Biofuels are
seen as one of the major solutions to decarbonizing transportation, especially
heavy-duty transportation like long-haul trucking and aviation. Plants are the
major source of biofuels, which makes them competitive with animal feed and
human food in many cases, such as corn ethanol and sugarcane biofuels. Slash
Gear published an article noting six disadvantages of biodiesel, a biofuel that
is a drop-in fuel that can be added to or replace diesel fuel. They note that
biodiesel is already commonly blended with diesel at gas pumps.
“Biodiesel is widely available across the U.S., denoted
by the "B" number at your pump. For instance, B5 has 5% biodiesel
blended with conventional diesel, and federal law allows pumps to sell it
without disclosing it to the customer. B20 contains between six and 20 percent
biodiesel, and is comparatively harder to find; B100 is pure unblended
biodiesel and you really only see commercial operators use this."
Biodiesel is made through a
process known as transesterification, shown below. In this process:
“…an alcohol and a catalyst are added to the oil, which
gives us usable fatty-acid methyl esters, or FAME. While this is a gross
oversimplification, the reaction happens multiple times over, and at the end,
you're left with FAME and glycerol. The FAME is then turned into biodiesel, and
the glycerol also serves commercial purposes.”
Unfortunately, biodiesel is
more expensive than diesel, and that is not likely to change. There are,
however, also some distinct advantages of biodiesel. These include less pollution,
less carbon emissions, and superior fuel lubricity, which can improve the longevity
of components inside the fuel system. The third of the three confers direct
economic advantages, and the first two confer societal advantages.
Disadvantage #1 – Higher Cost
The cost disadvantage is not
bad. The B20 is typically only a few cents higher in cost than diesel. B100 got
closest to diesel in price in 2022 when it was $4.96 per gallon compared to
diesel, which was $4.50 per gallon, just slightly more than a 10% increase.
While that may seem like a reasonable extra cost for some consumers, for those
who use thousands of gallons per year, it is significant.
Disadvantage #2 – Lower Energy Content
“Where conventional, unblended diesel has about 129,000
BTUs per U.S. gallon, B5 has about 128,450 – so it's 0.4 percent lower. B20 has
126,800, B100 has approximately 119,500; this makes B20 about 1.7 percent less
efficient than conventional diesel, and B100 about 8.4 percent lower.”
Of course, that energy
content disadvantage adds to the cost disadvantage. It also means a tankful of
biodiesel won’t take one as far as a tankful of diesel. They note that blends
like B5 won’t be noticed in terms of energy content, but if mandates eventually
require higher blending amounts, say, B20, then a full tank won’t go as far.
For commercial operations, this adds very significantly to the cost when added
to the cost disadvantage.
Disadvantage #3 - Biodiesel Can Turn to Gel Easily in Cold
Weather Due to Cloud Point and Gel Point
“To understand why biodiesel is at a disadvantage to
conventional petrodiesel here, you need to know about cloud points and gelling
points. A cloud point in a fuel is the particular temperature where wax
crystals begin to appear in the fuel, which can begin to hamper performance in
engines. The image below shows three different kinds of diesel after having
passed their respective cloud points.”
“On the left you have regular petroleum-based U.S.
diesel, and the other two are biomass derivatives. The second thing you need to
know is the gel point, sometimes called the pour point, and the clue is in the
name. For fuels, the pour point is where the fuel solidifies to a degree where
its flow is hindered, and it cannot easily be poured –- in other words, the
temperature past which diesel turns into a sticky gel.”
“Conventional U.S. petrodiesel has a cloud point of
about 20 degrees Fahrenheit and a gel point of about 0 degrees Fahrenheit with
additives. This means it can reliably be used in those temperatures, which
covers most of the mainland U.S. landmass. B20, for contrast, has a gel point
of 22 degrees Fahrenheit, and B100 can begin to gel at 26 degrees Fahrenheit.”
This is a pretty severe
difference in gel points, even in B20, which essentially limits it to seasonal
use.
Disadvantage #4 - Biodiesel Can Oxidize if Stored
Incorrectly
While
conventional diesel also oxidizes, biodiesel oxidizes more readily. Biodiesel
can oxidize within six months if stored incorrectly, while diesel will take
much longer. When biodiesel oxidizes, it creates acids that are corrosive to
engine metal parts, which eventually form gums and polymers that can clog up
fuel systems.
“These oxidation reactions are irreversible, and are
actually worse in B20 biodiesel than in B100. You see, when the gums and gels
form in B100, they get held within the fuel mixture quite well (and remain
dissolved), but in blends of fuel, the gum pulls together in clumps. This, once
again, can clog various parts of the fuel system, and would likely be a rather
expensive fix. However, governing standards such as the ASTM D6751 dictate that
any commercial biodiesel must pass a strict oxidation test before hitting the
market. Furthermore, for long term use, additives such as Pyrogallol can slow
the oxidation process, but it's still a hassle that biodiesel users have to go
through.”
It seems like this
disadvantage is surmountable, but requires correct fuel storage practices.
Disadvantage # 5 - Specialized Fuel System Upgrades Are
Required for Some Vehicles to Use Biodiesel
This is
only an issue for using higher biodiesel blends. B20 is a drop-in fuel and does
require upgrades. However, B99 and B100 have much higher viscosities and
require a higher sustained temperature to keep the viscosity low enough. The
problem is worse in cold weather. Thus, for most vehicles, B20 is likely the
highest amount of biodiesel that can be used, unless the fuel system is
upgraded at additional cost.
Disadvantage #6 – Biodiesel is Not Necessarily Carbon
Neutral
This is not so much a
disadvantage as a check on a perceived societal advantage. The carbon footprint
of biodiesels depends on the source. Biodiesel made from used vegetable oil, a
very limited source, has a lower carbon footprint than biodiesel made from
plant-based feedstock. Here, they also note some advantages of biodiesel:
“…reducing up to 85 percent or more of greenhouse gas
emissions, being biodegradable and safer to handle. With advancements in
technology, we're sure that it'll soon be competitive on price too.”
The Future of Biodiesel
Despite all the disadvantages
of biodiesel, they think its future is looking good and that some of the
disadvantages can be reduced or even overcome, and more advantages can arise.
“For example, one of the latest developments is the
now-commercially-viable production of biodiesel via plasma-assisted
transesterification, which is a process that finishes in mere seconds.
Companies are also experimenting with the addition of nanoparticles (such as
cerium oxide) to the fuel mixture to not only increase engine performance but
also further reduce emissions.”
“Additionally, new machinery advances mean that the
glycerol byproducts can be converted to more lucrative substances onsite, which
could be more revenue for the company — and may get passed down as savings to
the consumer, further lowering the price of biodiesel. Given enough time,
biodiesel might just become competitive on price and energy with conventional
diesel. With those being its two biggest challenges, things are looking bright.”
This was a really
informative and educational article.
References:
6
disadvantages of biodiesel you should know before switching fuel types. D Figg.
Slash Gear. August 1, 2026. 6
disadvantages of biodiesel you should know before switching fuel types
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