DE2029242A1 - Synthetic potassium zeolites - with improved thermal stability by direct synthesis - Google Patents

Abstract

Direct synthesis of K zeolites, with SiO2:Al2O3 molar ratio 2.5 and effective pore dia. preventing entry of benzene molecules comprises adding Al2O3 carrier in water-insoluble form to (partly) aqs. soln. of KOH, opt. containing K2SiO3 and keeping resultant reaction mixture, after thorough stirring, at >40 degrees C until crystals of zeolite concerned have formed. Suitable alumina carriers include synthetic Al (meta) silicate and SiO2 hydrogel or tempered xerogel containing Al(OH)3.

Description

The present invention relates to synthetic zeolites having a SiO2: Al2O3 molar ratio greater than 2 and a process for their direct synthesis in the potassium form.

Natural and synthetic zeolites are used because of their ability for selective adsorption also known as molecular sieves, since the use of natural Zeolites in lump form fail because they lose their hardness when they are dehydrated Losing or disintegrating into powder, numerous procedures have been going on over the past 15 years developed in order to produce such products synthetically observes the laws of isomorphic justifiability, whereby z.3. SiO2 under valence balance is replaced by Al2O3 as well as by diadochic ions such as P205.

Molecular sieves have the general formula 1 + 0.2 Me2O. 11203.x Si ° 2. y H20 where Me is a monovalent metal atom or the equivalent of a polyvalent one, for Replacement of capable metal atoms, as well as H or NH4 or an organic ammonium compound means x has a value greater than 1.9 and y has a value less than 10.

Characteristic for every molecular sieve are next to the chemical one Analysis of the X-ray diffraction diagram and the effective pore diameter.

Synthetic molecular sieves are used almost exclusively in the Sodium form because it is easy to obtain.

Of potassium zeolites, only the direct synthesis of type A is possible with a effective pore diameter of 3 angstroms, further a material with a molar ratio 2 SiO2: Al203 as well as the potassium zeolite described in patent oe (P 1 667 541 * 5) with an effective pore diameter of 2.8 Angstroms.

The potassium zeolite A produced in direct synthesis has the opposite a slightly increased capacity for the product made by ion exchange With this material, however, water vapor divides the less than the sodium form Thermostability.

The purpose of the present invention is to use direct synthesis of potassium To produce zeolites of high thermal stability and a ratio of SiO2: Al203, which is greater than 2.5 and at which the effective pore diameter in the synthesis form Benzene molecules are barely barred from entering.

The manufacturing process for potassium zeolites is based on the fact that within suitable ranges in a wholly or partially aqueous solution of potassium hydroxide The Al 2 O 3 carrier may optionally also contain potassium silicate in water-insoluble Form is entered and the resulting reaction mixture after uniform Stir as long as the temperature is above 4000, until the crystals of the respective zeolite.

The crystals separated from the mother liquor are then preferably washed out with water until the pH value of the water running off has reached a value below 9.5. No potassium ions should be passed through for special purposes Hydrogen ions are replaced as a result of too long washing, one can stick Remove Ilkali in the final phase by doing the rest of the washing with a organic medium such as alcohol, which can dissolve potassium hydroxide1 will.

The washed-out crystals can then undergo ion exchange be subjected, the potassium ion wholly or partially by 1 or more exchangeable ions are replaced.

Examples: 1.) 830 g aluminum metasilicate (filter cake with 18.2% Solid) were dispersed in 2 l of water.

A mixture of 1040 ml K2O 4 SiO2, d = 1.26, and 240 g of KOH in 800 ml of water were added.

The crystallization lasted 94 hours at 960C.

2.) The procedure was as in Example 1, except that 300 g of KOH were used used.

The crystallization at 96 ° C. was completed in 70 hours.

3.) 185 g of aluminum metasilicate with 0.75% residual moisture were in a boiling solution of 1040 ml of K20. 4 SiO2, d = 1.26, and 280 g KOH in 2.5 1 1120 stirred in.

The crystallization at 1000C lasted 80 hours, with the mixture was stirred briefly every day.

4.) 200 g mixed gel with a molar ratio SiO2: Al202 = 0 8.5, 1 hour tempered at 520 C according to patent ......

(P 2013593.7) were in a solution of 60 g of KOH in 1.5 1 of water After precrystallization at 100 ° C for one week, cautious another 100 g of KOH were added Days formed.

The following are the characteristic data of one of those produced according to the invention Potassium molecular sieves (according to Example 2).

1st chemical analysis: 1.03 K2O. Al2O3. 3.78 SiO2. 7.14 H2O 2. X-ray diagram : No.Intensity s D d ss (diff.) 3.00 9.41747 2 s 4.44 8.16034 3 s 6.11 7.07629 4 ss 10.30 5.30661 5 m 11.42 4.97612 6 s 14.19 4.31201 7 ss (diff.) 15.43 4.06982 8 sssCdiff.) 16.47 3.88703 9 sss (diff.) 18.14 3.62541 10 sss (diff.) 19.65 3.41955 11 m 21.27 3.22268 12 s 22.00 3.14120 13 m 24.11 2.92816 14 sss 26.63 2.71025 15 sss 27.33 2.65577 No. Intensity s D d 16 sss 28.08 2.59966 17 sss 29.09 2.52799 18 ass 32.00 2.34283 19 sss 36.89 2.08865 20 sss 40.23 1.94671 21 sss 49.09 1.65482 3. Adsorption data: Isotherm:% wt. T = 21 ° C% relative humidity - - - -20 14.6 40 15.2 60 17.0 80 23.0 100 29.4 CHCl3 uptake = 3.58% by weight (sat. at 20 ° C, air) CO2 - "" = 8.67 "" (700 mm Hg) SO2 - "" = 16.2 "" (700 "")

Claims (5)

Claims: 1. Process for the direct synthesis of potassium zeolites with a molar ratio of SiO2: Al205 equal to or greater than 2.5 and an effective Pore diameter in the synthesis form to which benzene molecules just barely have access denied, characterized in that within suitable areas in a whole or partially aqueous solution of potassium hydroxide, which optionally also potassium silicate may contain, the A1203 carrier is entered in water-insoluble form and the resulting reaction mixture, after stirring evenly, as long as Temperatures above 400C is kept until the crystals of the respective zeolite have formed. 2. The method according to claim 1, characterized in that after washing, which towards the end of the washing process, optionally with an organic solvent is made, the potassium ion in whole or in part by one or more to the Exchange capable ions is replaced. 3. The method according to claim 1, characterized in that the water-insoluble Aluminum oxide carrier is a synthetic aluminum silicate, preferably aluminum metasilicate. 4. The method according to claim 1, characterized in that an aluminum hydroxide - Containing silica gel in the form of a hydrogel, a xerogel or a tempered one Xerogeles according to patent ...... (P 2013593.7) as a water-insoluble carrier of aluminum oxide is used. 5. Synthetic potassium zeolites with a molar ratio Si02: A1203 equal to or greater than 2.5 and an effective pore opening, which in the synthesis form Benzene molecules are barely barred from entering and those by subsequent Ion exchange the potassium ion in whole or in part by others capable of exchange Ions is replaced.