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PRODUCTION OF BIOETHANOL FROM ELEPHANT GRASS (Pennisetum purpureum) STEM

ABSTRACT

The production of bio-ethanol from Elephant grass (Pennisetun purpureum) stem was carried out using elephant grass stem as a feedstock and a combination of Aspergillus niger at 0.2%(w/v) 0.4%(w/v), 0.6%(w/v), 0.8%(w/v) and 1%(w/v) concentrations and Saccharomyces cerevisiae (brewer’s yeast) at 0.5% (w/v), 1%(w/v), 1.5%(w/v), 2%(w/v)and 2.5%(w/v) concentrations as cells by simultaneous saccharification and fermentation (SSF). The study determined the most suitable pre-treatment method from the following pretreatment methods; 1M H2SO4, 0.1M H2SO4, 1M NaOH, 0.2M NaOH, Boiling, and 3M NH4OH. IM NaOH pre-treatment gave the highest cellulose and lowest lignin content. The effects of temperature at 25oC, 30oC, 35oC, 40oC and 45oC; pH values of 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 and 6.5; substrate concentration values of 1%(w/v), 2%(w/v), 3%(w/v), 4%(w/v) and 5%(w/v); particle size range of 53-106µm, 106-150µm, 150-250µm, 250-300µm and 300-425µm; and cell loading combination ofAspergillus niger at 0.2%(w/v) 0.4%(w/v), 0.6%(w/v), 0.8%(w/v), 1%(w/v) concentrations and Saccharomyces cerevisiae (brewer’s yeast) at 0.5% (w/v), 1%(w/v), 1.5%(w/v), 2%(w/v), 2.5%(w/v) on the hydrolysis and fermentation process were investigated to obtain optimum conditions of fermentation. The optimum conditions of fermentation were obtained at temperature of 350C, pH value of 5.5, substrate concentration of 30g/l, particle size range of 250-300µm and Aspergillus niger to yeast ratio of 0.6/1.5 after 72 hours of fermentation time. Also substrate concentration of 30g/l, gave highest ethanol concentration of 23.4g/l and a yield of 78%. From the research, the kinetic Parameters which are reaction constant k and order of reaction n were evaluated to be 8.172x10-8l/g.s and 2 respectively.

CHAPTER ONE

INTRODUCTION

1.1 Preamble

Energy availability, supply and use play a central role in the way societies organize themselves, from individual welfare to social and industrial development. By extension, energy accessibility and cost is a determining factor for the economical, political and social interrelations among nations. Considering energy sources, human society has dramatically increased the use of fossil fuels in the past 50 years in a way that the most successful economies are large consumers of oil. However, geopolitical factors related to security of oil supply, high oil prices and serious environmental concerns, prompted by global warming, the use of petrol for transportation which accounts for one-third of greenhouse gas emissions (Wyman, 1996), have led to a push towards decrease in its consumption. Indeed, the world's strongest economies are deeply committed to the development of technologies aiming at the use of renewable sources of energy. Within this agenda, the substitution of liquid fuel gasoline by renewable ethanol is of foremost importance. Biomass – derived ethanol represents one of the more promising commodities for long term sustainability of transportation fuels (Chum and Overend, 2001).