How Algae Biodiesel Works

Algae Biodiesel Engineering: Extracting Oil from Algae

Algae biodiesel may soon be on the menu at gas stations in your neighborhood.
Andreas Rentz/Getty Images

How can we get oil from algae? It's like getting juice from an orange -- with an additional chemical reaction thrown in. Algae are grown in either open-pond or closed-pond systems, which we'll discuss later. Once the algae are harvested, the lipids, or oils, are extracted from the walls of the algae cells.

There are a few different ways to extract the oil from algae. The oil press is the simplest and most popular method. It's similar to the concept of the olive press. It can extract up to 75 percent of the oil from the algae being pressed.


Basically a two-part process, the hexane solvent method (combined with pressing the algae) extracts up to 95 percent of oil from algae. First, the press squeezes out the oil. Then, leftover algae is mixed with hexane, filtered and cleaned so there's no chemical left in the oil.

The supercritical fluids method extracts up to 100 percent of the oil from algae. Carbon dioxide acts as the supercritical fluid -- when a substance is pressurized and heated to change its composition into a liquid as well as a gas. At this point, carbon dioxide is mixed with the algae. When they're combined, the carbon dioxide turns the algae completely into oil. The additional equipment and work make this method a less popular option.

Once the oil's extracted, it's refined using fatty acid chains in a process called transesterification. Here, a catalyst such as sodium hydroxide is mixed in with an alcohol such as methanol. This creates a biodiesel fuel combined with a glycerol. The mixture is refined to remove the glycerol. The final product is algae biodiesel fuel.

The process of extracting oil from the algae is universal, but companies producing algae biodiesel are using diverse methods to grow enough algae to produce large amounts of oil.

Now, we'll learn how they do it.