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Optimizing Ethanol Production Process using Sweet Sorghum Grain and Biomass

Abstract

Nowadays, there is a growing need for alternative energy sources because there has been a decline in fossil fuels. One of the alternative energy sources that we as globe have been utilizing is ethanol. Ethanol used for automotive fuel purposes has increased at least six times in the in the current century. Currently, the world all together produces about 19 billion gallons of ethanol annually with the United States and Brazil producing the majority of that fuel. It's estimated that by the year 2030 ethanol and other bio-fuels could replace 30% or more of U.S. gasoline demand by the year 2030.

Two of the main raw material that ethanol is being produced from are sugar cane and corn. However, the use of these feedstock has caused concerns dealing with food security, the environment, and food prices especially today when the world population has reached over 7 billion people. In the years 2008, 2010, and 2011 we saw a sudden rise in food prices and the use of maize for bioethanol has been blamed for the issue. According to several sources the price of foods is not expected to get any better in the future. Another thing is that world population is growing at a fast rate and we need to find better ways to feed the population. The use of sugar cane and maize has been creating concerns like I mentioned before so there has been a push to find a new energy crops dedicated exclusively for liquid automotive fuels.

Introduction

One of the new energy crops that has gained great level of interest is sweet sorghum (Sorghum bicoloor (L) Moench). Sweet Sorghum is a versatile sugar crop that contains starchy grains, soluble sugar juice in the stalk, and lignocellulose biomass. The three components can be used for different purposes such as producing ethanol, granulated sugar, animal feed, electricty, and others.There are several reasons for why this crop has received great amount of interest as an energy crop. Some of the main reasons are the following:

  • High biomass yield
  • Rich in fermentable sugars (53-85 sucrose, 9-33% glucose, and 6-21% fructose)
  • Short period of growth period(120-150 days)
  • Can be manipulated via genetic improvement
  • It's non-invasive
  • Excellent carbon sequestration rate
  • Highly resistant to insects, drought, salinity, and soil alkalinity
  • In my research, I spent the summer doing research on optimizing the production of ethanol from sorghum flour and biomass. The goal of this research was to enhance ethanol production using a model that worked to fully utilize fermentable sugars in sweet Sorghum. I spent the summer studying the whole process of how to make ethanol starting from the analysis of the raw material to producing ethanol in the lab.

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    Diffusion Method

    In order to produce ethanol from various organic matters the sugar must first be extracted. There are two primary means of extracting soluble sugars from organic matter such as sorghum: milling and diffusion. Milling is method that uses roller mills to press liquids from the organic substance. Diffusion is method that extracts sugar by using hot water to pull the fermentable sugars out. The diffusion method is considered to be the better method because of its efficiency. The milling method is more labor intensive, and less efficient recovering the sugars compared to the diffusion method.

    In my research I used the diffusion method to extract the sugars. I did several experiments carried out under different diffusion parameters to see which run produced the most amount of fermentable sugars. The parameters included diffusion time, temperature, and ratio of sorghum biomass to grain.

    For sugar extraction, a total of 40 grams of total content with about 10-30 percent of sorghum grain and about 70-90 percent of sweet sorghum biomass was prepared in two separate beakers. In a different beaker about 750 ml of distilled water was preheated in a microwave for a total time of 5 minutes then about 500 ml of the hot water was placed in a separate container. Then about 400 ml of the preheated water was carefully poured into a 1 L reaction vessel of a Parr reactor (Parr Instrument Co., Moline, IL). Then, the sweet sorghum biomass and grain were carefully poured into the reactor with the water. The remaining 100 ml of preheated water was used to rinse the beakers and placed the rest in the reactor. Thirty microliters Liquozyme SC DS (α-amylase 267 KNU/g, 1.266 g/ml; Novozyme, Franklinton, NC) was added into the mixture. The purpose of this enzyme is to break down the long chains of sugar into small chains. This is called liquefaction. The reactor was then assembled into the Parr reactor for heating. The mixture was heated at a constant temperature of 95°C for a time of 115- 120 minutes depending on the trail. After that time the reactor was cooled to about 40-50°C before placing about 150 microliter of Spirizyme Achieve (Glucoamylase > 900 AGU/g, 1.161 g/ml; Novozyme, Franklinton, NC) into the mixture. This enzyme breaks down the sugar compounds into simpler forms of sugar like sucrose, glucose, and fructose. The mixture was then heated for a time of 40 minutes with a constant temperature of 60°C. Figure 2 below shows how the mixture looked like after the diffusion method. The process that was just described was carried out under different diffusion parameters. Table 1 below shows the different experiments that I performed for the diffusion process with different conditions.

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    Filteration

    After the sugars were extracted using the diffusion method the sorghum mixture was still composed of solids and liquids. In order to prepare the samples for fermentation and sugar analysis using HPLC machine, the mixture needed to be separated from the two different phases. A pump and a filtering paper was used to separate the solids and liquids (Figure 3). Each sample went through this process. In order to test for sugar analysis a better filtering device was used because the filtering paper was not effective in separating the solids and liquids. In addition, each sample was centrifuged for about 12 minutes in order to separate the solids.
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    Fermentation

    Following the filtration process the fermentation was performed. The first thing that was done was preparing 19 ml of preculture broth (containing 20 g glucose, 5.0 g peptone, 3.0 g yeast extracts, 1.0 g KH2 PO4, 0.5 g MgSO4 ·7H2O per liter). The preculture broth was mixed with 1.0 g of active dry yeast (Ethanol Red from Lasaffre) and placed in incubator shaker for 30 minutes at 38°C, 200 rpm. The activated yeast culture had a cell concentration of about 109 cells/ml. The name of the yeast that was used is called Saccharomyces Cerevisiae. The next thing was to measure 100 ml of each sample of sorghum biomass and grain mixture that was created. Each sample was then mixed with 0.1 grams of potassium phosphate. Then about 1.0 ml of yeast extract and 1.0 ml of the active yeast that was in the shaker was mixed with the 100 ml of sorghum biomass and grain mixture plus the potassium phosphate. Each sample was then placed in an incubator shaker (Figure 4) for a total of 72 hours at 30°C, 150 rpm. Measurement of the mass of each sample was taken every 0, 4, 8, 24, 32, 44, 56, and 72 hours. The measurement of the mass (g) is recorded in table 2. Once the measurements were finished after three long days ethanol was produced. However, the ethanol that was produced was not pure ethanol. There was a decline in weight of each container because of carbon monoxide forming as a co-product during the fermentation process.
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    Ethanol Distillation

    After the fermentation was completed, the fermented material was ready to go through one last step before alcohol was produced. The last step in producing ethanol was distillation. The first thing that was done was to set up the distillation apparatus and made sure that all the tubing were connected properly. Then a 500 ml distillation flask was used to place each of the fermented samples. 100 ml of distilled water was used to wash the remaining contents of the Erlenmeyer flask that were used to do the fermentation. Then, about 2-3 drops of antifoam agent (antifoam 204) was added into each distillation flask. The distillation flasks were then attached into the distillation apparatus. A disposable pipette and distilled water was used to make air tight before fully tightening the flasks to the apparatus. The next thing that was done was to prepare 100 ml volumetric flask and place it into 400 ml beaker and surround with ice. The beaker was then filled halfway with distilled water. The flask was then attached behind the apparatus (Figure 5). The heat on the distillation apparatus was set to high (10). Then the system was monitored until ethanol approached about 100 ml in the volumetric flask. The heat was turned off after this and final product has been produced (Figure 6) after this step. The ethanol was then ready for HPLC analysis.
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    Results

    The table belows shows how the weight of each sample changed over time during fermentation.

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    Conclusions

    Sweet Sorghum is a very promising energy crop from what I saw working with it this whole summer. I believe it can be a great substitute for sugarcane and corn. I am a little unhappy about my results because I didn’t have enough time to do enough in depth analysis of the crop. However, this program and the research experience has given me plenty of connections and ideas about what I like to do in the future. I would like to thank my mentors Nana and Dr. Wang for their support and I also would like to thank the program coordinator and NSF for funding this experience.

    Hello, my name is Atakilti Berhe (Cool-t) and I am an Agricultural/ Biosystems Engineer at the University of Iowa State. I am currently entering my junior year. I am interested in sustainable energy dealing with alternative energy resources on the Biosystems side. I am also interested in pursuing a career in land and water conservation with the Agricultural Engineering side. Right now, I am leaning more toward the sustainable energy path because I have had more experience with that area. So I mainly enjoy working grain science, ethanol and biodiesel production.I am hoping to complete my undergraduate studies by May 2017.

    I am originally from the east African nation of Ethiopia. I was born and raised in a small and historical town called Adwa. Adwa is mostly known for the decisive battle known as the Battle of Adwa between the Italians and Ethiopians. The battle was so important because it was the climactic battle of the First Italo-Ethiopian War. This battle made us Ethiopians to be the only African nation to never be conquered by an European nation. Anyway, this is a little bit of a historical background on the area I came from.

    I moved to the United States of America when I was about 11 years old. I didn't speak any English when I came to America and this made the transition quite difficult. Also, in addition to the language barrier there was a huge cultural difference that I had to learn to adapt to.

    I have lived in Forth Worth, Texas the first two years of my life here in America. Then I have been living in the agricultural rich state of Iowa for the last 8 years or so. Living in Iowa is one of the reasons my love for Agricultural/Biosystems Engineering came to be.

    In my spare time I love to have fun and make most of my free time to have fun, make memories, and enjoy my life. I love doing sports and outdoors activities. I mainly enjoy playing soccer,playing basketball, running, and hiking. I also love travelling with my family and trying new foods. I also like going out with my friends and having fun on a Friday with music and dancing.

    Well, this summer have been exceptionally amazing I would say. I did not expect to have this much fun. I meet so many great people and I had so much fun doing research and exploring Kansas. Below are a few pictures that give a glimpse of the summer.

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    Thanks to the Biosystems Department at Kansas State University for supplying the resources necessary for my research work this summer. They were very friendly and approachable people that made my job easier . This material is based upon work supported by the National Science Foundation Grant: “This material is based upon work supported by National Science Foundation Grant: REU Site: Summer Academy in Sustainable Bioenergy; NSF Award No.: SMA-1359082 “"

    I would like to thank the following individuals for thier mentorship and support in the REU program: Nana Baah Appiah-Nkansah, graduate student mentor Dr. Wang, Faculty Professor Keith Rutlin, Program Coordinator

    References

    Appiah-Nkansah N B, Ke Zhang, William Rooney, and Wang D H (2015). Model study on extraction of both fermentable sugars and non-structural carbohydrate from sweet sorghum using diffusion process.

    Appiah-Nkansah N B, Saul K, Rooney W L, Wang D H. (2015). Adding sweet sorghum juice into the current dry-grind ethanol process for improving ethanol yields and eater efficiency. Int J Agric and Biol Eng, 8 (2): 97 – 103.

    "Ethanol." Alternative Fuels Data Center: U.S Department of Energy, n.d. Web. 06 July 2015. .

    L. Liu, A Maier, N. Klocke, S. Yan, D. Rogers, T. Tesso, Wang D H (2013). Impact of deficit of irrigation of sorghum physical and chemical properties and ethanol yield. American Society of Agricultural and Biological Engineers ISSN: 2151-0032

    Sergio O. Serna-Saldȋvar, Chirstina Chuck-Hernández, Esther Pȇrez- Carrilo and Erick Heredia- Olea (2012). Sorghum as a Multifunctional Crop for the Production of Fuel Ethanol: Current Status and Future Trends, Bioethanol, Prof. Marco Aurelio Pinheiro Lima (Ed.), ISBN: 978-953-51- 0008-9