Browsing by Author "Agudelo Aguirre, Roberto Arturo"
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- ItemIntegrated optimization of pretreatment conditions for bioethanol production from steam treated triticale straw(Stellenbosch : Stellenbosch University, 2016-03) Agudelo Aguirre, Roberto Arturo; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Cultivar/environmental variabilities in the production of triticale straw, and its impact on pretreatment-hydrolysis processes for conversion to bioethanol, were addressed in this study. Twenty triticale cultivars, grown in three geographical areas in the Western Cape of South Africa, were screened to select those cultivars with the largest combined ethanol output per hectare from grain and straw. A four-stage systematic approach was applied to screen and identify preferred cultivars: I. Triticale cultivars were screened to identify samples with better agronomic traits and estimate experimental combined ethanol yields per hectare from straw and grain II. Preferred cultivars were subsequently screened at bench-scale to maximise sugars from dilute-acid pretreatment followed by enzymatic hydrolysis and to estimate maximum potential for production of fermentable sugars from straw samples. III. Straw samples with higher processability at bench-scale and availability for further study were selected. Selected samples were subjected to maximisation of combined sugars yield (CSY) at pilot-scale steam explosion (SE) by two types of impregnation, and IV. Fermentability of treated materials from optimised pretreatment (optimum conditions) was evaluated using Simultaneous Saccharification and Fermentation (SSF). After the first selection, straws from cultivars grown in Mariendahl resulted in significant lowest ash and higher yields of xylose from pretreatment (~62% of theoretical maximum) and glucose from enzymatic hydrolysis (>10%), compared to straws from Swartland and Overberg. Cultivars 9, 13 and 14 (Mariendahl-site) displayed higher CSY values (43-45 g/100 g dry material) and were thus selected for pilot-plant pretreatment optimization. The set of SE conditions with temperatures between 190 and 205°C, together with times that resulted in severities between 3.35 and 3.79 and temperatures between 173 and 187°C combined with times that will give severities (Log (Ro’)) between 3.30 and 3.41 were found to maximise CSY from the preferred straws by uncatalysed and SO2-SE, respectively. Pretreatment optimisations led to improvement in CSY by up to 11%. Catalysed SE was the preferred method of pretreatment since more CSY was obtained from all the feedstocks (8-16%) and there were less differences in pretreatment requirements among straws. Estimated lignocellulosic ethanol (2G) yield based on measured sugars from optimized pretreatment-enzymatic hydrolysis was 434 L.ha-1, representing an overall improvement of ~28% in lignocellulosic ethanol yield estimate per hectare. Maximum ethanol yields of 171 L.ton-1 were estimated after SSF at 13% solid loading for pressed-WIS from uncatalyzed-SE, whilst ethanol yield per hectare using WIS intensively washed from SO2-SE of straw 14 was estimated above 200 L.ha-1. Thus, the final ethanol concentration was close to the benchmark of 4% (v/v). This study showed that cultivar selection based of feedstock quality, processability and further pretreatment optimisation impacted positively on the 2G ethanol yield per hectare. Such improvements in ethanol yield from straw are of relevance for the sustainability of triticale straw as potential bioethanol feedstock in South Africa. Besides, this study showed that higher 2G ethanol yield per hectare could be achieved without compromising the grain yield or ethanol yield from grain per hectare and thus providing a foundation for future selection of triticale by local farmers to better manage their farming economy. At the time of submitting the present thesis dissertation the findings in chapter 6 (Screening of steam explosion pretreatment conditions for realizing areas of maximal sugars release and improved digestibility from triticale straw) were published in New Biotechnology 33 (2016) 153 – 163.