Oldendorff and MIT Report on Biofuel Contamination Study
In 2019, Oldendorff Carriers signed a research agreement with the Massachusetts Institute of Technology’s (MIT) Center for Bits and Atoms to investigate disruptive improvements in ship design, propulsion, and alternative energy sources to help achieve the enhanced decarbonization targets to 2050. As part of their agreement, Oldendorff Carriers asked MIT to conduct a study on the long-term stability and degradation of a B20 advanced biofuel blend.
Biofuels offer a drop-in fuel option, reducing GHG emissions from a life-cycle perspective. However, they are more prone to oxidative degradation due to the presence of unsaturated fatty acids, which are inherent in the vegetable oils and animal fats from which they are derived. Therefore, there are concerns about the stability and degradation of biofuel blends with conventional marine fuels over time when stored in vessels’ bunker tanks.
Dr. Patricia Stathatou, the lead of the biofuel degradation study, presented the study findings on November 6, 2023 at the American Institute of Chemical Engineers Annual Meeting in Orlando, Florida.
The study relates to the January 2022 bunkering of the Edwine Oldendorff with an advanced B20 biofuel, consisting of a 20% bio-oil derived from used cooking oil, blended with very low sulfur fuel. Strathatou notes that there is a limited body of research on the degradation of biofuel blends, with existing studies primarily focusing on first-generation biofuels (derived from food-crops) and/or distillate biofuel blends rather than advanced residual biofuel blends.
A biofuel blend is more complex than a homogenous product. “Our study was comprehensive, monitoring eight chemical parameters over an extended one-year period, under a variety of storage conditions. Unlike similar studies in the literature that only focus on just a couple of these parameters, we investigated the impacts of various storage conditions on various parameters. The results of our study will be valuable for both biofuel producers and users, assisting them in planning their bunker storage and maintenance systems accordingly over time.”
The research team analyzed 15 samples of the B20 biofuel blend (Intertek, UK). The 15 samples (volume per sample: 1 L), were divided into three storage groups. Each group was stored at different temperatures: 3oC inside a refrigerator, 23oC at ambient lab conditions, and 50oC inside an incubator. Within each group, there were five samples stored in identical containers: sealed steel container, open steel container, open steel container with 5% water added, sealed steel container with 5% water added, and transparent sealed glass bottles. These storage conditions were selected to closely replicate typical onboard fuel storage conditions. The team investigated the impact of storage temperature, air, light, and water on the fuel quality over time.
The eight chemical parameters were acid value, microbial contamination, total sediment potential, water and sediment, peroxide value, density, viscosity, and oxidation onset temperature. The biofuel blend did not contain any biocide or antioxidant, allowing the researchers to assess its natural degradation over time. Acid value and microbial contamination were tested monthly, while the remaining parameters were tested quarterly from May 2022 to April 2023.
Low levels (<10 colony-forming units (CFU)/ mL) of microbial contamination were observed after the first month of storage in almost all samples, irrespective of storage conditions. Microbial contamination increased over time, reaching almost 50 CFU/mL in samples exposed to light. FAME content in biofuels encourages microbial growth as microorganisms biodegrade natural fats and oils.
Microbial contamination can lead to operational problems, including fouling of tanks, pipes and filters, tank corrosion, and fuel injection equipment damage. Stathatou concludes that biocide addition is highly recommended to preserve blended biofuel for an extended period.
Oxidative degradation began from M3-M6 onward as indicated by a significant increase in peroxide values, a slight increase in acid value, and a slight decrease in oxidation onset temperature. Therefore, addition of antioxidants is recommended together with regular monitoring of fuel quality for long-term onboard storage, especially with higher biofuel blends.
No sediment was generated after thermal ageing, and there was no observed sediment formation or water increase over time.
Stathatou concludes that although exposure to air, water and light contributed significantly to fuel degradation, the impact of storage temperature on degradation remains unclear.