Researchers from University of Michigan have developed a way to “pressure cook” algae for as little as one minute and transform up to 65 percent of the algae into biocrude. Phil Savage, a professor of chemical engineering at U of M, said the research team is trying to mimic the process nature uses when creating crude oil, and his algae of choice is green marine micro-alga.
To make their one-minute biocrude, Savage and Julia Faeth, a doctoral student in Savage’s lab, filled a steel pipe connector with 1.5 milliliters of wet algae, capped it and plunged it into 1,100-degree Fahrenheit sand. The small volume ensured that the algae was heated through. Previously the team heated the algae from 10 to 90 minutes and saw the best results when treating the algae for 10 to 40 minutes at 570 degrees. A small batch of algae can reach this temperature in one minute.
Savage and Faeth aren’t sure why the one-minute results so much better until they do more experiments. “My guess is that the reactions that produce biocrude are actually must faster than previously thought,” Savage surmised. Yet Faeth suggests that the fast heating might boost the biocrude by keeping unwanted reactions at bay. “For example, the biocrude might decompose into substances that dissolve in water, and the fast heating rates might discourage that reaction,” Faeth said.
The team also said that shorter reaction times mean that the reactors don’t have to be as large. By reducing the reactor volume, the cost to build a biorefinery also decreases. However, the researchers caution they won’t know for sure if the new method is faster and cheaper until the process is further developed.
Current commercial makers of algae-based fuel first dry the algae and then extract the natural oil. But at over $20 per gallon, this fuel is a long way from the gas pump, says Savage and Faeth. One of the advantages of the wet method is that it doesn’t just extract the existing fat from the algae, it also breaks down proteins and carbohydrates. Using the minute method, the oil contained about 90 percent of the energy in the original algae.
The Savage lab also is developing better methods for feeding biocrude into the refinery system for petroleum, and early results are promising. More details about the research are available in the paper, “The Effects of Heating Rate and Reaction Time On Hydrothermal Liquefaction of Microalgae.”