Humans have been producing alcohol (aka ethanol) for consumption dating back millennia. In more recent decades, ethanol has jumped from alcoholic beverages to fuel tanks, finding use as an octane booster for gasoline, especially during periods of fuel shortage such as World War II and the 1970s energy crisis.
Starting in 2007, the Renewable Fuel Standard (RFS) set a minimum production volume for renewable fuels, which has largely been filled by ethanol derived from corn. Looking to the future, cellulosic ethanol is starting to take root, which could both significantly reduce short term transportation carbon emissions and serve as a platform for many new kinds of lower carbon fuels and chemicals.
Why can’t we just use corn?
Corn ethanol is produced by using yeast to convert the sugar in corn to ethanol, much in the same way that beer is brewed using malt sugar or wine is fermented from grape sugar. Because the carbon in corn was absorbed from the atmosphere through photosynthesis, corn ethanol generates about 50% fewer carbon emissions per gallon than crude-derived gasoline. The problem with generating fuel grade ethanol from corn is that it competes with selling corn for human consumption or growing other crops that could be sold for human consumption.
What is cellulosic ethanol?
Instead of using the edible part of corn to make ethanol, cellulosic ethanol is derived from the inedible stalks, cobs, and leftover plant matter. This process is much harder because these inedible materials are designed by nature to resist degradation, as they provide structure and protection to the plant. One of the main structural materials in plants is called cellulose, hence ‘cellulosic ethanol.’ Because these structural materials are typically waste byproducts of other processes, when cellulosic waste is converted to fuel-grade ethanol, it provides greater than 70% fewer carbon emissions per gallon compared to crude-based gasoline.
“What’s so great about cellulosic ethanol is that it eliminates the Food vs Fuel debate, the feedstock is all non-edible plants. It also has solid economics incentives from the recently passed Inflation Reduction Act.” – Erik Selden Delek VP
Aren’t we trying to electrify? Why do we need more gasoline?
In addition to serving as a blending component for gasoline, ethanol is a very flexible molecule. If you remove an equivalent of water from ethanol, you make ethylene, the building block of many plastics. If you string a few ethylene molecules together, you can make jet fuel, also called sustainable aviation fuel (SAF), because it is derived from biomass. If you take a slip stream of the intermediates from the cellulosic ethanol process, you can access other chemical building blocks that could be used for sustainable materials. Because this lower carbon emitting ethanol can be used for so many end products, it is viewed as a platform to enable renewable fuels and chemicals.
“Cellulosic ethanol presents exciting opportunities for both near- and long-term fuel decarbonization.” – Madelyn Evans VC Principal, Delek Innovation
Cellulosic ethanol is just one of many options available to decarbonize transportation fuels and enable renewable materials. Because cellulosic feedstocks are waste material, collection and transportation to a conversion site remain a large hurdle. Technology for ethanol to jet conversion has also not been proven at commercial scale. These and other logistical and technological challenges will need to be addressed for cellulosic ethanol to contribute to a more sustainable future.