Retail diesel fuels widely contain up to 5% biodiesel (“fatty acid methyl ester” or FAME), a nontoxic, biodegradable and environmentally-friendly additive that reduces reliance on fossil fuels. Biodiesel is produced by a process called transesterification that reacts raw vegetable oils (such as rape, sunflower, canola, soybean, corn, and cottonseed) with methanol or ethanol. Increasing the use of biodiesel to meet government policies requires increased production, which in turn will require the allocation of further prime agricultural land. In addition, only relatively small proportions of biodiesel are currently blendable with petrodiesel without invalidating manufacturers’ compatibility guarantees. Quality control and cold weather issues are also important.

To increase the renewability and sustainability of transport fuels, it would be useful to supplement biodiesel with bio-oil produced from non-edible crops, which can be grown on more marginal agricultural land, or which are themselves by-products, such as woodchips and bark. Bio-oils are produced using a technique known as fast pyrolysis—the thermal decomposition of biomass in the absence of oxygen—and are much more efficient products in terms of land use. The use of water rich bio-oil as an environmentally-friendly additive to biodiesel blends nevertheless poses a serious technical challenge, due to its immiscibility with biodiesel.

Researchers at Aston University have devised a technique for blending water rich bio-oil with biodiesel. The end product is a stable biofuel blend comprising a single phase liquid that consists of biodiesel, bio-oil and other additives. The biofuel blend has an appropriate level of viscosity and density for direct use in diesel engines. It is also highly stable, easily storable and transportable, and increases the renewability and sustainability of renewable transport fuels.