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Recent advancements in greener transportation, such as electric vehicles (EVs) and hydrogen cars, have shown promise but still grapple with significant issues like a lack of charging infrastructure and aftermarket support. In the short term, biofuels, and specifically biodiesel, appear to offer a viable solution to vehicle-related pollution. Unlike fossil fuels, which originate from ancient organic matter, biofuels are derived from recently living biological materials, including plants like sugarcane and spent cooking oil, as well as animal fats.
Biodiesel, a subcategory of biofuel, can be produced from virtually any triglyceride oil, such as sunflower oil, canola oil, and animal fats like tallow. The manufacturing process involves 'transesterification,' which effectively converts organic matter into usable diesel fuel. In the U.S., biodiesel availability is indicated by a 'B' number at the pump: B5, containing 5% biodiesel blended with conventional diesel, is widely accessible and permitted for sale without explicit disclosure under federal law. B20, with 6-20% biodiesel, is comparatively harder to locate, while B100, pure unblended biodiesel, is primarily utilized by commercial operators. The U.S. Department of Energy's Alternative Fueling and Charging Stations map serves as a resource for finding nearby biodiesel pumps.
The commercial production of biodiesel typically commences with a triglyceride-based oil. The transesterification process involves introducing an alcohol and a catalyst to the oil, resulting in the creation of usable fatty-acid methyl esters (FAME) and glycerol. The FAME is subsequently refined into biodiesel, while glycerol also serves various commercial purposes.
It is worth noting that biodiesel production is more intricate and time-consuming than conventional diesel manufacturing, necessitating specialized equipment. Furthermore, the cost of raw materials, or 'feedstock,' is substantial. This high cost of initial triglyceride feedstock oils, such as canola and soybean (which are also in demand by end consumers), is the primary reason why biodiesel remains more expensive than conventional diesel. Unless these feedstock costs experience a drastic reduction, biodiesel is likely to maintain its price premium.
While biodiesel boasts numerous advantages over conventional diesel, including cleaner combustion, a lower carbon footprint, and enhanced longevity for fuel system components due to superior lubricity, it is not without its drawbacks. Here are six significant disadvantages that impact its broader adoption.
**1. Price:** The most prominent issue for biodiesel is its price. Historically, while B20 diesel has generally mirrored conventional diesel prices, 'pure' B99 or B100 biodiesel has consistently been more expensive. Data from the Alternative Fuels Data Center (AFDC), managed by the U.S. Department of Energy, indicates that B99 or B100 has never dropped below the price of conventional diesel. In April 2022, for instance, conventional diesel was priced at $4.50 per gallon, whereas B100 was $4.96, representing a premium of just over 10%. For commercial operations consuming thousands of gallons annually, this 10% increase translates into a meaningful additional cost; a semi-truck spending upwards of $70,000 annually on diesel would incur an extra $580 per month in operating expenses. Despite the potential to reduce greenhouse gas emissions by up to 86%, the commercial viability remains a hurdle, particularly given that diesel accounts for 6% of total U.S. energy consumption and a substantial 22% of the transport industry's energy needs.
**2. Lower Energy Content:** Biodiesel possesses less energy per unit volume than conventional diesel, a factor measured in British Thermal Units (BTUs). A U.S. gallon of conventional, unblended diesel contains approximately 129,000 BTUs. In contrast, B5 contains about 128,450 BTUs (0.4% lower), B20 contains 126,800 BTUs (1.7% lower), and B100 contains roughly 119,500 BTUs (8.4% lower). While this difference is negligible for low-bio blends like B5, higher blends, if mandated in the future, could lead to reduced vehicle range for the same amount of fuel. When coupled with the 10% higher cost of B100, this necessitates purchasing more gallons to cover the same distance, a factor that can quickly erode profit margins for commercial enterprises.
**3. Poor Cold Weather Performance:** Operations in cold weather have always posed challenges for conventionally fueled vehicles, but petrodiesel generally performs adequately. Biodiesel, however, is at a disadvantage due to its 'cloud point' and 'gel point.' The cloud point is the temperature at which wax crystals begin to form in the fuel, potentially impairing engine performance. The gel point, or pour point, is when the fuel solidifies to an extent that hinders its flow, effectively turning it into a sticky gel. For optimal engine function, fuel must remain liquid. Conventional U.S. petrodiesel typically has a cloud point of around 20 degrees Fahrenheit and a gel point of about 0 degrees Fahrenheit (with additives), making it reliable across most of the continental U.S. In stark contrast, B20 has a gel point of 22 degrees Fahrenheit, and B100 can begin to gel at 26 degrees Fahrenheit, rendering them unsuitable for many colder climates.
**4. Oxidation and Storage Instability:** While all forms of diesel are susceptible to oxidation (the process of binding with oxygen), conventional diesel is generally less prone to it than biodiesel. The main concern is that biodiesel oxidizes much more readily when stored improperly, often within six months, whereas conventional diesel can last significantly longer. When pure biodiesels like B100 begin to oxidize, the fuel's acidity increases. This acidic fuel is corrosive to metallic fuel system components. If the oxidation reaction continues unchecked, the fuel degrades, forming gums and polymers that accumulate, rendering the fuel unusable. These oxidation reactions are irreversible and can be worse in B20 biodiesel than in B100; in B20, gums tend to clump together, potentially clogging various parts of the fuel system, an expensive fix. However, governing standards like ASTM D6751 mandate that all commercial biodiesel must pass stringent oxidation tests before market release. Additionally, additives such as Pyrogallol can slow the oxidation process for long-term storage, though it remains an operational hassle for biodiesel users.
**5. Higher Viscosity:** B20 biodiesel is considered a 'drop-in' fuel, meaning it requires no vehicle modifications for safe use in modern consumer-grade vehicles as a replacement for conventional petrodiesel. However, challenges arise when using higher biodiesel blends like B99 or pure B100 because they exhibit significantly higher viscosity compared to B20 or regular diesel. The viscosity of liquid fuel is measured in mm²/s (centistokes) at 104 degrees Fahrenheit. Conventional U.S. No. 2 diesel has a low-end viscosity of approximately 2.0 mm²/s, while B20 ranges from 3.0 to 5.8 mm²/s. Both typically fall within the allowable viscosity limit of 4.1 mm²/s at 104 degrees Fahrenheit, though some B20 blends may approach the upper limit. While B100 usually also falls within this range, its viscosity increases dramatically as temperatures drop. Standard fuel systems are not equipped to handle the high viscosity of pure biodiesel or high blends effectively, and maintaining tank temperatures at 104 degrees Fahrenheit at all times is impractical for general use.
**6. Indirect Land-Use Change and Food vs. Fuel Debate:** The fundamental purpose of developing biodiesel was to improve environmental impact and reduce reliance on finite fossil fuels. Biodiesel derived from waste cooking oil (WCO) and animal fats can substantially reduce carbon emissions compared to petroleum-derived diesel. However, major commercial operations frequently rely on crop-based feedstock. The carbon-saving benefits of crop-based feedstock are highly debated, with a general consensus that they are not as significant as those from WCO or animal fat. Utilizing crops (e.g., rapeseed, soy, palm) for biodiesel production inherently carries the risk of indirect land-use change, such as deforestation. Moreover, it sparks the ethical debate regarding the prioritization of fuel over food; if biodiesel production becomes highly lucrative, farmers might be incentivized to cultivate fuel crops instead of food crops for human consumption.
Despite these existing disadvantages, the future of biodiesel and other biofuels is far from bleak. While the capability to produce 'moonshine diesel' has existed for decades, it remains a nascent technology at a commercial scale, and like all emerging technologies, it faces initial teething problems. Nevertheless, continuous advancements are being made annually. Regulators globally are increasingly supporting biofuel production. For instance, recent developments include the commercially viable production of biodiesel via plasma-assisted transesterification, a process that completes in mere seconds. Companies are also exploring the incorporation of nanoparticles (e.g., cerium oxide) into fuel mixtures to both enhance engine performance and further reduce emissions. Additionally, new machinery innovations enable the on-site conversion of glycerol byproducts into more lucrative substances, which could generate more revenue for producers and potentially translate into consumer savings, thereby lowering biodiesel prices. Given sufficient time, biodiesel may well achieve price and energy competitiveness with conventional diesel, addressing its two most significant challenges.
Source: SlashGear