CHAPTER ONE
INTRODUCTION AND LITERATURE REVIEW
1.1 Introduction
Biofuels (Bioethanol, Biodiesel, and Biogas) are fuels produced from biomass (a biodegradable material) for heating, electricity generation and transport purposes etc (Garba, 1999). Bioethanol can be produced from any biological feedstock’s that contains appreciable amount of sugar/carbohydrate or materials that can be converted into sugar such as starch or cellulose. Ethanol from renewable resources has been of interest in recent decades as an alternative fuel to the current fossil fuels. Lignocelluloses biomass like wood and agricultural crops residue, e.g., straw and sugar beet pulp are potential raw materials for producing several high-value products like fuel ethanol and biodiesel (Yoswathana et al., 2010). Because of the recent increase in the gas price and interest in environmental issues, the demand of ethanol as substitute of gasoline is rapidly increasing. Basically, there are five (5) steps in ethanol production, and these include; grinding, cooking, fermentation, distillation, and hydration. In each step, there are several ideas to improve its productivity and benefits (Onuki, 2010).
For a large production of bioethanol; it is convenient to use cheaper and abundant substrates always. So by using waste products from forestry, agriculture and industries, the cost of feedstocks may be reduced; if we consider producing ethanol from feedstocks such as maize, sugarcane, sweet potatoes, rice pulps etc; which constitutes a larger percentage of the production cost (Energy Commision of Nigeria, 2010).
For the reduction of food competition it is necessary to use lignocelluloses (a complex polymer made up of three components of carbohydrates; which are cellulose ((C6H10O5)n) hemicelluloses (Cx(H2nOn)y) and lignin (Paracoumaryl alcohol (C9H10O2,), Coniferyl alcohol (C10H12O3,) and Sinapyl alcohol (C11H14O4))) which is considered as an alternative and attractive feedstock for the production of ethanol due to its availability in large quantities and low in cost (Cardona and Sanchez, 2007 cited in Cardona et al., 2010).
n
Figure 1 Cellulose Unit Structure (Onuki, 2010).
Figure 2: 1Hemicellulose Unit Structure (Shakhashiri, 2009).
OH
OH
Figure 3: Lignin Structure (The three common monolignols: (1)Paracoumaryl Alcohol,
(2) Coniferyl Alcohol and (3)Sinapyl Alcohol) (Onuki et al., 2008).
Numerous studies for developing large scale production of ethanol from lignocelluloses have been carried out in the world. However the main limiting factor is the higher degree of complexity inherent to the processing of these feedstocks, which is related to the nature and composition of the substrate biomass. Also, the content cellulose and hemicelluloses by all means has to be broken down into fermentable sugars in order to be converted to ethanol (Ali and Khan, 2014).
But these degradation process of hydrolysis and fermentation are complicated, energy consuming and non completely developed (Sanchez and Cardona 2008 cited in Cardona et.al., 2010). With the advent of modern genetics and other technology; the cost of producing sugar from these wastes and converting them into products like ethanol can be significantly reduced in the future in which high cost of production from these feedstocks has been part of the major reason why ethanol has not made its breakthrough yet (Cardona et al., 2010).
Many Lignocellulosic materials has been treated for bioethanol production and reviewed as such; Nigeria produces large quantity of wastes in the form of agricultural wastes during harvestings and food processing. Most of these wastes end up in the environment thereby constituting environmental pollution and problems. However, the wastes mostly are rich in carbohydrate content which can be processed into sugars and subsequently fermented to ethanol
(Ado et al., 2009).
1.2 Research Problems
Certain procedures exist in the quantitative production of ethanol which were adopted and modified in such a way as to maximize yield and overcomes the challenges involved in the ethanol production. So this work uses the existing procedures and tries in finding out some of its challenges, which includes;
1. Among the Lignocellulosic plant materials used as substrates; which of the plants parts (rice husk, saw dust and g.nut shells) will be best in optimizing the yield of ethanol produced.
2. Find out among the most widely used acids (HCl and H2SO4) for pretreatment; which of them is the best within the chosen substrates in the case of ethanol production.
3. Also try to find out in what concentration does the two most widely used acids give an optimum yield in bioethanol production.
4. Also to find out whether factors like pH and temperature regulations affect and reduce the effect of the facultative inhibitors like acetone, acetic acids etc in the production of ethanol.
1.3 Scope and Limitation
This study is intended to cover the successful determination of an optimum percentage yield of ethanol produced from the saw dust, rice husk and groundnut shells using acidic medium.
And this is limited to, the identification and determination of the preliminary factors of investigations such as Moisture content, Ash content, carbon content and organic matter content. Also the concentration of the sugar content determination and the concentration of the Ethanol content after production.
1.4 Aim and Objectives
The main aim is to determine a simple way of attaining an optimum yield in the production of ethanol through the conversion of Saw dust, Rice Husk and Ground-nut shells into ethanol in a simultaneous saccharification and fermentation process using Saccharomyces cerevisiae.
To achieve this production process of optimum yield the following objectives are defined
• The Proximate compositions which includes:
o The moisture content and ash content of the sample substrates.
o The organic matter and carbon content of the samples substrates under study
• Determination of the sugar content of the hydrolysates after pretreatment.
• The ethanol concentration of the fermented hydrolysates.
1.5 Literature Review
1.5.1 Ethanol
Ethanol (ethyl alcohol, grain alcohol) is a clear, colorless liquid with a characteristic, agreeable odor. In dilute aqueous solution, it has a somewhat sweet flavor, but in more concentrated solutions it has a burning taste. Ethanol, (CH3CH2OH) is an alcohol, a group of chemical compounds whose molecules contain a hydroxyl group, –OH, bonded to a carbon atom (Onuki et al., 2008). Ethanol has been made since ancient times by the fermentation of sugars. All beverage ethanol and more than half of industrial ethanol is still made by this process. Simple sugars are the raw material. Zymase, an enzyme from yeast, changes the simple sugars into ethanol and carbon dioxide. The fermentation reaction, represented by the simple equation is actually very complex, and impure cultures of yeast produce varying amounts of other substances, including glycerine and various organic acids (Shakashiri, 2009).
C6H12O6 Yeast 2CH3CH2OH + 2CO2 ———————————–1.1
Starches from potatoes, corn, wheat, and other plants can also be used in the production of ethanol by fermentation. However, the starches must first be broken down into simple sugars. An enzyme released by germinating barley, diastase, converts starches into sugars. Thus, the germination of barley, called malting, is the first step in brewing beer from starchy plants, such as corn and wheat (Koseric et al., 1983).
Much ethanol not intended for drinking is now made synthetically either from acetaldehyde made from acetylene or from ethylene made from petroleum (Onuki et al., 2008). Ethanol can be oxidized to form first acetaldehyde and then acetic acid. It can be dehydrated to form ether. Butadiene, used in making synthetic rubber, may be made from ethanol, as can chloroform and many other organic chemicals. Ethanol is used as an automotive fuel by itself and can be mixed with gasoline to form gasohol. Ethanol is miscible (mixable) in all proportions with water and with most organic solvents. It is useful as a solvent for many substances and in making perfumes, paints, lacquer, and explosives. Alcoholic solutions of nonvolatile substances are called tinctures; if the solute is volatile, the solution is called a spirit (Onuki et al., 2008).
Ethanol may also be produced industrially from ethene (ethylene), by hydrolysis of the double bond in the presence of catalysts and high temperature (Allen et al., 1974).
C2H4 + H2O Catalyst C2H5OH ———————————-1.2 (Ethane) (Water) ∆ (Ethanol)
The by far largest fraction of the global ethanol production, however, is produced by fermentation. During ethanol fermentation, glucose and other sugars in the corn (or sugarcane or other crops) are converted into ethanol and carbon dioxide (Allen et al., 1974).
C6H12O6 Enzymes 2C2H5OH+ 2CO2 + heat ——————1.3
Like any fermentation reaction, the fermentation is not 100% selective and other side products such acetic acid, glycols and many other products are formed to a considerable extent and need to be removed during the purification of the ethanol. The fermentation takes place in aqueous solution and the resulting solution after fermentation has an ethanol content of around 15%. The ethanol is subsequently isolated and purified by a combination of adsorption and distillation techniques. The purification is very energy intensive. During combustion ethanol reacts with oxygen to produce carbon dioxide, water, and heat (Onuki et al., 2008).
C2H5OH + 3O2 Energy ∆ 2CO2 + 3H2O + heat —————–1.4
Starch and cellulose are molecules that are strings of glucose molecules. It is also possible to generate ethanol out of cellulosic materials. However, a pretreatment is necessary that splits the cellulose into glycose molecules and other sugars which subsequently can be fermented. The resulting product is called cellulosic ethanol, indicating its source (Onuki et al., 2008).
1.5.2 Bioethanol
Over the centuries; various forms of energy has been used by man in order to meet his basic life essentials such as food, water and shelter. Starting with energy and sunlight, he progressed to fuel-wood, draft animal power, water and wind power, then developed engine power fuelled by wood, coal, petroleum and nuclear energy (Energy Commission of Nigeria, 2010). As time passes; man developed industrially and in status, more by producing and maintaining cars, generating plants and other form of mechanical devices which operates on one form of fuel or the other; as a result of this, there has been an increase in the uses and demands for fuel in terms of transportation and power generation (Garba, 1999).
It is this urgeness of mans alternative energy option to live that has stimulated researchers to bend into various ways of finding more economically and environmentally acceptable alternative source of energy such as biogas, bioethanol, biodiesel etc (Subashini et al., 2011). There were numerous research efforts directed towards the development of alternative energy sources, such as ethanol production from agricultural products (Nagashima et al., 1984 in Subashini et al., 2011).
Generally, biofuels are defined as solid, liquid or gas fuels produced from biomass for general purposes applications (Koseric et al., 1983). They are produced from agricultural and forest products which are the biodegradable organic portions of industrial and municipal wastes. Generally, biofuels are renewable energy resources derived from recent biological materials, which distinguishes them from fossil fuels that are derived from long dead biological materials. There are various forms of biofuels which includes the bioethanols, biodiesel, biogas and other forms of fuels made from biomass (Energy Commission of Nigeria, 2010).
The emphasis of this generation on bioethanol promotion is driven not only by the energy security it provides but also the environmental benefits. Bioethanol just like other renewable energy sources produces considerably lower emissions on combustion and it only releases the same amount of carbon dioxide as plants take up for its life process. This helps to reduce greenhouse gas emissions; the world energy policy, therefore, is targeted at promoting the use of bioethanol and other biofuels (Energy Commission of Nigeria, 2010).
Bioethanol is an important renewable energy source that is now being used as fuel or fuel additive; though, using bioethanol is not a new idea it has being in process since
1872 when gasoline is not available; in particular ethanol make an excellent motor fuel (Keating et al. 2006). The reason alcohol fuel has not been fully exploited is that, up till recently, gasoline has been cheap, available and easy to produce. However crude oil is getting rare and historic price differential between alcohol and gasoline is getting narrower (Energy Commission of Nigeria, 2010).
1.5.3 Natural Occurrence of Ethanol
Ethanol is a byproduct of the metabolic process of yeast. As such, ethanol will be present in any overripe fruit and yeast habitat (Dudley, 2004). Ethanol produced by symbiotic yeast can be found in bertam palm blossoms. Although some species such as the pentailed treeshrew exhibit ethanol-seeking behaviors, most show no interest or avoidance of food sources containing ethanol (Cynthia, 2008). Ethanol is also produced during the germination of many plants as a result of natural anerobiosis (Sylva et al., 1974).
1.5.4 Uses of Ethanol
Uses of ethanol are many; among these applications includes.
I. It is used as a fuel and gasoline additive in automobiles
II. Used also in the productions of alcoholic drinks such as vodka among others
III. Widely used as solvent in productions of paints, vanish, drugs among others
IV. Used in thermometers and as an anti freezing agent
V.