Broadline 1H NMR investigations of the mobility of polymers supported on carbonaceous particles and silica substrates

Hodgins, Genevieve R. (2020) Broadline 1H NMR investigations of the mobility of polymers supported on carbonaceous particles and silica substrates. EngD thesis, University of Nottingham.

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This research consists of two parallel investigations using solid state NMR to study the mobility of polymers adsorbed on substrates, the first is a study on the use solid state proton NMR as a testing methodology for deposit control additives, and the second is the investigation into the mobility of the carbon capture material; polyethylene imine supported on silica.

Within the transport sector increased efficiencies are required if vehicles are to meet emissions targets, unfortunately the engine development implemented can be less tolerant to engine deposits, reducing efficiencies and causing engine failure. One solution to the problem of deposit formation is the use of deposit control additives in the fuel mixture. The development of these materials is costly due to the high expense associated with testing them; therefore the development of additional lower cost testing mechanisms is advantageous to manufacturers and consumers alike. Polyisobutylene derivatives are a common deposit control additive for use with automobile fuels.

Solid state broadline proton NMR has been used to study polyisobutylene derivatives at high temperatures replicating operational conditions. This method has shown the capacity to distinguish between polyisobutylene derivatives based on their interactions with carbon black, a deposit model. A series of different polyisobutylene derivatives with different chain lengths and headgroups were investigated at loadings of 2-50 \% on carbon black over 30-250 °C. The lowest loading samples often had significantly reduced mobility at operational temperatures (of 250 °C) indicating stronger interactions between the polymer and substrate, and enabling a distinction to be made between additives which may have deposit control features and those which likely do not. This low loading is likely indicative of the monolayer adsorption of these materials on carbon black and, in combination with other findings in this study, suggests the polyisobutylene chain is interacting with the carbon surface to a greater extent than had previously been assumed. Further investigation into these materials using carbon-13 NMR in the solid state has been hindered by the presence of paramagnetism within the carbon black material, and the use of silica as an alternate substrate investigated.

The release of CO2 into the atmosphere results in climate change which must be mitigated in order to limit devastating environmental effects. One of the most valuable mitigated technologies available is carbon capture and storage. Post combustion capture is the most mature of the carbon capture technologies and can be retrofitted to existing CO2 sources. Most commonly liquid amines are used for this, however to combat high energy costs and issues with corrosion associated with these materials solid adsorbents are also being developed. Polyethylene imine supported on mesoporous silica is a promising material in this field.

The mobility of the silica-supported branched chain polyethylene imine is studied over the operational temperature range of 60-130 °C, in association with the kinetics of CO2 adsorption. All of the samples show similar mobilities with little correlation between polyethylene imine molecular weight and mobility. Over the temperature range studied the mobility plateaus at approximately 80 °C which corresponds well with the maximum adsorption temperature and fastest rate of adsorption. In addition to this, the CO2 capacity of the samples prepared has shown to be in keeping with the existing literature, with the lowest molecular weight polyethylene imine studied, FG (800 mol/g), generally showing the highest CO2 adsorption. However a significant outlier to this trend has been noted with high CO2 capacities of up to 22 wt. % seen by some of the longer chain PEI samples when supported on macroporous silicas, with these materials providing a potential direction for future study.

Item Type: Thesis (University of Nottingham only) (EngD)
Supervisors: Castro-Diaz, Miguel
Snape, Colin
Stevens, Lee
Keywords: Nuclear magnetic resonance; Polyethylenimine; Silica; Carbon, Absorption and adsorption
Subjects: T Technology > TP Chemical technology
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 59910
Depositing User: Hodgins, Genevieve
Date Deposited: 26 Jan 2023 08:16
Last Modified: 26 Jan 2023 08:18

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