Chemistry
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Organic Structure-directing Agent-free Synthesis for *BEA-type Zeolite Membrane
Chapters
Summary February 22nd, 2020
A *BEA seed crystal was loaded on a porous α-Al2O3 support by the dip-coating method, and hydrothermally grown without using an organic structure-directing agent. A *BEA-type zeolite membrane having very few defects was successfully prepared by the secondary growth method.
Transcript
The preparation of zeolite membrane is based on knowhow and experience accumulated in the laboratory. We would like to share this protocol as a reference for everyone who wants to start membrane synthesis. This method enables us to obtain a BEA membrane, having a good separation performance without using organic structure-directing-agent.
Operationally, equipment for zeolite membrane preparation are quite unique. This video can help you to run how to prepare zeolite membranes. Demonstrating the procedure will be Yuto Tsuzuki, a graduate student from our laboratory.
To begin, cut out a three centimeter long tubular porous alpha aluminum oxide support. Wash the support with distilled water for 10 minutes. After that, wash the support with acetone for 10 minutes.
Repeat this washing process twice. Use a beaker to transfer the washed support into an incubator to dry at 110 degrees Celsius overnight. In the morning, measure the weight of the support piece.
First, add 26.2 grams of colloidal silica and 8.39 grams of tetraethylammonium hydroxide into a 250ml bottle made of polypropylene. Stir the mixture using a magnetic stirrer for 20 minutes in a 50 degrees Celsius water bath. After that, stir the mixture using a magnetic stirrer for 20 minutes at room temperature.
Then, add 8.39 grams of tetraethylammonium hydroxide, 5.79 grams of distilled water, 1.08 grams of sodium hydroxide, and 0.186 grams of sodium aluminate into a Teflon beaker. Stir the mixture, by using a magnetic stirrer for 20 minutes at room temperature. Next, add solution B to solution A in a 250ml bottle.
The mixture of solution A and B becomes milky. Cap the bottle, and shake it vigorously by hand for 5 minutes. After that, stir the mixture, using a magnetic stirrer, for 24 hours at room temperature.
The next day, the gel obtained is the synthesis gel, with the final composition of 24 sodium oxide to one aluminum oxide to 200 silicon dioxide to 69 tetraethylammonium hydroxide to 2905 water. To perform crystallization, pour the synthesis gel into a Teflon-lined autoclave. Place the autoclave in an air oven at 100 degrees Celsius for seven days.
Then, quench the autoclave with flowing water for 30 minutes. Remove the white sediment in the autoclave by a vacuum filtration apparatus with a 200 nanometer mesh filter. Wash the white sediment with 200ml of boiling water to remove amorphous and uncrystallized materials.
Dry the washed sediment in a dish at 110 degrees Celsius overnight. The dried sediment is the seed crystal. To prepare BEA seed slurry, add 0.5g of the seed crystals into 100ml of distilled water in a bottle.
Carry out sonication of the seed slurry for one hour to disperse the seed crystals. Then, fix a tubular support with a stainless steel rod, using Teflon tape, to plug the inside of the support. Pour the seed slurry into a glass tube, with a 19ml diameter.
Immerse the fixed support into the poured seed slurry and wait for one minute. After that, withdraw the seed slurry vertically at approximately 3 centimeters per second through the silicon cap. Repeat the dip-coating process one more time.
After dip-coating, dry the support at 70 degrees Celsius for two hours. Next, calsign the dip-coated support at 538 degrees Celsius for six hours with the increase and decrease temperature rates at 50 degrees Celsius per minute. This removes OSDA and chemically binds the seeds onto the support surface.
After calcination, measure the weight of the support. Calculate the amount of seed crystal loaded, as the difference in the support weight, before and after dip-coating. Add 92.9 grams of distilled water, 9.39 grams of sodium hydroxide, and 1.15 grams of sodium aluminate into a 250ml polypropylene bottle.
Stir the mixture using a magnetic stirrer for 30 minutes at 60 degrees Celsius in a water bath. After that, add 81.6 grams of colloidal silica in a step-wise manner of 1 drop per second into the mixture. Stir the mixture for another four hours at 60 degrees Celsius in a water bath.
The gel obtained is the synthesis gel, having a final composition of 30 sodium oxide to one aluminum oxide to 100 silicon oxide to 2000 water. Then, pour the synthesis gel into a Teflon-lined autoclave in which the seeded support is placed vertically. Place the autoclave in an air oven at 120 degrees Celsius for seven days for crystallization.
After crystallization, quench the autoclave with flowing water for 30 minutes. Wash the support with the membrane in boiling water for eight hours and dry overnight. This is the BEA membrane.
After drying, measure the weight of the prepared support with membrane. Calculate the weight of the membrane by the difference in support weight before and after crystallization. The X-ray defraction pattern of synthesized BEA seed crystal, shows typical strong reflection peaks, around two theta, equaling 7.7 and 22.1 degrees.
In addition, no obvious reflection peaks, other than the BEA type zeolite, were observed. Spherical seed crystals were observed through the FE-SEM image of the synthesized seed crystal and their size was uniformly approximately 200 nanometers. The X-ray defraction pattern of synthesized BEA membrane shows the same peaks observed in the seed crystals.
In addition, reflection peaks of alpha aluminum oxide with two theta equaling 26, 35.5 and 38 degrees were observed. FE-SEM image of the synthesized membrane reveals that the crystals had truncated octohedral morphology, uniformly covering the support surface. There are many kinds of zircon and aluminum sources for zeolite synthesis.
However, please do not change your materials for preparation of this BEA-type membrane.
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