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Title: Development of nitrogen doped resorcinol-formaldehyde gels for carbon capture
Author: Principe, Ivan Alejandro
ISNI:       0000 0004 6500 9444
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2017
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Resorcinol-Formaldehyde (RF) xerogels are organic materials that have been widely studied due to their industrially relevant characteristics, such as high surface areas, suitable pore size and pore volume on which target species can be adsorbed; additionally, RF gels have significant potential to be tailored to specific applications, including catalysis, thermal insulation, filtration, energy storage, and gas treatment, especially CO2 capture. This research focuses on controlling the chemical and physical properties, on both the macroscopic and microscopic scale, with an investigation into the effect these changes have on the application of these xerogels as carbon capture materials. Xerogel properties have been tailored, within this study, by altering the synthesis procedure with focus on monomer concentrations and catalyst to monomer ratio. Nitrogen has been incorporated into the gel structure in order to enhance the favourable Lewis acid-base interactions with CO2. Melamine (M) is used in order to incorporate Nitrogen (N) into the gel structure; and partially replace the Resorcinol (R) traditionally used, resulting in a Melamine-Resorcinol-Formaldehyde (MRF) gel. Repeatability is crucial to method development and validation was achieved by the preparation of a number of gels using a variety of synthetic conditions and process routes. There are a number of parameters that can be altered when synthesising a gel, namely, R/C (catalyst) and R/F molar ratios, concentration of M, solids content, solution pH, catalyst, solvent, temperature, time, and agitation. This research aims to tailor the gel structure (pore size and volume, surface area, etc.) to enhance the CO2 adsorption capacity and kinetic performance. It will also be important to obtain a better understanding of the N-CO2 interaction. Amongst all the parameters mentioned above, there are two main aspects influencing the sol-gel chemistry of xerogels synthesised by base catalysed routes, which are the concentration of monomers and catalyst, and the initial pH of the sol. Hence, R/C and R/F molar ratios, and M concentration, were chosen for in depth analysis. These factors were varied and their effect on gel properties characterised, allowing a better understanding of how gel characteristics can be tailored and their impact on gel performance. The remaining parameters were held constant throughout the experiments. RF gels produced were subsequently characterised using volumetric and gravimetric analysis to determine porous structure and quantify CO2 capture capacities and kinetics. The results obtained indicate that the family of materials synthesised in this study offer potential routes for carbon capture materials, through a combination of micropore structure development and incorporation of favourable Lewis acid-base interactions between MRF sorbents surface and CO2 molecules. This work has demonstrated that CO2 adsorption capacities of MRF xerogels have been enhanced as a consequence of incorporating nitrogen functionalities into their structure. This is important because the amount of sorbent required for a given uptake is reduced, which is a key factor for industrial applications given that volumes of equipment and vessels needed for MRF xerogels reduce in comparison to RF materials. The incorporation of melamine have been found to impact the structure of MRF xerogels similarly as R/C. Increasing the melamine content tend to reduce surface area while pore size and pore volume increase. However, the nitrogen functionalities on the surface of MRF xerogels promote successful interactions with CO2 molecules, resulting in higher capacities. Additionally, it was observed that higher R/F (0.75 and 1.0) results in weaker crosslinking and, consequently, the probabilities of gelation failing are high and, also, pore size becomes a random parameter. On the contrary, low R/F (0.25 and 0.5) offers a better control for pore size. Additionally, a fast kinetics of adsorption and desorption have been observed for MRF materials. Cycling studies have been performed using MRF xerogels, which have demonstrated high stability to cycling and an enhanced working capacity compared to RF sorbents. On another matter, flue gases are a complex mixture of different species, therefore, CO2 selectivity have been tested for MRF sorbents using different binary systems, and results show a significant increase, compared to RF xerogels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral