6 Disadvantages Of Biodiesel You Should Know Before Switching Fuel Types

In recent years, we've made good progress towards greener transportation -– hydrogen cars have hit the market, and we've seen a steady uptick in EV adoption. However, each technology has major problems, like a lack of charging infrastructure and aftermarket support. The answer to pollution from vehicles then, at least in the short term, seems to lie with biofuels. Unlike fossil fuels (which, as the name suggests, come from fossils), biofuels are made with things that were, until recently, living matter. For the vast majority of biofuels, this source living matter is plants –- things like sugarcane and spent cooking oil, for example –- but things like animal fat can also be used. 

Biodiesel is a subcategory of biofuel, and it can be created from basically any triglyceride oil, such as sunflower oil, canola oil, and even animal fat like tallow. The process involves transesterification, which we'll explain in the next section, but it's basically a process that makes the organic matter into usable diesel. Furthermore, 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. If you're looking to find a biodiesel pump near you, you can use the Alternative Fueling and Charging Stations map, published by the U.S. Department of Energy.

As we mentioned earlier, the process will start with a triglyceride-based oil, at least for commercial biodiesel manufacturing. A process called transesterification happens, wherein 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.

As you can imagine, the process is more complicated and time-consuming than for producing conventional diesel. Along with all the specialized equipment that is required to make biodiesel, the raw material cost is also staggering. That cost of the source material — feedstock — is the main reason why biodiesel is more expensive than conventional diesel, as we'll explain in the next section. Until and unless the cost of acquiring the initial triglyceride feedstock oils like canola and soybean (which end consumers also want) comes down drastically, biodiesel will likely remain more expensive then conventional diesel. 

Now, among the many benefits that biodiesel has over conventional diesel are the fact that it burns cleaner, has a lower carbon footprint, and can improve the longevity of components inside the fuel system due to better fuel lubricity. However, it's not without its downsides; here are six ones that are quite major.

Biodiesel's main issue at the moment is the price. Historically, while B20 diesel has not deviated much from the price of conventional diesel, only costing a few cents more -– and in some weeks being cheaper than diesel for short periods -– this is not the case with "pure" B99 or B100 biodiesel. Looking at information published by the Alternative Fuels Data Center (AFDC) run by the U.S. Department of Energy, we can see that B99 or B100 diesel has never dipped below the price of conventional diesel. 

The closest that the two diesels came was in April of 2022, when conventional diesel was $4.50 a gallon, while B100 was $4.96, meaning it was a hair over 10 percent more expensive. Considering that 10 percent is a lot of cost over the lifetime of a vehicle, especially for commercial operations that can consume thousands of gallons per year, that's a meaningful cost that operators cannot ignore. By some estimates, semi trucks spend upwards of $70,000 on diesel a year, so a 10 percent increase on that base cost would be an additional $580 a month in operating costs. However, consider that 6 percent of all energy consumed in the U.S. -– and a whopping 22 percent of the transport industry's energy –- comes from diesel, according to the U.S. Energy Information Administration. So, shifting to biofuels that can save up to 86 percent on greenhouse emissions is a real benefit; it just doesn't make commercial sense to do so yet.

One of the most pressing problems faced by biodiesel is that it has less energy than conventional diesel. The industry standard measure as to how much energy a particular diesel contains is measured in British Thermal Units (BTUs). One BTU is the amount of heat that would be needed to increase one pound of water by one degree Fahrenheit. 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. 

Now, logically, this doesn't matter much for low-bio blends like B5 diesel –- since the biodiesel is less than five percent, so there are no major efficiency losses. However, on higher blends, should they become mandated in the future, this might pose problems since the same amount of fuel would effectively take you less far. 

When coupled with the fact that the cost of using B100 biodiesel is about 10% higher than unblended or B5 diesel as we mentioned above, you quickly begin to see the problem. Not only is the acquisition price of biodiesel higher, but you also need more of it to go the same distance, which means you'll have to buy more gallons of the stuff. All of these seemingly minor percentages add up over each trip for each vehicle, and that can quickly eat into margins, especially for commercial enterprises.

Cold weather operations have always proven troublesome for conventionally fueled vehicles, but, for the most part, diesel manages to hold its own. 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.

Biodiesel Education/YouTube

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. For obvious reasons, we want our fuel to remain liquid so that it can circulate in the system, get through the injectors, and combust in the engine. 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 an eventuality with all forms of diesel, but conventional diesel is overall less prone to oxidization than biodiesel –- the process of a substance binding with oxygen from the air. The main issue here is that it is much easier for biodiesel to oxidize when stored incorrectly, often within six months, where conventional diesel can take much longer. Now, when pure biodiesels like B100 begin to oxidize, the acidity of the fuel will start to increase. Acids are corrosive to metals, which means the acidic fuel will eat away at metallic fuel system parts. If the oxidation reaction is allowed to continue, then the fuel will break apart and form different gums and polymers that will build up over time and render the fuel useless. 

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.

Now, let's get one thing clear before we begin explaining this point -– B20 biodiesel is considered a "drop-in" fuel. This means no vehicular modifications are needed to safely run biodiesel in consumer-grade modern vehicles, as it's meant as a full replacement for conventional petrodiesel. However, the issue arises when someone needs to use a high biodiesel blend like B99 or full biodiesel like B100. That's because the higher biodiesel blends (or pure biodiesel) have a much higher viscosity when compared to a consumer blend like B20 or regular diesel. 

The viscosity of a liquid fuel is measured in units called mm²/s –- sometimes called centistokes –- and international standards dictate that the measurement of fuel viscosity is to happen at 104 degrees Fahrenheit. If you're curious, those standards are ASTM D975, ASTM D7467, and ASTM D6751 for conventional petrofuels, B6–B20, and B100, respectively. Conventional U.S. no. 2 diesel has a low-end viscosity of about 2.0 mm²/s, while B20 has one of 3.0 to 5.8 mm²/s. 

Both of these fall within the allowable viscosity limit (which is 4.1 mm²/s at 104 degrees Fahrenheit), though some B20 blends might be pushing the limit. B100 biodiesel usually also falls within that range, but it becomes significantly more viscous as temperatures drop. Regular fuel systems would not be able to handle pure biodiesel or high-biodiesel blends properly, and it's impractical to assume that everyone would be able to keep their tanks at 104 degrees Fahrenheit at all times.

The entire purpose of inventing and using biodiesel was to have a better impact on the environment and to reduce dependence on fossil fuels, which are a finite resource. To begin with, biodiesel made from things like waste cooking oil –- also known as WCO in the industry –- and animal fats, that can greatly reduce carbon emissions when compared with conventional petroleum-derived diesel. However, major commercial operations tend to use crop-based feedstock -– "feedstock" is the term used to describe the organic matter that will eventually become biodiesel. 

The carbon-saving benefits of using crop-based feedstock are hotly debated, with consensus being that it's not as good as WCO or animal fat. Using crops (like rapeseed, soy, or palm) to make biodiesel also naturally carries with it the risk of indirect land-use change –- deforestation is a big example of that. Additionally, it raises the question of whether or not a fuel is more important than food; with the possibility of biodiesel production becoming lucrative in the future, farmers might opt to produce diesel feedstock in lieu of food crops for human consumption. 

Now, none of this is hard fact, but it is one of the disadvantages of biodiesel that needs to be thought about long and hard. It's not all doom and gloom though, as biodiesel has many benefits, including 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.

While it may seem that biodiesel and other biofuels have a bleak future, this is certainly not the case. While the ability to make "moonshine diesel" (as we like to call it) has existed for decades, it's still a very nascent technology at a commercial scale. And like all new technologies and production processes, it will also have teething problems. Yet, year on year, we're seeing new advancements being made in the field; as time passes, regulators around the world are opening up to the idea of backing biofuel production more and more. 

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.