DD289511A5 - METHOD OF REMOVING ZINC HYDROXIDE DEPOSITS ON NAZNA -BZW. NAZNX - CRYSTALS - Google Patents

Abstract

The invention relates to a method for removing zinc hydroxide deposits on NaZnA or NaZnX crystals. The preparation of the NaZnA or NaZnX zeolites is carried out in the usual way by cation exchange in a zinc chloride solution. The resulting zeolites are post-treated in an 8% ammoniacal solution under constant stirring. {Zeolite; NaA; NaX; Cation exchange; Zinc hydroxide deposits; Oberflaechenschicht; post-treatment; ammoniacal solution; mechanical stability; Lifespan; efficiency}

Description

The invention relates to a method for removing zinc hydroxide deposits on NaZnA or NaZnX crystals obtained by cation exchange by preparing a suspension of zinc salt solution and NaA or NaX, slurrying them in water and acidifying the zinc - Separated salt and sodium ions contained, the resulting crystals are washed in water and annealed. The process according to the invention makes it possible to remove superficial deposits of NaZnA or NaZnX zeolites.

Characteristic of the known state of the art

Zeolitic molecular sieves of types A, X and Y having the general formula

Me _{2 / n} O Al ₂ O ₃ · χ SiO ₂ · y H ₂ O

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

are directly synthesized by mixing sodium silicate or silica sol and sodium alumate solution followed by crystallization of the resultant aluminosilicate gel.

In the forming microporous zeolite structure, the atoms of silicon and aluminum are linked together via KV tetrahedra (T = Si, Al).

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 mobile and therefore interchangeable with other 1, 2 and / or 3-valent 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 microporous system. Thus, the diameter of the access holes from 4A for the zeolite NaA to 3A can be changed by exchanging

Reduced potassium ions and expanded to 5 A by the exchange of calcium ions and modified in the case of the zeolite NaX of 9A by incorporation of calcium ions to 8Ä. 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 are known using cation of the elements of the 1st and 2nd main group, the subgroups including the rare earths of the PSE by means of ion exchange.

Such species are i.a. Zinc ions contained modifications NaZnA and NaZnX, which are used according to DD-PS 241197 or 241202 as adsorbent for gas desulfurization.

With the exception of the incorporation of potassium ions in the zeolites NaA and NaX infoige 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 singular or mixed used werdon, is the general conventional way of cation exchange, since the way of direct synthesis is limited to the potassium ion and the exchange in the crystallized Syntheseansaüü without separation of the so-called mother liquor, the high hydroxide solubility the elements of the 1st main group of the PSE. With the exception of the barium and strontium, the elements of the second main group and even more the hydroxides which are sparingly soluble in alkaline solution form the subgroups, so that a cation exchange can not be carried out in an alkaline medium. The formation of sparingly soluble precipitates (solubility product of the hydroxides of aluminum 10 " ³³ , calcium 10 ~ ⁵ , magnesium 10 ~ ¹² and zinc 10" ¹⁷ ) 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 6 to 13% by weight of exchanged rare earths and 0.05 to 52.5% by weight of exchanged zinc. The crystalline aluminosilicate is contacted either simultaneously or sequentially in any order with solutions containing zinc cations, thereby adjusting the aforementioned rare earth and zinc contents. This known crystalline aluminosilicate is used as a catalyst which serves for the conversion of hydrocarbons, in particular gas oils.

DE-AS 2208214 discloses a zeolite A containing zinc ions which is prepared by ion exchange of part of the ion-exchangeable cations in zeolite A 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 faujasite-type zeolites, which are salts of a strong base (NaOH) and a weak hetaropolysäure

(H-zeolite), hydrolyze in aqueous solution to release hydroxyl ions, takes place in the process of

Exchange of sodium and / or potassium ions for 2- and / or 3-valent cations (with the exception of barium and Strontium) the deposition of their hydroxides on the crystal surface. Therefore, the preparation of zeolites according to DE-AS 2208214 (NaA), DE-PS 2312 999 (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 necessarily high temperatures during activation or regeneration

Phase transformations that lead to the superficial closure of the micropore system. From DE-OS 1792 231 a method for washing 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, maintaining the pH of the slurry in this range, allowing the slurry to stand at a temperature of 51 to 94 ° C to dissolve the precipitated compounds for at least 5 minutes, and then filtering the slurry ,

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

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

This known method has the disadvantage that it does not prevent Bilduno the surface layers, but on the Zeolite scaffold seeks to dissolve precipitated layers. Partial protonation of the zeolite framework is not

excludable, because in particular the Η-form of zeolite A is highly susceptible to hydrolysis.

If total destruction does not begin immediately, then defects occur especially under load. These zeolites therefore have no lasting stability and long life, but this is necessary for industrial processes Represent properties. 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 process is known in which a copper-exchanged zeolite by treatment of a Zeolites X in the sodium form with an aqueous solution of a copper salt and then at least partially Dehydration is produced by heating, which is used for the separation of olefins 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 1O ⁰ C and the boiling point of the olefinic hydrocarbon. The 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 doaluminating

of NaY zeolites, in which first the sodium ions are exchanged for ammonium ions in order to obtain the proton form after heat treatment of the zeolite material.

The Zeoüth HY is then partially dealuminated by acid or steam treatment. In the following, a Fractionation with elements of subgroups or rare earths. For the zeolites of the type NaX and above all NaA, the cation exchange via the stage of protonation, 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 aim of the invention is to improve the mechanical stability, increase the service life and the efficiency of the zeolites NaZnA or NaZnX.

Explanation of the essence of the invention The invention is based on the object, the resulting zinc hydroxide deposits on NaZnA or NaZnX crystals

to be replaced non-destructively.

According to the invention, this object is achieved in that the resulting NaZnA or NaZnX crystals at room temperature with

aftertreated 8% ammoniacal aqueous solution with stirring.

The technical-economic effects, in particular the effectiveness of the invention, consist in the improvement of

mechanical stability and increasing the lifetime of the zeolites. The process according to the invention is further distinguished by the efficiency of the zeolites of the NaZnA or NaZnX type, in particular their diffusion and NaZnA-type zeolites

Separation behavior improved. Ausführungsbelspiele The invention will be explained in more detail below with reference to two examples. example 1

A technical zeolite NaA is suspended in 300 ml of a 0.1 N zinc chloride solution at room temperature and stirred for 6 hours. The amount of zeolite NaA used was 30 g. The resulting material, slurried in water at a liquid / solid mass ratio of 50, showed a pH of 11.0.

The saline solution was freed from dilution caused by hydroxide formation by acidification with dilute hydrochloric acid prior to use. The pH of the solution changed to 3.5. After adjusting the cation exchange balance, the salt solution containing zinc and sodium ions was separated, the crystal mass was washed with water, and a sample thereof was annealed at 150 ° C. The X-ray analysis of this sample revealed additional characteristic lines in addition to the typical d values of the zeolite lattice.

The bulk of the batch was treated for 10 minutes in 600 ml of an 8% ammonia aqueous solution at room temperature with stirring. The X-ray analysis of these previously washed with water and dried at 150 ⁰ C showed only the d-values of the zeolite lattice in full intensity. With raster images and hull imprints of crystals of the starting material and the two treatment steps, the precipitate and its resolution were also detected by electron microscopy. The exchange value of the sodium for zinc ions present in the surface-pure zeolite NaZnA was 88.5%.

Example 2

As shown in Example 1, a zeolite NaX was measured with a pH of 10.7 and in a water / zeolite suspension of the mass ratio equal to 50 in the first stage first 4.5 hours in the zinc chloride solution and then in the second stage for Treated for 5 minutes in the ammoniacal solution.

Examination of a sample of the intermediate also provided evidence of surface purity.

After separation of these, an exchange value of 84% was present in the surface-pure crystals of the zeolite NaZnA.

Claims (1)

Process for removing zinc hydroxide deposits on NaZnA or NaZnX crystals obtained by cation exchange by first preparing a suspension of zinc salt solution and NaA or NaX, slurrying it in water and acidifying it, separating the zinc ions and saline solution containing sodium ions , the crystals obtained are washed and tempered, characterized in that the zeolite crystals are aftertreated at room temperature with an 8% strength ammoniacal aqueous solution while stirring. Field of application of the invention