DD296899A5 - HYDROPHOBIC ZEOLITHIC ALUMINOSILICATE WITH A HYDROPHILIC ALUMINUM-FINISHED SURFACE AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Abstract

The invention relates to a hydrophilic zeolite aluminosilicate having a hydrophilic surface and a process for its preparation. The hydrophobic zeolitic aluminosilicate has a gradient of the SiO 2 / Al 2 O 3 modulus from the crystal surface to the interior. This gradient is produced by a recrystallizing surface finish with a 0.01 to 5 N sodium aluminate solution at temperatures between 10 and 70 C. {Dealumination; aluminosilicates; Pretreatment, thermochemical, extractive, substitutional; Realization, recrystallization; Surface; sodium; aluminum gradient; Crystal inside; Stability, hydrothermal; Hydrophobizizaet}

Description

Field of application of the invention

The invention relates to a hydrophilic zeolite aluminum silicate having a hydrophilic aluminum-rich surface and a process for its preparation in which the starting materials are subjected to thermochemical or extractive or substitutional treatment steps.

The hydrophobic zeolitic aluminum silicate according to the invention is particularly suitable for selective separation of substances. With the method according to the invention it is possible to produce Y-zeolites of high hydrothermal stability, pronounced hydrophobicity and specific catalytic activity.

Characteristic of the known state of the art

Zeolitic molecular sieves of the general formula Me _{2 / n} O.XAl ₂ O ₃ .Y SiO ₂ .ZH ₂ O,

where Me is a metal cation, η is the charge number of the cation, X = 1, Y = 2 to 6, Z = 0 to 9, are known as adsorbents for selective separation and catalytic conversion.

These zeolites are known to be obtained directly by mixing sodium silicate and sodium aluminate in alkaline solution, optionally with the addition of further components, followed by crystallization of the resulting aluminosilicate gel.

In the developing microporous zeolite structure, the silicon and aluminum atoms are linked together via TO ₄ tetrahedra (T = Si, Al).

Quadruple coordination of the aluminum results in the negative charge of the zeolite framework. This is compensated by sodium ions, which remain in the zeolite after separation of the synthesis solution and washing of the crystals in a defined amount.

Traditionally known products of this class are zeolites of the type A, X and Y, which are in their structure and in their content of aluminum within the framework with у = 2 for the type А, у = 2 to 3 for the type X and у = 3 to 6 for the type Y differ. With decreasing content of aluminum and thus negative and positive Ladu ngsträger in the crystal increases its hydrophobicity in the sequence A <X <Y. Accordingly, polar molecules, such as water or hydrogen sulfide, preferably adsorbed on the zeolite Y. At the same time, the catalytic activity of the zeolites increases, preferably in cracking processes.

It is known to increase the hydrophobicity and catalytic activity of type Y zeolites by further increasing the S1O2 / Al2O3ZU modulus. Since this is not achievable for faujasites by direct route as a result of synthesis, methods for dealumination of the Y zeolites were used. This dealumination is known to be accomplished by a thermochemical, extractive or substitutional treatment procedure.

Whereas in the thermochemical process the aluminum dissolved out of the lattice remains in the crystal - but it can also be leached out by means of additional acid treatment - the zeolites dealuminated by the extractive or substitutional method are free of non-lattice aluminum.

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These so dealuminated Y-ZeotSthe achieve a higher thermal compared to the starting material, but have a lower hydrothermal stability value. Deahiminized Y zeolites for mass separation and material conversion processes are regenerated at high temperatures with steam, resulting in low zeolite lifetimes, high energy expenditure in their regeneration and significant environmental impact

 The selectivity and activity of the molecular sieves are adversely affected.

In dealumination by the thermochemical process, the dealuminate of the zeolite Y, which is obtained after exchange of the sodium for ammonium ions with subsequent thermal decomposition of the ammonium ion, the dealuminated form upon thermal treatment in the temperature range from SOO to 900 ⁰ C in the presence of water vapor manufactured. The aluminum removed from the framework remains as non-framework aluminum in the crystal. The defects formed during leaching heal by incorporation of silicon, which is liberated at the other sites. Thus, in addition to the micropores in the dealuminated material also mesopores are included.

From DE-AS 2906656 a hydrophilic zeolhhisches aluminum silicate and a process for its preparation is known. The hydrophobic zeolitic aluminum isocyanate has a molar SiO ₂ / AljO ₃ ratio of 4.5 to 35, preferably 4.5 to 9.0, an ion exchange capacity of not more than 0.070, a unit cell dimension of 24.2 to 24, 45A, a surface area of at least 350 mVg, an adsorption capacity for water vapor at 25 ° C and a p / p _o value of 0.10 of less than 5.0% by weight and a residual butanone test value of not more than 0.40% by weight. %.

This known hydrophobic zeolitic aluminum silicate is obtained by calcination at temperatures of 725 to 870 ⁰ C for a time sufficient to reduce the adsorption capacity for water vapor to less than 5.0 wt .-%, and after cooling by a Na ₂ O content less than 0.5 wt% of reducing ion exchange. DE-OS 3142057 discloses a catalytically active zeolite, a process for its preparation and the use thereof.

This known zeolite by exchanging a Natriumzeolithen Y-type with an ammonium salt solution, calcining the exchanged with ammonium ions, zeolite at a temperature of about 537-815 ° C and reacting the calcined zeolite with an acidic aluminum salt solution having a pH value of 2.0 to 3.7 made. The ammonium salt used is ammonium sulfate and the aluminum salt is aluminum sulfate.

The known thermochemical method according to DE-AS 2906656 and DE-OS 3142057 have the disadvantage of high energy consumption, which is caused by the exchange of ammonium ions, the calcination at temperatures above 500 ⁰ C and the thermal treatment in the steam stream. Extensive environmental protection measures, which are required for the protection of wastewater and exhaust air from ammonia, make these known technical solutions more expensive. Also disadvantageous are the condensation effects of sorptives in the mesopores and the incorporation of the non-lattice aluminum into the crystal, which may undesirably affect the selectivity and activity of the products. There are also extractive method according to DE-AS 1467149, DE-AS 2435716 and DE-PS 2510700 known.

DE-AS 1467149 describes a process for increasing the silica / alumina ratio in the crystal lattice of a crystalline aluminosilicate of the zeolite structure.

The crystalline zeolite is at least partially converted to the hydrogen form and then treated in the presence of a solvent and optionally a complex or chelating agent for aluminum until the desired amount of aluminum ions is removed from the tetrahedral sites of the crystal lattice.

These aluminum ions are converted into a complex or chelate by further reaction with a complexing or chelating agent and separated from the zeolite.

A process for the preparation of zeolites having improved high temperature and acid resistance is known from DE-PS 2510700, in which the crystalline aluminosilicate zeolite is subjected to a base exchange with a solution of salts of nitrogenous bases, wherein the alkali metal reduces by single or multi-stage base exchange, the Product of non-volatile anions washed and heated to temperatures between 150 and 650X, then the content of Alkatlmetatfionen reduced by renewed single or multi-stage base exchange, the product is washed free of non-volatile anions and calcined at temperatures between 540-820 ° C. The reaction products obtained after the second stage of the catination are treated with a solution of a strong mineral acid.

These known extraction methods have the disadvantage that they also cause a high energy attack and by the use of complex or chelating agents are environmentally problematic. In addition, chelating agents and concentrated acids are expensive.

In addition, these zeolites have impurities that lead to a partial amorphization, especially in their application. Another disadvantage is a low hydrothermal stability of the products produced by these known methods.

The deposition of non-lattice aluminum and the occurrence of impurities are known to counteract the substitution processes. These known methods replace the aluminum contained in the zeolite skeleton by silicon. From DE-PS 3132380 a process for the preparation of ultrastable zeolites of the Y-type is known in which activated zeolites are reacted at temperatures of 150 to 450X with gaseous chlorine, fluorine or bromosilane. DE-OS 3,719049 describes a method for incorporation of silicon atoms in place of aluminum atoms in the crystal lattice of a zeolite by reaction of an activated crystalline zeolite of the faujasite type with a halosilane at elevated temperature and subsequent washing. The reaction temperature is below 150X and the halosilane used is a chlorosilane, in particular silicon tetrachloride.

The washing is carried out with aqueous buffer solutions and water. However, these products produced by the known substitution process have a low hydrothermal stability, which leads to short lifetimes especially in the regeneration of hydrophobic adsorbents or catalysts with water due to the dissolution of material in the water. Furthermore, processes are known which improve the chemical or hydrothermal stability of dealuminated zeolites. These known methods follow a modification of the crystal surface.

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Thus, the process according to DE-OS 3806932 uses the alkalization of the surface of crystals by the material directly

is calcined after the synthesis in the alkaline state at high temperature. The modification is carried out by crystallization at elevated pressure and elevated temperature. Filtration, ion exchange, drying and optional activation by thermal treatment. The thermal pretreatment of the zeolite is in the alkaline state with subsequent

Internal exchange and renewed activation made. The process according to DE-OS 3806932 has the disadvantage that the generation of the alkaline layer is energy-intensive. sintered

and melting processes also affect access to the micropore system. Furthermore, damage to the

Crystal interior not excludable due to recrystallization. Another known process (DE-OS 3125251) discloses the preparation of hydrocarbon conversion catalysts

from zeolite, alumina or an inorganic oxide matrix. First, an aqueous slurry of fine zeolite is prepared to which an aluminum salt solution is added and the pH of the formed reaction mixture is adjusted to about 7 to 8 to achieve precipitation of hydrous alumina on the zeolite particles.

Subsequently, the pH of the reaction mixture with a base at about 9 to 11 to stabilize the alumina

elevated. As aluminum salt solutions are aluminum sulfate or Natriumaluminatlösungen or mixtures of these

Solutions used. The products produced by this known method are unprotected in their crystal interior. It also decreases

the proportion of active zeolite,

Furthermore, there is the disadvantage that access to the micro-terrorism system is impeded or prevented by the oxide layer

becomes.

H. Hamdan and J. Klinowski (ACS Sym. Ser. No398, Sehe448 to 464 [1989] -M .: Occellie, H. E. Robson, Eds.) Describe Process for the secondary synthesis of zeolites of types X and Y and ZSM-5. In this known method, aluminum is recovered due to isomorphous substitution of lattice silicon by aluminum

incorporated into the framework of dealuminated zeolites by alkaline leaching. As an alkaline solution, this method uses potassium hydroxide to prevent recrystallization processes.

The increase in hydrothermal stability, however, occurs in these products with the lifting of the dealumination

caused adsorptive and catalytic properties and the thermal stability bought.

Object of the invention

The object of the invention is to increase the hydrothermal and thermal stability, to improve the hydrophobicity, to eliminate the undesirable effects of selectivity and catalytic activity, to avoid partial amorphization, to reduce energy consumption and to improve environmental protection when using hydrophobic zeolite aluminosilicates.

Explanation of the essence of the invention The invention has for its object to develop a hydrophobic zeolitic aluminosilicate, a Aluminum gradient from the crystal surface to the crystal inside out. The invention is further based on the object, while ensuring a high hydrophobicity, catalytic and

thermal stability without limiting access to the micropore system to produce this gradient in the aluminosilicate.

According to the invention, this object is achieved in that the hydrophobic zeolitic aluminosilicate a gradient of SiO ₂ / Al ₂ Oj MOdUIs from a2 at the crystal surface to 200 in the crystal interior. The object is further solved by a recrystallizing realumination of the dealuminated zeolitic Aluminosilicates on its surface with a 0.01 to 5 η solution of sodium aluminate at temperatures between 10 and 70 ° C.

is carried out.

In a preferred embodiment of the process according to the invention, the sodium aluminate solution is sodium hydroxide solution in

the concentration of a 0.1 to 3n solution added

In a further preferred embodiment of the process according to the invention, the residence time in the Sodium aluminate solution a few seconds to 20 hours. A preferred embodiment of the method according to the invention provides a stepwise implementation of

recrystallizing realumination by starting the high concentration treatment in the first stage and terminating with decreasing solution concentration in the last stage with water.

In a further embodiment of the method according to the invention, the spent solution after the solid / liquid separation in

reused at the next stage, using fresh solution only for the first, stage.

The technical-economic effects of the invention, in particular their effectiveness, consists in the increase of

hydrothermal and thermal stability and in the improvement of hydrophobicity. The invention enables the

Elimination of undesirable effects on selectivity and catalytic activity. The partial amorphization becomes

avoided. At the same time, energy consumption is reduced and environmental protection improved.

embodiments The invention will be explained in more detail below with reference to four exemplary embodiments. As feedstocks for the stabilizing treatment zeolites are used, which are obtained after the

- Thermal process followed by extraction of the non-lattice aluminum by the starting material NaY of

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Module SiOj / Al ₂ Oj ^ш 4.6 exchanged in two steps with ammonium ions, calcined in the meantime at 520 ⁰ C, then annealed at 740 ⁰ C in the presence of water vapor of a partial pressure of 1 atm and leached in 1 η HCl in the reflux, or

-, Extraction process by leaching a twice with ammonium ions and meanwhile at 600 "C calcined zeolite in 2.5 η HNOj twice with stirring, or

- Substitution process by the de-watered zeolite was treated at 470 ⁰ C in an SiCI ₄ loaded inert gas stream.

Table 1 shows the degrees of dealumination achieved and the hydrothermal stability relative to the starting material

shown. Likewise, Table 1 also shows the hydrothermal stability of the treated samples, which is indicated by the

Module SiO ₂ / Al ₂ O _{3 of} the crystal surface was added in comparison to the volume phase. The hydrothermal stability test is basically carried out under saturation pressure of the water for 72 hours at a Mass ratio solid / liquid of 40. These tightened test conditions were chosen to obtain significant changes in the crystal structure. Table 1

sample Type d. dealumination Module SiO ₂ / Al ₂ O ₃ hydrothermally MOdUlSi (VAI ₂ O ₃ Surface. hydrothermal stable _ sometimes stable to ° C Vol. 16 to "C NaY _ 4.6 215 _ _ USI ThermoChem. u. 90 120 88 12 195 sr. extraction 19 USII extraction 56 105 48 17 175 USIII substitution 68 130 68 205 USIV substitution 68 130 65 195

US: ultrastable

(the distribution of SiO ₂ and Al ₂ O ₃ in the volume and on the surface was determined by means of wet-chemical analysis and ESCA).

Measurement determined). example 1 The dealuminated and extracted by the thermochemical process zeolite USI was at 40 ⁰ C for 1 hour in a 0.1 η Solution of sodium aluminate thoroughly stirred, washed and dried. Without loss of crystallinity and hydrophobicity, an increase in the hydrothermal stability from 12O ⁰ C to 195 ° C.

receive. While the volume phase of the crystals was almost unchanged, their surface was clearly enriched with aluminum.

Example 2 A zeolitic material USII dealuminated by acid extraction was reacted at room temperature in a 2 η solution of Sodium aluminate and stirred for 10 minutes, after solid / liquid separation into 0.15N solution of sodium aluminate

and stirred for 30 minutes and then after a further solid / liquid separation in a third stage for 3

Hours treated with water. With a slight loss of hydrophobicity, an increase in the hydrothermal stability by 70 ⁰ C due to the Realization of the crystal surface achieved. Example 3 A zeolite USIII dealalyated by substitution of lattice aluminum by silicon was used in its hydrothermal Stability due to the re-aluminization of the crystal surface in 0.3 N sodium aluminate solution and stirring at 60 ° C for 1 hour

considerably increased.

The crystallinity and the sorption properties of the material thus treated had not been demonstrably changed. Example 4 A substitution dealuminated zeolite USIV was used to increase its hydrothermal stability for 15 minutes in

a 1.2N solution of sodium aluminate containing sodium hydroxide solution corresponding to a 1.7 η solution treated.

Without loss of crystallinity and hydrophobicity, an increase in hydrothermal stability to 195 ° C was effected.

Claims (6)

-1- 295 899 Claims: 1. Hydrophobic zeolitic aluminosilicate with a hydrophilic aluminum-rich surface and a gradient of the SiO ₂ / Al ₂ O ₃ modulus of> 2 at the crystal surface to 200 in the crystal interior. 2. A process for the preparation of hydrophilic zeolitic aluminosilicate hydrophilic aluminum-rich surface according to claim 1, wherein the starting materials are subjected to thermochemical or extractive or substitutioneil process stages, characterized in that a recrystallizing realumination of the dealuminated aluminosilicate on its surface with a 0.01 η to 5 η solution of sodium aluminate at temperatures between 10 and 70 ⁰ C is performed. 3. The method according to claim 2, characterized in that the sodium aluminate solution of sodium hydroxide solution in the concentration of a 0.1 to 3n solution is added. 4. The method according to claim 2 and 3, characterized in that the residence time in the sodium aluminate solution is a few seconds to 20 hours. 5. The method according to claim 2 to 4, characterized in that the recrystallizing realumination is carried out stepwise by starting the treatment with high concentrate in the first stage and this is terminated with decreasing solution concentration in the last stage with water. 6. The method according to claim 2 to 5, characterized in that the spent solution is reused after the solid / liquid separation in the following stage and fresh solution is used only for the first stage.