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Polybenzimidazoles, a class of aromatic heterocyclic polymers, are well known due to their remarkable thermal stability, mechanical properties and chemical resistance which are often required in extreme operation conditions. Because of these properties, polybenzimidazoles are excellent candidates in various application areas including proton exchange membrane fuel cells, gas separation membranes, reverse osmosis and nanofiltration, and high performance coatings. The following studies are focused on the synthesis, characterization and related properties of polybenzimidazoles and polybenzimidazole based materials. A novel sulfonyl-containing tetraamino-substituted monomer (3,3',4,4'-tetraaminodiphenylsulfone) was synthesized and polymerized with three different diacid monomers to make polybenzimidazoles. The new monomer synthesis route with reduced steps relative to the existing literature method increased the overall yield by a factor of three. The sulfonyl-containing polybenzimidazoles have enhanced solubilities in common organic solvents including dimthylsulfoxide, dimethylacetamide and N-methyl-2-pyrrolidone in comparison with the commercial polybenzimidazole, Celazole®, poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole). The improvements in solubility are attributed to the introduction of polar sulfonyl linking moiety in the monomer. Remarkable thermal stabilities (high T_g, > 428 °C) were demonstrated through Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). A well designed film casting process was investigated and established. Polybenzimidazoles were fabricated into transparent thin films (20-30 μm thick) for gas transport measurements. These novel polybenzimidazole films exhibited extraordinary gas separation properties, especially for H₂/CO₂ separation. There is a trade-off relationship between gas permeability and selectivity through dense, non-porous polymer membranes that was discovered by Robeson in 1991. The ultimate goal for developing gas separation membranes is to improve both permeability and selectivity simultaneously. Gas permeability is related to the free volume between polymer chains. In order to improve gas permeability, we hypothesized a concept that increasing free volume could be achieved by thermally degrading sacrificial components and volatilizing their byproducts from a glassy matrix. Volatile components were introduced into the films to preoccupy the spaces between polymer chains. Once they were degraded and removed through the thermal treatment, it was hypothesized that the preoccupied spaces would remain empty due to the glassy nature of the matrix at the heat treatment temperature, thus resulting in more free volume. Two post- modification strategies including grafting and blending were utilized to incorporate the volatile components, poly(propylene oxide) and poly(ethylene oxide). Post-modified polybenzimidazole films impressively showed significant enhancements in both gas permeability and selectivity for H₂/CO₂ separation. The H₂ permeability of the post-modified TADPS-OBA polybenzimidazole increased from 3.1-6.2 Barrers to 5.2-7.5 Barrers (up to 66% increase). The selectivity for H₂/CO₂ increased from 7.5-10.5 to 10.1-13.0 (up to 33% increase). The study on the potential effects of water vapor on the separation performance of PBI membranes was discussed in the appendix. / Ph. D. / Polybenzimidazoles represent a class of polymeric high performance materials due to their remarkable thermal stability, mechanical properties and chemical resistance. They are competitive material candidates for applications involving extreme conditions including high pressure and high temperature. The following studies are focused on the synthesis, characterization and properties of polybenzimidazoles and polybenzimidazole based copolymers and blends. Of particular importance to this dissertation are the gas transport properties. The new materials are excellent candidates for making non-porous membranes that can separate very small molecules such as nitrogen, oxygen, carbon dioxide, and hydrogen. The non-porous membranes achieve separations of such small molecules by having the gases solubilize in the upstream side of a membrane, diffuse through it, then evaporate from the downstream side. This mechanism is known as the solution-diffusion mechanism. The monomer, 3,3’,4,4’-tetraaminodiphenylsulfone, was synthesized via our designed synthesis method that was simpler than previous methods described in the literature and with a 3 times higher yield. A series of polybenzimidazoles with systematically varied chemical structures were prepared and it was demonstrated that they all had enhanced solubilities in common organic solvents over the only known commercial polybenzimidazole, Celazole®. This is particularly important for membrane materials because they must be fabricated into thin films from solution. Remarkable thermal stabilities for polymeric materials with glass transition temperatures above 400 °C were found for these polybenzimidazoles. A well designed film casting process was investigated and established. Polybenzimidazoles were fabricated into transparent thin films (20-30 µm thick) and their gas transport properties were measured. These novel polybenzimidazole films exhibited extraordinary gas separation properties, especially for H₂/CO₂ separation. The gas transport properties involve two important parameters, permeability and selectivity. A trade-off relationship between the two parameters was discovered by Robeson in 1991. The ultimate goal for developing gas separation membranes is to improve permeability and selectivity at the same time. In order to improve gas permeability, we hypothesized a concept that increasing permeability could be achieved by creating more spaces between the polymer chains in non-porous films. Sacrificial components were introduced into the films, then thermally degraded and the byproducts were volatilized to remove them from the film. It was further hypothesized that conducting the heat treatment process at a temperature where the matrix polymer was in the glassy state would allow the matrix polymer to preserve the free volume introduced by the volatization. Two post-modification strategies including grafting and blending were utilized to incorporate the volatile components, poly(propylene oxide) and poly(ethylene oxide). Post-modified polybenzimidazole films impressively showed significant enhancements in both gas permeability and selectivity for H₂/CO₂ separation. This is an important separation that could economically be carried out at elevated temperatures (~250°C) if the polymer membrane would withstand such a temperature. It could be utilized to separate H₂ from CO₂ in pre-combustion syngas. This is the major method for H₂ production worldwide. The study on the potential effects of water vapor on the separation performance of PBI membranes was discussed in the appendix.

Wu Xiujuan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 88-93). / Abstracts in English and Chinese. / ABSTRACT (Chinese) / ABSTRACT / ACKNOWLEDGEMENT / TABLE OF CONTENTS / LIST OF TABLES / LIST OF FIGURES / Chapter CHAPTER ONE: --- INTRODUCTION / Chapter 1.1 --- General B ackground --- p.1 / Chapter 1.2 --- Chromium in Environment and its Analysis --- p.2 / Chapter 1.2.1 --- Source of Chromium and its Harmful Effects on Human --- p.2 / Chapter 1.2.2 --- Methods for Separation and Determination of Chromium Species --- p.4 / Chapter 1.3 --- Arsenic in the Environment and its Toxicity --- p.4 / Chapter 1.4 --- Properties of TiO2 and Its Applications --- p.6 / Chapter 1.4.1 --- Photocatalytic Property of TiO2 --- p.6 / Chapter 1.4.2 --- Surface Acid-Basic Property of TiO2 --- p.8 / Chapter 1.5 --- Adsorption --- p.11 / Chapter 1.6 --- Fundamental of ICP-AES and ICP-MS --- p.12 / Chapter 1.6.l --- Principle of ICP-AES --- p.12 / Chapter 1.6.2 --- Principle of ICP-MS --- p.14 / Chapter 1.7 --- Scope of Work --- p.18 / Chapter CHAPTER TWO: --- SEPERATION OF CHROMIUM SPECIES ON TIO2 / Chapter 2.1 --- Introduction --- p.19 / Chapter 2.2 --- Experimental --- p.23 / Chapter 2.2.1 --- Materials --- p.23 / Chapter 2.2.2 --- Instruments --- p.24 / Chapter 2.2.2.1 --- Coupling of TiO2 column and ICP-AES --- p.24 / Chapter 2.2.2.2 --- Coupling of TiO2 column and ICP-MS --- p.26 / Chapter 2.2.3. --- Procedure --- p.29 / Chapter 2.3 --- Results and Discussion --- p.33 / Chapter 2.3.1 --- Preliminary study on the adsorption of Cr(III) and Cr(VI) on TiO2 --- p.33 / Chapter 2.3.2 --- Development and Verification of the proposed method for speciation of Cr(III) and Cr(VI) in aqueous solution --- p.42 / Chapter 2.3.3 --- Practical application of the proposed method for separation and determination of Cr(III) and Cr(VI) --- p.46 / Chapter CHAPTER THREE: --- ADSORPTION OF ARSENIC SPECIES ON TiO2 / Chapter 3.1 --- Introduction --- p.61 / Chapter 3.2 --- Experimental --- p.66 / Chapter 3.2.1 --- Materials --- p.66 / Chapter 3.2.2 --- Instruments --- p.69 / Chapter 3.2.3 --- Procedure --- p.70 / Chapter 3.3 --- Results and Discussion --- p.71 / Chapter 3.3.1 --- Adsorption Kinetics --- p.71 / Chapter 3.3.2 --- Effect of pH on Adsorption of Arsenic Species --- p.71 / Chapter 3.3.3 --- Adsorption Isotherm --- p.74 / Chapter 3.3.4 --- Adsorption Model --- p.76 / Chapter 3.3.5 --- Factors Affecting the Adsorption of Arsenic Species on p25 and Rutile TiO2 --- p.83 / Chapter CHAPTER FOUR: --- CONCLUSION --- p.86 / REFERENCES --- p.88

Membrane chromatography is a promising process for the isolation, purification, and recovery of proteins, enzymes, and nuclear acids. Comparing with traditional beads column chromatography, membrane chromatography can faster, easier and cheaper to mass-produce. And also, it is easy to set up and scale up. In this thesis, we are trying to study the performance of membrane chromatography, and the mixture of HSA and chicken egg white is used as an example. We are investigating the purification of Human serum albumin (HSA) from chicken egg white in terms of precondition, dilution, purification method, product recovery, product purity and product cost. HSA, is a very important clinical protein. In order to obtain low cost, high efficiency and less risk HSA, recombinant DNA technology is used. Many kinds of host organism have been used to produce recombinant HSA (rHSA). In this thesis, a kind of ion-exchange membrane (Mustang Q membrane capsule) chromatography was used. The membrane capsule is disposable because it is designed for use in pharmaceutical production. For this project, a cleaning method was used which made the membrane capsule reusable. Washing with 4 mL 1 M NaCl and 4 mL NaOH was sufficient for this purpose. Since the egg white protein solution was very viscous, it needs to be diluted before loaded on FPLC. Dilute experiment was done to find the best dilution level. In this thesis, we found that 5 times dilution was best not only for high efficiency but also for FPLC operation. After getting the basic conditions, some purification experiments were done to find the optimal operation condition to purify HSA form chicken egg white protein solution by changing buffer pH, salt concentration in elution buffer and gradient used to elute proteins. The best purification condition for loading buffer is Tris-HCl buffer A (4.75g/L, pH 9.5) and the elution buffer is Tris-HCl buffer A + 0.2M NaCl. The purity of HSA recovered was 93% on the Mustang Q membrane capsule at 1 ml/min when the mixture of HSA and chicken egg white was diluted 10 times. And the yield was 85%. The impurity is probably ovoglobulin as suggested by the result of SDS-PAGE, whose molecular weight is close to 40kd. To characterize the separation capability of the Mustang Q membrane capsules, equilibrium adsorption and breakthrough curve studies were made using bovine serum albumin (BSA). 1mg/mL BSA solution was used to get the breakthrough curve with different flow rate ranging from 1 to 4 ml/min. With a flow rate is 1 ml/min, breakthrough curve were obtained with different concentrations of BSA ranging from 1 to 16 mg/mL. The dynamic binding capacity was found to be from 9.1 to 119.1 mg/mL. The equilibrium adsorption isotherm showed Langmuir isotherm behavior with dissociation constant and a maximum adsorption capability. According to the result of isotherm adsorption, a multi-plate mathematical model was used to get the theoretical breakthrough curve. By fitting the theoretical breakthrough curve to the experimental breakthrough curve, constants in the multi-plate model were obtained and were used to estimate the axial dispersion coefficient of the membrane capsule. The estimated axial dispersion coefficient of 2.45*10-6 cm2/s is very small which means that the axial ispersion is not significant. The adsorption process is therefore controlled by radial radius dispersion or film dispersion.

In this research project, systematic studies of polymer-assisted flocculation and dewatering behaviour of colloidal gibbsite (y-Al(OH)3) dispersions, together with polymeric flocculant structure-mediated interfacial chemistry and particle interactions, have been performed. Clear links between flocculation performance, interfacial chemistry, particle interactions, dispersion settling rate and sediment consolidation were established for improved dewaterability.

Thesis (M. Ing.)--University of Stellenbosch, 1997. / Bibliography. Also available via the Internet.