Polymerization of isatin towards polymers for anion exchange membranes and gas separation applications

Abstract

In a world where the problem of energy resources, pollution and all aspects related to these issues becomes more and more dominant, a greater commitment is needed in the search for solutions. The goal of this project is to make a contribution to the research and development of new materials to reduce the environmental impact in some fields. First of all, we tried to synthesize and prepare an isatin-based membrane which has the potential for use in separating industrial gases. Furthermore, ion exchange membranes, specifically hydroxide exchange membranes (HEMs) derived from the same material were developed for fuel cells (HEMFC) applications. These materials are essential for energy conversion and storage. The most difficult challenge is to guarantee their thermal stability and stability in corrosive environments such as alkali without losing efficiency. In recent years the polyhydroxyalkylation catalysed with superacids, e.g. TFSA, has become increasingly studied. This reaction is exploited for the synthesis of the compounds of this thesis. After a preliminary optimization of the reaction conditions it was concluded that, due to the rigidity and excessive reactivity of the monomers, it was not possible to obtain the isatin-based membrane to evaluate the gas separation properties. The synthesis of precursor materials for HEMs was successful. Instead of isatin, 1-(4-bromobutyl)indoline-2,3-dione (BID) was used as a substitute. A characterization of the polymers was carried out using NMR, TGA and DSC analyses, and subsequently the membranes were functionalized with different ammonium-based cations. Unfortunately, this last step was not successful due to the appearance of side reactions. Future studies on the mechanism and kinetics of the reaction may solve this obstacle.

Popular Abstract

It is no secret that one of the biggest problems of modern times is climate change. This topic has been avoided for many generations and in recent years all industries and the world of marketing have begun to move and raise awareness on this issue. There is already much evidence that links the connection between man-caused damage to the environment and increasingly frequent natural disasters. The increase in temperature due to the accumulation of carbon dioxide in the atmosphere has not only impacted the climate but also the life cycle of the animals. Related to that it is estimated that some species have been forced to change the place where they generally resided and move closer near inhabited centres, bringing new contacts and the onset of new diseases. The solution being adopted is the search for renewable energy sources such as solar, hydrogen and bio fuels, and the development of new technologies green-energy based. However, compounds such as membranes, capable of energy converting economically and efficiently, must support these technologies.
One of the most energy-intensive industrial processes is the selective separation of the components of a gas or a liquid gas stream. The classic methods such as extraction, distillation and absorption are essential and not very green. For this reason, an alternative solution was sought. The separation of gas mixtures employing polymeric membranes has been commercially utilized since the late 1970s. While the ability to separate gas mixtures was recognized much earlier, the commercial reality has only recently generated a significant amount of academic and industrial research activity. Membrane separation has many advantages such as low energy consumption, economy and versatility. Another area of emerging importance for these materials is the recapture of CO2 from industrial processes. For these reasons, we have in this work tried to design an isatin-based membrane for this purpose. There are various problems in the synthesis mechanism that did not allow control over the product structure. What was supposed to be a flexible film turned out to be fragile and of low quality and therefore unusable as it was initially thought.
The other field that this work was aimed at is that of fuel cells. Briefly, these are electrochemical devices that allows to obtain electrical energy directly from certain substances, typically from hydrogen, without any thermal combustion process-taking place. Between the anode and cathode there must be a means of connection between the two parts. Generally, this connection is composed of a liquid, but many polymeric membranes that can replace them are being studied. In our specific case, we are talking about anion exchange membranes (AEM), consisting of a neutral polymeric backbone to which positively charged chemical groups are attached. These, generally quaternary ammonium salts (QA), are responsible for the transport of anions, and therefore of the current, inside the batteries or fuel cells. In this project, a less reactive isatin derivative was synthesized and polymerized. The membrane precursor had the same problem found in the first part of the study. In addition, this time a side reaction prevented the functionalization of the polymer. The usage of this polymer need a more in-depth analysis of the reaction mechanism.
To summarize, the work focus on two main topics, the synthesis of a gas separation membrane and an AEM. The successful optimization of the reaction conditions led to obtaining the polymeric compounds. The quality of the isatin polymer films were brittle and not enough to provide films for gas separation characterizations. The functionalization reaction of the polymer for AEMs was unsuccessful. The thermal and structure characterization using TGA and NMR analysis had provided a likely explanation about the reasons of the problems encountered.

• author: Facchini, Simone
• supervisor: Dong Pan
• organization: Department of Chemistry
• course: KEMP30 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: organic chemistry, membranes, isatin, polymers
• language: English
• id: 9099880
• date added to LUP: 2022-09-13 14:37:55
• date last changed: 2023-09-01 03:45:17