기상전달방법으로 ZSM-5 필름 제조과정에서 젤의 숙성효과

정만규, 홍성선, 김만회*

충북대학교 화학공학과, 공군사관학교 화학과*

Aging effects of the gels in the synthesis of ZSM-5 film

by the vapor phase transport method

Man-Kyu Jung, Sung-Sun Hong, Man-Hoe Kim*

Dept. of Chem. Eng. Chungbuk National Univ., Cheongju 360-290, Korea

*Dept. of Chemistry, Airforce Academy, Chungbuk 363-849, Korea

INTRODUCTION

Recently, great interests have been focused on the synthesis of zeolite membranes and films, due to their uniform pore sizes, thermal and chemical resistance.1 Zeolte film could impart shape selective properties to the supporting materials, the surface area of the chemical sensor such as the surface acoustic divices and semicoductor gas sensors2 could be increased by imparting zeolite film. The specific synthesis conditions for the synthesis of zeolite film and membrane are disclosed. Gavalas et al. reported the synthesis composition producing good-quality membranes on porous □-alumina disk.3 Valtchev et al. investigated the influence of the chemical composition of the surface and the effect of the surface treatment on the synthesis of the zeolite films. In addition, they reported the chemical composition and the structure of the fibers determine the degree of coverage, and the amount of zeolite deposited on the fiber surface can be controlled by chemical and mechanical treatments.4,5,6 Dong et al. prepared the membranes of ZSM-35 and ZSM-5 by putting aluminosilicate gels on the glass plates in the vapors of amines and water.7 As aforementioned the state of the substrate surface and the composition of the synthesis solution are of decisive factors in preparing zeolite films and membranes.

In this paper we report the aging effect on the formation of ZSM-5 films on the quartz plate by the vapor phase transport method. The vapor phase transport method8 can cut down both the amount of chemicals used and pollution problems. This study could contribute to make ZSM-5 film and ZSM-5 membrane.

EXPERIMENTAL

To verify the aging effects of source materials, two sets of the samples are prepared. Each set of source materials has the same compositions but different aging periods. One set of the source materials is mixture of TEOS and TPAOH(40wt.%) and the other set of source materials is made of NaOH, NaAlO21.5H2O, Cab-O-sil (SiO2/Al2O3=40, SiO2/Na2O=10). Both the aged and not-aged mixtures and gels are attempted as the source materials of ZSM-5 film synthesis on the quartz surfaces.

These quartz plates are put into the upper position of Teflon vessel as shown at Figure 1. Distilled water (7 g) was also introduced at the bottom of the Teflon vessel. The bombs containing the Teflon vessels were sealed and kept in the air heated oven at 150。C for 4 days. After synthesis, the bombs were cooled down in air. The resulting surface layers of the quartz plates were washed with distilled water and investigated with X-ray diffraction analysis, scanning electron microscopy (SEM). The resulted solids over the quartz surfaces were also dried at 100。C without washing and characterized by XRD.

RESULTS AND DISCUSSION

Aging effects of gel mixtures on the formation of the ZSM-5 layer on the quartz plate were investigated. The powdered gels(SiO2/Al2O3=40, SiO2/Na2O=10, moisture ca. 30 wt.%) having a long aging period were transformed into ZSM-5 in autogenous pressure of 150。C for 4 days.8,9 The ZSM-5 crystals formed in this manner were not sticked to the quartz surface. However, a gel mixture having a short aging period (below 5 minutes) were transformed into ZSM-5 thick film on the quartz surface. These ZSM-5 crystals were strongly attached to the quartz surfaces. Different point between the powdered gels and the gel mixture is the long and short in the aging periods of the source materials. The powdered gels had a long aging period (at least 3 days), by comparison, the gel mixture had a relatively short aging period (below 5 minutes).

Another set of experiments was carried out to elucidate the aging effect on the ZSM-5 film synthesis. The one source material was an aged clear solution of the TEOS and TPAOH (0.2TPAOH-TEOS-7H2O). The other was a not-aged mixture of an aqueous TPAOH and TEOS (0.2TPAOH-7H2O/ TEOS). Both the aged clear solution and the not-aged mixture were attempted as the source materials for the synthesis of ZSM-5 films on the quartz surfaces. When the source materials were heated at 150。C for 4 days in the presence of water vapor, ZSM-5 crystals were synthesized. An uniform thin film of ZSM-5 crystals is obtained in case that the not-aged mixture used as shown in Figure 2. The resulted ZSM-5 crystals are strongly attached to the quartz surface. On the other hand, when the aged clear solutions were used, No ZSM-5 film but only the powder form of ZSM-5 crystals were obtained

From the experiments, It is concluded that ZSM-5 crystals can be agglutinated to quartz surface in the vapor phase transport method when the source materials are not aged.

The existences of cations are known as essential in most of zeolite syntheses. Without cation sources (Na+, TPA+), any ZSM-5 crystals are not obtained from the every ratio of SiO2/Al2O3 mixtures. Cation is believed as structure-directing agency or nuclei sites from the relations with anions such as silicates or aluminosilicates. The sites such as Na+ and TPA+ enclosed with silicate anions are believed as active sites. Also, these cation sites are also regarded as starting points of crystallization. Aging of the gel mixture influences the location of the cation sites (Na+, TPA+). It can be deduced that most of the active cation sites are located within the aged gel particles because every active sites are believed to be encapsulated with silicate anions. When the aged gels were put on the quartz surface as the source of ZSM-5 film, the quartz surface has very little chances to have cations as nuclei points. As a result, It is hard to observe chemical bonding between the resulted ZSM-5 crystals and the quartz surface. However, when the not-aged gels were tried on the quartz surface, the quartz surface had chances to have cations as nuclei points. ZSM-5 crystal grows started from the quartz surface, and chemical bondings between the ZSM-5 crystals and the quartz surface could be formed.

These results suggest that the existence and the location of active sites at the interface are very important in making the bonds between ZSM-5 crystals and the quartz surfaces. The not-aged gels or liquid mixture are apt to form ZSM-5 film on the quartz surface in the vapor phase transport method.

CONCLUSIONS

The existence and the location of active sites at the interface are very important in making the bonds between ZSM-5 crystals and the quartz surfaces. The not-aged gels or liquid mixture are apt to form ZSM-5 film on the quartz surface in the vapor phase transport method. The restriction of aging within the synthetic mixtures was helpful for the thin film synthesis.

ACKNOWLEDGEMENTS

This research is supported by the Korean Science and Engineering Foundation (KOSEF) under contract KOSEF 971-1108-055-2.

REFERENCES

1  Matsukata, M., Nishiyama, N. and Ueyama, K.; 'Zeolites and Related

Microporous Materials : State of the Art' 1994 84B; Elsevier; 1992; 1183.

2  Moseley, P. T.; Sensors and Actuators B; 1992; 6 149-156

3  Yan, Y., Davis, M. E., Gavalas, G. R.; Ind. Eng. Chem. Res.; 1995;

34 1652-1661

4  Mintova, S., Valchev, V.; Zeolites; 1995; 15 171-175

5  Mintova, S., Valchev, V., Konstantinov, L.; Zeolites; 1995; 15 679-683

6  Mintova, S., Valchev, V.; Zeolites; 1996; 16 31-34

7  Dong, J., Dou, T., Zhaos, X., Gao, L.; J. Chem. Soc. Chem. Commun.;

1992; 1056-1058

8  Kim, M.-H., Li, H.-X., Davis, M. E.; Microporous Materials; 1993,

1 191-200

9  Kim, M.-H., Jung, M., Rhee, H.-K.; Korean J. Chem. Eng.; 1995;

12 No.4