US: Pressure-cooker to extract bio-oil

Heating and squishing microalgae in a pressure-cooker could be the fastest way to turn it into a crude bio-oil.

Principal investigator Phillip Savage and colleagues at the University of Michigan are using the pressure-cooker method to replace the conventional technique that extracts the oil after drying special, oily types of algae.

The hydrothermal process overcame two major barriers to large-scale conversion of microalgae to liquid fuels by using less-oily types of algae and avoiding the need to dry it.

"We make an algae soup," Savage said. "We heat it to about 300oC and keep the water at high enough pressure to keep it liquid as opposed to steam. We cook it for 30 minutes to an hour and we get a crude bio-oil."

The high temperature and pressure allow the algae to react with the water and break down because they don't have tough cell walls. This leads to the release of oil along with decomposed proteins and carbohydrates, which add to the fuel yield.

"We're trying to do what nature does when it creates oil, but we don't want to wait millions of years," Savage said.

"The hard part is taking the tar that comes out of the pressure cooker and turning it into something you could put in your car, changing the properties so it can flow more easily, and doing it in a way that's affordable."

"We have not yet examined the economics," Savage told University World News.

Professor Qingyu Wu of China's Qinghua University told University World News: "This method is a good idea and may save costs in algae-based biodiesel production."

Wenqiao Yuan, an assistant professor of biofuel at Kansas State University, said the pressure cooker method or, more scientifically, hydrothermal conversion, could be significant.

"However, it is algal species specific. In other words, it does not work for all algal species or strains. Also, optimum operating conditions are different from species to species. The next step should be to optimise the reaction and develop a continuous process, and study how to use bio-oil."

Yuan said the process could be a viable technique in a developing world environment "if bio-oil has a good value".

Magdi Tawfik Abdelhamid, a biotechnologist at Cairo's National Research Centre, welcomed the new development, which he saw as "a cheap, environmentally friendly source for energy that doesn't endanger food security especially for developing countries.

"Carbon neutral bio-fuel produced from algae is a boon for a greener economy because it is a great alternative source for fossil-based fuel as the net effect is zero movement of carbon dioxide to or from the atmosphere," Abdelhamid said.

"Research must focus on the green algae Botryococcus braunii as a prime candidate for biofuel production because it was detected in petroleum and coal deposits and its oil, known as botryococcenes, is similar to petroleum and chemically identical to gasoline, diesel and kerosene."