SCIENTISTS have used acid treatment to “upgrade” bio-oil from mallee leaves for conversion into a renewable source of vehicle fuel.
This process of bio-refinery may have vast implications for many growers of the mallee plant (Eucalyptus loxophleba ssp. gratiae) and promote regional development, according to the team of researchers from Curtin University’s Fuels and Energy Technology Institute.
Acid-treatment or esterification is an important initial step in converting the natural product into fuel, as bio-oil contains carboxylic acid with corrosive properties which needs to be neutralised with alcohol.
Published in Bioresource Technology, the study is the first to use bio-oil from mallee eucalyptol leaves in the esterification process.
Previous studies mainly used bio-oil from wood.
Paper co-author Xun Hu says the leaves were targeted in the study because all parts of biomass—even bark—can be used.
“The structures of the different parts of biomass such as wood, bark and leaves are different,” he says.
“Pyrolysis (subjecting organic compounds to very high temperatures) of these different parts of biomass can be used to produce bio-oils with different compositions.”
According to the research team, one of the main compositional differences is that bio-oil from mallee leaves is rich in cyclic ethers (such as eucalyptol) and terpenoids.
This may be significant because, as the researchers discovered, these cyclic ethers and terpenoids convert during esterification into aromatic hydrocarbons, one of the main components of diesel, adding to the oil’s heating value as a fuel.
A less desirable compositional difference is that mallee leaves contain chlorophyll, which decompose to form nitrogen-containing organics that in turn neutralise the catalyst required to catalyse the esterification process, the researchers note.
“N-containing organics are alkaline [so] they will react with the acidic catalyst to form neutral salts, which will deactivate the catalyst,” Dr Hu says.
The researchers discovered that to counter this, they could increase the catalyst loading from 5 to 15 wt.% and effectively cause the N-containing organics to decrease in abundance.
Hence, the results suggest, large amounts of the solid acid catalyst Amberlyst 70 is required to allow the esterification of carboxylic acids and other important reactions (such as the conversion of eucalyptol to the aromatic hydrocarbon p-Cymene) to proceed at normal speed.
Dr Hu says the research team is now planning and carrying out further research on the production of bio-oil from biomass, an area of significant economic and social value.
“New research projects involving biofuel production are forthcoming and researchers [investigating this area of research] may increase significantly in the near future,” he says.