Department of Chemical Engineering

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https://scholar.sun.ac.za/handle/10019.1/321
Department Process Engineering now has a new name, and will be known from March 2023, as Department of Chemical Engineering.

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Browsing Department of Chemical Engineering by Subject "Acetone-Butanol-Ethanol (ABE) fermentation"

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    Process modelling in production of biobutanol from lignocellulosic biomass via ABE fermentation
    (Stellenbosch : Stellenbosch University, 2016-03) Naleli, Karabo; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: The interest in production of biobutanol as a fuel has increased significantly in the last two decades. The main reason is that biobutanol is recognised as superior biofuel than ethanol, which is already being blended with gasoline in USA and Brazil. In addition, biofuels have potential to reduce greenhouse gas (GHG) emissions when they are used as replacement of gasoline in transportation industry. A major drawback in Acetone-Butanol-Ethanol (ABE) fermentation is the low final product concentration, due to limited biomass growth and product inhibition. Low concentrations of butanol in the fermentation broth have severe disadvantage of high energy requirement during downstream processing. Fermentation technology improvement like in situ gas stripping for butanol recovery during the fermentation has potential to provide a more concentrated feed to downstream purification. For downstream product recovery and purification, alternative methods to double effect distillation (DD), which may be more energy efficient, have been investigated, including liquid-liquid extraction and distillation (LLE&D). The main objective of this study was to develop six conceptual process model scenarios for production of biobutanol from lignocellulosic biomass, from the literature data available, using ASPEN Plus® V8.2 software. These include: (1) Batch Simultaneous Saccharification and Fermentation (SSF) integrated with Gas Stripping and double effect distillation used as recovery and purification method(SSF-GS/DD). (2)Batch SSF integrated with Gas Stripping and liquid-liquid extraction and distillation used as recovery and purification method(SSF-GS/LLE&D). (3) Continuous Separate Hydrolysis and Fermentation (SHF) and double effect distillation used as recovery and purification method(CONT-SHF/DD). (4) Continuous SHF and liquid-liquid extraction and distillation used as recovery and purification method(CONT-SHF/LLE&D). (5) Batch SHF and double effect distillation used as recovery and purification method(B-SHF/DD). (6) Batch SHF and liquid-liquid extraction and distillation used as recovery and purification method(B-SHF/LLE&D). The impacts of different fermentation methods, fermentation technology improvements and products recovery/purification methods on the energy demand, energy efficiency and economics of the various process scenarios were investigated. Furthermore, the best performing process scenario was compared to previously process model on biobutanol production from molasses on the basis of same butanol capacity, in terms of energy demand and efficiency and economic feasibility. Among the six scenarios modelled for a plant capacity of 1 million dry tonnes feedstock per year, the economic assessment showed that only Batch SSF-GS/DD and SSF-GS/LLE&D scenarios were viable under current market conditions. These scenarios gave net present values (NPV) of US$140million and US$47million and internal rates of return (IRR) of 16% and 11% respectively. Sensitivity analysis showed that change in the feedstock price from US$30/tonne to US$150/tonne has greatest impact in minimum butanol selling price (MBSP) (US$0.41/kg – US$1.76/kg) with the market price at US$0.78/kg. The total capital investment (TCI) of butanol production from molasses (US$187million) was significantly lower than the TCI of US$585million for scaled best performing SSF-GS/DD process scenario; on the basis of equal annual butanol production of 118800 tonnes. The comparison further showed that molasses based butanol had higher IRR and NPV of 36% and US$958million compared to 14% and US$112million of SSF-GS/DD. With regards to energy demand and efficiency, energy demand was met in all of the scenarios by combustion of solid residues after fermentation-purification together with 10% of the lignocellulose feedstock. Onsite electricity production was in excess to process demands, providing surplus electricity that could be sold for additional revenue. SSF-GS/DD and SSF-GS/LLE&D scenarios gave highest liquid fuel energy efficiencies of 26% and 23% respectively, and overall energy efficiencies of 36% and 30% respectively.Butanol production from lignocellulose required more process energy per unit of butanol produced, compared to butanol production from molasses. This was evidenced by lower energy demand of23MJ/kg for molasses based butanol compared to 58MJ/kg of the best selected scaled up SSF-GS/DD process scenario.