Myongjin Lee

Date of Award

Fall 2022

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Xingjian Xue

Abstract

Air separation is a widely used process for oxygen production. Several separation technologies have been developed for air separation, including cryogenic distillation, swing adsorption, redox process of metal oxides, and electrochemical process. Among these technologies, electrochemical permeation process stands out as a cost-effective and simple process for pure oxygen production from air. The electrochemical permeation process employs a gas-tight membrane to permeate and separate oxygen from air directly, where the membrane conducts both ions and electrons simultaneously. Different membrane designs have been studied to obtain the improved performance for oxygen permeation, typically planar and tubular designs. Among these membrane configurations, micro-tubular type of membranes has demonstrated some advantageous characteristics, such as high surface to volume ratio, short sealing length, dynamic/transient thermal stability. Nonetheless, it is usually very difficult to fabricate micro-tubular membranes, especially for miniaturization designs where the diameters of micro-tubular membranes may reach millimeter or sub-millimeter scales. In the past few years, the fabrication of hollow fiber membranes has been demonstrated using the phase inversion-based spinning process. However, the small diameter of hollow fibers together with the brittleness of ceramic materials usually leads to insufficient mechanical strength for robust and durable operations particularly under harsh thermal cycling conditions. The insufficient mechanical strength also prevents conventional hollow fiber membranes from upscaling into hollow fiber membrane stacks and modules for industrial application.

The first goal of this dissertation is to develop a novel composite hollow fiber-supported thin film membrane. The sintering behaviors and TECs of a set of metal oxides were systematically measured in a wide range of temperatures. The results were used to guide material selection for hollow fiber substrate. The composite hollow fiber substrate precursor was then fabricated using slurry spinning process in combination with modified phase inversion method. The thin film separation layer and catalyst layer were then successfully fabricated on the composite substrate, forming an asymmetric hollow fiber substrate-supported thin film membrane device. Oxygen permeation test of the device was systematically conducted, and the fundamental mechanisms were analyzed. An accelerated long-term stability test of the membrane was also conducted (~ 550 h, ~ 46 thermal cycles), demonstrating excellent robustness and durability. The device was characterized and analyzed before and after the test.

Built upon the successful fabrication and testing of the asymmetric hollow fiber substrate-supported thin film membrane device, the second goal of the dissertation is to upscaling the single hollow fiber membrane technology for membrane stack and module development. In particular, the study elucidated the design of hollow fiber membrane stack, developed a novel reliable gas-tight high temperature sealing technology, and implemented the assembly of hollow fiber membrane stack. Using the upscaling approach, two membrane stacks with a slightly different materials systems were developed. Oxygen permeation performance of the stacks was systematically measured and compared with a single hollow fiber membrane. The fundamental mechanism was discussed. Accelerated long-term stability tests were also conducted to demonstrate the robustness and reliability of the hollow fiber stacks.

Rights

© 2022, Myongjin Lee

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