-free method as the seed crystal, and carried out a transfer of the synthetic seed crystal in the template-free system. Synthetic Beta molecular sieves are still microporous materials.

As a carrier of active species (metals, alloys, oxides), stepped pore molecular sieves can effectively prevent the aggregation of these active species during the preparation process and improve their dispersion; and the prepared bifunctional catalysts have dual active centers ( Loading active species and grade pore molecular sieve's own active sites) can better contact with reactants and play a synergistic effect.

In recent years, with the gradual deepening of research on the synthesis of Beta molecular sieves, Beta molecular sieves with stepped pores have been successfully synthesized by introducing hard templates such as carbon nanomaterials, organosilanes, and porous silicon carbide into the synthesis. At the same time, published literature (Angew Chem Int Edit, 2006, 45(19), 3090-3093) reported that Beta molecular sieves with stepped pores were successfully synthesized using polycationic polydimethyldiallylammonium chloride as a template. However, the mesoporous/macroporous templates used are often difficult to obtain, not only expensive, but also the removal process may cause the collapse of the molecular sieve framework structure and generate pollution emissions, which is a non-green process.

In addition, the synthetic step-pore Beta molecular sieve can also form mesoporous channels by selectively removing the central atoms of the framework in the microporous Beta molecular sieve. The open literature (Microporous Mesoporous Materials 2008, 114, 93) reported that the step-pore Beta molecular sieve was obtained by the method of dissolving silicon; the open literature (Journal of Catalysis 2014, 312, 46-57) reported that the Beta molecular sieve was treated with NaOH and TBAOH. Obvious mesoporous channels appeared in the obtained product and the SiO ₂ /Al ₂ O ₃ of the product decreased. The advantage of this post-treatment method is that it is convenient and simple, but it is difficult to control the pore size of the formed mesopores, and the post-treatment may damage the molecular sieve crystal framework, and generate a large amount of waste liquid discharge, which is also a non-green process.

To sum up, synthesizing step-pore Beta molecular sieves without templates is still the focus and difficulty in the synthesis of Beta molecular sieves. If cheap natural clay minerals can be used as raw materials, step-pores can be directly synthesized under the conditions of no template and no post-treatment. Beta molecular sieve is bound to reduce the cost of molecular sieve while improving the greenness of its preparation process and the performance of the product.

Contents of the invention

In order to solve the shortcomings and deficiencies that exist in the prior art, the object of the present invention is to provide a method for synthesizing Beta molecular sieves using sub-molten salt-activated kaolin or retort clay without a template, and the synthetic Beta molecular sieves are macroporous- Microporous composite graded pore material with high BET specific surface area (600-700 m ² /g).

For realizing above-mentioned purpose of the invention, concrete technical scheme of the present invention is:

A method for green synthetic Beta molecular sieve utilizing kaolin or retort clay activated by sub-molten salt, the natural minerals activated by sodium hydroxide, sub-molten salt, supplementary silicon source, crystal seed and deionized water according to SiO ₂ : Al ₂ O ₃ :Na ₂ O:H ₂ O=1:0.01~0.05:0.2~0.35:8~20 molar ratio mixed evenly, then aging and hydrothermal crystallization to obtain Beta molecular sieve.

The SiO ₂ /Al ₂ O ₃ molar ratio of the Beta molecular sieve seed crystal is 15-30:1, and the added mass is 1-10% of the mass of the silicon source in the synthesis system. In the present invention, the Beta molecular sieve used as the seed crystal can be a commercially available Beta zeolite, or a roasted or uncalcined lab-synthesized Beta molecular sieve.

The preferred aging temperature of the present invention is 50-80°C, and the aging time is 2-24 h; the crystallization temperature is 110-160°C, and the crystallization time is 12-72 h.

The sub-molten salt activation of natural clay minerals described in the present invention is prepared according to the method provided by CN201310217164.5, specifically, the natural clay minerals and sodium hydroxide solution are mixed uniformly according to the mass ratio of 1:2~1:20 , and then dried at 100°C to 300°C, the resulting product is activated clay mineral; the natural clay mineral is kaolin or retort clay; wherein, the sodium hydroxide solution is composed of sodium hydroxide solid and Water is mixed according to the mass ratio of 1:1~1:10.

The supplementary silicon source in the present invention is one or more of white carbon black, silica sol or water glass.

The Beta molecular sieve prepared by the above preparation method is a high crystallinity macropore-micropore compound graded pore material, its relative crystallinity is 80-120%, and its specific surface area is 600-700 m ² /g.

The Beta molecular sieve synthesized by the invention is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol. A fixed bed reactor is used for continuous reaction; the reaction temperature for synthesizing ethyl acetate from acetic acid and ethanol is 100-150°C, preferably 110-140°C; the reaction pressure is 0.08-0.2MPa, preferably 0.09-0.15 MPa; The molar ratio is 1:0.8~1:3, preferably 1:0.9~1:2; the weight hourly space velocity is 0.8~2.0 h ^-1 , preferably 0.9-1.5 h ^-1 .

The beneficial effects of the present invention are:

1) The present invention can use natural minerals to synthesize macropore-micropore composite stepped-pore Beta molecular sieve products with good crystallinity within a wide range of silicon-aluminum ratio without templates, completely avoiding the environmental impact of the removal of organic templates Cause pollution, achieve the purpose of green synthesis of Beta molecular sieves, and also avoid damage to the molecular sieve skeleton, so that the synthesized products have a higher BET specific surface area;

2) The present invention applies the synthesized step-pore Beta molecular sieve to the esterification reaction of acetic acid and ethanol, and has achieved remarkable results: compared with the commercially available Beta molecular sieve, under the same reaction conditions, the Beta molecular sieve synthesized by the present invention Molecular sieves can increase the conversion rate of acetic acid by 6-15 percentage points, and at the same time, the selectivity of ethyl acetate can be increased by 6-10 percentage points.

Description of drawings

Fig. 1 is the XRD spectrogram of commercially available Beta molecular sieve;

Fig. 2 is the XRD spectrogram of the synthetic Beta molecular sieve of embodiment 1 of the present invention;

Fig. ₃ is the N adsorption-desorption isotherm of the Beta molecular sieve synthesized in Example 1 of the present invention

Fig. 4 is the pore size distribution figure of the synthetic Beta molecular sieve of embodiment 1 of the present invention;

Fig. 5, Fig. 6, Fig. 7, Fig. 8, and Fig. 9 are the XRD spectra of the Beta molecular sieves synthesized in Examples 2-6 of the present invention respectively.

detailed description

In order to further disclose rather than limit the present invention, the present invention will be further described in detail below in conjunction with examples.

Comparative example 1

Commercially available Beta molecular sieves were used as standard samples to calculate the relative crystallinity of the synthesized samples, and the crystallinity was defined as 100%. The BET specific surface area of the molecular sieve was 520 m ² /g.

The Beta molecular sieve is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol, and the reaction is continuously reacted in a fixed-bed reactor.

Example 1

Dissolve 0.8 g of NaOH solid in 16.6 g of deionized water and stir well. Then add 0.65 g of kaolin activated by sub-molten salt, and stir in a water bath at 70°C for 4 hours; then slowly add 3.3 g of white carbon black and 0.3 g of Beta molecular sieve seeds into the above solution, and stir for 30 minutes; the molar ratio in terms of oxide It is: 40SiO ₂ :Al ₂ O ₃ :10Na ₂ O:660H ₂ O. The above mixture was charged into a stainless steel reaction kettle lined with polytetrafluoroethylene, and statically crystallized at 140° C. for 18 hours. After cooling, the solid product was filtered, washed, and dried at 120°C for 12 hours to obtain the original Beta molecular sieve powder. After powder X-ray diffraction analysis, it was determined that the product was a pure-phase BEA molecular sieve with a relative crystallinity of 110%, and a BET specific surface area of the product was 666m ² /g.

The Beta molecular sieve is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol, and the reaction is continuously reacted in a fixed-bed reactor.

Example 2

Same as Example 1, except that silicon source silica was replaced by silica sol (SiO ₂ content was 30 wt%), and the molar ratio of raw materials was kept as 40SiO ₂ :Al ₂ O ₃ :10Na ₂ O:660H ₂ O. After powder X-ray diffraction analysis, it was determined that the product was a pure-phase BEA molecular sieve with a relative crystallinity of 102%, and a BET specific surface area of the product was 605 m ² /g.

The Beta molecular sieve is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol, and the reaction is continuously reacted in a fixed-bed reactor.

Example 3

Same as Example 1, except that the water-to-silicon ratio is changed to 20 (that is, the amount of water added becomes 20.2 g), and the molar ratio in terms of oxides is: 40SiO ₂ :Al ₂ O ₃ :10Na ₂ O:800H ₂ O. Static crystallization at 140°C for 18 hours. After powder X-ray diffraction analysis, it was determined that the product was a pure-phase BEA molecular sieve with a relative crystallinity of 105%, and a BET specific surface area of the product was 625 m ² /g.

The Beta molecular sieve is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol, and the reaction is continuously reacted in a fixed-bed reactor.

Example 4

Same as Example 1, except that the crystallization temperature was changed to 120° C., and static crystallization was performed for 72 hours. After powder X-ray diffraction analysis, it was determined that the product was a pure-phase BEA molecular sieve with a relative crystallinity of 118%, and a BET specific surface area of the product was 680 m ² /g.

The Beta molecular sieve is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol, and the reaction is continuously reacted in a fixed-bed reactor.

Example 5

Same as Example 1, except that the amount of NaOH is reduced by 0.3 g, that is, the molar ratio of raw materials is 40SiO ₂ :Al ₂ O ₃ :8Na ₂ O:660H ₂ O. After powder X-ray diffraction analysis, it was determined that the product was a pure-phase BEA molecular sieve with a relative crystallinity of 108%, and a BET specific surface area of the product was 656 m ² /g.

The Beta molecular sieve is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol, and the reaction is continuously reacted in a fixed-bed reactor.

Example 6

Same as in Example 1, except that silicon source silica was replaced by water glass (SiO ₂ content 28 wt%), and the molar ratio of raw materials was kept at 40SiO ₂ :Al ₂ O ₃ :10Na ₂ O:660H ₂ O. After powder X-ray diffraction analysis, it was determined that the product was a pure-phase BEA molecular sieve with a relative crystallinity of 95%, and a BET specific surface area of the product was 620 m ² /g.

The Beta molecular sieve is used in the reaction of synthesizing ethyl acetate from acetic acid and ethanol, and the reaction is continuously reacted in a fixed-bed reactor.

The Beta molecular sieves synthesized in Examples 1-6 were used in the esterification reaction of acetic acid and ethanol, and the reaction product was analyzed by a SHIMADZU GC-2014 gas chromatograph, and the chromatographic column model was Inertcap wax. The analysis results are shown in Table 1.

Table 1 comparative example and the acetic acid conversion rate and ethyl acetate selectivity of each embodiment

As can be seen from the above table, compared with commercially available Beta molecular sieves, the Beta molecule synthesized by the present invention has higher acetic acid conversion rate and ethyl acetate selectivity to the esterification reaction of acetic acid ethanol. Therefore, the Beta molecular sieve synthesized by the present invention has more excellent performance in catalyzing the esterification reaction of acetic acid and ethanol.

The above-mentioned several embodiments are only a few cases of the present invention, and do not limit the present invention in any form. Although the present invention has disclosed the preferred reaction conditions as above, it is not intended to limit the present invention. Anyone familiar with this field Those skilled in the art, without departing from the scope of the technical solutions of the present invention, may use the technical content disclosed above to make some changes or modify them into equivalent implementation cases with equivalent changes. However, any simple amendments, equivalent changes and modifications made to the above implementation cases according to the technical essence of the present invention are within the scope of the technical solutions of the present invention.

Claims (8)

1. A kind of 1. preparation method of step hole Beta molecular sieves, it is characterised in that：The kaolin or rectorite activated with sub-molten salt For whole silicon sources and part silicon source, under conditions of any organic formwork agent is not added, have by step hydrothermal crystallizing synthesis The compound step hole Beta molecular sieves of macropore-micropore.
2. A kind of 2. preparation method of step hole Beta molecular sieves as claimed in claim 1, it is characterised in that：By sodium hydroxide, The kaolin or rectorite of sub-molten salt activation, silicon source, crystal seed and deionized water are supplemented according to SiO₂:Al₂O₃:Na₂O:H₂O=1: 0.01~0.05:0.2~0.35:8 ~ 20 molar ratio is well mixed, and Beta molecules are then obtained after aging, hydrothermal crystallizing Sieve.
3. A kind of 3. preparation method of step hole Beta molecular sieves as claimed in claim 1 or 2, it is characterised in that：Described Asia Fused salt activates kaolin or the preparation method of rectorite is：By kaolin or rectorite with sodium hydroxide solution according to 1:2~1:20 Mass ratio be well mixed, then dried at 100 DEG C ~ 300 DEG C, products therefrom be activate after clay mineral；Wherein, It by sodium hydrate solid and water according to mass ratio is 1 that the sodium hydroxide solution, which is,:1~1:10 mix.
4. A kind of 4. preparation method of step hole Beta molecular sieves as claimed in claim 2, it is characterised in that：Described crystal seed choosing With SiO commodity production or that laboratory synthesizes₂/Al₂O₃Mol ratio is 15 ~ 30:1 Beta molecular sieves, quality is added to close The 1 ~ 10% of architectonical silicon source quality.
5. A kind of 5. preparation method of step hole Beta molecular sieves as claimed in claim 2, it is characterised in that：Described supplement silicon Source is the one or more in white carbon, Ludox or waterglass.
6. 6. step hole Beta molecular sieves made from preparation method as claimed in claim 1 or 2, it is characterised in that：Synthesized Beta molecular sieves are the compound step Porous materials of macropore-micropore of high-crystallinity, and its relative crystallinity is 80 ~ 120%, compares surface Product is 600 ~ 700 m²/g。
7. A kind of 7. application of step hole as claimed in claim 6 Beta molecular sieves, it is characterised in that：For being catalyzed acetic acid and second In the reaction of alcohol synthesizing ethyl acetate.
8. 8. application according to claim 7, it is characterised in that：Using fixed bed reactors successive reaction, acetic acid and ethanol The reaction temperature of synthesizing ethyl acetate is 100 ~ 150 DEG C, and reaction pressure is 0.08 ~ 0.2MPa, and the mol ratio of acetic acid and ethanol is 1:0.8~1:3, weight (hourly) space velocity (WHSV) is 0.8 ~ 2.0h^-1。