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Understanding the Effects of Water Exposure and Fabrication Parameters of LTA Membranes for Achieving High Dehydration Performance for Industrially Important Mixtures

  • Pyoseop Kim (김표섭, 대학원 화공생명공학과 화공생명공학전공)

초록/요약

The separation process of liquid mixtures has been widely used in the chemical industry, such as in the petrochemical, pharmaceutical, and biological industries. Distillation, mainly used in the conventional liquid mixture separation process, has technical limitations such as high energy consumption, the need for large-scale complex facilities, and thermodynamic limitations on separating azeotropic mixtures. The membrane-based separation process is attracting attention as a technology that can replace and supplement the limitations of the conventional distillation process. In particular, pervaporation technology is a promising alternative in the organic solvent purification and dehydration process due to its advantages of high energy efficiency, space-intensive facilities, and selective separation of azeotropic mixtures. Materials considered for pervaporation membranes include polymers, ceramics, metal-organic frameworks, and zeolites. Among these materials, zeolites are attracting attention as promising membrane materials based on the molecular sieve effect due to their uniform pore sizes. In particular, LTA zeolite is evaluated as an effective material for organic solvent dehydration processes due to its pore size, which is suitable for the selective separation of water molecules and high hydrophilicity. Despite the superiority of LTA zeolite in the dehydration process, several issues need to be supplemented through research to apply LTA zeolite to industrial processes. LTA zeolite membrane has low stability with respect to water because of its high Al content (Si/Al ratio of ca. 1). However, to the best of my knowledge, only few studies were reported on the water stability of LTA zeolite membrane. In addition, previous studies of pervaporation using LTA membranes have mainly focused on dehydration performance for binary mixtures. Nevertheless, the feed composition in actual industrial processes is more complicated, such as in the case of ternary mixtures. It is important to conduct research on the water stability of LTA membranes and their separation performance for ternary mixtures because they can be useful for actual industrial application of the pervaporation process and future research. In this study, I fabricated LTA membranes and investigated their water stability and the effect of the parameters in fabrication on the LTA zeolite membranes. In addition, I evaluated and compared dehydration performance of LTA membrane for H2O/IPA binary and H2O/IPA/ECH ternary mixtures. First, in Chapter 1, the general concept of zeolite membranes, LTA zeolites, and the necessities of this study were introduced. In Chapter 2, the effects of water exposure of LTA membranes were investigated by immerse the zeolite membrane in water for a different duration. Fluorescence confocal optical microscopy (FCOM) measurement was conducted to confirm the effect of long-term water exposure on the internal structure of the LTA zeolite membrane. In addition, the effects of water exposure time and seed layer on the H2O/CH3OH separation performances were investigated. The optimal water exposure time and seed layer formation conditions were confirmed to manufacture an LTA membrane with high separation performance. Under optimal synthetic conditions, the LTA membrane showed high separation performance with the H2O flux ~0.31 kg·m-2·h-1 and corresponding H2O/CH3OH separation factor of ~910. In Chapter 3, LTA capillary membranes with higher flux than conventional tubular membranes were fabricated, and their separation performance in a ternary feed mixture was confirmed. The properties of the support used in the membrane substantially contribute to the separation performance of the zeolite membrane. Based on the theoretical approach, I improved the flux of the zeolite membrane by 2-3 times by using a support with low penetration resistance. In addition, the separation performance of the LTA zeolite membrane for H2O/IPA binary and H2O/IPA/ECH ternary mixtures was measured and compared. As a result, the differences in separation performance between binary and ternary systems and the effect of the component system of the feed mixture on the separation performance of the zeolite membrane were elucidated.

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목차

ABSTRACT ........................................................................................................................... i
국문 초록 ............................................................................................................................. iv
TABLE OF CONTENTS ................................................................................................... viii
LIST OF TABLES ............................................................................................................... xi
LIST OF FIGURES ............................................................................................................. xii
LIST OF SCHEME ............................................................................................................ xxi
CHAPTER 1. INTRODUCTION .......................................................................................... 1
1.1. Zeolite ......................................................................................................................... 1
1.2. LTA zeolite membranes for dehydration processes and challenges to overcome for actual industrial applications ............................................................................................. 2
CHAPTER 2. On the effects of water exposure of as-synthesized LTA membranes on their structural properties and dehydration performances .................................................... 4
2.1. Introduction ................................................................................................................ 4
2.2. Experimental ............................................................................................................... 9
2.2.1. Synthesis of LTA zeolite particles ....................................................................... 9
2.2.2. Formation of LTA seed layers and membranes ................................................... 9
2.2.3. Characterization ................................................................................................. 14
2.3. Results and discussion .............................................................................................. 16
2.3.1. Synthesis of disc-supported LTA zeolite membranes and their immersion in water ............................................................................................................................ 16
2.3.2. Structural properties and separation performances of LTA tube membranes ... 34
2.3.3. Long-term stability test of the LTA tube membranes ....................................... 59
2.3.4. Evaluation of the separation performance of the LTA tube membranes ........... 59
2.4. Conclusions .............................................................................................................. 61
CHAPTER 3. LTA zeolite membranes on thin-walled capillary tubes for the high-throughput dehydration of industrially important ternary water/isopropanol/epichlorohydrin mixtures ....................................................................... 63
3.1. Introduction .............................................................................................................. 63
3.1.1. Epoxy resin production process ......................................................................... 67
3.2. Experimental ............................................................................................................. 68
3.2.1. Synthesis of LTA type zeolite particles ............................................................. 68
3.2.2. Formation of LTA seed layers and synthesis of LTA membranes .................... 68
3.2.3. Characterization ................................................................................................. 71
3.3. Results and discussion .............................................................................................. 75
3.3.1. Formation of LTA membranes on α-alumina tubular and capillary supports ... 75
3.3.2. Defect structure of the LTA membranes on the tubular and capillary supports 82
3.3.3. Separation performance of the LTA membranes on the tubular and capillary supports ....................................................................................................................... 84
3.3.4. Dehydration performance with respect to the H2O concentration in the H2O/IPA/ECH ternary feed ......................................................................................... 94
3.3.5. Evaluation of the dehydration performance of TM and CM ........................... 103
3.4. Conclusions ............................................................................................................ 108
CHAPTER 4. Summary and perspective .......................................................................... 110
REFERENCES .................................................................................................................. 114
ACKNOWLEDMENTS .................................................................................................... 127

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