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.
No comments:
Post a Comment