Organic Structure-directing Agent-free Synthesis for *BEA-type Zeolite Membrane

Summary

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.

Abstract

Membrane separation has drawn attention as a novel-energy saving separation process. Zeolite membranes have great potential for hydrocarbon separation in petroleum and petrochemical fields because of their high thermal, chemical, and mechanical strength. A *BEA-type zeolite is an interesting membrane material because of its large pore size and wide Si/Al range. This manuscript presents a protocol for *BEA membrane preparation by a secondary growth method that does not use an organic structure-directing agent (OSDA). The preparation protocol consists of four steps: pretreatment of support, seed preparation, dip-coating, and membrane crystallization. First, the *BEA seed crystal is prepared by conventional hydrothermal synthesis using OSDA. The synthesized seed crystal is loaded on the outer surface of a 3 cm long tubular α-Al₂O₃ support by a dip-coating method. The loaded seed layer is prepared with the secondary growth method using a hydrothermal treatment at 393 K for 7 days without using OSDA. A *BEA membrane having very few defects is successfully obtained. The seed preparation and dip-coating steps strongly affect the membrane quality.

Introduction

Membrane separation has drawn attention as novel-energy saving separation process. Many types of membranes have been developed for the past decades. Polymeric membranes have been widely used for gas separation, creating drinkable water from sea water¹, and wastewater treatment².

Inorganic membrane materials like silica³, carbon molecular sieve⁴, and zeolite have advantages for thermal, chemical, and mechanical strength compared with polymeric membranes. Therefore, inorganic membranes tend to be used under more severe conditions, such as hydrocarbon separation....

Protocol

1. Support preparation

1. Pretreatment of support
   1. Cut out a 3 cm long tubular porous α-Al₂O₃ support (see Table of Materials).
   2. Wash the support with distilled water for 10 min. After that, wash the support with acetone for 10 min. Repeat this washing process 2x.
      NOTE: Do not touch the outer surface of a support after the washing step. No other treatment was carried out (e.g., sonication, and rubbing by sandpaper, etc.)
   3. Dry the washed support at 110 °C overnight prior to use for dip-coating.
      NOTE: Measure the weight of the support piece after drying. The final me....

Results

Figure 1 shows the preparation procedure of the *BEA seed crystal. Figure 2 shows the X-ray diffraction (XRD) pattern of synthesized *BEA seed crystal. Typical strong reflection peaks of (101) and (302) around 2q = 7.7 and 22.1° appeared. In addition, no obvious reflection peaks other than the *BEA-type zeolite were observed. These results showed that the pure phase of *BEA zeolite was successfully synthesized.

A typical.......

Discussion

There are many kinds of Si and Al sources for zeolite synthesis. However, we cannot change raw materials for preparation of this *BEA-type membrane. If raw materials are changed, the phase of zeolite crystallized and/or growth rate may be changed.

Glass beakers cannot be used for synthesis gel preparation because the synthesis gel has high alkalinity. Bottles and beakers made of polyethylene, polypropylene, and Teflon can be used instead.

To prepare a higher quality.......

Materials

Name	Company	Catalog Number	Comments
a-Al2O3 support	Noritake Co. Ltd.	NS-1	Average pore size, 150 nm; Outer diameter, 10 mm; Innar diameter, 7 mm
Colloidal silica	Nissan Chemical	ST-S	SiO2 30.5%, Na2O 0.44%, H2O 69.1%
Mesh filter (PTFE membrane)	Omnipore	JGWP04700	Pore size, 200 nm
NaAl2O	Kanto Chemical	34095-01	Na2O 31.0-35.0%; Al2O3 34.0-39.0%
NaOH	Kanto Chemical	37184-00	97%
Tetraethylammonium hydroxide	Sigma-Aldrich	302929-500ML	35 wt% solution