The iron and steel industry is responsible for 30% of all industrial CO2 emissions, largely emitted via hot Basic Oxygen Furnace (BOF) gas (CO, H2, CO2). Gas fermentation can convert the BOF gas into valuable chemicals such as the disinfectant and platform chemical isopropyl alcohol (IPA), which is currently only produced with petrochemical cracking. The goal of this research was to model the state-of-the-art industrial-scale BOF gas fermentation to IPA and identify the key process parameters affecting technical performance. The designed and modelled industrial-scale process was based on the published LanzaTech technology with Clostridium autoethanogenum. In the process model, the IPA is purified through extractive distillation with pure glycerol as an entrainer. During sensitivity analysis, eleven process parameters were investigated for their effect on the eighteen chosen technical Key Performance Indicators (KPIs). These process parameters are (product selectivity (YIPA/CO), CO volumetric mass transfer rate (VMTCO), CO conversion, reactor dilution rate (D), temperature off-gas condenser, biomass separation liquid loss, extractive distillation glycerol mole fraction, extractive distillation molar reflux ratio, glycerol recycle purge, broth recycle purge and anaerobic digestion waste conversion). The sensitivity analysis identified that the key technical parameters affecting the KPIs are the gas fermentation parameters (CO conversion, VMTCO, YIPA/CO, and D) as well as the biomass filtration liquid loss. Moreover, increasing CO conversion, VMTCO, YIPA/CO as well as decreasing D and the biomass filtration liquid loss all individually had the greatest positive impact on the KPIs. Thus, this study has successfully synthesised and modelled a state-of-the-art industrial-scale BOF gas fermentation to IPA process and identified the key process parameters to improve its technical process performance. These findings can be used both to optimise the BOF gas fermentation to IPA process, and perform further economic evaluations and environmental impact assessment.

Syngas fermentation is an up-and-coming technology that uses acetogenic microorganisms to produce ethanol at the commercial scale. Acetogens can produce many different types of products via their metabolic pathway called the Wood Ljugdahl Pathway (WLP). The WLP can natively produce many different fatty acids and alcohols, and with metabolic engineering, other molecules could be produced through syngas fermentation that are not native to the WLP. In this work isopropanol, 3-hydroxybutyric acid, hexanol, octanol, hexanoic acid, butyric acid and lactic acid were assessed for their feasibility to be produced through syngas fermentation. Two syngas cases were analysed; bio-syngas (H₂:CO of 1:1.907) and basic oxygen furnace gas (H₂:CO of 1:21.667). The feedstock capacity was fixed at 350 ktons/yr based on its availability. Using thermodynamic values, process reactions from the substrate to the product were found. To verify the metabolic feasibility, ATP yields were calculated based on the respective WLPs from the literature. Sensitivity studies of H₂:CO ratios on the carbon yield are carried out to check its effect on the production yields of the product, biomass, and CO₂. Sensitivity analysis showed that a higher H₂:CO ratio in the feedstock will lead to higher production.

Syngas fermentation is a biochemical pathway to produce ethanol and has been commercialized successfully. The economic viability of this process could be further improved to become more competitive in the existing ethanol market. Improving gas utilization is the key, and can be done by recycling the unreacted syngas. This work is an early-stage techno-economic assessment of recycling in producing ethanol from Basic Oxygen Furnace (BOF) gas. Economic viability is measured in terms of Relative Competitive Percentage (RCP) and is a measure of closeness to the current market. Two scenarios, firstly a once-through process, and secondly a process with recycling (0.9 split ratio: recycle/purge) of gas is considered. None of them showed a positive RCP as compared to the current ethanol market. Comparing these scenarios, beyond the single pass conversion of 60%, the additional production costs due to recycling become dominating and lead to a lower RCP compared to once-through systems.