Fruit – fuel of future?

A lot of researchers are nowadays focused on biofuels. Biofuels which are now used are called first generation of biofuels. These fuels suffer from several disadvantages. It is reason why research of new biofules is needed. One of biofuel of second generation could be 2,5-dimethylfuran (DMF) a liquid transportation fuel with 40% greater energy density than ethanol.

Research team from University of Wisconsin-Madison published in the June 21 issue of the journal Nature article about chemical reaction which turns sugars to DMF. It means that fruit and other products of agriculture containing fructose could be used as reactant for this reaction. Chemical reaction leads from fructose to DMF is known for a long time but professor James Dumesic and his research team come with many innovations.

Currently, ethanol is the only renewable liquid fuel produced on a large scale," says Dumesic. "But ethanol suffers from several limitations. It has relatively low energy density, evaporates readily, and can become contaminated by absorption of water from the atmosphere. It also requires an energy-intensive distillation process to separate the fuel from water." Not only does dimethylfuran have higher energy content, it also addresses other ethanol shortcomings. DMF is not soluble in water and therefore cannot become contaminated by absorbing water from the atmosphere. DMF is stable in storage and, in the evaporation stage of its production, consumes one-third of the energy required to evaporate a solution of ethanol produced by fermentation for biofuel applications.

Dumesic's team improved the process for making an important chemical intermediate, hydroxymethylfurfural (HMF). The team's method for making HMF and converting it to DMF is a balancing act of chemistry, pressure, temperature and reactor design. Fructose is initially converted to HMF in water using an acid catalyst in the presence of a low-boiling-point solvent. Although other researchers had previously converted fructose to HMF, Dumesic's research group made a series of improvements that raised the HMF output and made the HMF easier to extract. For example, the team found that adding natrium chloride (NaCl) dramatically improves the extraction of HMF from the reactive water phase and helps suppress the formation of impurities.

Process of conversion of HMF to DMF is based on copper catalyst. The conversion removes two oxygen atoms from the compound lowering the boiling point, and making it suitable for use as transportation fuel. Natrium chloride, while improving the production of HMF, presented a problem in the production of DMF. Chloride ions poison copper catalyst. It is reason why team instead developed a copper-ruthenium catalyst providing chlorine resistance and superior performance.

Dumesic says more research is required before the technology can be commercialized. For example, while its environmental health impact has not been thoroughly tested, the limited information available suggests DMF is similar to other current fuel components. "There are some challenges that we need to address," says Dumesic, "but this work shows that we can produce a liquid transportation fuel from biomass that has energy density comparable to petrol."

Stanislav Obruča

Source: Web sites of University of Wisconsin-Madison