Renewable diesel? This phrase may create confusion. Normally, diesel is known as a fractional distillate of petroleum fuel oil. True, there are well-known green alternatives with different primary raw materials. Biodiesel, for example, made from plant-based or animal-based oil is renewable and can be used in standard diesel engines. Even methods like Biomass to Liquid (BtL) or Gas to Liquid (GtL) are no great mysteries.
The production of methanol with yeast and sugar is a worldwide established procedure and applied successfully for many years. The same cannot be said, however, for the production of diesel with yeast. Undoubtedly, this process still needs to be improved. The more powerful fuel diesel is much more suited for huge large vehicles like airplanes, ships, buses or trucks due to the high energy density. Unfortunately, the fossil source is anything but environmentally friendly. And the clean alternative biodiesel derived from edible oil isn’t an affordable solution. But let’s get to the point.
Production of renewable diesel with abundantly available resources
Researchers at Massachusetts Institute of Technology (MIT) have recently reprogrammed a yeast strain in a way that it enables to transform common sugar into fat much more efficiently. Of course, we know that it is possible to produce large amounts of fat by using yeast and sugar. But their findings could make the production of renewable diesel more cost-effective, and thus more realistic. By changing the metabolic pathways of yeast, the production process becomes 30 percent more efficient.
“What we’ve done is reach about 75 percent of this yeast’s potential, and there is an additional 25 percent that will be subject of follow-up work,” says Stephanopoulos, who is the senior author of the study.
Sugar cane and corn are affordable sources for starch and abundantly available. Yarrowia lipolytica, a popular and frequently used yeast for the production of lipids, can use uncommon carbon sources with a large natural yield. With synthetic pathways, the researchers transformed Yarrowia and produced a surplus of NADH. This can be converted in NADPH – a raw material for the synthesis of lipids. In the end, several synthetic pathways have been tested. Allegedly, the new findings enable to save one-third of the needed amount of glucose compared to unmodified yeast cells producing the same amount of oil.
“It turned out that the combination of two of these pathways gave us the best results that we report in the paper,” Stephanopoulos says. “The actual mechanism of why a couple of these pathways work much better than the others is not well-understood.” Still, there is scope for further improving the process to increase the output. Furthermore, the chemists try to use cheaper raw material, such as agriculture waste or grass.