New Methods for Ethanol Production
By Ashlee Bushee
Ethanol production is currently limited by low efficiency and high energy processes with the dominant process also using agriculture products that require water, chemicals, and take away from the food supply. With droughts and flooding happening more regularly across the United States and the world, new approaches for ethanol production are of particular interest. Ethanol is being heavily researched for its widespread use as an alternative fuel, fuel additive, hydrogen carrier, sanitizer, and feedstock for the production of pharmaceuticals and polymers, and its use in food, cosmetics and the growing CBD and hemp industries. A new method for ethanol synthesis from methanol in the presence of syngas and unique composite catalysts demonstrated a 98% conversion rate was reported from Xiamen University. This article will further dive into how ethanol is currently produced and expand on the new method, including its potential for scalability and cost outside of a traditional laboratory setting.
How Ethanol is Currently Processed
Ethanol has been manufactured primarily from two production processes: ethanol sugar fermentation and ethylene hydration. Ethanol from sugar fermentation starts with a sugar feedstock that can come from sugar cane juice, sugar beet juice, cane or beet molasses, raw sugar, or refined sugar – commonly referred to as production from sucrose. The sugar needed can also come from barley, corn, grain, sorghum, or wheat – commonly referred to as production from a starch. Ninety-seven percent of the estimated 15 billion gallons of ethanol produced each year in the United States starts with corn as the feedstock. This process consumes large amounts of agricultural products – for every bushel of corn (around 56 pounds) the estimated ethanol yield is between 2.65 and 2.75 gallons (Table 1). Diverting these raw materials to be feedstock for ethanol has not occurred without a lot of public pushback and the amount going to ethanol has steadily increased from 13% in 2004 to 45% in 2018. Barley, corn, sorghum and wheat all also require a significant amount of land, water, and agricultural chemicals to get to harvest before they start their next life as a feedstock for the fermentation process.
Table 1: Ethanol conversion from different feedstocks. Information from USDA.
| Ethanol conversion factors for grain feedstock | |
| Commodity | Ethanol Conversion |
| Barley | 1.40 gallons per bushel |
| Corn – wet mill | 2.65 gallons per bushel |
| Corn – dry mill | 2.75 gallons per bushel |
| Grain Sorghum | 2.70 gallons per bushel |
| Wheat | 2.80 gallons per bushel |
Ethanol from sucrose is primarily produced in Brazil with an estimated 7.5 billion gallons produced each year. The difference between the starch or sucrose feedstock is relative to the ethanol manufacturer’s location to the agricultural industries that they utilize for feedstock. In the U.S., ethanol distilleries are usually located in proximity to corn farms while in Brazil the ethanol industry is located near large sugar cane farms. The robust ethanol industry in Brazil grew largely during the collapse of both the oil industry and sugar cane markets in the early 1970’s. This devastated the economy and led Brazil to a creative political strategy to revive their sugar cane industry and become less dependent on foreign fuel. Proálcool was a government initiative to make their cars run on ethanol manufactured from sugar cane. This approach worked with farmers, distillers, auto manufacturers and consumers to make the switch from petroleum to ethanol. Today 90% of cars in Brazil can run on either petroleum or ethanol, allowing the consumer to choose based on the best fuel price. The rise of ethanol production in Brazil has not come without a cost and in 2019 protections of the rainforest were removed. Slash and burn has become a widespread practice and 90,000 fires were seen from satellite views.
Table 2: Total production costs for ethanol not including capital or transportation costs, information from USDA.
| Total Ethanol Production Costs (dollars per gallon) |
|
| Corn wet milling | 1.03 |
| Corn dry milling | 1.05 |
| Sugar Cane | 2.40 |
| Sugar Beets | 2.35 |
| Molasses | 1.27 |
| Raw Sugar | 3.48 |
| Refined Sugar | 3.97 |
| Brazil Sugar Cane | .81 |
Moving onto the second method for ethanol production: ethylene hydration.
Ethylene Hydration for ethanol production was first introduced by Shell in 1947. It is a three-step process including the reaction in which ethylene and water are preheated up to 300°C. They then enter into a catalytic reactor which uses phosphoric acid for a conversion between 4-25%. Acetaldehyde is a byproduct and can be reacted over a nickel catalyst. These products then enter a distillation column where the ethanol and water vapor are separated out. The ethanol and water vapor are then purified. In 2010 this method only accounted for 7% of the global production of ethanol. It uses a lot of energy, has poor reaction yields, and ethylene is often more expensive than ethanol so this process doesn’t financially make a lot of sense.
To reiterate, the current processes for ethanol manufacturing from fermentation or by ethylene hydration require high energy consumption and have low reaction efficiency. Ethanol is widely used as an essential component or raw feedstock for many products and processes and because of this need there has been an uptick in research working to find a more efficient means of production. “For the first time a method to successfully convert methanol into ethanol in the presence of a syngas by tandem catalysis over a composite catalyst has been reported” (Zhang et al., 2022). The catalytic reaction was carried out on a high-pressure fixed-bed flow reactor. The first step was to load the uniform mixture of catalysts H-MOR-DA@C and Pt-Sn. Then the reactant gasses, 48% carbon monoxide, 48% hydrogen gas, and 4% argon, were introduced into the reactor. The last step was the introduction of liquid methanol. The methanol carbonylation to acetic acid and then the acetic acid hydrogenation to ethanol. The conversion rate from methanol to ethanol was as high as 98%. This process has the potential to be an affordable means to produce ethanol but would depend on the ability and length of time that the H-MOR-DA@C and Pt-Sn zeolites could be reused, and the cost for liquid methanol. This approach would reduce the destruction of the Amazon rainforest for sugar cane and reduce the land, chemicals and water needed for corn in the United States.
It usually takes years for research at the academic level to gain enough credibility and momentum to enter into industrial processes, but this is a promising progression that could revolutionize ethanol production.
A quick refresher of a few terms that you may or may not have heard in Organic Chemistry.
Carbonylation: A reaction that introduces carbon monoxide
Syngas: A gas mixture of hydrogen and carbon monoxide in various ratios
Hydrogenation: A reaction involving hydrogen gas usually in the presence of a catalyst
Zeolite: The non-chemistry definition is to think of these as sponges (primarily made from aluminum, silicone and oxygen) and the holes in the sponge are the perfect size for other molecules to sit and they would rather be in this safe little sponge than the reaction.
H-MOR-DA@C: A catalyst that was specially prepared in a lab and was innovative by this group to aid in the process of getting ethanol to methanol
Pt-Sn Alloy: Platinum-tin nanoalloy catalyst
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References
Adesanya, Y., Atiyeh, H. K., Olorunsogbon, T., Khanal, A., Okonkwo, C. C., Ujor, V. C., Shah, A., & Ezeji, T. C. (2022). Viable strategies for enhancing acetone-butanol-ethanol production from non-detoxified switchgrass hydrolysates. Bioresource Technology, 344, 126167. https://doi.org/10.1016/j.biortech.2021.126167
Basel, C. L. (n.d.). Mordenite Zeolites (MOR). Clariant Ltd. Retrieved October 24, 2022, from https://www.clariant.com/en/Solutions/Products/2019/04/24/08/30/Mordenite-Zeolites-MOR
Current status and future prospective of bio-ethanol industry in China | Elsevier Enhanced Reader. (n.d.). https://doi.org/10.1016/j.rser.2021.111079
Decarbonizing ethanol production via gas fermentation: Impact of the CO/H2/CO2 mix source on greenhouse gas emissions and production costs | Elsevier Enhanced Reader. (n.d.). https://doi.org/10.1016/j.compchemeng.2022.107670
Filatova, E. G., & Pozhidaev, Y. N. (2020). Development of Natural Zeolites Regeneration Scheme. IOP Conference Series: Earth and Environmental Science, 459(3), 032035. https://doi.org/10.1088/1755-1315/459/3/032035
Fuel ethanol production in major countries 2021 | Statista. (n.d.). Retrieved October 23, 2022, from https://www.statista.com/statistics/281606/ethanol-production-in-selected-countries/
Gong, C., Cao, L., Fang, D., Zhang, J., Kumar Awasthi, M., & Xue, D. (2022). Genetic manipulation strategies for ethanol production from bioconversion of lignocellulose waste. Bioresource Technology, 352, 127105. https://doi.org/10.1016/j.biortech.2022.127105
how much ethanol is produced a year—Google Search. (n.d.). Retrieved October 23, 2022, from
Li, J., Zhang, Y., Yang, Y., Zhang, X., Wang, N., Zheng, Y., Tian, Y., & Xie, K. (2022). Life cycle assessment and techno-economic analysis of ethanol production via coal and its competitors: A comparative study. Applied Energy, 312, 118791. https://doi.org/10.1016/j.apenergy.2022.118791
Limited Irrigation | Water | Agronomy | Sunflower District. (n.d.). Retrieved October 23, 2022, from https://www.sunflower.k-state.edu/agronomy/irrigation/limited_irrigation.html
Liu, S., Yang, C., Zha, S., Sharapa, D., Studt, F., Zhao, Z.-J., & Gong, J. (2022). Moderate Surface Segregation Promotes Selective Ethanol Production in CO2 Hydrogenation Reaction over CoCu Catalysts. Angewandte Chemie, 134(2), e202109027. https://doi.org/10.1002/ange.202109027
Memon, S. F., Wang, R., Strunz, B., Chowdhry, B. S., Pembroke, J. T., & Lewis, E. (2022). A Review of Optical Fibre Ethanol Sensors: Current State and Future Prospects. Sensors, 22(3), Article 3. https://doi.org/10.3390/s22030950
Mohsenzadeh, A., Zamani, A., & Taherzadeh, M. J. (2017). Bioethylene Production from Ethanol: A Review and Techno-economical Evaluation. ChemBioEng Reviews, 4(2), 75–91. https://doi.org/10.1002/cben.201600025
Padmanabhan, S., Giridharan, K., Stalin, B., Elango, V., Vairamuthu, J., Sureshkumar, P., Jule, L. T., & Krishnaraj, R. (2022). Sustainability and Environmental Impact of Ethanol and Oxyhydrogen Addition on Nanocoated Gasoline Engine. Bioinorganic Chemistry and Applications, 2022, e1936415. https://doi.org/10.1155/2022/1936415
Saunders, J., Izydorczyk, M., Levin, D. B., Saunders, J., Izydorczyk, M., & Levin, D. B. (2011). Limitations and Challenges for Wheat-Based Bioethanol Production. In Economic Effects of Biofuel Production. IntechOpen. https://doi.org/10.5772/20258
The Rise of Brazil’s Sugarcane Cars. (n.d.). Retrieved October 23, 2022, from https://www.rapidtransition.org/stories/the-rise-of-brazils-sugarcane-cars/
Yakubu, O., Olawale, O., Umaru, I., Abu, M., Abah, M., & Terhemba, E. (2022). Purification and Determination of Antioxidant Effects of Ethanol Extract Fractions in Phyllanthus amarus Leaves. https://doi.org/10.17311/ajbs.2022.259.270
Zhang, F., Chen, K., Jiang, Q., He, S., Chen, Q., Liu, Z., Kang, J., Zhang, Q., & Wang, Y. (2022). Selective Transformation of Methanol to Ethanol in the Presence of Syngas over Composite Catalysts. ACS Catalysis, 12(14), 8451–8461. https://doi.org/10.1021/acscatal.2c01725
