Frehiwot Hailu | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Frehiwot Hailu. This seminar is open to the general public to attend.

MSc with Dr. David Bressler.

Thesis Topic: Desulfurization of Low-Value Agricultural Lipid Feedstocks and the Resulting Diesel for Renewable Fuel Applications

Abstract: 

Generating energy is essential for global socio-economic development and fundamental for producing valuable goods and services. Fossil fuels are the predominant source of energy now. However, their limited supply and environmental harm from greenhouse gas emissions make them unsustainable, necessitating the need for eco-friendly, renewable fuels. Renewable energy, replenished naturally within a short time frame, offers a sustainable alternative. Among renewable sources, biomass, particularly non-edible lipid feedstocks like plant oils and animal fats, is especially promising due to its high energy density and simpler structure. Converting these lipids into biofuels is attractive for sustainable energy production, waste management, and public health benefits. These biofuels are compatible with existing infrastructure and possibly can address environmental and energy concerns.

Sulfur compounds are among the most common impurities in transportation fuels. Their emission during combustion poses serious environmental and health risks, including acid rain, ecosystem disruption, respiratory issues, and equipment corrosion. In response, global regulations mandate a sulfur content cap of around 15 ppm in diesel fuels, driving research into effective desulfurization techniques. Desulfurization is a process that efficiently removes sulfur from different types of samples. Therefore, this study focuses on removing sulfur compounds from poultry fat (100.0 ± 0.8 ppm), brown grease (515 ± 5 ppm), hardwood (1490 ± 40 ppm), and softwood (2040 ± 40 ppm) crude tall oils, to be used for renewable fuel applications.

The first approach assessed desulfurization techniques, including solvent extraction, oxidation, ultrasonication, and adsorption, to eliminate sulfur from feedstocks. Solvent extraction with water, acetonitrile, methanol, and diethylene glycol mono ethyl ether separated sulfur compounds based on polarity difference. The oxidative desulfurization method used glacial acetic acid and hydrogen peroxide to oxidize sulfur-containing compounds to sulfoxides and sulfones. The study investigated the influence of temperature, catalyst-oxidant molar ratio, and catalyst-oxidant concentration relative to feedstock on sulfur removal, achieving the highest removal at 90 °C, 1:3.57, and 36.5% w/w, respectively. Ultrasonic-assisted oxidative desulfurization using water significantly reduced sulfur levels in poultry fat through cavitation effects. The potential of adsorbents was explored in adsorptive desulfurization, with Al-MCM-41 exhibiting superior performance in poultry fat and brown grease despite separation challenges.

In summary, for poultry fat and brown grease, the most effective method was ultrasonic-assisted oxidative desulfurization and extractive desulfurization using water as a solvent, achieving sulfur removal efficiencies of 78.9 ± 0.4% (21.1 ± 0.3 ppm) and 50 ± 1% (257 ± 3 ppm), respectively. For hardwood and softwood crude tall oils, adsorptive desulfurization with raw bentonite clay was the most effective, with removal efficiencies of 49 ± 3% (760 ± 30 ppm) and 36 ± 2% (1300 ± 20 ppm), respectively.

The second approach of the study examined sulfur removal during the thermochemical conversion of non-food lipid feedstocks into diesel equivalents. The process involved hydrolysis to break acylglycerols into free fatty acids, followed by pyrolysis, converting them into hydrocarbons. Caustic washing of pyrolyzed products reduced the sulfur content by separating the hydrocarbons from unconverted free fatty acids that could trap sulfur compounds. Distillation of caustic-washed samples refined diesel-equivalent products by enhancing purity and reducing sulfur content. Hence, the thermochemical conversion process significantly lowered sulfur content by 56 ± 1% in poultry fat-derived diesel (43.9 ± 0.6 ppm) and by 78.4 ± 0.4% in brown grease-derived diesel (111 ± 2 ppm). The comprehensive method greatly improved the quality of the final diesel products, showcasing its ability to develop renewable fuel while protecting the environment.

The third approach extended the work from the first and second approaches by integrating the adsorptive desulfurization technique for diesel equivalents produced through thermochemical conversion. This method successfully decreased sulfur content in poultry fat-derived diesel using Amberlyst®-A21 and Al-MCM-41, reaching levels of 26 ± 1 ppm and 29 ± 2 ppm, with removal efficiencies of 41 ± 3% and 34 ± 6%, respectively.

In conclusion, this study of desulfurizing low-value agricultural lipid feedstocks and the resulting diesel for renewable fuel applications has yielded promising results that indicate the potential for practical applications. It emphasizes the importance of selecting the appropriate desulfurization technique based on the specific feedstock. Therefore, the findings of this research can potentially contribute to sustainable energy production and environmental protection from sulfur emissions.