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Disposable nappies to fine chemicals

Maunder, Rhodri 2022. Disposable nappies to fine chemicals. PhD Thesis, Cardiff University.
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Abstract

Chapter 1 introduces the general principles of catalysis, along with the scope and objectives of this study. This is followed in Chapter 2 by a literature review of previous catalysis-focussed research in the fields of biomass conversion and the direct synthesis of reactive oxygen species. Chapter 3 details the experimental procedures that were undertaken to fulfil this study’s objectives. Firstly, the catalyst synthesis and testing methods used are described, followed the analytical methods that were used to characterise the catalysts and to identify and quantify their post-reaction products. Chapter 4 describes the efforts to characterize NappiCycle’s ‘recycled nappy fibre’ (RNF) material. It was found from thermogravimetric analysis that cellulose was the most abundant component of the material by weight, at ≈ 40 wt.%. Both the RNF and Avicel PH-101, a reference microcrystalline cellulose, were subjected to cellulose hydrolysis reactions in a pressure reactor to determine the RNF’s response. Both materials were pre-treated by a mechanical and chemical method to establish whether such treatments would decrease RNF’s recalcitrance to hydrolysis. It was found, using a relatively mild cellulose hydrolysis reaction, that glucose was produced by the RNF in a comparable, albeit low yield when compared to Avicel. However, neither of the pre-treatments were effective at increasing glucose yield from RNF; a 0.5% increase was the most pronounced when ball-milling was used. When the time, energy, and additional pre- and post-treatment reagents required are considered, it was determined that neither treatment would be viable for scaled-up processes involving RNF’s conversion into value-added commodities. Chapter 5 investigates an alternative pathway for cellulose conversion to hydrolysis; a one-pot hydrogenolysis/hydrogenation to sorbitol. It was hoped that such a reaction would minimise the formation of undesirable by-products (namely, humins) that typically arise in hydrolysis reactions. RNF was found to produce a very low yield of sorbitol when compared to Avicel (0.2% for RNF versus 32.7% using Avicel), which iv was attributed in part to the presence of residual chlorides arising from NappiCycle’s recycling process; when CaCl2 was added in incremental concentrations to a model glucose hydrogenation reaction, the yield of sorbitol obtained decreased from 50.4% to 1.9%. Focus shifted to the synthesis of Ru/C catalysts for glucose hydrogenation using a microwave-assisted solvothermal method. Screening experiments were conducted that investigated the effect of modifying catalyst synthesis parameters on the yield of sorbitol produced. Here, it was found that the choice of ruthenium precursor and activated carbon support type had the greatest influence upon catalytic activity. A selected series of Ru/C catalysts were characterised to determine if differences in their performance could be attributed to surface and bulk characteristics. All XC72R-based catalysts had a close agreement between their actual and expected metal loading, however much greater discrepancies were observed with the Black Pearls-based catalysts. No differences could be found in ruthenium’s oxidation state across the catalysts that were analysed by XPS; ruthenium was present as RuO2 in all instances. In the case of Ru/TiO2 catalysts, a mixture of metallic ruthenium and RuO2 was found on the surfaces. In a similar manner to the Ru/C catalysts, it is likely that the presence of RuO2 was a consequence of air oxidation between catalyst preparation and analysis. Chapter 6 investigates the direct synthesis of H2O2 from gaseous H2 and O2, by applying the same microwave-assisted solvothermal method as that used in Chapter 5 to produce series of mono- and bi-metallic 1 wt.% x/TiO2 catalysts (x = Au, Pd, Ni, AuPd, NiPd). The 1 wt.% NiPd catalyst with a nominal molar ratio of metals of 1:1 had a H2O2 synthesis activity of 77 molH2O2 kgcat h-1, performing well against the most active AuPd catalyst (also with a 1:1 nominal molar ratio of metals), producing 85 molH2O2 kgcat h-1. It was found that the Au, Pd and AuPd catalysts had a good agreement with their nominal metal loadings, however in the case of the Ni and NiPd catalysts, it was found that there was an inadequate attachment of Ni to the TiO2 support, likely due to an inadequate catalyst preparation temperature.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 20 July 2022
Last Modified: 20 Jul 2022 15:12
URI: https://orca.cardiff.ac.uk/id/eprint/151377

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