Author Identifier

Tawanda Matamba: http://orcid.org/0000-0002-8703-2755

Date of Award

2025

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Engineering

First Supervisor

Stefan Iglauer

Second Supervisor

Alireza Keshavarz

Abstract

The world energy vision is centred on transitioning from fossil fuels to green and renewable energy resources such as biomass, wind, solar, nuclear, and hydrogen. Among these potential energy sources, hydrogen has received great attention from researchers due to its physiochemical properties that enable it to be utilized in many industries. Biomass is also considered a green energy source and is readily available to be converted into clean energy via different conversion routes. Pyrolysis is considered a clean method to convert biomass into renewable energy - in particular H2. Thus, this study systematically investigated the clean production of H2 rich biogas from both renewable and non-renewable resources via pyrolysis. The effect of pyrolysis parameters like temperature, pressure and H2O ratio on known H2 production secondary reactions were analysed and optimum conditions for production were determined. However, H2 is a low-density gas and cannot be easily compressed, making the process of storing it difficult and expensive. Thus, a H2 economy cannot be fully established if drawbacks in H2 storage are not remedied. Therefore, this study also investigated the feasibility of non-conventional resources materials such as waste biomass, biochar, waste plastics and organic metal frameworks to adsorb and store H2. The effect of materials surface textural properties, adsorption pressure and temperature were studied. In overall, the major part of this work is converting waste materials into energy (H2) and porous storage materials for H2. An in house built fixed bed pyrolysis system was used for all the pyrolysis reactions. Materials surface characterization was performed using Fourier-Transformed infrared spectroscope (FTIR), X-ray powder diffraction (XRD), Brunauer-Emmet-Teller (BET), Scanning Electron Microscopy (SEM), and Transmission electron microscopy (TEM). The thermal degradation behaviour of the samples was done by a Thermogravimetric Analyser (TGA) analysis. Adsorption experiments were conducted using an automated Sievert’s PCT Pro instrument. It is not certain if renewable energy sources can cover the energy demand and supply, hence we still need energy from fossil fuels and we also need to identify other potential energy sources that are abundantly found everywhere and use clean technologies to convert them into energy. Thus, kerogen which is the most abundant type of organic matter with a high hydrogen content was thermally converted to H2 via pyrolysis. Interestingly, H2 and CH4 were the main gas produced, with H2 having the highest concentration in all the temperatures studied. CO and CO2 emission was only in trace amounts, and the process can be considered very environmentally friendly. H2 production reached 81.28 Vol.%, 79.49 Vol.%, and 68.82 Vol.% at 350 ⁰C, 600 ⁰C, and 800 ⁰C.

Biomass from waste wheat straw was successively converted into H2 concentrated gas with very low greenhouse gas emission. Elevated temperatures and high biomass-water mass ratios were necessary to converted the biomass waste into H2 rich biogas, while simultaneously minimizing greenhouse gas production. Maximum H2 yield reached 92.53 Vol.% (equivalent to 224.14 gH2/kg.WS) at 1000 ⁰C and 1:4 WS:H2O ratio. The impact of pressure and temperature (500-900 ⁰C, and 1.01-30 bar range) on the selectivity of H2 rich biogas production was also investigated and both temperature and pressure, influenced H2 formation. Increasing temperature and pressure increased H2 production (which peaked to 86.07 Vol.% at 800 ⁰C and 30 bar).

The feasibility of pyrolysis derived biochar to store H2 at atmospheric and cryogenic temperatures, i.e. 30 ⁰C and -196.0 ⁰C and under vacuum to 70 bar pressure) was investigated. The maximum H2 adsorption capacity at ambient temperature was 2.50 mol/kg at 66.33 bar (for 900 ℃ biochar) which significantly increased to 15.29 mol/kg at cryogenic temperature at 46.21 bar. Microplastic waste (MicroPE)– a significant environmental pollutant – was tested for H2 storage. H2 adsorption capacity of MicroPE increased with increasing the adsorption pressure (from 0.06 mol/kg at 17.21 bar to 0.20 mol/kg at 68.11 bar for raw MicroPE). MicroPE 4 activated with aqueous NaOH significantly changed H2 adsorption under the same operating conditions. H2 adsorption increased to 0.50 mol/kg at 68.11 bar when MicroPE was treated with 0.002 mol/L aqueous NaOH.

The physicochemical properties of Metal Organic Frameworks (MOFs) make them suitable for H2 storage. Therefore, the relationship between adsorption temperature and pressure with the MOFs surface textural properties towards H2 storage was studied. Two Iron-based MOFs (12- MIL-88B(Fe), 24-MIL-88B(Fe) with different surface textural properties were synthesized and tested for H2 adsorption at 30 ˚C, 0 ˚C, -78.5 ˚C, and -196 ºC and from vacuum pressure to 55 bar. Results showed that at 30 ˚C and 0 ˚C adsorption temperature, pore volume, surface area, and adsorption pressure greatly influenced H2 adsorption performance, while under low temperature (-78.5 ˚C) and cryogenic temperature (-196 ˚C) the Fe-MOF with the wider pore size adsorbed more H2 molecules. While pressure continued to positively promote the amount of H2 adsorption at all temperatures studied.

DOI

10.25958/wgj7-a020

Access Note

Access to this thesis is embargoed until 1st July 2030

Access to chapters 3 and 5 of this thesis is not available

Download

Available for download on Monday, July 01, 2030

Share

 
COinS