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EP-4739628-A2 - METHOD FOR THE PREPARATION OF MONOLITHS OF ZEOLITE LTA

EP4739628A2EP 4739628 A2EP4739628 A2EP 4739628A2EP-4739628-A2

Abstract

The present invention relates to a method for the preparation of monoliths of zeolite A, allowing the 3D printing of zeolite precursor gels, the product crystallization taking place contemporary to the component solidification, and to form monolithic objects with optimized designs in terms of the properties required for each application.

Inventors

  • FRANCHIN, GIORGIA
  • D'AGOSTINI, Marco Lorenzo
  • COLOMBO, PAOLO
  • CONTE, ALBERTO
  • CROCELLÀ, Valentina
  • CAVALLO, MARGHERITA
  • PORCARO, Natale Gabriele
  • BONINO, Francesca Carla

Assignees

  • Universita' Degli Studi Di Padova
  • Università degli Studi di Torino

Dates

Publication Date
20260513
Application Date
20240606

Claims (20)

  1. 1 . A method for the preparation of monoliths of zeolite A (LTA) comprising the following steps: i) preparing a gel by mixing a silica precursor, a sodium precursor and an alumina precursor in aqueous solution, so that the concentration of silica in said gel is comprised between 13% and 19% by weight and wherein said mixing takes place at a speed such as to obtain a homogeneous mixture; ii) forming and subsequently crystallizing the gel obtained in step i) for at least 12 hours, at a temperature of at least 60°C, so as to obtain a monolith of zeolite A; iii) drying the product obtained in step ii) for at least 12 hours, at a temperature between 75 and 500°C.
  2. 2. The method according to claim 1 , wherein said alumina precursor is selected from sodium aluminate (NaAIO2), aluminium hydroxide, aluminium alkoxides, boehmite, alumina, aluminium salts (nitrates and sulphates), kaolin, metakaolin, metallic aluminium.
  3. 3. The method according to any one of claims 1 or 2, wherein said alumina precursor is used in solution and is present in a concentration comprised between 0.5M and 0.7M, preferably about 0.6M.
  4. 4. The method according to any one of claims 1 to 3, wherein said silica precursor is selected from colloidal silica, (pyrogenic or precipitated) solid phase silica, sodium silicates, silicon alkoxides, kaolin, metakaolin, silicic acid.
  5. 5. The method according to any one of claims 1 to 4, wherein said silica precursor e colloidal silica.
  6. 6. The method according to claim 5, wherein said colloidal silica is present in a concentration between 16 and 17% by weight, preferably about 16.35% by weight.
  7. 7. The method according to any one of claims 1 to 6, wherein said sodium precursor is selected from sodium hydroxide, sodium aluminate, sodium silicates, sodium salts (sulphates, borates, carbonates, fluorides, bromides).
  8. 8. The method according to any one of claims 1 to 7, wherein said sodium precursor and said alumina precursor are the same precursor, preferably sodium aluminate (NaAIO2).
  9. 9. The method according to any one of claims 1 to 8, wherein said alumina and sodium precursor is sodium aluminate (NaAIO2), and said silica is colloidal silica.
  10. 10. The method according to any one of claims 1 to 9, wherein said gel obtained in step i) has a molar composition [x SiO2:AI2O3: y Na2O: z H2O], wherein x is a number from 1 .8 to 3, y is a number from 0.8 a 1.2, and z is a number from 20 to 30.
  11. 11. The method according to any one of claims 1 to 11 , wherein said gel obtained in step i) has a molar composition [x SiO2:AI2O3: y Na2O: zH2O], wherein x is 2, y is 1 , and z is 25.
  12. 12. The method according to any one of claims 1 to 11 , wherein said step i) takes place in a mechanical mixer at a range between 300 and 700 rpm, preferably 500 rpm, with progressive increase in speed when adding silica up to 220 rpm.
  13. 13. The method according to any one of claims 1 to 12, wherein said step ii) takes place in humid environment, with relative humidity (U.R.) of at least 95%, preferably 100%.
  14. 14. The method according to any one of claims 1 to 13, wherein said step ii) takes place at a temperature from 60 to 90°C, preferably 75°C.
  15. 15. The method according to any one of claims 1 to 14, wherein iii) takes place at a temperature of 75°C.
  16. 16. The method according to any one of claims 1 to 15, further comprising a step iv) of grinding the zeolite A monolith obtained in step iii) so as to obtain powdered zeolite A (LTA).
  17. 17. The method according to any one of claims 1 to 16, wherein said said forming step ii) is performed by pouring the gel obtained in step i) into a mould.
  18. 18. The method according to any one of claims 1 to 17, comprising after said step i) a step i-a) wherein a rheological additive and/or powder of zeolite A (LTA) is added to said gel, so as to obtain a slurry.
  19. 19. The method according to claim 18, wherein the concentration of said rheological additive in the slurry is comprised between 0 and 5% by weight, preferably 2%.
  20. 20. The method according to any one of claims 18 to 19, wherein the concentration of said zeolite A powder (LTA) in the slurry is comprised between 30% and 50% by weight, preferably 40%.

Description

METHOD FOR THE PREPARATION OF MONOLITHS OF ZEOLITE LTA FIELD OF THE INVENTION The present invention relates to a method for the preparation of monoliths of zeolite A, allowing the 3D printing of zeolite precursor gels, the product crystallization taking place contemporary to the component solidification, and to form monolithic objects with optimized designs in terms of the properties required for each application. STATE OF ART Zeolites are aluminosilicates of natural or synthetic origin provided with an extremely regular and repetitive three-dimensional structure, that is containing ordered microcavities having variable size: such feature gives the zeolites a high specific surface, thus making them extremely suitable to the use in phenomena of industrial interest such as adsorption and catalysis, in the latter case only if suitable modified so as to give them an essential feature such as acidity. The porosity size is comparable to that of simple molecules such as carbon dioxide or water, which then can interact with zeolite differently from other molecules having greater sizes: for this reason the zeolites are also called "molecular sieves". Considering the existence of several zeolitic structures (more than 200) which have been identified or synthetized over the years, each one thereof with a different size and shape of the micro-cavities, it is possible to select a specific zeolitic structure so as to obtain a high selectivity for a determined molecule or group of molecules. Moreover, thanks to their inorganic nature, zeolites are stable at high temperatures. This feature, together with the high specific surface and their peculiar selectivity, makes these materials easily applicable in many industrial chemical processes. In particular, zeolite A (officially known as LTA), has been one of the first synthetic zeolites due to the related simplicity of the synthesis method which does not provide the use of critical raw materials. The main feature of LTA is its three-dimensional structure of micropores with size of about 0.4 nm: such size makes that it has an extremely high selectivity towards molecules with sufficiently reduced kinetic radius so as to be able to penetrate inside the ordered microstructure, thereamong the carbon dioxide. Optionally, with wholly reversible post-synthesis treatments, the accessible internal volume can be reduced to 0.3 nm or increased to 0.5 nm, by improving (in the latter case) the capability of adsorbing CO2 for applications such as the capture and sequestration of carbon dioxide. Zeolites are mainly produced through hydrothermal synthesis processes, where the precursors are placed inside high pressure and temperature reactors for several hours or days until the complete crystallization of the product. Such processes have high costs due to the required conditions and the need for specialized reactors. Moreover, in a traditional hydrothermal synthesis of zeolite, it is necessary to use huge amounts of solvent with respect to the mass of the material precursors. This involves that the reaction yield, in terms of product mass obtained with respect to the mass of the used reagents, is quite low and that the zeolites, obtained under the form of powder inside the synthesis mixture, are to be separated from the mother water through long and expensive filtration and/or centrifugation processes. Another problem is linked to the fact that the zeolites obtained from the hydrothermal processes as fine powders are not suitable to the immediate use in applications of industrial type, for safety factors and ease of use, and then are to be subjected to forming processes such as grinding or extrusion through insertion of a foreign binder which, apart from diluting the active phase, can limit the mass transportation and the performances of the finished product. Moreover, the forming processes most commonly used at industrial level often require high temperature treatments for consolidating the binder, feature which apart from constituting an energy cost, often causes a porosity variation in the material affecting the final properties of the product. SUMMARY OF THE INVENTION The present invention relates to a method for the production of monoliths of zeolite A which, with respects to the methods known in the prior art, results to be less expensive in terms of time and costs, since the crystallization method allows to use only a furnace working at low temperatures and any not necessarily hermetic container. The method of the present invention does not require intermediate passage of solidifying or aging the synthesis gel before the crystallization treatment. In fact, generally when the zeolitebinder compound is not dried before conversion, they are usually used as clay material binders or other silicates or aluminosilicates in solid form, mixed with water and the zeolitic powder so as to form a paste. On the contrary, in the present invention, the used binder is the same mixture of sodium alumi