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“The future is green energy, sustainability, renewable energy.”
– Arnold Schwarzenegger
Fully grown cassavas on the field.
Source: tinglee1631, https://www.gardeningknowhow.com/edible/vegetables/cassava/growing-cassava-yuca.htm
It cannot be denied that the energy reserves on Earth are running low. Although saving energy is a smart step to prevent depletion of energy reserves, the increase in energy consumption, which also acts as an indicator of Indonesia's economic development, must be facilitated by a supportive energy source. The World Counts noted that Earth’s reserves can only supply us coal for 179 more years, oil for 36.2 years, and natural gas for 48.6 years. Over the last century, the burning of fossil fuels (coal and oil) has increased the concentration of atmospheric carbon dioxide (CO2), which according to NASA, amounted to a 47% increase. This results in the ‘greenhouse effect’: warming due to the atmosphere trapping heat which is radiating from Earth toward space. Moreover, technological and industrial advancements, especially the revolutions of Industry 4.0, brings an increase in energy consumption. Bernard Marr in a Forbes article defines Industry 4.0, or the Fourth Industrial Revolution, as the fourth revolution that has occurred in manufacturing. This revolution is signified by the adoptions of computers and automations which are enhanced with smart and autonomous systems fueled by data and machine learning. Facing these challenges, our country needs to expand the use of other energy sources to replace the use of oil and fossil energy.
To circumvent the depletion of fossil fuel, many countries are now developing sources of renewable, alternative, and sustainable energy. The Oxford English Dictionary defines alternative energy as ‘electricity or power that is produced from the sun, wind, water, etc. in ways that do not use up the earth's natural resources or harm the environment’. Many alternative energy sources can be used to replace fossil fuels. We chose bioethanol as our material of focus because bioethanol is an environmentally friendly fuel and its manufacturing process is relatively easy and cheap. Bioethanol is classified as a renewable alternative fuel because it is a biofuel in the form of ethanol (C2H5OH) produced from biomass. Biomass, in the industry of energy production, refers to living or recently dead biological materials that can be used as a fuel source or used for industrial production. Meanwhile, biofuel is an energy source made from living matter, usually plants. Bioethanol is made using fermentation techniques from biomass such as tubers, corn, or sugarcane, followed by distillation. Ethanol also burns more cleanly and completely than gasoline or diesel fuel. Ethanol has an octane number of 109.
An illustration of bioethanol production from sugarcane.
Source: https://www.technologytimes.pk/2018/08/09/bioethanol-production-sugarcane/
During ethanol fermentation, glucose and other sugars in the biomass are converted into ethanol and carbon dioxide in the reaction
C6H12O6(s) → 2C2H5OH(l) + 2CO2(g); ∆H = –101.43 kJ
This reaction takes place in an aqueous solution. The resulting solution has an ethanol content of around 15%. The fermentation has several side products, such as acetic acid and glycols, which are mostly removed during purification. Ethanol is subsequently isolated and purified through adsorption and distillation. During combustion, ethanol reacts with oxygen to produce carbon dioxide, water, and heat, in the reaction
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l); ∆H = –1367 kJ
Most ethanol is produced by fermentation. Outside the context of alternative energy, ethanol can also be produced industrially from ethene (ethylene) by hydration of the double bond in the presence of a catalyst and high temperature. The catalyst used is solid silicon dioxide coated with phosphoric (V) acid. This reaction of ethanol production can be written as
C2H4(g) + H2O(l) → C2H5OH(l)
There are several types of plant-based raw materials that can be used in the manufacturing of ethanol:
Starchy ingredients, such as cassava, sweet potato, corn kernels, sago flour (known locally as aci kawung), sorghum seeds (known locally as biji cantel), arrowroot, and other starch-based ingredients.
Sugary materials, such as molasses, sugarcane juice, coconut juice, sugar palm (Arenga sp.) juice, nipa palm (Nypa fruticans) juice, gebang palm (Corypha sp.), lontar (Borassus flabellifer) sap, and many more.
Cellulosic materials, such as logging waste and agricultural waste, including rice straw, bagasse, corn corms, onggok (tapioca waste), banana tree trunk, sawdust, and others.
Starch and cellulose molecules are strings of glucose molecules. Generating ethanol out of cellulosic materials requires a pretreatment that splits the cellulose into glucose molecules and other sugars that can be fermented. The resulting product is called ‘cellulosic ethanol’, indicating its source. In this article, we choose cassava as the main material in the manufacturing of bioethanol. The process of making bioethanol from cassava is as follows.
Peel 125 kg of fresh cassava (any type will do). Clean and chop them into small pieces.
Dry the chopped cassava to a maximum moisture content of 16%. Then, squeeze the chopped cassava to make gaplek (dried cassava). This is done to make the cassava more durable so the producers can keep them for longer.
Bioethanol distillation tool for small and medium scale businesses.
Put 25 kg of gaplek into a stainless steel tank with a capacity of 120 liters, then add water until it reaches a volume of 100 liters. Heat the gaplek to 100 °C for half an hour. Stir the gaplek stew until it thickens and becomes a slurry.
Cool the gaplek slurry, then put it in the saccharification tank. Once cool, add the Aspergillus fungi which will break down the starch into glucose. To decompose 100 liters of cassava starch pulp, 10 liters of the Aspergillus fungi solution or 10% of the total slurry is needed. The concentration of the fungi needs to be around 100 million cells/ml. Before being used, the Aspergillus is cultured in the dried gaplek slurry, so it will adapt to the chemical properties of the slurry. The fungi will then reproduce and break down the starch.
Let the gaplek slurry sit for two hours. The gaplek slurry will turn into two layers: water and sugar sediment. Stir once more the starch that has turned into sugar, then put it in the fermentation tank. However, before fermentation, make sure the maximum sugar content of the starch solution is 17–18%. If the sugar level is higher, add water until the desired level is reached. If it is lower, add the sugar solution to achieve the maximum sugar content.
Close the fermentation tank tightly to prevent contamination. In a closed tank, Saccharomyces will break down glucose more optimally. Fermentation takes place anaerobically (it doesn't need oxygen). For optimal fermentation, maintain the temperature at 28–32 °C and the pH at 4.5–5.5.
After two to three days, the starch solution will turn into 3 layers. The lowest layer is a protein deposit. Above it is water, and the uppermost layer is ethanol. The fermentation product is called beer, which contains 6–12% ethanol.
Suck the ethanol solution with a plastic tube through a 1-micron filter paper to filter out the protein deposits.
Even after filtration, ethanol is still mixed with water. To separate them, do distillation. Heat the mixture of water and ethanol at 78 °C, equivalent to the boiling point of ethanol. At that temperature, ethanol evaporates before water (which has a boiling point of 100 °C). Ethanol vapor will flow through a pipe that is submerged in water, so the ethanol vapor will condense and return to liquid ethanol.
The distillation product is 95% ethanol — insoluble in gasoline. In order to dissolve, an ethanol concentration of 99% (also known as dry ethanol) is needed. Therefore, absorbent distillation is necessary. The 95% ethanol is heated to 100 °C. At that temperature, both the ethanol and water will evaporate. The vapor is then passed into a pipe whose walls are coated with zeolite or starch. Zeolite will absorb the remaining water content until 99% ethanol is obtained which is ready to be mixed with gasoline. Producing 10 liters of 99% ethanol requires 120–130 liters of beer, which is produced from 25 kilograms of cassava.
In conclusion, we are running out of energy and we need new sources of energy. Bioethanol can be used as an alternative fuel because it is environmentally friendly and renewable. Its process of production is also quite simple and can be easily done on small scales or small businesses. The raw materials needed to process bioethanol are also cheap and can be easily found. In the future, bioethanol might eventually be one of the most important and valuable fuels.
References
Huda, N. (2017, January). Buku Proses Pembuatan Bioetanol 2017. Retrieved from http://repositori.kemdikbud.go.id/16324/1/Buku%20Proses%20Pembuatan%20Bioetanol%20%202017%2822%29.pdf
Marr, B. (2018, September 2). What is Industry 4.0? Here's A Super Easy Explanation For Anyone. Retrieved from https://www.forbes.com/sites/bernardmarr/2018/09/02/what-is-industry-4-0-heres-a-super-easy-explanation-for-anyone/#16eb88649788
Alternative Energy – noun. (n.d.). Retrieved from https://www.oxfordlearnersdictionaries.com/definition/english/alternative-energy
Apa itu bioetanol, biodiesel, dan biogas. (n.d.). Retrieved from http://indonesiabaik.id/infografis/apa-itu-bioetanol-biodiesel-dan-biogas
Cadangan Energi Indonesia Menipis, Saatnya Melek Energi Terbarukan. (2017, August 1). Retrieved from https://www.kompasiana.com/cakmat/599aefc15af02c183e6ca1d2/cadangan-energi-indonesia-menipis-saatnya-melek-energi-terbarukan
Ethanol. (2020, May 15). Retrieved from https://www.nrcan.gc.ca/energy-efficiency/energy-efficiency-transportation/alternative-fuels/biofuels/ethanol/3493
Ethanol fuel. (n.d.). Retrieved from https://en.wikipedia.org/wiki/Ethanol_fuel
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Sustainable energy. (n.d.). Retrieved from https://en.wikipedia.org/wiki/Sustainable_energy
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