Browsing by Author "Louw, Johannes Petrus"
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- ItemTechno-economic and life-cycle analysis of polyethylene, polyethylene furanoate and polyethylene terephthalate production in integrated sugarcane biorefineries(Stellenbosch : Stellenbosch University, 2024-03) Louw, Johannes Petrus; Görgens, Johann Ferdinand; Farzad, Somayeh; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.ENGLISH ABSTRACT: The South African sugar industry is under threat due to ageing infrastructure and a decreasing local sugar demand, caused by growing consumer awareness and taxes, such as the Health Promotion Levy, forcing local producers to export sugar at prices lower than production cost. A potential solution is to diversify the sugarcane value chain by converting sugarcane-based feedstock into valuable fuels and chemicals. Bioplastics have gained considerable interest in recent years, due to concerns such as diminishing fossil reserves and climate change. Polyethylene (PE), polyethylene terephthalate (PET) and polyethylene furanoate (PEF) are three favoured plastics that can be produced from biomass. The primary aim of this project was to assess the sustainability of producing these bioplastics, along with their respective monomers and precursors, in integrated sugarcane biorefineries. Biorefineries were designed to be bioenergy self-sufficient, meaning the energy demands of both the sugar mill and biorefinery were met using the available biomass on-site. Process simulations were developed in Aspen Plus® for PE, PET, PEF, ethylene, monoethylene glycol (MEG), terephthalic acid (TPA), isobutanol (iButOH), 5-hydroxymethyl furfural (HMF), p-xylene and 2,5-furandicarboxylic acid (FDCA). The mass and energy results obtained from the simulations were utilized in a discounted cash flow analysis (DCFA) to assess the economic feasibility of biorefineries. The environmental impacts of bioproducts were assessed in a SimaPro based life-cycle assessment. A multi-criteria analysis, which considered both economic and environmental performance, was used to determine the sustainability of bioproducts. A-molasses (1G) emerged as the optimal biorefinery feedstock due to its high concentration of simple sugars, in contrast to 2G lignocellulosic biomass, which required costly and energy-intensive processing, even when used in combination with molasses in a 1G2G biorefinery feed. Among the bioplastics, 1G PEF required the lowest “green” price premium (GPP) (44.4%), followed by 1G PE (56.1%) and 1G PET (128.1%). PEF was more profitable than PET due to the relative ease and lower cost of producing its primary monomer, FDCA, compared to TPA. PE was less profitable than PEF due to its low production rate, a consequence of significant mass elimination during ethanol dehydration. The top five most economically viable biorefinery scenarios were 1G iButOH (-19.0% GPP), 1G2G iButOH (11.9% GPP), 1G FDCA (11.9% GPP), 1G PEF (44.4% GPP) and 1G PE (56.1% GPP). FDCA and iButOH production involved fewer steps, lower energy demands, and lower equipment and operating costs when compared to more complex monomer and polymer processes. PE and iButOH had the lowest environmental footprints, with weighted impact factors (IF) of 0.37 and 0.40, respectively. In contrast PET (IF: 1.35), PEF (IF: 1.15), and FDCA (IF: 1.20) demonstrated lower sustainability due to their increased reliance on metal catalysts, organic solvents, and other material inputs compared to PE and iButOH. Bioproducts showcased 33.2% - 81.2% lower CO2 equivalent emissions and consumed 41.9% - 90.1% less fossil-fuels compared to their fossil-based counterparts, in exchange for higher impacts (except for iButOH) in other categories, including eutrophication, https://scholar.sun.ac.za iii acidification, and ecotoxicity. These elevated impacts were primarily attributed to adverse side-effects of sugarcane cultivation. Among all the scenarios, iButOH was the most sustainable investment, displaying both exceptional economic and environmental performance. The potential for emerging technologies to produce MEG and TPA directly from sugars holds promise for achieving greater sustainability of bioplastics in the future.