Ethanol in Fuel

I have never been a fan of adding ethanol to fuel, but that may be changing. MIT researchers have found a way to achieve high yields of ethanol with different types of cellulosic feedstocks. Most ethanol in the U.S. is made from corn, not cellulose waste and though corn ethanol is technically a “renewable” energy source it has a large environmental footprint. Currently, around 40 % of the U.S. corn harvest goes into ethanol. Corn that could be used to feed people is instead used to make ethanol. This uses cropland, pesticides, fertilizer, and water to produce the corn just for that.

The Renewable Fuel Standard (RFS) is a federal program that requires fuel sold in the United States to contain a minimum volume of renewable fuels. The RFS required renewable fuel to be blended into transportation fuel in increasing amounts each year, escalating to 36 billion gallons by 2022. The RFS program only looks at  greenhouse gases (GHGs) relative to the petroleum fuel it replaces, the program does not look at the overall environmental costs of the “renewable” fuel. It was calculated that the RFS increased the need for cropland by 23% because ethanol production is limited in large part by its reliance on corn to produce ethanol.

from LuoyeChen et al 2021 Environ. Res.

According to Tyler Cowen, professor of Economics at George Mason University, in his book, An Economist Gets Lunch, New Rules for Everyday Foodies, “(To put ethanol into gasoline) costs a lot more money than does traditional gasoline, once the cost of the subsidy is included. Sadly, it does not even make the environment a cleaner place. The energy expended in growing and processing the corn is an environmental cost too…the nitrogen-based fertilizers used for the corn are major polluters. Ethanol subsidies are a lose-lose policy on almost every front, except for corn farmers and some politicians.” “For millions of (people in poor countries) it is literally a matter of life and death and yet we proceed with ethanol for no good reason…(Biofuels) has thrown millions of people around the world back into food poverty.”

According to a recently published article “The economic andenvironmental costs and benefits of the renewable fuel standard” LuoyeChen et al 2021 Environ. Res. Lett. 16 034021, maintaining the corn ethanol mandate at 15 billion gallons until 2030 will lead to a discounted cumulative value of an economic cost of $199 billion over the 2016–2030 period. Their cost estimate includes $109 billion of economic costs and $85 billion of net monetized environmental damages, however; they do not account for the cost of water resources. The additional implementation of the cellulosic biofuel mandate for 16 billion gallons by 2030 increases the economic cost by $69 billion which they find will be partly offset by the net discounted monetized value of environmental benefits of $20 billion, resulting in a net additional cost of $49 billion over the 2016–2030 period.

Currently, feedstocks such as straw and woody plants which are wastes are difficult to use for biofuel production because they first need to be broken down to fermentable sugars, a process that releases numerous byproducts that are toxic to yeast, the microbes most commonly used to produce biofuels. Yet, there are more than a billion tons of cellulosic biomas including switchgrass, wheat straw, and corn stover (what is left in the fields after the corn is harvested). According to a U.S. Department of Energy study this is enough biomass to replace 30%-50% of the petroleum used for transportation if the cellulosic biomass could be cleanly and efficiently turned into ethanol.

Now, MIT researchers have found a way to achieve high yields of ethanol with different types of cellulosic feedstocks, including switchgrass, wheat straw, and corn stover. From MIT News: “The MIT team built on a technique they had developed several years ago to improve yeast cells’ tolerance to a wide range of alcohols. In their new study, the researchers engineered yeast so that they could convert the cellulosic byproduct aldehydes into alcohols, allowing them to take advantage of the alcohol tolerance strategy they had already developed. They tested several naturally occurring enzymes that perform this reaction, from several species of yeast, and identified one that worked the best. Then, the scientists used directed evolution to further improve it.”

Yeast are generally not very efficient at producing ethanol from toxic cellulosic feedstocks; however, when the researchers used their improved enzyme and spiked the reactor with the membrane-strengthening additives, the strain more than tripled its cellulosic ethanol production, to levels matching traditional corn ethanol. “What we really want to do is open cellulose feedstocks to almost any product and take advantage of the sheer abundance that cellulose offers,” says Felix Lam, an MIT research associate and the lead author of the new study.

Gregory Stephanopoulos, the Willard Henry Dow Professor in Chemical Engineering, and Gerald Fink, the Sokol Professor at the Whitehead Institute of Biomedical Research and the American Cancer Society Professor of Genetics in MIT’s Department of Biology, are the senior authors of the paper, which appeared open access in Science Advances.

Though the President has gone all in on electric vehicles looking to transition to half the vehicles sold in the United States to be electric vehicles by 2030, that goal would require more electricity, a re-imagined and modernized grid, charging stations and still there would remain a tremendous number of gas-powered vehicles. The average age of a car in the United States is almost 12 years.  So, even in the world where half of all cars sold in the United States are electric, there would still be fuel burning vehicles for decades to come. Ethanol is a renewable, domestically produced transportation fuel. Whether used in low-level blends, such as E10 (10% ethanol, 90% gasoline), E15 (10.5% to 15% ethanol), or E85 (flex fuel cars) a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season ethanol blends can reduce emissions and be part of the fuel lineup for the future.