DD289026A5 - METHOD FOR PRODUCING TWO AND / OR THREE-DIMENSIONAL CATIONES OF SURFACE-FREE CREAMS OF THE FAUJASITE TYPE - Google Patents

Abstract

The invention relates to a process for the preparation of divalent and / or trivalent cations containing surface-pure zeolites of the faujasite type. The ion exchange is carried out in at least two discrete steps at room temperature, namely a) adjustment of a pH to 9.5 to 9 initially by complete replacement of the sodium for calcium ions as an intermediate step in aqueous calcium salt solution and b) again reducing the pH by exchanging zinc ions in acidified zinc salt solution {zeolite; faujasite; NaA, NaX; Cation exchange; Surface layer; Intermediate; alkalinity; Calcium chloride solution; Zinc chloride solution; pH-lowering}

Description

Field of application of the invention

The invention relates to a process for the preparation of di- and / or trivalent cations containing surface-pure zeolites of the faujasite type, which are obtained by cation exchange from the zeolites NaA or NaX by sodium silicate or silica sol and sodium aluminate directly mixed, the resulting aluminosilicate gel crystallized , The synthesis solution is separated, the crystals are washed with water and tempered.

The process according to the invention makes it possible to provide surface-pure zeolites of the NaA and NaX type for drying and separating tasks.

Characteristic of the known technical solutions Zeolitic molecular sieves of types A, X and Y having the general formula Me _2M O Al ₂ O ₃ · χ SiO ₂ · y H _a O

(n · - charge number of the cation, χ = 2 to 5)

are directly synthesized by mixing sodium silicate, silica sol, and sodium aluminate solution with subsequent crystallization of the resulting aluminosilicate gel. In the developing microporous zeolite structure si. id the atoms of silicon and aluminum via TOj tetrahedra (T = Si, Al) linked together. The 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.

In contrast to the atoms of silicon and aluminum in the framework, the sodium ions are freely movable and therefore exchangeable with other mono-, di- and / or trivalent cations. The goal of the cation exchange is both to influence the specific sorption properties of the zeolite and to vary the access openings in its micropore system. Thus, the diameter of the access holes of 4A for the zeolite NaA can be reduced to 3A by exchanging potassium ions and expanding to 5 A by the exchange of calcium ions and, in the case of the zeolite NaX of 9 A, by the incorporation of calcium ions on eA. These known species and the zeolite NaY represent the worldwide commercially available basic patterns of synthetic molecular sieves of the faujasite type.

In addition, a variety of other faujasite-based zeolite modifications using cations of the 1st and 2nd main group elements, the minor groups including the rare earths of the PSE by ion exchange are known. Such species are i.a. Zinc ions containing modifications NaZnA and NaZnX, which are used according to DD-PS 241197 and DD-PS 241202 as adsorbent for gas desulfurization.

With the exception of the incorporation of potassium ions into the zeolites NaA and NaX as a result of a direct synthesis according to DD-PS 57115 or DD-PS 58957 and the exchange of cations of the elements of the 1st main group of the PSE by addition of appropriate salts for strongly alkaline synthesis approach after completion The crystallization according to DD-PS 111192, the cation exchange is usually carried out by treatment of the zeolite crystals in aqueous salt solution. This type of chemical zeolite treatment, in which the cations to be exchanged can be used singularly or mixed, is the generally customary way of cation exchange, since the route of direct synthesis is limited to the potassium ion and the exchange in the crystallized synthesis approach without separation of the so-called mother liquor the high hydroxide Solubility of the elements of \. Main group of the PSE. With the exception of the barium and strontium, the elements of the second main group, and even more so, are the hydroxides which are sparingly soluble in alkaline solution in the subgroups, so that a cation exchange can not be carried out in an alkaline medium. The formation of sparingly soluble precipitates (solubility of the hydroxides of aluminum 10 " ³³ , calcium 10" ^B , magnesium 10 ~ ¹² and zinc 10 "") is used in DE-PS 1542644 to precipitate so-called easily filterable mixed silicates with alkali silicate solution.

In DE-PS 2312999 a crystalline aluminosilicate and a process for its preparation is described. This known aluminosilicate has a content of β to 13% by weight of exchanged rare earths and 0.05 to 2.5% by weight of exchanged zinc. The crystalline aluminosilicate is contacted either simultaneously with or in succession in any order with solutions containing zinc cations, resulting in the aforementioned levels of rare earths and zinc

be set. This known crystalline aluminosilicate is used as a catalyst for the conversion of

Hydrocarbons, especially gas oils is used. DE-AS 2208214 discloses a zeolite A containing zinc ions which is obtained by ion exchange of a part of the

ion exchangeable cations in zeolite A is prepared with a solution containing zinc ions.

The ion exchange with potassium ions and zinc ions containing solutions is achieved until a balanced state

in which 16.7 to 33.3% of the ion-exchangeable cations are exchanged for potassium ions and 66.7 to 83.3% for zinc ions.

As the known zeolites of the faujasite type 3, as the salts of a strong base (NaOH) and a weak heteropolyacid

(H-zeolite framework) apply, hydrolyze in aqueous solution with the release of Hydioxylionen carried out in the process c'es

Exchange of sodium and / or potassium ions for divalent and / or trivalent cations (with the exception of barium and Strontium) the deposition of their hydroxides on the crystal surface. Therefore, the production of Zeolitho according to DD-PS 2208214 (NaA), DE-PS 2312999 (NaX) and DD-PS 52131 (NaA, NaX) not surface clean. The deposition of foreign phases on the surface of zeolite crystals affects both the diffusion behavior of Sorptiven and their mechanical stability of binders produced zeolite moldings disadvantageous. About that

In addition, these deposits conduct at the necessary high temperatures during activation or regeneration

Phase transformations that lead to the surface closure of the micropore system. From DE-OS 1792231 a method for the washing of calcined aluminosilicate with exchanged cations for Removing such precipitated compounds known in which the calcined zeolite in so much acid solution with a

pH in the range of 3.5 to 5.5 slurries, the pH of the slurry is maintained in this range, the slurry at a temperature of 51 ⁰ C to 94 "C to dissolve the precipitated compounds for at least 5 minutes and then the Slurry filtered.

Subsequently, the zeolite is washed with a buffered acid solution and filtered, then washed, filtered and

dried. The acid solution used is an ammonium sulfate, acetate or chloride-containing, buffered acid solution.

This known method has the disadvantage that it does not prevent the formation of the surface layers, but only the

seeks to dissolve precipitated layers on the zeolite scaffold. A partial protonation of the zeolite framework is not excludable, because in particular the Η-form of the zeolite A is highly susceptible to hydrolysis. If not equal to the total

Destruction sets in, but defects occur especially under load. These known zeolites therefore have no lasting stability and long life, but for industrial processes

necessary properties are.

Furthermore, it is expensive to adjust the pH in the range of 3.5 to 5.5 exactly during the entire process. According to DE-AS 2049584 a method is known in which einos a copper-exchanged zeolite by treatment Zeolite X in the sodium form with an aqueous solution of a copper salt and then at least partially Drainage is produced by heating, which is used for the separation of olefinic and saturated hydrocarbons The zeolite is treated before dehydration with a mixture of an olefinic hydrocarbon and a Copper (I) salt at a temperature between 10 ⁰ C and the boiling point of the olefinic hydrocarbon. DOS known method according to DE-AS 2049584 is limited in its applicability to the X-type, because zeolites of the A-type

have a significantly higher alkalinity.

The known technical solutions according to DE-PS 1567550 and DD-PS 93540 describe a method of dealumination

of NaY zeolites, in which first the sodium are exchanged for the ammonium ions, after tempering of the

Zeolite material to obtain the proton form. The zeolite HY is then treated by acid or steam treatment

partially dealuminated. Furthermore, a fractionation with elements of the subgroups b / w.Seltenen earth takes place.

For the zeolites of the type NaX and above all NaA the cation exchange over the step of protonsienng, since in the X-zeolite already partial and in the A-zeolite strong damage to the crystal structure to complete amorphization

occur.

Object of the invention

The object of the invention is to improve the mechanical stability, to avoid damage to the framework and defects, to increase the lifetime and diffusion and separation behavior of the faujasite zeolites while at the same time eliminating entire treatment steps and saving costs, material and energy.

Explanation of the essence of the invention Dor invention is based on the object, the formation of surface deposits by lowering the alkalinity

prevent.

According to the invention, this object is achieved in that the ion exchange in at least two discrete Treatment steps carried out at room temperature:

a) adjustment of the alkalinity in a Zwiachenschritt by lowering the pH from 11.0 to 10.5 to 9.5 to 9 initially by means of complete exchange dor sodium against calcium ions in aqueous calcium solution and

b) further reduction of the pH by exchanging the zinc ions in acidified zinc salt solution.

The technical-economic effectiveness of the invention consists in the improvement of the mechanical stability and in the avoidance of skeleton damage and Dofekte on zeolite.

The inventive method further improves the diffusion and separation behavior of the faujasite zeolites. It also eliminates the need for entire treatment stages for the subsequent removal of formed surface layers, thereby saving costs, material and energy.

The invention will be explained in more detail below with four examples.

example 1

A surface trainer and zinc ion-containing zeolite A or X should be prepared by the process of the invention.

First, a technical zeolite NaA is converted by means of ion exchange in the form CaA. The zeolite material used has a pH of 11.0. The measurement was carried out in an aqueous zeolite suspension with the mass ratio liquid / solid

The deception of the calcium ions is carried out in three steps, each with fresh 0.1 η calcium chloride solution with constant stirring. The stirring time was 1.5 hours.

For each 5g of zeolite 150ml of calcium chloride solution are required. The resulting crystal mass is then freed from excess salt with water.

Negligible small amounts of calcium hydroxide had precipitated on the crystal surface.

The cation exchange value of sodium versus calcium ions was a 98%.

The Ca form of the zeolite reached a pH of 9.4, measured under the conditions mentioned above.

In the following treatment step, the Ca form of the zeolite is stirred in a 0.1 N zinc chloride solution at room temperature for 6 hours. For 2g of zeolite 100ml of zinc chloride solution was used. In order to free the zinc chloride solution from turbidity caused by hydroxide formation, acidification was carried out with n / 10 hydrochloric acid.

The X-ray analysis of the washed CaZnA crystals shows j surface layer not typical for the NaZnA sample, which occurs as an additional phase, when the exchange of zinc ions without intermediate stage via the Ca form into the NaA zeolite.

In the phase-pure zeolite CaZnA, there was an exchange value of calcium to zinc ions of 34.5%.

Example 2

It is a surface-pure and containing zinc ions zeolite A or X are prepared according to the invention with a higher cation exchange degree.

For this purpose, as in Example 1, a technical zeolite NaA is converted into the CaA form.

A higher degree of cation exchange is achieved by using a higher concentrated zinc chloride solution for the exchange of zinc ions. An exchange value of 62% of the calcium against the zinc ions was achieved with a 0.5 N zinc chloride solution. The resulting CaZnA crystals were again surface clean.

Example 3

According to Example 1, a zeolite NaX having a pH of 10.7 is first converted into the CaX form with an exchange value of 97%. The pH became liquid / solid in an aqueous zeolite suspension with the mass ratio equal to 50

certainly. When transferred to the CaX form, the pH dropped to 9.5. For the subsequent exchange of zinc ions, a zinc chloride solution was used, which corresponded to that of Example 2.

After preparation of the crystal mass by means of washing in water and heat treatment at 150 ° C Idg a zeolite CaZnA exchanged to 54% before.

Bet game 4

A technical zeolite NaA was immersed in an exchanger column using 5 g of zeolite, measured on the dehydrated adsorbent, of 1 liter of a 0.1 η calcium chloride solution at room temperature for a period of 5 hours. The cation exchange succeeded completely.

After passing through washing water, the treatment was carried out with 2 liters of 0.1 π zinc chloride solution under analogous conditions. The resulting after washing and annealing at 150 ° C as a surface-pure zeolite CaZnA sample had an exchange value of 59% of the calcium against the zinc ions.

Claims (1)

Process for the preparation of divalent and / or trivalent cations containing surface-pure zeolites of the faujasite type, which are obtained by cation exchange from the zeolites NaA or NaX by sodium silicate or silica sol and sodium aluminate directly mixed, the resulting aluminosilicate crystallized gel, the synthesis solution separated in that the crystals are washed and tempered with water, characterized in that the ion exchange is carried out in at least two discrete treatment steps at room temperature: a) adjustment of the alkalinity in an intermediate step by lowering the pH from 11.0 to 10.5 to 9.5 to 9 initially by means of complete replacement of the sodium against calcium ions in aqueous calcium salt solution and b) further reduction of the pH by exchanging the zinc ions in acidified zinc salt solution.