Biodiesel, Renewable Diesel, and Petroleum Diesel: What’s the Difference?

The last thing you want to be doing in an emergency is waiting in line at a convenience store when essential services shut down. In real disasters, fuel shortages occur and can prompt people to consider alternatives to traditional petroleum-based gasoline and diesel fuels. In scenarios like this, it is important to understand which fuels will work and how they are made. In this article, we break down the similarities and differences between three well-known diesel fuels – petroleum diesel, biodiesel, and renewable diesel.

Understanding Biodiesel, Renewable Diesel, and Petroleum Diesel

Diesel is a common fuel often used in medium- and heavy-duty trucks that transport goods and fuel to and from distribution hubs, as well as in fire trucks, ambulances, utility trucks, and other essential equipment that provide critical services to our communities. Diesel is also commonly used in boats and locomotives that transport cargo, people, and commodities, and is often the primary fuel used to power both stationary and mobile backup generators that supply power to hospitals, schools, town halls, and emergency facilities.

The ease of transport and relative fungibility of diesel fuel make it an excellent choice for emergency response. However, diesel is vulnerable to supply scarcity as refineries can be forced to shut down in emergencies such as hurricanes and other natural disasters. Refineries are also vulnerable to armed conflict when essential infrastructure becomes a target, as seen in the ongoing conflict between Ukraine and Russia.

So what’s the difference between petroleum diesel (sometimes called petrodiesel or fossil diesel) and biodiesel? And what’s up with renewable diesel?

As showcased above, petroleum diesel, renewable diesel, and biodiesel are all distinct fuels with their own characteristics, considerations, and quality specifications. Making it even more complicated, these fuels are often blended in varying concentrations with one another due to factors like cost, availability, and operability. 

Some of the key differences in chemical and physical composition between petroleum diesel, renewable diesel, and biodiesel are:

Biodiesel and renewable diesel are two terms that are often confused, but they are, in fact, distinct fuels with different ASTM specifications and chemical structures.

Difference Between Biodiesel and Renewable Diesel

Biodiesel is chemically known as Fatty Acid Methyl Esters, or FAME. This product is made by reacting plant oils and animal fats with alcohol (typically methanol) and a chemical catalyst to remove the glycerin and produce a fuel that is similar to diesel fuel. When reacted with methanol and a catalyst (such as sodium hydroxide), the chemical reaction creates a new substance known as FAME or biodiesel. In order to be legally considered either, it must meet ASTM D6751 quality standards.

While biodiesel can be mixed with petroleum diesel or renewable diesel in varying blends, it is generally not used in blends above B20 due to its cold flow and solvent-like properties. However, mining operations and public and private fleets across the U.S. have successfully used blends like B30, B50, and even B100 with little or no modifications. Recent developments from Optimus Technologies have enabled fleets like PepsiCo and ADM to operate on B100 year-round with their patented Vector upfit and refueling ecosystem.

Renewable diesel is created through a process called hydrotreating, which chemically converts oils and fats into a fuel that meets the ASTM D975 standard for petroleum diesel fuel. This is because renewable diesel is composed of hydrogen and carbon molecules that have a similar structure to petroleum diesel. Because of the chemical similarities of the final product, renewable diesel is often considered a one-to-one replacement for petroleum diesel fuel. However, cold-weather operations are a consideration with renewable diesel due to its make-up as a predominantly parraffinic fuel. As a result, proper isomerization is required to make the fuel fit for winter operations. Highly isommerized renewable diesel tends to be more expensive because of yield losses in the process.

Performance and Environmental Impact

If you already have a diesel engine and are interested in alternative fuel for it, there’s an understandable concern about which diesel fuel will perform the best. Below, we compare the three types of diesel — petroleum, biodiesel, and renewable diesel, across key metrics such as fuel economy, emissions, and environmental impacts.

Petroleum Diesel

Fuel efficiency: Diesel engines are typically about 10 -15% more fuel efficient than gasoline engines, which is one reason why diesel use is popular in long-haul trucks. The better fuel economy can lead to significant savings over longer periods.

Emissions: Diesel engines produce a number of emissions that have concerns for human health, including carbon dioxide, sulfur, carbon monoxide, and particulate matter. These are what produce “smog,” or the hazy cloud that can affect breathing. However, modern diesel engines are equipped with after-treatment technologies that reduce the most concerning emissions by up to 99% compared to engines produced prior to 2000.

Environmental Impacts: Diesel fumes can damage the ozone and produce acid rain, which affect the water and food supply. The lifecycle carbon emissions are petroleum diesel fuel are also considerable, with every gallon of diesel fuel releaseing approximately 22.38 pounds of carbon dioxide (CO2) into the atmosphere.

Biodiesel

Emissions: Biodiesel doesn’t contain sulfur, which removes one of the key polluting elements of diesel fuel – and that signature rotten-egg smell. It also contains more oxygen and tends to burn more completely, reducing emissions of PM, HCs, and CO. Engines may need adjustment to reduce the nitrous oxide (NOx) emissions that may be created by biodiesel blends over B20. Over time, biodiesel has been shown to reduce engine and DPF wear and lower overall maintenance costs.

Environmental Impacts: Biodiesel diverts feedstocks like excess soybean oil from soybean meal production, used cooking oil, and animal fats from landfills and repurposes them into a low-carbon fuel. On a lifecycle greenhouse gas emissions basis, biodiesel lowers emissions by up to 86% compared to petroleum diesel.

Fuel Efficiency: Biodiesel has slightly less energy per volume than petroleum diesel – about 2-5% less. Although biodiesel may be slightly less fuel-efficient, the difference is often minimal or undetectable as variability in driving styles impact fuel economy at a greater level. Fleets like ADM have also experienced slight improvements in MPGs when using B100 biodiesel with the Vector System from Optimus Technologies.

Renewable Diesel 

Fuel Efficiency: Because its chemical structure is nearly identical to petroleum diesel, renewable diesel has about the same fuel efficiency as petroleum diesel, despite having around 4% less energy content. Renewable and petroleum diesel are hydrocarbon fuels. Renewable diesel is considered a drop-in fuel, meaning it can replace petroleum diesel fuel on a one-to-one basis. 

Emissions: Renewable diesel is often made from waste products, such as used cooking oil and animal fats, because of the carbon credit value they generate when participating in low-carbon fuel standards in places like California and British Columbia. Renewable diesel burns cleaner than petroleum diesel, significantly reducing emissions of SO2, NOx, CO, PM, and HCs.

Environmental Impacts: Renewable diesel can be made from the same renewable materials as biodiesel, but with a slightly more carbon-intensive manufacturing process. Like biodiesel, renewable diesel reduces lifecycle greenhouse gas emissions by more than 70% on average.

Compatibility and Practicality in Existing Engines

Renewable diesel and biodiesel sound like great options for producing our own energy-efficient, low-polluting, renewable fuel. So why doesn’t everyone use them? Well, the answer is complicated.

Because the way we produce fuel, build engines, and distribute these goods was all built around petroleum, the newer renewable energy fuels need some adjustments to replace the existing fuel system. Biodiesel often requires additional heating and additives for winter operations, while renewable diesel typically requires additional processing at the refinery. In both cases, additional costs are associated. It is important to note that in some cases renewable diesel requires the same heating systems as biodiesel.

Engine Compatibility 

Biodiesel often needs to be blended with petroleum diesel to work with most engines. A blend of 20%, known as B20, is generally accepted by OEMs and is widely used by fleets across the United States, Canada, and Europe. However, recent technological advancements and improvements in biodiesel quality have led some OEMs to approve blends up to B100 as fleet operators like PepsiCo, Convenant Logistics, and ADM look to decarbonize operations.  

Modifications to the fueling system and engine allow the units to run up to 100 percent biodiesel, or B100, utilizing a two-tank system. A smaller tank holds petroleum diesel, which is used to start the engine and warm both tanks. Then, a built-in sensor switches over to the B100 tank and runs the engine entirely on biofuel unless a regeneration (regen) of the diesel particulate filter (DPF) is needed. When a DPF regen is needed, the system defaults back to petroleum diesel or renewable diesel. This is because biodiesel has a higher flash point and may not burn completely in some DPF systems.

Unlike biodiesel, most engines don’t need any modification to run renewable diesel. However, renewable diesel is a dry fuel and often requires lubricity additives, of which biodiesel is a low-carbon option. For this reason, the ASTM D975 standard allows for up to 5 percent (B5) biodiesel blended into petroleum diesel or renewable diesel without the need to label the fuel.

Blending Options

Biodiesel is typically blended by splash blending or in-line injection blending at the terminal to ensure proper mixing of the finished fuel. Users may also opt to blend on-site. When blending on-site, operators must ensure proper blending through the use of in-tank agitators or in-line blending at the dispenser. Once biodiesel is properly blended, it does not come out of solution.

When blending biodiesel with petroleum-based diesel, it is essential that operators carefully label the resulting fuel blend according to the percentage of petroleum diesel it contains. B20 (20% biodiesel/80% diesel), B50 (50% biodiesel/50% diesel), etc.

Specific guidance on blending, handling, and storage of biodiesel is available from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL). NREL’s Biodiesel Handling and Use Guide is a great starting point for those interested in blending their own fuel.

Cost Considerations

There are several government incentives in place to promote the production and blending of biodiesel and renewable diesel into the diesel fuel market. Available incentives include:

Production Costs 

Biodiesel has the lowest production costs between renewable diesel and biodiesel as it’s a relatively simple chemical process called transesterification. The chemicals used in the process – typically lye and methanol or ethanol – are inexpensive and readily available. However, the rising cost of feedstocks for use in other fuel markets, namely renewable diesel and sustainable aviation fuel, have increased the cost of production in recent years.

Renewable diesel production costs are typically higher than biodiesel because it requires a full-scale petroleum refinery to produce the fuel. This is why renewable diesel is chemically similar to petroleum diesel – because they are both hydrotreated to create hydrocarbon fuels. Differences between the production process include the utilization of unique catalysts and additional isomerization to improve the cold flow properties of renewable diesel – a process that leads to loss of yield and additional costs.

Current Market Pricing 

The pricing for the three primary fuels varies widely depending on your region. If you live in a state or locality with a low-carbon fuel standard, incentive, or blending standard, biodiesel and renewable diesel will most likely be available at a lower price point than petroleum diesel. Similarly, if you live in a state with nearby diesel refining, the cost of petroleum diesel will likely be lower than in states without access.

You can track prices at the Alternative Fuels Data Center here. For example, as of April 2024, United States national average prices per gallon were:

While there is often an increased cost for biodiesel and renewable diesel fuel, the reduced carbon emissions and available incentives can make it a good option. 

Source: Alternative Fuels Data Center 

Long Term Maintenance 

Biodiesel has a higher concentration of oxygen than petroleum diesel and renewable diesel. This helps it burn cleaner, reducing tailpipe emissions and limiting certain chemical deposits in your engine.  It also has a higher lubricity, which means it acts as an engine lubricant. This can be a good thing, as it reduces wear and tear on the engine. 

Because of its higher cloud point, biodiesel can start to gel at higher temperatures than petroleum diesel and renewable diesel. This can clog engine filters, meaning they need to be replaced more often. However, modern winter additives and vehicle upfit technologies can easily overcome biodiesel’s cold-weather operability challenges.

It is important to note that the quality of biodiesel significantly impacts the amount of maintenance required. High-quality biodiesel is less likely to cause maintenance problems than lower-quality biodiesel. It is recommended that end-users or fuel marketers source biodiesel from a BQ-9000 accredited producer to ensure all quality standards and protocols are followed.

Renewable diesel is a relatively new fuel that has shown promise in the diesel industry, with OEMs such as Cummins, Detroit Diesel, and PACCAR providing support for up to 100% blends of the fuel. OEMs and fleet operators have also noted improvements in maintenance when using renewable diesel. Similarly, fleets have noted the need for a lubricity enhancer in renewable diesel, often turning to biodiesel to boost lubricity in the finished fuel.

Whether you own a large trucking fleet or a gas station, having a dependable fuel delivery service is a cost-effective way to get top-quality fuel for your business — partner with SC Fuels to get bulk diesel, renewable diesel, and biodiesel fuel delivery straight to your location.

Conclusion

While there are certainly considerations that need to be made when making the transition to biodiesel or renewable diesel, most would agree that the benefits far outweigh the potential problems. The market growth in the biodiesel and renewable diesel space is only going to continue as both fuels becomes more readily available to consumers. While most diesel vehicles are already running some level of biodiesel or renewable diesel in most states, considering higher blends in emergency situations will help to extend fuel supplies while benefiting the environment and the equipment you operate each and every day.

Article adapted from Car and Driver and others.