Stability and Degradation of Biofuel

7th November 2023

In 2019, Oldendorff Carriers signed a research agreement with the Massachusetts Institute of Technology’s (MIT) Center for Bits and Atoms (CBA). The purpose of the research agreement was 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. Oldendorff would like to share the results of the study with the shipping community to help progress the path toward decarbonization.

One of the alternative energy sources that Oldendorff Carriers has been testing on our ships is the use of second-generation advanced biofuels. Biofuels offer a drop-in fuel option, reducing GHG emissions from a life-cycle perspective (as shown by a previous Oldendorff-MIT study) 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.

For those interested in the findings of the study, the following information explains the study procedures and conclusions.

Dr. Patricia Stathatou, the lead of the biofuel degradation study, was a Research Scientist at the MIT Center for Bits and Atoms when the project started in April 2022. She has recently moved to the Georgia Institute of Technology, where she is a Research Faculty at the Renewable Bioproducts Institute. Patricia is also still affiliated with the MIT, Center for Bits and Atoms.

In January 2022, our vessel, Edwine Oldendorff, bunkered with an advanced B20 biofuel, consisting of a 20% bio-oil derived from used cooking oil, blended with very low sulphur fuel. Furthermore, 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, as in our case.

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.

We analysed 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, i.e., 3 oC inside a refrigerator, 23 oC at ambient lab conditions, and 50 oC inside an incubator. Within each group, there were 5 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. We investigated the impact of storage temperature, air, light, and water on the fuel quality over time.

The 8 chemical parameters that we tested 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 us 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.

After a thorough analysis, fuel degradation was observed:

  • Low levels (<10 CFU/ mL)1 of microbial contamination (MBC) were observed after the first month of storage in almost all samples, irrespective of storage conditions. MBC 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. MBC can lead to operational problems, including fouling of tanks, pipes and filters, tank corrosion, and fuel injection equipment damage. Conclusion: 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. 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.
  • Although exposure to air, water & light contributed significantly to fuel degradation, the impact of storage temperature on degradation remains unclear.

Patricia presented these findings on November 6, 2023 at the American Institute of Chemical Engineers (AIChe) Annual Meeting in Orlando, FL, during the session titled “Advances in Biofuels Production and Alternative Fuels I”, which focused on advanced biofuels and alternative fuels for decarbonizing aviation and maritime industries. Her presentation was titled “Assessing the long-term stability & degradation of an advanced marine biofuel blend”.

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  • CFU/mL - colony-forming units per milliliter