Emergent research could forge new paths to biodiesel's future

By Ron Kotrba | January 31, 2018

Young scientists presented their ongoing biodiesel research projects during a panel at the National Biodiesel Conference & Expo last week in Fort Worth, Texas. The students are part of the Next Generation Scientists for Biodiesel, a free student professional organization managed by the National Biodiesel Board to help foster collaboration, networking and career development. 

Mary Kate Mitchell, a Ph.D. student at Yale University’s Center for Green Chemistry and Green Engineering, presented her project on heterogeneous catalysis in carbon dioxide (CO2) for the sustainable conversion of vegetable oils to biodiesel. The research revolved around heterogeneous catalysis and an organic cosolvent such as CO2 because, as Mitchell said, the catalyst is recoverable and does not require downstream biodiesel purification, and the high-pressure CO2 cosolvent is inherently green and nontoxic. She said the CO2 cosolvent has “really interesting features” when it surpasses its very achievable critical point of 1,100 psi and 88 degrees Fahrenheit. Mitchell said above this point, the selectivity can be adjusted. She added that the process is used in caffeine and hops extraction for the coffee and beer industries.

Three oils were used in her biodiesel research—coconut, canola and palm. The oils were loaded with methanol and catalyst, and pressurized with carbon dioxide after the mixture was heated. Reaction times were one, two and four hours.

“The carbon dioxide expands the methanol solvent system,” she said, “so you can get better reaction properties.”

The results are still being analyzed, but one of the findings was the C18:1 group (chains with 18 carbon atoms and one double bond) for all three oils achieved around 35 percent conversion at one hour. Extended conversions were done for palm oil and, at four hours, nearly 100 percent conversion of C18:1 chains was achieved. She said more selective conversion of C18:1 was seen over C18:0 and C18:2 because the optimized conditions were for C18:1.

The research has application for real-world biorefineries, Mitchell said, because selective conversion can allow use of C18:1 for biodiesel, for instance, and the other carbon chains can be selected for various products by adjusting the temperature and pressure.

Ahmed Al Hatrooshi, a Ph.D. student from Newcastle University in the U.K., discussed his research on a biorefinery model based on fish waste. With 71 percent of the Earth’s surface covered in water and 144 million tons of annual fish production—50 percent of which is waste—marine waste feedstock is a plentiful candidate for biodiesel production. The idea behind his research, Hatrooshi said, is to develop a cost-effective technique to process biodiesel from fish oil and waste. But to do this, production of more than just biodiesel must be pursued.

In his project, the fish waste was separated into its oily and solid components. The oil sample with which Hatrooshi worked was roughly 20 percent free fatty acids, 44 percent triglycerides, 14 percent diglycerides, and 21 percent monoglycerides. He tested both alkali and acid catalysts. The alkali catalyst was mixed at 1.5 percent by weight to the waste fish oil using a methanol ratio of 1:6 with one hour of reaction time. The sulfuric acid catalyst was also mixed at 1.5 percent, but a methanol ratio of 1:30 was used in the one-hour reaction. Given that the alkali catalyst reacted with the FFA to produce soaps, the acid catalyst performed much better, he said. Three stirring speeds were used: 400 rpm, 720 rpm and 1,080 rpm. Hatrooshi said 720 rpm was most effective. He said 20 different experiments were run with various reaction variables. He found the optimal setting for biodiesel yield of 99.8 percent was 10.3 molar ratio of methanol to oil, 6.5 hours of reaction time and 5.9 percent by weight of acid catalyst.

While the oils from fish waste can go to biodiesel and omega-3 fatty acids production in a biorefinery, Hatrooshi said the solids can be used for fish meal and fertilizer.

Hatrooshi said next he hopes to examine the best technique to separate eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) omega-3 fatty acids, conduct a process techno-economic study, and set up a pilot plant for conversion of marine waste.

William Gray, a bachelor student in chemical engineering at Rowan University, presented on a switchable ionic liquid solvent for lipid extraction from microalgae. He said using this method bypasses the drying phase for algae by bubbling CO2 and nitrogen to recycle the solvent, not only bypassing the costly algae drying phase but also eliminating the need for energy-intense distillation to recover the solvent.

The solvent was added at a 1:1 ratio and heated for two hours, Gray said.

“By bubbling CO2 and an inert gas, the nitrogen, we’re able to switch the polarity of the solvent, and extract out and recycle the solvent,” Gray said. The CO2 switches the polarity of the solvent, and the nitrogen expels the CO2 and switches the polarity back.

The extraction yields three phases: On top is the lipids/solvent; the middle phase contains the carbohydrates/sugars; and on bottom is the proteins. To extract the solvent from the lipids, water is added, also at a 1:1 ratio, and CO2 is bubbled through the mixture to phase-separate the solvent and lipids.

Proton nuclear magnetic resonance was used to verify lipid extraction.

The carbohydrate layer yielded mostly glucose and some fructose. Gray said another project at Rowan University is working to convert those sugars to 1,3-propanediol.

“The key thing,” Gray said, “is that the reusable nature of the solvent and being able to work from a wet algae standpoint drastically reduce the cost of the extraction process, hopefully making microalgae a more realistic biodiesel feedstock.”

Future work on this, Gray said, includes gaining a better understanding of how much and what kind of lipids are yielded in the process, analyzing the percent of solvent being recycled, and scaling up to determine industrial viability.

The final panelist, Matin Hanifzadeh, a Ph.D. chemical engineering student at the University of Toledo, shared his $2.5 million U.S. DOE grant-funded work on sustainable and low-cost production of biodiesel from microalgae. Hanifzadeh said even though open raceway ponds for algae growth are challenged by low productivity, culture crash and the high cost of CO2 and nutrients, their use decreases the end-cost of algae oil by 50 percent compared to oil from algae grown in photobioreactors.

Hanifzadeh summarized several solutions to these open-pond productivity problems, including cultivation at high pH/alkalinity, in low calcium and magnesium media along with low nitrogen media, and in wastewater under high pH without CO2 input. He also noted the ability to use saline water for cultivation—thereby lowering the freshwater requirement—is critical for sustainability.

When asked why biodiesel has a promising future, the students responded with savvy answers like, “Biodiesel is one of the solutions to the ever-growing energy demands,” and, “We have to diversify our sources of energy and increase the choices for the next generation.” Other responses focused on biodiesel’s domestic characteristics and environmental benefits.

While the immediate importance of these kinds of research projects for the industrial biodiesel industry may not be overtly evident, consider this: Biodiesel research on soybean and other vegetable oils began in the 1980s under similar scales and conditions. Three decades later, the global biodiesel industry is a multibillion gallon force. Research into feedstock development such as fish waste and algae could very well provide the impetus this industry needs to hit the tipping point in a future that is not so distant.

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