Browsing by Author "Pieters, Ruhardt Jacobus"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- ItemPotable ethanol production from raw corn using simultaneous saccharification and fermentation(Stellenbosch : Stellenbosch University, 2016-03) Pieters, Ruhardt Jacobus; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Corn starch is one of the most widely used substrates for the production of potable ethanol, such as Scotch grain whisky or South African single grain whisky. High energy demands in these processes led to extensive research on the development of more cost-effective production methods with lower energy demands and higher corn-to-ethanol efficiency. Therefore, finding and optimising less energy intensive methods are of utmost importance. In this study 30 South African corn cultivars were used as substrate to perform a comprehensive process comparison in 1 L shake flask cultures between cooked starch hydrolysis (CSH) and raw starch hydrolysis (RSH) ethanol production processes, where STARGENTM 002 was used as a raw starch hydrolysing enzyme (RSHE). Information based on optimisation experiments were used in an Aspen Plus® process simulation to predict the energy requirements and cost per litre ethanol for both the CSH and RSH processes. Furthermore, the RSH process was investigated to establish weather bacterial contamination had a significant impact on process performance. Similar final ethanol concentrations and ethanol yields as fraction (%) of theoretical maximum were observed in both methods, with final ethanol concentrations of 9.82% and 9.63% (v/v) for the CSH and RSH processes, respectively. Ethanol productivity for the RSH process was beyond any doubt higher than that of the CSH process, with the highest RSH process productivity of 1.3 g/L.h, which was 20% higher than the highest productivity of the CSH process. The absence of starch gelatinization during the pre-treatment section of the RSH process led to the opportunity for very higher gravity fermentations. Small-scale optimisation of the RSH process showed a maximum solids loading of 40% during pre-treatment, due to the inability to obtain homogenously mixed slurries. Surface response models with final ethanol concentration, ethanol productivity and ethanol yield as fraction (%) of theoretical maximum as dependent variables, were successfully used to find an optimum solids loading (37.5%) and an enzyme dosage (1.4 g/kg corn) for the RSH process. Scale-up of the preferred RSH process to pilot-scale achieved a final ethanol concentration of 13.12% (v/v) at a productivity of 1.23 g/L.h, with a solids loading not higher than 37.5% and at an enzyme dosage of 1.4 g/kg, indicating that the process may be applicable under industrial conditions. Aspen Plus® simulations, based on the industrial ethanol production process at the James Sedgwick distillery, together with optimum process parameters for the RSH process, were used to predict and compare the energy requirements for the CSH and RSH processes. The Aspen Plus® simulation predicted an energy requirement of 1.97 kg steam per litre ethanol produced for the RSH process, while the value of 2.8 kg steam per litre ethanol was predicted for the CSH process. The RSH process was more energy efficient, due to the lower pre-treatment temperatures, when compared to the CSH process. A cost model developed for each process, based on the performance fixtures of the Aspen Plus® simulations, showed that the RSH process had higher enzyme costs, when compared to the CSH process, which was due to high STARGENTM 002 dosage requirements and high STARGENTM 002 price. However, the lower energy requirements and lower water consumption by the RSH process outweighed the drawbacks of STARGENTM 002 dosage and price. The cost models predicted a total cost of R 7.70 per litre ethanol produced for the RSH process, while the CSH process had a predicted value of R 8.97 per litre ethanol. All the experimental and simulation work show that the STARGENTM 002 is ready to be tested and as a raw RSHE at an industrial ethanol production process, such as the James Sedgwick distillery. It is recommended that the industrial-scale testing should be at solids loading not higher than 37.5% and at an STARGENTM 002 dosage of 1.4 g/kg.