Part 1: In Search for Zero Emission Fuels

By: Mimi Martinez 

Electrification efforts will be a significant component of the solution for decarbonizing many industries, but sectors like shipping[i] and aviation, where electrification would require a major redesign, face large challenges. These high-emission industries may need more immediate solutions, which could be addressed through the use of alternative fuels. This makes the development of the market for alternative fuels crucial, with the potential for attracting strong investment and fostering widespread adoption[ii].

You may remember the wave of excitement when ethanol was heralded as the next big fuel. The hope was that ethanol would be a lower-emission, environmentally friendly, and efficient alternative to fossil fuels. The wave of excitement helped turn ethanol into a well-established biofuel, as innovation was accompanied by subsidies and mandates, designed to help pave the way for the fuel source to grow. 

Made from renewable biological sources, including plant starches and sugars, in several countries including the U.S., corn is its primary feedstock. This has led to the reality that growing corn for ethanol has proven to have a significant environmental impact. This impact could worsen if the ethanol content in gasoline is increased. Higher ethanol blends, while reducing certain emissions, also contribute to air pollution, decrease fuel efficiency, and increase food prices due to higher demand for crops like corn. Additionally, some car manufacturers have raised concerns about the damage these blends may cause to engines[iii]. While the idealized expectations of ethanol have not fully materialized, it has, nonetheless, opened doors to rethinking energy sources beyond traditional petroleum-based fuels.

Biodiesel and renewable hydrocarbon fuels are other types of biofuels that have benefited from respective innovation and development waves. Biodiesel, a renewable liquid fuel made from sources like vegetable oils, animal fats, and used cooking oils, was developed as a cleaner-burning alternative to petroleum-based diesel. Biodiesel is non-toxic, biodegradable, and is produced through a process that combines alcohol with these fats or oils. While biodiesel can be blended with petroleum diesel in various amounts, it still results in lower emissions compared to fossil fuels. However, concerns remain about its environmental impact, particularly related to land use and food production when crops like corn are used as feedstock. Additionally, biodiesel has a lower energy density than petroleum diesel, which can affect fuel efficiency.

Renewable hydrocarbon fuels, derived from biomass using biological or thermochemical processes, closely resemble traditional petroleum-based fuels, such as gasoline, diesel, and jet fuel, making them compatible with existing infrastructure like engines and fueling stations. The main advantage of these fuels is their compatibility with current technology, allowing them to replace petroleum fuels without requiring significant changes. However, challenges remain in scaling up production and ensuring that biomass sourcing is sustainable[iv].

With these persistent challenges to eliminate emissions today, the larger conversation has shifted attention to hydrogen e-fuels.  Derived from hydrogen produced through electrolysis, hydrogen molecules are isolated from water using electricity, which can be powered by renewable energy sources to reduce the fuel's carbon footprint. There are different types of hydrogen, based on the energy source used in the electrolysis process. Yellow (powered by solar energy), pink (powered by nuclear energy), and green (powered by renewable energy sources) hydrogen are the hydrogen types that offer the potential to produce hydrogen with zero emissions[v]. However, emissions reenter the picture when the hydrogen is converted into fuels. 

E-ammonia and e-methanol are the two main emerging e-fuels that offer potential benefits over traditional petroleum-based fuels, but they also come with certain risks. E-ammonia is produced by synthesizing ammonia (NH₃), using renewable energy for electrolysis and nitrogen fixation. It has high energy density and is easier to store and transport than hydrogen, but its combustion can produce harmful nitrogen oxides (NOₓ), which contribute to smog and acid rain. Additionally, the production of ammonia can be carbon-intensive unless renewable energy is used, and it poses risks due to its toxicity and corrosiveness. E-methanol, made by converting CO₂ into methanol (CH₃OH) using renewable energy, is considered cleaner than gasoline, as it produces lower carbon emissions when burned. However, it still releases some CO₂, and, like ammonia, it requires careful handling due to its toxicity and flammability. Both fuels, while cleaner than traditional fuels, still require advanced safety protocols and infrastructure to mitigate risks[vi].

Perhaps the answer lays in hydrogen fuel cells. A fuel cell uses the chemical energy of hydrogen or other fuels to cleanly and efficiently produce electricity.  When hydrogen is used as fuel, the only byproducts are electricity, water, and heat developed to provide power for systems as large as a utility power station and as small as a laptop computer. This highly efficient process ticks several of Green Chemistry Principle boxes, such as the reduction of waste and the maximum use of reactant atoms. Furthermore, when using renewable energy sources, like solar or wind power, rather than fossil fuels, to obtain hydrogen for the fuel cells, we are one step closer to achieving the goal of increasing the use of cost-effective, zero-emission fuels.

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