Modified Metal-Organic Frameworks Based Mixed Matrix Membrane for Carbon Dioxide Separation

Abstract

A transition towards sustainable and eco-conscious industrial practices, coupled with fostering behavioral change among individuals, is essential for effectively addressing environmental challenges. Greenhouse gases have a noticeable impact on global warming, causing significant variations in climatic patterns. Foremost among these gases is carbon dioxide (CO2), whose continuous release serves as the primary instigator of climate change. This highlights an urgent need for change, emphasizing the imperative to redefine our interactions with the environment before irreversible damage occurs. Various CO2 capture technologies, amine absorption, and cryogenic distillation are expensive, complex operations, or numerous environmental issues. CO2 capturing through adsorption technology has been the considerable focus of extensive research. In the past few years, most efforts have been dedicated to developing adsorbents with exceptional CO2-capturing capacity, minimizing the energy penalty, and implementing the technology for commercial use. However, Membrane-based gas separation has great potential for reducing environmentally hazardous CO2 gas. Mixed matrix membranes (MMMs) are a viable option for addressing challenges in conventional polymeric membranes. MMMs have been proposed due to their potential to combine the incorporated particles' gas transport and separation properties with the polymers' favorable processability and mechanical properties. However, limitations still need to be addressed, such as the lack of proper compatibility between the fillers and the polymer matrix, which leads to non-selective pathways. This problem becomes even more crucial when using higher filler loadings, which are typically necessary to enhance the separation performance. Including enough filler in MMMs to create a percolative network is challenging. This PhD dissertation mainly focuses on membrane-based CO2 adsorption and separation. The main objective was to fabricate a filler that is compatible with the polymer and improves the mechanical properties, CO2 adsorption and separation capabilities of MMMs compared to membranes made entirely of polymers. To accomplish this goal, we have xx investigated different fillers, such as Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), to incorporate in the polymer matrix to prepare MMMs. Characterizations such as UTM, SEM, XRD, FTIR, and contact angle measurement were carried out to explore the physical, mechanical, and chemical characteristics of fabricated MMMs. Adsorption and mixed gas (CO2/CH4) permeation experiments were conducted to investigate the properties of fabricated MMMs. In the first part of the thesis, the CO2 adsorption performance of Cu-MOF-GO MMMs, Graphene-grafted bimetallic MOFs (GG-BM MOF) MMMs, and ACOF-1-based MMMs were performed. The effect of increasing the filler concentration on CO2 adsorption in MMMs was also investigated at various pressures. MMMs possess a high capacity for CO2 adsorption due to the characteristics of both polymers and fillers. Among all fabricated MMMs, Cu-MOF-GO MMMs exhibit better CO2 adsorption capacity was 1.79 mmol/g and 7.98 wt.% at 15 bar in comparison to GG-BM MOF-based MMMs, i.e., 0.70 mmol/g and 3.1 wt.% at 10 bar and 5 wt.% loaded ACOF-1-based MMM 0.53 mmol/g and 2.46 wt.% at 15 bar. The second section of the thesis describes mixed gas CO2/CH4 separation analysis for ACOF-1-based MMM. The fabricated MMMs enhance the CO2 permeability of the pure polymeric membrane while maintaining its inherent selectivity for CO2/CH4. The results demonstrate that adding ACOF-1 improved permeability and CO2/CH4 selectivity compared to neat Pebax—the MMM with 5 wt. % of ACOF-1 showed the best separation performance, i.e., CO2 permeability of 103.2 to 183.8 Barrer when the operating temperature increased from 24 to 70 oC, and CO2/CH4 selectivity was 19.4 to 14.5. This study gives valuable information for developing advanced MMMs for CO2 and CH4 separation.