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Upgrading ethanol to butanol: An ideal solution?

Upgrading ethanol to butanol: An ideal solution?
Photo courtesy of Gevo

Samuel Morey first used ethanol in an American internal combustion engine prototype way back in 1826. By 1860, ethanol was used extensively as a lighting fuel. A short-lived tax on alcohol in the early 1860s, to pay for the U.S. civil war, curtailed usage. After the tax was repealed, demand started to return.

In 2017, global ethanol use was estimated at 104 billion litres, according to the International Energy Agency (IEA). By 2023, it is projected to reach 119 billion litres. Despite the wide adoption of ethanol as a fuel, Dr. Kapil Lokare, founder of Methuselah Holding UG, based in Berlin, Germany, believes there are issues with using ethanol as a fuel. Concerns include a high oxygen content, limited miscibility with gasoline, and the risk of phase separation — meaning it needs to be blended at terminals.

Most vehicles made before 2005 can only handle E5 to E10 or ethanol blends of between 5% and 10%, and Reid Vapor Pressure (RVP) regulations have previously prevented the sale of E15 in the United States, by far the largest ethanol market in the world. This results in a blend wall of 10% in the United States that limits the use of ethanol as a fuel, says Lokare. The Reid Vapor Pressure Test is used to determine the front-end volatility of products in gasoline. On 31 May 2019, the U.S. Environmental Protection Agency (EPA) lifted a restriction on the sale of E15 during the summer months — removing a major roadblock to expanded ethanol sales.

Speaking at the annual Fuels of the Future conference held virtually in January 2021, Lokare presented a concept for the conversion of bio-ethanol to bio-butanol — alongside a diverse range of potential applications. Lokare emphasised the importance of innovating with ethanol, including a potential opportunity for 95 billion litres of ethanol for valorisation. When upgrading ethanol, it is important to consider the market value of new products (as compared to ethanol), demand, and the availability of technologies, says Lokare. He also stressed the significance of a business model that does not rely on government subsidies.

What should you valorise ethanol to? Currently, 80% of ethanol is used as a fuel, the remainder as a chemical. When converting ethanol as a fuel, prices are dictated by fluctuating oil prices, government subsidies, and ongoing success depends on long-term off-take agreements, Lokare says. It is essentially high volume but low value. The chemical route offers greater opportunity. A single technology can access multiple product and profit streams that are lower in volume but higher in value. At the five-day fuels conference, Lokare considered several compounds from the upgrading of ethanol.

Acetaldehyde has a high market value compared to ethanol. Technically, the ethanol supply chain could produce sufficient acetaldehyde to supply the entire world’s requirements by upgrading ethanol to acetaldehyde and hydrogen. However, there is limited demand for the compound, and acetaldehyde can be more easily converted from other processes, he says. Therefore, this conversion process is not necessarily a profitable venture, he adds.

Converting ethanol to ethylene is more profitable with a high market value. Lokare also noted adequate global demand. Though, almost 40% of mass is lost in water during the chemical process. Ethanol could address a major chunk of global ethylene requirements, although the volumes pale in comparison to ethylene capacity from leading steam cracking plants around the world.

Upgrading ethanol to butanol: An ideal solution?
Photo courtesy of Lanzajet

Lokare also highlighted the conversion of ethanol to diethyl ether. This chemical compound has low market value meaning we are essentially downgrading ethanol — therefore it is not a good candidate, he says.

Upgrading to butadiene can be pursued, Lokare says. Butadiene is higher in value than ethanol, there is requisite demand, and technologies are available. Still, the renewable energies consultant considers the process less economical than butane or butene routes for larger volumes.

Jet fuel is where it “starts to get interesting,” he says. Twelve units of ethanol are required per unit of jet fuel, with a significant loss of water. High subsidies and an intensive push from governments are necessary to make this option commercially successful. Lokare suggests a parallel could be drawn to methanol-to-gasoline (MtG) for economic viability. There are quite a few technologies available, such as ethanol to ethylene to jet fuel, and isobutene to jet fuel. At present, this is less economical than traditional routes for large volumes of jet fuel, he says.

Lokare proposed an “ideal solution” of upgrading ethanol to butanol. Options include butanol as a fuel or as a specialty chemical — providing greater versatility when it comes to developing a profitable business venture, he says. Butanol can be blended at 16.5% with gasoline and 12% with diesel — offering a much larger market share. Two conversion technologies exist for ethanol to butanol. The “100-yearold technology” of ABE Fermentation can produce acetone/butanol and ethanol, although it is not economically viable for large volumes. The petrochemical-based LP Oxo Process starts with propylene and syngas to make butanol.

Lokare proposes to develop a green process that combines the fermentation route to make ethanol and uses chemical catalysis to upgrade it to butanol. This process combines the best of both worlds, he says. It is independent of the ethanol source, and the catalytic process — as opposed to microbial – enables a higher turnover, higher conversion, lower CAPEX/OPEX, and a greater stability of chemical conversion.

In terms of the most effective business model, he proposes a pilot to prove the technology, before moving to a demo and eventually a custom-built facility. Given the fact that ethanol production is distributed throughout the globe, Lokare recommended subsequent licensing of the technology to ethanol producers to further monetise the technology. Lokare emphasised the importance of keeping supply chain top of mind when developing such a project. For Europe,

Lokare proposes an agriculture to flight pathway. Renewable jet fuel is very relevant to Europe and funded heavily by the European Commission. Alcohol to jet fuel is also an approved pathway that is recognised by standards organisation ASTM International. Though, not many technologies are available in the market that can bring the product to commercial reality, he says. It is imperative to keep production costs as low as possible — as airlines are sensitive and vulnerable to prices and price fluctuations, he adds.