There is now a new method of converting squalene, produced by microalgae, to gasoline or jet fuel.
This new method is the result of a project to make use of oil-producing algae in wastewater treatment. The result will help to expand the utilization of oil produced from wastewater.
The process is the result of research of Professor Keiichi Tomishige and Dr. Yoshinao Nakagawa from Tohoku University’s Department of Applied Chemistry, and Dr. Hideo Watanabe from the University of Tsukuba. This study is part of a research project entitled “Next-generation energies for Tohoku recovery. Task 2: R&D on using algae biofuels.”
This new method uses a highly dispersed ruthenium catalyst supported on cerium oxide. Squalane — easily obtained from squalene — reacts with hydrogen over this catalyst, producing smaller hydrocarbons. The produced hydrocarbons consist of only branched alkanes with simple distribution and do not contain toxic aromatics. These molecules have high stability and low freezing points. These features are very different from the hydrocarbons obtained by conventional petroleum refinery.
Biofuels have attracted attention because of the declining amount of fossil fuels around the world and the rise of global warming. Some algae produce more oil than terrestrial plants, so they are a promising source of oil.
Recently, Professor Makoto M. Watanabe and his team at the University of Tsukuba discovered a heterotrophic alga Aurantiochytrium 18W-13a strain, which rapidly produces squalene from organics in water.
After the Great Eastern Japan Earthquake hit the Sendai area in March 2011, destroying the city’s wastewater treatment system. Tohoku University, the University of Tsukuba and Sendai City got together to develop a next-generation wastewater treatment system that cleans wastewater and produces oil simultaneously.
Squalene is a “heavy oil” range of hydrocarbon. Right now they gather it from deep sea sharks where is sees use as a component of cosmetics. However, wastewater-derived squalene is not suitable for such sensitive uses and has little demand. Most uses of oil, such as gasoline and jet fuels, require reforming. This study focused on the development of the reforming method most suited to algal oil.
The method uses a catalyst with cerium oxide support and ruthenium metal particles. The catalyst ended up prepared by mildly decomposing the ruthenium precursor at 300 degrees Celsius under inert atmosphere after impregnation. This procedure led to sub-nanometer-sized ruthenium particles supported on cerium oxide.
Squalane, easily obtained by the hydrogenation of squalene, ended up treated with this catalyst and hydrogen at 60 atm and 240 degrees Celsius to produce smaller hydrocarbons. This reaction did not produce toxic aromatics at all. The C-C bonds located between the methyl branches selectively dissociated, and branched alkanes ended up produced without the loss of branches.
Branched hydrocarbons are good components for gasoline and jet fuels because of the high octane number, low freezing point and good stability. Researchers tested other noble metal catalysts, but the results were inferior to the sub-nanometer-sized ruthenium on cerium oxide catalyst in terms of activity and selectivity.
The conventional catalyst, the combination of platinum and strong solid acid, produces a very complex mixture of products because of acid-catalyzed isomerization. In this catalyst system, the deposition of carbonaceous solid on the catalyst is negligible, while it is often problematic in many catalytic reactions in petroleum refinery. The catalyst was reusable 4 times without loss of performance.
This catalytic system makes good use of the squalene’s branched structure, while conventional methods are suitable to straight-chain molecules in petroleum. In the future, this catalytic conversion method can apply to real wastewater samples and other important algal hydrocarbons.