Integrated optimization of pretreatment conditions for bioethanol production from steam treated triticale straw

Agudelo Aguirre, Roberto Arturo (2016-03)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANSE OPSOMMING: Kultivar- of omgewingsverwante veranderlikheid in die produksie van triticale (koringrog) strooi, en die impak daarvan op voorbehandeling hidrolise vir die omsetting na bioetanol, is ondersoek in hierdie studie. Twintig triticale kultivars, verbou in drie geografiese areas in die Wes-Kaap provinsie van Suid-Afrika, is geevalueer om dié kultivars te selekteer wat die hoogste gekombineerde etanol opbrengs lewer per hektaar graan en strooi. ‘n Vier-fase sistematiese benadering is toegepas om die geskikte kultivars te evalueer en identifiseer: I. Triticale kultivars is geevalueer om monsters te identifiseer met beter agronomiese kenmerke asook om die gekombineerde eksperimentele etanol opbrengste per hektaar strooi en graan te peil. II. Kultivars geïdentifiseer in fase I is verder geevalueer op laboratorium-skaal om suiker opbrengs te maksimaliseer vanuit verdunde suur voorbehandeling gevolg deur ensiematiese hidrolise. Sodoende kon die maksimum potensiaal vir die produksie van fermenteerbare suiker vanuit strooi gepeil word. III. Strooi monsters met hoër proseseerbaarheid op laboratorium-skaal en met groter beskikbaarheid vir verdere studie is geselekteer. Geselekteerde monsters is onderwerp aan eksperimente vir die maksimalisering van gekombineerde suiker opbrengs (CSY) vanuit loodsaanleg-skaal stoomploffing (SE) met die gebruik van twee tipes deurwekingstegnieke, en IV. Fermenteerbaarheid van die behandelde materiaal, verkry uit die geoptimiseerde voorbehandeling, is geevalueer deur gebruik te maak van Gesamentlike Versuikering en Fermentasie (SSF). Gedurende die eerste stel evaluerings, het strooi monsters van kultivars wat gegroei is in Mariendahl noemenswaardig verskil van strooi monsters verkry uit die Swartland en Overberg areas. Dié Mariendahl monsters het naamlik die laagste asinhoud getoon asook hoër opbrengs van xilose uit voorbehandeling (~62% van die teoretiese maksimum) asook hoër glukose uit ensiematiese hidrolise (>10%) in vergelyking met strooi monsters uit die ander areas. Kultivars 9, 13 en 14 (Mariendahl area) het hoër CSY waardes (43-45 g/100 g droeë material) getoon en is dus geselekteer vir loodsaanleg voorbehandeling optimisering. SE kondisies met temperature tussen 190 en 205°C, tesame met tye wat gelei het tot felheidsgrade van tussen 3.35 en 3.79 het die CSY uit voorkeurkultivars gemaksimaliseer vir ongekataliseerde SE. SE kondisies met temperature tussen 173 en 187°C, tesame met tye wat gelei het tot felheidsgrade (Log (Ro’)) van tussen 3.30 en 3.41 het die CSY uit voorkeurkultivars gemaksimaliseer vir SO2-SE. Voorbehandeling optimiserings het gelei tot ‘n verbetering in CSY van tot 11%. Gekataliseerde SE is geïdentifiseer as die voorkeur metode vir voorbehandeling omdat meer CSY daardeur verkry is vir al die voermateriale (8-16%) en omdat daar minder verskille in voorbehandeling vereistes was tussen strooi monsters vir hierdie voorbehandeling. Geskatte etanol (2G) opbrengs vanuit lignosellulose, gebasseer op analities bepaalde suikers verkry uit geoptimiseerde voorbehandeling ensiematiese hidrolise, was 434 L.ha-1. Dit verteenwoordig ‘n totale verbetering van ~28% in geskatte lignosellulose etanol opbrengs per hektaar. Maksimum geskatte etanol opbrengs was 171 L.ton-1 na SSF by 13% soliede materiaal lading vir gepersde-WIS (water onoplosbare soliede materiaal) van ongekataliseerde SE. Etanol opbrengs per hektaar vir intensief gewaste WIS vanuit SO2-SE van strooi 14 is geskat om bo 200 L.ha-1 te wees. Dus is finale etanol konsentrasies naby die bedryfstandaard van 4% (v/v) bereik. Hierdie studie het aangetoon dat kultivar seleksie gebasseer op toevoermateriaal kwaliteit en proseseerbaarheid asook verdere voorbehandeling optimisering ‘n positiewe invloed het op die 2G etanol opbrengs per hektaar. Sulke verbeteringe in etanol opbrengs uit strooi is van belang vir die volhoubaarheid van triticale strooi as potensiële bioetanol grondstofmateriaal in Suid-Afrika. Verder het hierdie studie ook aangetoon dat hoër 2G etanol opbrengs per hektaar verkry kan word sonder verlies in graan opbrengs of etanol opbrengs per hektaar graan. Sodoende is ‘n goeie fondasie geskep vir die toekomstige seleksie van triticale deur plaaslike boere om hul boerdery ekonomie optimaal te bestuur.

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