CA1139735A - Mordenite synthesis - Google Patents

Abstract

ABSTRACT

Kaolin which has been converted to meta-kaolin is employed as the alumina source in the hydrothermal synthesis of mordenite; aging of the reactants prior to autoclaving improves the particle size and filtration characteristics of the product.

Description

D~ket H-1550 , ~ ' .
~39~3S

TECHNICAL FIELD
This invention relates to an improvement in the art of the manufacture of synthetic large port mordenite.
BACKGROUND ART
The basic patent covering the synthesis of large port mordenite, i.e. mordenite capable of absorbing mole-cules larger than 5 Angstroms effective diameter - or more simply, as distinguished from natural mordenite, mordenite capable of absorbing benzene, is U.S. patent 3,436,174, issued April 1, 1969.
DISCLOSURE OF THE INVENTION
A variety of raw material, synthetic and natural, have been employed in the synthesis of large port sodium mordenite (U.K. patent 298,606, U.S. patent 3,436,174, U.S.
patent 3,445,184). The synthesis is usually carried out in one step at relatively low temperatures (75-260C~ under autogenous pressure.
Normally the process of manufacture consists of mixing of the reactant, autoclaving of the batch for a given length of time during which the raw material is con-verted to the zeolite, filtration of the batch to separate the zeolite from the mother liquors and the drying of the zeolite to remove excess water.
While kaolin is a particularly desirable raw material because of its availability and relatively low cost, when synthesis of mordenite is carried out using kaolin as the primary source of alumina the particle size is low and very poor filtration ~ate is obtained. The present invention relates to a process of producing synthetic large port mordenite using kaolin such that the increase particle size and filtration rates are obtained.
~.

,., ~ .
. . .

3~'~35i The process, according to the invention consists of the conversion of kaolin to metakaolin by calcination followed by aging of the reaction mixture which contains the metakaolin and other ingredients in the temperature 5 range of 25 to 100C for two hours or more followed by the autoclaving of 150-~60C. The resultant slurry contains zeolite of large particle size (average particle size > 6.0 ~ and gives fast filtration.
PREFERRED EMODIMENTS OF INVENTION AND COMPARATIVE EXAMæ~æS
10 Examnle 1 (com~arative) h sample o~ finely divided kaolin weighing 790 grams was dispersed in a solution containing 6734 grams sodium silicate (0.3 Na2~.1.0 Si02.7.5 H20) and 11186 grams water. To the resulting mixture 7g4 grams of dia-15 tomaceous silica was added with continuous stirring.
These quantities have a molar fomulation of 0.91 kaolin, 10.90 sodium silicate, 210.22 water, 3.98 diatomaceous silica. The overall composit~on of the mixture, in terms of oxidemole ratios, then correspond to N~20/Si02 0.20 Si02/A1203 = 16.70 ~H20/Na20 89.91 The reactant mixture was placed in a five gallon jacketed autoclave, provided with a mechanical stirrer and 25 an oil heating unit, and allowed to crystallize at 174Cfor five hours. At the end of the crystallization period the mixture was quenched into an equal amount of water.
A portion of the slurry was filtered and the resulting solid was washed with water to a neutral pH, then dried 30 overnight at 100C. This solid showed an X-ray crystal-linity of 92~ rompared to a commercial mordenite sample obtained from Norton Company, and a median particle size of 5.4 microns. A 200 ml of the slurry was filtered us-ing a Buchner funnel of 7.11 cm in diameter, a dacron 35 filter cloth of air porosity of 0.1-1.0 cfm/ft2 and pres-sure of 202 mmHg. It took 14 minutes for the filtration of this slurry.
Example 2 ~comparative) This example was carried out under identical - \ i conditions ~o those described in Example l; except that the reaction mixture was digested at room temperature for 24 hours prior to autocla~ing. The product median parti-cle size and cake formation time were 7.5 microns and 2 5 minutes, respectively. The mordenite content, however, was 32~.
Example 3 (comparative) A mix~ure consisting of 6734 grams sodium sili-cate, 794 grams diatomaceous ~ilica, 598 grams kaolin cal-10 cine~ a~ 610C for four hours and 11379 grams water, wasprepared. These ~uantities corresponded to Example 1 molar formulation with the exception of water (213.86 moles~ to account for that lost upon calcina~ion of ~he kaolin. The oxide-mole ratios of the mixture were the same as listed 15 in Example 1~ The mixture was autoclaved at 174C for five hours. The median particle size, crystallinity and cake formation time were 6 microns, 89% and 6.5 minutes, respectively.
Examples 4-8 The following examples were carried out using the same formulation as in Example 3.
Each mixture was digested at 50C for 24 hours followed by autoclaving at 174C for a gi~en period of time. Following this treatment the product particle size, 25 filtration and percent mordenite were determined as des-cribed in Example 1. The results are summarized in the table below.

Example No. ~ 4 5 6 7 8 Autoclave Time, ~rs 5 5.5 6 6.5 7 30 Percent Mordenite 28 87 103 90 72 Median Particle Size, ~ 40 7.5 6.6 8 6.9 Cake Formation Time, min 0.05 4.95 5.53 0.97 1.67 Example 9 (comparative) Using the same oxide-mole ratios of Example 1, a 35 mixture of 6734 grams sodium silicate, 794 grams diatoma-. .

, , .: .

~9~

ceous silica/ 790 grams raw kaolin and ~1186 grams water, was prepared. The mixture was digested at 50C for 24 hours followed by autoclaving at 174C for six hours. The run qave 77% crystallinity, 4.6 microns median particle 5 size ana I5.~ minutes cake formation time.
SUMMARY OF EXANPLES
_ Example 1 This example shows ~he median particle size and cake formation time of a given formulation using raw kao-10 lin without pradigestion.
Example 2 Here we show that the room temperature digestionof a reaction mixture, utilizing the same molar foxmulation as in Example 1, leads to an increase in the product parti-15 cle size and decrease in the cake formation time.Example 3 This example shows that the utilization of cal-cined kaolin leads to some improvements in the product particle size and filtration and no impact on the product 20 quality.
Exc~mples 4-8 These examples show that the utilization of cal cined kaolin along with digesting the reaction mixture, prior to crystallization, result in improvin~ the particle 25 size and filtration of the product. Howe~er, it is nec-essary to increase the crys~allization timè to achieve the highest ~uality product as shown by Example 6. In all these examples the product particle size and filtration are superior to those of ~xamples 1 and 2 30 Example 9 This example demonstrates that the utilization of a predigested raw kaolin based formulation does not lea~ to any impxovements in either particle size or fil-tration of the product.
Further tests have shown that the diatomite ~diatomaceous silica) should not be employed in excess of that amount required to provide 25% of the total silica in the mix.

.

.

Claims (3)

WHAT IS CLAIMED IS:

1. A method of making large port mordenite, capable of adsorbing molecules larger than 5 Angstroms, by autoclaving from 150° to 26°C a mixture of water, silica, sodium silicate, and kaolin, characterized in that the kaolin is in the form of meta kaolin and the mixture is aged at 25 to 100°C for more than 2 hours prior to auto claving, said autoclaving being carried out for a time sufficient to produce mordenite having a weight median particle size of at least 6 µm.

2. A method as in Claim 1 in which the free silica is present in the mix in an amount not more than 25% of the total free and combined silica in the mix.

3. A method as in Claim 2 in which the free silica is in the form of diatomaceous earth.