Production of Ethanol Through the Fermentation of Reducing Sugars Resulting From the Hydrolysis of Pretreated Sawdust (Hardwood)

Production of Ethanol Through the Fermentation of Reducing Sugars Resulting From the Hydrolysis of Pretreated Sawdust (Hardwood)

Chapter One

Aim and Objectives

Aim: To produce ethanol through the fermentation of reducing sugars resulting from the hydrolysis of pretreated sawdust (Hardwood).  The objectives are as follows:

1. To characterize the sawdust
2. To assess the yield of bioethanol produced
3. To characterize the bioethanol produced
4. To evaluate the effects of process parameters on the yield of bioethanol.

CHAPTER TWO

LITERATURE REVIEW

INTRODUCTION  

To satisfy the desire to make life better for man through science and technology and having in view the potentials ethanol has in this regard, there have been some concerted efforts directed at perfecting the fermentation techniques and feedstock used.

CELLULOSE

Cellulose was first discovered in 1838 by French chemist Anselme Payen, who isolated it from plant matter. He found that cellulose contains 44% to 45% carbon, 6 to 6.5% of hydrogen and the rest containing of oxygen. Based on these data, the empirical formula was deduced to be C₆H₁₀O₅. However, the actual macromolecular structure of cellulose was still unclear. Haworth proposed a chain-like macromolecular structure in the late 1920s. Staudinger delivered the final proof of the highly polymer nature of the cellulose molecule. This will be discussed under the structure of cellulose [16].

ETHANOL

Ethanol or ethyl alcohol has existed since the beginning of recorded history. The ancient Egyptians produced alcohol by naturally fermenting vegetative materials. Also, in ancient times, the Chinese discovered the art of distillation, which increases the concentration of alcohol in fermented solutions. Ethanol was first prepared synthetically in 1826, through the independent effort of Henry Hennel in Britain and S.G in France. Michael Faraday prepared ethanol by the acid-catalyzed hydration of ethylene in 1828, in a process similar to that used for industrial synthesis of ethanol today [4].

Ethanol was used as lamp fuel in the United States as early as 1840, but a tax levied on industrial alcohol during the Civil War made this use uneconomical. This tax was repelled in 1906. In 1907, Henry Ford re-introduced ethanol to the Americans motoring public by producing his first vehicle to run on ethanol. The first Ford Motor Company Automobile was designed to use corn alcohol called ethanol. The most common substrate used for nearly 99% of ethanol production in the United States today is starch from agricultural crops, primarily corn [4].

In 1940s the first fuel ethanol plant was built in the U.S. army built and operated an ethanol plant in Omaha, Nebraska, to produce fuel for the army and for regional fuel blending. Major quantities were not manufactured until the 1970s due to low cost of gasoline between 1940s and 1970s, however the ethanol industry began to remerge when ethanol was used as a fuel extender during gasoline shortages caused by the OPEC oil embargoes [9].

In 1980s, after investing heavily in renewable fuels in the 1970s, Brazil kept the program alive during the 1980s. With its robust ethanol programs, Brazil developed an extensive ethanol industry. By the mid-1980s, ethanol-only cars accounted for almost 90% of all newauto sales in Brazil, making the country the biggest alternative fuel market in the world. In 1988 ethanol began to be added to gasoline for the purpose of reducing carbon dioxide emissions. By 2000, Brazil deregulated the ethanol market and removed its subsidies. However on market conditions, all fuels are required to be blended with 20 to 25 percent of ethanol.

As the production has increased, the effect of biofuels on agricultural markets and the environment have become increasingly important topics, yet much uncertainty still remains. Biofuels have the potential to displace the use of petroleum as a transportation fuel and lower toxic emissions. The evolution of new biofuel production technologies could help alleviate some of the concerns regarding the use of food for fuel by facilitating the use of non-food feedstock’s, and could alleviate some of the environmental concerns associated with grain ethanol production. In particular, cellulosic ethanol is believed to hold great promise in this regard, even though there are currently no commercial scale plants in the United State [12].

CELLULOSIC ETHANOL

Cellulosic ethanol i.e. ethanol from forestry or agricultural waste is considered a way to prevent displacement of crops to feed humans. Corn-based ethanol has been blamed by some for higher food prices and shortages because food producers are at times forced to compete with energy companies for grain. Some also argue that the growing demand for such crops is also responsible for indirect land-use change, the destruction of rain forest and wetlands to make room for more farmland. The joint study sees cellulosic ethanol as a viable alternative for reducing oil dependences while protecting food crops. Corn-Stover and switch grass are very potential cellulosic feed stock.

Gallagher et al (2003), also found that crop residues are likely the lowest cost biomass source. According to Atchison and Hettenhaus in 2003, over 240 million dry tons of corn Stover is produced each year in the United States. Brechbill and Tyner (2008) found through research that corn Stover collection risk soil loss from wind erosion and runoff from water erosion depending on the amount of corn Stover collected [12]. However, as cellulosic ethanol technologies advance the use of organic content of the municipal solid waste as a transportation fuel feedstock and simultaneously reduce externalities associated with waste disposal.

Wood is the most common cellulosic feedstock used to manufacture ethanol. Extraction of ethanol from wood alcohol dates as far back as 1819, a memorandum was published on wood alcohol by braconnet, after which numerous attempts have been made on the distillation of wood alcohol.

The various works on wood alcohol are briefly discussed below:

1. About eighty years after the memorandum by Braconnet, Simonsen in 1894 recommended the treatment of sawdust with dilute acids of about 0.3-0.7 at high pressure of about 7-8atm. It however did not become an industrial process because of excessive dilution of saccharine juices. Ekstrom attempted to solve the same problem by using strong sulphurous acid. [4].
2. In 1899, the hydrolysis of wood was studied by Classen who recommended sulphric acid as the hydrolysis agent instead of sulphrous acid used by his predecessors because from his findings, volatile acids had better penetration of wood. Heating was carried out at 150⁰C, 7atm for 4 to 6hrs; residua are extracted by percolation and filtrate is neutralized and fermented. It was applied in America and abandoned due to corrosion, difficulty in stripping, consumption of coal and sulphuric acid. [6].
3. Beginning in the 1910, two chemical engineers, Messrs. Ewen and Tomlinson used the same procedure as Classen. They however improved the process by using a much shorter and wider converter (12 ft. by 18 ft.), and lining it with firebrick instead of with lead 1 sculpture dioxide gas to the extent of one percent, of the weight of wood treated is introduced into the converter, and steam passed in until a pressure of 100 lb. is obtained. The steam is then turned off and the cylindrical converter slowly revolved for forty-five minutes, the temperature is raised as quickly as possible to the critical point, between 135⁰C and 163⁰C, above which there is an excessive destruction of sugar and production of fermentable substances. The filtrate or juice obtained is partly neutralized, filtered, cooled and sent on for fermentation using yeast as enzyme. This was implemented on a large scale, in America for the manufacturing of ethanol from sawdust. Industrial yield, under normal conditions, reached 7.3 liters of 100-degree alcohol per 100 kilograms of dry wood, and the factory’s annual production is 20 000 hectoliters of alcohol [4].
4. Before 1914, in France, alcohol manufacture from sawdust was studied and implemented industrially in a distillery in the Ardeche region. Due to the need for alcohol for national defense during the World War. Wood alcohol was reconsidered during the 1914-1918 war, production of wood alcohol was achieved in Germany with either the classen or the Windesheim-ten-Doornkaat process. The latter involved heating sawdust with dilute hydrochloric acid in the presence of catalysts (metallic salt), in rotatory autoclaves, at 7 to 8 atmospheres for 20 to 30 minutes. Yield is 6 liters of alcohol per 100 kilograms of dry matter, but it is surely possible to improve this [4].

A research by Dubose led to the following conclusions:

1. In saccharifying sawdust with 2 parts of sulphuric acid (90-95% H₂SO₄) per 100 parts of dry sawdust, maximum yield is obtained with a pressure of 7.5 atmospheres; yield decreases above or below this pressure.

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CHAPTER THREE

MATERIALS AND METHOD

There are two methods in the production of ethanol from cellulose which are separate hydrolysis and fermentation (SHF) ad simultaneous saccharification and fermentation. These methods have been extensively discussed in the previous chapter respectively and will be used in the experimental production of ethanol from 100g hardwood sawdust (cellulose) in this chapter.

LIST OF REAGENTS AND APPARATUS

The list of reagents and apparatus are presented below:

LIST OF APPARATUS

The following are the apparatus that will be used in the course of this experiment:

1. Weighing
2. Autoclave
3. Pipettes
4. Buchner funnel (this is used because the material is made up of is resistance to strongly acidic solutions).
5. Stirring rod
6. Shaker
7. pH meter
8. Thermometer
9. Conical flasks
10. Beakers
11. Density meter analyzer

LIST OF REAGENTS  

Lists of reagents required are listed below:

1. Distilled water (pH 7.0)
2. Water (pH 9.7)
3. 18M H₂SO₄
4. 4m H₂SO₄
5. 5m NaOH
6. Saccharomyces cerevisiac
7. Hardwood sawdust
8. Tween 80
9. 01m Ca(OH)2

CHAPTER FOUR

RESULTS AND DISCUSSION

ANALYSIS OF SEPERATION HYDROLYSIS FERMENTATION OF SAWDUST

The procedure for the production of ethanol from cellulose by SHF has been discussed in chapter 3; section 3.2.1, here 100g of hardwood sawdust is used to produce ethanol by acid hydrolysis using H₂SO₄ as the acid. 32.4g of sugar was obtained on completion of the hydrolysis; however, theoretically 52.2g of sugar can be produce from 100g of sawdust. The yield obtained by acid hydrolysis of hardwood sawdust can be calculated as follow:

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION

This research work based on the extraction of sugar and subsequent fermentation of the sugar from cellulose. Study was carried out on ethanol from starch and ethanol and cellulose were compared. However, for the experiment the cellulosic material or biomass used is sawdust. Two methods were used to produce the cellulosic ethanol: SHF and SSF.

It can be inferred that the SHF is a very dangerous method as highly concentrated acid is being use for the hydrolysis. However, it is less costly compared to SSF method due to the use of cellulose enzymes. The SSF, however, produces more ethanol compared to SHF but the difference in the ethanol production doesn’t account for the difference in cost of production making the SHF more cost effective. This may not be applicable on a large scale though.

Experiment data of production of ethanol from corn during the course of the literature was compared to the values for the production of ethanol from cellulose. It can be deduced from the data that from same mass of corn, more ethanol is produced using SHF (enzymatic though) and SSF. It is also seen that production of ethanol from cellulose is more costly compared to corn ethanol. Thus if ethanol is made from cellulose it will result in an increase in ethanol prices. Therefore, this will make the future of cellulosic ethanol very oblique.

Fuel derived from cellulosic biomass is essential in order to overcome our excessive dependence on petroleum for liquid fuels and also address the build-up of greenhouse gases that cause global climate change. The conversion offers the potential for radical technical advancement through application of powerful tools of modern biotechnology to realize truly low costs.

However, if strict bans are made on the production of food ethanol, cellulosic ethanol will thrive well and costs of enzymes may fall. Also, a breakthrough in genetically engineering an organism that will directly convert cellulose to ethanol will be more desirable in the production of cellulosic ethanol.

REFERENCES

• Arland Johannes (2002). Biomass to Ethanol: Process Simulation Validation and sensitivity Analysis of a Gasifier and a Bioreactor, pp 10-12.
• Asia Pacific Forum on Science, Learning and technology (June 2007) Volume 8, issue 1, Article 16.
• B.L. (1967). The Chemistry of Wood, Interscience, New York, pp 703.
• Boullanger 1924, distilleria Agricole et industrielle. Translation from the French   by     F.  Marc de piolen, pp. 3-8.
• Electronic Journal of Biotechnology (2009). Simultaneous Saccharification and Fermentation process of different cellulosic substrate using a recombinant Saccharomyces cerevisiae harboring the β-glucosidase gene, vol. 13 no. 2, pp. 1-8.
• Harris, E.E., Beglinger, G.J. Hajny and Sherrard EC (1945). “Hydrolysis of Wood: Treatment with Sulfuric Acid in a stationary digester” Industrial and Engineering Chemistry, 37(1): 12-

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